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HVAC SYSTEMS TESTING, ADJUSTING & BALANCING

SHEET METAL AND AIR CONDITIONING CONTRACTORS’ NATIONAL ASSOCIATION, INC.


HVAC SYSTEMS TESTING, ADJUSTING & BALANCING

THIRD EDITION — AUGUST, 2002

SHEET METAL AND AIR CONDITIONING CONTRACTORS’ NATIONAL ASSOCIATION, INC. 4201 Lafayette Center Drive Chantilly, VA 20151-1209


HVAC SYSTEMS TESTING, ADJUSTING & BALANCING COPYRIGHT2002 All Rights Reserved by

SHEET METAL AND AIR CONDITIONING CONTRACTORS’ NATIONAL ASSOCIATION, INC. 4201 Lafayette Center Drive Chantilly, VA 20151 Printed in the U.S.A.

FIRST EDITION - 1983 SECOND EDITION - JULY, 1993 THIRD EDITION - AUGUST, 2002

Except as allowed in the Notice to Users and in certain licensing contracts, no part of this book may be reproduced, stored in a retrievable system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher.


FOREWORD This handbook has been extensively updated for 2002 from the original 1983 publication and includes all of the many changes that have takes place in the industry since the 1990’s. We have added many new sections covering variable frequency drives (VFD), direct digital control (DDC) systems, lab hood exhaust balancing, and the latest changes in the balancing equipment and procedures. All of the system testing, adjusting, and balancing fundamentals that make up the original text has been updated, and all helpful reference tables and charts in the Appendix have been extensively updated. This handbook will provide any SMACNA contractor already familiar with mechanical system operation basics, with the information necessary to balance most heating, ventilation, and air conditioning (HVAC) systems. Chapters on both air and water side HVAC system adjusting and balancing are included, and the chapters on system controls have been totally rewritten to reflect the trend away from pneumatic controls and towards programmable micro−processor controls. Most of today’s HVAC systems are being designed with many more individually controlled temperature zones to im− prove occupant comfort, and variable speed fans and pumps are now commonplace to provide the exact amount of heating and cooling system capacity necessary to minimize energy usage. New occupant air ventilation codes are much more restrictive, at the same time building envelopes are becoming much tighter. The combination of constantly changing HVAC flows and increased demand for fresh and filtered ventilation air for all occupants is placing much more emphasis on proper HVAC system operation and balancing. Any SMACNA contractor wanting to become part of this rapidly growing field is strongly encouraged to read other related SMACNA publications available, and take part in the many training courses offered to become a certified TAB Contractor. The International Training Institute provides a Certified Technician program for journeyman sheet metal workers who already have a basic understanding of system testing and balancing, and many of these courses are avail− able in versions for home study. The building construction industry is experiencing a major growth in demand for trained and experienced contractors who can balance today’s much more complex HVAC systems.

SHEET METAL AND AIR CONDITIONING CONTRACTORS’ NATIONAL ASSOCIATION, INC.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

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TASK FORCE Bill Freese, Chairman International Testing & Balancing, Ltd. Seaford, New York

Ray Coleman Certified Testing & Balancing, Inc. Riverton, Utah

David Aldag Aldag−Honold Mechanical, Inc. Sheboygan, Wisconsin

Ben Dutton SMACNA, Inc. Chantilly, Virginia

John Brue Balancing Precision, Inc. Bloomington, Illinois

Eli P. Howard, III SMACNA, Inc. Chantilly, Virginia

OTHER CONTRIBUTORS J. R. Yago & Associates Consulting Engineers Manakin−Sabot, Virginia

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HVAC SYSTEMS Testing Adjusting & Balancing • Third Edition


NOTICE TO USERS OF THIS PUBLICATION

1.

DISCLAIMER OF WARRANTIES

a) The Sheet Metal and Air Conditioning Contractors’ National Association (“SMACNA”) provides its product for informational purposes. b) The product contains “Data” which is believed by SMACNA to be accurate and correct but the data, including all information, ideas and expressions therein, is provided strictly “AS IS”, with all faults. SMACNA makes no warranty either express or implied regarding the Data and SMACNA EXPRESSLY DISCLAIMS ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR PARTICULAR PURPOSE. c) By using the data contained in the product user accepts the Data “AS IS” and assumes all risk of loss, harm or injury that may result from its use. User acknowledges that the Data is complex, subject to faults and requires verification by competent professionals, and that modification of parts of the Data by user may impact the results or other parts of the Data. d) IN NO EVENT SHALL SMACNA BE LIABLE TO USER, OR ANY OTHER PERSON, FOR ANY INDIRECT, SPECIAL OR CONSEQUENTIAL DAMAGES ARISING, DIRECTLY OR INDIRECTLY, OUT OF OR RELATED TO USER’S USE OF SMACNA’S PRODUCT OR MODIFICATION OF DATA THEREIN. This limitation of liability applies even if SMACNA has been advised of the possibility of such damages. IN NO EVENT SHALL SMACNA’S LIABILITY EXCEED THE AMOUNT PAID BY USER FOR ACCESS TO SMACNA’S PRODUCT OR $1,000.00, WHICHEVER IS GREATER, REGARDLESS OF LEGAL THEORY. e) User by its use of SMACNA’s product acknowledges and accepts the foregoing limitation of liability and disclaimer of warranty and agrees to indemnify and hold harmless SMACNA from and against all injuries, claims, loss or damage arising, directly or indirectly, out of user’s access to or use of SMACNA’s product or the Data contained therein.

2.

ACCEPTANCE

This document or publication is prepared for voluntary acceptance and use within the limitations of application defined herein, and otherwise as those adopting it or applying it deem appropriate. It is not a safety standard. Its application for a specific project is contingent on a designer or other authority defining a specific use. SMACNA has no power or authority to police or enforce compliance with the contents of this document or publication and it has no role in any representations by other parties that specific components are, in fact, in compliance with it.

3.

AMENDMENTS

The Association may, from time to time, issue formal interpretations or interim amendments, which can be of significance between successive editions.

4.

PROPRIETARY PRODUCTS

SMACNA encourages technological development in the interest of improving the industry for the public benefit. SMACNA does not, however, endorse individual manufacturers or products.

5.

FORMAL INTERPRETATION

a) A formal interpretation of the literal text herein or the intent of the technical committee or task force associated with the document or publication is obtainable only on the basis of written petition, addressed to the Technical Resources Department and sent to the Association’s national office in Chantilly, Virginia. In the event that the petitioner has a substantive disagreement with the interpretation, an appeal may be filed with the Technical Resources Committee, which has technical oversight responsibility. The request must pertain to a specifically identified portion of the document that does not involve published text which provides the requested information. In considering such requests, the Association will not review or judge products or components as being in compliance with the document or publication. Oral and written interpretations otherwise obtained from anyone affiliated with the Association are unofficial. This procedure does not prevent any committee or task force chairman, member of the committee or task force, or staff liaison from expressing an opinion on a provision within the document, provided that such person clearly states that the opinion is personal and does not represent an official act of the Association in any way, and it should not be relied on as such. The Board of Directors of SMACNA shall have final authority for interpretation of this standard with such rules or procedures as they may adopt for processing same. b) SMACNA disclaims any liability for any personal injury, property damage, or other damage of any nature whatsoever, whether special, indirect, consequential or compensatory, direct or indirectly resulting from the publication, use of, or reliance upon this document. SMACNA makes no guaranty or warranty as to the accuracy or completeness of any information published herein.

6.

APPLICATION

a) Any standards contained in this publication were developed using reliable engineering principles and research plus consultation with, and information obtained from, manufacturers, users, testing laboratories, and others having specialized experience. They are

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subject to revision as further experience and investigation may show is necessary or desirable. Construction and products which comply with these Standards will not necessarily be acceptable if, when examined and tested, they are found to have other features which impair the result contemplated by these requirements. The Sheet Metal and Air Conditioning Contractors’ National Association and other contributors assume no responsibility and accept no liability for the application of the principles or techniques contained in this publication. Authorities considering adoption of any standards contained herein should review all federal, state, local, and contract regulations applicable to specific installations. b) In issuing and making this document available, SMACNA is not undertaking to render professional or other services for or on behalf of any person or entity. SMACNA is not undertaking to perform any duty owed to any person or entity to someone else. Any person or organization using this document should rely on his, her or its own judgement or, as appropriate, seek the advice of a competent professional in determining the exercise of reasonable care in any given circumstance.

7.

REPRINT PERMISSION

Non-exclusive, royalty-free permission is granted to government and private sector specifying authorities to reproduce only any construction details found herein in their specifications and contract drawings prepared for receipt of bids on new construction and renovation work within the United States and its territories, provided that the material copied is unaltered in substance and that the reproducer assumes all liability for the specific application, including errors in reproduction.

8.

THE SMACNA LOGO

The SMACNA logo is registered as a membership identification mark. The Association prescribes acceptable use of the logo and expressly forbids the use of it to represent anything other than possession of membership. Possession of membership and use of the logo in no way constitutes or reflects SMACNA approval of any product, method, or component. Furthermore, compliance of any such item with standards published or recognized by SMACNA is not indicated by presence of the logo.

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HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


TABLE OF CONTENTS


TABLE OF CONTENTS FOREWORD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

iii

TASK FORCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

iv

NOTICE TO USERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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TABLE OF CONTENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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CHAPTER 1 1.1 1.2 1.3

INTRODUCTION INTRODUCTION TO TAB WORK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . THE TAB TECHNICIAN/TEAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . GENERAL REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1.1 1.1 1.2

CHAPTER 2 HVAC FUNDAMENTALS 2.1 2.2 2.3 CHAPTER 3 3.1 3.2 3.3 3.4 3.5 3.6 CHAPTER 4 4.1 4.2 4.3 4.4 4.5 4.6 4.7 CHAPTER 5 5.1 5.2 5.3 5.4 5.5 CHAPTER 6 6.1 6.2 6.3 6.4 6.5

HEAT FLOW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PSYCHROMETRICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . FLUID MECHANICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2.1 2.6 2.19

ELECTRICAL EQUIPMENT AND CONTROLS ELECTRICAL SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ELECTRICAL SERVICES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . TRANSFORMERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MOTORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MOTOR CONTROLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VARIABLE FREQUENCY DRIVES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3.1 3.1 3.5 3.5 3.8 3.9

TEMPERATURE CONTROL AUTOMATIC TEMPERATURE CONTROL SYSTEMS . . . . . . . . . . . . . . . . . . . . CONTROL LOOPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CONTROL DIAGRAMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CONTROL RELATIONSHIPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ATC SYSTEM ADJUSTMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . TAB/ATC RELATIONSHIP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CENTRALIZED CONTROL SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4.1 4.2 4.5 4.5 4.6 4.6 4.7

FANS FAN CHARACTERISTICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . FAN CONSTRUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . FAN AIRFLOW AND PRESSURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . FAN/SYSTEM CURVE RELATIONSHIP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . FAN CAPACITY RATINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5.1 5.4 5.10 5.13 5.17

AIR DISTRIBUTION AND DEVICES AIR TERMINAL BOXES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VARIABLE AIR VOLUME (VAV) TERMINAL BOXES . . . . . . . . . . . . . . . . . . . . . OTHER AIRFLOW DEVICES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . AIR DISTRIBUTION BASICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ROOM AIR DISTRIBUTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

6.1 6.3 6.3 6.6 6.9

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CHAPTER 7 7.1 7.2 7.3 7.4 7.5 CHAPTER 8 8.1 8.2 8.3 8.4 8.5 CHAPTER 9 9.1 9.2 9.3 9.4

AIR SYSTEMS INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . TYPES OF AIR SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . AIR SYSTEM DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . DUCT SIZING EXAMPLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7.1 7.2 7.9 7.11 7.14

HYDRONIC EQUIPMENT PUMPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PUMP / SYSTEM CURVE RELATIONSHIP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PUMP INSTALLATION CRITERIA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HYDRONIC HEATING AND COOLING SOURCES . . . . . . . . . . . . . . . . . . . . . . TERMINAL HEATING AND COOLING UNITS . . . . . . . . . . . . . . . . . . . . . . . . . . .

8.1 8.7 8.11 8.13 8.14

HYDRONIC SYSTEMS HYDRONIC SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HYDRONIC SYSTEM DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HYDRONIC DESIGN PROCEDURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . STEAM SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9.1 9.8 9.13 9.14

CHAPTER 10 REFRIGERATION SYSTEMS 10.1 10.2 10.3 10.4 10.5 10.6 10.7 CHAPTER 11 11.1 11.2 11.3 11.4 11.5 11.6 11.7 11.8

REFRIGERATION SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . REFRIGERATION TERMS AND COMPONENTS . . . . . . . . . . . . . . . . . . . . . . . . SAFETY CONTROLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OPERATING CONTROLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . REFRIGERANTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . THERMAL BULBS AND SUPERHEAT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . COMPRESSOR SHORT CYCLING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

10.1 10.2 10.4 10.4 10.4 10.4 10.6

TAB INSTRUMENTS INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . AIRFLOW MEASURING INSTRUMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PRESSURE GAGE, CALIBRATED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ROTATION MEASURING INSTRUMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . TEMPERATURE FUNCTION TACHOMETER MEASURING INSTRUMENTS ELECTRICAL MEASURING INSTRUMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . COMMUNICATION DEVICES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HYDRONIC FLOW MEASURING DEVICES . . . . . . . . . . . . . . . . . . . . . . . . . . . .

11.1 11.1 11.9 11.12 11.16 11.22 11.23 11.24

CHAPTER 12 PRELIMINARY TAB PROCEDURES 12.1 12.2 12.3 12.4 12.5 12.6

INITIAL PLANNING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CONTRACT DOCUMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SYSTEM REVIEW AND ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . THE AGENDA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PLANNING FIELD TAB PROCEDURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PRELIMINARY FIELD PROCEDURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

12.1 12.1 12.2 12.4 12.5 12.6

CHAPTER 13 GENERAL AIR SYSTEM TAB PROCEDURES 13.1 13.2 13.3 13.4 13.5 13.6 13.7 viii

BASIC FAN TESTING PROCEDURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SYSTEM STARTUP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . FAN TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . DEFICIENCY REVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . RETURN AND OUTSIDE AIR SETTINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ANALYSIS OF MEASUREMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . RECORDING DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

13.1 13.1 13.1 13.2 13.2 13.3 13.3


13.8 13.9 13.10 13.11 13.12 13.13 13.14 13.15 13.16 13.17 13.18 13.19 13.20 13.21 13.22 13.23 13.24 13.25

PROPORTIONAL BALANCING (RATIO) METHOD . . . . . . . . . . . . . . . . . . . . . . . 13.3 PERCENTAGE OF DESIGN AIRFLOW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.3 SYSTEM AIRFLOW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.5 BASIC OUTLET BALANCING PROCEDURES . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.5 STEPWISE METHOD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.5 FAN ADJUSTMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.6 WET COIL CONDITIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.6 AIRFLOW TOTALS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.6 EXHAUST FANS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.6 FAN DRIVE ADJUSTMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.6 DAMPER ADJUSTMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.7 DUCT TRAVERSES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.7 SYSTEM DEFICIENCIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.7 FUME HOOD EXHAUST BALANCING PROCEDURES . . . . . . . . . . . . . . . . . . . 13.7 DUST COLLECTION AND EXHAUST BALANCING PROCEDURES . . . . . . . 13.8 AIR FLOW MEASUREMENTS ON DISCHARGE STACKS . . . . . . . . . . . . . . . . 13.11 INDUSTRIAL VENTILATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.12 SELECTION OF INSTRUMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.12

CHAPTER 14 TAB PROCEDURES FOR SPECIFIC AIR SYSTEMS 14.1 14.2 14.3 14.4 14.5 14.6 14.7

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VARIABLE AIR VOLUME (VAV) SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MULTI-ZONE SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . INDUCTION UNIT SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . DUAL DUCT SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SPECIAL EXHAUST AIR SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PROCESS EXHAUST AIR SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

14.1 14.1 14.13 14.14 14.14 14.16 14.17

CHAPTER 15 HYDRONIC SYSTEM TAB PROCEDURES 15.1 15.2 15.3 15.4 15.5 15.6 15.7

HYDRONIC SYSTEM MEASUREMENT METHODS . . . . . . . . . . . . . . . . . . . . . . 15.1 BASIC HYDRONIC SYSTEM PROCEDURES . . . . . . . . . . . . . . . . . . . . . . . . . . . 15.3 PIPING SYSTEM BALANCING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15.4 BALANCING SPECIFIC SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15.5 VARIABLE VOLUME FLOW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15.9 PRIMARY-SECONDAR Y SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15.11 SUMMER-WINTER SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15.11

CHAPTER 16 TAB REPORT FORMS 16.1 16.2

PREPARING TAB REPORT FORMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . DESCRIPTION OF USE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

APPENDIX A

16.1 16.1

DUCT DESIGN TABLES & CHARTS DUCT DESIGN TABLES AND CHARTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HVAC EQUATIONS - (I-P) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HVAC EQUATIONS - (SI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SI UNITS AND EQUIVALENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SOUND DESIGN EQUATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . FITTING EQUIVALENTS (WATER) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PROPERTIES OF STEAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . STEAM PIPING (I-P) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . STEAM PIPING (SI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

A.1 A.31 A.35 A.39 A.41 A.43 A.44 A.45 A.49 A.54

GLOSSARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

G.1

INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

I.1

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

ix


TABLES

5-1 6-1

Typical Fan Rating Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.7 Typical Ratios of Damper to System Resistance for Flow Characteristic Curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.6 6-2 Guide to Use of Various Outlets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.12 6-3 Recommended Return Air Inlet Face Velocities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.14 6-4 Air Outlets and Diffusers Total Pressure Loss Average—in. wg (Pa) . . . . . . . . . . . 6.15 6-5 Supply Registers Total Pressure Loss Average—in. wg (Pa) . . . . . . . . . . . . . . . . . . 6.15 6-6 Return Registers Total Pressure Loss Average—in. wg (Pa) . . . . . . . . . . . . . . . . . . 6.15 8-1 Characteristics of Centrifugal Pumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3 8-2 Characteristics of Common Types of Pumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3 8-3 Flow vs Total Head (Cooling Tower Application) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.11 9-1 Hydronic Trouble Analysis Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.8 11-1 Airflow Measuring Instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.9 11-2 Instruments for Hydronic Balancing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.11 11-3 Hydronic Measuring Instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.11 11-4 Rotation Measuring Instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.13 11-5 Instrumentation for Air & Hydronic Balancing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.16 11-6 Instruments for Air Balancing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.17 11-7 Temperature Measuring Instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.21 15-1 Load-Flow Variations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15.10 A-1 Duct Material Roughness Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.3 A-2 Circulation Equivalents of Rectangular Ducts for Equal Friction and Capacity (I-P) (2) Dimensions in Inches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.5 A-2 Circulation Equivalents of Rectangular Ducts for Equal Friction and Capacity (I-P) (2) Dimensions in Inches (continued) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.6 A-3 Circular Equivalents of Rectangular Ducts for Equal Friction and Capacity (SI) (2) Dimensions in mm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.7 A-3 Circular Equivalents of Rectangular Ducts for Equal Friction and Capacity (SI) (2) Dimensions in mm (continued) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.8 A-4 Velocities/Velocity Pressures (I-P) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.9 A-5 Velocities/Velocity Pressures (SI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.10 A-6 Angular Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.10 A-7 Loss Coefficients for Straight-Through Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.11 A-8 Recommended Criteria for Louver Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.12 A-9 Typical Design Velocities for Duct Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.13 A-10 Elbow Loss Coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.14 A-1 1 Transition Loss Coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.17 A-12 Rectangular Branch Connection Loss Coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . . A.19 A-13 Round Branch Connection Loss Coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.23 A-14 Miscellaneous Fitting Coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.27 HVAC Equations (I-P) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.31 A-15 Converting Pressure In Inches of Mercury to Feet of Water at Various Water Temperatures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.33 A-16 Air Density Correction Factors (I-P) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.34 HVAC Equations (SI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.35 A-17 Air Density Correction Factors (SI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.38 A-18 SI Units And Equivalents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.39 A-19 SI Equivalents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.40 A-20 Sound Design Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.41 A-21 Equivalent Length in Feet of Pipe for 90 Elbows . . . . . . . . . . . . . . . . . . . . . . . . . . A.43 A-22 Equivalent Length in Meters of Pipe for 90 Elbows . . . . . . . . . . . . . . . . . . . . . . . . A.43 A-23 Iron and Copper Elbow Equivalents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.43 A-24 Properties of Saturated Steam (I-P) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.44 A-25 Properties of Saturated Steam (SI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.44 A-26 Steam Piping (I-P) Flow Rate of Steam in Schedule 40 Pipe at Initial Saturation Pressure of 3.5 and 12 psig (Flow Rate expressed in Pounds per Hour) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.45 x

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


TABLES (continued) A-27 Comparative Capacity of Steam Lines at Various Pitches for Steam and Condensate Flowing in Opposite Directions (Pitch of Pipe in Inches per 10 Feet – Velocity in Feet per Second) . . . . . . . . . A.45 A-28 Pressure Drops In Common Use for Sizing Steam Pipe (For Corresponding Initial Steam Pressure) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.46 A-29 Length in Feet of Pipe to be Added to Actual Length of Run — Owing to Fittings — to Obtain Equivalent Length . . . . . . . . . . . . . . . . . . A.46 A-30 Steam Pipe Capacities for Low Pressure Systems (For Use on One-Pipe Systems or Two-Pipe Systems in which Condensate Flows Against the Steam Flow) . A.47 A-31 Return Main and Riser Capacities for Low-Pressure Systems—Pounds per Hour (Reference to this table will be made by column letter G through V) . . . . . . . . . A.48 A-32 Flow Rate in kg/h of Steam in Schedule 40 Pipe at Initial Saturation Pressure of 15 and 85 kPa Above Atmospheric . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.49 A-33 Comparative Capacity of Steam Lines at Various Pitches for Steam and Condensate Flowing in Opposite Directions . . . . . . . . . . . . . . . . . . . . . . . . . . A.49 A-34 Equivalent Length of Fittings to be Added to Pipe Run . . . . . . . . . . . . . . . . . . . . . . A.50 A-35 Steam Pipe Capacities for Low-Pressure Systems (For Use on One-Pipe Systems or Two-Pipe Systems in which Condensate Flows Against the Steam Flow) . A.51 A-36 Return Main and Riser Capacities for Low-Pressure Systems — kg/h . . . . . . . . A.52

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

xi


FIGURES

2-1 Heat Transfer by Conduction and Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2 Convection Heat Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3 Counterflow Airstreams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4 Parallel Flow Airstreams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5 Cross-flow Airstreams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6 Parallel and Counterflow Heat Transfer Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7 Psychrometric Chart (I-P) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-8 Psychrometric Chart - Typical Condition Points (SI) . . . . . . . . . . . . . . . . . . . . . . . . . 2-9 Psychrometric Chart - Typical Condition Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-10 Sensible Heating and Cooling (I-P) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1 1 Humidification and Dehumidification (I-P) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-12 Psychrometric Chart - Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-13 Cooling and Dehumidifying (I-P) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-14 Heating and Humidification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-15 Mixing of Two Airstreams (SI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-16 Tank Static Head . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-17 Velocity Profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-18 Pressure Changes During Flow in Ducts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-19 Sample Fitting Loss Coefficient Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-20 Pump with Static Head and Suction Head . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-21 Pump with Suction Lift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1 Series-Parallel Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2 Single-Phase AC Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3 Current And Voltage-T ime Curves and Power Factor . . . . . . . . . . . . . . . . . . . . . . . . 3-4 220-Volt Three-Wire Delta Three-Phase Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5 220-Volt Delta Three-Phase Circuit with 110-V olt Single-Phase Supply . . . . . . . 3-6 120/208-Volt Four-Wire Wye Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7 Transformer with TaPped Secondary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-8 Typical Performance of Standard Squirrel Cage Induction Motors . . . . . . . . . . . . . 3-9 Interlocked Starters with Control Transformers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-10 VFD Added to Existing Air Handling Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1 Valve Throttling Characteristic Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2 ATC Valve Arrangements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3 Typical Multiblade Dampers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4 Desktop Computer Displaying Status of Building HVAC Systems . . . . . . . . . . . . . . 4-5 Functional Block Diagram A Centralized Computer Control System . . . . . . . . . . . 4-6 HVAC Controls Panel with Original Pneumatic Controls. . . . . . . . . . . . . . . . . . . . . . 4-7 The Same HVAC Control Panel After Upgrading to Direct Digital Control (DDC). 4-8 Portable Computer Plugged Into Electronic Wall Thermostat During System Balancing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1 Centrifugal Fan Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2 Characteristic Curves for FC Fans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3 Characteristic Curves for BI Fans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4 Characteristic Curves for Air Foil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5 Axial Fan Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6 Characteristic Curves for Propeller Fans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7 Characteristic Curves for Vaneaxial Fans (High Performance) . . . . . . . . . . . . . . . . 5-8 Tubular Centrifugal Fan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-9 Characteristic Curves for Tubular Centrifugal Fans . . . . . . . . . . . . . . . . . . . . . . . . . 5-10 Fan Class Standards (I-P) (SW BI Fans) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1 1 Fan Class Standards (SI) (SW BI Fans) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-12 Drive Arrangements For Centrifugal Fans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-13 Arrangement 1 In-Line Fans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-14 Arrangement 4 in-line fans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-15 Arrangement 9 in-Line fans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-16 Centrifugal Fan Motor Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-17 Direction of Rotation And Discharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xii

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

2.2 2.2 2.3 2.3 2.4 2.4 2.9 2.10 2.11 2.12 2.13 2.14 2.15 2.15 2.17 2.20 2.21 2.22 2.24 2.28 2.29 3.2 3.2 3.3 3.4 3.4 3.4 3.5 3.7 3.9 3.10 4.3 4.4 4.4 4.7 4.8 4.9 4.10 4.10 5.1 5.1 5.2 5.2 5.2 5.3 5.3 5.3 5.4 5.4 5.4 5.5 5.8 5.9 5.9 5.10 5.11


FIGURES (continued) 5-18 Fan Total Pressure (TP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-19 Fan Static Pressure (SP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-20 Fan Velocity Pressure (VP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-21 Tip Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-22 System Resistance Curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-23 Operating Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-24 Variations from Design Air Shortage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-25 Fan Law - RPM Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-26 Effect of Density Change (Constant Volume) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-27 Effect of Density Change (Constant Static Pressure) . . . . . . . . . . . . . . . . . . . . . . . . 5-28 AMCA Fan Test - Pitot Tube . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-29 Effect of Density Change (Constant Mass Flow) . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-30 Effects of System Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-31 Fan Outlet Effective Duct Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-32 Non-Uniform Flow Conditions Into Fan Inlet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1 Constant Volume Fan-Powered Box . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2 Bypass-Type Fan-Powered Box . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3 Multiblade Volume Dampers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4 Flow Characteristics for a Parallel Operating Damper . . . . . . . . . . . . . . . . . . . . . . . 6-5 Flow Characteristics for an Opposed Operating Damper . . . . . . . . . . . . . . . . . . . . . 6-6 Volume Dampers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-7 Surface (Coanda) Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-8 Some Elements Affecting Body Heat Loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-9 Four Zones in Jet Expansion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-10 Typical Supply Outlets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1 Single Duct System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2 Typical Equipment for Single Zone Duct System . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3 Variable Air Volume (VAV) System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-4 Terminal Reheat System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-5 Induction Reheat System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6 Dual Duct High Velocity System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-7 Multi-Zone System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-8 System Layout (I-P Units) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-9 System Layout (SI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-10 Fan Duct Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1 Typical Centrifugal Pump Cross Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-2 Descriptions of Centrifugal Pumps Used in Hydronic Systems . . . . . . . . . . . . . . . . 8-3 Coupling Alignment with Straight Edge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-4 Typical Required NPSH Curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-5 Pump Curve for 1750 rpm Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-6 Typical Design Pump Selection Point (from Abbreviated Curve) . . . . . . . . . . . . . . 8-7 System Curve Plotted on Pump Curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-8 Typical Open Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-9 Typical Cooling Tower Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-10 System Curve for Open Circuit False Operating Point . . . . . . . . . . . . . . . . . . . . . . . 8-1 1 System Curve for Open Circuit True Operating Point . . . . . . . . . . . . . . . . . . . . . . . . 8-12 Pump Operating Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-13 Multiple Pumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-14 Pump and System Curves for Parallel Pumping . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-15 Pump and System Curves for Series Pumping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-16 Gage Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-17 Relative Gage Elevations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-18 Effect of Viscosity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1 A Series Loop System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-2 A One-Pipe System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-3 Direct Return Two-Pipe System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-4 Reverse Return Two-Pipe System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-5 Example of Primary and Secondary Pumping Circuits . . . . . . . . . . . . . . . . . . . . . . . 9-6 Return Mix System Room Unit Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

5.12 5.12 5.13 5.13 5.14 5.14 5.15 5.15 5.16 5.17 5.18 5.18 5.19 5.20 5.20 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.10 6.11 6.12 7.3 7.3 7.4 7.5 7.6 7.7 7.8 7.11 7.12 7.14 8.1 8.2 8.4 8.6 8.7 8.8 8.8 8.9 8.9 8.9 8.10 8.10 8.11 8.11 8.12 8.12 8.12 8.13 9.2 9.2 9.3 9.3 9.4 9.5 xiii


FIGURES (continued) 9-7 Four Pipe System Room Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-8 Boiler Piping for a Multiple-Zone, Multiple-Purpose Heating System . . . . . . . . . . 9-9 Water Cooled Condenser Connections for City Water . . . . . . . . . . . . . . . . . . . . . . . 9-10 Cooling Tower Piping System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1 1 Basic Piping Circuits for Gravity Flow of Condensate . . . . . . . . . . . . . . . . . . . . . . . 9-12 Basic Piping Circuits for Mechanical Return Systems . . . . . . . . . . . . . . . . . . . . . . . 9-13 Typical Two-Pipe Vacuum Steam System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-14 Thermostatic Trap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-15 Inverter Bucket Trap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-16 Float and Thermostatic Trap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-17 Typical Connections to Finned Tube Heating Coils . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1 Refrigerant Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-2 Locations of Thermal Bulbs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-1 U-T ube Manometer Equipped with Over-Pressure Traps . . . . . . . . . . . . . . . . . . . . 11-2 Inclined-V ertical Manometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-3 Electronic/Multi-meter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-4 Pitot Tube Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-5 Pitot Tube . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-6 Magnehelic Gage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-7 Rotating Vane Anemometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-8 Electronic Analog Rotating Vane Anemometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-9 Deflecting Vane Anemometer Set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-10 Thermal Anemometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-1 1 Flow Measuring Hood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-12 Calibrated Pressure Gages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-13 Single Gage Being Used to Measure a Differential Pressure . . . . . . . . . . . . . . . . 11-14 Single Gage Being Used to Measure a Differential Pressure . . . . . . . . . . . . . . . . 11-15 Differential Pressure Gage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-16 Chronometric Tachometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-17 Digital Optical Tachometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-18 Digital Contact Tachometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-19 Stroboscope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-20 Multi-range, Dual Function (Optical/Contact Tachometer) . . . . . . . . . . . . . . . . . . 11-21 Glass Tube Thermometers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-22 Dial Thermometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-23 Thermocouple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-24 Thermistor Thermometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-24 Infrared Digital Thermometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-26 Resistance Temperature Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-27 Electronic Thermometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-28 Sling Psychrometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-29 Digital Psychrometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-30 Thermohygrometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-31 Clamp-on Volt Ammeter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-32 Accessing Automation System with Laptop Computer . . . . . . . . . . . . . . . . . . . . . . 11-33 Orifice as a Measuring Device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-34 Flow Meter Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-35 Annular Flow Indicator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-36 Calibrated Balancing Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-1 Schematic Duct System Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-2 Instruments Selected for a Specific Job . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-1 Sample Supply Air Duct (Part) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-2 Typical Air Diffuser CFM Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-3 Measuring Exhaust Air Velocity on Lab Exhaust Hood with Sash Height . . . . . . 13-4 Example of Exhaust Hood Air Balance Label . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-5 Sample Dust Collection Exhaust System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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9.5 9.7 9.12 9.13 9.14 9.16 9.16 9.17 9.17 9.18 9.18 10.2 10.5 11.1 11.2 11.2 11.3 11.4 11.5 11.6 11.6 11.7 11.7 11.8 11.10 11.12 11.12 11.13 11.14 11.14 11.15 11.15 11.15 11.18 11.18 11.19 11.19 11.19 11.20 11.20 11.22 11.22 11.23 11.23 11.24 11.25 11.26 11.26 11.26 12.3 12.5 13.4 13.6 13.7 13.8 13.9


FIGURES (continued) 14-1 Typical Variable Air Volume (VAV) System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-2 Open Loop Fan Volume Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-3 Closed Loop Fan Volume Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-4 Fan and System Curves, Constant Speed Fan . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-5 Fan and System Curves, Variable Speed Fan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-6 Series Fan Powered VAV Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-7 Parallel Fan Powered VAV Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-8 Paper Strip at VAV Box Return Before Balancing . . . . . . . . . . . . . . . . . . . . . . . . . . 14-9 Paper Strip at VAV Box After Balancing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-10 Constant Fan VAV Box . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-1 1 Intermittent Fan VAV Box (Parallel) Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-12 Multi-zone System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-13 Dual Duct System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-14 Induction Unit System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-1 Hydronic Flow Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-2 External Ultrasonic Flow Sensor on Pipe with Insulation Removed . . . . . . . . . . . 15-3 Ultrasonic Flow Meter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-4 Effects of Flow Variation on Heat Transfer 20F (11C) ∆t at 200F (93C) . . . 15-5 Percent Variation to Maintain 90% Terminal Heat Transfer . . . . . . . . . . . . . . . . . . 15-6 Chilled Water Terminal Flow Versus Heat Transfer . . . . . . . . . . . . . . . . . . . . . . . . . 15-7 Pump With Variable Speed Drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-8 Example of Primary and Secondary Pumping Circuits . . . . . . . . . . . . . . . . . . . . . . 15-9 Summer-Winter Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1 Duct Friction Loss Chart (I-P) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-2 Duct Friction Loss Chart (SI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-3 Duct Friction Loss Correction Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-4 Velocities/Velocity Pressures (I-P) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-5 Air Density Friction Chart Correction Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-6 Louver Velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-7 Elbow Equivalents of Tees at Various Flow Conditions . . . . . . . . . . . . . . . . . . . . . .

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14.1 14.2 14.3 14.4 14.4 14.9 14.9 14.9 14.10 14.12 14.13 14.14 14.15 14.16 15.1 15.2 15.2 15.9 15.9 15.10 15.11 15.12 15.13 A.1 A.2 A.4 A.9 A.11 A.12 A.43

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CHAPTER 1

INTRODUCTION


CHAPTER 1 1.1

INTRODUCTION TO TAB WORK

1.1.1

New Buildings

Testing, adjusting and balancing (TAB) of all HVAC systems in a new building is needed to complete the installation and to make the systems perform as the de− signer intended. Assuming that the system design and installation meets the comfort needs of the building occupants, good testing, adjusting and balancing of the HVAC system provides occupant comfort with minimum en− ergy input. This is extremely important in this era of rising energy costs. It is also important to make sure all factory equipment startup service has been completed before beginning any TAB work. Most specifications on new building construction usually require a factory representative to be present during the initial startup and adjustment of central boilers, chillers, large variable speed motor drives, and cooling towers. This initial equipment checkout is also usually required to activate the factory warranties and are not be part of the TAB contractor’s responsibility. After this initial startup service has been completed, the TAB contractor should be in− formed that the systems are operating properly, that all safety interlocks and protective devices are function− ing, and the systems are ready to be balanced. The Testing, Adjusting, and Balancing or TAB phase of any building construction or renovation is intended to verify that all HVAC water and air flows and pres− sures meet the design intent and equipment manufac− turer’s operating requirements. It is rare to find an HVAC system of any size that will perform completely satisfactorily without the benefit of TAB work. This is why it is necessary for the designer to specify that TAB work be part of the HVAC system installation. A sam− ple TAB specification can be found in the Appendix. Commissioning services for any new building construction or renovation are intended to verify all HVAC, lighting, plumbing, electrical, and security systems operate properly and meet performance crite− ria.

INTRODUCTION It should be made clear that the Testing, Adjusting, and Balancing (TAB) services may be the only HVAC sys− tem testing services contracted on most projects, but TAB work is not intended to be ?commissioning." Most commissioning services are completed by firms having technicians experienced with each of the indi− vidual building systems mentioned above. These firms will usually subcontract the services of an independent TAB contractor to verify HVAC system balancing as part of their more inclusive commission− ing contract. 1.1.2

There are few buildings in existence that have not ex− perienced changes in internal loads and wall reloca− tions since they were designed and built. These build− ings should have their HVAC systems rebalanced to achieve maximum operating efficiency and comfort. Many buildings require rebalancing twice each year with the seasonal change from heating to cooling or the reverse. Firms with a good TAB team have had a natural lead−in to service contracts and retrofit work because the TAB work identifies system operating deficiencies. 1.2

THE TAB TECHNICIAN/TEAM

1.2.1

The Technician

Throughout this publication, TAB technician will be used to designate the person in charge of the TAB work being done on the HVAC system discussed. It will be apparent after reading this publication and observing TAB procedures on a complicated HVAC system that the TAB technician must be a highly skilled and knowledgeable individual. This person must know the fundamentals of airflow, hydronic flow, refrigeration and electricity and be familiar with all types of HVAC temperature control and refrigeration systems. They must also know how to take pressure, temperature and flow measurements; and be able to perform effective trouble−shooting. The days of bal− ancing using a wet finger and cigarette smoke are long gone! 1.2.2

Commissioning also includes the testing of all build− ing controls for each mode of operation to verify all systems are being sequenced correctly with each other, and that all interlocks are functioning. The commis− sioning agent must document the results of each equip− ment test performed as it is completed.

Existing Buildings

The Team

There are TAB jobs that can be done by one person. However, many HVAC systems need a TAB team to complete the TAB work in a reasonable time period. It is equally important that the other members of the TAB team be trained and become knowledgeable in

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

1.1


the basic fundamentals and procedures of TAB work. Many of the local Joint Apprentice Training Programs have TAB courses, and the International Training In− stitute (ITI) has a Testing Adjusting and Balancing Bu− reau (TABB) training program.

1.3

GENERAL REQUIREMENTS

In addition to having the training to meet the demand− ing requirements of a TAB technician, a complete cali− brated set of balancing instruments is necessary to do TAB work on any commercial or institutional project.

1.2

The required instruments are detailed in Chapter 11CTAB Instruments. Sample test report forms may be found in Chapter 16CTAB Report Forms. These TAB report forms may be copied and used by SMACNA Contractors who fol− low the procedures and methods outlined in this manu− al. The forms are preceded by a description of their use. A sample outline specification has been included in the Appendix that can be used by the HVAC system de− signer to obtain a good, accurate TAB report based on the methods and procedures found in this manual.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


CHAPTER 2

HVAC FUNDAMENTALS


CHAPTER 2 2.1

HEAT FLOW

2.1.1

Introduction

Large HVAC systems must be designed by profession− al engineers who have received a high degree of educa− tion and practical experience in the fundamentals of heating, ventilating, and air conditioning. The TAB technician does not have to be an expert in the funda− mentals of HVAC systems, but must have had experi− ence in these systems and a basic knowledge of these fundamentals in order to perform a good balancing job and to understand what is happening. This chapter on HVAC fundamentals will include ba− sic thermodynamic and fluidic fundamentals that in− clude heat transfer, psychometrics, and fluid mechan− ics. 2.1.2

There are two fundamental laws of thermodynamics which can be stated in different, but equivalent ways: First Law

Energy can neither be created nor destroyed (the net increase in the energy content of a particular system in a given period is equal to the energy content of the ma− terial leaving the system, plus the work done on the system, plus the heat added to the system). 2.1.2.2

Second Law

It is impossible for a self−acting machine, unaided by any external agency, to convey heat from a body of lower temperature to one of higher temperature (heat flow always occurs from the higher temperature level to the lower temperature level). 2.1.3

scale of a thermometer, but the Celsius scale is used in the rest of the world. A typical temperature spectrum for the HVAC industry is where water freezes at 32F (0C) and boils at 212F (100C). The temperature at which a substance has no molecu− lar action is called absolute zero, which is −460F (−273C). The absolute temperature used in tempera− ture/pressure/volume calculations can be obtained by using the following equations: Equation 2-1 (I-P) R  °F  460°F Where: R  Absolutetemperature(Rankine) °F  Fahrenheittemperature

Thermodynamics

Heat is one of the several forms of energy which can be converted by various methods to, or from, energy in mechanical, chemical, electrical, and nuclear forms. Thermodynamics is the science of heat energy and its transformations to and from these other forms of energy.

2.1.2.1

HVAC FUNDAMENTALS

Units of Measurement

The intensity of heat of a substance traditionally has been measured in the United States on the Fahrenheit

Equation 2-1 (SI) K  °C  273°C Where: K  Absolutetemperature(Kelvin) °C  Celsiustemperature The quantity or amount of heat in a substance is mea− sured in British Thermal Units (Btu) which is the heat required to heat one pound of water one degree Fah− renheit. It is easy to realize that a swimming pool full of water at 95F, needs substantially more heat than a cup of water at 95F to increase each of them to 96F. In the metric system, the amount of heat required to heat one kilogram of water one degree Celsius is 4.18 kilojoules (kJ). 2.1.4

Heat Transfer

Heat flow is adding or removing heat at a given rate, which is measured in Btu per hour (Btuh) in the U.S. system and is measured in joules per second (J/s) or watts (W) in the metric system (1 J/s = 1 W). Figures 2−1 and 2−2 give examples of heat conduction, convection, and radiation, which are the three methods of heat transfer in environmental systems. Equation 2−2 may be used for heat flow through a ma− terial(s) that separates different air temperatures.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

2.1


Radiant heat

Heat Flow Heat flows from warmer body to cooler body by conduction

from flame

Rod heated by flame becomes hot as heat flows by conduction from one end to the other.

FIGURE 2-1 HEAT TRANSFER BY CONDUCTION AND RADIATION Q  A  U  Dt

Equation 2-2

Where: Q  Rateofheattransfer  Btuh(W) A  Areaofsurface  sq.ft.(m2) U  Coefficientofheattransfer Dt  Temperaturedifference  °F(°C) ?Delta" (  ), as used above, usually indicates a small change or difference; in this case, Dt is the tempera− ture difference. In Equation 2−2, neither Dt or Q represent heat. In the past, heat was thought to be a tangible quantity like a gallon of water, a pint of milk, or a bushel of wheat. Despite this carryover from the past, one cannot feel ?hot," as heat is not a tangible quantity. What one does feel is temperature. Temperature can be ?hot" when compared to some other reference point such as 98.6F (37C) body temperature, but one cannot feel how much heat is in an object. The amount of heat con− tained within the object varies with the object. The amount of heat contained within the object varies with the object’s temperature, mass, and substance. The

amount of heat in any given object at any given tem− perature can be calculated, but the HVAC industry does not find that a particularly useful function. What is useful is to know how fast heat is given up from that object, or the rate of heat transfer (Q) expressed in Btu per hour or watts. There also are other equations for calculating ?Q". Figures 2−3, 2−4, and 2−5 show the difference between counterflow, parallel flow, and cross−flow airstreams in coils or heat exchangers. The importance of the il− lustration in Figure 2−6 is that the final temperature at− tained by both of the mediums is affected by the direc− tion of the flow of the two different mediums at the heat transfer points.

Example 2.1 (I−P) A room (70F) has two separate walls which have an unheated space on the other side. The wall exposed to outdoors (30F) is 20’ × 8’ and has a ?U" factor of 0.12. The 24’  8’ wall exposed to the unoccupied space (55F) has a ?U" factor of 0.30. Which wall has the greatest heat loss?

Heating Coil

Steam or Hot Water in Pipes

Airflow

(A) Heat Flow by Natural Convection

(B) Heat Flow by Forced Convection

FIGURE 2-2 CONVECTION HEAT TRANSFER 2.2

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


B

A

B

A

B A

A

B A

B

A B

B

FIGURE 2-3 COUNTER FLOW AIRSTREAMS Solution Outside wall: Q  A  U  Dt  20  8  0.12  (70°F  30°F)  160  0.12  40°F  768Btuh Inside wall: Q  A  U  Dt  24  8  0.30  (70°F  55°F)  192  0.30  15°F  864Btuh (or the higher loss wall)

Example 2.1 (SI) A room (21C) has two separate walls which have an unheated space on the other side. The wall exposed to outdoors (0C) is 6 m  2.5 m and has a ?U" factor of 1.2. The 7 m  2.5 m wall exposed to the unoccupied space (12C) has a ?U" factor of 3.0. Which wall has the greatest heat loss?

Solution Outside wall: Q =MA  U  nt = 6 2.5 1.2 (21_C  0C) =M15  1.2  21C = 378 watts Inside wall: Q =MA × U × nt = 7 × 2.5 × 3.0 × (21_C − 12C) =M17.5 × 3 × 9_C = 473 watts

FIGURE 2-4 PARALLEL FLOW AIRSTREAMS

(or the higher loss wall) To illustrate the difference between temperature and the heat flow rate, and to show that a system can be bal− anced to either, assume that the airflow being supplied to different rooms is to be balanced so that each room has the same temperature reading. This procedure can be used in existing buildings when original engineer− ing calculations are not available and when the build− ing is experiencing large differences in temperatures between rooms. The TAB technician would then at− tempt to balance the system by adjusting the airflow so that each room had the designed space temperature. The other balancing procedure usually is required in new buildings where the designer has calculated the airflow rates that normally establish equal tempera− tures for each of the various room spaces. The TAB technician then balances the airstream flow rate to that scheduled for each room. The rooms should achieve the desired temperatures if the design calculations were correct. If a change in temperatures is required after occupancy, the additional balancing should not be done at no cost unless there was a provision for this extra work included in the TAB contract. In any event, the TAB technician balances to the flow rate of the me− dium, which actually is balancing to the heat flow rate that is being transferred by the medium. Balancing by heat flow and temperature are therefore not the same. In Equation 2−2 (Q = A U nt), ?U" is the variable affected by building insulation materials. Insulation ?values" can become quite confusing. They can be given per inch of thickness of material or for the actual thickness of the material, such as a ?six inch thick batt." Values can be given as conductance or resistan− ce. Chapter 25 of the 2001 ASHRAE Fundamentals

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

2.3


A1

A2

”C” AIRSTREAM

each component of the wall is the only way the total resistance (RT) can be obtained for a particular wall construction. Other building enclosure surfaces are treated in a similar manner (windows, floors, ceilings, etc.). ?R" values of air surface films must be used as indicated After the total resistance is obtained by adding the in− dividual resistances, the ?U" value is obtained by tak− ing its reciprocal as shown in Equation 2−4. Insulating materials play a large role in reducing the heat flow rate into or from buildings, ducts, pipes, etc. Obvious− ly, exterior surfaces having high resistances or low ?U" values will have less heat transfer between the outside environment and the interior of the structure, duct, or pipe.

EXCHANGER C2

“A” AIRSTREAM

Equation 2-3 RT =R1 +R2 +R3 +. . . +Rn

FIGURE 2-5 CROSS-FLOW AIRSTREAMS

Equation 2-4 Handbook entitled Thermal and Water Vapor Trans− mission Data contains thermal resistance values for different materials. Conductivity (k) indicates how much heat will pass through an inch of a material. Conductance (C) is a somewhat similar value, but is for a given thickness of material. Resistances (R), which are the reciprocals of ?k" or ?C", can be added sequentially for the heat flow through combinations of different materials. Conduc− tivity (k) and conductance (C) values can not be added in this manner. Therefore, addition of the resistance of

U  1 RT Where: U = Coefficient of heat transfer C Btuh/ ft2N⋅N°F (W/m2N⋅N°C) RT = Total of the resistances The values of U for the SI system are about 17.6 per− cent of the values in I−P Units, i.e., a ?U" of 1.0 in I−P Units is 0.176 in SI units.

TB (WARM)

TA (HOT)

TA (WARM)

TB (COLD) Distance Through Exchanger

TEMPERATURE

TEMPERATURE

TA (HOT)

TA (WARM)

TB (WARM)

TB (COLD) Distance Through Exchanger

FIGURE 2-6 PARALLEL AND COUNTERFLOW HEAT TRANSFER CURVES 2.4

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


Example 2.2 An outside wall of a building has the following resist− ances:

Outside surface film

— 0.17

Masonry

— 1.60

Furring (air space)

— 0.94

Drywall

— 0.45

Inside surface film

— 0.68

Find the coefficient of heat transfer U for this wall.

Solution R T  R1  R2  R3   R n R T  0.17  1.6  0.94  0.45  0.68 R T  3.84 U  1  1  0.26 RT 3.84 2.1.5 EQUIPMENT HEAT FLOW Heat flow in HVAC equipment is normally from a fluid (or gas) through a thin wall into another fluid (or gas); or it is into a transfer substance which moves into or to another cooler fluid (or gas) to deposit its energy. Major factors in the transfer of heat by conduction are: a.

temperature difference

b.

size and shape of the transfer surface

c.

type of fluid (or gas) and flow velocity

d.

conductivity of heat transfer material

e.

conductivity of the boundary layer

There also are many other factors to consider such as film coefficients, fouling, corrosion, condensables, frost or freezing, and poor maintenance.

Going back to the ?laws of thermodynamics" stated earlier in this chapter, the concept can be restated that the same amount of heat that is given up by one me− dium is gained by the other, and that all heat can be ac− counted for (energy can neither be created nor de− stroyed). This is not quite true in this atomic era, but it can be used as a basic principle for this TAB work. Equation 2-5 (I-P) Hydronic systems: Q  500  gpm  Dt Where: Q  Heatflow(Btuh) gpm  Gallonsperminute(water) Dt  Temperaturedifference(°F) Equation 2-5 (SI) Q  4190  m3s  Dt or Q  4.19  Ls  Dt Where: Q  Heatflow(kW) m 3s  Cubicmeterspersecond(water) Ls  Literspersecond(water) Dt  Temperaturedifference(°C) Note that in Equation 2−5 the 500 (4190 or 4.19) is a ?constant" that is used specifically for water. This constant will change when the system medium is other than water, such as a glycol mixture, steam, refriger− ant, or air. In fact, the comparable equation for sensible heat flow of air is shown below. Equation 2-6 (I-P) Air systems: Q  1.08  cfm  Dt Where: Q  Sensibleheatflow(Btuh) cfm  Cubicfeetperminute(air) Dt  Temperaturedifference(°F)

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

2.5


Equation 2-6 (SI) Q  1.23  Ls  Dt Where: Q  Sensibleheatflow(watts) Ls  Literspersecond(air) Dt  Temperaturedifference(°C) Sensible heat is defined as the heat associated with temperature differences only as measured by a ther− mometer. This is not affected by the method of heat transfer, such as radiation, convection, and conduc− tion. Transmission heat gains are those which occur through conduction of the heat through a surface as a wall. Convection has been taken into account by film coefficients on each side of the wallCwhether inside or outside. Example 2.3 (I−P) 30 gpm of water at 200F circulates through a heating coil. If 4000 cfm of air increases in temperature from 50F to 120F, determine the leaving temperature of the water. Solution Q  1.08  cfm  Dt  1.08  4000  (120°F  50°F)  302, 400Btuh  500  gpm  Dt Q 302, 400 Dt    500  gpm 500  30  20.16°F  (T1  T2) T2%  T1MM∆tNN200F ON20.16F N179.84F Water with a temperature of 180F is leaving the coil. Example 2.3 (SI) 2 L/s of 93F water circulates through a heating coil. If 2000 L/s of air increases in temperature from 10F to 50C, determine the leaving temperature of the wa− ter. Solution Q  1.23  Ls  Dt  1.23  2000  (50°C  10°C)  98, 400watts(98.4kW)  4.19  Ls  Dt Q   98.4kW 4.19  Ls 4.19  2Ls ∆tPM11.74CMM(T1 M–MT2 ) 2.6

T2 PMT1M – ∆tMM93CM–M11.74CM=M81.26C Water with a temperature of 81.3C is leaving the coil. 2.2

PSYCHROMETRICS

2.2.1

Introduction

Psychrometrics is a study of the thermodynamic prop− erties of moist air and the application of these proper− ties to the environment and environmental systems. Thermodynamics previously has been defined as the science of heat energy and its transformation, or change, from one form of energy to another. Since air is the final environment and one of the major fluids of the systems, whatever affects air affects the systems and the environment. Whatever happens to the air and the moisture it contains, under both natural circumstances and artificial conditions imposed by the systems and the environment, is of concern to the TAB technician. The language of psychrometrics, and to be able to use psychrometric charts and tables as tools to change existing conditions to those desired or re− quired, is a requirement for a good TAB technician. 2.2.2

Properties of Air

Dry air is an unequal mixture of gases consisting prin− cipally of nitrogen, oxygen, and small amounts of neon, helium, and argon. The percentage of each gas normally will be the same from sample to sample, al− though carbon dioxide and pollutants might be present in varying quantities. Air in our atmosphere, however, is not dry but contains small amounts of moisture in the form of water vapor, and the percentage may vary from sample to sample. This air−water mixture is the moist air referred to in the subject of psychrometrics. The amount of water vapor in atmospheric air normally represents less than 1 per− cent of the weight of the moist air mixture. If the aver− age weight of air is approximately 0.075 pounds per cubic foot (1.204 kg/m3), the moisture contained therein will weight less than 0.00075 pounds per cubic foot (0.012 kg/m3). This would seem to be an insignificant amount to cause so much concern. Normally, atmospheric air contains only a portion of the water it is able to absorb (partially saturated). If the proper conditions occur, air will absorb additional moisture until it can absorb no more, and it is then saturated. Air and water vapor be− have as though the other were not present. Each will act as an independent gas and exert the same pressure as if it were alone. The barometric pressure is the sum

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


of the two pressuresCthe partial pressure of the air, plus the partial pressure of the water vapor. The dry air component of the moist air exists only as a gas under all environmental conditions. it cannot be liquified by pressure alone, and therefore acts as a per− fect gas. However, water vapor does coexist with water as a liquid at all environmental temperatures, and it can be liquified by pressure. As it is not a perfect gas, the properties of water vapor are determined experi− mentally. 2.2.3

Air-V apor Relationship

Throughout the normal ranges of atmospheric pres− sures and temperatures, the air and water vapor mix− ture behaves as a perfect gas provided no condensation or evaporation takes place. A perfect gas is one where the relationship of pressure, temperature, and volume may be defined and predicted by Equation 2−7. Equation 2-7 PV  R T

T  70°F(21°C) P  14.696psi(101.325kPa)] V  13.33ft 3lb(0.831m3kg) d  0.075lbft 3(1.204kgm3) Example 2.4 (I−P) Using Equation 2−9, any condition other than standard may be calculated if one of the final conditions is known. For example, if one pound of standard air was heated to 700F, as in a process application, find the new volume of air per pound. Solution VT V 2  1 2  13.33  460  700 T1 460  70 1160  13.33   29.2ft 3lb 530 Similar calculations may be made for any value of temperature so long as the pressure remains constant. Example 2.4 (SI) If one kilogram of standard air is heated to 370C, find the new volume of air per kilogram.

Where: P'=MAbsoluteM pressureMMlb/Mft 2M(kPa) V'=MVolumeMMft3M(m3) T'=MAbsoluteMtemperature 460M + FM(273M+MC) R'=MGas constant The actual value of R has little meaning here, but the fact that R remains constant for any given perfect gas is extremely important. It is possible to equate the P, V, T values for two different conditions for the same gas: Equation 2-8 P 1V 1 PV  2 2 T1 T2

Solution 0.831  (273°C  370°C) V 1T 2  T1 (273°C  21°C) 8  0.831  643°  1.817m 3kg 294°

V2 

Example 2.5 (I−P Units) It is possible to make similar calculations which in− clude pressure variations. An example might be to find the correct volume for an altitude of 5000 feet. Assume that the temperature is the same at both points for con− venience.

If it is assumed that atmospheric pressure remains es− sentially constant at a given elevation on earth, then: Equation 2-9 VT V2  1 2 T1 Using Standard Air, which is the fixed reference for air conditioning calculations, the following properties oc− cur:

Solution P 1V 1 PV  2 2 , T 1  T 2 and P1V 1  P 2V2 T1 T2 P orV 2  V1 1 P2 The standard atmospheric pressure at 5000 feet is 24.90 inches of mercury (see Table A−16).

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

2.7


V 2  V 1

P1  13.33  29.92  16.02ft 3lb P2 24.90

Referring to the sample charts in Figures 2−7 and 2−8, note that the groups or families of curves have been la− beled to indicate which part or parts of the graph are for the different properties of most air. Definitions of the properties may be found in the Glossary.

Example 2.5 (SI) 2.2.4.1 Find the correct volume for an altitude of 1500 meters (T1 = T2 ) at standard conditions.

Solution V P 0.831  101.3 V2  1 1  P2 95.1(fromTableA  17)  0.989m3kg The conclusion to be reached from these examples is that large deviations from standard air temperature and pressure values require corrections to the calculations, while relatively small variations may be ignored. In the case of pressure, a correction normally is not used in applications below 2000 feet (600 m) above sea le− vel. Above 2000 feet (600 m) it becomes necessary to make the correction, since air has a significant reduc− tion in its ability to carry heat. By a series of calcula− tions and laboratory measurements, a long list of val− ues are obtained and are listed in Air Density and Correction Factor Tables in Appendix ACEngineer− ing Data, Tables and Charts. To be meaningful, these values must have a reference, which has been stated to be standard atmospheric pressure at sea level: 29.92 inches of mercury (101.325 kPa). Since the variations caused by pressure are not serious below an altitude of 2000 feet (600 m), the values obtained by maintaining the 29.92 inches of mercury (101.325 kPa) are ade− quate for use with HVAC systems. However, as seen in Example 2−4, temperature varia− tions in process systems can cause wide variations in air density: density = 1/29.2 = 0.034 lb/ft3, or a reduc− tion of 54 percent. For this reason, many engineering catalogs use standard cfm (scfm) which is ?cfm" cor− rected to ?standard air" conditions. Similar conditions apply to the SI system. 2.2.4

Using the Psychrometric Chart

A psychrometric chart is a series of graphs or curves arranged in such a way that, by knowing a specific val− ue of each of two different properties, a point can be obtained that will determine the values for all other properties under the same conditions. Charts are avail− able for different elevations above sea level, higher or lower temperatures, and many other variations. 2.8

Basic Grid, Humidity Ratio (Specify humidity)

The horizontal parallel and equidistant grid lines (with the scale displayed along the right side of the chart) in− dicate the grains of moisture per pound of dry air or pounds of moisture per pound of dry air. The bottom line of the chart is zero humidity and represents totally dry air. The chemical industry prefers to use mol−ra− tios, and grams of moisture per kilogram of dry air is used in the SI system. 2.2.4.2

Enthalpy (Total Heat)

Enthalpy lines are slanted from the top−left to the bot− tom−right. Enthalpy is designated by the letter ?h" and, as all values on the chart, is referred to a pound (kilo− gram) of dry air. This is the only value which does not change through various processes, such as heating− cooling, compression−expansion, and humidification− dehumidification. Other constant value lines are su− perimposed upon this basic grid by plotting and are neither equidistant nor parallel, although they may ap− pear to be so. 2.2.4.3

Dry Bulb Temperature

Constant dry bulb temperature lines on the chart are nearly vertical. They diverge slightly towards the top of the chart. The scale is at the bottom, along the dry air line (zero humidity ratio) from left to right, and val− ues are given in F in Inch−Pound units, English or cus− tomary, and in C in SI Units, the International System of Units, Metric. 2.2.4.4

Saturation Line, Dew Point and Wet Bulb

The curved upper borderline of the chart, which runs from the bottom left to the mid−top, is an experimen− tally plotted saturation line. It shows the maximum amount of water vapor (in pounds or kilograms) which can be associated with a pound (kilogram) of dry air at a given dry bulb temperature. Air is said to be saturated with moisture at this point. The temperature at this point is known as the saturation temperature. It can be seen from the saturation line that at higher temperatures air can hold more moisture than at lower temperatures. Conversely, the capacity to hold mois−

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


Pounds of moisture per pound of dry air Enthalpy at saturation Btu per pound of dry air Grains of moisture per pound of dry air 85 90 95 100 105 .35 180 .025 170 .024 160

150

.023

.021 140

130

.45

.020 .019 .018

120

.40

.022

.50

.55

.017 .60

110

.016 .65 .015

100 .014 90

80

.013 .012

.70 .75 .80 .85 .90 .95

.011 70

60

.010

Sensible heat factor

.009 .008

50 .007 40

.006 .005

30 .004 20

80% 60%

10

40%

0 25

30

.002 .001

20% 20

.003

35

40

45

50

55

60

65

70

75

80

85

90

95

100

105

0 110

Wet-Bulb, Dewpoint or Saturation Temperature F

FIGURE 2-7 PSYCHROMETRIC CHART (I-P) ture is less at lower temperatures. Therefore, if the al− ready saturated moist air is being cooled, the excess moisture instantly begins to separate from the moist air by condensation either in the form of fog (the left side of the saturation curve is the fog area) or as dew if it condenses on a cold surface.

The point of saturation (saturation temperature) is also called the dew point. At this point the saturation tem− perature, the dry bulb temperature and the wet bulb temperature are all the same value. The saturation temperature values (also dew point or wet bulb tem− peratures) are shown in F (C) along the saturation line where it is crossed by the same value dry bulb lines.

2.2.4.5

Specific Volume

Specific volume lines run at a steep angle from top left to bottom right. The numerical values, along the bot− tom of the chart at the end of these lines, are given in cubic feet per pound of dry air in I−P Units (and in cu− bic meters per kilogram in the SI System).

The slant and spacing of the specific volume lines show that moist air becomes lighter (by expansion) with an increase in temperature and with an increase in moisture content (moist air is lighter than dry air at the same temperature). The specific volume of dry air can be found at the intersection with the bottom, zero humidity ratio line. The volume of the water vapor can be found by subtracting the volume of the dry air from the volume of the moist air. 2.2.4.6

Relative Humidity

The curves of constant relative humidity (RH) lie be− tween the zero humidity ratio line at the bottom and the curved saturation line above. The curvature decreases as curves approach the dry air line. Relative humidity expresses the proximity of the sub− ject moist air to that of saturated air at the same tem− perature. The saturation line represents 100 percent RH and the bottom line of the chart is 0 percent RH. Another term used to define proximity of the moist air to saturation is the degree of saturation which is the ra− tio of the humidity ratio of the moist air to that of the saturated moist air at the same temperature and pres−

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

2.9


30

28 30

26

H H

24

SENSIBLE HEAT TOTAL HEAT

25

=

22

HUMIDITY RATIO (w) GRAMS MOISTURE PER KILOGRAM DRY AIR

20

20

15

18

16

14

12 0.85 0.90

10

0.95 1.0

8

10

6 5

4

2

0

20

30

40

50

DRY BULB TEMPERATURE C

FIGURE 2-8 PSYCHROMETRIC CHART - TYPICAL CONDITION POINTS (SI) sure. The difference between both meanings is small but still noticeable within the comfort conditions. While the degree of saturation of 50 percent lies on the dry bulb temperature line directly in the middle be− tween 0 percent and 100 percent, the 50 percent RH point is slightly below the mid point. Measurement of relative humidity depends on changes in humidity responsive materials. While low cost and quite accurate, these instruments require frequent cal− ibration. 2.2.4.7

Wet Bulb Temperature

The wet bulb method was developed to obtain a more practical way to measure relative humidity and de− pends on the evaporation of water around the bulb of a mercury thermometer. Since evaporation and the de− pression of the wet bulb temperature depends on the relative humidity of the moist air, it can be used to measure relative humidity by use of conversion tables.

bulb temperatures are equal at this point and are also equal to the dew point temperature (saturation temper− ature). As the wet bulb lines run so close to the enthal− py lines, most psychrometric charts use the same lines for both wet bulb temperatures and enthalpy and show correction of either enthalpy values or wet bulb values by another family of curves. 2.2.4.8

Plotting Conditions

Consider point A, in Figure 2−9, representing summer outdoor design conditions. By finding the point which represents 95F DB and 78F WB, the values for the other properties are:

Dew point temperature = 71.98F Relative humidity = 48% Enthalpy (total heat) = 41.6 Btu/lb dry air Moisture content = 118 grains/lb dry air

At the saturation point, there is no evaporation. Since the wet bulb depression is zero, the wet bulb and dry 2.10

or 0.0169 lb moisture/lb dry air.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


Enthalpy at saturation Btu per pound of dry air 85

90

Grains of moisture per pound of dry air 95

100

Pounds of moisture per pound of dry air

105 .35

180 .025

170 .024

.023

160

.40

.022 150

41.6 BTU/Lb

78F WB

.021

POINT “A”

.45

140

.020

.019

.50

130 .018 .55 120

.017 .60 .016

110

118 GR/Lb

.65 .015

71.9F DP

.70

100 .014

.75

48% RH

62.7F WB

.0169 Lb/Lb

.013

90

.80 .85

.012

.90 .95

80

28.3 BTU/Lb

.011

70

.010

.009

Sensible heat factor

60

POINT “B”

65 GR/Lb

.008

50 .007

50% RH

55F DP

.006 40

.0093 Lb/Lb

.005 30 .004

.003

20 80%

Wet-Bulb Dewpoint or Saturation Temperature F

60%

.

40%

95F DB

75F DB

.002 10 .001

20% 0

Dry-Bulb F

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

105

0 110

FIGURE 2-9 PSYCHROMETRIC CHART - TYPICAL CONDITION POINTS Now consider point B in Figure 2−9 representing sum− mer indoor design conditions. By finding the point which represents 75F DB and 50 percent RH, the val− ues for the other properties are: Dew point temperature = 55F Wet bulb temperature = 62.7F Enthalpy (total heat) = 28.3 Btu/lb dry air Moisture content = 65 grains/lb dry air or 0.0093 lb moisture/lb dry air.

a change are the environmental systems. The designer, by knowing what design conditions must be satisfied, but without knowing the airflow rate, is able to plot the various changes in different portions of the system and the environment. The designer then is able to deter− mine what systems are capable of accomplishing the necessary results. In addition, the heat values are used in the design calculations to see immediately if the de− sign conditions are practical or impossible. But first, the various condition changes must be illus− trated and understood. For this purpose, skeleton psychrometric charts have been used in the related dia− grams, alternating between I−P Units and SI units. 2.2.5.1

In this way, any condition may be plotted on the chart for normal environmental systems. Other charts are available for plotting from tabular data for conditions not found here, but the need for such variations is not common. 2.2.5

Condition Changes on Psychrometric Charts

Using the chart, simple logic leads to the conclusion that there must be some way to change the properties of the air, initially at the condition of point A, to the conditions of point B. The means to accomplish such

Sensible Changes

Sensible heat, by definition, indicates only dry bulb temperatures changes. Therefore, any heating system not including humidification is a sensible heat process or system and is represented on the chart as a horizon− tal straight line. Conversely, any cooling system utiliz− ing a dry coil which does not dehumidify or where the surface of the coil does not fall to or below the air dew point is also a horizontal straight line. a.

Heating

Assume that air which is at 70F and 20 percent RH is heated to 105F. This process is indicated in Figure

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

2.11


2−10. Conditions other than those mentioned here have been determined from the psychrometric chart.

a change in latent heat. This process is indicated on the sample metric chart in Figure 2−11. Humidification and dehumidification are defined as the addition or subtraction of moisture from air. Since each is a change of state from liquid to gas and gas to liquid, each occurs at a constant dry bulb temperature, but a varying wet bulb temperature. Note that this is the same process as the addition or subtraction of latent heat and is also the same vertical line on the chart in Figure 2−11 at a constant dry bulb temperature. Hu− midification and dehumidification are both latent heat processes, and both are shown on the same chart.

105F DB 8% RH 20F DP 64F WB

70F DB 20% RH 28F DP 50F WB

HEATING

COOLING

FIGURE 2-10 SENSIBLE HEATING AND COOLING (I-P)

In this example, the only constant value is the dry bulb temperature; all other properties increase for humidifi− cation and decrease for dehumidification. Note that this process is essentially an illustration and cannot normally be reproduced in environmental systems. 2.2.5.3

By considering the values, it may be seen that the dew point has not changed and the total moisture content in grains/lb has not changed. The dry bulb temperature has gone up, the heat content has gone up, the wet bulb temperature has gone up, and the ability of the air to absorb moisture has gone up as indicated by the de− crease in relative humidity. The example is theoretical because moisture from people, cooking, infiltration, etc., will make some contribution to the moisture in the air. However, this is the design diagram for heating without deliberate humidification. b.

Cooling

Now consider the process and ignore the extraneous moisture sources noted above. In ideal conditions, air gives up its heat along the same line to maintain the oc− cupied spaces at the given 70F DB and 20 percent RH. A cooling coil, selected to cool air from 105F DB and 20F DP to 70F DB would also produce condi− tions along the same line as long as the coil surface temperature was above 20F. In most systems, this would be impractical if not impossible, since the coil would immediately clog with frost. 2.2.5.2

Latent Changes

Latent heat, by definition, involves a change of state to or from a fluid; and in the case of air, this means the addition or removal of moisture. It must be remem− bered that the dry bulb temperature does not change during this addition or removal of moisture. Therefore, a vertical line on the psychrometric chart between any two points at constant dry bulb temperature represents 2.12

Combination Changes

Combination sensible−latent heat processes are the rule in most systems. The addition or subtraction of la− tent and sensible heat appears as a combination pro− cess with all changes occurring simultaneously. The result is neither a horizontal nor vertical line but a slanted one tilted in the direction dictated by process. Referring to Figure 2−12, consider the general rules be− low based on the two endpoints of the process; the first being the initial condition of the air; and the second be− ing the final condition after the process or a portion of the air treatment has been completed. On the chart, all processes have the same initial point, and the arrow point indicates each arbitrary final point: Sensible heating is a horizontal line from left to right. Sensible cooling is a horizontal line from right to left. Humidification is a vertical line upward. Dehumidification is a vertical line downward. Heating and humidification is a line sloping upward to the right. Cooling and dehumidification is a line sloping down− ward to the left. Evaporative cooling is a line sloping upward to the left. Chemical dehydration or dehumidification is a line sloping downward to the right. Now consider the specific cooling−dehumidifying ex− ample which might represent the conditions obtained

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


Humidification—Addition of Moisture and Latent Heat by Evaporation of Steam Injection

Dehumidification— Removal of Moisture and Latent Heat by Condensation

41C DB 28.2C WB 24C DP 38% RH 90 kJ/kg 18.9 g/kg 41C DB 20.1C WB 6.8C DP 13% RH 58.9 kJ/kg 6.2 g/kg

FIGURE 2-11 HUMIDIFICATION AND DEHUMIDIFICATION (I-P) from a cooling coil using 100 percent recirculated air. Assume that the entering air and room conditions are 80F DB and 50 percent RH. Also assume that the cooling coil can produce leaving conditions of the air at 55F DB and 54F WB. The illustration of the pro− cess is shown in Figure 2−13. The line drawn between the initial and final conditions represents the change of air properties produced by the cooling coil and is conveniently drawn straight. In ac− tual fact, the process follows a curve, but the deviation is not usually important to the system analysis. To the coil designer, however, the curvature is critical, since it indicates the heat transfer conditions from point−to− point through the coil depth. The amount of moisture that was removed from the air (condensed on the coil) was 16 grains/lb of dry air (77T–T61T=T16). The reverse operation, heating and humidifying, could be explained by working the cooling−dehumidifying diagram backwards. However, a more practical ap− plication may be obtained by using a new diagram. As− suming that 21C DB, 40 percent RH air returns to a heating coil and that a humidifier has been added, the

combination process, assuming the required leaving conditions to be 41C DB and 38 percent RH, is illus− trated in Figure 2−14. 12.7 grams of moisture per kilo− gram of dry air was added in the process (18.9T–T6.2T=T 12.7) Equation 2−10 is used for the change in the total heat content of the air, including the moisture content. Equation 2-10 (I-P) Q(Total)  4.5  cfm  Dh Where: Q  Totalheatflow(Btuh) cfm  Airflow Dh  Enthalpydifference(Btuhlbdryair) Equation 2-10 (SI) Q(Total)  1.2  Ls  Dh Where: Q  Totalheatflow Ls  Airflow Dh  Enthalpydifference(kJkgdryair)

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

2.13


49

Pounds of moisture per pound of dry air

Grains of moisture per pound of dry air

48

Enthalpt at saturation Btu per pound of dry air

90

100

95

105

47

85

.35

46

180

45

.025 170

43

44

.024

.023

.40

42

80

160

41

.022 150 .45

39

40

.021

.020

.019

75

37

38

-0.1 Btu

140

.50

130

-0.2 Btu

.018 .55 120

Heating & Humidification

Evaporative Cooling

.017 .60 .016

-0.3 Btu

70

33

34

90% Relative Humidity

35

36

Humidification

110 .65 .015 .70

80% 30

100

65

28 27

26 25

55

50% -.06 Btu

23 22

Sensible Cooling

.80 .85

.012

.90

.010

Sensible heat factor

.95

80

70

.009 -.08 Btu

21

.75

90

Sensible Heating

-.02 Btu

24

60% 60

20

18

Common Initial Reference

70%

Enthalpy deviation Btu per pound of dry air

29

.014

60

40%

18

17

.008 50

16

50 .007

11

13

40

20%

35

9

12

10

Chemical Dehydration or Dehumidification

Cooling & Dehumidification Dehumidification

14

12

15

30% 45

30

.006 40

.005 30 .004

40.1 Btu

.003

8

20 40.2 Btu

.002

60%

Saturation Temperature F

40.3 Btu

40%

10 40.4 Btu

.001

20% 40.5 Btu

0 60

55

65

70

80

75

85

90

100

95

105

0 110

14.0 cu ft

50

13.5 cu ft

45

13.0 cu ft

40

35

30

12.5 cu ft

20

25

14.5 cu ft per pound of dry air

Wet-Bulb, Dewpoint or

10%

80%

7

25

FIGURE 2-12 PSYCHROMETRIC CHART - PROCESSES Psychrometric charts base all the information given in content per pound (kilogram) of dry air. The standard equations are derived from these values and give a very close approximation of the actual calculation if all the conditions would have been worked out using the basic figures on the psychrometric chart. From any two given points on a psychrometric chart, the Btuh (watts) obtained for enthalpy is always equal to or greater than the Btuh obtained for sensible heat only. The reason for this is that the moisture contained in the air has heat content.

b. Locate the final condition on the chart as Point ?B". The wet bulb temperature is 62.7F and the en− thalpy is approximately 28.3 Btu per pound of dry air. c.

The decrease in enthalpy is: h = 41.6 − 28.3 = 13.3 Btu per pound

d.

Q (Total)

= 4.5  10,000  13.3 Q (Total) e.

Solution a. Locate the initial condition on the psychrometric chart, as Point ?A" in Figure 2−9. The corresponding wet bulb temperature is 78F, and the enthalpy is approximately 41.6 Btu per pound of dry air. 2.14

= 598,500 Btuh

Tonsofrefrigeration  Btuh  Btuhton 12, 000 

Example 2.6 (I−P) Air at 95F DB and 48 percent RH enters a cooling coil at a rate of 10,000 cfm. If the air is cooled to a condi− tion of 75F DB and 50 percent RH, find the cooling load in Btuh, and in tons of refrigeration.

= 4.5  cfm  h

598, 500  49.9tons 12, 000

Example 2.6 (SI) Air at 36C DB and 50 percent RH enters a coil at a rate of 5000 L/s. If the air is cooled to a condition of 24C and 50 percent RH, find the cooling load in watts and kilowatts (use Figure 2−8). Solution a. The enthalpy for 36C DB and 50 percent RH is approximately 85.3 kJ/kg.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


AIR ENTERING 80F DB 67F WB 50% RH

AIR LEAVING 55F DB 54F WB 94% RH

FIGURE 2-13 COOLING AND DEHUMIDIFYING (I-P)

AIR LEAVING

AIR ENTERING

21C DB 40% RH 6.8C DP 13.1C WB 37.1 kJ/kg 6.2 g/kg

41C DB 38% RH 28.2C WB 24C DP 90 kJ/kg 18.9 g/kg

FIGURE 2-14 HEATING AND HUMIDIFICATION

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

2.15


b. The enthalpy for 24C and 50 percent RH is approximately 48.0 kJ/kg. c.

The decrease in enthalpy is: ∆h = 85.3 − 48.0 = 37.3 kJ/kg

d.

Q (Total) = 1.2 x L/s × h = 1.2 × 5000 × 37.3 Q (Total) = 223,800 (223.8 kW)

It is sometimes necessary to calculate the weight of the air. This is shown in the solution to Example 2.7 (I−P). The average person is not used to thinking of air as having weight. Air is a fluid and has weight just as wa− ter is a fluid and has weight. As a reminder, ?Standard air," at 0.075 pounds per cubic foot (1.204 kg/m3) is very much lighter than water at 62.4 pounds per cubic foot (1000 kg/m3). The specific volume of standard air is the reciprocal: 1  0.075  13.33 cubic feet per pound 1/0.075 = 13.33 cubic feet per pound (1/1.204 = 0.8305 m3/kg).

Solution 10, 000cuftmin  750.2poundsperminute 13.33cuftlb 750.2  60 minutes = 45,012 pounds per hour 45,012  13.3 (∆h) = 598,660 Btuh 598,660/12,000 = 49.9 tons The total heat content of air also can be taken from tables when the wet bulb temperature is known.

Example 2.7 (SI) Obtain the solution to Example 2.6 (SI) using the weight of the airflow volume.

Solution 5.0m 3s  6.02kgs 0.83m 3kg 6.02kgs  37.3kJkg  224.5kJs

Example 2.7 (I−P) 1W  1Js, so Obtain the solution to Example 2.6 (I−P) using the weight of the airflow volume.

2.16

224.5kJs  224.5kW

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


85.3

MIXED AIR

_ _

Q 3=10,000 l/s t 3=DB = ?3 WB3 = ?

C

_

Point B

_ _

56.3

49

_ Condition of mixture (Point C) 35_C DB

_

Point A

FIGURE 2-- 15 MIXING OF TWO AIRSTREAMS (SI)

2.2.5.4

Airstream Mixtures

Mixtures of two or more airstreams are a common requirement of the environmental system. The mixing of outside and return air on the entering side of the air cooling and heating equipment is the common method of introducing the outside ventilation air to the system. Outside air can be one of the greatest heating and cooling loads in more extreme climates.

 Assume that the airstreams are being mixed in a 50 percent ratio which causes the mixed point to be directly between points “A” and “B”.  Then assume that the damper moves to a position to take in less hot outside air (“B”). This will cause point “C” to move away from “B” (the line “B” to “C” gets longer when less air is taken in). If point “C” coincides with point “A,” 100 percent return air “A” will be used.

Figure 2-15 illustrates the mixing of an outside airstream and a return airstream, which usually is found in most air handling unit system applications.

 The mixed air temperature will be closest to the air temperature of the largest airstream.

When two airstreams are mixed and are plotted in graph form, the following steps should be used:

 Only the dry bulb air temperature can be obtained by using this method or by using Equation 2-11.

HVAC SYSTEMS Testing, Adjusting & Balancing  Third Edition

2.17


Equation 2--11 Xo T o + X r T r Tm = 100

b) From Figure 2-15:

Where:

27_C WB = 85.3 kJ/kg

Tm = Temperature of mixed air — _F (_C) Xo = Percentage of outdoor air — %

Using Equation 2-12:

To = Temperature of outdoor air—_F (_C)

X oH o + X rH r 100 20% × 85.3 + 80% × 49.0 Hm = 100 1706 + 3920 Hm = = 56.26 kJ∕kg 100 On a psychrometric chart, 56.26 kJ/kg = approximately 19.7_C wet bulb temperature.

Xr = Percentage of return air — % To = Temperature of return air—_F (_C) The wet bulb of the mixed airstream can be obtained by substituting the enthalpies of the two airstreams in Figure 2-15 in Equation 2-12 and calculating the enthalpy of the mixed airstream. From this value, the mixed airstream wet bulb temperature can be obtained from the psychrometric chart. Equation 2--12 X oH o + X rT r Hm = 100 Where: Hm = Mixed air enthalpy — Btu/lb (kJ/kg) Xo = Percentage of outdoor air — % Ho = Outdoor air enthalpy — Btu/lb (kJ/kg) Xr = Percentage of return air — % Ho = Return air enthalpy — Btu/lb (kJ/kg) Example 2.8 (SI) Calculate the dry bulb and wet bulb temperatures of the mixed airstream of Figure 2-15 using equations and by plotting in graph form on a psychrometric chart. Solution a)

Using Equation 2-11 for the dry bulb temperature: X oT o + X rT r 100 20% × 35˚C + 80% × 24˚C Tm = 100 700 + 1920 Tm = = 2620 = 26.2˚C (DB) 100 100 Tm =

2.18

17_C WB = 49.0 kJ/kg

Hm =

The psychrometric chart provides a quick method for calculating the mixed airstream conditions using only a scale as is shown in Figure 2-15. First, plot the two conditions (“A” and “B”) on the chart and draw a straight line between the two. Divide this distance in proportion to the mixed air quantities, and to scale, plot the mixed air point “C” so that it is closest to the conditions of the largest original quantity in the mixture. This is usually closest to the lowest dry bulb point since outside air quantities are usually less than 50 percent. (If they are 100 percent, no mixture determination is required.) The point “C” represents what mixture conditions should be if the air quantity proportions are correct. All of the properties of the mixture at point “C” are immediately available from the psychrometric chart (26.2_C DB and 19.7_C WB are two of them). One common error made by many novices, is the improper location of the mixed air point on the charts. Some reverse the ratio of the mixing streams, causing the mixed point shown in Figure 2-15 to occur near the top right hand point “B”. When two airstreams are mixed and are plotted in graph form, the following steps should be remembered: Assume that the air streams are being mixed a 50 percent ratio which causes the mixed point to be directly between points “A” and “B”. Then assume that a damper moves to a position to take in less hot outside air (at “B”). This will cause the point to move away from “B” (as the line “B” to “C” gets longer when less air is taken in). By the time it reaches “A”, 100 percent of the air of quality “A” will be used. It should be noted that the use of the psychrometric chart in the design to determine the properties of the

HVAC SYSTEMS Testing, Adjusting & Balancing  Third Edition


mixture does not establish the airflow quantity. This determination must be made independently. The de− signer must establish the total air quantity required from the sensible heat load and the outside air quantity from the design ventilation requirements. 2.2.5.5

Related Tables and Equations

Air (standard) density = 0.075 lb/ft3 (1.204 kg/m3 ) Water (standard) density = 62.4 lb/ft3 (1000 kg/m3) Specific volume is the reciprocal of density and is used to determine cubic feet of volume if the pounds of weight are known:

Chapter 6, Psychrometrics of the 2001 ASHRAE Fun− damentals Handbook has more detailed theory and data on this subject along with the necessary equations and psychrometric tables. Chapter 8, Thermal Comfort includes the comfort zone and effective temperature scale superimposed on a standard psychrometric chart. 2.3

FLUID MECHANICS

When the word fluid is mentioned, the average person thinks in terms of water. However, the full definition of fluid in the Glossary is ?gas, vapor, or liquid." In TAB work, the word fluid normally means air (from the atmosphere), water (or a heat transfer fluid), steam, refrigerants, and occasionally, a few other gases. This section will contain a detailed description of the behavior of air and water, as the properties of these two fluids affect most TAB work. Air and water generally have similar fluid properties except that the numerical values assigned to each property vary considerably. 2.3.1

Compressibility

For TAB purposes, water cannot be compressed. Air can be compressed and the volume of air can be pre− dicted by using Equations 2−7 to 2−9. 2.3.1.2

Water (Standard) specific volume = 0.016 ft3/lb(0.001 m3/kg) Standard Conditions for air as used above correspond to dry air to 70F (21C) and at an atmospheric pres− sure of 29.92 in. Hg. (101.325 kPa). For water, stan− dard conditions are 68F (20C) at the same baromet− ric pressure. 2.3.1.3

Weight, Density and Specific Volume Relationships

In TAB work, weight is measured in pounds (kilo− grams) and density in pounds per cubic foot (kg/m3); therefore, for standard conditions:

Specific Heat

The following specific heat values at standard condi− tions were used to develop Equations 2−5 (for water) and 2−6 (for air). Water: Specific Heat (Cp ) = 1.00 Btu/lbF (4190 J/kg C)

Fluid Properties

The basic categories of fluid properties are state, com− pressibility, viscosity, weight or density, volume or specific volume, volatility, specific heat and heat con− tent; but only those important to TAB technicians will be discussed. 2.3.1.1

Air (Standard) specific volume = 13.33 ft3/lb (0.831 m3/kg)

Air: Specific heat (Cp ) = 0.24 Btu/lbF (1000 J/kg C) Air Equation 2−6 only applies to sensible heat transfer (that which affects the dry bulb thermometer). 2.3.2

Fluid Statics

Static head is the pressure developed by the weight of the fluid at rest (not moving) in a system. The static head of air is insignificant and is ignored in TAB cal− culations, but not the static head of water. As Standard Atmospheric Pressure is measured at 14.696 psi (101.325 kPa), then Absolute Pressure is obtained by adding the 14.696 psi (101.325 kPa), atmospheric pressure to the gage pressure of the system static head.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

2.19


To obtain the weight of one foot of water in psi and also absolute pressure: 62.4lbsqft 1footofwater  144sqinsqft = 0.433 psi gage pressure (psig) or 1 ft of water= 0.433 + 14.696 =15.129 psia (absolute pressure) Other I−P Unit pressure/weight/height relations are: 1 inch of mercury (Hg) = 13.6 inches of water gage (in.wg) 1 foot of mercury (Hg) = 5.89 psi 1 psi = 2.31 ft wg = 2.04 in.Hg 14.696 psi = 29.92 in.Hg = 33.9 feet of water gage (ft wg) In the SI system: 1 meter (water) = 9.807 kPa

1 millimeter (mercury) = 133.32 kPa From the above relationships, it can be seen that using water instead of mercury in a U−tube manometer for a pressure of 15 psi (103.4 kPa) would be quite cumber− some. However, it would be feasible to use when mea− suring the pressure of HVAC duct systems. Figure 2−16 shows the relationship between height and pressure of an open tank of water. The hydrostatic head at point B is 30 feet (9 m) and the fluid head at point B is 30 feet of water (9 m) which is equal to 13.0 psi gage (90 kPa) and to 27.7 psia (191.3 kPa a). 2.3.3 2.3.3.1

Fluid Dynamics Velocity

The term ?dynamics" is used to describe the condi− tions of motion of a fluid or gas in a system. The ?ve− locity" of the fluid is based on the cross−sectional area of the conduit (pipe or duct) through which it is flow− ing and the volume of fluid within the conduit. When there is no turbulence, the velocity varies within the conduit as shown in the diagram in Figure 2−17, ?Velocity Profile." This phenomenon, known as the velocity profile, is caused by the friction between the conduit walls and the fluid.

OPEN TANK MAINTAINS

ATMOSPHERIC PRESSURE

CONSTANT WATER LEVEL

14.7 psi (101.3 kPa)

GAGE 10ft(3m)

HYDROSTATIC HEADS

30ft(9m) 50ft(15m)

PRESSURES

ABSOLUTE PRESSURES

4.3 psi (29.7 kPa)

19.0 psi (131.1 kPa a)

13.0 psi (89.7 kPa)

27.7 psia (191.1 kPa a)

21.7 psi (149.7 kPa)

36.4 psia (251.2 kPa a)

30.3 psi (209.1 kPa)

45.0 psia (310.5 kPa a)

70ft(21m)

FIGURE 2-16 TANK STATIC HEAD

2.20

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


V min (Zero at Wall) V avg

V max

FIGURE 2-17 VELOCITY PROFILE

The only purpose of this device is to produce a pressure sufficient to overcome the resistance of the system to the flow of the fluid. The pressure produced is indi− cated by the pressure difference from the pump or fan inlet to the pump or fan discharge. This is exactly equal to the system resistance to flow and, in the case of wa− ter, the elevation differences for the amount of fluid being pumped. A measurement of the difference be− tween the inlet and discharge pressures of a pressure device of any kind is then a measurement of the system resistance at a particular flow rate. 2.3.4

When the flow is ?turbulent," the friction rate in− creases, heat transfer through the walls of an exchang− er increases, and usually, so does the system noise that is created by the fluid flow.

Q  AV

Equation 2-13

Where: Q = Fluid flow A = Area

Air

Water

cfm (L/s)

gpm (L/s)

ft2 (m2)

ft2 (m2)

V = Velocity fpm (m/s) fpm (m/s) *Correction constants are needed so that the units in the equation are compatible. 2.3.3.2

Friction

It has been indicated that the flow of the fluid is re− sisted by a well known paradox of nature called fric− tion. Friction is the natural resistance caused by a sub− stance with which it is in contact. One substance may be stationary and the other moving or both may be moving at different velocities. If it were possible to start the fluids flowing in a system and then eliminate friction losses of the conduit and the dynamic losses of the fittings, it would be possible to eliminate all power consuming pumping equipment in closed systems. The only purpose of the pumps is to overcome these losses which result from the flow they produce. 2.3.3.3

Pressure

Pressure is the force required to overcome the friction and dynamic losses of a system. This pressure is pro− duced by a pumping device which in HVAC systems may be a circulating pump, fan, or a gaseous refriger− ant compressor.

2.3.4.1

Air System Basics Duct Pressure Changes

The pressures in air systems are simpler than those in hydronic systems because the weight of air in the sys− tems is ignored in most calculations. The resistance to airflow, imposed by a duct system, is overcome by the fan, which supplies the energy (in the form of total pressure) to overcome this resistance and maintain the necessary airflow. Figure 2−18 illustrates an example of the typical pressure changes in a duct system with the total pressure and static pressure grade lines in ref− erence to the atmospheric pressure datum line. In air conditioning and ventilating work, the pressure differences are ordinarily so small that incompressible flow is assumed. Relationships are expressed for air at a standard density of 0.075 lb/ft3 (1.204 kg/m3) and corrections are necessary for significant differences in density due to altitude or temperature. Static pressure and velocity pressure are mutually convertible and can either increase or decrease in the direction of flow. To− tal pressure, however, always decreases in the direc− tion of airflow. At any cross−section, the total pressure (TP) is the sum of the static pressure (SP) and the velocity pressure (Vp ): TP  SP  Vp

Equation 2-14

For all constant−area straight duct sections, the change in static pressure losses are equivalent to the total pres− sure losses because the change in velocity pressure (Vp ) equals zero, as the velocity is constant. These pressure losses in straight duct sections are termed friction losses. Where the straight duct sections have smaller cross−sectional areas, such as duct sections BC and FG in Figure 2−18, the pressure lines fall more rap− idly than those of the larger area ducts (pressure losses increase as the square of the velocity). When the duct cross−sectional areas are reduced, such as at converging sections B (abrupt) and F (gradual),

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

2.21


A

B

C

D

E

F

G

AIR FLOW

ENTRY

H EXIT Diffuser

TP

SP

TP

Vp

ATMOSPHERIC PRESSURE SP TOTAL PRESSURE (TP)

VELOCITY PRESSURE (V ) p

STATIC PRESSURE (SP)

FIGURE 2-18 PRESSURE CHANGES DURING FLOW IN DUCTS both the velocity and velocity pressure increase in the direction of airflow and the absolute value of both the total pressure and static pressure decreases. The pres− sure losses at points B and F are dynamic losses.

Dynamic losses are due to changes in direction or ve− locity of the air and occur at transitions, elbows, and duct obstructions, such as dampers, etc. Dynamic losses can be expressed as a loss coefficient (the constant which produces the dynamic pressure losses when multiplied by the velocity pressure) or by the equivalent length of straight duct which has the same loss magnitude.

Increases in duct cross−sectional areas, such as at di− verging sections C (gradual) and G (abrupt), cause a decrease in velocity and velocity pressure, a continu− ing decrease in total pressure and an increase in static pressure caused by the conversion of velocity pressure to static pressure. This increase in static pressure is commonly known as static regain and is expressed in terms of either the upstream or downstream velocity pressure. 2.22

At the exit fitting, section H, the total pressure loss co− efficient may be greater than one upstream velocity pressure, equal to one velocity pressure, or less than one velocity pressure. The static pressure just upstream of the discharge fit− ting can be calculated by subtracting the upstream ve− locity pressure from the total pressure upstream. The entrance fitting at section A in Figure 2−18 also may have total pressure loss coefficients less than 1.0 or greater than 1.0. These coefficients are references to the downstream velocity pressure. Immediately downstream of the entrance, the total pressure is sim− ply the sum of the static pressure and velocity pressure. Note that on the suction side of the fan, the static pres− sure is negative with respect to the atmospheric pres− sure. However, velocity pressure is always a positive value. It is important to distinguish between static and total pressure. Static pressure is the blow−up pressure (like a balloon) which commonly has been used as the basis for duct system design. Total pressure determines how much energy must be supplied to the system to main−

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


tain airflow. Total pressure always decreases in the di− rection of airflow. But static pressure may decrease, then increase in the direction of airflow (as it does in Figure 2−18) and may go through several more in− creases and decreases in the course of the system. It can become negative (below atmospheric) on the dis− charge side of the fan, as demonstrated by points G and H. The distinction must be made between static pres− sure loss (sections BC or FG) and static pressure change as a result of conversion of velocity pressure (section C or G). The total resistance to airflow is noted by nTPsys in Figure 2−18. Since the prime mover is a vaneaxial fan, the inlet and outlet velocity pressures are equivalent; i.e. nTPsys = nSPsys . When the prime mover is a cen− trifugal fan, the inlet and outlet areas usually are not equal, thus the suction and discharge velocity pres− sures are not equal, and obviously nTPsys nSPsys . If one needs to know the static pressure requirements of a centrifugal fan, knowing the total pressure require− ments, the following relationship may be used: Equation 2-15 FanSP  TP d  TP s  Vp d (orasSP  TP  Vp) FanSP  SP d  TP s where the subscripts d and s refer to the discharge and suction sections respectively of the fan.

Above 2000 feet (600 m) altitude, below 50F (10C), or above 90F (32C) temperature, the friction loss obtained from Tables A−1 and A−2 must be corrected for the air density. Table A−12 presents the correction factors for temperature and altitude. The actual air vol− ume is used to find the friction loss from Table A−1 and A−2 and this loss is multiplied by the correction factor or factors from Tables A−3 and A−4 to obtain the actual friction loss. 2.3.4.3

HVAC duct systems usually are sized first as round ductwork. Then, if rectangular ducts are desired, duct sizes are selected to provide flow rates equivalent to those of the round ducts originally selected. Tables A−5 and A−6 give the circular equivalents of rectangu− lar ducts for equal friction and flow rate. Note that the mean velocity in a rectangular duct will be less than in its circular equivalent. Rectangular duct sizes should not be calculated direct− ly from the actual duct cross−sectional area. Tables A−5 and A−6 should be used. If this is not done, the resulting duct sizes will be smaller, with a greater velocity and friction loss for the given airflow. 2.3.4.4

2.3.4.2

Circular Equivalent for Rectangular Ducts

Dynamic Losses

Friction Losses

Pressure drop in a straight duct is caused by surface friction, and varies with the air velocity, the duct size and length, and the interior surface roughness. Friction loss is most readily determined from Air Friction Charts, Tables A−1 and A−2 in the Appendix. They are based on standard air with a density of 0.075 lb/ft3 (1.204 kg/m3 ) flowing through average, clean, round, galvanized metal ducts (with an absolute roughness factor of 0.0003 ft. The values may be used without correction for temperatures between 50F (10C) and 90F (32C) and for altitudes up to 2000 feet (600 m) and for any relative humidity. Beyond those limits, corrections should be made for other than standard air densities, and when using other duct materials or flex− ible duct. Tables A−3 and A−4 are new tables and charts that pro− vide correction factors for ducts of materials other than hot−dipped galvanized sheet metal construction. The correction factor is multiplied by the friction loss ob− tained from Table A−1 and A−2 for each straight duct section.

Where turbulent flow is present, brought about by sud− den changes in the direction or magnitude of the veloc− ity of the air flowing, a greater loss in total pressures takes place than would occur in a steady flow through a similar length of straight duct having a uniform cross−section. The amount of this loss in excess of straight−duct friction is termed dynamic loss. 2.3.4.5

Duct Fitting Loss Coefficients

The duct fitting loss coefficient ?C" is dimensionless and represents the number of velocity heads lost at the duct transition or bend. Values of the loss coefficient for elbows and other duct elements have been deter− mined experimentally or computed and can be found in tables in the SMACNA HVAC Systems 9 Duct De− sign manual or the ASHRAE Fundamentals Hand− book. Tables A−4 and A−5 which show the relation of veloc− ity to velocity pressure for standard air, can be used to find the dynamic pressure loss for any duct element whose loss coefficient ?C" is known.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

2.23


Fitting loss coefficient Velocity pressure—in.wg

Tee, 45 Entry, Rectangular Main and Branch Use the Vp of the upstream section Ac

Branch, Coefficient C

Qc

Vc

V / V b c

Qs Ab

Qb

Vs Ac = A s

As

Qb/ Qc 0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.2

0.91

0.4

0.81

0.6

0.77

0.72

0.70

0.8

0.78

0.73

0.69

0.66

1.0

0.78

0.98

0.85

0.79

0.74

1.2

0.90

1.11

1.16

1.23

1.03

0.86

1.4

1.19

1.22

1.26

1.29

1.54

1.25

0.92

1.6

1.35

1.42

1.55

1.59

1.63

1.50

1.31

1.8

1.44

1.50

1.75

1.74

1.72

2.24

1.63

0.79

FIGURE 2-19 SAMPLE FITTING LOSS COEFFICIENT TABLE

TP  C  Vp

Equation 2-16

Equation 2-17 (SI) Q V 1000A Where:

Where:

V = Velocity (m/s) TP = Total pressure loss C in. wg (Pa) Q = Duct airflow (L/s) C = Fitting loss coefficient Vp = Velocity pressure C in. wg (Pa) The velocity pressure (Vp) used for rectangular duct fittings must be obtained from the velocity (V) ob− tained by using the following equation:

A = Duct cross−sectional area (m2) Where different areas are involved, letters with or without subscripts are used to denote the area at which the mean velocity is to be calculated, such as A for in− let area, A1, for outlet area and Ao for orifice area, etc. The equation for obtaining the velocity pressure (Vp) from the velocity is:

Equation 2-17 (IP)

Q V A

Equation 2-18 (I-P)

Vp  V 4005

2

Equation 2-18 (SI) V p  0.602V 2

Where: V = Velocity (fpm) Q = Duct airflow (cfm)

Where: Vp = Velocity pressure C in. wg (Pa) V = Velocity C fpm (m/s)

A = Duct cross−sectional area (sq ft)

2.24

Commonly used fitting loss coefficient tables ex− tracted from the SMACNA HVAC Systems9Duct De− sign manual can be found in Tables A−17 and A−20.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


Equation 2-19

Example 2.8 (I−P) Q2 rpm  rpm2 1 Q1

A main duct has an airflow of 10,000 cfm at 2000 fpm. A 45 entry tap is used for the branch duct that requires 3,000 cfm at 1,600 fpm. Find the pressure loss to the branch of the fitting.

d2 rpm  rpm2 1 d1

Using the data from Figure 2−19: Qb 3, 000   0.3 Qc 10, 000 Vb 1, 600   0.8 Vc 2, 000 Branch loss coefficient C = 0.69 2, 000

 (0.5)  0.25 V  4, 005 2

2

p

TP  C  Vp  0.69  0.25 TP  0.1725in. wg Example 2.8 (SI) A main duct has an airflow of 5,000 L/s at 10 m/s. A 45 entry tap is used for the branch duct that requires 1500 L/s at 8 m/s. Find the pressure loss to the branch of the fitting. Solution Using the data from Figure 2−19: Qb  1500  0.3 Qc 5000 Vb  8  0.8 Vc 10 BranchlosscoefficientC  0.69 V p  0.602  (10) 2  60.2Pa TP  C  Vp  0.69  60.2Pa  41.5Pa

2.3.4.6

bp 2 rpm  rpm2 1 bp 1

Solution

Fan Laws

The TAB technician can use fan curves or tables pub− lished by the fan manufacturer to determine the output of a fan under certain conditions. The following fan law equations also allow the TAB technician to calcu− late the necessary changes to be made to a system or a system component prior to the actual work.

Equation 2-20

P2 rpm  rpm2 P1 1

2

Equation 2-21 3

Equation 2-22 2

Where: QPP=MAirflow C cfm(L/s) rpmP=Fan revolutions per minute P'P=Static or total pressure – in. wg (Pa) bpPM=Fan brake power – HP (W) dPP=Density C lb/ft3 (kg/m 3) The relationship between the fan laws, fan curves, and system curves will be discussed in Chapter 5 Fans. One of the most important things to remember is that the fan brake power increases as the cube of the fan rpm increase (or of the airflow increase by combining Equations 2−17 and 2−19). So when the TAB technician attempts to increase the airflow in a system without making other changes, the fan brake power (and the fan energy consumption) in− creases dramatically. 2.3.4.7

System Pressure

The total system pressure that the system fan must han− dle then is the sum of the friction losses of each straight duct section, the dynamic losses of each duct fitting or obstruction, and the pressure loss of each duct compo− nent such as coils, filters, dampers, etc. Examples can be found in Chapter 7 Air Systems. In a given duct system with a known airflow rate, and when the position of all dampers is stable, a specific total pressure can be measured. If the airflow is in− creased without any other changes, then Equation 2−21 can be used (this equation was derived from fan law Equations 2−17 and 2−18);

P2 Q2  P1 Q1

Equation 2-23 2

Where:

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

2.25


P  Systempressure  in.wg(Pa) Q  SystemAirflow  cfm(Ls)

Obviously, the 5 HP motor would be inadequate and a 10 HP motor would be marginal.

Example 2.9 (I−P Units) Example 2.10 (SI) A duct system is operating at 2.0 in.wg with an airflow of 10,000 cfm. If the airflow is increased to 13,000 cfm without any other change, determine the new duct sys− tem pressure.

Solution

000 QQ  2.0 13,

10, 000 2

P 2  P 1

The same system used in Example 2.9 has a 3.8 kilo− watt motor operating at 3.6 kilowatts. Find the fan brake power and standard motor size that would be re− quired if the airflow was increased to 6500 L/s.

2

2

Solution

1

 2.0(1.3)2  3.38in.wg

 7.91kilowatts  3.6 6500 5000

Q bp 2  bp1 2 Q1

Example 2.9 (SI) A duct system is operating at 500 Pa with an airflow of 5000 L/s. If the airflow is increased to 6500 L/s without any other change, determine the new duct sys− tem pressure.

 845Pa  500 6500 5000

Q P 2  P 1 2 Q1

2

2

Example 2.10 (I−P Units) The same system used in Example 2.9 has a 5 HP mo− tor operating at 4.82 bhp. Find the bhp and standard motor size that would be required if the airflow was in− creased to 13,000 cfm. Solution

000 QQ  4.82 13,

10, 000 3

bp 2  bp1

2 1

  4.82(1.3)3  10.59

2.26

3

3

3

The 3.8 kW motor is inadequate and a 7.5 kW motor would be marginal. 2.3.5 2.3.5.1

Hydronic System Basics Hydronic Pressure Losses

In air systems, the weight of air in the system is ignored by system designers and TAB technicians. In hydronic systems, it is the velocity head that is ignored because the values usually are insignificant. Otherwise, hy− dronic systems are subject to similar friction losses in the straight runs and dynamic losses in the fittings. Manufacturers normally supply pressure loss data for equipment used in piping systems. Pressure losses for hydronic systems are given in terms of equivalent feet of pipe, in pounds per square inch (psi), or in feet of water (ft wg) in I−P Units. In SI units, meters of water and Pascals or kilopascals are used.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


Equation 2−22 is the hydronic equivalent of air systems Equation 2−21: Equation 2-24

P2 Q2  P1 Q1

2

towers, are subject to greater corrosion and therefore have higher pressure losses per 100 feet of pipe. Prop− erly sized pumps used with these systems generally will deliver a higher flow rate than required by a newly installed system because the anticipated corrosion has not occurred. However, after a few years, a partially closed balancing cock at the pump will have to be opened.

Where: 2.3.5.3 PP= Pressure difference C psi(Pa or kPa) QP= Flow rate C gpm(L/s)

Example 2−11 (I−P) A piping system has a flow rate of 100 gpm at a 20 ft wg head. Calculate the flow rate if the flow resistance is reduced to a 10 ft wg head.

Solution

2

P2 Q2  ; Q2  Q1 P1 Q1 Q 2  100

PP

10  71gpm 20

2

A piping system has a flow rate of 6.3 L/s at a 6 meter head. Calculate the flow rate if the flow resistance is reduced to a 3 meter head.

2

P2 Q2  ; Q2  Q1 P1 Q1 Q 2  6.3

PP

36  4.45Ls

Static head, discussed earlier, is the pressure due to the weight of the fluid above the point of measurement. In a closed system, the selection of the pump capacity is not affected as the static head is equal on both sides of the pump. However, the pump casing must be designed to handle the highest static head. Suction head is the height of fluid from the centerline of the pump on the suction side to the level of the fluid surface as is shown in Figure 2−20. The actual static head pressure loss that is added to the piping and sys− tem pressure loss in order to size the pump is the differ− ence between A minus B.

1

Example 2−11 (SI)

Solution

Heads

2 2

Suction lift is the height of fluid that a pump must lift on the suction side of the pump from the level of the fluid surface to the pump centerline as shown in Figure 2−20. This pressure loss value is added to any other sys− tem or pump pressure losses if additional piping or equipment is involved. 2.3.5.4

Pump Laws

The following equations are similar to (or the same as) the fan law equations. Again, they allow the TAB tech− nician to calculate changes that could occur in a given hydronic system when one or more of the conditions is altered. Most equations required for TAB work also can be found in the Appendix along with the SI equiva− lents. Equation 2-25

2.3.5.2

Friction Losses

Friction loss tables for hydronic systems vary in value depending on the condition of the piping system and the type of pipe or tubing used. Closed systems, where the fluid continuously recirculates, such as hot and chilled water systems for HVAC work, stay relatively clean and free from deposits that could roughen the in− terior surfaces. Open systems, such as domestic hot water systems and condenser water systems with normally open cooling

Q2 rpm  rpm2 1 Q1 Equation 2-26 Q2 D  2 D1 Q1

H2 rpm  rpm2 H1 1

H2 D2  H1 D1

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

Equation 2-27 2

Equation 2-28 2

2.27


STATIC PRESSURE

STATIC HEAD (DIFFERENCE = A - B) TO BE ADDED TO PUMP HEAD

A

SUCTION HEAD

B

CLOF PUMP TANK

PUMP

FIGURE 2-20 PUMP WITH STATIC HEAD AND SUCTION HEAD

bp 2 rpm  rpm2 1 bp 1

bp 2 D2  D1 bp 1

2.28

Equation 2-29

Equation 2-30 3

Where:

3

Q rpm D H bp

= Fluid flowCgpm (L/s) = Revolutions per minute = Impeller diameterCinches (mm) = HeadCfeet (meters) = Brake powerCHP (kW)

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


CLOF PUMP

PUMP

L SUCTION LIFT

TANK

FIGURE 2-21 PUMP WITH SUCTION LIFT

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

2.29


THIS PAGE INTENTIONALLY LEFT BLANK

2.30

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


CHAPTER 3

ELECTRICAL EQUIPMENT AND CONTROLS


CHAPTER 3

ELECTRICAL EQUIPMENT AND CONTROLS

3.1

ELECTRICAL SYSTEMS

3.1.1

Basic Electricity

Equation 3-3 1R t  1R1  1R2  1R3    1R n (Parallel Circuits)

The electrical industry concerns itself with a broad range of subjects, many of which are not necessarily directly related to the HVAC industry. However, it is necessary to know basic electricity as it applies to that part of building construction which is related to me− chanical and electrical systems. Electric motors drive or power almost all HVAC equipment, including fans and pumps. Understanding the operation of, and the differences between, the many types of motors, the related controls, and the control circuits, is a necessity for the TAB technician. The TAB technician must be able to determine the brake horsepower that is being applied to air handling equipment and ensure that the motor is properly con− nected and protected. A few simple equations should be kept in mind when dealing with electricity. The first is a derivative of Ohm’s law: The current in a circuit is equal to the elec− tromotive−force activity in the circuit divided by the resistance in the circuit.

Where: R t  TotalSystemResistance R n  IndividualResistances

Equation 3−3 states mathematically that the parallel current flow will work similarly to hydronic flow, with the circuit with the highest resistance receiving the lowest flow. 3.1.2.2

Series Circuits

Resistances are added together for electrical circuits in series as in hydronic circuits. As more resistances are added, the flow becomes less and less. Equation 3-4 R t  R1  R2  R3    R n (Series Circuits) Where: R t  TotalResistance R n  IndividualResistances

Equation 3-1 I  E (or)E  IR R P  IE

Equation 3-2

Where: I  Amps(A) E  Volts(V) R  Ohms(W) P  Watts(W) 3.1.2 Electrical Resistances 3.1.2.1

Parallel Circuits

Parallel electrical circuits resemble HVAC terminal units piped in parallel circuits. Using a simple circuit with two units and one pump, it is known that the water flow will split in accordance with the resistance across each unit. If both resistances are the same, the flow will split 50−50.

The electrical diagram in Figure 3−1 is similar to a pip− ing circuit with a pump at ?E", two chillers in series at ?R1" and ?R2", seven terminal units piped in parallel, and a strainer, valve, etc., piped in series in the pump suction piping. This shows the similarity of electrical calculations to those for hydronic and air, where resist− ances in series are added, and those in parallel are com− bined. 3.2

ELECTRICAL SERVICES

3.2.1

Single Phase Circuit Voltages

A measured voltage may not be exactly one of the val− ues of voltages indicated in Figure 3−2. Voltages can vary, and in normal situations a variation of ±10 per− cent will not adversely affect equipment operation. The basic 115 volt two−wire circuit shown in part ?A" of Figure 3−2 is very common. There is a potential or pressure of 115 volts between the hot wire and the neu− tral or ground. Normal household use, such as a lamp, is representative of such a circuit. The 115 volt poten− tial in the hot wire will exist between the hot wire and the neutral, or between the hot wire and any other

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

3.1


Parallel

IT

R1

R2

(Etc.)

Series E Series

Series-Parallel

FIGURE 3-1 SERIES-P ARALLEL CIRCUIT

FUSE MAIN SWITCH

TO LOAD

115 V

GROUND

TO EQUIPMENT

GROUND LINE GROUNDS

A. TWO-WIRE CIRCUIT

GROUND LINE GROUND TO EQUIPMENT

MAIN FUSE HOT

MAIN SWITCH 115 V

115 V LOAD

115 V

115 V LOAD

NEUTRAL MAIN FUSE HOT CIRCUIT FUSES GROUND LINE

B. THREE-WIRE CIRCUIT

FIGURE 3-2 SINGLE-PHASE AC SERVICE

3.2

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

230 VOLT LOAD


+

Time

+

Time

+

Time

Current I

Voltage E

Voltage E

Voltage E

Current I

Current I

--

-Difference in Peaks Causing Power Loss Inductance Load Current Voltage

-Difference in Peaks Causing Power Loss Capacitance Load Current Voltage

Peaks Concurrent Providing Maximum Useful Power Inductance -- Capacitance Current Voltage (Power Factor Corrected)

FIGURE 3--3 CURRENT AND VOLTAGE-- TIME CURVES AND POWER FACTOR ground, such as a pipe or a person which might contact the wire.

The neutral or ground wire is another matter. The neutral normally has no voltage potential. Theoretically, if the neutral contacts a pipe or a person, nothing will happen. The neutral is connected to the ground. The term theoretically is used, because in actual field conditions, stray currents can find their way into the neutral and it then can be dangerous. A neutral should be treated with the same respect as a known hot wire.

Part “B” of Figure 3-2 shows another common single phase circuit. It is also a household circuit which serves items requiring greater power such as ranges, clothes driers and air conditioners. This circuit represents the type of three-wire service normally entering residences. Two of the three wires are hot wires and one is neutral. The voltage potential between either of the hot wires and the neutral is 115 volts. There are actually three circuits; two separate 115 volt circuits (from each of the hot wires to the neutral) and a 230 volt circuit (between the two hot wires). The neutral in a 230 volt circuit found in some appliance connections serves as a ground for safety, but it is not used as part of the power circuit. It is connected to the frame of the machine to carry off any stray currents or any short circuits resulting from failures. Ground or neutral wires are never switched or fused. The main advantage of the 230 volt, two hot wire circuit is that it allows each of the hot wires to carry half of the current flow. Therefore, twice the current will be handled by the same size wires.

3.2.2

Three Phase Circuit Voltages

The three-phase (3∞) concept is somewhat more difficult to understand. Figure 3-3 shows alternating current pulses of voltage and current changing with time. In the case of the single-phase, three-wire circuit, two different pulses are being sent down two different hot wires. After one starts, the second starts 1/120th of a second later. These pulses continue indefinitely at the same frequency and have the same phase relationship between the 2 wires. This can be thought of as +115 volts and -115 volts between the hot wires and the neutral wire. The pulses would average 115 volts between the hot wire and the neutral wire, would change to -115 volts and back to +115 volts and so on 120 times per second. The pulses going down the other wire would do the same, but because their timing is out of phase, an instantaneous look at the two 115 volt wires would show that the voltage in one wire would be +115 volts, and the other wire (because of its delay in phase) would be -115 volts. When voltage readings are taken with a voltmeter, there is no apparent way to tell the difference between 220 volt single phase circuits and 220 volt three-phase circuits. When measurements are taken, it is found that voltages do vary somewhat; that three-phase circuits are usually 220 volt, and that single-phase circuits are usually 230 volt. However, phasing cannot be determined by just voltage readings. Four-wire, three-phase circuits, as illustrated in Figure 3-6, produce 208 volts between phase wires. This arrangement is commonly used in commercial buildings, as the 120 volt loads can be divided equal between the three hot (phase) wires.

HVAC SYSTEMS Testing, Adjusting & Balancing  Third Edition

3.3


Three-Phase Motor (220 V)

L1 Main Switch Fuse

220 V

220 V

L2

220 V L3

FIGURE 3-4 220-VOL T THREE-WIRE DELTA THREE-PHASE CIRCUIT

Center Tap

Approx. 177 V

Fuse

Three-Phase Motor (220 V)

L1 Transformer

Main Switch L2

110 V 220 V L2

Fuses

Single-Phase Loads (110 V) Neutral

FIGURE 3-5 220-VOL T DELTA THREE-PHASE CIRCUIT WITH 110-VOL T SINGLE-PHASE SUPPLY

Fuse

Three-Phase Motor (208 V)

L1 Main Switch

208 V

208 V

L2

208 V L2

Fuses

Single-Phase Loads (120 V) Neutral

FIGURE 3-6 120/208-VOL T FOUR-WIRE WYE CIRCUIT

3.4

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


3.3

TRANSFORMERS

For the voltage reduction indicated for the transformer illustrated in Figure 3−7, the number of turns shown on the primary side should be twice the number of turns shown on the secondary side. Voltage is transformed by the transformer stepping down the voltage to one half the original voltage. By swapping the primary and secondary connections, this same transformer could step up the voltage from 440 volts to 880 volts. The ballasts in fluorescent lights in buildings step up the voltages from 115, 220, or 227 volts to voltages near 2500 volts, the required voltage to produce light in the tubes. The function of the center tap of a transformer also is illustrated in Figure 3−7. If a 220 volt difference exists between the legs of the secondary side, it is logical that a 110 volt difference would exist between one leg and a center tap. Most single−phase residential transform− ers have high voltages on the primary side, but the sec− ondary voltages use a ?center tap" (the ground) to fur− nish two 110 volt circuits along with the 220 volt power (Figure 3−2). This size transformer, which looks like a large can, usually is attached to a pole near the residence. It can supply power to several residences or buildings, or just to a single building. Larger transformers are ground mounted, and if out− side, are usually in a metal housing. These transform− ers can be either single−phase or three−phase. The ?tap" (or neutral) cannot be used with hot line ?L2" for 110 volt single−phase loads (Figure 3−5) from a three− wire, 220 volt circuit. However, all three hot line or phase wires may be used for 120 volt loads in four− wire, 208 volt circuits (Figure 3−6).

110 V Secondary 440 V Primary

(Center Tap) 220 V Secondary 110 V Secondary

FIGURE 3-7 TRANSFORMER WITH TAPPED SECONDARY 3.4

MOTORS

3.4.1

Types of Motors

Most motors used on HVAC system equipment are de− signed for alternating current. Small motors will use single−phase current, while the larger motors will use three−phase current. However, some rural areas must use larger motors on single−phase current, as three−

phase current is not available. There are many differ− ent motor speeds, but 1800 rpm and 3600 rpm are the most common. The actual speed of the motor will vary with the load imposed. Split phase, capacitor start, synchronous, induction, shaded poleCall are part of the many different types of motors that the TAB team will need to recognize. The characteristics of each is important for troubleshooting, as the wrong type of motor may be used. 3.4.2

Rotation

Motors rotating in the wrong direction are a common occurrence when a new system is started. The normal TAB procedures deal with this situation, as correct motor rotation is vital to the performance of the unit. The direction of the motor usually is changed in three− phase motors by switching any two of the three−phase power wires. In single−phase motors, the change of di− rection is accomplished by switching two of the inter− nal motor leads that connect to the motor line terminal lugs. CAUTION: Certain fans and most pumps will develop measurable pressures and some fluid flow when the rotation is incorrect. Rotation arrows can be found on many types of equipment. Correct rotation is obvious on some units. Flow and amperage readings also can be used to determine whether something is amiss. Whenever a piece of equipment does not perform as specified and the current flow is much lower than de− sign, rotation is one item to be checked. 3.4.3

Nameplate Data

Except for some small motors, an attached nameplate will supply the basic information that the TAB techni− cians needs: full load amps, rpm, horsepower or watts capacity, voltages, line phase, and cycles. Many motor nameplates contain starting load amps that are quite large compared to full load amps. Although starting load amps are not as important (and are not recorded), the amperage value must be used by the system design− er for electrical circuits, circuit breaker panels, and motor starting equipment. Information on special motors might have to be ob− tained from specification sheets or from the HVAC unit nameplate. Since voltage and amperage measure− ments are seldom the same as the nameplate values, the actual motor horsepower being produced can be es− timated. However, the no load amps reading is difficult to obtain from close−coupled equipment where the load cannot easily be detached from the motor. The motor must be running with all drives disconnected for this no load amps reading.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

3.5


3.4.4

Operating Temperatures

Every electric motor generates heat as well as power. The more inefficient the motor, the greater the amount of heat produced. Unless this heat is dissipated, the temperature within the motor will rise until the insula− tion is destroyed. The amount of heat produced in the motor also de− pends upon the load. Therefore, most motors are rated on the basis of a certain temperature rise when running fully loaded. Open motors are generally designed to run at a temperature rise of 72F (40C) above the sur− rounding (ambient) air temperature. In other words, an open motor when running at full nameplate condi− tions, could be running at a temperature of 142F (61C) if the surrounding air is 70F (21C). Totally enclosed motors generally are rated at a 99F (55C) temperature rise. Under the latter conditions, a totally enclosed motor would run at 169F (76C). 3.4.5

Motor Performance

Figure 3−8 indicates ways in which various motor fac− tors are interrelated. The point at which the speed and the amperes cross corresponds to 55 percent of the maximum amps and over 60 percent of the maximum horsepower. At this point, the speed is between 97 and 98 percent of the maximum synchronous speed (which is not a great change) and the efficiency curve stays fairly flat close to 90 percent. The power factor also stays between 80 and 90 percent. Single−Phase Circuits: Equation 3-5 (I-P) I  E  P.F.  Eff. bhp  746 Equation 3-5 (SI) I  E  P.F.  Eff. kW  1000 Three−Phase Circuits: Equation 3-6 (I-P) I  E  P.F.  Eff.  1.73 bhp  746

3.6

Equation 3-6 (SI) kW 

I  E  P.F.  Eff.  1.73 1000

Where: bhp'= Brake horsepower (I−P) kW' = Kilowatts (brake power) (SI) I' = Amps E' = Volts P.F.'= Power factor Eff.'= Efficiency In Equation 3−5 and 3−6, the power factor and efficien− cy values must be used to obtain the actual motor brake power. As these values usually are difficult to obtain, a reasonable estimate can be used. Referring to Figure 3−8, the normal range of both curves is between 80 and 90 percent. Therefore, 80 percent might be used for one value and 90 percent for the other value to obtain a brake power estimate. Brake power is calculated to verify that the proper size motor has been installed, i.e., that the installed motor is not overloaded and is operating within its service factor. It also is used to determine that the pump or fan is operating with the required efficiencies. The system designer usually has specified the total amount of pow− er or energy that may be consumed to perform a specif− ic function. For example, a pump is selected to circulate 120 gpm (7.6 L/s) of water at a 40 foot (12 m) head and consume not more than two horsepower (1.5 kW). Designers in the past may have used a three horsepower (2.3 kW) motor on the pump in order to have a safety factor, or to have extra capacity for future loads that may be planned for the system. With energy conservation con− siderations, the installation of a three horsepower (2.3 kW) motor just to have a safety factor should not be used unless a future load is planned. When the designer does not want to use more than the rated two horse− power (1.5 kW), it is essential to calculate the actual power consumption unless the amperage reading is well within the full load amperage rating of the motor. There are two equations that must give a less theoreti− cal, but more practical approach to the calculation of motor full load (F.L.) amperage and brake horsepower (kW).

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


Equation 3-7 ActualF.L.amps 

Solution

F.L.amps *  voltage * Actualvoltage

a.

Using Equation 3−7: 8.16  220V 210V  8.55amps

ActualF.L.amps 

Equation 3-8 bhp(kW)  HP * (kW *)  (Motoroperatingamps)  (Noloadamps  0.5)

b.

Using Equation 3−8:

(ActualF.L.amps)  (Noloadamps  0.5) bph (kW)'= 3 HP (2.3 kW)

Use Equations 3−7 and 3−8 to obtain an accurate (but not exact) brake power by measuring motor amper− ages and voltages under no load and full load condi− tions.



(6.2)  (4.7  0.5) (8.55)  (4.7  0.5)

bph(kW)  3HP(2.3kW)  *Nameplate ratings that supply the basic information.

(6.2)  (2.35) (8.55)  2.35)

bph(kW)  approx.1.86HP(1.43kW)

Example 3.1 Example 3.2 A fan has a 3 HP (2.3 kW), 220 volt, 3 phase motor that actually draws 6.2 amps at 210 volts. The full load am− perage shown on the nameplate is 8.16 amps and the ?no load" measurement is 4.7 amps. Determine the approximate fan brake power.

The following loads are paralleled across a 220 volt, single−phase, 60 Hz (hertz) source: a.

A 10,000 watt electric heater

90 100

80

Efficiency 90

% Power Factor

100

70 100 100

60

99

50

98

40

97

30 96 20

75

50

25

% Current (Amperes)

70

% Synchronous Speed

% Efficiency

80

95

10

0 0

10

20

30

40

50

60

70

80

90

100

% Motor Horsepower

FIGURE 3-8 TYPICAL PERFORMANCE OF STANDARD SQUIRREL CAGE INDUCTION MOTORS HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

3.7


b.

A 5 horsepower (3.8 kW) electric motor oper− ating at a P.F. of one, with a 90 percent effi− ciency and pulling full load

The reason for the variance in answers between the I−P and SI examples is that the 3.8 kW motor size is a nom− inal size, but 3.73 kW is the exact equivalent.

c.

A 220 to 110 volt transformer (assume 100 percent efficient) with fifty 100 watt incan− descent light bulbs in parallel with the secon− dary.

3.5

MOTOR CONTROLS

3.5.1

Safety Switches

Heater

Transformer 110 V

220 V

10,000 Watt

1&

Motor 5HP 50 @ 100 watts each

Determine the total current requirements on the 220 volt source. Solution a.

b.

P

= EI, I = P/E = 10,000 W/220 V

I

= 45.5 amps

Using Equation 3−5 (I−P):

I  E  P.F.  Eff. 746 P  P.F.  Eff. bhp  746 bhp  746 5  746  4144watts P  P.F.  Eff. 1  0.9 bhp 

Using Equation 3 − 5 (SI): I  E  P.F.  Eff. 1000 P  P.F.  Eff. kW  1000 kW  1000 3.8  1000  4222watts P  P.F.  Eff. 1  0.9 I  P  4144  18.8amps) E 220 I  4222 220 = 18.8 amps (I−P) kW 

c.

For transformers with 100 percent efficiency, P(in) = P(out) P  50  100watts  5000watts I  P  5000  22.7amps E 220

I (Total) = 45.5 + 18.8 + 22.7 = 87.0 amps (I−P) I (Total) = 45.5 + 19.2 + 22.7 = 87.4 amps (SI) 3.8

A simple on−off toggle switch, a safety switch, or an individual circuit breaker in an electrical power panel is not an overload protection device for a motor. Many ordinary looking toggle switches do contain overload protection for smaller single−phase motors. Many small motors do have built−in overload protec− tion, and do not need additional protection. The circuit breaker only provides overload protection for the wir− ing circuit, but not any connected motor(s). The electric current to a motor must be switched off and on to stop and start the motor (manually or auto− matically). The switching device is commonly called a motor starter. This is not to be confused with a safety switch, which is a device that must be placed in the off position before any work is done on a motor or electri− cal equipment. This prevents the motor from acciden− tally starting from remote control devices. 3.5.2

Motor Starters

There are a large number of different types of starters, each with various advantages and limitations. In most cases a specific type of starter is required by a particu− lar type of motor. For example, a full voltage magnetic starter usually is used with an induction motor. Re− duced voltage or reduced current starters, while more expensive than a magnetic starter, often must be used with larger horsepower motors to prevent disruption (by producing large drops in line voltage) of marginal− ly adequate power services. Many electrical utility companies have mandatory requirements for these starters above a certain horsepower (this varies with the type of equipment and voltage). The motor starter or the safety switch is the main source of access to motor terminal leads for measure− ment of voltage and amperage. The starter also can contain holding coils, auxiliary contacts, control trans− formers, and a push−button station or a hand−off−auto− matic selector switch. This last item is useful in trou− bleshooting. If the switch is turned to the hand position, the motor should run if each phase line is hot, unless there is trouble in the motor. This is because the hand portion of the switch bypasses the various con− trols in the circuit. The automatic portion of the switch is connected to the circuit containing auxiliary devices

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


such as thermostats, safety lockouts and other external switches used to control or turn off the motor. If the motor runs on hand, but not on automatic, contacts in one of the control or safety interlocks should be open.

The TAB technician can find many different voltages around starters and starter combinations (see Figure 3−9). If a remote room thermostat is added in series with the push button station of the ?A" unit, the 110 volt control circuit then may be required to be 24 volts.

It is not good practice to use line voltages (110 volt or higher) for control circuits, but to reduce costs, 240 volt control circuits are not uncommon.

The motor starter overload protection devices or heat− er coils should be sized from the actual motor name− plate data rather than from data from motor or starter manufacturer’s catalogs. Heater coils never should be oversized under any condition.

3.5.3

Push Button Stations

There are two basic types of push button stationsCthe maintained contact station and the momentary contact station. The important point to remember is that after an interruption of the current with the momentary con− tact station, the motor will not restart until the start but− ton is pushed. 3.6

VARIABLE FREQUENCY DRIVES

Variable speed or variable frequency drives (VFD) are becoming commonplace in new commercial and insti− tutional construction. On renovation projects, this electrical component is ?spliced" into the existing wir− ing between the electrical source and the fan or pump motor disconnect. Figure 3–10 shows an existing H & V unit that was retrofitted with a VFD wired into the motor disconnect. Drive manufacturers achieve variable motor speed op− eration by modulating the frequency of the electrical power being supplied to the motor during normal op− erations, as well as voltage adjustment during startup

440/3/60

MAINTAINED CONTACT PUSH BUTTON STATION

220/3/60 MAIN CONTACTS

L1

L2

L3

L1

L2

L3

T1

T2

T3

STOP AUXILIARY CONTACT

START T1

T2

HOLDING COILS

T3

HEATER COILS

110 V

440/110 V CONTROL TRANSFORMER

M A. CONTROLLING STARTER-MOT OR

110 V 220/110 V CONTROL TRANSFORMER

M B. CONTROLLED STARTER-MOT OR

FIGURE 3-9 INTERLOCKED STARTERS WITH CONTROL TRANSFORMERS HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

3.9


to approximately 40% of their full design speed with no noticeable effect on motor performance or life. However, unless specifically designed for variable fre− quency operation, most motors will develop a notice− able increase in noise level and temperature below this point. Continuous operation below 25 percent of full load speed is not recommended and this lower range should only be used to reduce high current surges and belt stress during fan startup or shutdown. Just as lowering the frequency below 60 cycles per sec− ond will lower the motor speed below nameplate RPM, you can also increase motor speed above name− plate rating by increasing the frequency above 60 cycles per second. All initial air balancing should be carried out with the VFD set for approximately 55 cycles per second (Hz), even if drive pulleys and belts must be changed to achieve the design peak air flow. This will provide added ?headroom" for fan capacity when the system experiences duct and coil static pres− sure loses from dirt buildup. 3.6.1 FIGURE 3-10 VFD ADDED TO EXISTING AIR HANDLING UNIT and shutdown. Although most 3−phase motors will op− erate satisfactorily on a VFD, low cost motors and some energy efficient motors may experience higher noise or heat levels, especially at very low speed op− eration. Many manufacturers now offer modified mo− tor designs specifically for VFD operation. Varying the speed of an AC motor is much more com− plex than DC motor speed control. Most traditional DC motors have a commutator and brushes to provide electrical power to the rotating armature coil. Varying the voltage to this coil using a resistor or a rheostat changes the motor’s speed fairly effectively. AC motors do not have a commutator or brushes since the constantly alternating electricity induces an oppos− ing electrical field in the armature coil much like the primary coil of a transformer inducing a voltage in the secondary coil. Each AC motor is designed for a spe− cific voltage and reducing the supply voltage below this value will cause the motor to quickly lose its load capacity and stall, causing overheating and eventual motor burnout. Keeping the supply voltage to an AC motor at its de− sign point while varying the frequency of this voltage results in a corresponding change of motor speed. Most AC motors can be operated continuously down 3.10

VFD Operation During TAB Work

Most VFD devices can be programmed with a maxi− mum and minimum motor speed, and ?ramp up" and ?ramp down" rates to reduce wear on drive belts and bearings. The days of a TAB technician replacing mo− tor pulleys to adjust fan speed is drawing to a close, and today’s TAB technician needs to become familiar with variable frequency motor drives and their setpoint pro− gramming. In most cases, drive and motor manufacturers do not recommend operating these systems for extended peri− ods of time below 40 percent motor speed, and all VFD programmed setpoints should be verified and recorded during the balancing process. 3.6.2

VFD Bypass

Almost all VFD devices include a hand−off−auto switch and a manual speed control dial that can be used in manual operation. If the VFD device is placed in manual mode during TAB work, be sure it is returned to the auto mode before completing this work. Also note that in manual mode it is possible to operate the fan or pump at full speed. Since a remote duct or piping pressure sensor may be connected to the VFD device to allow maintaining a fixed duct or water sup− ply pressure, manually operating the fan or pump while down stream dampers or valves may be closed could cause very high pressures to develop in ducts or piping.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


CHAPTER 4

TEMPERATURE CONTROL


CHAPTER 4 4.1

AUTOMATIC TEMPERATURE CONTROL SYSTEMS

4.1.1

Introduction

Automatic temperature control of HVAC includes the control of temperature, humidity, and sometimes sys− tem or building pressures. The automatic temperature control (ATC) system constantly adjusts the HVAC systems to maintain design conditions within the occu− pied space. Because TAB work is concerned with the operation of the HVAC system, and because the control system constantly adjusts the HVAC system, it is imperative that the TAB technician understands the function and use of automatic temperature control systems. It must be remembered that motor controls covered in Chapter 3, are not automatic temperature controls, but the automatic temperature control system may moni− tor or operate motors and motor controllers. The use of the word control for both systems and devices some− times causes this basic difference to be overlooked re− lated to responsibility. 4.1.2

Types of ATC Systems

There are four basic types of controls for HVAC or en− vironmental systems:

   

electric pneumatic electronic self−contained

There are also combinations of the above types. 4.1.2.1

Electric Controls

Electric controls are those which are line voltage or less (generally 110 volts maximum). Reduced volt− ages are obtained from transformers, either locally or centrally situated. Many of these controls are simply on−off devices such as a high limit thermostat control− ling an exhaust fan. Generally, complex systems re− quire more sophistication than these controls can pro− duce. 4.1.2.2

Pneumatic Controls

Until the advent of micro−electronics, all HVAC con− trols of air handling systems, chillers, and boilers were pneumatic controls. These systems used compressed air to operate diaphragms and mechanical relays to

TEMPERATURE CONTROL position dampers and valves. Although fairly easy to visually observe the operation of each control device, changing the sequence of operation for any HVAC sys− tem was in many cases a plumbing ?nightmare," since everything was interconnected by air tubes. At the close of the 1990’s, most pneumatic logic controls have been replaced by direct digital controls (DDC), with the exception of very large dampers and valves which may still utilize pneumatic damper motors as large electronic motors are still relatively expensive. On most of today’s commercial and institutional pro− jects, the TAB technician may find that all HVAC con− trols are now based on micro−electronics. However, we are still including a review of pneumatic control basics in this chapter as these systems still exist and may be encountered during HVAC system renovation and expansion. 4.1.2.3

Electronic Controls

The term ?electronic controls" was first used to de− scribe newer control technology being installed to re− place some of the functions of the older pneumatic control devices. Most of these first generation elec− tronic controls did little more than monitor HVAC sys− tem operation and provide on/off control of fans, valves, and dampers. The control ?logic" was special− ized software operating on a large main frame central computer, communicating with field interface panels connected to temperature sensors and relays. Any pneumatic controlled dampers or valves were still op− erated by their original pneumatic controls, with E/P relays switched between fixed setpoints. These earlier electronic control systems were of little interest to the TAB technician other than requesting an unseen con− trol operator to start or stop a fan. During the 1990’s this older technology was replaced by DDC which no longer required the pneumatic con− trol devices to carry out the positioning of dampers, valves, and setpoint controllers. In addition, with the advent of micro−electronics, the operating program software is now contained within the remote field pan− els and the large central computer is no longer re− quired. Unlike the earlier electronic control systems, this new DDC technology does have a significant impact on the balancing contractor on all but the smallest projects. HVAC system manufacturers are finding that it is less expensive to use these easily programmed ?black box" control devices. There are no longer pneumatic control devices that must be constantly calibrated and ad− justed to maintain system reliability. The days of a TAB technician adjusting a pneumatic controller to reposition the damper on a VAV box may

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

4.1


be coming to an end, and today’s TAB technician may find a hand held computer indispensable on a balanc− ing job. What may have required above ceiling linkage adjust− ments while standing on a shaky ladder, can now be ac− complished by plugging a hand held device into the nearest electronic wall thermostat. The TAB techni− cian can instantly verify high and low air flows, adjust operating setpoints, and monitor room conditions as the HVAC system responds to these control input changes. It is very important for any SMACNA contractor en− tering today’s TAB field to have a good understanding of DDC basics. 4.1.2.4

Self-Contained Controls

Self−contained controls differ from the above types in that they do not use an external source of power, but develop their own power. Often used in automatic valves, a bellows or other sensing element has enough strength to move the valve. Because of strength and large mass involved in its construction, it is not capa− ble of providing as close control as other types of sys− tems. Applications include:

   

condenser water regulating valves on refrig− eration compressor units (city water). thermostatic expansion valves. steam control valves for heating domestic hot water. self−contained radiator control valves.

Other combinations are electro−hydraulic, commonly applied to valve operators, and electro−pneumatic sys− tems using electronic devices to sense temperature and pressure, and pneumatic devices to operate valves and dampers. This dual system combines advantages of electronic systems (sensitivity, wide range of adjust− ability) with simplicity of pneumatic operators. 4.1.3

Control Categories

Control systems also are divided into two categories: operating controls and safety or limit controls. 4.1.3.1

Operating Controls

Operating controls are used for the control of room conditions and system setpoints. The most common example of an operating control is a room thermostat. 4.2

4.1.3.2

Safety Controls

Safety or limit controls are used to provide safe equip− ment operation. Safety or limit controls must be set properly to avoid unsafe conditions such as pressures or temperatures that are too high or too low, and imple− ment emergency equipment shut off. Safety or limit controls may interrupt the operating controls at any given time to ensure safe system opera− tion. Examples of safety controls are freeze stats, fire stats, flow switches, smoke detectors, and refrigera− tion high−low pressure cutouts. 4.2

CONTROL LOOPS

No matter which type of control system is used, all control applications must involve a fundamental con− trol loop. A control loop consists of three components:

  

a controller (thermostat) a controlled device (valve, damper) a sensing device (transmitter, bi−metal strip)

For example, a sensing device (remote bulb) monitors the temperature of a supply air duct and sends a signal to the controller. The controller monitors the signal as sent by the sens− ing device, and reacts by either opening or closing a controlled device (valve or damper). As a result of the resulting change in system output, (such as hot water in a heating coil), the action of the controlled device creates a change in the sensing device which provide feedback to the controller that the system change took place. The operation of any control loop is continuous during normal operation of the HVAC system. 4.2.1

Controllers

Controllers (such as thermostats and humidistats) have two possible sets of control actions:

  4.2.1.1

Modulating or two position Direct or reverse acting Modulating/Two Position

Modulating control (also called proportional control) is obtained when the control signal sent by the control− ler to the controlled device is constantly changing in small increments to gradually increase or decrease the capacity of a system component to suit the load condi− tions. Two position control, which also can be on−off,

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


only assumes two positions; fully open or fully closed. Two position controllers are normally used with equip− ment that only operates in an on−off application. Equipment such as gas valves or small air conditioning compressors would fall under this category. 4.2.1.2

Two−way valves are normally used for water or steam service. Three−way mixing and diverting valves are used only in hydronic piping (Figure 4−2). The valve constant or flow coefficient is used to calculate the flow and pressure drop of ATC valves in the wide open position.

Direct/Reverse Acting Equation 4-1 (I-P)

Modulating system control devices may increase or decrease the output (branch) control signal with changes in space conditions monitored by the sensing element. A direct acting controller will increase the output (branch) control signal as the controlled vari− able (temperature, humidity, pressure) increases. A re− verse acting controller increases the control signal as the controlled variable decreases. The action of the controller must be properly matched with the control device or the control loop will produce unexpected re− sults or those opposite of that desired.

DP 

CQ

2

v

Where: DP  Pressuredifferential(psi) Q  Flowthroughvalve(gpm) C v  FlowCoefficient

Equation 4-1 (SI)

DP 

KQ

2

v

The position of a controlled device when de−energized is considered the normal position. Control devices such as valves or dampers are either normally open (N.O.) or normally closed (N.C.). Some electric de− vices also contain switches that are normally open or normally closed until moved to the opposite position by a controller.

Where: DP  Pressuredifferential(kPa) Q  Flowthroughvalve(Ls) K v  FlowCoefficient

4.2.2

A control valve must be selected to control a flow of 20 gpm at a maximum 4 psi pressure drop. Calculate the Cv of the valve.

Controlled Devices

Controlled devices that affect the TAB technician the most are automatic control dampers and automatic control valves. Both affect flow and both can be two position or modulating.

Example 4−1 (I−P)

Solution 4.2.2.1

CQ ; DP  CQ 2

ATC Valves

DP 

v

Figure 4−1 illustrates the throttling characteristics of the different types of modulating ATC valves. Two position valves such as those used for automatic shut− off in seasonal change−over piping need no specific throttling characteristic, the major concern being tight shutoff. Gate

Butterfly

100%

v

Q C v    20  10 DP 4 Example 4.1 (SI) A control valve must be selected to control a flow of 1.3 L/s at a maximum 28 kPa pressure drop. Calculate the Kv of the valve.

Ideal Straight Line Characteristic Throttling Plug Travel 50%

Globe

Solution

KQ ; DP  KQ 2

50%

100%

DP 

% Flow

FIGURE 4-1 VALVE THROTTLING CHARACTERISTIC COMPARISON

K v 

v

v

Q   1.3   0.25 D P 28

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

4.3


IN

OUT

OUT

IN

OUT

IN 3 Way Mixing

3 Way Diverting

FIGURE 4-2 ATC VALVE ARRANGEMENTS For proper control action, it is desirable for an ATC valve to be sized so the pressure drop cross the wide open valve at design flow rate will give an appreciable pressure drop. For example, in the case of a steam valve, it is considered good practice for the pressure drop at design flow to be approximately 50 percent of the absolute steam pressure available at the valve. 4.2.2.2

closed, produces a control characteristic that is unsat− isfactory. Opposed blade dampers do not eliminate the above problems, but they improve the control ability by clos− ing blades toward each other so that throttling begins sooner. Close and accurate control is improved but still limited. The linear operating characteristic is not as

ATC Dampers

Dampers used for automatic temperature control have either parallel or opposed blades as shown in Figure 4−3. Quality, tight fitting dampers with long lasting blade edge seals or the equivalent are necessary for ATC work. Parallel blade dampers are almost always used for two position or open−closed control. Opposed blade damp− ers are used for modulating control of airflow. Damp− ers present throttling problems similar to valves which is difficult to correct. Parallel blade dampers often have a throttling characteristic which is worse than gate valves. This deficiency is complicated by the pro− cedure of selecting damper sizes based on low air ve− locities across the dampers. The play in the dampers and damper linkages caused by flexibility and distor− tion, and the difficulty of seating the blades when 4.4

PARALLEL OPERATION

OPPOSED OPERATION

FIGURE 4-3 TYPICAL MULTIBLADE DAMPERS

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


nearly achieved as in the case of valves, but may be more closely approximated by sizing the dampers on higher velocities and by providing more sections and more rigidly constructed.

the sequence of control and the ATC diagrams would indicate which devices to inspect.

4.2.2.3

Most control system sensors and controllers are linear (which means straight line). Figure 4−1 indicates the error induced by non−linear control devices such as dampers and valves. Linear control in pneumatic sys− tems may translate to one degree of temperature change from one psi of air pressure change. One psi (kPa) or fluid pressure change on the discharge side of a pump also could result in a two or three psi (kPa) of control pressure change. These systems are linear as long as each increment of controlled variable produces the same increment of signal. The system would be non−linear if different amounts of signals emanate from a fixed increment of the controlled variable. For example, a system is non−linear if at 70F (21C), a one degree change produces a one psi (kPa) control signal; but at 90F (32C), a one degree change pro− duces a two psi (kPa) control signal.

Valve and Damper Linkages

The operation of automatic valves can often be re− versed in the field to suit the action of the controllers, although in some cases it may be necessary to change the operator. The action of automatic dampers can usu− ally be reversed by resetting the damper arm or other parts of the linkage. Sometimes it is necessary to limit the travel of dampers or valves in order to provide proper control. Most pneumatic and electric devices have operator stops that can be adjusted so that the valve or damper operator is permitted to complete a portion of its stroke. Electric operators have limit switches which can be positioned to electrically stop the operator at a desired position. The correct setting of stops and/or limit switches is important for the suc− cessful operation of a system, and personnel must un− derstand such adjustments, or equipment could be damaged. Although adjustments of ATC valves and dampers on larger systems are normally made by the Temperature Control Contractor, the TAB technician needs to un− derstand the factors required for proper valve and damper adjustment. 4.3

4.4

CONTROL RELATIONSHIPS

An actuator is considered linear if it has a signal range of ten psi (kPa) from fully open to fully closed. So a five volt or five psi (kPa) signal will cause a 50 percent travel. However, if the actuator device is used on a valve or damper, an actuator change of 50 percent will seldom change the fluid flow by the same 50 percent. From Figure 4−1, one can see that a 50 percent stem travel of a gate valve from wide open will have little effect on the fluid flow.

CONTROL DIAGRAMS Equation 4-2 (I-P)

In a typical job specification, there are general descrip− tions of various types of control applications , called the sequence of controls, which the automatic Temper− ature Control Contractor must translate into a set of drawings called control diagrams. These control dia− grams and related written sequence of controls for each HVAC system, are used by the ATC contractor for control system installation in coordination with the HVAC system contractor. The data found in these dia− grams is extremely important to the TAB technician and these diagrams frequently are the only description of how a complicated HVAC system will operate. Control system diagrams also can be used to assist the TAB technician in troubleshooting. For example, when the hand−off−automatic switch of a fan motor starter is in the automatic position, it is found that the fan will not run. But the fan will run when the switch is in the hand position. This indicates that some type of automatic temperature control device or safety switch is preventing the fan from running. A review of

C v  Q

(2.3)½   Q (H)½

2.3 H

Equation 4-2 (SI) Q K v  DP

Equation 4-3 Q21 H1 DP 1   2  H2 Q2 DP 2 Where: Cv Kv Q P H

= = = = =

Flow coefficient or valve constant (I−P) Flow coefficient or valve constant (SI) Fluid flow rateCgpm (L/s) Pressure differenceCpsi (kPa) Head loss or pressure dropCfeet (meters)

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

4.5


Equations 4−2 and 4−3 indicate that the pressure drop across the valve is proportional to the square of the fluid flow rate. This relationship is indicated by the general curve shown in Figure 4−1, which can apply to most systems, although the numbers may vary. The non−linearity of the controlling device is apparent with this curve. In order to minimize the resulting control inaccuracies, the controller and the controlled device must be carefully matched so that an average linearity is achieved. This cannot be done across the entire range of the device, therefore, the devices are matched for a normal operating range, which is a matter of judg− ment of the system designer or the ATC Contractor.

trol system is required. Outside air and exhaust air dampers usually are interlocked with the supply fan to open to a fixed minimum outside air position when the fan is started. A mixed air temperature sensor could then control the outside air, return air, and exhaust air dampers to maintain a set mixed air temperature. At a pre−set temperature or a high outside air humidity, the outside air damper often will be returned to a mini− mum position to decrease the cooling load of the out− side air. In a case of power or control system failure, the outside air damper usually closes automatically. A freeze stat also can stop the fan and close the outside air dampers.

4.5

4.6.2

ATC SYSTEM ADJUSTMENT

After completion of the physical installation, the ATC system components must be adjusted and calibrated so that they may operate individually and collectively to provide the specified environmental system control. The amount of adjustment and calibration will depend on the complexities of the ATC system. All calibration of ATC system instruments should have been done by the ATC installer prior to system balan− cing. However, there are some specific adjustments which should be done in conjunction with TAB per− sonnel during system adjustment and balancing. Fail− ure to provide this coordination may lead to the inabil− ity of the HVAC system to perform satisfactorily under load. Setting automatic dampers for proper air quantities, positioning hot and cold deck dampers, and maintain− ing valves open or closed to maintain design operating conditions are among the multitude of factors which affect systems operation and TAB work. After the installation has been completed, accepted, and the building occupied, problems can arise which may or may not be attributable to the TAB work. It is not unusual for accidental maladjustment of controls to produce symptoms which seem to point to improper HVAC system balancing. Outside air dampers that have slipped, or a reheat coil thermostat that malfunc− tions, are excellent examples. The ability to recognize the real source of the problem not only saves time but vindicates the TAB work. 4.6

TAB/ATC RELATIONSHIP

4.6.1

Related Problems

To properly balance and adjust any HVAC system, a thorough knowledge of the installed temperature con− 4.6

Controllers

A thermostat in the duct system often will control a heating or cooling coil valve, face and by−pass damp− ers or mixing dampers. A room thermostat can control a hot water, steam, chilled water or electric booster coil, and/or hot and cold mixing dampers. A humidis− tat can control a humidifier or a cooling coil for dehu− midification. Controls can be direct acting, reverse acting, modulating or two position, stepped, master, sub−master, series, or parallel. Controls can actuate dampers, valves, and relays; start, modulate or stop motors, fans, and other equipment; and be controlled by time clocks, time delay relays, static pressure con− trollers, air switches, flow switches, level controllers, fire and smoke detectors. They can be connected to alarm systems, and be controlled, readjusted, and be indicated from or at remote control panels. Finally, controls can be very simple or very complex. 4.6.3

Ventilation Air

Probably the most important effect on TAB work is the setting of the outside air, return air, and exhaust air dampers. After the fan speed (rpm) and airflow capac− ity have been checked out, set the outside air dampers for minimum outside air. Use thermometers or a ther− mocouple to measure outside air, return air and mixed air temperatures. Use the mixed air temperature Equa− tion 4−4 to determine the amount of outside air. Work− ing with the temperature control contractor, set the minimum outside air conditions. Mark the dampers for the minimum position and recheck the air flows. If an economizer cycle is used, next check using 100 percent outside air and again check air flows. Follow the procedure for 25, 50, 75 percent outside air. The mixing of the return air with outside air to give a known mixed air temperature can be determined by the following:

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


X oT o  X rT r T m  100

Equation 4-4

Tm = Temperature of the mixture of return air− and outdoor air Xo = Percentage of outdoor air Xr = Percentage of return air To = Temperature of outdoor air, F (C) Tr = Temperature of return air, F (C) Being familiar with the interactions and functions of these control systems will go a long way in reducing on site system balancing time. The following equations are used for determining per− centages of outside air. For this work, more convenient forms of expressing Equation 4−4 are given in Equa− tion 4−5 and 4−6.

(Tr  Tm) X o  100 (T r  T o)

(Tm  To) X r  100 (Tr  To)

Equation 4-5

Example 4.2 (SI) 24C return air is mixed with −4 outside air and the mixed air temperature is 13C. Find the percentage of outside air.

Solution (Tr  Tm) (T r  T o) (24°C  13°C)  100 [24°C  ( 4°C)]  100  11°C  39.3% 28°C X o  100

4.7

CENTRALIZED CONTROL SYSTEMS

The concept of centralized controls or energy manage− ment systems (EMCS) briefly addressed in the begin− ning of this Chapter is applied to many buildings being constructed or modernized today.

Equation 4-6

Example 4−2 (I−P) 75F return air is mixed with 25F outside air and the mixed air temperature is 55F. Find the percentage of outside air.

Solution (Tr  Tm) (T r  T o) (75°  55°)  100 (75°  25°)  100  20°  40% 50° X o  100

FIGURE 4-4 DESKTOP COMPUTER DISPLAYING STATUS OF BUILDING HVAC SYSTEMS

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

4.7


Figure 4−4 shows a standard desktop computer being used to monitor and control all HVAC systems in a hos− pital. These software programs are becoming very easy to use and can display photos and diagrams of a given system, with all ?live" temperature and setpoint data displayed next to each system component. Almost all new buildings will utilize a computerized HVAC control system. Even the most basic dial time clock for start/stop control have been replaced by less expensive electronic time clocks that can adjust for seasonal length of daylight and changing outdoor tem− peratures. Large HVAC systems now have one or more field control panels that include programmable com− puterized memories containing all of the sequence of control logics and control algorithms for the systems and devices being controlled. These field panels include four types of control inputs and outputs, plus the ability to communicate local con− ditions and setpoints to other field panels or remote monitoring locations.

Digital Input Digital Output Analog Input Analog Output

4.7.1

4.7.2

In addition to these input and output field devices, a typical centralized computer control system consists of one or more field interface devices, and one or more programmable stand alone controllers as shown in Fig− ure 4−5. Each programmable stand alone controller contains a microcomputer and battery backed up memory con− taining all of the programming for all field devices and

SENSORS

Many field interface panels include a manual/auto switch for each control output. This allows local by− pass of the control system during system testing and balancing, but bypassing any controls should be autho− rized by the system operator and all switches returned to ?auto" mode when the TAB work is complete. Digital Input

A digital input is an on/off, open/closed, hi/low, or oth− er two position feedback signal input to the computer− ized control system from the HVAC equipment being monitored.

Four basic EMCS signals:

   

HVAC systems it controls. After this software has been created on a desktop computer, it is ?downloaded" to each field controller. Since the actual sequence of con− trols and operating schedules reside in the field stand alone controller, the central control computer is only needed when operating schedules or system setpoints need to be changed by the operator, or to display sys− tem alarms sent from the field controllers. Since the programmable stand alone controllers are a micro− computer device, a field interface device provides re− lays and analog to digital transducers which allows the tiny electronic circuits to control larger current field devices like motor starters and damper operators.

Digital Output

A digital output is an on/off, open/close, hi/low, or oth− er two position control signal command output from the computerized control system to the HVAC system being controlled. 4.7.3

Analog Input

An analog input is a variable feedback signal to the computerized control system from the HVAC system being monitored. It could indicate the position of a

DESKTOP COMPUTER FIELD INTERFACE DEVICES & RELAYS

PROGRAMMABLE STAND ALONE CONTROLLER(S)

ACTUATORS

FIGURE 4-5 FUNCTIONAL BLOCK DIAGRAM A CENTRALIZED COMPUTER CONTROL SYSTEM 4.8

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


valve or damper, speed of a fan or pump, or a room temperature or humidity. 4.7.4

Analog Output

An analog output is a variable command signal output from the computerized control system to the HVAC system being controlled. This signal could be adjust− ing a 0 to 20 psi pressure to a valve or damper motor, or a 0 to 10 volt signal to a variable speed fan motor drive, or other variable signal to match the device be− ing controlled. 4.7.5

EMCS Communications

In addition to the above control inputs and outputs, al− most all computerized building control systems have the ability to communicate with other field panels or central monitoring displays and alarm printers.

vision of the Centralized Control installer or ATC con− tractor. Also, readings obtained from centralized sys− tems can be used by the TAB technician to balance the HVAC system being controlled. 4.7.7

How an EMCS Helps TAB Work

A person entering the TAB field may be wondering what all this has to do with the testing and balancing field. Prior to micro−electronics and DDC, all HVAC sys− tems were controlled by pneumatic devices. Figure 4−6 shows a typical pneumatic control cabinet for a large air handling unit. Notice the high concentration of ?spaghetti" tubing which are used to interconnect all of the pneumatic control devices including pneu− matic relays, receiver/controllers, and various pneu− matic logic controls.

Originally, this communication was by direct hard wire or dial up phone connection, but the trend today is towards less manufacturer specific and more open communication ?protocols," allowing any computer on the same computer ?network" having the proper software and access codes to view and/or change any HVAC system on the same network. This system of in− terconnect also reduces the need for multiple sensors. For example, one outside air sensor can now have its present temperature reading accessed by all air han− dling units and their controls for outside temperature reset instead of a separate sensor for each. 4.7.6

EMCS Points List

In addition to the control contractor providing a writ− ten sequence of controls and related control diagrams, the control documentation for a computerized automa− tion control system should also include a ?points list." This list is actually a table or chart, which at a glance indicates each physical piece of equipment being con− trolled down the ?y" axis, and the different types of software programs utilized across the top ?x" axis. The type of points, analog input (AI) analog output (AO), digital input (DI), and digital output (DO) is also indi− cated. By placing an ?x" or ?dot" where each column and row intersect, it is easy to see the interaction of the physical world with the software programming. Reviewing this points list is helpful to the TAB technician to under− stand how a system is being operated. The TAB technicians should not attempt to adjust or change control settings except when under the super−

FIGURE 4-6 HVAC CONTROLS PANEL WITH ORIGINAL PNEUMATIC CONTROLS.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

4.9


Unfortunately, many times this calibration has not been completed prior to the TAB work. For this reason, if you have access to the automation system display during the balancing work, be sure to record air and water flows being displayed at the time of your own measurements and advise the automation system con− troller. This is especially critical on variable air volume sys− tems since out of calibration automation flow stations can cause an air handling unit that was just balanced to produce much higher or lower flow rates than in− tended. Figure 4−8 shows a TAB technician using a small por− table laptop computer to adjust the minimum and max− imum air flows on an above ceiling VAV box. Note how the computer is ?plugged" directly into a jack that is provided under each electronic wall thermostat con− nected to a DDC system. The computer screen is displaying actual VAV box dis− charge air cfm, discharge air temperature, percent damper position, reheat coil discharge temperature, branch duct supply temperature, duct static pressure, maximum discharge cfm setpoint, and minimum dis− charge cfm setpoint. All of these values can be easily read and adjusted if necessary during system testing

FIGURE 4-7 THE SAME HVAC CONTROL PANEL AFTER UPGRADING TO DIRECT DIGITAL CONTROL (DDC).

Figure 4−7 shows the same control cabinet after all of the pneumatic controls and control tubing were re− placed with a DDC system. Now changing discharge air temperature from the unit or adjusting the outside air damper is as simple as moving the ?mouse" across the control screen in the building manager’s office. Many building automation systems include air flow and water flow measuring stations in addition to the many temperature and humidity sensors. Before being tempted to use these easy to read values, keep in mind that these control input devices require calibration in the software program which may not have been com− pleted. On new construction projects, many control contractors will install all of these field devices using factory ?default" settings. This allows faster system startup and the default valves are acceptable for initial startup operation. 4.10

FIGURE 4-8 PORTABLE COMPUTER PLUGGED INTO ELECTRONIC WALL THERMOSTAT DURING SYSTEM BALANCING.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


and balancing without the need to climb a ladder or re− move ceiling tiles and access covers. Since each control manufacturer may have their own custom software and plug−in thermostat to computer cables, most TAB technicians have developed a good working relationship with the control system installers

who may be able to provide these programs and cables at little or no cost. The ability of a TAB technician to use these portable control devices can reduce the time the control contractor needs to be on site during the TAB work, and in return, the TAB technician does not need to schedule his site times to meet the availability of the control contractor.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

4.11


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4.12

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


CHAPTER 5

FANS


CHAPTER 5 5.1

FAN CHARACTERISTICS

5.1.1

Introduction

This chapter will apply the basic airflow fundamentals discussed in Chapter 2 HVAC Fundamentals to fans. As stated earlier, each type of system needs a pump to overcome the friction and dynamic losses of the sys− tem. This device can be either a centrifugal pump, a fan, a compressor, a turbine, or some other sophisti− cated device. Therefore, each device must be studied by the TAB technician so that not only all of its unique characteristics are known, but that the device has been applied properly within the system, and that the system has been designed to circulate fluid in the most eco− nomical manner and to provide maximum comfort. With an in−depth understanding of HVAC fans and their relationship to HVAC systems, it becomes easy for the TAB technician to apply proper balancing pro− cedures in the correct sequence when on the job. Centrifugal Fans

Three basic types of fans are used in HVAC systems, the centrifugal fan or blower, the axial flow fan, and special designs using fans or blowers in different hou− sings. The airflow within the centrifugal fan is sub− stantially radial through the wheel, while the airflow through the axial flow fan is parallel to the fan shaft. The components of centrifugal fans are identified in Figure 5−1. The three variations of the centrifugal fan used in HVAC work are forward curved, backward in− clined, and airfoil. 5.1.2.1

*SCROLL SIDE SCROLL PIECE SIDE SHEET SIDE PLATE

*OUTLET DISCHARGE

*BACKPLATE HUB DISK HUBPLATE *BLADES FINS INLET CONE INLET RING INLET BELL INLET FLARE INLET NOZZLE VENTURI

*SCROLL CASING HOUSING *IMPELLER WHEEL SCROLL HOUSING *RIM VOLUTE MOTOR SHROUD WHEEL RING WHEEL CONE *SUPPORTS RETAINING RING STIFFENERS INLET RIM *INLET COLLARWHEEL RIM INLET SLEEVEFLANGE INLET BAND INLET PLATE * PREFERRED NOMENCLATURE

PEDESTAL

FIGURE 5-1 CENTRIFUGAL FAN COMPONENTS shape of its performance curve, which allows the pos− sibility of overloading the motor, if system static pres− sure decreases. It also is not suitable for material han− dling because it has an inherently weak structure. Therefore, FC fans are generally not capable of the high speeds necessary for developing higher static pressures. STATIC PRESSURE CURVE STATIC EFFICIENCY CURVE BHP CURVE

100

Forward Curved (FC) Fans

The FC centrifugal fan turns at a relatively slow speed and generally is used for producing high airflow vol− umes at low static pressures. The FC fan will surge, but the magnitude is less than for other types. The static pressure proportion of the total pressure discharge is 20 percent while the velocity pressure is 80 percent. Typical operating range of this type of fan is from 30 percent to 80 percent wide open volume (see Figure 5−2). The maximum static efficiency of 60−80 percent generally occurs slightly to the right of peak static pressure. The horsepower curve has an increasing slope and therefore is referred to as an overloading type fan.

70 SE. SP AND BHP

5.1.2

FANS

0

30

80

100

FIGURE 5-2 CHARACTERISTIC CURVES FOR FC FANS 5.1.2.2

Advantages of the FC fan are its low cost, and the slow speed which minimizes shaft and bearing size, and its wide operating range. Disadvantages include the

0

Backward Inclined (BI) Fans

Backward inclined fans travel at about twice the speed of the FC fan. The normal selection range of the BI fan

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

5.1


is approximately 40−85 percent of wide open airflow volume (see Figure 5−3). Maximum static efficiency of about 80 percent generally occurs close to the edge of its normal operating range. Generally, using a larger fan will allow greater efficiency for a given selection. The magnitude of surge for a BI fan is greater than for the FC fan.

STATIC PRESSURE CURVE STATIC EFFICIENCY CURVE BHP CURVE

100

STATIC PRESSURE CURVE STATIC EFFICIENCY CURVE BHP CURVE

SE. SP AND BHP

86

SE., SP AND BHP

100

80 0

50

CFM

85

100

FIGURE 5-4 CHARACTERISTIC CURVES FOR AIR FOIL are shown in Figure 5−4. For a specific application, the airfoil fan has the highest rpm of the three centrifugal fans. 5.1.3 0

0

40

CFM

85

100

FIGURE 5-3 CHARACTERISTIC CURVES FOR BI FANS Advantages of the BI fan include its higher efficiency and non−overloading horsepower curve. The horse− power curve generally reaches a maximum in the middle of the normal operating range, thus overload− ing is normally not a problem. Inherently stronger de− sign makes it suitable for the higher static pressure op− eration of 70 percent of the total pressure measured at the fan discharge. This leaves the measured velocity pressure at only 30 percent. Disadvantages include the higher speed, which re− quires larger shaft and bearing sizes and places more importance on proper wheel balance; and unstable op− eration, which occurs as block−tight static pressure is approached. 5.1.2.3

Airfoil Fans

A refinement of the flat bladed BI fan is a fan that uses airfoil shaped blades. This improves the static effi− ciency to about 86 percent and reduces noise level slightly. The magnitude of surge also increases with the airfoil blades. Characteristic curves for airfoil fans 5.2

0

Axial Fans

Components of axial fans are illustrated in Figure 5−5. HVAC axial fans may be divided into three groups, propeller, tubeaxial, and vaneaxial.

GUIDE VANE

INLET CONE OR INLET BELL WHEEL ROTOR IMPELLER

MOTOR

BLADE

HOUSING CASING

HUB

NOSE COVER PLATE SPINNER

FIGURE 5-5 AXIAL FAN COMPONENTS 5.1.3.1

Propeller Fans

HVAC propeller fans normally are not connected to duct systems. They are well suited for handling high volumes of air at very low or no static pressures and low efficiencies (see Figure 5−6). 5.1.3.2

Tubeaxial and Vaneaxial Fans

Tubeaxial and vaneaxial fans are simply propeller fans mounted in a cylinder and are similar except for vane−

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


STATIC PRESSURE CURVE STATIC EFFICIENCY CURVE BHP CURVE

STATIC PRESSURE CURVE STATIC EFFICIENCY CURVE BHP CURVE

100

SE.SP ANDBHP

SE. SP AND BHP

100

50

80

0 0

0

CFM

65

0

CFM

100

FIGURE 5-6 CHARACTERISTIC CURVES FOR PROPELLER FANS

Tubeaxial fans and vaneaxial fans generally are used for handling large volumes of air at low static pres− sures.

90 100

FIGURE 5-7 CHARACTERISTIC CURVES FOR VANEAXIAL FANS (HIGH PERFORMANCE) 5.1.4.1

type straighteners on the vaneaxial. These vanes re− move much of the swirl from the air and improve the efficiency. A vaneaxial fan is more efficient than a tu− beaxial fan and can reach higher pressures. Note that with axial fans the brake horsepower (BHP) is maxi− mum at the blocktight static pressure (see Figure 5−7).

65

Tubular Centrifugal Fans

Tubular centrifugal fans, illustrated in Figure 5−8, gen− erally consist of a single width airfoil wheel arranged in a cylinder to discharge air radially against the inside of the cylinder. Air is then deflected parallel with the fan shaft to provide straight−through flow. Vanes are used to recover static pressure and to straighten air flow.

SW CENTRIFUGAL FAN WHEEL

Advantages of tubeaxial fans and vaneaxial fans in− clude the reduced size and weight, and the straight− through airflow which frequently eliminates elbows in the ductwork. The maximum static efficiency of an in− dustrial vaneaxial fan is approximately 65 percent. The operating range for axial fans is from 65 percent to 90 percent. Disadvantages of axial fans include high noise levels and efficiencies lower than those of centrifugal fans. 5.1.4

Special Designs

There are variations of both centrifugal and axial fans that are designated special design fans. These include tubular centrifugal fans and power roof ventilators.

STREAMLINE INLET

AIR OUT AIR IN

STRAIGHTENING VANES

FIGURE 5-8 TUBULAR CENTRIFUGAL FAN Characteristic curves are shown in Figure 5−9. The selection range is generally about the same as the scroll type BI or airfoil bladed wheelC50 to 85 per− cent of wide open volume. However, because there is

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

5.3


limitations of the wheels, bearings, and housing of fans. Under the most recent class standards, there are three classifications, as shown in Figures 5−10 and 5−11.

STATIC PRESSURE CURVE STATIC EFFICIENCY CURVE BHP CURVE

Note the line of demarcation between Class I and Class II construction.

100

SE. SP AND BHP

Example 5.1 (I−P) A fan operates at 9056 cfm, 1478 rpm, requiring 5.08 BHP at 1.0 in. wg SP. The airflow must be increased to 10,188 cfm to handle an additional load. Find the new SP and BHP.

70

15 14 13 1/2” @ 3780 13 RATINGS MAY BE PUBLISHED IN THIS UPPER RANGE

12

0

50

85

100

CFM

FIGURE 5-9 CHARACTERISTIC CURVES FOR TUBULAR CENTRIFUGAL FANS no housing of the turbulent air flow path through the fan, static efficiency is reduced to a maximum of about 72 percent and noise level is increased.

(SP)INCHES OF WATER

0

10

STATIC PRESSURE

11

6

TYPICAL CLASS II CHARACTERISTIC CURVE MINIMUM PERFORMANCE CLASS III

9 8 1/2” @ 3000 8

CLASS III SELECTION ZONE

7 6 3/4” @ 5260

5” @ 2300 5 4 3

CLASS I SELECTION ZONE

1000

2000

5000

6000

7000

3750 3500 3375 Pa @ 18.9 3250 RATINGS MAY BE PUBLISHED IN THIS UPPER RANGE

3000 2750

STATIC PRESSURE (SP)-P ASCALS (Pa)

Fan Classes

4000

FIGURE 5-10 FAN CLASS STANDARDS (I-P) (SW BI FANS)

TYPICAL CLASS II CHARACTERISTIC CURVE

2500

5.2.1

3000

OUTLET VELOCITY (OV) FEET PER MINUTE

Power roof ventilators allow the air to discharge in a full circle from the impeller, which may be either cen− trifugal or axial with similar characteristics. A large advantage is that they provide positive exhaust ven− tilation over gravity ventilators.

FAN CONSTRUCTION

RATINGS MAY BE PUBLISHED IN THIS LOWER RANGE

1

Power Roof Ventilators

5.2

4 1/2” @ 4175

2 1/2” @ 3200

Frequently, the straight−through flow results in signifi− cant space savings. This is the main advantage of tubu− lar centrifugal fans.

Disadvantages include lower available static pressures than centrifugal fans and loss of the discharge velocity pressure component that is recovered.

CLASS II SELECTION ZONE

MINIMUM PERFORMANCE CLASS I

2

5.1.4.2

MINIMUM PERFORMANCE CLASS II

MINIMUM PERFORMANCE CLASS III

2250 2125 Pa @ 15.0 2000

CLASS III SELECTION ZONE

1750 1563 Pa @ 26.3 1500 MINIMUM PERFORMANCE CLASS II

1250 Pa @ 11.5 1250 1000

MINIMUM PERFORMANCE CLASS I

750

1063 Pa @ 20.9

CLASS II SELECTION ZONE

625 Pa @ 16.0

When using a fan rating table published by the fan manufacturer, if fan speeds and static pressures in− crease above certain given conditions, the class of the fan changes. Class again refers to an Air Movement and Control Association, Inc. (AMCA) standard which has been developed to regulate actual structural 5.4

500

CLASS I SELECTION ZONE

RATINGS MAY BE PUBLISHED IN THIS LOWER RANGE

250

5

10

15

20

25

30

OUTLET VELOCITY-METRES PER SECOND (m/s)

FIGURE 5-11 FAN CLASS STANDARDS (SI) (SW BI FANS)

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

35


SW—Single Width SI—Single Inlet

DW—Double Width DI—Double Inlet

Arrangements 1, 3, 7 and 8 are also available with bearings mounted on pedestals or base set independent of the fan housing. For designation of rotation and discharge (see Figure 5–17) For motor position, belt or chain drive (see Figure 5–16)

ARR. 2 SWSI For belt drive or direct connection. Impeller overhung Bearings in bracket supported by fan housing.

ARR. 3 SWSI For belt drive or direct connection. One bearing on each side and supported by fan housing.

ARR. 1 SWSI For belt drive or direct connection. Impeller overhung. Two bearings on base.

ARR. 3 DWDI For belt drive or direct connection. One bearing on each side and supported by fan housing.

ARR. 4 SWSI For belt drive. Impeller overhung on prime mover shaft. No bearings on fan. Prime mover base mounted or integrally directly connected.

ARR. 7 SWSI For belt drive or direct connection. Arrangement 3 plus base for prime mover.

ARR. 7 DWDI For belt drive or direct connection. Arrangement 3 plus base for prime mover.

ARR. 8 SWSI For belt drive or direct connection. Arrangement 1 plus extended base for prime mover.

ARR. 9 SWSI For belt drive. Impeller overhung, two bearings with prime mover outside base.

ARR. 10 SWSI For belt drive. Impeller overhung, two bearings with prime mover inside base.

FIGURE 5-12 DRIVE ARRANGEMENTS FOR CENTRIFUGAL FANS HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

5.5


THIS PAGE INTENTIONALLY LEFT BLANK

5.6

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


VEL

OUT VEL

Press

CFM

FPM

H20

2264 2547

800 900

2830 3113

VOL

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

0.125

SP

0.250

SP

0.375

SP

0.500

SP

0.625

SP

0.750

SP

0.875

SP

1.000

SP

1.250

SP

1.500

SP

1.750

SP

2.000

SP

RPM

BHP

RPM

BHP

RPM

BHP

RPM

RPM

RPM

BHP

RPM

BHP

RPM

BHP

RPM

BHP

RPM

BHP

BHP

BHP

RPM

BHP

RPM

BHP

0.04 0.05

398 434

0.10 0.13

456 487

0.15 0.19

507 536

0.21 0.25

567 578

0.26 0.30

608 624

0.32 0.37

656 669

0.40 0.44

703 712

0.47 0.51

747 755

0.55 0.60

835

0.78

1000 1100

0.06 0.08

472 510

0.17 0.21

519 552

0.23 0.27

565 595

0.29 0.34

608 636

0.36 0.42

645 675

0.42 0.49

686 708

0.49 0.56

727 745

0.57 0.63

767 782

0.65 0.71

843 855

0.83 0.89

916 924

1.03 1.10

991

1.31

3396

1200

0.09

549

0.26

587

0.33

627

0.40

666

0.48

702

0.56

738

0.64

768

0.71

802

0.79

870

0.97

936

1.17

999

1.39

1062

1.63

3679

1300

0.11

589

0.32

624

0.39

661

0.47

697

0.55

731

0.64

765

0.73

798

0.81

825

0.89

888

1.07

950

1.26

1012

1.48

1070

1.71

3962

1400

0.12

629

0.39

662

0.46

695

0.54

729

0.63

762

0.72

794

0.81

826

0.91

856

1.01

909

1.17

967

1.37

1026

1.58

1083

1.82

4245

1500

0.14

668

0.46

700

0.54

730

0.62

762

0.72

794

0.81

825

0.91

854

1.01

884

1.12

936

1.30

989

1.50

1043

1.71

1097

1.94

4528

1600

0.16

709

0.55

739

0.63

767

0.72

796

0.81

827

0.91

856

1.02

884

1.13

912

1.23

967

1.46

1013

1.64

1063

1.86

1114

2.09

4811

1700

0.18

749

0.65

778

0.74

805

0.83

832

0.92

860

1.03

888

1.14

915

1.25

942

1.36

994

1.59

1044

1.82

1087

2.01

1134

2.25

5094

1800

0.20

790

0.75

818

0.85

843

0.95

868

1.05

894

1.15

921

1.26

948

1.38

973

1.50

1023

1.74

1073

1.99

1115

2.21

1157

2.43

5377

1900

0.23

830

0.88

857

0.98

882

1.08

906

1.19

930

1.29

955

1.40

980

1.53

1005

1.65

1053

1.90

1100

2.16

1146

2.42

1185

2.64

5660

2000

0.25

872

1.01

897

1.12

921

1.23

944

1.33

966

1.44

989

1.56

1014

1.68

1038

1.81

1084

2.08

1129

2.34

1173

2.61

1217

2.89

5943

2100

0.27

913

1.16

937

1.27

960

1.39

982

1.50

1004

1.61

1025

1.73

1048

1.85

1071

1.99

1116

2.26

1160

2.54

1202

2.82

1245

3.12

6226

2200

0.30

954

1.32

977

1.44

999

1.56

1021

1.68

1042

1.80

1062

1.91

1083

2.04

1104

2.17

1148

2.46

1191

2.75

1231

3.04

1272

3.34

6509

2300

0.33

995

1.50

1017

1.62

1039

1.75

1059

1.87

1080

1.99

1100

2.12

1119

2.24

1139

2.38

1181

2.57

1222

2.97

1262

3.28

1301

3.58

6792

2400

0.36

1037

1.70

1067

1.82

1079

1.95

1099

2.08

1118

2.21

1137

2.34

1156

2.47

1175

2.60

1215

2.90

1255

3.20

1293

3.52

1331

3.84

7358

2600

0.42

1120

2.13

1139

2.26

1159

2.40

1178

2.55

1196

2.68

1214

2.82

1231

2.97

1248

3.10

1284

3.40

1321

3.72

1358

4.06

1393

4.40

7924 8490

2800 3000

0.49 0.56

1204 1287

2.64 3.23

1221 1303

2.78 3.38

1239 1320

2.93 3.53

1257 1337

3.08 3.70

1274 1353

3.23 3.86

1291 1370

3.38 4.02

1308 1385

3.53 4.18

1324 1401

3.69 4.34

1356 1431

3.99 4.67

1389 1461

4.32 5.00

1424 1492

4.67 5.35

1458 1525

5.03 5.73

9056 9622 10754

3200 3400 3600 3800

0.64 0.72 0.81 0.90

1371 1455 1539 1623

3.90 4.66 5.51 6.46

1386 1469 1552 1636

4.05 4.82 5.68 6.64

1401 1483 1566 1648

4.21 4.99 5.86 6.82

1417 1498 1579 1661

4.39 5.16 6.04 7.01

1433 1513 1594 1674

4.56 5.35 6.24 7.21

1448 1528 1608 1688

4.74 5.54 6.43 7.42

1464 1542 1621 1701

4.91 5.72 6.63 7.63

1478 1556 1636 1714

5.08 5.91 6.82 7.84

1507 1583 1661 1740

5.43 6.27 7.20 8.25

1535 1611 1687 1764

5.77 6.64 7.59 8.65

1663 1637 1713 1768

6.13 7.00 7.99 9.06

1593 1664 1737 1813

6.51 7.39 8.37 9.48

11320

4000

1.00

1707

7.52

1719

7.70

1731

7.89

1743

8.09

1755

8.29

1769

8.52

1781

8.74

1794

8.95

1818

9.39

1841

9.80

1865

10.24

1888

10.68

10188

IN

Pressure class limits:

Class I II

Maximum RPM 1550 2140

Table 5-1 Typical Fan Rating Table 5.7


MOTOR LEFT

VIEW FACING DISCHARGE

FIGURE 5-13 ARRANGEMENT 1 IN-LINE FANS for motors too large for fan casing. Arrangement 4 (Figure 5−14)Cdirect drive with wheel overhung on motor shaft.

Solution New static pressure

 1.0  10188 9056 2

cfm2 P 2  P1  cfm1

2

 1.27in.8 8 wgSP New brake horsepower:

cfm

 5.08  10188 cfm 9056 3

BP 2  BP1 

3

2 1

BP 2  7.23BHP A review of Table 5−1 not only confirms the calcula− tions, but also indicates that the change in capacity moved the fan into a different pressure classification which could result in a failure of the fan wheel and/or bearings. CAUTION)Always check with the published rat− ings of fan equipment to make sure that revised op− erating conditions do not require a different class fan. Often this type of change also could change the pressure classification of part or all of a duct system to higher duct construction and sealing require− ments. 5.2.2

Fan Nomenclature

5.2.2.1

Drive Arrangements

AMCA has developed standard fan drive arrange− ments (shown in Figure 5−12) for various bearing and drive locations. Axial or in−line fans are designated in much the same way as standard centrifugal fans. Stan− dard arrangements for in−line are: Arrangement 1 (Figure 5−13)Cbelt drive with motor mounted independent of fan casingCtypically used 5.8

Arrangement 9 (Figure 5−15)Cbelt drive with motor located on periphery of casing in one of eight standard locations designated by the letters beginning with A at the top and proceeding clockwise at eight equal inter− vals through the letter H when viewing the fan from the discharge. Vertical units are designated as either upblast or down− blast and generally are available only in Arrangements 4 and 9. 5.2.2.2

Motor Arrangement Locations

Motor location is specified at W, X, Y, and Z as shown in Figure 5−16. This motor location always is deter− mined by facing the fan drive sheave. It is independent of the discharge or rotation. 5.2.2.3

Rotation

Rotation is determined by the direction the fan wheel will be turning for proper operation as viewed from the drive side of the fan. Rotation is designated as clock− wise (CW) or counter clockwise (CCW). 5.2.2.4

Non-Sparking Construction

For applications where sparks generated in the air stream could be dangerous, AMCA provides three non−sparking construction classifications based on the degree of assurance desired. For all classes, bearings must be out of the air stream, the fan must be grounded, and non−sparking belts are required. The three classes are: 1.

AMCA A. Requires all components in the airstream be made of nonferrous material.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


VIEW FACING DISCHARGE

FIGURE 5-14 ARRANGEMENT 4 IN-LINE FANS

A B

H

G

C

D

F MOTOR SHOWN IN POSITION A

E VIEW FACING DISCHARGE

FIGURE 5-15 ARRANGEMENT 9 IN-LINE FANS 2.

AMCA B. This requires all components in the airstream be made of nonferrous material. Housing can be steel.

3.

AMCA C. Nonferrous wear ring is required on the inlet cone so that, if the impeller shifts, it will rub the nonferrous material.

Generally, AMCA A is the most expensive and AMCA C is the least expensive. 5.2.3

Fan Motors and Drives

5.2.3.1

General

Most fans are driven at constant speed by constant speed motors, and they generally deliver a constant air quantity. The motors range from small single phase fractional horsepower motors to large polyphase mo− tors. Motors generally are connected to the driven fan by means of a V belt drive which not only transmits power but allows the synchronous speed of the motor such as 1200, 1800, 3600 rpm, to be converted to the lower fan speed. Some small fans have motors directly connected. Some V belt drives have an adjustable speed range by providing a variable drive sheave on which the pitch diameter can be manually adjusted to allow for minor speed variations. Variable air volume (VAV) systems are now commonly used, and some reduce system air− flow by using variable speed motors or drives.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

5.9


d.

Ratios should not exceed 8:1.

e.

Belt speed, preferably should not exceed 5,000 fpm (25 m/s), or be less than 1,000 fpm (5 m/s). Best practice is about 4,000 fpm (20 m/s).

f.

Sheaves should be dynamically balanced when used for speeds in excess of 5,000 fpm (25 m/s) rim speed.

FAN MOTOR

Z

W Y

X DRIVE

Equation 5-1 rpm(fan) Pitchdiam.motorpulley   rpm(motor) Pitchdiam.fanpulley

FIGURE 5-16 CENTRIFUGAL FAN MOTOR LOCATIONS

5.2.3.3

Drive Installations

When installing or reviewing fan drives, these points should be particularly watched: Of major importance to the TAB technician, is that the V belt drives must be properly aligned before testing, and the belt tension adjusted properly. Too little belt tension results in belt slippage and excessive belt wear. Too much belt tension can cause excessive bearing loading, causing motor bearing or fan bearing failure. One further caution to the TAB technician is that the motor must have sufficient starting torque to over− come the inertia of the fan wheel and drive package. Most HVAC supply air systems do not have this pro− blem. However, in return air or exhaust air systems where design airflow volumes may be high and fan to− tal pressures low, check to assure that the installed mo− tor has sufficient starting torque to accelerate the fan to its design speed. 5.2.3.2

b.

c.

5.10

Be sure that shafts are parallel and sheaves are in proper alignment. Check again after a few hours of operation.

b.

Do not drive sheaves on or off shafts. Wipe shaft, key, and bore clean with oil. Tighten screws carefully. Recheck and retighten after a few hours of operation.

c.

Belts should never be forced over sheaves.

d.

In mounting belts be sure the slack in each belt is on the same side of the drive. This should be the slack side of the drive.

e.

Belt tension should be reasonable. When in operation, the tight side of the belts should be in a straight line from sheave to sheave and with a slight bow on the slack side. All drives should be inspected periodically to be sure belts are under proper tension and are not slipping.

f.

When making replacements of multiple belts on a drive, be sure to replace the entire set with a new set of matched belts.

Drive Design

Regardless of whether drives consist of stock or spe− cial items, there are certain primary conditions to con− sider with respect to the design of satisfactory drives. The conditions most commonly encountered are: a.

a.

Drives should be installed with provisions for center distance adjustment. This is essential, as all belts stretch.

5.3

FAN AIRFLOW AND PRESSURES

5.3.1

Fan Air Volume

Centers should not exceed 2½ to 3 times the sum of the sheave diameters nor be less than the diameter of the larger sheave.

The airflow volume (cfm or L/s) produced by a fan in a given system is independent of the air density.

Arc of contact on the smaller sheave should not be less than 120.

cfm (L/s)Ccubic feet per minute (liters per second) of air handled by a fan at any air density.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


Counter Clockwise Top Horizontal

Clockwise Top Horizontal

Clockwise Bottom Horizontal

Counter Clockwise Bottom Horizontal

Clockwise

Counter Clockwise

Counter Clockwise

Clockwise

Up Blast

Up Blast

Down Blast

Down Blast

Counter Clockwise

Clockwise

Clockwise

Counter Clockwise

Top Angular Down

Top Angular Down

Bottom Angular Up

Bottom Angular Up

Clockwise

Counter Clockwise

Counter Clockwise

Clockwise

Bottom Angular Down

Bottom Angular Down

Top Angular Up

Top Angular Up

FIGURE 5-17 DIRECTION OF ROTATION AND DISCHARGE

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

5.11


scfm (sL/s)Ccubic feet per minute (liters per second) of standard air (0.075 lb/ft3 or 1.2041 kg/m3 density) handled by a fan. 5.3.2

Where it is possible to take field measurements, care must be taken to measure fan total pressure at the fan inlet duct rather than fan static pressure.

Fan Total Pressure (TP)

Fan total pressure is the difference between the total pressure at the fan outlet and the total pressure at the fan inlet. The fan total pressure is a measure of the total mechanical energy added to the air or gas by the fan. This generally can be measured accurately only (as il− lustrated in Figure 5−18) in a test laboratory.

IMPACT TUBE

FAN

FAN

STATIC TUBE

IMPACT TUBE

AIR FLOW

AIR FLOW

SP

FIGURE 5-19 FAN STATIC PRESSURE (SP)

5.3.4 IMPACT TUBE

TP

Fan velocity pressure (Figure 5−20) is the pressure cor− responding to the fan outlet velocity pressure. It is the kinetic energy per unit volume of flowing air.

FIGURE 5-18 FAN TOTAL PRESSURE (TP)

5.3.3

Fan Static Pressure (SP)

Fan static pressure (Figure 5−19) is the fan total pres− sure less the fan velocity pressure. It can be calculated by subtracting the total pressure at the fan inlet from the static pressure at the fan outlet. This is a source of some confusion within the industry, but, by definition: Fan SP = Fan TP (outlet)  TP (inlet)  Vp (out− let) Also, TP (outlet)  SP (outlet) = Vp (outlet)

5.3.5

Fan SP = SP (outlet)  TP (inlet)

Fan Outlet Velocity

Fan outlet velocity is the theoretical velocity of the air as it leaves the fan outlet, and is calculated by dividing the air volume in cfm (L/s) by the fan outlet area in square feet (m2). However, all fans have a non−uni− form outlet velocity; that is, the velocity varies over the cross−section of the fan outlet. Therefore fan outlet velocity as calculated above is only a theoretical value that could occur at a point downstream from the fan. All velocity (velocity pressure) readings, including to− tal pressure and static pressure should be taken down− stream in a straight duct connected to the fan discharge where the flow is more uniform. A large portion of the discharge airflow occurs at the side of the fan outlet farthest from the fan shaft. Veloc− ity readings taken at the side of the duct nearest the shaft, may indicate air appearing to flow from the duct back into the fan. 5.3.6

and substituting:

5.12

Fan Velocity Pressure (Vp)

Fan Brake Power

Fan brake power is the actual power required to drive the fan. It is greater than a theoretical air power be−

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


Example 5.2 (I−P) Find the tip speed of a 30 inch diameter fan wheel ro− tating at 954 rpm.

PITOT TUBE TOTAL PRESSURE

VELOCITY PRESSURE

Solution TipSpeed  p  D  RPM  p  30  954 12 12 Tip Speed = 7493 (fpm)

STATIC PRESSURE

Example 5.2 (SI) VELOCITY PRESSURE  TOTAL PRESSURE = STATIC PRESSURE

Find the tip speed of a 750 mm diameter fan wheel ro− tating at 954 rpm.

FIGURE 5-20 FAN VELOCITY PRESSURE (VP) Solution cause it includes loss due to turbulence and other inef− ficiencies in the fan, plus bearing losses. Fan brake power is an important value to the TAB technician be− cause it is the power furnished by the fan motor. 5.3.7

Tip8 8 Speed  p  D  RPM  p  0.75  954 60 60 Tip Speed = 37.46 (m/s)

TIP SPEED

Also called peripheral velocity, tip speed equals the circumference of the fan wheel times the rpm of the fan and is expressed in feet per minute (meters per second) (Figure 5−21)

RPM

D

Equation 5-2 (I-P) TipSpeed  p  d  RPM 12in.ft. Where: TipSpeed  Feetperminute D  Wheeldiameter  inches RPM  Revolutionsperminute Equation 5-2 (SI) p  d  RPM TipSpeed  60secmin Where: TipSpeed  Metersperminute D  Wheeldiameter  meters RPM  Revolutionsperminute

FIGURE 5-21 TIP SPEED

5.4

FAN/SYSTEM CURVE RELATIONSHIP

5.4.1

System Curve

Duct system resistance is the sum of all pressure losses through filters, coils, dampers, and ductwork. The sys− tem curve or system resistance curve (Figure 5−22) is a plot of the pressure that is required to move air through the system. For fixed systems, that is, with no changes in damper settings, etc., system resistance

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

5.13


varies as the square of the airflow. The system curve for any system is represented by a single curve. For exam− ple, consider a system handling 1,000 cfm (500 L/s) with a static pressure (SP) resistance of 1 in. wg (250 Pa).

System Curve BHP Curve (W) Fan Curve

Operating Point

3

(750)

AND

(1000)

SP

4

(500)

BHP

Static Pressure - In wg (Pa)

5

2 1 (250) 0

1000 (500) AIRFLOW - CFM (l/s)

2000 (1000)

CFM (L/S)

FIGURE 5-22 SYSTEM RESISTANCE CURVE

FIGURE 5-23 OPERATING POINT If the airflow is doubled, the SP resistance will in− crease by that ratio squared (4) to 4 in. wg (1000 Pa). This system curve changes, however, as filters load with dirt, coils start condensing moisture, or when bal− ancing dampers are moved to a new position.

reading across the fan and concluding that if it is at or above design requirements, the airflow is also at or above design requirements. 5.4.3

5.4.2

The system operating point (Figure 5−23), a point at which the fan and system will simultaneously perform, is determined by the intersection of the system curve with the fan performance curve for each designated speed (rpm). Every fan operates only along its perfor− mance curve. If the designed system SP resistance is not the same as the SP resistance in the installed sys− tem, the operating point will move along the fan curve and the SP and volume delivered will not be as calcu− lated. In Figure 5−24 the actual duct system has more pres− sure drop then predicted by the system designer. Thus, airflow is reduced because the SP increased. The shape of the horsepower curve typically would result in a re− duction in fan power. Typically, the fan rpm would then be increased, and more fan power would be need− ed to achieve the desired airflow. In many cases, when there is a difference between actual and calculated fan output, the difference is due to a change in system re− sistance rather than to any shortcomings of the fan or motor. Frequently, the mistake is made of taking the SP 5.14

Fan Law Relationships

System Operating Point Fan law equations 2−17 and 2−18 from Chapter 2 ap− plying a change only in fan rpm (with the system re− maining unchanged), are graphically shown in Figure 5−25. Use Equation 2−17 to obtain rpm 2: rpm 2  rpm1 

Q2 Q1

Then use Equation 2−18 to obtain the new static pres− sure:

rpm P 2  P1 rpm 2 1

2

5.4.4

Density

5.4.4.1

When Volume is Constant

The resistance of an HVAC duct system is dependent on the density of the air flowing through the system. Air density at standard conditions of 0.075 pounds per cubic feet (1.2041 kilograms per cubic meter) is used for rating fans in the HVAC industry. A fan is a constant volume machine and will produce the same

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


volume of airflow regardless of the air density being handled (see Figure 5−26). The fan SP and fan power, however, will vary directly as the air density increases or decreases.

SP. The fan is drawing 9.22 Bhp from a 10 HP motor. If the fan is run with the oven off (70F ambient), cal− culate the new SP and Bhp. (Air density at 250F = 0.0563 lb/ft3 ).

Equation 5-3 SP 2 d   2 SP 1 d1

Solution Equation 5-4

FP 2 d   2 FP 1 d1

Using Equations 5−3 and 5−4: d2  2.6  0.075 d1 0.0563 SP 2  3.46in.w.g. d FP 2  FP1  2  9.22  0.075 0.0563 d1 FP 2  12.28Bhp With only a 10 HP motor, a 23 percent motor overload occurs. SP 2  SP1 

Where (airflow1 = airflow2 ): SP  Staticpressure  in.wg(Pa) 3

d  Density  lbft (kgm3) FP  Fanpower  Bhp(W) In other words, the heavier or more dense the air, the greater the fan power or SP will be.

SP @ RPM

2

System Curve

Fan Curve Actual System Curve Design System Curve

SP

2

New Operation Point Change

SP

SP Increase

SP @ RPM 1 SP

1

AIirflow Reduction CFM (L/S)

FIGURE 5-24 VARIATIONS FROM DESIGN AIR SHORTAGE

Example 5.3 (I−P) A 15,000 cfm fan is delivering 250F air from an oven through an air−to−air heat exchanger against 2.6 in. wg

Airflow 1

Airflow 2

FIGURE 5-25 FAN LAW - RPM CHANGE

Example 5.3 (SI) A 7500 L/s fan is delivering 125C air from an oven through an air−to−air heat exchanger against 650 Pa SP. The fan is drawing 6.88 kW from a 7.5 kW motor. If the fan is run with the oven off (20C ambient) calcu− late the new SP and kW. (Air density at 125C = 0.891 kg/m 3).

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

5.15


Where: (SP1 = SP2 ):

Solution

Q  Airflow  cfm(Ls) d  Density  lbft3(kgm3) RPM  FanSpeed FP  Fanpower  Bhp(W)

Using Equations 6−2 and 6−3: d SP 2  SP1  2  650  1.2041 0.891 d1 SP 2  878Pa d FP 2  FP1  2  6.88  1.2041 d1 0.891 FP 2  9.30kW With only a 7.5 kW motor, a 24 percent motor overload occurs. 5.4.4.2

When Static Pressure is Constant

SP @ d 1

SP1

If the system SP remains constant, the airflow volume, fan speed and fan power will vary inversely as the square root of the density (see Figure 5−27).

Q1   Q2

SP @ d

Chg. 2

Equation 5-5

SP 2

d2 d1

SYSTEM d 1

RPM 1   RPM 2

Equation 5-6 SYSTEM d 2

d2 d1

Airflow1= Airflow 2

FIGURE 5-26 EFFECT OF DENSITY CHANGE (CONSTANT VOLUME) FP 1   FP 2

d2 d1

Equation 5-7 5.4.4.3

Constant Mass Flow

With a constant mass flow rate in a system that remains constant without any changes and using the same fan with a variable drive, the airflow rate, RPM and SP will vary inversely with the air density. The fan brake power will vary inversely with the square of the densi− ty (see Figure 5−28). Equation 5-8 Q1 d   2 Q2 d1 Equation 5-9 RPM 1 d   2 RPM 2 d1 Equation 5-10 SP 1 d   2 SP 2 d1

FP 1 d   2 FP 2 d1

5.16

Equation 5-11 2

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


Static Pressure

Example 5−4 SI SP@d1

SP@d 2

A fan is required to handle 7500 L/s at 500 Pa, 75C, 950 rpm, 750 meters altitude and 4.2 kW. Find the fan airflow, SP, RPM and fan brake power that must be se− lected from the fan table.

Solution

Chg.

SP1 -SP2

Using an air density correction factor table found in Appendix A, the correction factor to standard condi− tions is 0.78 or: d 2(Actual)   0.78 d 1(Standard) Airflow (d1< d 2)

Using Equations 5−8 to 5−11:

FIGURE 5-27 EFFECT OF DENSITY CHANGE (CONSTANT STATIC PRESSURE)

d2 d1 Q 1  7500  0.78  5850Ls SP 1(Std)  500  0.78  390Pa RPM 1(Std.) RPM 2(Act.)  d 2d 1 RPM 2  9500.78  1218rpm FP1(Std.) FP 2(Act.)  (d2d 1)2 FP 2  4.2(0.78)2  6.90kW FAN CAPACITY RATINGS Q 1(Std)  Q2(Act.)

Where:  Airflow  cfm(Ls) Q d  Density  lbft 3(kgm3) RPM  Fanspeed SP  Staticpressure  in.w.g.(Pa) FP  Fanpower  Bhp(W) 5.5 Example 5.4 (I−P) 5.5.1 A fan is required to handle 15,000 cfm at 2 in. wg, 150F, 950 RPM, 2000 feet altitude and 5.6 Bhp. Find the fan cfm, SP, Bhp and RPM that must be selected from the fan table.

Solution Using an air density correction factor table found in Appendix A, the correction factor to Standard condi− tions is 0.81 or: d 2(Actual)   0.81 d 1(Standard)

Using Equations 5−8 to 5−11:

Fan Testing

Most fan manufacturers rate the performance of their products from tests made in accordance with ANSI/ AMCA Standard 210, Laboratory Methods of Testing Fans for Rating. The purpose of Standard 210 is to es− tablish uniform methods for laboratory testing of fans and other air moving devices to determine perfor− mance in terms of flow rate, pressure, power, air densi− ty, speed of rotation and efficiency, for rating or guar− antee purposes. Two basic methods of measuring airflow are included, the Pitot tube and the long radius flow nozzle. These are incorporated into a number of different setups or figures. In general, a fan is tested on the setup which most closely simulates the way in which it will be installed in an HVAC system. Centrif− ugal, tubeaxial and vaneaxial fans are usually tested with only an outlet duct. Figure 5−29 is a reproduction of a test setup from AMCA Standard 210. Note that this particular setup includes a long straight duct connected to the outlet of the fan. A straightener is located upstream of the Pitot

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

5.17


PL.1

PL.2

PL.3 L 2,3 10 D3 MIN. +0.25

8.5 D 3

-0.00

D3 MIN. D3 5 D3

+0.25 -0.00

D3 t d3

D3

FAN

PITOT TUBE STRAIGHTENER

TRAVERSE

TRANSFORMATION PIECE

THROTTLING DEVICE

FIGURE 5-28 AMCA FAN TEST - PITOT TUBE tube traverse to remove swirl and rotational compo− nents from the airflow and to ensure that the flow at the plane of measurement is as near to uniform as possible.

A manufacturer may test a fan with or without an outlet duct or inlet duct. Catalog ratings should state whether ducts were used during the rating tests. If the fans are not to be applied with similar duct configurations as used in the test setup, an allowance should be made for the difference in the resulting performance.

Static Pressure

SYSTEM @ d 1

SP2 @ d AND RPM 2

5.5.2

SP2 SP @ d 1 AND RPM 1

Chg.

Airflow1

System Effect

For years, many HVAC system designers, system in− stallers, fan company sales engineers and testing, ad− justing, and balancing (TAB) contractors have found that system total pressure measurements and airflow capacities were considerably less than the fan horse− power and rpm curves indicated.

SP1

Airflow2

FIGURE 5-29 EFFECT OF DENSITY CHANGE (CONSTANT MASS FLOW)

The angle of the transition between the test duct and the fan outlet is limited to ensure that uniform flow will be maintained. A steep transition, or abrupt change of cross−section would cause turbulence and eddies, and lead to non−uniform flow. 5.18

Uniform flow conditions ensure consistency and re− producibility of test results and permits the fan to de− velop its maximum performance. In any installation where uniform flow conditions do not exist, the fan’s performance will be reduced.

This derating of duct system fans is called system ef− fect, and it is very important that this phenomenon be taken into account by all concerned with HVAC sys− tems if they are to operate as designed. System effect diminishes a fan’s performance because of the interaction of the fan and the connected duct sys− tem; and system effect factors are used to compensate for the fan’s decreased performance. In general, sys− tem effect factors are approximations obtained from many research studies. Some studies have been pub− lished previously by individual fan manufacturers, and

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


many represent the consensus of engineers with con− siderable experience in fan applications. Fans of different types (and even fans of the same type from different manufacturers) will not necessarily react with a duct system in exactly the same way. Therefore, it is necessary to use judgment, based on ac− tual experience, in applying the system effect factors. 5.5.2.1

Fan Selection

Figure 5−30 illustrates deficient fan/system perfor− mance caused by system effect. HVAC system pres− sure losses have been determined and the fan selected to operate at Point 1 (system curve A). However, no al− lowance has been made for the effect of poor duct con− nections to the fan. To compensate, a system effect fac− tor must be added to the calculated system pressure losses to determine a new system curve that is then used to select the fan. The point of intersection between the fan performance curve and this new ?phantom" system curve B is Point 4. Therefore, the actual system flow volume is defi− cient by the difference from Point 1 to Point 4. To achieve the design airflow volume, a system effect factor equal to the pressure difference between Point 1 and Point 2 should be added to the calculated system pressure losses. The fan should be selected to operate at Point 2 where the new corrected rpm curve crosses phantom system curve B. A higher fan brake horse− power will also be required.

corrected fan, the airflow volume and static pressure will be established as point 1, because that is where the system actually is operating. The system is not operat− ing on the phantom system curve, which was used only to select the derated capacity fan. System effect cannot be measured in the field, but only calculated after a visual inspection is made of the fan/duct system con− nections. Because system effect is velocity related, the differ− ence between Points 1 and 2 is greater than the differ− ence between Points 3 and 4. The system effect factor includes only the effect of the system configuration on the fan’s performance. All duct fitting pressure losses are calculated as part of the HVAC system pressure losses and are part of system curve A. 5.5.2.2

Figure 5−31 shows the changes in velocity profiles from the fan outlet to where a uniform velocity profile has developed in the duct. The distance of this point from the fan is called the effective duct length. To ob− tain 100 percent of the energy recovery or static regain, duct fittings or abrupt changes in duct configuration should not be used within that space. In other words, any changes to the discharge duct con− figuration within the effective duct length (which dif− fers from the duct configuration used when the fan was tested and rated) may cause the fan to perform less effi− ciently. 5.5.2.3

However, when a testing and balancing technician measures the actual HVAC system conditions with the

PHANTOM CURVE B WITH SYSTEM EFFECT CURVE A CALCULATED DUCT SYSTEM WITH NO ALLOWANCE FOR SYSTEM EFFECT 2

SYSTEM EFFECT LOSS AT DESIGN VOLUME

4

DESIGN PRESSURE

1 3

SYSTEM EFFECT AT ACTUAL FLOW VOLUME

SELECTED FAN CURVE FAN CATALOG PRESSURE-VOLUME CURVE

DEFICIENT PERFORMANCE DESIGN VOLUME

FIGURE 5-30 EFFECTS OF SYSTEM EFFECT

Fan Outlets

Fan Inlets

Power roof exhausters are tested and rated when mounted on a roof curb through which the exhaust air duct passes, so system effect is not a problem. The problem occurs with HVAC centrifugal and axial flow fans that are tested without any inlet obstructions or in− let duct connections. For rated performance, the air must enter the fan uni− formly over the inlet area in an axial direction without pre−rotation. Non−uniform flow into the inlet is the most common cause of reduced fan performance. Such inlet conditions are not equivalent to a simple in− crease in the system resistance, so they cannot be treated as a percentage decrease in the fan airflow and pressure output. A poor inlet condition results in an en− tirely new fan performance. Many system effect curves for various round and rec− tangular elbows may be found in AMCA Publication 201−90, Fans and Systems or the SMACNA HVAC

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

5.19


BLAST AREA CENTRIFUGAL CUTOFF FAN

OUTLET AREA

DISCHARGE DUCT

LENGTH OF DUCT R

100% EFFECTIVE DUCT LENGTH

a. Round Elbow

FIGURE 5-31 FAN OUTLET EFFECTIVE DUCT LENGTH

System9Duct Design manual. When a suitable (often sizeable) length of duct is used between the fan inlet and return air duct elbow, system effect may be avoi− ded. These improvements help maintain uniform flow into the fan inlet and thereby approach the flow condi− tions of the laboratory test setup. Most often where space is at a premium, the inlet duct will be mounted directly to the fan inlet, as shown in Figure 5−32 b. The reduction in capacity and pressure for this type of inlet condition is impossible to tabulate. The many possible variations in width and depth of the duct influence the reduction in performance to varying degrees. Therefore, this inlet should be avoided. Fans and Systems and the HVAC Systems9Duct De− sign manual states that capacity losses as high as 45 percent have been observed in poorly designed inlets, such as those shown in Figure 5−32 b. Field fabricated or factory designed inlet boxes (see Figure 5−32 c) may often eliminate or substantially reduce system effect at fan inlets. Inlet elbows at axial fans may cause an instability in fan operation in addition to system effect that could re− sult in serious damage to the fan. It is strongly advised that inlet elbows be installed at least three duct diame− ters away from any axial fan inlet.

5.20

b. Rectangular Duct

c. Inlet Box

FIGURE 5-32 NON-UNIFORM FLOW CONDITIONS INTO FAN INLET 5.5.2.4

Field Measurements

Recent research has determined that accurate duct ve− locity measurements cannot be made until a near uni− form velocity profile has developed. This point may vary from 3 to 20 duct diameters downstream from the object causing the turbulence. So, any accurate mea− surements on the discharge side of a fan must be well away from the point where system effect occurs. On the fan inlet, non−uniform airflow, spin in the air− flow or a duct condition that produces a vortex create the problem. When one observes the various poor duct fan inlet conditions normally installed, accurate mea− surements are impossible. However, on the fan inlet side, the system effect loss usually occurs within the entry to the fan wheel, so it is not field−measurable. Finally, system effect is a real and often occurring pro− blem. It may be avoided by using better fan/system duct connections where space permits. it also may be avoided if the installing contractor would order HVAC fans and equipment with the proper inlet and discharge connection configurations so that elbows would not have to immediately change airflow direction. Just re− member that: fan capacity reductions due to system ef− fect cannot be measured in the field by TAB techni− cians, system effect losses are approximate, and that system effect factors must not be confused with duct fitting loss coefficients.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


CHAPTER 6

AIR DISTRIBUTION AND DEVICES


CHAPTER 6

AIR DISTRIBUTION AND DEVICES

6.1

AIR TERMINAL BOXES

6.1.2.1

6.1.1

Introduction

Constant flow rate controllers may be of the pneumatic or electric volume regulator type. They typically re− quire internal differential pressure sensing, selector devices, and pneumatic or electric motors for opera− tion.

An air terminal box or terminal unit is a device that controls the volume of conditioned air introduced into a space or zone from the HVAC air duct system. The air terminal box manually or automatically fulfills one or more of the following functions. 6.1.1.1

Pressure

The air terminal box may control the pressure of the discharge airflow. 6.1.1.2

Airflow Rate

The air terminal box may control the rate and velocity of the discharge airflow. 6.1.1.3

Temperature

The air terminal box may mix airstreams of different temperatures or humidities, or include a coil to add additional heating or cooling capacity.

6.1.2.2

Air Blending

Variable Air Volume

Variable air volume (VAV) controllers incorporate a means to reset the constant volume regulation auto− matically to a different control point within the range of the control device in response to an outside signal, such as from a thermostat. Boxes with this feature are pressure independent and may be used with reheat components. Variable flow rate may also be obtained by using a modulating damper ahead of a constant vol− ume regulator. This arrangement typically allows for variations in flow between high and low limits or be− tween a high limit and shutoff. These boxes are pres− sure dependent and volume limiting in function. Pneu− matic variable volume may be either pressure independent, volume limiting, or pressure dependent, according to the equipment selected. 6.1.3

6.1.1.4

Constant Airflow

Box Power Sources

A terminal box commonly integrates a sound chamber to reduce noise generated by the manual damper or flow controller reducing the inlet air velocity or pres− sure. The sound attenuation chamber is typically lined with thermal and sound insulating material and is equipped with baffles. Special sound attenuation in the air discharge ducts usually is not required in smaller boxes.

Terminal boxes can be further categorized as being system powered, wherein the assembly derives all of the energy necessary for its operation from the supply air within the distribution system, or as externally powered, wherein the assembly derives part or all of the energy necessary for its operation from a pneumat− ic or electric outside source. In addition, assemblies are self−contained (when they are furnished with all necessary controls for their operation, including actua− tors, regulators, motors, and thermostats), as opposed to non−self−contained assemblies (where part or all of the necessary controls for operation are furnished by someone other than the terminal box manufacturer). In this latter case, the controls may be mounted on the as− sembly by the assembly manufacturer or may be mounted by others after delivery of the equipment.

6.1.2

6.1.4

Types of Air Terminal Boxes

6.1.4.1

Reheat Terminal Boxes

The air terminal box may mix primary air at high ve− locity and/or secondary air from the conditioned space. 6.1.1.5

Sound Attenuation

Categories

Terminal boxes are typically categorized according to the function of their airflow volume controllers, which are generally either constant or variable air volume (VAV) devices. They are further categorized as being pressure dependent, where the airflow rate through the assembly varies in response to changes in system pres− sure, or as pressure independent where the airflow rate through the device does not vary in response to changes in system pressure.

Reheat terminal boxes add sensible heat to the supply air. They cannot be used in many applications unless the added heat is recovered heat due to energy con− servation codes. Water or steam coils or electric resist− ance heaters can be located within or attached directly to the air discharge end of the box. These boxes typi− cally are single duct, and operation can be either

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

6.1


constant or variable volume. However, if they are VAV, they must maintain some minimum airflow to accomplish the reheat function. 6.1.4.2

Dual Duct Terminal Boxes

Duct terminal boxes receive warm and cold air from separate air supply ducts in accordance with space re− quirements. Pneumatic and electric volume regulated boxes often have individual modulating dampers and operators to regulate the amount of warm and cool air. When a single modulating damper operator regulates the amount of both warm and cold air, a separate pres− sure reducing damper or volume controller (either pneumatic or mechanical) is needed in the box to re− duce pressure and limit airflow. Specially designed baffles may be required within the unit or at the box discharge to mix varying amounts of warm and cold air and/or to provide uniform flow downstream. Dual duct boxes can be equipped with constant flow rate or vari− able flow rate devices to be either pressure indepen− dent or pressure dependent to provide a number of vol− ume and temperature control functions. 6.1.4.3

Ceiling Induction Boxes

The ceiling induction box provides either primary air or a mixture of primary air and relatively warm air to the conditioned space. It accomplishes this function by permitting the primary air to induce air from the ceil− ing plenum or via inducted return air from conditioned space. A single duct supplies primary air at a tempera− ture cool enough to satisfy all zone cooling loads. The ceiling return air inducted into the primary air is at a higher temperature than the room because heat from recessed lighting fixtures enters the plenum directly. The induction box contains damper assemblies con− trolled by an actuator in response to a thermostat to control the amount of cool primary air and warm in− duced air. As reduction in cooling is required, the pri− mary air flow rate is gradually reduced and the induced air rate is generally increased. Reheat coils can be used in the primary air supply and/or in the induction open− ing to meet occasional interior and perimeter load re− quirements. 6.1.4.4

Fan Powered Boxes

Fan powered boxes differ from the above induction boxes in that they are equipped with a blower. This blower, generally driven by a fractional horsepower motor, draws air from the conditioned space (secon− dary air) to be mixed with the cool primary air. The ad− vantage of fan assisted boxes over basic VAV boxes is 6.2

that for a small energy expenditure to the terminal fan, constant air circulation can be maintained in the space. Fan assisted boxes operate at a lower primary air static pressure than air induction boxes, and perimeter zones can be heated without operating the primary fan during unoccupied periods. Warm air from the ceiling return can be used for low to medium heating loads depend− ing on construction of the building envelope. As the load increases, heating coils in the perimeter boxes can be activated to heat the recirculated plenum air to the necessary level. Fan assisted boxes can be divided into two categories: constant volume and bypass−type units. Constant volume, fan assisted boxes (Figure 6−1) are used when constant air circulation is desired in the space. The unit has two inletsCone for cool primary air from the central fan system and one for the secon− dary air. All air delivered to the space passes through the blower. The blower operates continuously when− ever the primary air fan is on and can be cycled to de− liver heat, as required, when the primary fan is off. As the cooling load decreases, a damper throttles the amount of primary air delivered to the blower. The blower makes up for this reduction of primary air by drawing air in the space or ceiling plenum through the return air opening.

DISCHARGE AIR FAN

(CONSTANT VOLUME)

PRIMARY AIR

DAMPER

RETURN AIR (PLENUM)

FIGURE 6-1 CONSTANT VOLUME FAN-POWERED BOX

In the bypass−type fan assisted box (Figure 6−2), the cool primary air bypasses the blower portion of the unit and is delivered directly to the space. The blower section draws in plenum air only and is mounted in par− allel with the primary air damper. A back draft damper prevents primary air from flowing in to the blower sec− tion when the blower is not energized. The blower in these units generally is energized after the damper in the primary air is partially or completely throttled. Some electronically controlled units gradually in− crease the fan speed as the primary air damper is throttled to maintain constant airflow, while permit− ting the fan to shut off when it is in the full cooling mode.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


6.2

VARIABLE AIR VOLUME (VAV) TERMINAL BOXES

6.2.1

Introduction

A VAV system controls the dry bulb temperature with− in a space by varying the volume of supply air rather than the supply air temperature. VAV systems can be applied to interior or perimeter zones, with common or separate fan systems, common or separate air tempera− ture control, and with or without auxiliary heating de− vices. As the VAV boxes on a given supply duct system begin to reduce their air flow, duct pressure controls sense this duct pressure increase and the supply fan air flow is reduced accordingly.

PRIMARY AIR

DAMPER DISCHARGE AIR

6.2.3

Combination Pressure Dependent-Independent Boxes

These combination boxes regulate maximum volume, but the airflow volume below the maximum flow rate varies with the inlet pressure variation. Generally, air− flow will oscillate when pressure varies. They are less expensive than pressure independent units and can be used where pressure independence is required only at maximum volume, where system pressure variations are relatively minor, and where some degree of hunt− ing is tolerable. 6.2.4

Pressure Dependent Boxes

Pressure dependent boxes do not regulate the airflow volume, but position the volume regulating device in response to the thermostat. They are the least expen− sive and should only be used where there is no need for limit control and the system pressure is stable. 6.2.5

Bypass (Dumping) Boxes

(VARIABLE VOLUME) RETURN AIR (PLENUM)

FAN

FIGURE 6-2 BYPASS-TYPE FANPOWERED BOX

A space thermostat can control flow by varying a damper, or a volume regulating device in the duct, or a pressure reducing terminal box. Depending on the complexity of the air distribution system, and consid− erations, VAV may or may not be combined with fan or system static pressure controls. The fan system is designed to handle the largest simul− taneous block load, not the sum of the individual peaks. As each zone peaks at a different time of day, it borrows the extra air from off−peak zones. This transfer of air from low−load to high−load zones occurs only in a true VAV system. 6.2.2

Pressure Independent Boxes

Pressure independent boxes regulate the airflow vol− ume in response to the thermostat’s call for heating or cooling. The required airflow is maintained regardless of fluctuation of the VAV unit inlet or system pressure. These units can be field or factory adjusted for maxi− mum and minimum cfm (L/s) settings. They will oper− ate at inlet static pressures as low as 0.2 in. of water (50 Pa) at maximum system design volumes.

VAV room supply is accomplished in constant volume systems by returning excess supply air into the return ceiling plenum or return air duct, thus bypassing the room. However, this reduction of system volume is not energy efficient. Use generally is restricted to small systems where a simple method of temperature control is desired, initial cost is modest, and energy conserva− tion is deemed unimportant. 6.3

OTHER AIRFLOW DEVICES

6.3.1

Pressure Reducing Valves

Pressure reducing valves or air valves each consist of a series of gang operated vane sections mounted within a rigid casing and gasketed to reduce as much air leak− age as possible between the valve and duct. They usu− ally are installed between a high pressure trunk duct and a lower pressure branch duct. Pressure is reduced by partially closing the valve, which results in a high pressure drop through the valve. This action generates noise, which must be attenuated in the low pressure discharge duct. The length and type of duct lining depend on the amount and frequency of noise to be attenuated. Volume control is obtained by adjustment of the valve manually, mechanically, or automatically. Automatic adjustment is achieved by a pneumatic or electric con− trol motor actuated by a pressure regulator or a thermo− stat. Pressure reducing valves are generally equal in size to the low pressure branch duct connected to the valve

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

6.3


discharge. This arrangement provides minimum pressure drop with valves opened fully. 6.3.2

thermostatically controlled. The opening varies in approximate proportion to the air volume to maintain discharge throw pattern stability, even with low air quantities. Since these units are pressure dependent, constant pressure regulators are usually required in the duct system. Noise is a particular concern when selecting outlets.

Supply Outlet Throttling Units

The area of the throat or the discharge opening of these supply outlets, which are usually linear diffusers, is

FRAME: 2’ or 1 1_w" ¢ 1 1_w" ¢ 1_i" STRUCTURAL OR FORMED CHANNEL

FRAME 3_i" OR 1_w" DIA.

SHAFTS

18 GA MIN. BLADES

ANGLE STOP 1_w" ¢ 1_w" BAR OPTIONAL

SHAFT EXTENSION

SECTION

FIG. A OPPOSED ACTION

CHANNEL FRAME

PIN & BRONZE BUSHING

CONNECTING BAR FRAME

NOTICE 48" MAX. WIDTH FRAME

STOP SHAFT EXTENSION FIG. B PARALLEL ACTION

SEE TEXT ON VOLUME DAMPERS

SECTION FIG. C

FIGURE 6--3 MULTIBLADE VOLUME DAMPERS

6.4

HVAC SYSTEMS Testing, Adjusting & Balancing  Third Edition


Volume Dampers

6.3.3.1

Introduction

Volume dampers are primary elements in the duct sys− tem. They are used for controlling airflow rates by introducing a resistance to airflow in the system. In higher pressure systems, the damper is referred to as a pressure reducing valve. Volume control or balancing dampers should be installed in each branch of zone duct. Single leaf dampers which are part of a manufactured air grille are not acceptable for system balancing. Opposed blade dampers which are part of a manufactured air grille can be used if there is not enough room for a regular damper and if sufficient space is provided behind the grille face for proper operation of the damper. Other− wise, a balancing damper should be installed in the branch register termination at a location where it is ac− cessible from the grille or diffuser opening, or a quad− rant damper should be used. Volume dampers installed in branch ducts where the total estimated static pressure is less than 0.5 in. wg (125 Pa) can be single leaf type. Volume dampers installed in ductwork where the total estimated system static pressure exceeds 0.5 in. wg (125 Pa) should be manufactured in accordance with Figure 6−3. 6.3.3.2

Multiblade Dampers

Figure 6−3 shows two types of multiple blade dampers: parallel blade and opposed blade. The terms parallel and opposed refer to the movement of the adjacent bla− des. In the parallel blade damper, all of the blades move in parallel. The opposed blade damper has a linkage which causes the adjacent blades to move in opposite directions. Partial closing of a damper increases the resistance of the duct system to airflow. The reduction in airflow with closure of the damper may or may not be propor− tional to the amount of adjustment of the damper. That is, closing the damper half way does not necessarily mean that the air volume will be reduced to fifty per− cent of that volume which flows through the damper when it is wide open. The relation between the position of the damper and the percent of air that flows through the damper with respect to the airflow through the wide open damper is termed the flow characteristic. Typical flow characteristic curves for parallel blade and opposed blade dampers are shown in Figures 6−4 and 6−5. In Figure 6−4 the flow characteristic curves for

the parallel blade damper show that as the damper is closing, the flow reduction may be proportional to the closing of the damper as is shown by curve J, or partial closure of the damper may have little effect on the flow as is shown by curve A. 100 90 PERCENT OF MAXIMUM FLOW

6.3.3

80 A B

70

C D

60

E F G

50

H J

40

K

30 20 10 0 10

20

30 40 50 60 70 DAMPER POSITION, DEGREES OPEN

80

90

FIGURE 6-4 FLOW CHARACTERISTICS FOR A PARALLEL OPERATING DAMPER The manner in which the damper performs in any duct system is determined by how complicated the system is. If the system is very simple and the damper makes up a major part of the resistance, then any movement of the damper will change the resistance of the entire system and good control of the airflow will result. If the damper resistance is very small in relation to that of the entire system, a poor flow characteristic such as curve ?A" in Figures 6−4 and 6−5 will result. Typical ratios of damper to system resistance are shown in Table 6−1 for each flow characteristic curve. The set of curves for the opposed blade damper (Figure 6−5) shows that for a given ratio of damper to system resistance, a better flow characteristic usually results than with the parallel blade damper (Figure 6−4). As the opposed blade damper is closed, it introduces more resistance to airflow for a given position than a parallel blade damper. When balancing systems, it should be realized that the flow characteristics of a damper are not constant and will vary from one system to another. The actual effect of closing the damper can only be determined by mea− surements in the particular system unless the system designer has taken into account the damper flow char− acteristics in his system design. It is important that the TAB technician understand the airflow patterns of multiblade dampers. The parallel blade damper has a tendency to throw the air toward one side of the duct. This uneven pattern may adverse− ly affect coil or fan performance, or airflow into

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

6.5


branch ducts if the damper is located just upstream of any system component. 100 PERCENT OF MAXIMUM FLOW

90 80 70

Where dampers should have tight shutoff when closed, the linkage between blades must be properly adjusted. Damper motor linkage also must be properly adjusted. Cold deck and hot deck dampers, as used in multi−zone units, must close tightly, as must face and by−pass dampers used in some air handling units.

A

60

B C

50

D E F

40

G H

30 20 10 0 10

20

30 40 50 60 70 DAMPER POSITION, DEGREES OPEN

80

90

FIGURE 6-5 FLOW CHARACTERISTICS FOR AN OPPOSED OPERATING DAMPER

These flow patterns should be noted when it is neces− sary to measure airflow in a duct near a damper. Where possible, make any measurements upstream rather than downstream of a damper. 6.3.3.3

Parallel−leaf dampers

0.5− 1.0 1.0− 1.5 1.5− 2.5 2.5− 3.5 3.5− 5.5 5.5− 9.0 9.0−15.0 15.0−20.0

6.4

AIR DISTRIBUTION BASICS

6.4.1

Introduction

Air distribution criteria will vary considerably in com− mercial and institutional buildings as well as zone tem− perature and humidity levels. People sitting with little activity require closer tolerances than those actively moving about. Spillover from open refrigerated dis− play equipment in super markets causes frequent com− plaints from customers. An understanding of the prin− ciples of room air distribution helps in the selection, design, control, and operation of HVAC duct systems. The real evaluation of air distribution in a space, how− ever, is if most occupants are comfortable.

Quadrants and Linkages

When dampers are located within ducts and are manu− ally controlled, they are usually secured in place with locking linkage or quadrant such as those shown in Figure 6−6. Varying in strength and locking ability, they should be of suitable size for the damper with which they are used. When adjusting a damper, the regulator or quadrant must be tightened securely to en− sure that the damper remains as set.

Open damper resistance, percent of system resistance

Do not always accept the position of the regulator pointer as indicating the actual position of the damper blade. When in doubt, inspect the end of the damper rod at the face of the regulator. A groove, usually cut by a hacksaw, will indicate that the damper blade runs in the same direction as the cut.

Opposed−leaf dampers

Flow character− istic curve

Open damper resistance, percent of system resistance

Flow character− istic curve

A B C D E F G H

0.3− 0.5 0.5− 0.8 0.8− 1.5 1.5− 2.5 2.5− 5.5 5.5−13.5 13.5−25.5 25.5−37.5

A B C D E F G H

The object of good air distribution in HVAC systems is to create the proper combination of temperature, hu− midity, and air motion, in the occupied zone of the con− ditioned room from the floor to 6 feet (2 m) above floor level. To obtain comfort conditions within this zone, standard limits have been established as acceptable ef− fective draft temperature. This term includes air tem− perature, air motion, relative humidity, and the physio− logical effects on the human body. Any variation from accepted standards of one of these elements causes dis− comfort to occupants. Lack of uniform conditions within the space or excessive fluctuation of conditions in the same part of the space may produce less than ac− ceptable conditions. Although the percentage of room occupants who ob− ject to certain conditions may change over the years, more recent research has shown that a person tolerates higher air flow velocities and lower temperatures at ankle level than at neck level. Because of this, condi− tions in the zone extending from approximately 30 to 60 inches (0.75 to 1.5 m) above the floor are more criti− cal than conditions nearer the floor.

6.4.2 Table 6-1 Typical Ratios of Damper to System Resistance for Flow Characteristic Curve 6.6

Air Velocity And Air Entrainment

For comfortable air distribution, room air velocities within the occupied zone (floor to 6 feet [2 m] above

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


ROD. WASHER, LOCK NUT OR HINGE

MIN.-12 " FLOW

SET SCREW 1 ROD TO 24" DEPTH 2 RODS 25" TO 60" 3 RODS 61" & OVER

SPLITTER DAMPER

BEARING OPTION

ROD CONTINUOUS ON 2" WG CLASS AND ON ALL DAMPERS OVER 12" DIA.

NUT

ARM FIG D ELEVATION TWO BLADE ARRANGEMENT

FIG C ROUND DAMPER

DUCT

CIRCULAR DUCTS

3 8

DUCT

" QUADRANT

DUCT

QUADRANT 1" 2

" PIN

ROD-PIN

12" MAX

3 8

1" 2

22 Ga. BLADE. 1" 8

16 Ga. BLADE 1" 8

CLEARANCE ALL AROUND UP TO 18" FIG A

CLEARANCE ALL AROUND 19" TO 48" FIG B

NOTE: OVER 12" HIGH USE MULTIPLE BLADES. SEE FIG 14-3

D

DUCT DEPTH

STIFFEN AS REQUIRED

D

1" 2

FIG A OR B SIDE ELEVATION

RECTANGULAR DUCTS

FIGURE 6-6 VOLUME DAMPERS HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition

6.7


floor level) should be in a range of 20 fpm to 70 fpm (0.1 to 0.35 m/s) with 50 fpm (0.25 m/s) normally be− ing used. Stagnant air areas should be avoided as tem− perature in these areas may not be acceptable to the oc− cupants. Room air velocities less than 50 fpm (0.25 m/s) are ac− ceptable; however, even higher velocities may be ac− ceptable to some occupants. ASHRAE Standard 55−1981 recommends elevated air speeds at elevated air temperatures. No minimum air speeds are recom− mended for comfort, although air speeds below 20 fpm (0.1 m/s) are usually imperceptible. The velocity of the air (primary air) emerging from the supply outlet induces air movement within the room area (secondary air). This process of entrainment or capturing of secondary air into the primary air is an es− sential part of air distribution to create total air move− ment within the room, thereby eliminating stagnant air areas and reducing temperature differences to accept− able levels before the air enters the occupied zone. Air entrainment will also tend to overcome natural con− vection and radiation effects within the room. 6.4.3

Surface Effect

Air entrainment takes place only along one surface of the outlet discharge jet when the outlet discharges air directly parallel and adjacent to a wall or ceiling. The

surface effect (Coanda effect) is illustrated in Figure 6−7. Since turbulent jet airflow from a grille or diffuser is dynamically unstable, it may veer rapidly back and forth. When the jet airflow veers close to a parallel and adjacent wall or ceiling, the surface interrupts the flow path on that side as shown in Figure 6−7B. The result is that no more secondary air is flowing on that side to replace the air being entrained with the jet airflow. This causes a lowering of the pressure on that side of the outlet device, creating a low pressure bubble that causes the jet airflow to become stable and remain at− tached to the adjacent surface throughout the length of the throw. The surface effect counteracts the drop of horizontally projected cool airstreams. Ceiling diffusers exhibit surface effect to a high degree because a circular air pattern blankets the entire ceil− ing area surrounding each outlet. Slot diffusers, which discharge the airstream across the ceiling, exhibit sur− face effect only if they are long enough to blanket the ceiling area. Grilles exhibit varying degrees of surface effect, depending on the spread of the particular air pattern. In many installations, the outlets must be mounted on an exposed duct and discharge the airstream into free space. In this type of installation, the airstream en− trains air on both its upper and lower surfaces; as a re− sult, a higher rate of entrainment is obtained and the throw is shortened by approximately 33 percent. Air− flow per unit area for these types of outlets can, there−

SEPARATION BUBBLE CEILING

CEILING JET FLOW

WALL

JET FLOW

ENTRAINED AIRFLOW (SECONDARY AIR)

FLOOR (A)

ENTRAINED AIRFLOW (SECONDARY AIR)

FLOOR (B)

FIGURE 6-7 SURFACE (COANDA) EFFECT

6.8

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


fore, be increased. Because there is no surface effect from ceiling diffusers installed on the bottom of ex− posed ducts, the air drops rapidly to the floor. There− fore, temperature differentials in air conditioning sys− tems must be restricted to a range of 15F to 20F (8C to 1C). Airstreams from slot diffusers and grilles show a marked tendency to drop because of the lack of surface effect. 6.4.4

Smudging

Smudging may be a problem with ceiling and slot dif− fusers. Dirt particles held in suspension in the secon− dary (room) air are subjected to turbulence at the outlet face. This turbulence, along with surface effect, is pri− marily responsible for smudging. Smudging can be ex− pected in areas of high pedestrian traffic (lobbies, stores, etc.) When ceiling diffusers are installed on smooth ceilings (such as plaster or metal pan), smudg− ing is usually in the form of a narrow band of discolor− ation around the diffuser. Anti−smudge rings may re− duce this type of smudging. On highly textured ceiling surfaces (such as rough plaster and sprayed−on com− position), smudging often occurs over a more exten− sive area. 6.4.5

Sound Levels

The sound level of an outlet is a function of the air dis− charge velocity and the transmission of HVAC equip− ment noise, which is a function of the size of the outlet. Higher frequency sounds can be the result of excessive outlet velocity, but may also be generated in the duct by the moving airstream. Lower pitched sounds are generally the result of mechanical equipment noise transmitted through the duct system and outlet. The cause of higher frequency sounds can be pin− pointed as outlet or equipment sounds by removing the outlet during operation. A reduction in sound level in− dicates that the outlet is causing noise. If the sound lev− el remains essentially unchanged, the system is at fault. Chapter 46 Sound and Vibration Control in the 1999 ASHRAE HVAC Applications Handbook has more information on design criteria, acoustic treat− ment, and selection procedures. 6.4.6

Effect Of Blades

Blades affect grille performance if their depth is at least equal to the distance between the blades. If the blade ratio is less than one, effective control of the air− stream discharged from the grille by means of the blades is impossible. Increasing the blade ratio above

two has little or no effect, so blade ratios should be be− tween one and two. A grille discharging air uniformly forward (blades in straight position) has a spread of 14 to 24, depend− ing on the type of outlet, duct approach, and discharge velocity. Turning the blades influences the direction and throw of the discharged airstream. A grille with diverging blades (vertical blades with uniformly increasing angular deflection from the cent− erline to a maximum at each end of 45) has a spread of about 60, and reduces the throw considerably. With increasing divergence, the quantity of air dis− charged by a grille for a given upstream total pressure decreases. A grille with converging blades (vertical blades with uniformly decreasing angular deflection from the centerline) has a slightly higher throw than a grille with straight blades, but the spread is approximately the same for both settings. The airstream converges slightly for a short distance in front of the outlet and then spreads more rapidly than air discharged from a grille with straight blades. In addition to vertical blades that normally spread the air horizontally, horizontal blades may spread the air vertically. However, spreading the air vertically risks hitting beams or other obstructions or blowing primary air at excessive velocities into the occupied zone. On the other hand, vertical deflection may increase adher− ence to the ceiling and reduce the drop. In spaces with exposed beams, the outlets should be lo− cated below the bottom of the lowest beam level, pre− ferably low enough to employ an upward or arched air path. The air path should be arched sufficiently to miss the beams and prevent the primary or induced air− stream from striking furniture and obstacles and pro− ducing objectionable drafts. 6.5

ROOM AIR DISTRIBUTION

6.5.1

Natural Airflow

The natural air convection currents flowing down the glass during heating, and up the glass during cooling as shown in Figure 6−8, are a major influence on the air distribution in the perimeter zones of a building. During heating, these currents carry cool air down to the floor level causing a stratification of air in layers of increasing temperatures from the floor to the cei− ling. The severity of the temperature gradient depends

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

6.9


0

75F

95F

75F 80F

HEATING

COOLING

FIGURE 6-8 SOME ELEMENTS AFFECTING BODY HEAT LOSS on outdoor temperature, construction, and air distribu− tion. It is easily understood that warm supply air introduced at the base of the wall would tend to coun− teract these currents and reduce or eliminate stratifica− tion. Optimum air distribution in perimeter zones re− quires perimeter introduction of air or supplementary radiation at the perimeter. During cooling, currents carry warm air up the wall to ceiling level. Stratification then forms from the ceiling down. To eliminate stratification, cool air should be projected into this region near the ceiling. To do this most effectively, supply air outlets should be located high in the wall or in the ceiling. 6.5.2

Supply Air Outlet Performance

6.5.2.1

Outlet Throw

Extensive studies of supply outlet performance have shown that air discharge throw from free round open− ings, grilles, perforated panels and ceiling diffusers are related to the average velocity at the face of the supply outlet or opening. An air jet discharged from a free opening has four zones of expansion and the centerline velocity of the jet in any zone is related to the initial velocity as shown in Figure 6−9. Regardless of the type of outlet, the air stream will tend to assume a circular shape in free space. The important point is that the performance of any supply outlet is related to the initial velocity and initial area as shown in Figure 6−9.

the initial volume of the jet at any distance from the point of origin depends mainly on the ratio of the initial velocity (Vo) to the terminal velocity (Vx). For exam− ple, doubling the initial velocity for the same terminal velocity doubles the induction ratio and also the throw. In zone 4 where the terminal velocity is relatively low and specifically for terminal velocities of 50 fpm (0.25 m/s), the throw should be reduced 20 percent. The buoyant forces with non−isothermal jets cause the air jet to rise during heating and drop during cooling. These conditions result in shorter throws when the throw is reduced to a terminal velocity less than 150 fpm (0.75 m/s) The discussion of throw and drop has been limited to free space applications. If the air discharge jet is pro− jected parallel to and within a few inches of a surface, the jet performance will be affected by the surface, which limits the induction on the surface side of the jet. This creates a low pressure region between the jet and the surface which draws the jet toward the surface. In fact, this effect will prevail if the angle of discharge be− tween the jet and the surface is less than 40. Surface effect will draw the jet from a sidewall outlet to the ceiling if the outlet is within one foot (0.3 m) of the ceiling. The jet from a floor outlet will be drawn to the wall and the jet from a ceiling outlet will be drawn to the ceiling. Surface effect increases the throw for all types of outlets and decreases the drop for horizontally projected air streams. 6.5.2.2

Beyond the second zone, the jet is a mixture of supply and room air. The air jet expands because of induction of room air. The ratio of the total volume of the jet, to 6.10

VAV Applications

Air distribution is very important in VAV applications. Consideration must be given to distribution and to

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


1

3

2

4

X

PRIMARY

HIGH VELOCITY USUALLY ON OR NEAR ROOM SURFACES

PRIMARY AND INDUCED ROOM AIR

AIR

HIGH TEMP-HEATING LOW TEMP-COOLING

ROOM AIR GENTLE MOVEMENT

GREATEST POSSIBLE SOURCE OF DRAFTS FREE JET—ROOM AIR INDUCED ON ALL SIDES JET NEAR A SURFACE—HIGH VELOCITY AIR HUGS SURFACE AND INDUCES AIR ON ONLY ROOM SIDE OF JET

ZONE

SUPPLY VELOCITY,VO JET CENTERLINE VELOCITY,VX

1

V

2

V

3

V

4

V

X

X

=

V

X

»

V

O

X

»

V

O

O

/

X

/

X

APPROACHES ROOM VELOCITY

FIGURE 6-9 FOUR ZONES IN JET EXPANSION sound levels at maximum and minimum airflow. If the combined sound level of the terminal unit and diffuser at maximum flow is at least 3 dB below the room ambi− ent sound level, variations will not be noticed. In gen− eral, several important considerations are listed for variable volume system air distribution using outlets for horizontal discharge patterns as follows: a.

b.

An outlet with a low throw coefficient should be used. A small throw coefficient gives a smaller absolute change in the throw values with variation in volume and thus tends to minimize the change in air motion within the occupied space due to change in airstream pattern. Outlets should be chosen for small quantities of air. In this manner, absolute values of throw will vary a minimum with the variation in flow rate for the outlet. If the system ap− plication requires modular outlet arrange− ments for occupancy flexibility, as with dif− fusers in combination with light troffers or with ceiling suspensions, no increase in the

number of outlets is necessary to satisfy this requirement. For under window air distribution, vertical throw out− lets with nonspreading pattern should be used. To pre− vent cool air dropping back into the occupied space at minimum flow conditions, the outlet discharge veloc− ity should be 500 fpm (2.5 m/s) minimum. The throw coefficient should be higher to project air up to the cei− ling. With these exceptions, the preceding items also apply to under window distribution. 6.5.3

Supply Outlets

Outlets are selected for each specific room, based on air quantity required, distance available for throw or radius of diffusion, structural characteristics and ar− chitectural concepts being considered. Table 6−2 is based on experience and typical ratings of various out− lets. It may be used as a guide to the outlets applicable for use with various room air loadings. Special condi− tions, such as ceiling heights greater than the normal 8 to 12 feet (2.4 to 3.5 m) and exposed duct mounting,

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

6.11


FIGURE 6-10 TYPICAL SUPPLY OUTLETS

as well as product modifications and unusual condi− tions of room occupancy, can modify this table.

6.5.3.1

The adjustable blade grille is the most common type of grille used as a supply outlet. The single deflection blades install behind and at right angles to the face bla− des. This grille controls the airstream in both the hori− zontal and vertical planes.

Grille Slot Perforated Panel Ceiling Diffuser Perforated Ceiling

Air Loading, cfm/ft2 (L/s per m2) of Floor Space

Approx. Max. Air Changes @Hour for 10’ (3 m) Ceiling

0.6 to 1.2 (3 to 6) 0.8 to 2.0 (4 to 10) 0.9 to 3.0 (5 to 15) 0.9 to 5.0 (5 to 25) 1.0 to 10.0 (5 to 50)

7 12 18 30 60

Table 6-2 Guide to Use of Various Outlets 6.12

Fixed Blade Grilles

The fixed blade grille is similar to the single deflection grille, except that the blades are not adjustable; the blades may be straight or set at an angle. The angle at which the air is discharged from this grille depends on the type of deflection blades.

Adjustable Blade Grilles

Type of Outlet

6.5.3.2

6.5.3.3

Stamped Grilles

The stamped grille is stamped from a single sheet of metal to form a pattern of small openings through which air can pass. Various designs are used, varying from square or rectangular holes to intricate ornamen− tal designs. 6.5.3.4

Variable Area Grilles

The variable area grille is similar to the adjustable double deflection grille but can vary the discharge area to achieve an air volume change (variable air volume outlet) at constant pressure, so that the variation in throw is minimized for a given change in supply air volume.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


6.5.3.5

Slot Diffusers

6.5.3.9

Perforated Face Ceiling Diffusers

A slot diffuser is an elongated outlet consisting of a single or multiple number of slots. It is usually installed in long continuous lengths. Outlets with di− mensional aspect ratios of 25 to 1 or greater and a max− imum height of approximately 3 inches (75 mm) gen− erally meet the performance criteria for slot diffusers.

Perforated metal diffusers meet architectural demands for air outlets that blend into perforated ceilings. Each has a perforated metal face with an open area of 10 to 50 percent which determines its capacity. Units are usually equipped with a deflection device to attain multi−pattern horizontal air discharge.

6.5.3.6

6.5.3.10 Variable Area Ceiling Diffusers

Air-Light Diffusers

Air−light slot diffusers have a single slot discharge in nominal 2, 3, and 4 foot (0.6, 0.9, and 1.2 m) lengths and are available for use in conjunction with recessed fluorescent light troffers. A diffuser mates with a light fixture and is entirely concealed from the room. It dis− charges air through suitable openings in the fixture and is available with fixed or adjustable air discharge pat− terns, air distribution plenum, inlet dampers for bal− ancing, and inlet collars suitable for flexible duct con− nections. Light fixtures adapted for slot diffusers are available in styles to fit common ceiling constructions. Various slot diffuser and light fixture manufacturers may furnish products compatible with one another’s equipment. 6.5.3.7

Multi-Passage Ceiling Diffusers

Multi−passage ceiling diffusers consist of a series of flaring rings or louvers, which form a series of concen− tric air passages. They may be round, square, or rectan− gular. For easy installation, these diffusers are usually made in two parts; an outer shell with duct collar and an easily removable inner assembly. 6.5.3.8

Flush And Stepped-Down Diffusers

Flush and stepped−down diffusers also are available. In the flush unit, all rings or louvers project a plane sur− face, whereas in the stepped−down unit, they project beyond the surface of the outer shell. Common variations of this diffuser type are the adjust− able pattern diffuser and the multi−pattern diffuser. In the adjustable pattern diffuser, the air discharge pat− tern may be changed from a horizontal to a vertical or downblow pattern. Special construction of the diffuser or separate deflection devices allow adjustment. Mul− tipattern diffusers are square or rectangular and have special louvers to discharge the air in one or more di− rections. Other outlets available as standard equipment are half round diffusers, supply and return diffusers, and light fixture air diffuser combinations.

Variable area ceiling diffusers may be round, square, or linear and have parallel or concentric passages or a perforated face. In addition, they feature a means of ef− fectively varying the discharge area to achieve an air volume change (VAV outlet) at constant pressure, so that the variation in throw is minimized for a given change in supply air volume. 6.5.4

Under Floor Distribution

Raised floor plenums for air distribution are primarily used in computer rooms or research facilities having high concentrations of heat generating electronic equipment requiring very clean and cool supply air. Distributing conditioned air under a raised floor al− lows supply diffusers to be located directly under elec− tronic equipment cabinets having high sensible heat generation. To meet these high equipment cooling needs with ceiling supply diffusers would require dis− charge air flows that would be very uncomfortable for most room occupants, and may still not provide ade− quate cooling air flow into these equipment cabinets. In most applications, these spaces are served by a dedi− cated packaged air conditioning unit also located in the space, which discharges supply air directly down and into the under floor cable access plenum. Since the primary purpose of this system is to provide adequate cooling of very expensive electronic equip− ment, it is important for the TAB technician to obtain direction from those responsible for this equipment before balancing these floor registers. In some cases, equipment nameplate data may indicate a design air flow temperature and flow rate, if this information is not provided by the design drawings. It should also be understood that most raised floors are constructed of manufactured removable metal panel sections to allow easy access to the high concentration of wiring and easy addition or removal of equipment. For this reason, the air distribution must remain flex− ible and easy to modify.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

6.13


6.5.5

Return Air Inlet Performance

6.5.5.1

Location

Return air and exhaust air inlets should be located to suit architectural design requirements including ap− pearance and compatibility with supply outlets and ductwork. Generally, inlets are installed to return room air of the greatest temperature differential that collects in the stagnant areas. The location of return and ex− haust inlets does not significantly affect air motion. The location of return and exhaust inlets will not com− pensate for ineffective supply air distribution. A return air inlet should not be located directly in the primary airstream from supply outlets. To do so will short circuit the supply air back into the return air sys− tem without allowing it to mix with the room air. The TAB technician should remember that the supply air maintains the conditions within a space by mixing and dilution. Any removal of excess warm or cold air which is allowed to stratify before mixing within the space will permit lower temperature differentials or lower airflow rates. Removal of excess warm or cold air is accomplished with hoods in certain industrial processes. It can also be done by selecting the supply outlet performance to promote the formation of the stagnant zone directly from the local heat gain or loss. The return intake or exhaust would then be located in the stagnant zone. 6.5.5.2

Noise

In addition to the location of the return intake as dis− cussed above, the intake should be sized to return the proper amount of air to the HVAC unit with minimum static pressure requirements and noise levels. In gener− al, most commercial return grilles have a free area of between 45 and 55 percent, because they are designed so that one cannot see through them. With this type of grille, the velocity should not exceed approximately 500 fpm (2.5 m/s) to have reasonable pressure drop re− quirements and a reasonable sound level (see Table 6−3). In general, return air inlets should be sized on available pressure requirements and sound data, rather than relying on indicated free area values. The problem of return inlet noise is the same as that for supply outlets. In computing resultant room noise lev− els from operation of an air conditioning system, the return inlet must be included as a part of the total grille area. The major difference between supply outlets and return inlets is the frequent installation of the later at ear level. When they are so located, the return inlet ve− 6.14

locity should not exceed 75 percent of maximum per− missible outlet velocity.

Inlet Location Above occupied zone Within occupied zone Not near seats Within occupied zone Near seats Door or wall louvers Undercut doors

Velocity Over Gross Inlet Area−fpm (m/s) 800 Up (4.0 Up) 600−800 (3.0−4.0)

400−600 (2.0−3.0) 200−300 (1.0−1.5) 200−300 (1.0−1.5)

Table 6-3 Recommended Return Air Inlet Face Velocities 6.5.6

Return Air Inlets

6.5.6.1

Adjustable Blade Grilles

The same adjustable blade grilles used for air supply are used to match the deflection setting of the blades with that of the supply outlets. 6.5.6.2

Fixed Blade Grilles

The same fixed blade grilles described in the supply air section are used. This grille is the most common return air inlet. Blades are straight or set at a certain angle, the latter being preferred when appearance is important. 6.5.6.3

V-Blade Grille

The V−blade grille is made with blades in the shape of inverted v’s stacked within the grille frame, this grille has the advantage of being sight proof; it can be viewed from any angle without detracting from appea− rance. Door grilles are usually v−blade grilles. The air− flow capacity of the grille decreases as visibility through the grille decreases. 6.5.6.4

Light Proof Grille

The light proof grille is used to transfer air to or from darkrooms. The blades of this type of grille form a lab− yrinth and are painted black. The blades may take the form of several sets of v−blades or be of some special interlocking louver design to provide the required lab− yrinth. 6.5.6.5

Stamped Grilles

Stamped grilles frequently are used as return air and exhaust air inlets, particularly in more demanding areas like rest rooms and utility areas. 6.5.6.6

Ceiling And Slot Diffusers

Supply air ceiling diffusers also may be used as return air and exhaust air inlets.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


Neck VelocityCfpm (m/s)

400 (2.0)

500 (2.5)

600 (3.0)

700 (3.5)

800 (4.0)

1000 (5.0)

Round Diffuser Half Round Diffuser Half Round Diffuser, Flush Square Diffuser Square Diffuser, Adjustable Rectangular Diffuser Curved Blade Diffuser Perforated Diffuser High Capacity Diffuser Slimline Diffuser, 2 Way* Extruded Fineline Diffuser 0.25 in.(6.4 mm) Bar Spacing* Linear Slot Diffuser*

0.024 (6.0) 0.035 (8.7) 0.046 (11.5) 0.021 (5.2) 0.036 (9.0) 0.043 (10.7) 0.056 (13.9) 0.037 (9.2) — 0.010 (2.5)

0.039 (9.7) 0.054 (13.4) 0.074 (18.4) 0.033 (8.2) 0.057 (14.2) 0.066 (16.4) 0.090 (22.4) 0.058 (14.4) C 0.015 (3.7)

0.056 (13.9) 0.080 (19.9) 0.106 (26.4) 0.048 (12.0) 0.080 (19.9) 0.096 (23.9) 0.131 (32.6) 0.083 (20.7) C 0.022 (5.5)

0.075 (18.7) 0.107 (26.6) 0.143 (35.6) 0.064 (15.9) 0.112 (27.9) 0.131 (32.6) 0.175 (43.6) C 0.050 (12.5) 0.028 (7.0)

0.096 (23.9) 0.141 (35.1) 0.184 (45.8) 0.083 (20.7) 0.144 (35.9) 0.170 (42.3) 0.225 (56.0) 0.148 (36.9) 0.060 (14.9) 0.040 (10.0)

0.152 (37.8) 0.219 (54.5) 0.290 (72.2) 0.130 (32.4) 0.226 (56.3) C 0.355 (88.4) 0.230 (57.3) 0.100 (24.9) 0.063 (15.7)

0.011 (2.7) 0.051 (12.7)

0.015 (3.7) 0.079 (19.7)

0.024 (6.0) 0.110 (27.4)

0.030 (7.5) 0.150 (37.4)

0.044 (11.0) 0.200 (49.8)

0.069 (17.2) C

Extractor

0.004 (1.0)

0.006 (1.5)

0.010 (2.5)

0.013 (3.2)

0.017 (4.2)

0.023 (5.7)

*Velocity Through Face Open Area

Table 6-4 Air Outlets and Diffusers Total Pressure Loss Average—in. wg (Pa)

VelocityCfpm (m/s)

300 (1.5)

400 (2.0)

500 (2.5)

600 (3.0)

800 (4.0)

1000 (5.0)

0 Deflection

0.010 (2.5)

0.017 (4.2)

0.028 (7.0)

0.038 (9.5)

0.069 (17.2)

0.107 (26.6)

22½ Deflection

0.011 (2.7)

0.019 (4.7)

0.031 (7.7)

0.043 (10.7)

0.078 (19.4)

0.120 (29.9)

45 Deflection

0.016 (4.0)

0.029 (7.2)

0.047 (11.7)

0.064 (15.9)

0.117 (29.1)

0.181 (45.1)

Table 6-5 Supply Registers Total Pressure Loss Average—in. wg (Pa)

Velocity—fpm (m/s)

300 (1.5)

400 (2.0)

500 (3.0)

600 (3.0)

800 (4.0)

900 (4.5)

0.033 (8.2)

0.060 (14.9)

0.092 (22.9)

0.068 (16.9)

0.122 (30.4)

0.187 (46.6)

0.134 (33.4)

0.238 (59.3)

0.302 (75.2)

0.272 (67.7)

0.483 (120.7)

0.055 (13.7)

0.098 (24.4)

0.614 (152.9)

0.152 (37.8)

0.222 (55.3)

0.390 (97.1)

0.496 (123.5)

0.025 (6.2)

0.060 (14.9)

0.080 (19.9)

0.100 (24.9)

0.180 (44.8)

0.230 (52.3)

0.012 (3.0)

0.020 (5.0)

0.032 (8.0)

0.046 (11.5)

0.080 (19.9)

0.102 (25.4)

0.033 (8.2)

0.055 (13.7)

0.088 (21.9)

0.126 (31.4)

0.220 (54.8)

0.275 (68.5)

Register, 0Deflection

0.054 (13.4)

0.090 (22.4)

0.144 (35.9)

0.207 (51.5)

0.360 (89.6)

C

Register, 30 Deflection

0.042 (10.5)

0.070 (17.4)

0.112 (27.9)

0.161 (40.1)

0.280 (69.7)

0.350 (87.2)

Rectangular Diffuser 12  24 in. (300  300 mm) 24  24 in. (600  600 mm) 12  21 in. (300  525 mm) Perforated Return Diffuser (Neck Velocity)

Register, 45 Deflection Register, Perforated Face

Table 6-6 Return Registers Total Pressure Loss Average—in. wg (Pa) HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

6.15


THIS PAGE INTENTIONALLY LEFT BLANK

6.16

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition


CHAPTER 7

AIR SYSTEMS


CHAPTER 7

AIR SYSTEMS

7.1

INTRODUCTION

7.1.2

7.1.1

Categories

In general, air systems offer the following advantages:

This chapter covers design and application of air sys− tems used in single and multiple zoning applications. An air system is defined as a system that provides total sensible and latent cooling in the cold air supplied by the system. No additional cooling is required at the ter− minal units. Heating may be accomplished by the same airstream, either from the central system or at the terminal devices. In some applications, heating is ac− complished by a separate air, water, steam, or electric heating system. The term zone implies the provision or the need for separate thermostatic control, while the term room implies a partitioned area which may or may not require separate control. Air systems may be classified into two basic catego− ries: single−path systems and dual−path systems. 7.1.1.1

Single-Path Systems

Single−path systems are those which contain the main heating and cooling coils in a series flow air path, using common duct distribution system at a common air temperature to feed all terminal apparatus.

7.1.2.1

Air System Advantages

Consolidation

Air systems permit centralized location of major equipment, they consolidate operation and mainte− nance in unoccupied areas, and permit maximum choice of filtration systems, odor and noise control, and high quality, durable equipment. There is com− plete absence of drain piping, electrical equipment power wiring, and filters in the conditioned space. 7.1.2.2

Outdoor Air Cooling

The greatest advantage of air systems is the number of free cooling season hours that may be had when out− door air can be used for cooling in lieu of mechanical refrigeration. Economizer control systems usually are more trouble−free than enthalpy control systems. 7.1.2.3

Flexibility

Air systems allow a wide choice of zonability, flexibil− ity, and humidity control under all operating condi− tions, with simultaneous availability of heating and cooling during off season periods. 7.1.2.4

Heat Recovery

Single−path systems may be: a.

single duct, single zone, constant volume,

b.

single duct, variable air volume (VAV),

c.

single duct, VAV induction, and

d.

single duct zoned reheat.

7.1.1.2

Dual-Path Systems

Dual−path systems are those which contain the main heating and cooling coils in a parallel flow, or series− parallel flow air path, using either: (1) a separate cold and warm air duct distribution system, which is blended at terminal (dual duct systems); or (2) a sepa− rate supply duct to each zone, with blending of warm and cold air at the main supply fan. Dual−path systems may be: a.

dual duct (including dual duct, VAV), and

b.

multi−zone.

Air systems are readily adapted to heat recovery de− vices. 7.1.2.5

Design Freedom

Air systems allow full design freedom for optimum air distribution in air motion, draft control, and extenuat− ing local requirements. 7.1.2.6

Makeup Air

Air systems are best suited to applications requiring abnormal exhaust makeup. 7.1.2.7

Adaptable

Air systems are easily adaptable to automatic seasonal changeover and winter humidification. 7.1.3

Air System Disadvantages

Air systems have the following disadvantages: 7.1.3.1

Duct Space Requirements

Additional duct clearance requirements can penalize floor space for duct risers and fan rooms, and building

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

7.1


height for ceiling clearances. (Particularly true of low velocity systems). 7.1.3.2

Longer Fan Hours

In those systems which use air (not radiation) for pe− rimeter heating, longer fan−operating hours are re− quired to take care of unoccupied period heating (in low temperature locales). 7.1.3.3

System Balancing

In those systems which have no built−in zone self−bal− ancing devices, air balancing is difficult and may have to be done several times when a common air system serves areas which are not rented simultaneously. 7.1.3.4

Temporary Heat

Air heating perimeter systems may not be available for use during building construction as rapidly as perime− ter hydronic systems. 7.1.3.5

Terminal Devices

Accessibility to terminal devices demands close coop− eration between architectural, mechanical, and struc− tural designers.

ment stores, small individual shops in a shopping cen− ter, individual classrooms of schools, computer rooms, etc. A rooftop unit, for example, complete with refrig− eration system serving an individual space, would be considered a single zone system. The refrigeration sys− tem, however, could be remote and serve several single zone units in a larger installation. A schematic of a more sophisticated single zone cen− tral system is shown in Figure 7−2. The return air fan may be used if 100 percent outdoor air is used for cool− ing purposes, and may be eliminated if air is relieved from the space with very little pressure loss through the relief system. However, objectionable pressuriza− tion of conditioned spaces should be avoided to allow entrance doors to open or close normally. Control of the single zone system can be affected by varying the quantity of cooling medium, providing re− heat, face and bypass dampers or a combination of these. Single duct systems with reheat satisfy varia− tions in load by providing independent sources of heat− ing and cooling. When a humidifier is used, humidity control may be completely responsive to space needs. Single duct systems without reheat offer cooling flexi− bility, but cannot control summer humidity indepen− dent of temperature requirements. 7.2.2

7.1.3.6

Reheat Prohibition

Energy inefficiency of reheat type systems may pro− hibit use. 7.2

TYPES OF AIR SYSTEMS

7.2.1

Single Zone Systems

The simplest form of the air system is a single condi− tioner serving a single temperature control zone (see Figure 7−1). The unit may be installed within or remote from the space it serves and may operate with, or with− out distributing ductwork. Ideally, this can provide a system which is completely responsive to the needs of the space. Well designed systems can maintain tem− perature and humidity closely and efficiently. They can be shut down when desired, without affecting the operation of adjacent areas. A single zone system responds to only one set of space conditions. Its use is limited to situations where varia− tions occur almost uniformly throughout the zone or where the load is stable; but when multiple units are installed, they can handle a variety of conditions effi− ciently. Single zone systems are used in small depart− 7.2

Variable Air Volume (VAV) Systems

Control of dry bulb temperatures within a space re− quires that a balance be established between the space load and the air supplied to offset the load. The design− er may choose between varying the supply air temper− ature (constant volume) or varying the airflow volume (variable air volume) as the space load changes. To control part load volume reduction, supply air temper− atures and air volumes may be controlled simulta− neously. VAV systems (Figure 7−3), may be applied to interior or perimeter zones, with common or separate fan sys− tems, common or separate air temperature control, and with or without auxiliary heating devices. The VAV concept may apply to volume variation in the main system total airstream and to the zones of control. Variation of flow under control of a space thermostat may be accomplished by positioning a simple damper or a volume regulating device in a duct, in a VAV ter− minal box, or at a diffuser or grille. Depending on the complexity of the air distribution system, first cost considerations, the lowest throttling ratio expected at part load, and the complexibility of the initial and part load balancing problems, VAV may or may not be

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


POSSIBLE PREHEAT COIL

OUTDOOR AIR INTAKE

FILTERS

OUTDOOR DAMPER

COOLING COIL

HEATING COIL

SUPPLY AIR FAN RETURN AIR DAMPER

RELIEF AIR LOUVER

USE OF BAROMETRIC RELIEF AIR LOUVERS NOT RECOMMENDED

SUPPLY AIR SYSTEM

RELIEF AIR DAMPER RETURN AIR SYSTEM

FIGURE 7-1 SINGLE DUCT SYSTEM

EXHAUST AIR OR RELIEF AIR LOUVER & DAMPER RETURN AIR FAN

RETURN AIR DUCT REHEAT COIL IF BYPASS IS USED

RETURN AIR DAMPER BYPASS DAMPER SPRAYS

MIN. O.A. DAMPER MAX. O.A. DAMPER

SUPPLY AIR DUCT

FACE AND BYPASS DAMPER

SUPPLY AIR FAN OUTDOOR AIR LOUVER

MIXED AIR PLENUM

FILTERS PREHEAT COIL

COOLING COIL

REHEAT COIL IF BYPASS IS NOT USED

SPRAY PUMP

FIGURE 7-2 TYPICAL EQUIPMENT FOR SINGLE ZONE DUCT SYSTEM

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition

7.3


OUTDOOR AIR INTAKE

POSSIBLE PREHEAT COIL

FILTERS

HEATING COIL

COOLING COIL

PRIMARY AIR DUCT S.P. CONTROLLER

SUPPLY FAN WITH RETURN S.P. CONTROL AIR DAMPER

OUTDOOR DAMPER

VAV TERMINAL UNITS

EXHAUST AIR LOUVER

EXHAUST AIR DAMPER

OPTIONALRETURN AIR FAN RETURN AIR SYSTEM

T

T

FIGURE 7-3 VARIABLE AIR VOLUME (VAV) SYSTEM

combined with fan volume or system static pressure controls. It is possible to permit system airflow volume varia− tions without fan volume variation by using a simple fan bypass. It is possible to vary zone air volume only, while keeping fan and system volume substantially constant, by dumping excess air into a return air ceil− ing plenum or directly into the return air duct system. These methods of system control do not provide the fan horsepower savings usually associated with VAV systems. 7.2.3

Terminal Reheat Systems

The terminal reheat system (Figure 7−4) is a modifica− tion of the single zone system. It permits zone or space control for areas of unequal loading, provides heating or cooling of perimeter areas with different exposures, and promotes process or comfort applications where close control of space conditions is desired. As the word reheat implies, the application of heat is a secondary process being applied to either precondi− tioned primary air or recirculated room air. Under present energy codes, the use of Na reheat system is dis− couraged or prohibited unless recovered heat is used. A single low pressure reheat system is produced when a heating coil is inserted into the duct system down− stream of the cooling coil(s). The more sophisticated 7.4

systems use higher pressure duct designs and pressure reduction devices to permit system balancing at the re− heat zone. The medium for heating may be hot water, steam, or electricity. A big advantage of the reheat sys− tem is that it has the capability of maintaining very close control of space humidity. The system is generally applied to hospitals, laborato− ries, or spaces where wide load variations are expec− ted. Terminal units are designed to permit heating of primary air, or secondary air inducted from the condi− tioned space, located either under the window or in the duct system overhead. Conditioned air is supplied from a central unit at a fixed cold air temperature de− signed to offset the maximum cooling load in the space(s). The control thermostat simply calls for heat as the cooling load in the space drops below maxi− mum. 7.2.4

Induction Reheat Systems

The induction reheat system is shown schematically in Figure 7−5. Full cooling capacity is provided in the pri− mary higher pressure airstream and supplied by the central equipment to the terminal. Zone control is ac− complished by heating the secondary or induced air− stream. This type of terminal is used when it is desir− able to introduce supply air to the space at a higher temperature, or permit higher space air movement without increasing the quantity of primary air over the amount of air required for cooling.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


POSSIBLE OUTDOOR PREHEAT AIR INTAKE COIL

COOLING COIL

RETURN AIR DAMPER

EXHAUST AIR EXHAUST AIR DAMPER LOUVER

POSSIBLE RETURN AIR FAN

SUPPLY AIR SYSTEM

SUPPLY AIR FAN REHEAT COIL NO. 1

RETURN AIR SYSTEM

REHEAT COIL NO. 2

T

T SUPPLY DUCT TO ZONE 1

SUPPLY DUCT TO ZONE 2

FIGURE 7-4 TERMINAL REHEAT SYSTEM The primary airN is discharged from nozzles arranged to induce room air into the induction unit approximate− ly four times the volume of the primary air. The in− duced air is cooled or heated by a secondary water coil. The water coil may be supplied by a 2−pipe system where either chilled water or heated water is available, but not simultaneously; by a 3−pipe system where sep− arate supplies of hot or chilled water are continuously available and, after passing through the unit, are mixed into a common return; or by a 4−pipe system, where a supply and return of hot water and chilled water are both continuously available. Induction units generally are located under the win− dow to offset winter downdrafts. Overhead installa− tions are limited, since ductwork connections carrying induced air have limited static pressure available, thereby decreasing induction air volume and unit ca− pacity. When installed under the window, this unit has the advantage of providing gravity heating during off− hour operation, permitting shutdown of the air system. The primary supply air fan operates at high pressures requiring high horsepower input. When balancing, at− tempt to reduce the primary air volume and pressure to the minimum required to operate the induction ter− minal units under full load conditions. Induction unit nozzles may be worn through many years of cleaning and operation, resulting in increased primary air quantity at lower air velocities with lower induced air volumes. Check each induction unit and either repair the nozzles or replace them before at− tempting any balancing work on the system.

7.2.5

Variable Air Volume (VAV) Reheat Systems

The VAV concept, when applied to reheat systems, permits flow reduction as a first step in control, there− by suspending the application of heat until flow condi− tions reach a predetermined minimum. By proper application of VAV, the reheat system may be designed to permit initial and operating cost sav− ings. With air volume selected for maximum instanta− neous peak loads rather than the sum of all peaks, the total system air volume is reduced. Also, any addition− al system diversity, such as areas with intermittent loads (conference rooms, office equipment rooms, etc.) may be included in the total volume reduction. When air volume reduction is used as a first step in control, reheat is not applied until the minimum vol− ume is reached. This procedure reduces system operat− ing costs appreciably for summer and intermediate weather. 7.2.6

Dual Duct Systems

7.2.6.1

Low Velocity Systems

The low velocity dual duct system distributes condi− tioned air through two parallel ducts. One duct carries cold air and the other warm air, allowing heating or cooling at all times. In each conditioned space or zone, automatic control dampers, responsive to a room ther− mostat, mix the warm and cold air in proper propor− tions to satisfy the prevailing heat load of the space. The return air fan shown in Figure 7−6 may be elimi− nated on small installations if provisions are made to

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

7.5


OUTDOOR AIR INTAKE

POSSIBLE PREHEAT COIL

FILTERS

HEATING COIL

COOLING COIL

HIGH VELOCITY PRIMARY AIR SYSTEM

T

RETURN SUPPLY FAN AIR DAMPER

OUTDOOR AIR DAMPER

T

INDUCED AIR POSSIBLE EXHAUST AIR EXHAUST AIR DAMPER RETURN LOUVER AIR FAN

SECONDARY WATER

INDUCTION

FIGURE 7-5 INDUCTION REHEAT SYSTEM relieve excess outdoor air from the conditioned spaces. They generally are required for economizer cooling cycles and in systems with substantial return air ductwork. 7.2.6.2

High Velocity Systems

High velocity dual duct systems operate in the same manner as the low velocity systems except that the supply fan runs at a much higher pressure and each zone requires a mixing box with sound attenuation. A large amount of energy is required to operate the fan at high pressure. When balancing, a close analysis of the pressure drops within the duct system should be made and the fan pressure reduced to the minimum re− quired to operate the mixing boxes. 7.2.6.3

Energy Savings Ideas

In conditions when there is no cooling load, install controls to close off the cold air duct; de−energize chillers and cold water pumps and operate as a single duct system, rescheduling the warmer air duct temper− ature according to heating loads only. Under conditions where there is no heating load, install controls to close off the warm air ducts; shut off hot water, steam, or electricity to the warm duct and operate the system with the cold duct air only; resched− uling supply air temperature according to cooling loads. 7.6

Replace obsolete or defective mixing boxes to elimi− nate leakage of hot or cold air when the respective damper is closed. Provide volume control for the supply air fan and re− duce capacity preferably by speed reduction when both the hot deck and cold deck air quantities can be reduced to meet peak loads. Reducing the heat loss and heat gain provides an opportunity to reduce the amount of air circulated. When there is more than one air handling unit in a dual air system, modify duct work, if possible, so that each unit supplies a separate zone to provide an opportunity to reduce hot and cold duct temperatures according to shifting loads. Change dual duct systems to VAV systems when ener− gy analysis is favorable and the payback in energy saved is sufficiently attractive by adding VAV boxes and fan control. 7.2.7

Multi-Zone Systems

The multi−zone system (Figure 7−7) is applicable for serving a relatively small number of zones from a single, central air handling unit. The requirements of the different zones are met by mixing cold and warm air through zone dampers at the central air handler in response to zone thermostats. The mixed conditioned air is distributed throughout the building by a system of single zone ducts. Either packaged HVAC units complete with all components or field fabricated HVAC components may be used. Return air is usually handled in a conventional manner.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


EXHAUST AIR LOUVER

EXHAUST AIR DAMPER

RETURN AIR FAN (OPTIONAL)

SUPPLY AIR

RETURN AIR DAMPER

HEATING COIL

FAN

Ô Ô Ô

OUTDOOR AIR INTAKE

FILTERS

OUTDOOR AIR DAMPER

COOLING COIL RETURN AIR SYSTEM

POSSIBLE PREHEAT COIL

T

ZONE 2

T

ZONE 1

MIXING BOXES SUPPLY DUCT

SUPPLY DUCT

SYSTEM (COLD)

SYSTEM (HOT)

FIGURE 7-6 DUAL DUCT HIGH VELOCITY SYSTEM Multi−zone systems are somewhat similar to dual duct systems. They can provide a smaller building with some of the advantages of dual duct systems at a lower first cost with a wide variety of packaged HVAC units, but are limited to handling smaller projects by multi− ple runs of single zone ducts. Most packaged HVAC units lack the control sophistication for comfort and operating economy that can be built into dual duct sys− tems.

Multi−zone systems may handle more than one room with a single duct. Multizone packaged HVAC equip− ment is usually limited to about 12 zones, while built− up systems may have as many as can be physically in− corporated into the layout.

7.2.7.1

VAV Terminal Devices

VAV may be applied to multi−zone systems with pack− aged or built−up systems having the necessary zone volume regulation and fan controls. However, it is sel− dom applied in this manner for entire distribution sys− tems except for TV studios and other critical noise lev− el applications. More often, a few select rooms in a zone may incorporate VAV terminal devices, when off−peak requirements permit this approach and air balancing considerations indicate there will be no problems from omission of fan control or static pres− sure regulation. 7.2.7.2

Zone Coils

Some multi−zone units have individual heating and cooling coils for each zone supply duct. These units

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

7.7


use less energy then units with common coils as the supply air is heated or cooled only to the degree re− quired to meet the zone load. 7.2.7.3

Install controls or adjust existing controls to give the minimum hot deck temperature and maximum cold deck temperature consistent with the loads of critical zones.

TAB Arrange the controls so that when all of the hot duct dampers are partially closed, the hot deck tempera− tures will progressively reduce until one or more zone dampers are partially closed; the cold duct tempera− ture will progressively increase until one or more of the zone dampers are fully opened.

Before starting testing and balancing work, analyze multi−zone systems carefully and treat each zone as a single zone system. Adjust air volumes and tempera− ture accordingly. 7.2.7.4

Energy Savings Ideas Install controls to shut off the fan and all heating con− trol valves during unoccupied periods in the cooling season, and shut off the cooling valve during unoccu− pied periods in the heating season.

Hot and cold deck dampers are often of poor quality and allow considerable air leakage even where fully closed. Modify these dampers to avoid leakage.

EXHAUST AIR LOUVER

EXHAUST AIR DAMPER

POSSIBLE RETURN AIR FAN RETURN AIR SYSTEM ZONE 4

SUPPLY AIR FAN

OUTDOOR AIR INTAKE OUTDOOR AIR DAMPER

FILTERS COOLING COIL

HEATING COIL ZONE MIXING DAMPERS

RETURN AIR DAMPER

ZONE 3 ZONE 2 ZONE 1 SUPPLY AIR SYSTEMS

POSSIBLE PRE-HEAT COIL

FIGURE 7-7 MULTI-ZONE SYSTEM

7.8

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


7.3

AIR SYSTEM DESIGN

7.3.1

Introduction

Knowing the basics of good air system duct design will allow the TAB technician to determine if HVAC sys− tems can be balanced properly, in addition to helping solve routine problems while balancing. This section contains highlights only of duct design basics found in the SMACNA HVAC Systems9Duct Design manual. The tables and charts found in the Appendix of this manual are not as extensive as those found in the duct design manual, but they should be adequate for all TAB work. Air systems may be designed at higher or lower pres− sures. Higher friction rates and system pressures are required with higher velocity systems to reduce duct sizes and save space. For some lower velocity systems, higher pressures may be desirable for ease of balanc− ing and for flow control regulators that have a substan− tial pressure drop. On any of the variable air flow systems, there will be an infinite set of operating conditions which will create rates of airflow in the ducts entirely different from those used in the design. Every effort should be made when designing the ductwork to reduce the total fan power needed. This will assure a quieter system, reduced duct leakages, and in most cases maximum operating economy for the system owner. High velocity duct systems have been used mainly be− cause of space limitations created by architectural and structural practices. On the other hand where space is not at a premium, the use of high velocities and pres− sures are not economical. Some installations have areas of great space restriction where duct velocities must be higher. As soon as these points are passed and space becomes less critical, ve− locity rates should be sharply dropped, then gradually reduced toward the end of the duct system. 7.3.2

Equal Friction Design Method

The equal friction method of duct sizing probably has been the most universally used means of sizing low pressure supply air, return air and exhaust air duct sys− tems. It also is being adapted by many HVAC system designers for use in medium pressure systems. It nor− mally has not been used for sizing high pressure sys− tem. This design method automatically reduces air ve− locities in the direction of the airflow, so that by using a reasonable initial airflow velocity the chances of

introducing airflow generated noise are reduced or eliminated. When noise is an important consideration, the system velocity may be readily checked at any point during the design. Then there is the opportunity to reduce ve− locity created noise by increasing duct size or adding sound attenuation materials (such as duct lining). The major disadvantages of the equal friction method are there are no natural provisions for equalizing pres− sure drops in the branches (except in the few cases of a symmetrical layout); and there are no means of pro− viding the same static pressure behind each supply or return terminal device. Consequently, balancing can be difficult, even with a considerable amount of damp− ering in short duct runs. However, the equal friction method can be modified by designing portions of the longest run with different friction rates from those used for the shorter runs (or branches from the long run). Duct static regain (or loss) due to airflow velocity changes is included in the duct fitting pressure losses calculated using the duct fitting loss coefficient tables found in the Appendix. Otherwise, the omission of sys− tem static regain, when using older tables, could cause the calculated system fan static pressure to be greater than actual field conditions, particularly in larger, more complicated systems. Equal friction does not mean that total friction remains constant throughout the system. It means that a specific friction loss or stat− ic pressure loss per 100 feet (per meter) of duct is se− lected before the ductwork is laid out, and that this loss per 100 feet (per meter) is used constantly throughout the design. The SMACNA Duct Design System Calcu− lator makes this design method easy to use. 7.3.3

Supply Air Duct Sizing Procedures

To size the main supply air duct leaving the fan, the usual procedure is to select an initial velocity from Figures A−1 and A−2 found in the Appendix of this Manual. This velocity could be selected above the low velocity shaded section of the Duct Friction Loss Chart (I−P) A−1, and the Duct Friction Loss Chart (SI) A−2 if higher sound levels and energy conservation are not limiting factors. The charts on Appendix A.1 and A.2 are used to determine the friction loss by using the de− sign air quantity (cfm or L/s) and the selected velocity (fpm or m/s). A friction loss value commonly used for low pressure duct sizing is 0.1 in. wg per 100 feet of ductwork (0.8 Pa/m), although other values found in the low velocity shaded area, both lower and higher, are used by some designers as their standard or for spe−

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

7.9


cial applications. This same friction loss value gener− ally is maintained throughout the design, and the re− spective round duct diameters are obtained from the charts in Figures A−1 and A−2. The round duct diame− ters are used to select the equivalent rectangular duct sizes from chart A−1, unless round ductwork is to be used. Round ductwork is generally preferred on the higher pressure duct systems. The friction losses of each duct section may be cor− rected for otherN materials and construction methods by use of Table A−1 and Figure A−3. The correction factor from the Duct Friction Loss Correction Factors Figure A−3 is applied to the duct friction loss as only for the straight sections of the duct. The airflow rate used in the next section (and subsequent sections) of the main supply duct after each branch takeoff, is the original airflow rate (cfm or L/s) of the preceding sec− tion reduced by the amount of airflow into the branch. Using charts in Figures A−1 and A−2, the new airflow rate value (using the recommended friction rate of 0.1 in. wg per 100 ft (or 0.8 Pa/m) will determine the duct velocity and diameter for that section. The equivalent rectangular size of that duct section again is obtained from the Circulation Equivalents of Rectangular Ducts for Equal Friction and Capacity (I−P) (2) Dimen− sions in Inches Table A−2 and the (SI) version Table A−3 (if needed). All additional sections of the main supply air duct and all branch duct sections can be sized using charts in Figures A−1 and A−2 and approxi− mately the same friction loss rates. The pressure drop at each terminal device or air outlet (or inlet) of a small duct system, or of branch ducts of a larger system, should not differ more than 0.05 in. wg (12 Pa). If the pressure difference between the termi− nals exceeds that amount, dampering would be re− quired that could create objectionable air noise levels, and balancing may become more complicated. Example 7.1 (IP) A 70 foot section of N36 × 24 in. galvanized sheetN met− al duct is handling 10,000 cfm of air. What is the actual pressure loss and velocity of this duct section, and is it in the ?low velocity" category?

Solution Using Table A−2, a 36 × 24 in. duct has a circular equivalent of 32.0 inches. From Figure A−1, the 32.0 in. equivalent diameter duct has a velocity of 1800 fpm at a 10,000 cfm airflow rate and a pressure loss rate of 7.10

0.12 in. wg per 100 ft. It is in the low velocity shaded area. From Table A−1 the duct roughness category is medium smooth and from Figure A−3, a correction fac− tor is not needed. 0.12in.wg  70ft. Sectionpressureloss  100ft. 8 8  0.084in.wg NOTE: The pressure loss of any duct% fittings or ac− cessories contained in this 70 foot section of duct would be added to the above duct friction pressure loss.

Example 7.1 (SI) A 21 meter section of 900 × 600 mm galvanized sheet metal duct is handling 5000 L/s of air. What is the actu− al pressure loss and velocity of this duct section, and is it in the ?low velocity" category?

Solution Using Table A−3, a 900 × 600 mm duct has a circular equivalent of 799 mm. From Figure A−2, the 799 mm equivalent diameter duct has a velocity of 10 m/s at a 5000 L/s airflow rate, and a pressure loss rate of 1.1 Pa/ m. It is in the low velocity shaded area. From Table A−1, the duct roughness category is medium smooth, and from Figure A−3, a correction factor is not needed. Section pressure loss = 1.1 Pa/m × 21 m = 23.1 Pa 7.3.4

Modified Design Method

The modified equal friction method is used for sizing duct systems that are not symmetrical or that have both long and short runs. Instead of depending upon volume dampers to artificially increase the pressure drop of short branch runs, the branch ducts are sized (as nearly as possible) to dissipate (bleed off) the available pres− sure by using higher duct friction loss values. Only the main duct, which is usually the longest run, is sized by the original duct friction loss rate. Care should be exer− cised to prevent excessive high velocities in the short branches (with the higher friction rates). If calculated velocities are found to be too high, then duct sizes must be recalculated to yield lower velocities, and opposed blade volume dampers or static pressure plates must be installed in the branch duct at or near the main duct to dissipate the excess pressure. Regardless, it is good de− sign practice to always include balancing dampers in HVAC duct systems to balance the airflow to each branch.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


Return Air Duct Systems

32"

× 16"

A DAMPER

× 16"

Return air ducts should be sized using the equal fric− tion method at lower velocities. One scheme to simpli− fy return air systems is to use the space above hung ceilings or corridors for return air plenums and collect all return airflows at central points on each floor. In some localities there are code restrictions to using this method.

30’

45’

32"

7.3.5

2000 cfm

Terminal Unit Ductwork

7.4

DUCT SIZING EXAMPLES

7.4.1

Sizing In I-P Units

Example 7.2 (I−P Units) What is the total pressure loss of the portion of the fi− brous glass HVAC duct system shown in Figure 7−8.

× 16"

Low pressure ducts leaving terminal units are sized as any other conventional low pressure ductwork. Expe− rience indicates that the least expensive and the safest way to assure a quiet installation is to have some length of lined ductwork on the leaving side of terminal units. Lined ductwork, especially when it contains one or two elbows, can be a very effective sound attenuator. Lined ductwork helps if noise regeneration should oc− cur in the air distributing system because of poorly constructed ducts, fittings, and taps.

B 35’

22"

7.3.6

C

2000 cfm

25’

2000 cfm

D

14"

× 16"

×

28" 14" Grille PD=0.12 in. wg

FIGURE 7-8 SYSTEM LAYOUT (I-P UNITS)

Figure A−3, Correction factor = 1.43 Table A−14D, Opposed Blade Damper (set wide open), C = 0.52 Table A−10F , Sq. Elbow, 4.5 in. ?R", single thickness vanes, C = 0.23

Solution Using the figures, tables, and charts from the Appen− dix:

Velocity = 6000 cfm/32 × 16/144 = 1688 fpm Table A−4, Vp = 0.18 in. wg

Duct AB: Duct ABC32 × 16 inches, 6000 cfm Table A−2, Circ. Equiv. = 24.4 in. diameter

DuctC45 ft + 30 ft = 75 ft/100 ft × 0.17 × 1.43 = 0.182 in. wg DamperCVp × C = 0.18 × 0.52 = 0.094 in. wg

Figure A−1, Friction loss = 0.17 in. wg/100 ft, velocity = 1850 fpm

ElbowCVp × C = 0.18 × 0.23′ = 0.041 in. wg

Table A−1, category = medium rough

Duct Section <AB" Total = 0.317 in. wg

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

7.11


Duct BC:

10 m

Duct BCC22 × 16 in., 4000 cfm

× 400

A

× 400

DAMPER

15 m

550

Table A− 2, Circ. Equiv. = 20.4 inches diameter

800

Figure A−1, Friction loss = 0.19 in. wg/100 ft, velocity = 1790 fpm

1000 L/s

B

× 400

Figure A−3, Correction factor for medium rough = 1.45

550

Table A−11C, 32 × 16 inches to 22 × 16 inches

12 m

60

1000 L/s

C

contraction, A1/A = 1.45

8m

C = 0.06 Velocity = 4000 cfm/22 × 16/144 = 1636 fpm,

1000 L/s

D

350

Table A−4, Vp = 0.17 in. wg DuctC35 ft/100 ft × 0.1 9 × 1.45 = 0.096 in. wg

× 400

×

700 350 Grille PD= 30 Pa

FIGURE 7-9 SYSTEM LAYOUT (SI)

TransitionCVp × C = 0.17 × 0.06 = 0.010 in. wg

TransitionCVp × C = 0.11 × 0.06 = 0.007 in. wg

Duct Section <BC" Total = 0.106 in. wg Duct CD:

ElbowCVp × C = 0.11 × 1.2 = 0.132 in. wg

Duct CDC14 × 16 inches, 2000 cfm

Grille (given) = 0.120 in. wg

Table A−2, Circ. Equiv. = 16.3 in. diameter Figure A−1, Friction loss = 0.16 in. wg/100 ft

Duct Section <CD" Total = 0.316 in. wg Duct−Run ABCD:

Figure A−3, Correction factor for medium rough = 1.43 (velocity = 1380 fpm)

ABC0.317 in. wg BCC0.106 in. wg

Table A−11C, 22 × 16 in. to 14 × 16 in. 60 contraction, A1/A = 1.57, C = 0.06 Table A−10D, 90 mitered elbow, H/W =6/14 = 1.14, C = 1.2

CDC0.316 in. wg Total Pressure Loss)0.739 in. wg 7.4.2

Sizing In SI Units

Velocity = 2000 cfm/14 × 16/144 = 1286 fpm Table A−4, Vp = 0.11 DuctC25 ft/100 ft × 0.16 × 1.43 = 0.057 in. wg 7.12

Example 7−2 (SI) Find the total pressure loss of the portion of the fibrous glass HVAC duct system shown in Figure 7−9.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


Solution Using the figures, tables, and charts from the Appen− dix:

C = 0.06 Velocity = 2.0 m3/s/(0.55 × 0.4) = 9.1 m/s Table A−5, Vp = 49.9 Pa

Duct AB:

DuctC12 m × 1.9 Pa/m × 1.46 = 33 Pa

Duct ABC800 × 400 mm, 3000 L/s: Table A− 3, Circ. Equiv. = 609 mm diameter, Figure A−2, Friction loss = 1.6 Pa/m,

TransitionCVp × C = 49.9 × 0 .06 = 3 Pa Duct Section <BC" Total = 36 Pa Duct CD:

velocity = 10 m/s

Duct CDC350 × 400 mm, 1000 L/s:

Table A−1, category = medium rough,

Table A−3, Circ. Equiv. = 409 mm diameter,

Figure A−3, Correction factor = 1.45,

Figure A−2, Friction loss = 1.5 Pa/m

Table A−14D, Opposed Blade Damper (set wide open), C = 0.52,

Velocity = 7.7 m/s

Table A−10F, Sq. Elbow, 114 mm ?R", single thickness vanes, C = 0.23, Velocity = 3.0 m3/s/0.8 × 0.4 = 9.4 m/s (1000 L/s = 1.0 m3/s) (1000 mm = 1.0 m)

Figure A−3, Correction factor for medium rough = 1.46 Table A−11C, 550 × 400 mm to 350 × 400 mm, 60 contraction, A1/A = 1.57, C = 0.06

Table A−5, Vp = 53.2 Pa DuctC10m + 15m = 25m × 1.6 Pa/m × 45 = 58 Pa DamperCV p × C = 53.2 × 0.52 = 28 Pa ElbowCV p × C = 53.2 × 0.23 = 12 Pa Duct Section <AB" Total = 98 Pa Duct BC:

Table A−10D, 90 mitered elbow, H/W = 1.14, C = 1.2 Velocity = 1.0 m3/s/(0.35 × 0.4) = 7.1 m/s Table A−5, Vp = 30.3 Pa DuctC8 m × 1.5 Pa/m × 1.46 = 18 Pa TransitionCVp × C = 30.3 × 0.06 = 2 Pa ElbowCVp × C =30.3 × 1.2 = 36 Pa

Duct BCC550 × 400 mm, 2000 L/s: Table A−3, Circ. Equiv. = 511 mm diameter, Figure A−2, Friction loss = 1.9 Pa/m,

Grille (given) = 30 Pa Duct Section <CD" Total = 86 Pa Duct−Run ABCD:

velocity = 10 m/s

ABC98 Pa

Figure A−3, Correction factor for medium rough = 1.46

BCC36 Pa

Table A−11C, 800 × 400 mm to 550 × 440mm, 60 contraction, A1/A = 1.45,

CDC86 Pa Total Pressure LossC220 Pa

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

7.13


7.5

SUMMARY

if it is, and calculations are painstakingly made in ac− cordance with all tables and charts, the actual total sys− tem losses can vary from the design losses. Generally, balancing a system adds additional losses to the system total or static pressure losses when compared to a sys− tem with all dampers wide open.

Step by step procedures for sizing a low pressure sup− ply and return system and a medium pressure system can be found in the SMACNA HVAC Systems9Duct Design manual. On new construction work, and with a good background in duct system design, TAB techni− cians will be able to recognize where problems exist and what can be done to correct them before construc− tion has progressed to the point where changes are dif− ficult to make.

Testing and balancing personnel also must know about diffusers and air patterns in order to establish a truly comfortable system with even temperatures through− out the entire space. The system designer and the TAB team have the same objectivesCa properly operating HVAC system. Understanding system design is the key to it all.

The TAB technician must know how duct systems are designed in order to troubleshoot problem jobs. The ductwork is seldom installed exactly as shown. Even

POOR POOR

BEST

IMPROVED

POOR

IMPROVED

POOR

IMPROVED

IMPROVED BEST

POOR

IMPROVED

IMPROVED

IMPROVED

POOR

IMPROVED

POOR

FIGURE 7-10 FAN DUCT CONNECTIONS

7.14

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

IMPROVED


CHAPTER 8

HYDRONIC EQUIPMENT


CHAPTER 8 8.1

PUMPS

8.1.1

Pump Laws

HYDRONIC EQUIPMENT

Centrifugal pumps are used in heating and air condi− tioning systems to produce fluid flow in piping. This section provides general information on centrifugal pumps and their application to heating and air condi− tioning or hydronic systems. Other pumps, such as re− ciprocating or rotary pumps, play a minor role in the HVAC industry. Pumps interact with a hydronic system in almost the same manner as fans do in an air system, and pump laws are similar to fan laws. Pumps usually are direct driven by being coupled to the shaft of the motor, and their speed is not changed unless a variable speed drive or motor is used. If the pump speed can be changed, the volume of liquid that is pumped will vary directly as the speed. The pressure or head imposed within the piping system will vary as the square of the rpm. The power required to run the pump will vary as the cube of the rpm.

Cutoff Discharge Nozzle Impeller



The pressure or head within the system varies directly as the square of the diameter of im− peller,



The horsepower or power required to drive the pump varies directly as the cube of the di− ameter of the impeller.

It is more efficient to change the pump impeller than to throttle a pump (using a discharge valve) to ?short circuit" part of output flow. On hydronic systems having larger pumps, or for spe− cialized systems requiring the ability to adjust water flow based on system loads, a variable frequency drive (VFD) may be used. Although the pump motor ramp up and ramp down set− points are usually programmed differently than for a motor driving a fan, the same VFD can be used. Since motor horsepower input is a cubic function of pump rpm, even a small 10 percent reduction in pump flow can reduce motor horsepower and corresponding electrical consumption over 30 percent. Most HVAC systems are sized for maximum calcu− lated loads, which may only occur for several hours during an entire year. The ability to reduce system wa− ter flow rates to meet reduced radiation or air handling unit coil loads for the remainder of the year can result in a significant utility cost savings.

Casing or Volute

Vanes

Impeller “Eye” Shaft

FIGURE 8-1 TYPICAL CENTRIFUGAL PUMP CROSS SECTION

In small HVAC hydronic systems having pumps under 5 hp, the design flow rate is usually reduced by the pump supplier by reducing or ?trimming" the diameter of the pump’s impeller. Changing the diameter of the impeller has the same affect as changing the pump speed. Pump laws found in subsection 2.3.5 of Chapter 2 and in the Appendix can be restated in a different way:



The pump volume (gpm) varies directly with the impeller diameter,

As recommended in section 3.6 dealing with VFD con− trol of HVAC fans, understanding how to program VFD motor controls can be very helpful for any TAB controller. 8.1.2

Pump Types

Types of centrifugal pumps used in the heating and air conditioning industry can be defined by the type of im− peller, number of impellers, type of casing, method of connection to driver, and mounting position. Two types of pump impellers are used in these pumps, single suction and double suction. The single suction impeller has one suction or intake, while the double suction impeller has two suctions or intakes. Most cen− trifugal pumps for heating and air conditioning are single suction; the significant example of double suc− tion impeller is the single stage, horizontal split−case pump. Pumps also may have single or multiple impel− lers. When they have multiple impellers, they are called multistage pumps. As with impellers, there are two basic types of casings for these pumps, volute and diffuser. The volute types

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

8.1


include all pumps that collect water from the impeller and discharge it perpendicularly to the pump shaft. Diffuser−type casings collect water from the impeller and discharge it parallel to the pump shaft. All pumps described here are the volute type, except the vertical turbine pump, which is a diffuser type.

sure and temperature limitations vary depending on the liquid being pumped and the style of seal. The seal material and style are supplied by the manufacturer af− ter being informed of the kind of liquid to be pumped and the temperature and pressure limitations. 8.1.3.4

Pumps can be classified by their method of connection to an electric motor, close coupled or flexible coupled. The close coupled pump has the impeller mounted di− rectly on a motor shaft extension, while the flexible coupled pump has an impeller shaft supported by a frame or bracket, connected to the electric motor through a flexible coupling. Pumps also are labeled by their mounting position; either horizontal or vertical. Seven significant types of pumps are used in heating and air conditioning or hydronic systems, and are shown in Figure 8−2. Many variations of these pumps are offered by manufacturers for particular applica− tions. 8.1.3

Packing Glands

Pumps with packing glands are extensively used, par− ticularly where abrasive substances included in the water are not detrimental to system operation. Some leakage at the packing gland is needed to lubricate and cool the area between the packing material and the shaft. 8.1.3.5

Shaft Sleeves

Shaft sleeves protect the motor or pump shaft, espe− cially with packing.

Pump Construction Features FORM

Important construction features of centrifugal pumps follow. 8.1.3.1

Material Types

Centrifugal pumps are generally offered in bronze fitted, all bronze, or iron fitted construction. In bronze fitted construction, the impeller, shaft sleeve (if used), and wear rings are bronze, and the casing is cast iron. These construction materials refer to the liquid end of the pump (those parts of the pump that contact the liq− uid being pumped). 8.1.3.2

Stuffing Box

The stuffing box is that portion of the pump where the rotating shaft enters the pump casing. To seal undesir− able leakage at this point, a mechanical seal or packing is used in the stuffing box.

TYPICAL APPLICATIONS  Residential Hydronic System  Domestic Hot Water  Recirculation  Multizone Circulation

CIRCULATOR

CLOSE-COUPLED END SUCTION

FRAME-MOUNTED END SUCTION

BASE-MOUNTED HORIZONTAL SPLIT CASE SINGLE-ST AGE DOUBLE-SUCTION BASE-MOUNTED MULTISTAGE HORIZONTAL SPLIT CASE

 Cooling Tower  Condenser Water  Chilled Water  Primary & Secondary  Hot Water  Boiler Feed  Condensate Return

VERTICAL INLINE VERTICAL TURBINE SINGLE-ST AGE OR MULTISTAGE

8.1.3.3

Mechanical Seals

Pumps with mechanical seals are used successfully in a wide variety of applications. Like pumps, many styles and types of seals are available. There are unbal− anced and balanced (for higher pressures) seals. Inside seals operate inside the stuffing box while outside seals have their rotating element outside the box. Pres−

8.2

SUMP MOUNTED

CAN PUMP

FIGURE 8-2 DESCRIPTIONS OF CENTRIFUGAL PUMPS USED IN HYDRONIC SYSTEMS

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


Impeller Type

Type

Number of Impellers

Motor Mounting Position

Motor Connection

Casing

Circulator

Single suction

One

Volute

Flexible coupled

Horizontal

Close coupled, end suction

Single suction

One or two

Volute

Close coupled

Horizontal

Frame mounted, end suction

Single suction

One or two

Volute

Flexible coupled

Horizontal

Double suction, horizontal split case

Double suction One

Volute

Flexible

Horizontal

Horizontal split split case, multistage

Single suction

Two to five

Volute

Flexible coupled

Horizontal

Vertical inline

Single suction

One

Volute

Flexible or close

Vertical

Vertical turbine

Single Suction

One to twenty Diffuser

Flexible coupled

Vertical

Table 8-1 Characteristics of Centrifugal Pumps

Positive Displacement Pumps

Centrifugal Pumps

Characteristics Rotary

Piston

Radial

Mixed Flow

Axial Flow

Flow

Even

Pulsating

Even

Even

Even

Effect of increasing head: on flow on bhp

Negligible decrease Increase

Increase

Decrease Decrease

Decrease Large increase

Effect of decreasing head: on flow on bhp

Decrease Small decrease to large increase

Negligible increase Decrease

Decrease

Increase Increase

Increase Slight increase to decease

Increase Decrease

Up to 30% increase Decrease 50%-60%

Considerable increase 10% decrease to 80% increase

Large increase Increase 80%-150%

Effect of closing discharge valve: on pressure

Can destruct unless relief valve is used Increase to destruction

on bhp

Table 8-2 Characteristics of Common Types of Pumps 8.1.3.6

Bearings

Ball bearings are most frequently used in larger pumps. Circulators use sleeve type bearings for motor and pump bearings.

8.1.3.7

Wearing Rings

Wearing rings are for the impeller and/or casing. They are replaceable and prevent wear to the impeller or casing.

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;˘ Third Edition

8.3


8.1.3.8

Balance Rings

The balance ring is placed on the back side of a single inlet, enclosed impeller to reduce the axial load. Double inlet impellers are inherently balanced axially.

Straight Edge C L Pump and Water P

M Aligned Gap

8.1.3.9

Rotation of any pump is fixed by the configuration and type of vanes and the suction and discharge connec− tions. An arrow to indicate proper direction is often cast directly into the casing metal. In addition to prop− er position of the pump in the piping, rotation is also dependent upon the motor or driven rotation. Rotation of motor and pump must be tested prior to operation. However, pumps with mechanical seals must not be run dry, even for ?bumping," to determine rotation.

C L Pump M

A pump may be driven by any appropriate means. For the most part, environmental system pumps are motor driven, and the shafts of the motor and pump are con− nected end to end by some type of coupling. Some pumps, usually those employed in pumping fuel oil, are belt driven. In this case the belts may be used as a protective device, either slipping or breaking before damage to the pump can occur in the event of overload. The couplings between motor shaft and pump shaft are made in two pieces so that the two coupling halves may be disconnected for removal of the pump without disturbing the motor, for running the motor indepen− dently of the pump, or for removal of the motor with− out disturbing the pump. The coupling also serves as a means of adjustment of the pump and shaft align− ment. The ideal alignment condition is that both shafts are in a straight line and concentric under all condi− tions of operation and shut down. Because of tempera− ture changes, an unequal expansion of parts causes a change of alignment during operation. Base mounted pumps, especially in larger sizes, re− quire at least an alignment check in the field. This may be done in a superficial but often satisfactory way with a straight edge since the outside perimeters of the cou− pling halves are machined to the same diameter and are perpendicular to each shaft. Center lines and cou− pling faces must be true as shown in Figure 8−3. 8.1.3.11 Operating Speeds Operating speeds of motors may be selected in the range between 600 and 3500 rpm, with 1800 rpm being the most common speed. Pumps operating at higher speeds are generally less expensive, but for quieter

P C L Motor Coupling (Typ.) Misaligned C L Pump

C L Motor M Gap and Angle Straight Edge Misaligned

8.1.3.10 Pump Drives

8.4

Straight Edge

Pump Rotation

FIGURE 8-3 COUPLING ALIGNMENT WITH STRAIGHT EDGE performance or lesser NPSH requirements, lower speeds are preferred. 8.1.4

Pump Pressure or Heads

The purpose of a pump for HVAC work is to establish fluid flow and produce sufficient pressure to overcome the resistance of a system and the system components at the design flow rate. 8.1.4.1

Pump “Head” Definitions

When working with pumps, the word head often will be used to define pressure. Definition of these and oth− er common head terms are noted here, even though some may be defined again under other discussions: Friction head is the pressure in psi or feet (pascals or meters) of the liquid pumped which represents system resistance that must be overcome. Velocity head is the pressure needed to accelerate the liquid being pumped. (For practical purposes, the ve− locity head is insignificant and usually can be ignored in HVAC system calculations.) Static suction lift is the distance in feet (meters) be− tween the pump centerline and the source of liquid be− low the pump centerline. Suction lift is the combination of static suction lift and friction head in the suction piping when the source of liquid is below the pump centerline.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


Suction head is the positive pressure on the pump inlet when the source of liquid supply is above the pump centerline. Static suction head is the positive vertical height in feet (meters) from the pump centerline to the top of the level of the liquid source. Dynamic suction lift is the sum of suction lift and ve− locity head at the pump suction when the source is be− low the pump centerline. Dynamic suction head is positive static suction head minus friction head and minus velocity head. Dynamic discharge head is static discharge head plus friction head plus velocity head. Total dynamic head is dynamic discharge head (static discharge head, plus friction head, plus velocity head) plus dynamic suction lift, or dynamic discharge head minus dynamic suction head. 8.1.4.2

Pressure Relationships

For the pressure relationship to the inlet and suction side of the pump, the discharge pressure is higher. In the process of establishing this head, the impeller pro− duces a lower or relatively negative pressure on the suction side. It is important to note the deliberate use of the term rel− ative in a discussion of the pressures which pumps pro− duce. The system elevation static pressure is of major consequence in the liquid system. During the time when the pump is running, there is a redistribution of pressures in the system because of the combination of the elevation pressures and the pressures produced by the pump. However, when the pump is shut down, the system pressures return to the same values of elevation static as before the pump was started. The pressures produced by the pump merely add to or subtract from the initial shutdown pressures. Since the operating discharge pressure produced by the pump is an increase, this value is added to the shut− down pressure in the discharge piping. Since the oper− ating suction pressure produced by the pump is a de− crease, this value is subtracted from the shutdown pressure in the suction piping. Assuming that the sys− tem piping and equipment losses were properly calcu− lated and that the pump was properly selected to over− come those losses and to withstand the system static and dynamic pressures, it would be expected that the pump would produce the required fluid flow. Howev−

er, this may not be the case because of the pump’s sen− sitivity to the pressure conditions on its inlet (the dis− charge conditions of the pump do not generally present a problem). 8.1.4.3

Frequent Pumping Problems

The fluid being pumped, usually water, generally con− tains some entrained air which has been absorbed as a result of atmospheric pressure when the fluid was ex− posed to the atmosphere prior to being introduced into the system. This air is released because of an increase in fluid temperature, a decrease in fluid pressure, or because of the fluid vapor pressure. Air driven out of the water when it is heated must be vented from the piping, often several times at the be− ginning of the season, and throughout the heating op− eration if fresh water must be continuously added to re− place that amount dripped through pump packing. Most of the air released in the process of heating of the water should be removed at or near the heat exchanger or hot water generator. Therefore, there may be a point in the environmental fluid pumping system where air may be released from the fluid being pumped if the pressure is low enough and/or the liquid may change to a gas. Should these conditions occur, the pump, which has been designed to move liquid, is generally unable to cope, and the flow of liquid is either greatly reduced or stopped com− pletely. However, at some point within the pump where the impeller produces sufficient pressure, the bubbles of gaseous liquid will be re−liquified and the bubbles of air will be reabsorbed. This transition oc− curs suddenly and is accompanied by crackling or ex− plosive noise. The phenomenon is called cavitation and may cause destructive pitting and wearing of the impeller and casing as well as noise and vibration. Any one or all of these conditions will reduce pump perfor− mance and life. 8.1.4.4

Net Positive Suction Head (NPSH)

To eliminate the cavitation problem, it is necessary to maintain a minimum suction pressure at the inlet side of the pump. The actual value in psi or ft. wg (pascals or meters) of internal pump losses depends on the pump size and de− sign, and the volume of water being pumped. This must be determined by the pump manufacturer, and is given by numerical values of NPSH. Required NPSH, sometimes designed NPSHR, can be considered to be the amount of pressure, in excess of the vapor pressure, required to overcome internal pump losses and so keep

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

8.5


water flowing into the pump. For a given pump, the re− quired NPSH increases as capacity increases. Each system, as a result of design and physical limitations, will produce an available NPSH sometimes desig− nated NPSHA. When the available NPSH is greater than the required NPSH, the problems of air release, vaporization, and cavitation will not arise. The required NPSH for a specific pump is available from the manufacturer, either in catalogue data or upon request. Although usually given as a single num− ber, the value varies with flow and head. For any pump, the full range of values for each impeller size and oper− ating speed is expressed as a curve (see Figure 8−4). The TAB technician must remember, however, that for satisfactory pump operation, NPSHA must always ex− ceed the NPSHR; if it does not, bubbles and pockets of vapor will form in the pump. The results will be reduc− tion in capacity, loss of efficiency, noise, vibration, and cavitation. The available NPSH in a specific system may be ex− pressed by the following equation: Equation 8-1 NPSHA  P a  Ps  V   P vp 2g 2

Where: NPSHA = Net positive suction head available − ft wg (m wg) Pa = Atmospheric pressure at elevation of installationCuse 34 ft wg (10.32 m wg) at sea level

strainer on the suction side of the pump should become clogged. 8.1.4.5

Vortex

Vortex is not a pressure, but a term used to describe whirling or spinning of the liquid in a piping system. The condition is similar to a weather cyclone or torna− do and may occur anywhere in the piping system where conditions cause or allow the vortex to be pro− duced. On the discharge or relatively positive pressure side of a pump the worst effect of a vortex is normally noise, and the configuration of the piping is usually the cause. Several elbows, always turning the same way, may produce a vortex with a low pressure center in the pipe, and noise bubbles of air can temporarily be released in the same way as a pump suction with inadequate NPSH. On the suction, or relatively negative pressure side of the pump, the same condition may also occur. Howev− er, the suction vortex problem is more commonly caused by placing the suction pipe termination too close to the surface of the system liquid, as might occur in a cooling tower pan. The low pressure produced at the pipe entrance produces a vortex or whirlpool simi− lar to that produced when a stopper is removed from a sink full of water. The result of this condition is to introduce air directly into the eye of the pump impel− ler, impairing the efficiency of the pump and produc− ing undesirable noise. This condition may occur even though calculations indicate adequate NPSH.

Ps = Pressure at pump centerlineCft wg (m. 2 wg) V = Absolute vapor pressure at 2g pumping temperatureCft wg (m wg) g = Gravity accelerationC32.2 ft/s2 (9.81 m/s2) NPSH is normally not a consideration in closed sys− tems, especially where the pump is at the bottom of a riser. It is also not ordinarily a factor in most open sys− tems unless pumping hot water, or if there is a consid− erable suction lift, or if there is considerable friction in the pump suction pipe. In unusual considerations of excessive suction line friction, there could be insuffi− cient NPSHA. Such a condition could exist because of an undersized pipe, or too many fittings, or if a valve in the suction line was throttled, or if a fine mesh

8.6

Total Head - Ft

Pump Performance Curve

Required NPSH Flow Rate - gpm

FIGURE 8-4 TYPICAL REQUIRED NPSH CURVE

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


Some vortex producing conditions can be eliminated by proper piping. In cooling tower sumps, a plate often is installed to prevent a vortex from forming. 8.2

PUMP / SYSTEM CURVE RELATIONSHIP

8.2.1

Pump Curves

Pump performance characteristics are presented in graphical curves or tabular form in the same manner as fans. However, pump curves usually are available, and performance tables are not; which is contrary to the situation with fan data. The result is a relatively quick, visual pump selection to determine the conse− quences of system pressure changes. Typical pump selection curves are illustrated in Figure 8−5. The curves presented might illustrate the ratings of a single pump of a family similar to the fan curves pre− viously discussed. In addition, the same pump may have two sets of curves. The one illustrated represents operation at 1750 rpm, while another set of conditions is available for the same pump operating at 3500 rpm (or 3450 rpm). The group or sub−family of curves on each graph is produced by different impeller sizes in the same ca− sing. Those impeller sizes shown are for standard im− peller diameters, usually in inch or half inch incre− ments in U.S. units and similar increments in metric units. Within the minimum and maximum impeller sizes indicated, any impeller diameter may be made to accomplish specific requirements simply by shaving a standard size on a lathe.

TOTAL HEAD IN FEET

The position of the pump capacity selection point is best located in or slightly to the left of the highest effi−

45% 55% 60%

60 50

7” 6 1_w”

68% 65% 60% 55%

40 30

5 1_w”

8.2.2

Closed System Curve

The system curve is simply a plot of the change in en− ergy head resulting from a fluid flow change in a fixed piping circuit. System curve construction methods dif− fer between open and closed piping circuits. From the pipe size and design flow rate, a calculated energy head pressure drop is determined. It should be particularly noted that system static height is of no im− portance in determining energy head pressure drop. This is because the static heights of the supply and re− turn legs are in balance; the energy head required to raise water to the top of the supply riser is balanced by the energy head regain as water flows down the return riser.

Example 8.1 (I−P)

45%

5”

3HP

20 10 0

The motor size must be made so that the pump will not overload at the design conditions and if possible at any curve condition along the selected impeller curve.

A design flow rate of 200 gpm (12.0 L/s) establishes 30 foot (9 m) pressure drop in a typical system. This particular point can be plotted on a foot head versus gpm pump curve as shown in Figure 8−7. What pres− sure drop would occur if the flow were changed to 163 gpm (9.8 L/s) through the piping circuit?

65% 68%

ciency area. Not only is efficiency high, but should it be a factor, NPSH is low. Just as important is the matter of quiet operation. Therefore, the selection is not nor− mally made at or near either the maximum or mini− mum impeller sizes. When the impeller diameter is chosen in the mid−range, it may be replaced in the field, if required, with either a larger or smaller size. Furthermore, the slope of the pump curve requires se− rious consideration. Too flat a curve results in large changes in flow rate for small changes in system head. Too steep a curve will often dip at the left, which will produce surging or unstable operation should the pump need to operate in this area.

2HP 1 1/2 HP

20

3 HP 1HP 1_w HP 4 40 60 80 100 120 140 160 CAPACITY IN U.S. GALLONS PER MINUTE

180

FIGURE 8-5 PUMP CURVE FOR 1750 RPM OPERATION

Solution Using Equations 2−24 and 2−26 (combined) 2 Q2 H 2  H 1 Q1

2

H 2  30 163   19.9feet 200

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

8.7


CUT-OFF FOR SELECTED IMPELLER DIAMETER PUMP HEAD-CAPACITY CURVE FOR FIXED IMPELLER SIZE MOTOR POWER (STANDARD SIZES)

TOTAL HEAD

MOTOR WILL OVERLOAD IF OPERATING POINT SHIFTS TO THE RIGHT OF THIS INTERSECTION, SELECT MOTOR B FOR NONOVERLOADING

HEAD - CAPACITY CURVE FOR DESIGN CONDITIONS AND IMPELLER DIAMETER

DESIGN HEAD

DESIGN OPERATING POINT

MOTOR B MOTOR A DESIGN FLOW FLOW

EFFICIENCY CURVES - SELECTION AT OR TO LEFT OF MAXIMUM MAINTAINS HIGH EFFICIENCY IF ACTUAL OPERATING POINT OCCURS TO RIGHT OF DESIGN OPERATING POINT

FIGURE 8-6 TYPICAL DESIGN PUMP SELECTION POINT (FROM ABBREVIATED CURVE) The same procedure carried out for a 116 gpm (7.0 L/s) flow rate would result in a 10.1 (3 m) pressure drop. These points may be plotted on a foot head versus gpm chart as shown in Figure 8−7. Connection of these three points, along with other condition combinations, de− scribes a system curve. The system curve is a statement of the change in pipe friction drop with water flow change for a fixed piping circuit. This is a most impor− tant working tool for pump application.

Equation 8-2

H2 Q2   H1 Q1

2

Where: H = HeadCft wg (m wg)

TOTAL HEAD - FEET(m)

Q = Fluid flowCgpm (L/s or m3/s)

50 (15) 40 (12) 30 (9) 20 (6) 10 (3) 0

The operation of the pump in Figure 8−7 installed in the piping circuit described by the system curve must be at the intersection of the pump curve with the system curve because of the First Law of Thermodynamics.

PUMP CURVE

POINT OF OPERATION

8.2.3

SYSTEM CURVE 50 (3)

100 (6)

150 (9)

200 (12)

250 (15)

CAPACITY - US GALLONS PER MINUTE (LITERS PER SECOND)

FIGURE 8-7 SYSTEM CURVE PLOTTED ON PUMP CURVE 8.8

Open System Curve

In plotting the system curve for an open system, the statics of the system must be analyzed in addition to the friction loss. The different static conditions are il− lustrated in Figure 8−8. A typical cooling tower application is illustrated in Figure 8−9. In this system, the pump is drawing water from the tower sump and discharging it through the condenser to the tower nozzles, at a 10 foot (3 m) high− er elevation than the sump level.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


TOTAL STATIC HEAD

TOTAL STATIC HEAD STATIC SUCTION HEAD

STATIC STATIC DISCHARGE DISCHARGE HEAD HEAD

TOTAL STATIC HEAD

STATIC SUCTION HEAD

STATIC DISCHARGE HEAD

STATIC SUCTION LIFT

STATIC SUCTION HEAD LESS THAN STATIC DISCHARGE HEAD

STATIC SUCTION LIFT PLUS STATIC DISCHARGE HEAD

STATIC SUCTION HEAD GREATER THAN STATIC DISCHARGE HEAD

FIGURE 8-8 TYPICAL OPEN SYSTEMS

This system curve cannot be applied directly to the pump curve and the intersection taken as the accurate pumping point for the open system. A false evaluation using this criteria, but without evaluating the static height of the tower, is shown in Figure 8−10. The illustration is false because the pump must also provide the necessary energy to raise water from the tower sump to the spray nozzles. In this case, the pump NOZZLES

10 FT(3 m) TOTAL STATIC HEAD

COOLING TOWER SUMP

must raise each pound of water 10 feet (3 m) in height, or it must provide 10 feet (3 m) of energy head due to the static difference in height between the water levels. The static difference of 10 feet (3 m) must be added to the piping pressure drop to provide total required head for each of the gpm points previously noted. The re− vised fluid flow versus total required head is shown in Table 8−3.

60 (18)

TOTAL HEAD - FEET(m)

Total friction loss (suction and discharge piping, con− denser, nozzles, etc.) is 30 foot (9 m) at a design flow rate of 200 gpm (12 L/s), the change in piping pressure drop for a change in water flow rates is determined and plotted to develop a system curve.

PUMP No. 1 PERFORMANCE CURVE

50 (15) 40 (12)

FALSE OPERATING POINT

30 (9) 20 (6)

SYSTEM CURVE

10 (3)

STATIC DISCHARGE HEAD STATIC SUCTION HEAD

0

75 (4.5)

150 (9.0)

225 (13.5)

300 (18.0)

375 (22.5)

CAPACITY - US GALLONS PER MINUTE (LITERS PER SECOND) CONDENSER

FIGURE 8-9 TYPICAL COOLING TOWER APPLICATION

FIGURE 8-10 SYSTEM CURVE FOR OPEN CIRCUIT FALSE OPERATING POINT

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

8.9


PUMP HEAD CAPACITY CURVE PUMP NO.2 PERFORMANCE CURVE

POINT 4

POINT 2

50 (15)

POINT 1 DESIGN HEAD

TRUE OPERATING POINT PUMP NO.2

40 (12)

DESIGN SYSTEM HEAD CURVE

PUMP NO.1 PERFORMANCE CURVE

30 (9)

SYSTEM CURVE

20 (6)

TRUE OPERATING POINT PUMP NO.1 10 (3) 10’(3m) 0 75 (4.5)

150 (9.0)

225 (13.5)

300 (18.0)

375 (22.5)

CAPACITY - US GALLONS PER MINUTE (LITERS PER SECOND)

SYSTEM AND PUMP HEAD

TOTAL HEAD - FEET(m)

60 (18)

OVERPRESSURE WITH CONSTANT SPEED PUMP POINT 3

ACTUAL SYSTEM HEAD CURVE

POINT 5

FIGURE 8-11 SYSTEM CURVE FOR OPEN CIRCUIT TRUE OPERATING POINT

50% DESIGN 100% DESIGN FLOW

FLOW

SYSTEM FLOW

FIGURE 8-12 PUMP OPERATING POINTS

The correct procedure for plotting a system curve for the circuit shown in Figure 8−9 is illustrated in Figure 8−11. 8.2.4

Pump Operating Points

In Figure 8−12, if the system is of the free flowing type without control valves, with an actual system head curve as shown, the pump will operate at Point 2, not Point 1; the pump will produce a higher flow rate than design flow rate. If the system is of the controlled flow type with two way valves on all heating or cooling coils, at design flow, the pump will operate at Point 1 and will create an over−pressure on the coils and con− trol valves equal to the head difference between Points 1 and 3. If the system flow is reduced to 50 percent of design on such a system, the over pressure will in− crease to the amount between Points 4 and 5. Pump op− eration will be as follows.

head and system head being converted into over−pres− sure, consumed by the control valves. Recognizing that over−pressure can occur in con− trolled flow systems where coils are equipped with two way control valves, the selection of pumps for these systems must include methods of limiting over−pres− sure to an economic minimum. These methods in− clude: a.

multiple pumps operating in parallel

b.

multiple pumps operating in series

NON-CONTROLLED FLOW

c.

multi−speed pumps

On a system without control valves, the pump will al− ways operate at the point of intersection of the pump head capacity curve and the system head curve.

d.

variable speed pumps

8.2.4.1

8.2.4.2

CONTROLLED FLOW

On controlled flow systems, the pump will follow its head capacity curve, the difference between pump

8.10

The actual method used on a specific hydronic system depends on the economics of that system. The effects of these methods on over−pressuring a particular sys− tem can be determined by developing the system head curve and plotting pump head capacity curves on the same graph with the system head curve.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


0 (0) 0 (0)

116 (7.0) 10 (3)

Feet (Meters) of Head Design 163 185 200 (9.8) (11.1) (12.0) 20 (6) 25 (7.5) 30 (9)

Static Head

10 (3)

10 (3)

10 (3)

10 (3)

10 (3)

10 (3)

10 (3)

Total Head

10 (3)

20 (6)

30 (9)

35 (10.5)

40 (12)

45 (13.5)

50 (15)

GPM (L/s) Piping System

215 (12.9) 35 (10.5)

230 (13.8) 40 (12)

Table 8-3 Flow vs Total Head (Cooling Tower Application) 8.2.5

Multiple Pumps

PUMP HEAD CAPACITY CURVE ONE-PUMP OPERATION

SYSTEM DESIGN HEAD

SYSTEM AND PUMP HEAD

Multiple pumps in parallel is the most common meth− od of eliminating over−pressure. Figure 8−13A de− scribes two pumps piped in parallel, while Figure 8−14 includes a system head curve as well as the head capac− ity curves for single pump and two pump operation. It is obvious from Figure 8−14 that one pump at 50 per− cent system flow will reduce the over−pressure caused by two−pump operation or one pump designed to han− dle maximum design flow and head.

Figure 8−13B illustrates two pumps piped in series with bypasses for single pump operation. Figure 8−15 indicates the use of series pumping on a hydronic sys− tem with a system head curve consisting of a large amount of system friction. For such systems, series pumping can greatly reduce the overpressure on a con− trolled flow system. Series pumping should not be used on hydronic systems with flat system head curves similar to the one shown in Figure 8−14.

For such a system, one pump operation with series connection would result in the pump running at shutoff head and producing no flow in the system.

CHECK VALVE

CHECK VALVE

BYPASSES FOR SINGLE PUMP OPERATION

A. PARALLEL PUMPING

B. SERIES PUMPING

FIGURE 8-13 MULTIPLE PUMPS

TWO-PUMP OPERATION

TWO PUMPS ONE PUMP MAXIMUM POINTS OF OPERATION

SYSTEM HEAD CURVE

INDEPENDENT HEAD

50% DESIGN FLOW

100% DESIGN FLOW

SYSTEM FLOW

FIGURE 8-14 PUMP AND SYSTEM CURVES FOR PARALLEL PUMPING

8.3

PUMP INSTALLATION CRITERIA

8.3.1

Pressure Gage Location

To eliminate the effect of pipe friction, fittings, valves, and other obstructions, the most desirable gage loca− tion for accuracy would be at the pump flanges. How− ever, this is not usually practical. Gages should be lo− cated as close to the flanges as possible as shown in Figure 8−16. To eliminate an elevation static head correction, the gages on suction and discharges should be at the same height with respect to the pump centerline. If this pre− caution is not taken, the difference in gage elevation, even though usually of small numerical value, must be accounted for in the gage differential.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

8.11


versed or if one or both gages were located below the horizontal pipe or pump centerline. Gate Valve

Unacceptable Locations

Gate Valve Check Valve

Strainer

Pump

Preferable Location on Each Side

Acceptable Location Each Side

FIGURE 8-16 GAGE LOCATION

In Figure 8−17 there is a physical difference in height of 2 feet (0.6 m). If the gage pressure, when converted, measured 50 feet (15 m) on the discharge and 30 feet (9 m) on the suction, subtraction alone would indicate a differential of 20 feet (6 m). However, with respect to the discharge gage which is two feet (0.6 m) lower in the piping, the suction gage reads two feet (0.6 m) of head too little, and at the same elevation as the dis− charge gage would read 32 feet (9.6 m). The correct differential is then 50 − 32 = 18 feet (15 − 9.6 = 5.4 m). A similar analysis would apply if the positions were re−

TWO-PUMP OPERATION

Fluid Viscosity

It should be noted that as long as the head − fluid flow curve is based on feet (meters) of head, no correction need be made for temperature or density since feet (meters) of head and gallons per minute (liters per sec− ond) account for these factors. However, density does increase the pump power requirements. The pump wa− ter power curves are developed at near maximum den− sity at approximately 85F (29C). Since density de− creases as temperature rises, pump water power will decrease, but the change usually is ignored. Viscosity can change the pump impeller head capacity curve provided the change in viscosity is greater than the change of water viscosity between 40F and 400F (4C and 204C). The effect on the curve is illustrated in Figure 8−18.

2 ft (0.6m)

Pump PUMP HEAD CAPACITY CURVES TWO PUMPS

100% DESIGN HEAD

SYSTEM AND PUMP HEAD

8.3.2

Difference in Gage Readings is Not Pump Differential

ONE-PUMP

FIGURE 8-17 RELATIVE GAGE ELEVATIONS

MAXIMUM POINTS

ONE-PUMP OPERATION

OF OPERATION

8.3.3

Installation Criteria

SYSTEM HEAD CURVE 50% DESIGN HEAD

Some of the important points for the TAB technician to consider in installing a pump are:

INDEPENDENT HEAD

100% DESIGN FLOW

a.

suction piping should be air tight and free of air traps

b.

piping should provide a smooth flow into the suction without unnecessary elbows

c.

suction pipe should be one or two sizes larger than pump inlet (eccentric reducer or reduc− ing elbow to connect inlet to piping)

d.

reduce or eliminate restrictions at pump suc− tion

SYSTEM FLOW

FIGURE 8-15 PUMP AND SYSTEM CURVES FOR SERIES PUMPING

8.12

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


e.

piping supported independently of pump cas− ing

f.

use of vertical silent check valve in pump dis− charge in multi−pump installations

g.

manual air vent in pump casing and piping

h.

pressure gages on suction and discharge at same elevation

i.

when vibration isolation is used, isolate pip− ing and pump as a system (preferable), or pro− vide pump isolators and piping flexible con− nectors

j.

recheck pump alignment after installation even if guaranteed by manufacturer

k.

lubricate prior to start up

l.

check rotation, but do not run mechanical seals dry

Total Head

Water Impeller Curve

Increased Viscosity Curve for Same Impeller

Flow

Boiler heating surface is the area of fluid backed sur− face exposed to the products of combustion, or the fire side surface. Various codes and standards define al− lowable heat transfer rates in terms of heating surface. Boiler design provides for connections to a piping sys− tem which delivers heated fluid to the place of use and returns the cooled fluid to the boiler. 8.4.2

Heat exchangers or converters are used as heat sources for many hot water heating systems. Heat exchangers may be of three general types: a) steam−to−water, b) water−to−water, or c) water−to−steam (generators). Steam−to−water heat exchangers usually take the form of shell and tube units. Steam is admitted to the shell, and water is heated as it circulates through the tubes. Steam−to−water converters are useful where an addi− tion is to be made to an existing steam system and where hot water heating is desired. They are also wide− ly used in areas where district steam is available and individual buildings are to be heated with a hot water system. High rise buildings can be zoned vertically by using steam distribution and installing converters at various levels to serve several floors, thus limiting maximum operating pressures in the zone. Water−to−water heat exchangers (generally shell and tube units) are used in high temperature water (HTW) systems to produce lower temperature water for cer− tain zones or in process water or domestic water ser− vices. Water−to−steam heat exchangers generally consist of U−tube bundle installed in a tank or pressure vessel to provide space for the release of steam. They are used in HTW systems to provide process steam where re− quired. 8.4.3

FIGURE 8-18 EFFECT OF VISCOSITY

Heat Exchangers

Water Chillers

8.4

HYDRONIC HEATING AND COOLING SOURCES

The source of cooling in a chilled water or a dual tem− perature system is a water chiller. There are three gen− eral types of water chillers: (1) reciprocating, (2) cen− trifugal, and (3) absorption. For further information, see the 2000 ASHRAE Systems and Equipment Hand− book.

8.4.1

Boilers

8.4.4

A boiler is a cast iron or steel pressure vessel heat ex− changer, designed with and for fuel burning devices and other equipment to burn fossil fuels (or use electric current) and transfer the released heat to water (in wa− ter boilers) or to water and steam (in steam boilers).

Heat Pumps

A heat pump may serve as a source for both hot water and chilled water in a dual temperature system. Heat pumps are described in the 2000 ASHRAE Systems and Equipment Handbook. Water temperatures avail− able are generally low in winter (about 90F to 130F

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

8.13


or 32C to 54C) and terminal heat transfer must be designed for operation under these conditions. In some cases, a supplementary heat source is used to raise temperature levels. 8.5

TERMINAL HEATING AND COOLING UNITS

8.5.1

General

Many types of terminal units are available for central water systems. Some are suited to only one type of sys− tem and others may be used in all types of systems. Terminal units may be classified in several ways. 8.5.1.1

Natural Convection

Natural convection units include cast iron radiators, cabinet convectors, baseboard and finned tube radi− ation are used in heating systems. 8.5.1.2

Forced Convection

Forced convection units include unit heaters, unit ven− tilators, fan coil units, induction units, air handling units, heating and cooling coils in central station units, and most process heat exchangers. Fan coil units, unit ventilators, and central station units can be used for heating, ventilating and cooling. 8.5.1.3

Radiation

Radiation units include panel systems, unit radiant panels, and certain special types of cast iron radiation. All transfer some heat by convection. Such units are generally used for heating in low temperature water (LTW) systems. However, special designs of overhead radiant surfaces, both tubular and panel, are being used in medium and high temperature water systems to take advantage of the lowered surface requirements achieved through the use of high surface temperatures. Panel cooling is applied in conjunction with control of space humidity to maintain the space dew point below the panel surface temperature. 8.5.1.4

Mixing Different Types Of Units

In any single circuit having similar loads and a single control point, the terminal units should be of similar response types. Cast iron radiation should not be installed in the same controlled circuit as baseboard or fin tube type units. Caution should be exercised when including fan operated units with natural convection units on the same pumping circuit. 8.14

8.5.2

Radiators And Convectors

Cast iron radiation and cabinet convectors have been widely used in LTW systems. Ceiling hung radiators frequently were used where floor space was not avail− able for other types of units. Convectors are used ex− tensively in areas where high output is needed and lim− ited space is available, and where linear heat distribution is not desired. Typical areas heated with radiators or convectors include corridors, entries, toi− let rooms, storage areas, work rooms, and kitchens. 8.5.3

Baseboard And Fin Tube Radiation

Baseboard and fin tube radiation permits the blanket− ing of exposed surfaces for maximum comfort. Base− board and fin tube elements are generally rated at vari− ous average water temperatures and at one or more water velocities. Velocity corrections may be applied. Many designers feel that these units are thus limited to systems designed to a 20F (11C) temperature drop. However, careful selection can result in successful ap− plication with temperature drops much higher than 20F (11C). 8.5.4

Unit Ventilators

Unit ventilators, originally developed for specific ap− plication in school classrooms, are being used today in a much wider range of applications. Unit ventilators consist of a forced convection heating or cooling unit with dampers permitting introduction of controlled amounts of outdoor air to provide a complete cycle of heating, ventilating, ventilation cooling, or mechani− cal cooling as required. Condensation may be a prob− lem during summer operation unless chilled water flow is stopped when fans are not operating. Conden− sate drains are necessary. Comparatively low supply temperature and rise may be required. 8.5.5

Fan Coil And Induction Units

Fan coil units are generally used, with or without out− door air, in dual temperature water systems. The same coil is often used for both heating and cooling. Individ− ual control is usually achieved by the use of valves, or by using intermittent or multi−speed fan operation. Hot water ratings are usually based on flow rates or tem− perature drops at various entering water and air tem− peratures. Temperature drops of 40F to 60F (22C to 33C) frequently are used. Induction units are simi− lar to fan coil units except that air circulation is pro− vided by a central air system which handles part of the load, instead of a blower in each cabinet. 8.5.6

Unit Heaters

Unit heaters are available in several types: a) horizon− tal propeller fan, b) downblow or c) cabinet. They are

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


used where high output in a small space is required, and where no cooling is to be added. Cabinet units are frequently applied in corridors and at entrances to

blanket doors which are frequently opened. Normally, unit heaters do not provide ventilation air.

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;˘ Third Edition

8.15


THIS PAGE INTENTIONALLY LEFT BLANK

8.16

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition


CHAPTER 9

HYDRONIC SYSTEMS


CHAPTER 9 9.1

HYDRONIC SYSTEMS

9.1.1

General

HYDRONIC SYSTEMS 9.1.2.2

Medium Temperature Water Systems (MTW)

A hydronic or all water system is one in which hot or chilled water is used to convey heat to or from a condi− tioned space or process through piping connecting a boiler, water heater, or chiller with suitable terminal heat transfer units located at the space or process.

Medium temperature systems are hot water heating systems that operate at temperatures of 350F (177C) or less, with pressures not exceeding 150 psi (1035 kPa). The usual design supply temperature is approxi− mately 250F to 325F (121C to 163C), with a usu− al pressure rating for boilers and equipment of 150 psi (1035 kPa).

All water systems may be classified by:

9.1.2.3

a.

temperature

b.

generation of flow

c.

pressurization

d.

piping arrangement

e.

pumping arrangement

In terms of flow generation, hot water heating systems are of two types: (1) the gravity system, in which cir− culation of the water is due to the difference in weight between the supply and return water columns of any circuit or system; and (2) the forced system in which a pump, usually driven by an electric motor, maintains the necessary flow. Water systems can be either once− through or recirculating systems.

High temperature systems are hot water heating sys− tems that operate at temperatures over 350F (177C) and pressures of about 300 psi (2070 kPa). The maxi− mum design supply water temperature is 400F to 450F (204C to 232C), with a pressure rating for boilers and equipment of about 300 psi (2070 kPa). It is necessary that the pressure temperature rating of each component be checked against the design charac− teristics of the particular system. 9.1.2.4

Temperature Classifications

Water systems may be classified according to operat− ing temperature as follows. 9.1.2.1

Low Temperature Water Systems (LTW)

Low temperature systems are hot water heating sys− tems that operate within the pressure and temperature limits of the ASME boiler construction code for low pressure heating boilers. The maximum allowable working pressure for low pressure heating boilers is 160 psi (1104 kPa) with a maximum temperature limi− tation of 250F (121C). The usual maximum work− ing pressure for boilers for LTW systems is 30 psi (207 kPa), although boilers specifically designed, tested, and stamped for higher pressures may frequently be used with working pressures to 160 psi (1104 kPa). Steam−to−water or water−to−water heat exchangers also are used.

Chilled Water System (CW)

A chilled water system operates with a normal design supply water temperature of 40F to 55F (4C to 13C) and a pressure range of 125 psi (62 kPa). Anti− freeze or brine solutions may be used for systems (usu− ally process applications) that require temperatures below 40F (4C). Well water systems may use supply temperatures of 60F (16C) or higher. 9.1.2.5

9.1.2

High Temperature Water Systems (HTW)

Dual Temperature Water System (DTW)

A dual temperature system is a combination hot water heating and chilled water cooling system that circu− lates hot and/or chilled water to provide heating or cooling using common piping and terminal heat trans− fer apparatus. They are operated within the pressure and temperature limits of LTW systems, with winter design supply water temperatures of 100F to 150F (3C to 66C) and summer supply water temperatures of 40F to 55F (4C to 13C). 9.1.3

Piping Classifications

Generally, the most economical hydronic distribution system layout has pipe mains that are run by the short− est and most convenient route to the terminal equip− ment that has the largest flow rate requirements. Branch or secondary circuits then are connected to these mains. Hydronic distribution mains are most frequently lo− cated in corridor ceilings, above hung ceilings, along

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

9.1


a perimeter wall, in pipe trenches, in crawl spaces and in basements. System piping need not be run at a defi− nite level or pitch, but may change up or down as re− quired by architectural or structural needs. Hydronic system piping may be divided into two arbitrary size classificationsCsmall systems and large systems. 9.1.3.1

Small Systems

Piping circuits suitable for complete small systems or for terminal or branch circuits on large systems consist of: a.

series loops

b.

one−pipe systems

c.

two−pipe reverse return systems

d.

two−pipe direct return systems

9.1.3.2

Large Systems

Main distribution piping used to convey water to and from terminal units or circuits in large systems consist of: a.

two−pipe direct return systems

b.

two−pipe reverse return systems

c.

three−pipe systems

d.

four−pipe systems

9.1.3.3

Pump

Series Loop System

A series loop system is a continuous run of pipe or tube from a supply connection to a return connection. Ter− minal units are a part of the loop. Figure 9−1 shows a system of two series loops on a supply and return main (split series loop). One or more series loops may be used in a complete system. Loops may connect to mains, or all loops may run directly to and from the boiler. The water temperature drops progressively as each ra− diator transfers heat to the air, the amount of drop de− pending on radiator output and the water flow rate.

Boiler Adjusting Cock

FIGURE 9-1 A SERIES LOOP SYSTEM considered one radiator, and all units can be sized at the AWT of the loop. One floor of a small dwelling with open interior doorways is such an interconnecting space. If individual units on a loop are in separate en− closed spaces, each unit must be sized at the actual AWT at that point. A decrease in loop water flow rate increases the tem− perature drop in each unit and in the entire loop. The average water temperature shifts downward progres− sively from the first to the last unit in the series. Conse− quently, comfort may not be able to be maintained in separate spaces heated with a single series loop if wa− ter flow rate is varied. Control of output from individu− al terminal units on a series loop is impractical except by control of heated airflow. Manual dampers can be used on natural convection units; automatic fan or face and bypass damper control can be used on forced air units.

One Special Return Fitting (Upfeed) Boiler

Pump Downfeed (Two Special Fittings)

The true system operating water temperature and flow rate must be known to calculate the average water temperature (AWT) for each unit in the loop. If all ter− minal units are in series on one loop in one zone of in− terconnecting air space, the entire set of units can be 9.2

FIGURE 9-2 A ONE-PIPE SYSTEM

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


9.1.3.4

One Pipe System (Diverting Fitting)

One−pipe circuits form a single loop to and from the boiler. For each terminal unit, a supply and a return tee are installed on the same pipe main. One of the two tees is a special diverting tee which creates a pressure drop in the fluid flow to divert a portion of the flow to the unit. One (return) diverting tee usually is sufficient for upfeed (units above main) systems. Two special fit− tings (supply and return tees) are usually required for downfeed units to overcome the thermal head. Special tees are proprietary, so consult the manufacturer’s lit− erature for flow rates and pressure drop data. One−pipe circuits allow manual or automatic control of flow to individual connected heating units. On−off control rather than flow modulation control is advis− able because of the relatively low pressure drop and low diverted flow. Piping length and load imposed on a one−pipe circuit are usually small because of the lim− itations listed.

ed balancing fitting pressure drops at the same flow rate. 9.1.3.6

Combination Piping Systems

The basic piping circuits exist only to describe func− tion as one type can grade into another. A piping sys− tem can contain one or more types and thus cannot be described as a particular type. Figure 9−5 illustrates a primary circuit and two secondary pumping circuits. As pipe lengths and number of units vary, and as circuit types are combined, basic names for piping circuits be− come meaningless; flow, temperature, and head must be determined for each circuit and for the complete system.

T S

9.1.3.5

Two-Pipe Systems R

Two−pipe circuits may be direct return where the re− turn main flow direction is opposite the supply main flow and the return water from each unit takes the shortest path back to the boiler; or reverse return where the return main flow is in the same direction as the sup− ply flow. After the last unit is supplied, the return main returns all water to the boiler. The direct return system is popular because less piping is required; however, circuit balancing valves usually are required on all units and/or sub−circuits. Since water flow distance from and to the boiler is virtually the same through any unit on a reverse−return system, balancing valves are adjusted less. Operating (pumping) costs are likely to be higher with direct return piping because of the add−

Z Y X Terminal Units Pump

Boiler or Chiller

FIGURE 9-3 DIRECT RETURN TWO-PIPE SYSTEM

Pump

Terminal Units Boiler or Chiller

FIGURE 9-4 REVERSE RETURN TWO-PIPE SYSTEM

9.1.3.7

Three-Pipe Systems

The three−pipe system satisfies variations in load by providing independent sources of heating and cooling to a terminal unit in the form of constant temperature, primary and secondary chilled, and warm water. The terminal unit contains a single secondary water coil. A modulating three−way valve at the inlet of the coil admits water from either the warm water or cold water supply, as required. The water leaving the coil is carried in a common return pipe to either the secon− dary cooling or heating equipment. The usual room control for three−pipe systems is a special three−way modulating valve that modulates either the warm or the cold water in sequence, but does not mix the streams. The cold primary air is furnished at the same temperature all year. During the period between seasons, if both hot and cold secondary water is available, any unit can be op− erated within a wide capacity range from maximum

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

9.3


Control Valves

Terminal Unit 3-W ay control Valve for secondary circuit

Common Flow

Secondary Pump

Common Flow Secondary Pump B

C

D

Balance Cock

Boiler or Chiller

E

F A

Primary Pump

FIGURE 9-5 EXAMPLE OF PRIMARY AND SECONDARY PUMPING CIRCUITS

cooling to maximum heating within the limits set by the temperature of the secondary chilled or warm wa− ter. Any unit in the system can be operated through its full range of capacity without regard to the operation of any other unit in the system, recognizing the operat− ing cost penalty that will result from simultaneous heating and cooling loads. All units are selected on the basis of their peak capacity requirements.

The three−way control valves used (Figure 9−6) are a special design in which the hot port gradually moves from open to fully closed, and the cold port gradually moves from fully closed to open. The valves are constructed so that at mid−range there is an interval in which both ports are completely closed. Room control action is the same during all seasons. 9.4

9.1.3.8

Four-Pipe Systems

Four−pipe systems used for induction, fan coil, or ra− diant panel systems derive their name from the four pipes connected to each terminal unit. These pipes connect to the cold water supply, cold water return, warm water supply, and warm water return. The four− pipe system satisfies variation in cooling and heating to the room unit in the form of constant temperature primary air, secondary chilled water, and secondary warm water. The terminal unit usually is provided with two inde− pendent secondary water coils, one served by warm water, the other by cold water. The primary air is cold and remains at the same temperature year−round. Dur− ing peak cooling and heating, the four−pipe system performs in a manner similar to the two−pipe system,

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


with essentially the same operating characteristics. During the period between seasons, any unit can be op− erated at any capacity level from maximum cooling to maximum heating, if both cold water and warm water are being circulated. Any unit can be operated at or be− tween these extremes without regard to the operation of any other unit.

T UNIT THERMOSTAT

HOT WATER RETURN

R

HOT WATER SUPPLY

HOT COIL CONTROL VALVE COLD COIL

Since the primary air is supplied at a constant cool tem− perature at all times, it is sometimes feasible for fan coil or radiant panel systems to extend the interior sys− tem supply to the perimeter spaces, eliminating the need for a separate primary air system. The type of ter− minal unit and the characteristics of the interior system will be determining factors.

T

CHECK VALVE

UNIT THERMOSTAT

COLD WATER RETURN A - SEPARATE COILS

COLD WATER SUPPLY

T UNIT THERMOSTAT R HOT WATER RETURN

HOT WATER SUPPLY

COMMON SECONDARY WATER COIL

COLD WATER RETURN

2 - POSITION DIVERTING VALVE

SEQUENCE VALVE

COMMON SECONDARY WATER COIL COMMON RETURN

FIGURE 9-6 RETURN MIX SYSTEM ROOM UNIT CONTROLS

The four−pipe terminal unit is usually provided with two completely separated secondary water coils, one receiving hot water and the second receiving cold wa− ter. The coils are operated in sequence by the same thermostat. The coils are never operated simulta− neously, and the unit receives either hot water or cold water in varying amounts, or else no flow is present. This is shown in Figure 9−7A. Figure 9−7B illustrates another unit and control config− uration which sometimes is used. A single secondary water coil is provided at the unit, and three−way valves located at the inlet and leaving side of the coil admit the water from either the warm or cold water supply, as required, and divert it to the appropriate return pipe. This arrangement requires a special three−way modu− lating valve, originally developed for one form of the three−pipe system, described earlier, which controls the warm or cold water selectively and proportionally but does not mix the streams. The valve at the coil out−

COLD WATER SUPPLY

FIGURE 9-7 FOUR PIPE SYSTEM ROOM UNIT

SEQUENCE VALVE COLD WATER SUPPLY

HOT WATER SUPPLY

let is a two−position valve that opens to either the warm or cold water return. 9.1.4

Hydronic Piping Devices

9.1.4.1

Air Control And Venting

If air and other gases are not eliminated from hydronic flow circuits, they may cause air binding in the termi− nal heat transfer elements and noise in the piping cir− cuits. High points in piping systems and terminal units should be vented with manual or automatic air vents. As automatic air vents may malfunction, valves should be provided at each vent to permit service or re− placement without draining the system. If a common tank is used for an expansion tank, free air should be routed from the piping circuit into the expansion tank by a boiler dip tube or air separation device. If a dia− phragm−type tank is used, all air should be vented from the system at all high points. 9.1.4.2

Drains And Shut-Offs

All low points should be equipped with drains. Provi− sions should be made for separate shutoff and drain of individual equipment and circuits so that the entire system does not have to be drained for service of a par− ticular item.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

9.5


9.1.4.3

Balance Fittings

Balance fittings should be applied as needed to permit balancing of individual terminal units and major sub− circuits. Such fittings should be placed at the circuit re− turn when possible. 9.1.4.4

Pitch

9.1.4.6

Thermometers or thermometer wells assist the system operator and the TAB technician, and may be used for troubleshooting. Permanently installed thermometers with separable sockets should be used at all points where temperature readings are regularly needed. Thermometer wells only may be installed where read− ings will be needed during start−up and balancing. 9.1.4.7

Hydronic piping need not be pitched, but may be run level, provided that flow velocities in excess of 1.5 feet per second (0.45 m/s) are maintained. 9.1.4.5

Strainers

Strainers should be used where necessary to protect the elements of a system. Strainers at the pump suction need to be large enough to avoid cavitation. Large sep− arating chambers are available, which serve as both main air venting points and dirt strainers. Automatic control valves require protection from particles that may readily pass through the pump and its larger mesh strainer. Individual fine mesh strainers may therefore be required ahead of each control valve. If a cooling tower is used, the strainer provided in the tower basin usually is adequate.

9.6

Thermometers

Flexible Connections

Flexible connectors are installed at pumps and ma− chinery to reduce vibration into the piping circuit. However, vibrations may be transmitted through the water across flexible connections, reducing the effec− tiveness of the connectors. Flexible connectors, how− ever, do prevent damage caused by slight misalign− ment of equipment connections to the piping. 9.1.4.8

Gages

Gage cocks should be installed at points where pres− sure readings will be required. At a minimum, these shall be located immediately entering and leaving each devise to be measured. There must be no fittings or transistors between port location and device. Note that gages permanently installed in the system may de− teriorate due to vibration and pulsation, and may not be reliable when needed.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


SYMBOLS GATE VALVE FLOW OR WEIGHTED CHECK VALVE AIR CONNECTION

ADJUSTING COCK GLOBE VALVE

EXPANSION TANK

GAGE GLASS

AUTO MIXING VALVE CIRCULATING PUMP

WATER FEEDER

DRAIN

A

ALTITUDE GAGE

ZONE SUPPLIES

THERMOMETER

MANUAL AIR VENT

A

A

A BOILER

BOILER

AIR SEPARATOR

DRAIN

DRAIN

DRAIN ZONE RETURN

FIGURE 9-8 BOILER PIPING FOR A MULTIPLE-ZONE, MULTIPLE-PURPOSE HEATING SYSTEM

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition

9.7


COMPLAINT POSSIBLE CAUSE

RECOMMENDED ACTION

Shaft misalignment

 Check and realign

Worn coupling

 Replace and realign

Worn pump/motor bearings

 Replace, check manufacturer’s lubrica− tion recommendation  Check and realign shafts

Improper founda− tion or installation

Pump or system noise

 Check foundation bolting or proper grout− ing.  Check possible shift− ing due to piping expan− sion/contraction  Realign shafts.

COMPLAINT POSSIBLE CAUSE

RECOMMENDED ACTION

Pump running backwards (3-phase)

 Reverse any two-motor leads.

Broken pump coupling

 Replace and realign

Improper motor speed

 Check motor nameplate wiring and voltage.

Pump (or impeller diameter) too small

 Check pump selection (impeller diameter) against specified system requirements.

Clogged strainer(s)

 Inspect and clean screen.

Inadequate or no circulation

Pipe vibration and/ or strain caused by pipe expansion/ contraction

 Inspect, alter or add hangers and expansion provision to eliminate strain on pump(s)

System not completely filled

 Check setting of PRV fill valve.  Vent terminal units and piping high points

Water velocity

 Check actual pump performance against spe− cified and reduce impel− ler diameter as required.  Check for excessive throttling by balance valves or control valves.

Balance valves or isolating valves improperly set

 Check settings and adjust as required.

Air-bound system

 Vent piping and terminal units.  Check location of expansion tank connection line relative to pump suction.  Review provision for air elimination.

Pump Operating close to or beyond end point of perfor− mance curve

 Check actual pump performance against spe− cified and reduce impel− ler diameter as required.

Table 9-1 Hydronic Trouble Analysis Guide

9.1.4.9

Pump Location

Pump location varies with the size and type of system. Figures 9−3, 9−4 and 9−8 illustrate pumps in the supply main from the boiler or chiller, while Figures 9−2 and 9−5 have the pumps in the return piping. A pump (cir− culator) in the boiler return is acceptable for small sys− tems when pump head is at 12 foot (3.6 m) head or less, the compression tank is on the boiler (or a nearby main), and the highest piping and radiation is main− tained at a static pressure greater than full pump head. These conditions apply to most residential systems. When the pump head is equal to or greater than the dif− ference between the boiler fill and relief valve dis− charge pressures, or when the highest piping or radi− ation can be at a static pressure less than the total pump head, the pump(s) must be located on the supply side of the boiler with the compression tank at the pumps inlet, as illustrated in Figure 9−8. This assures that pump cycling will not cause excessive pressure varia− tions in the boiler that will create subatmospheric pres− sure at topmost system points causing air leakage into 9.8

the system. Pump cavitation is prevented by locating a properly sized compression tank near the pump inlet. 9.1.4.10 Trouble Shooting Table 9−1 is a handy chart for the TAB technician to use when balancing a hydronic system and/or when trouble is encountered. This list may be expanded as experience dictates. 9.2

HYDRONIC SYSTEM DESIGN

9.2.1

Closed Loop Systems

9.2.1.1

General

Pipe sizes for heating and chilled water systems should be based on clean pipe pressure drop charts. This is be− cause the system is closed, eliminating most normal corrosion to the piping. The use of pressure drop charts based on age−corroded pipe leads to oversized piping and pumps, which together will result in unwarranted system flow rates in excess of design. The excess flow and pressure heads, in turn, may cause control prob−

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


lems, system noise, pumping troubles, and excessive pumping power usage. All hydronic system sizing charts may be found in the Appendix, Engineering Data, Tables and Charts. 9.2.1.2

General Design Range

The general range of pipe friction loss used for design of hydronic systems occurs between 1 to 4 ft/100 ft (0.1 to 0.4 kPa/m). A value of 2.5 ft/100 ft (0.25 kPa/m) represents the mean to which many systems are desig− ned. Wider ranges may be used in specific designs, if the precautions described below are considered. 9.2.1.3

Piping Noise

Closed loop hydronic system piping generally is sized below certain arbitrary upper limits, a velocity limit of 4 fps (1.2 m/s) for 1 inch pipe and under, and a pressure drop of 4 ft/100 ft (0.4 kPa/m) for piping over 1 inch diameter. Velocities in excess of 4 fps (1.2 m/s) may be used in piping of larger size, although they normally are not used for smaller pipe sizing. This limitation is generally accepted, although it is based on relatively inconclusive experience with noise in piping. It seems apparent that water velocity noise is caused, not by wa− ter, but by free air, sharp pressure drops, turbulence, or a combination of these, which in turn cause cavitation, or flashing of the water into steam. Therefore, higher velocities may be used if proper pre− cautions are taken to eliminate air and turbulence. Be− cause piping noise can be caused by free air, hydronic systems must be equipped with sufficient air separa− tion devices to minimize entrained air in the piping cir− cuits. 9.2.1.4

9.2.1.5

Valve And Fitting Pressure Drop

Valve and fitting pressure drop usually is listed in el− bow equivalents. The elbow equivalent relates the pressure drop through a valve or fitting to an equiva− lent length of pipe. The pressure drop of one elbow is approximately the same as that of a length of straight pipe 25 times the pipe diameter. Tables may be found in the Appendix under Engineering Data, Tables and Charts.

Example 9.1 (I−P) Determine the equivalent feet of pipe for a 4 inch open gate valve at a flow velocity of 4 fps (use Tables and Figures in the Appendix).

Solution From Table A−21, at 4 fps, each equivalent elbow is equal to 10.5 feet of 4 inch pipe. From Table A−23, a gate valve is equal to 0.5 elbows. The actual equivalent pipe length (added to measured circuit length for pres− sure drop determination) will be 10.6  0.5 = 5.3 equivalent feet of 4 inch pipe.

Example 9.1 (SI) Determine the equivalent meters of pipe for a 100 mm open gate valve at a flow velocity of 1.33 m/s (use Tables and Charts in Appendix A).

Air Purge Velocities

Air will be entrained in and carried along with the wa− ter flow at velocities of 1.5 to 2 fps (0.45 to 0.6 m/s) or more in pipe sizes 2 inches and under. Minimum ve− locities of 2 fps (0.6 m/s) are therefore recommended. For pipe sizes 2 inches and over, minimum velocities corresponding to a head loss of 0.75 ft/100 ft (0.075 kPa/m) normally are used. Attention to maintenance of minimum velocities should be observed in the upper floors of higher buildings because air may come out of solution because of reduced pressures. Higher veloci− ties should be used for downfeed return mains at air separation units.

Solution From Table A−22, at 1.33 m/s, each equivalent elbow is equal to 3.2 meters of 100 mm pipe. From Table A−23, a gate valve is equal to 0.5 elbows. The actual equivalent pipe length will be 3.2  0.5 = 1.6 equiva− lent meters of 100 mm pipe. Pressure drop through pipe tees varies with flow through the branch. Pressure drops are illustrated in Figure A−7 for tees of equal inlet and outlet sizes, and for the flow patterns illustrated.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

9.9


Example 9.2 (I−P) Determine the main equivalent pipe length for a 4 inch tee (size of all openings) flowing 25% to a side branch, 75% through the tee at an entering velocity of 3 fps.

Example 9.3 (I−P) Determine the side branch equivalent length for a 100 mm tee (all openings) with the same flow ratios as in Example 9.2.

Solution Solution From Table A−23, the number of equivalent elbows as applied to the main flow in the tee is equal to 0.15 el− bows. A 4 inch elbow is equivalent to 10.2 feet of 4 inch pipe (Table A−21), so the equivalent length of 4 inch pipe is 0.15  10.2 = 1.5 feet.

From Table A−21, the side branch elbow equivalent is about 13. Thus, the side branch equivalent length would be 13  3.1 = 40.3 meters of 100 mm pipe. Most tees are sized to a reduced side branch flow, in which case the curve in Figure A−7 does not apply ex− cept through the main. The side branch pressure drop, in any case, will not exceed 2 elbow equivalents for the branch pipe size in question.

Example 9.2 (SI) Determine the main equivalent pipe length for a 100 mm tee (size of all openings) flowing 25 percent to a side branch, 75 percent through the tee at an entering velocity of 1.0 m/s.

Example 9.4 (I−P) Determine the side branch equivalent length for a 4  4  2 inch tee with 100 gpm entering the tee and 50 gpm flowing out the side.

Solution

Solution

From Table A−23, the number of equivalent elbows as applied to the main flow is equal to 0.15 elbows. A 100 mm elbow is equivalent to 3.1 meters of 100 mm pipe (Table A−22), so the equivalent length of 100 mm pipe is 0.15  3.1 = 0.47 meters.

The side branch loss is approximately that of 2 equiva− lent elbows. For 2 inch pipe, each equivalent elbow is equal to about 5 feet. Thus, the side branch equivalent length is 2  5 = 10 equivalent feet of 2 inch pipe.

Example 9.4 (SI) Example 9.3 (I−P) Determine the side branch equivalent length for a 4 inch tee (all openings) with the same flow ratios as in Example 9.2.

Determine the side branch equivalent for a 100  100  50 mm tee with 6 L/s entering the tee and 3 L/s flow− ing out the side.

Solution Solution From Table A−23, the side branch elbow equivalent is about 13. Thus, the side branch equivalent length would be 13  10.2 = 133 feet of 4 inch pipe.

The side branch loss is approximately that of 2 equiva− lent elbows. For 50 mm pipe, each equivalent elbow is equal to about 1.5 meters. Thus the side branch equivalent length is 2  1.5 = 3 equivalent meters of 50 mm pipe. 9.2.1.6

It should be noted that the actual pipe friction loss through a 4 inch side branch pipe could actually be lower because of reduced side branch flow rates. 9.10

Water Flow-Pressure Drop

The energy head required to force water through pip− ing, valves and fittings, or heat transfer elements var−

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


ies as the square of the change in water flow rate, as previously stated in Chapter 8. With conditions of flow and energy head (pressure drop) known at one point, one can determine pressure drop for any other flow rate by using Equation 8−2 (from Chapter 8).

H2 Q2   H1 Q1

be used to compute pressure drop through the valve at any flow rate. If the pressure drop and flow are known, the valve selection can be made in terms of a specific Cv rating.

2

DP 

CQ

Equation 9-1 2

v

Where:

Where:

H= Head – ft water (m water) Q = Flow – gpm (L/s or m3/s)

DP  Pressuredrop  psi(kPa) Q  Flow  gpm(m3sorLs) C v  Valveconstant(dimensionless) Example 9.6 (I−P)

Example 9.5 (I−P) Determine the pressure drop at 1 gpm for a fan coil unit that has a catalog rating of a 4 foot pressure drop at a flow rate of 2 gpm.

Calculate the Cv rating for a control valve to be se− lected for a pressure drop of 5 psi at a flow rate of 20 gpm.

Solution Using Equation 9−1: Solution H 2  H 1

QQ

2

2 1

2

H 2  4 1   1ftwater 2

Determine the pressure drop at 0.06 L/s for a fan coil unit that has a catalog rating of a 1.2 meter pressure drop at a flow rate of 0.12 L/s.

Q H 2  H 1 2 Q1

CQ

2

v

Q C v    20  8.95 DP 5

A valve is selected as closely as possible to the Cv rat− ing of 9.

Example 9.5 (SI)

Solution

DP 

Calculate the Cv rating for a control valve to be se− lected for a pressure drop at 34 kPa at a flow rate of 1.25 L/s.

2

Example 9.6 (SI)

2

H 2  1.2 0.06   0.3mwg 0.12 9.2.1.7 Valve Coefficients

Solution DP 

CQ

2

v

Control valve manufacturers state their pressure drop in terms of a coefficient (Cv). The coefficient is numer− ically equal to the flow rate through the valve at which a known pressure drop is obtained. When the Cv is known, the water flow pressure drop relationship can

Q C v    1.25  0.21 DP 34 Check valves, strainers, etc., may also be rated by Cv. When so rated, pressure drop at any given flow may be determined as in Example 9.7.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

9.11


Example 9.7 (I−P ) Calculate the pressure drop in ft wg at 750 gpm for a check valve that has a Cv of 500 (a pressure drop of 1 psi = 2.3 ft).

UNIONS FOR HEAD REMOVAL

OPEN SIGHT DRAIN

THERMOMETERS

T T

Solution DP 

CQ

2 STRAINER

v

Example 9.7 (SI) Calculate the pressure drop in kPa and meters water gage at 50 L/s for a check valve that has a Cv of 12.7 (1 kPa = 0.102 m water).

CQ

DRAIN

2

DP  750   2.25psi 500 DP  2.25psi  2.3  5.18ftwg

DP 

CONDENSER

CONTROL VALVE

2

v

50   15.5kPa 12.7

FIGURE 9- 9 WATER COOLED CONDENSER CONNECTIONS FOR CITY WATER corrosion on a continuing basis. For this reason, the piping will have an increased pressure drop with time, and fouling factors must be included in the condenser design. Provisions also must be made to treat the water for bacteria as well as for scale and corrosion.

2

DP 

DP  15.5kPa  0.102  1.6mwg 9.2.2

Open Systems

9.2.2.1

Condenser Water Systems

Condenser water systems for refrigerant compressors may be classified either as cooling tower systems, or as other systems of the once−through type, such as city water, well water, or pond or lake water systems. They are all open systems, in which air is continuously in contact with the water, and require a somewhat differ− ent approach to pump selection and pipe sizing than do closed heating and cooling systems. Some heat con− versation systems rely on a split condenser heating system which includes a two section condenser. Heat from one section of the condenser is used for heating in closed circuit systems, occasionally interconnected with chilled water systems. The other section of the condenser serves as a heat reject circuit, an open sys− tem connected to a cooling tower. In selecting a pump for a condenser water system, con− sideration must be given to the static head as well as to the system friction loss in sizing the pump. Proper provision must be made to assure an adequate net posi− tive suction head at the pump inlet. In addition, continuous contact with air in an open sys− tem introduces impurities which can result in scale and 9.12

Cooling tower water is available at a temperature sev− eral degrees above the design wet bulb temperature, depending on tower performance. For city, lake, river, or well water systems, the maximum water tempera− ture occurring during the operating season must be used for equipment selection. From manufacturers’ performance data with known condenser water temperature, the required flow rate may be determined for any condensing temperature and capacity. A condensing temperature and corre− sponding flow rate may then be selected to produce the required capacity with a minimum of energy input and purchased water within the load capacity of the driver. 9.2.2.2

Once-Through Systems

Figure 9−9 shows a water cooled condenser using city, well, or river water. The return is run higher than the condenser so that the condenser is always full of water. Water flow through the condenser is modulated by a control valve in the supply line, usually actuated from condenser head pressure to maintain a constant con− densing temperature with variations in load. City wa− ter systems usually require check valves and open sight drains, as shown. When more than one condenser is used on the same circuit, individual control valves are used to avoid balance problems. Piping should be sized in accordance with the prin− ciples outlined earlier in this chapter and in Chapter 2, with velocities of 5 to 10 fps (1.5 to 3.0 m/s) for the

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


flow rates. Where city water is used, a pump is not re− quired. For well or river water, pumps may be neces− sary, in which case the procedure for pump sizing gen− erally would be that indicated below for cooling tower systems. 9.2.2.3

Cooling Tower Systems

Figure 9−10 illustrates a typical cooling tower system for a refrigerant condenser. Water flows to the pump from the tower basin and is discharged under pressure to the condenser and back to the tower. Since it is usu− ally desirable to maintain condenser water tempera− ture above a predetermined minimum, water is di− verted through a control valve to maintain minimum sump temperature. Piping from the tower sump to the pump requires some cautions. Sump levels should be above the top of the pump casing to provide positive prime. Piping pressure drop should be minimized. All piping must pitch up either to the tower or the pump suction to eliminate air pockets. Suction strainers should be equipped with inlet and outlet gages to indi− cate when cleaning is required. Vortexing in the tower basin is prevented by piping connections at the tower in accordance with manufac− turer’s specification and by limiting flow to the maxi− mum allowed by the sump design. A straight section of suction pipe five times the diameter in length con− tributes to achieving expected pump performance.

If multiple cooling towers are to be connected, the pip− ing should be designed so that the pressure loss from the tower to the pump suction is approximately equal for each tower. Large equalizing lines or a common reservoir are used to maintain the same water level in each tower. 9.3

HYDRONIC DESIGN PROCEDURES

9.3.1

Determination Of Flows

Regardless of the method used to determine the flow through each item of terminal equipment, the desired result should be in terms of gpm (L/s). In an equipment schedule or on the plans, starting from the most remote terminal and working back towards the pump, progres− sively list the cumulative flow in each of the mains and branch circuits in the entire hydronic distribution sys− tem. 9.3.2

Preliminary Pipe Sizing

For each portion of the piping circuit, a tentative pipe size is selected from flow charts, in the Appendix, us− ing a value of pipe friction loss ranging from 0.75 to 4 ft per 100 ft (0.075 to 0.4 kPa/m). Residential piping size is often based on pump prese− lection, using pipe sizing tables, which are available

COOLING TOWER

The elements of required pump head are illustrated in Figure 9−10. Since there is an equal head of water be− tween the level in the tower sump and the pump on both the suction and discharge sides, these heads can− cel each other and may be disregarded. The elements of pump head are: static head from tower sump to the tower header; friction loss in suction and discharge piping; pressure loss in condenser; control valves; and strainer and tower nozzles, if used. These elements added in feet (meters) of water determine the required pump total dynamic head.

FLOAT VALVE

ROOF 3-W AY DIVERTING VALVE

MAKE-UP WATER

ALTERNATE BYPASS

T

Normally, piping is sized to yield water velocities be− tween 5 and 12 fps (1.5 to 3.6 m/s). Friction factors for 15 year old pipe commonly used are in the range of 1.5 to 1.75. The pressure drops for condenser, cooling tow− er, control valves, and strainers are obtained from manufacturers’ data. If condensers are installed in parallel, only the one with the highest pressure drop is counted. Combina− tion flow measuring and balancing valves can be used to equalize pressure drops.

GAGES

THERMOMETERS CONDENSER T

CONTROLLER DRAIN

FIGURE 9-10 COOLING TOWER PIPING SYSTEM

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

9.13


from the Hydronics Institute or from pump manufac− turers. 9.3.3

summarized for several of the longest piping circuits, to determine the precise head against which the pump must operate at design flow.

Preliminary Pressure Drop 9.3.6

Using the preliminary pipe sizing indicated above, cal− culate the pressure drop through each portion of the piping. Find the total pressure drop in several of the longest circuits to determine what maximum pressure drop through the piping, including the terminals and control valves, must be available in the form of pump head. 9.3.4

Preliminary Pump Selection

The preliminary selection should be based on the abili− ty of the pump to fulfill the capacity requirements as determined. It should be selected at a point left of cen− ter on the pump curve, and should not overload the mo− tor. Because of the squared relationship between flow and head, it will generally be found that flow capacity variation between the next closest stock selection and an exact point selection will be relatively minor. 9.3.5

Final Piping Layout

An overall examination of the piping layout should be made at this point, to determine if readjustments in the sizes of piping in some areas may be necessary. It is de− sirable to have the pressure drop in a number of the principal circuits be about equal, so that excessive heads are not required to serve a small portion of the building. In determining the final system friction loss, both the first cost of the piping system and the pump, and the operating costs of the pump should be considered. In general, lower heads and larger piping become more economical when longer amortization periods are con− sidered, especially in larger systems. On the other hand, in small systems, e.g., residences, it may be most economical to select the pump first and design the pip− ing system to meet the available head. In any event, ad− justments should be made in the piping system design and in the pump selection, until such time as the opti− mum design has been achieved. When the final piping layout has been established, the friction loss for each section of the piping system can be determined by reading directly from the pressure drop charts. After the friction loss at design flow for all sections of the piping system, all fittings, terminal units, and con− trol valves have been calculated, they should then be 9.14

Final Pump Selection

After the final pressure drop calculations have been completed, a final selection of the pump is made, using the procedure of plotting a system flow and pump curve, and selecting the pump that operates closest to the actual calculated design point. 9.4

STEAM SYSTEMS

9.4.1

General

A steam system does not need to be balanced nor can it be balanced manually in the true sense that air and hydronic systems need to be tested, adjusted and ba− lanced. However, the TAB technician needs to have a working knowledge of steam systems and their rela− tionships to air and hydronic systems. A steam heating system uses the vapor phase of water to supply heat to a conditioned space or a process, con− necting a source of steam, through piping, with suit− able terminal heat transfer units located at the space or process (water heater, fan coil units, or the heating coils of an absorption refrigerating machine). Steam heating systems are referred to as vacuum, return line vacuum, vapor, low, medium, and high pressure sys− tems. They are also referred to as central or district heating systems. The temperature and heating effects of steam systems vary over wide ranges to control space temperatures or heating processes. The steam supply temperature may be controlled according to outdoor temperature in much the same manner as a hot water system. They op− erate at 2188F (1038C) or higher during winter de− sign conditions and as low as 1258F (528C) in mild weather, so that the average temperature of the radi− ation may vary in direct relation to heating demands. 9.4.2

Properties Of Steam

Steam has particular characteristics related to specific volume, temperature, pressure, and heat content. Tables in the Appendix are a condensed version of these properties. Note that the conditions indicated are for saturated steam. This means that the steam at any given temperature and pressure will begin to condense if the temperature is even slightly lowered and will be− come superheated if the temperature is slightly increa− sed. Except when ensuring dry steam at the point of use, there is small advantage to superheating in envi−

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


ronmental systems because the increase in heat con− tent is relatively small for the limited amount of super− heat which might normally be provided.

1000lb.hr. 8.33lb.gal.8 8 60minhr. =M2.0 gpm condensate In a similar manner, the pounds per hour of steam re− quired by the heat exchanger may also be calculated.

Also note that there are three enthalpy figures given. The enthalpy of saturated liquid is the heat content of the water just before evaporation and the enthalpy of saturated vapor is the heat content of the gas just after evaporation. The enthalpy of evaporation is the differ− ence between the two, or the amount of heat in Btu/lb (kJ/kg) required to change from liquid to gas at satura− tion. At standard conditions of 212F (100C) and 14.696 psia (101.325 kPa), this value is 970.3 Btu/lb (2256 kJ/kg), quite a difference from 1 Btu/lb.CF (4.19 kJ/kg.C) for liquid water. By use of the ap− propriate value, the pounds of condensate to be re− turned and pumped may be determined. For example:

970, 300Btuhr.   1000lb.hr.condensate 970.3Btulb.

Similar calculations may be made in metric units. 284, 300WorJs   0.126kgscondensate 2, 256, 00Jkg 0.126 kg/s  60 s/minP=M7.56 kg/min or L/min Once the condensate is formed, it will normally cool below the condensing temperature before returning to the boiler. The reduction in temperature is referred to as sub−cooling. 9.4.3

Types Of Steam Systems

9.4.3.1

Piping Designations

A steam heating system is known as a one−pipe system when a single main serves the dual purpose of supply−

WET RETURN (BELOW W.L.)

DRY RETURN

DRY RETURN

VENT TRAP

DRIP CONNECTION

STEAM MAIN

DRY RETURN

STEAM MAIN

WET RETURN (BELOW W.L.)

A. One-Pipe System

B. Two-Pipe System (Piping Typical of Atmospheric and Vapor System, etc.)

FIGURE 9-11 BASIC PIPING CIRCUITS FOR GRAVITY FLOW OF CONDENSATE

ing steam to the heating unit and conveying conden− sate from it. Each transferring device usually has only one connection which must serve as both the supply and the return, although separate supply and return connections may be used. A steam heating system is known as a two−pipe system when each transferring device is provided with two piping connections, and when steam and condensate flow in separate mains and branches.

9.4.3.2

Steam Flow

Heating systems may also be described as upfeed or downfeed, depending on the direction of steam flow in the risers; and as a dry return or a wet return, depending or whether the condensate mains are above or below the water line of the boiler or condensate receiver.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

9.15


TRAP

DRY RETURN

DRY RETURN

PUMP

PUMP A. Two-Pipe Direct-Return System Return-line vacuum, variable vacuum, subatmospheric, condensation on return, etc.

DRIP TRAP

TRAP

STEAM MAIN

DRIP TRAP

STEAM MAIN

B. Two-Pipe Reversed-Return System

FIGURE 9-12 BASIC PIPING CIRCUITS FOR MECHANICAL RETURN SYSTEMS 9.4.3.3

Return Systems

In gravity systems, the condensate returns to the boiler solely by gravity, but the steam flows by the effect of the steam pressure. When the condensate cannot be re− turned to the boiler by the action of gravity, either traps or pumps must be employed. These systems are known as mechanical return systems, and may be either open return systems or vacuum (closed) systems. In these systems, the condensate flows to the mechanical con− densate returning device by gravity, and the gradient for steam circulation is provided by steam pressure. However, in vacuum systems, the partial vacuum pro− duced by the pump provides a part or all of the gradi− ent, depending on the operating steam pressure. Vacu− um and condensate pumps both return condensate to the boiler. 9.4.3.4

Steam Piping Systems

The functions of the piping system are the distribution of low pressure steam, the return of the condensate, and, in systems where no local air vents are provided, the removal of the air. The distribution of the steam should be rapid, uniform, and noiseless. The release of air should be at a rate equal to or greater than the in− tended steam distribution. An air bound system will not heat readily or properly. In designing the piping ar− 9.16

TRAP

VALVE

STEAM MAIN

TRAP EQUALIZER LINE AIR DISCHARGE

BOILER WATERLINE

PUMP CONTROL

VACUUM HEATING PUMP

DRIP TRAP

RETURN

FIGURE 9-13 TYPICAL TWO-PIPE VACUUM STEAM SYSTEM

Pressures

Steam heating systems may also be classified as high pressure, intermediate (medium) pressure, low pres− sure, vapor, and vacuum systems, depending on the pressure conditions under which the system is de− signed to operate. 9.4.4

rangement, it is desirable to maintain equivalent re− sistances through the supply piping to, and the return piping from, each terminal unit or heat exchanger.

The condensate collecting in steam piping and termi− nal units must be drained to prevent interference with the ready flow of steam and air. It is important that steam piping systems distribute steam not only at full design load, but also during ex− cess and partial loads. Usually, the average winter steam demand is less than half the demand at the de− sign outdoor temperature. Moreover, when rapidly warming up a system even in moderate weather, the load on the steam main and returns momentarily may exceed the maximum operating load for severe weath− er, due to the necessity of raising the temperature of metal in the system to the steam temperature and the building to design indoor temperature.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


The basic tables for checking the sizes of low pressure system steam and condensate return piping may be found in the Appendix of this manual. 9.4.5

THERMOSTATIC DISC ELEMENT

Heating Unit Piping Connections INLET

It is important that the following good practices be fol− lowed when making piping connections to steam heat− ing units.

VALVE AND ORIFICE UNION OUTLET

a.

Condensate from steam main drip traps should not be piped into heating units.

b.

If it is necessary to keep the heater in service at all times, a bypass with globe or plug valve should be installed around the automatic tem− perature control valve.

c.

A strainer should be provided on the steam supply side of a control valve.

d.

The sizing of control valves should be based on the steam load and not on the heater supply connection.

e.

Each heater or bank of heaters installed in se− ries should have a separate trap.

FIGURE 9-14 THERMOSTATIC TRAP In general, steam traps consist of, a) an inlet connec− tion that opens into a chamber or passage into which condensate and non−condensable gases flow, b) an ori− fice through which the condensate and fixed gases are discharged, c) a valve which regulates or throttles the flow through the orifice port, and d) an outlet connec− tion. OPTIONAL INLET

OUTLET INLET

f.

Return piping from heater to trap should be of the same size as the heater outlet connection.

g.

Return piping should not be run to a main which is above the discharge connection of the heater or trap, or into mains under pres− sure regulated by control valves (modulating or on−off), but rather the heater condensate trap should discharge to a pump and receiver, or lifting trap, which then discharges to the overhead main or return main under pressure.

h.

9.4.6

Steam piping and heater sections should be supported independently. Steam Traps & Strainers

Steam traps are important components of most steam heating systems. These devices enable such systems to properly distribute the heating medium, and operate to perform two different functions: (1) to hold steam in the radiation and supply piping until its latent heat has been given up, and (2) while at the same time releasing non−condensables and condensate. Steam traps are usually regarded as drainage devices which release liquids and gases from a higher to a lower pressure.

VALVE AND ORIFICE

AIR VENT

FLOAT

DRAIN

FIGURE 9-15 INVERTER BUCKET TRAP

Without a trap as the means of confining the steam to heat transfer equipment, proper distribution and heat transfer related to the load could not take place since the pressure obtained in each unit is virtually unaf− fected by the pressure in the return piping. All steam traps, except the small thermostatic type and all steam control valves, should have a strainer installed immediately before each unit to prevent pipe scale and other debris from entering and damaging or clogging it. Whenever a TAB technician encounters

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

9.17


9.4.7

THERMOSTATIC DISC ELEMENT

INLET

OUTLET

Steam Systems—Medium And High Pressure

Medium and high pressure systems are used when heat transfer must be accomplished at higher temperatures, either to satisfy process conditions or for economy in equipment and piping costs. Higher pressure steam supply sources may be used to provide thermal capac− ity or to reduce carry over effects. To satisfy actual op− erating conditions, steam generated at higher pres− sures is reduced to various lower pressure levels by one or more pressure regulating stations.

FLOAT VALVE AND ORIFICE

FIGURE 9-16 FLOAT AND THERMOSTATIC TRAP

steam heat transfer equipment that is not operating properly, usually a clogged strainer or defective trap will be the problem if the automatic control valve is operating correctly. Leaking steam traps are a common maintenance prob− lem on all steam systems. Live steam in the return lines can cause overheating by some nearby units and create live steam problems with condensate or vacuum pumps. A critical problem in environmental systems is the re− moval of condensate from coils, especially those for 100 percent outside air. Proper operation dictates even steam flow and distribution in the coil. Condensate trapped in the coil prevents even distribution and should the temperature fall low enough, freeze−up might occur. Air must be allowed to enter the atmo− spheric system coil to prevent tubing collapse during the fall of pressure during initial heating, but it must then be immediately vented to prevent holding con− densate in the coil. Further, the coil must be rapidly drained of condensate so chance freezing can be redu− ced. Even under the best operating conditions, a ?non− freeze" coil (tube−in−tube) can freeze. It is imperative that improper venting and condensate removal is not allowed to add to the possibility.

9.18

Medium and high pressure systems may be classified as follows: 1) medium pressure, 10 to 44 psig (69 to 380 kPa) and 250 to 305F (121 to 152C); at high pressure, 55 to 125 psig (475 to 860 kPa) and 305 to 350F (152 to 177C).

GATE VALVE STRAINER FLOAT AND THERMOSTATIC TRAP

STEAM MAIN

REGULATING VALVE VACUUM EQUALIZER

STRAINER

GATE VALVES

HEATING COILS

DIRT POCKET

DIRT POCKET STRAINER RETURN MAIN

GATE VALVE

FLOAT AND THERMOSTATIC TRAP

FIGURE 9-17 TYPICAL CONNECTIONS TO FINNED TUBE HEATING COILS

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


CHAPTER 10

REFRIGERATION SYSTEMS


CHAPTER 10 10.1

REFRIGERATION SYSTEMS

10.1.1

General Checklist

There is no testing and balancing work for refrigera− tion systems, but TAB technicians must be familiar with them since they affect the work that must be done. The lack of ?cooling" can affect TAB work, so the fol− lowing is a checklist of common problems, assuming that all equipment has been turned on. a.

Check to see if the outdoor air dampers have been properly set as this can place an exces− sive load on the cooling coils.

b.

With direct expansion coils, check to see the air quantity crossing the cooling coil is ade− quate, as frost could be the result of insuffi− cient air.

c.

All automatic temperature control devices should be operating satisfactorily and chilled water should be flowing at the correct tem− perature.

REFRIGERATION SYSTEMS i.

A low water temperature differential across the chiller may also indicate fouling of the tubes.

j.

A low water flow across either condenser or evaporator will produce a high water temper− ature differential.

k.

A malfunctioning safety device such as a flow switch will prevent machine start up even with water flow.

l.

A malfunctioning operating device such as a refrigerant solenoid will prevent proper op− eration and perhaps shut down the machine.

m. Improper operation of centrifugal machine suction damper controller may cause surg− ing of the machine. These and the many other conditions which may occur do not necessarily cause immediate loss of cooling. However, if any are apparent during TAB work, nui− sance calls may be avoided by bringing the conditions to the attention of the responsible parties. 10.1.2

d.

e.

A frosted DX coil can be the result of insuffi− cient system refrigerant and a reduced evapo− rator temperature caused by the compressor trying to meet the load. A cooling tower cell fan shut down or high ambient wet bulb may cause high condenser pressures. The machine may operate, but the condensing temperature could rise above the maximum design. This condition is referred to as high head.

f.

A compressor shutdown may be the result of operation of a safety device such as high con− densing pressure (high head) cutout or low evaporator temperature (freeze protection or low temperature) cutoff.

g.

A water valve closed to condenser and/or chilled water heat exchanger will shut the machine down on a safety switch.

h.

A high water temperature differential across the condenser, even though not sufficient to shut down the machine, may indicate accu− mulation of fouling solids on the water side of the tubes which would require cleaning by rodding or acid.

Refrigeration Cycle

There are four basic components of the compression refrigeration cycle: the pump (compressor), the heat rejector (condenser), the metering device (capillary tube, thermal expansion valve, float valve), and the heat absorber (evaporator, chiller, cooler, direct ex− pansion coil). Figure 10−1 partially defines these com− ponents in terms of function in the cycle, and shows common names used for them. The refrigerant flow from the pump through the heat rejector to the port of the metering device is called the high side of the refrigeration circuit. From the meter− ing device through the heat absorber to the pump is called the low side of the circuit. These two terms refer to both pressure and temperature. The nature of the re− frigerants, which will be discussed further in later paragraphs, produces this effect. Beginning at the evaporator, the liquid refrigerant is boiled off at reduced pressure into a gas as it absorbs heat from the heat exchanger, and water, air or other environmental fluids are cooled by the heat removal. The gaseous refrigerant moves through the suction pipe or line to the compressor, which has reduced the inlet pressure to cause fluid flow. The compressor pumps the gas to the condenser through the hot gas (pipe) line. In the pump, the gas is compressed to a smaller volume, and heat (heat of compression) is add−

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

10.1


Low Side

High Side

Liquid Line Solenoid Valve Sight Glass Expansion Valve (metering device)

Bulb Evaporator (Heat Absorber)

Hot Gas Piping

Suction Piping

Condenser (Heat Rejector)

Compressor (Pump) Low Side

Liquid Receiver

High Side

FIGURE 10-1 REFRIGERANT CYCLE

ed to the low pressure, low temperature gas to produce the high pressure, high temperature conditions found in the high side.

In the condenser heat exchanger, water from a cooling source such as a tower, or air moving across the con− denser coil, converts the high pressure hot gas to a high pressure, warm liquid. This warm liquid moves through the liquid line to the metering device, which allows the proper amount of liquid to flow into the evaporator, where the cycle starts over. Without the metering device, excess liquid would flow, causing loss of evaporator control and likely allowing liquid to enter the compressor, where damage could occur, since the compressor is only designed to pump gas. 10.2

10.2

REFRIGERATION TERMS AND COMPONENTS

10.2.1

Evaporator

The heat exchanger in which the medium being cooled, usually air or water, gives up heat to the refrig− erant through the exchanger transfer surface. The liq− uid refrigerant boils into a gas in the process of heat ab− sorption. Part of the evaporator contains liquid refrigerant, part contains a liquid−gas mixture, and part contains all gas. The amount of each will be deter− mined by the load and the control provided by the me− tering device.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


10.2.2

Thermal Expansion Valve

The metering device or flow control that regulates the amount of liquid refrigerant which is allowed to enter the evaporator. Flow of refrigerant is automatically regulated by the valve reaction to the pressure varia− tions in the sensing bulb being transmitted through the capillary tube to the thermal valve bellows. Since liquid flow to the compressor is undesirable and can be damaging, the thermal expansion valve is usu− ally adjusted to produce approximately 10F (5.6C) superheat in the gas leaving the evaporator to assure a dry condition of this gas entering the compressor. Slugging liquid into the compressor may cause dama− ge. The expansion valve connection to the evaporator may be a single pipe or multiple small pipes to individ− ual circuits. 10.2.3

Capillary Tube

The capillary tube is a metering device made from a thin tube approximately 2 to 20 feet (0.6 to 6 m) long and from 0.025 to 0.090 inches (0.6 to 2.3 mm) in di− ameter which feeds liquid directly to the evaporator. Usually limited to systems of 1 ton or less, it performs most of the functions of a thermal expansion valve when properly sized. 10.2.4

Suction Piping

Suction piping is the piping that returns gaseous refrig− erant to the compressor. This may be the most critical piping in the system design. Sizes must be large enough to maintain minimum friction to prevent re− duced compressor and system capacity, but must be small enough to produce adequate velocity to return oil to the compressor. Oil separates from the refriger− ant in the evaporator and must be entrained in the gas in small particles by gas flow velocity, or excess oil may collect in the piping and evaporator. 10.2.5

10.2.7

Discharge Stop Valve

The manual service valve on the discharge side or at the leaving connection of the compressor. Similar to the suction stop valve except for size and location. 10.2.8

Hot Gas Piping

The compressor discharge piping that carries the hot refrigerant gas from the compressor to the condenser. Sizing may be as critical as suction piping, as veloci− ties must be high enough to carry entrained oil. 10.2.9

Condenser

The heat exchanger in which the heat absorbed by the evaporator and some of the heat of compression introduced by the compressor are removed from the system. The gaseous refrigerant changes to a liquid, again taking advantage of the relatively large heat transfer by the change of state in the condensing pro− cess. Part of the condenser contains all gas, part con− tains a gas−liquid mixture, and part contains solid liq− uid refrigerant, in the reverse manner as the evaporator. 10.2.10 Receiver The receiver is an auxiliary storage receptacle for re− frigerant when the system is pumped down (shut down). When completely isolated by valving, this equipment provides a storage place to contain refriger− ant even when the system, including the condenser, may be opened for servicing. Receivers are optional except in systems where condenser storage capacity is inadequate, especially when the system design re− quires pump down. 10.2.11

Filter-Drier

The filter−drier is a combination device used as a strainer and moisture remover. Normally used with a three−valve bypass to allow removal of the cartridge during system operation.

Compressor 10.2.12 Liquid Solenoid Valve

The compressor is the pump that provides the pressure differential to cause fluid to flow, and in the pumping process, increases pressure of the refrigerant to the high side condition. The compressor is the separation between the low side and the high side. 10.2.6

Suction Stop Valve

The manual service valve on the inlet side of the com− pressor.

The electrically operated, automatic shut off valve in the liquid piping that closes on system shut down. It also closes off the receiver discharge when used in a pump down cycle, which prevents refrigerant migra− tion into the system. 10.2.13 Liquid Sight Glass The glass ported fitting in the liquid line used to indi− cate adequate refrigerant charge. When bubbles ap−

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

10.3


pear in the glass, there is insufficient refrigerant in the system. 10.2.14 Hot Gas Bypass And Valve The piping and manual, but more often automatic, valve used to introduce compressor discharge gas di− rectly into the evaporator. This type of arrangement will maintain compressor operation at light loads by falsely loading the evaporator and compressor. 10.2.15 Relief Devices Codes require excess pressure relief devices which may be reseating relief valves, ?one shot" rupture discs, or both. Either should or must be piped to atmo− sphere. 10.3

SAFETY CONTROLS

The two most common safety controls are the high pressure cutout and the low temperature cutout. The high pressure cutout is a pressure actuated switch with its sensing connection in the compressor head. To pro− tect the compressor from pressures often caused by high condenser temperatures and pressure due to foul− ing and lack of water or air, this switch shuts the com− pressor down when the pressure setting is reached. A distinctive, increasing pitch sound is emitted from the compressor before shut down. The low pressure cutout is either a pressure or temper− ature actuated device with the sensing element in the evaporator, which will shut the system down at its con− trol setting to prevent freezing chilled water or to pre− vent coil frosting. Direct expansion equipment may not use thus device. 10.4

OPERATING CONTROLS

Many variations of operating controls are available. Some are: a.

cycling compressor with a thermostat,

b.

unloading compressor cylinders with step controllers operated from multi−stage ther− mostats,

c.

cycling fan and compressor in an air system, and

d.

reducing capacity by using compressor cylin− der unloaders actuated by refrigerant pres− sure changes.

10.4

10.5

REFRIGERANTS

Equipment manufacturers select refrigerants that will change state in the cycle at the temperatures required by the system. Consequently, the refrigerants are se− lected that will change from liquid to gas in the evapo− rator while absorbing heat, and will change back to a liquid from a gas in the condenser while rejecting heat. The ASHRAE Refrigeration Handbook lists the cur− rently used refrigerants found in HVAC work, as re− frigerant types are changing due to environmental problems. 10.6

THERMAL BULBS AND SUPERHEAT

If warmer air is passed over an evaporator coil, the re− frigerant will evaporate more quickly and the last drop of refrigerant will evaporate at a point at or before the coil outlet. This will cause the suction header to in− crease in temperature. The expansion valve bulb will then sense the increase in superheat and cause the ex− pansion valve to open further. This action will allow more refrigerant to flow through the expansion valve into the coil to overcome the higher rate of evaporation (an increase in superheat), thereby again moving the point where the last drop of refrigerant evaporated to the location just ahead of the bulb. It is in this manner that the expansion valve and its sensing bulb act to closely control the cooling load of the system by mea− suring the effects of the load at the outlet of the evapo− rator coil. Example ?C" in Figure 10−2 is an undesirable location because liquid can be trapped at the location of the bulb, giving a false temperature reading. The location of ?B" is incorrect because the bulb can never sense the refrigeration gas or liquid properly in the lower portion of the coil. Location ?A" is good from an accuracy of sensing standpoint, but liquid cannot be allowed to drain directly into the compressor or slugging could occur. The solution, therefore, is to use location?D" and to allow superheat to occur. Superheat is the temperature increase in the refrigera− tion gas after evaporation has been completed. All re− frigerant liquid evaporation should occur far enough ahead of location ?A" in Figure 10−2 to allow a temper− ature rise of 5F to 15F (2.8C to 8.3C) (or the tem− perature recommended by the manufacturer) to occur before the sensing bulb. This superheat establishes the point, where the last drop of refrigerant evaporated, deeper into the evaporator coil, thereby preventing liq− uid refrigerant from flowing into the suction line and then into the compressor. In other words, ?insurance" is being added so that all refrigerant is evaporated by

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


the time it reaches the bulb. This is also the reason that loops are used in suction line piping to collect liquid refrigerant in the event of an expansion valve malfunc− tion. To see superheat in a slightly different way, if at a certain rate of heat transfer or load condition, the

bulb was set to maintain a fully opened expansion valve, then lowering superheat would slightly close the valve to ensure that all liquid had evaporated be− fore reaching the compressor.

Evaporator Suction Header

Bulb

B. Wrong

A. Good

(Alternate direction)

or

C. Wrong

D. Good

FIGURE 10-2 LOCATIONS OF THERMAL BULBS HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

10.5


10.7

COMPRESSOR SHORT CYCLING

When the load on a coil requires an expansion valve to be half open, a compressor running fully loaded would quickly reduce the suction pressure from the evapora− tor coil and the low pressure control would stop the compressor. Since the expansion valve would still be controlled to remain at the half open point by the bulb, pressure would again build up in the suction piping, re− starting the compressor. Rapid stopping and starting of a compressor is called short cycling. This can quickly damage a compressor. Many compressors have unloading devices to prevent this short cycling (or a hot gas line bypass might be used). These devices selectively allow one or more of the cylinders of the compressor to cease operation al−

10.6

lowing the compressor to adjust to the changing load condition. To continue with the half opened expansion valve example, if the compressor has 4 cylinders, 2 of the cylinders would be unloaded or ineffective. The compressor could now run without being able to re− duce the suction pressure to a point sufficient to shut itself off. It is in this manner that the compressor is ad− justed to match the load. When the compressor is unloaded to its minimum ca− pacity during light load conditions, the compressor can once again short cycle. To prevent this, an anti− short cycle timer is used. This timer is put in the start− ing circuit of the compressor so that when the com− pressor stops, 5 minutes (or some other set time interval) is required to elapse before the compressor can again come on.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


CHAPTER 11

TAB INSTRUMENTS


CHAPTER 11 11.1

TAB INSTRUMENTS

INTRODUCTION

Instruments for the measurement of airflow, water flow, rotation, temperature and electricity are the tools of the trade for the TAB technician. Many instruments are available to accomplish TAB tasks and gather TAB data and information. For example, the instruments covered in this section are proven by experience to be reliable and accurate. In addition, new electronic mul− tipurpose instruments that are capable of providing more than one measurement, such as airflow and tem− perature, as well as other electronic types, are avail− able. 11.2

AIRFLOW MEASURING INSTRUMENTS

11.2.1

Manometer, U-Tube

cause rapid deterioration of any copper it touches in the system. c.

U−tube manometers should not be used for readings under 1.0 in. wg (250 Pa). OVER-PRESSURE TRAPS, WITH SHUT-OFF COCKS

11.2.1.1 Description The manometer (Figure 11−1) is a simple and useful means of measuring partial vacuum and pressure, both for air and hydronic systems. It is so universally used that both the inch (millimeter) of water and the inch (millimeter) of mercury have become accepted units of pressure measurements. In its simplest form, a ma− nometer consists of a U−shaped glass tube partially filled with a liquid such as tinted water, oil or mercury. The difference in height of the two fluid columns de− notes the pressure differential. U−tube manometers are made in different sizes and can be used for measuring pressure drops above 1.0 in. wg (250 Pascals) across filters, coils, fans, terminal devices, and sections of ductwork; and are not recommended for readings of less than 1.0 in. wg (250 Pa). 11.2.1.2

Recommended Uses

Air and gas (with water or oil instrument): a.

Measuring pressure drops above 1.0 in. wg (250 Pa) across filters, coils, eliminators, fans, grilles and duct sections.

b.

Measuring low manifold gas pressures.

FIGURE 11-1 U-TUBE MANOMETER EQUIPPED WITH OVER-PRESSURE TRAPS

11.2.2 11.2.1.3

Manometer, Inclined/Vertical

Limitations 11.2.2.1 Description

a.

b.

Manometer tubes should be chemically clean to be accurate and filled with the correct fluid. Use collecting safety reservoirs on each side of a mercury manometer to prevent blowing out mercury into the water system, which can

The inclined−vertical manometer (Figure 11–2) for airflow pressure readings is usually constructed from a solid transparent block of plastic. It has an inclined scale that provides accurate air pressure readings be− low 1.0 in.wg (250 Pa) and a vertical scale for reading greater pressures. Note that all air pressures are given

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

11.1


in ?inches of water (millimeters or pascals)". For ex− ample, ?3.0 inches of water" (75 mm of water or 750 Pa) means that the air pressure on one end of a U− shaped tube is enough to force the water 3 inches (75 mm) higher in the other leg of the tube. Instead of wa− ter, this instrument uses colored oil which is lighter than water. This means that although the scale reads in inches of water (mm), it is longer than a standard rule measurement. Whenever a manometer is used, the oil must be at normal room temperatures or the reading will not be correct. The manometer must be set level and mounted so it does not vibrate. Note the leveling screw and the magnetic clips. Some manometers have two scales C one indicating some pressure in inches (mm) of water and the other indicating velocity in feet per minute (meters per sec− ond). The manometer (or inclined draft gage) is the standard in the industry. It can be read accurately down to approximately 0.03 in. wg (7 Pa) and contains no me− chanical linkage. It is simple to adjust by setting the piston at the bottom until the meniscus of the oil is on the zero line. This instrument can be used with a Pitot tube or static probe to determine pressures or air veloc− ity in ducts across coils and fans.

11.2.2.2 Recommended Uses Use with Pitot tube or static probe. 11.2.2.3 Limitations When air velocities are extremely low, a micro−ma− nometer (hook gage) or some other more sensitive in− strument should be used for acceptable accuracy. 11.2.3

Electronic (Digital) Manometer

11.2.3.1 Description The electronic manometer (Figure 11−3) is designed to provide accurate readings at very low differential pres− sures. Some manometers measure an extremely wide range of pressures from 0.0001 to 60.00 in. wg (0.025 to 15,000 Pa). Airflow and velocity are automatically corrected for the density effect of barometric pressure and temperature. Readings can be stored and recalled with ?average" and ?total" functions. A specially de− signed grid enables the reading of face velocities at fil− ter outlets, coil face velocities and exhaust hood open− ings. Some millimeters provide additional functions such as temperature measurement.

FIGURE 11-3 ELECTRONIC/ MULTI-METER FIGURE 11-2 INCLINED-VERTICAL MANOMETER 11.2

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


11.2.3.2 Recommended Uses DUCT

a.

Use with Pitot tube or static pressure probe.

AIR FLOW SP

b.

With the velocity grid the instrument can be used for velocity measurements at HEPA fil− ter outlets, at hood openings and at coil faces.

PITOT TUBE

V TP

11.2.3.3 Limitations

Description

TP

A) PITOT TUBE CONNECTIONS FOR SUPPLY AIRSTREAM

Because the meter utilizes a time weighted average for each reading, it is often difficult to measure and identi− fy the pulsations in pressure. For this reason it may be difficult to repeat single point readings. 11.2.4

SP

DUCT AIR FLOW SP PITOT TUBE

SP V

TP

The standard Pitot tube (Figure 11−5), which is used in conjunction with a suitable manometer, provides a simple method of determining the air velocity in a duct. The Pitot tube is of double concentric tube construction, consisting of an 1_i inch (3.2 mm) O.D. inner tube which is concentrically located inside of a 5_qy inch (8.0 mm) O.D. outer tube. The outer ?static" tube has 8 equally spaced, 0.04 inch (1 mm) diameter holes around the circumference of the outer tube, lo− cated 2−1_r inches (57 mm) back from the nose or open end of the Pitot tube tip. At the base end, or tube con− nection end, the inner tube is open ended as at the head, and the outer tube has a side outlet tube connector per− pendicular to the outer tube and directly parallel with and in the same direction as the head end of the Pitot tube. Both tubes have a 90 degree radius bend in them lo− cated near the measuring end to allow the open end of the inner ?impact" tube to be positioned so that it faces directly into the airstream when the main shaft of the Pitot tube is perpendicular to the duct and the side out− let static pressure tube outlet connector is pointed in a parallel direction with airflow facing upstream. 11.2.4.1 Recommended Uses a.

Measurement of airstream ?total pressure" by connecting the inner tube outlet connector to one side of a manometer or gage (see ?TP" connections in Figure 11−4).

b.

Measurement of airstream ?static pressure" by connecting the outer tube side outlet con− nector to one side of a manometer or gage (see ?SP" connections in Figure 11−4).

TP B) PITOT TUBE CONNECTIONS IF AIRSTREAM IS EXHAUSTED FROM DUCT & TP IS POSITIVE DUCT AIR FLOW SP PITOT TUBE

SP V

TP TP C) PITOT TUBE CONNECTIONS IF AIRSTREAM IS EXHAUSTED FROM DUCT & TP IS NEGATIVE

FIGURE 11-4 PITOT TUBE CONNECTIONS

c.

Measurement of airstream velocity pressure by connecting both the inner and the outer tube connectors to opposite sides of a ma− nometer or gage (see ?Vp" connections in Figure 11−4).

d.

This instrument when used with a gage, ma− nometer or micro−manometer is a most reli− able and rugged instrument and its use is pre− ferred over any other method for the field measurement of air velocity, system total air, outdoor air, return air, fan static pressure, fan total pressure and fan outlet velocity pres− sures.

e.

The following are some of the instruments that may be used with the Pitot tube:

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

11.3


2 1_w" in. (63 mm)=8D

5 in. (125 mm)=16D 1_r”

(6.4 mm)

0.125 in. (3.2 mm) DIAM.

A 0.313 in.(8.0 mm)=1D A 0.938 in. (23.8 mm.) RAD

0.156 in. (4.0 mm) RAD 8 HOLES - 0.04 in (1mm) DIAM. NOSE SHALL BE FREE EQUALLY SPACED FROM NICKS AND BURRS. FREE FROM BURRS

90  1

SECTION A-A

INNER TUBING - APPROX 0.125 in. (3.2 mm) O.D.  21B & S GA STATIC PRESSURE OUTER TUBING 0.313 in. (8 mm) O.D.  APPROX. 18 B & S GA.

NOTE: Other sizes of pitot tubes when required, may be built using the same geometric proportions with the exception that the static orifices on sizes larger than standard may not exceed .04 in. (1 mm) in diameter. The minimum pitot tube stem diameter recognized under this code shall be 0.10 in. (2.5 mm). In no case shall the stem diameter exceed 1/30 of the test duct diameter.

TOTAL PRESSURE

FIGURE 11-5 PITOT TUBE

11.2.4.2



Micro−manometer (analog or digital), very low pressure differential; 0 to 6 inch (150 mm or 1500 Pa) range;



Inclined or digital manometer, moder− ate pressure differential; 0 to 10 inch (250 mm or 2500 Pa) range;



U−tube manometer, medium pressure differential; 1.0 to 100 inch (25 mm to 2500 mm or 250 Pa to 25 kPa) range;



Magnehelic gage, 0 to 0.5 inch (0 to 12 mm), 0 to 1.0 inch (0 to 25 mm), and 0 to 5 inch (0 to 125 mm) ranges. Limitations

The accuracy depends on uniformity of flow and com− pleteness of traverse. Several shapes and sizes of Pitot tubes are available for different applications. A rea− sonably large space is required adjacent to the duct penetration for maneuvering the instrument. Care must be taken to avoid pinching instrument tubing. Al− low a few seconds for duct pressures and probe tem− perature to stabilize after inserting probe. 11.4

If static pressure, velocity pressure, and total pressure are to be measured simultaneously, three draft gages are connected depending on the specific application. In any case, however, the three values measured will then fulfill the equation: TP = SP + Vp. In conducting tests, it frequently is sufficient to measure only two of these three pressures, since the third one can be ob− tained by simple addition or subtraction. Care must be taken, however, so that the signs of the pressures moni− tored are correct. If the airstream is exhausted from the duct, the static pressure is negative and the hose connections will de− pend on whether the velocity pressure is greater or smaller than the numerical value of the static pressure. If it is greater, the total pressure will be positive; if it is smaller, the total pressure will be negative. The various connections between the Pitot tube and gage are frequently made with rubber hose. Precaution must be taken so that all passages and connections are dry, clean and free of leaks, sharp bends and other ob− structions. The branching out of the rubber hose can be accomplished by the use of a T−fitting or by the use of a 2−stem nipple adapter which can be purchased as an accessory.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


11.2.5

Pressure Gage (Magnehelic)

11.2.5.1 Description A dry type diaphragm operated differential pressure gage that employs a calibrated spring loaded horse− shoe magnet lever operated from the differential pres− sure on the diaphragm. This causes rotation of a highly magnetic permeable helix that positions a pointer on the pressure scale. The Magnehelic pressure gage is operated by magnetic field linkage only, which makes it extremely sensitive and accurate. However, the construction of the gage makes it resistant to shock and vibration. The helix rotates on anti−shock mounted sapphire bearings. A zero calibration screw is located on the plastic cover. Common ranges are: 0 to 0.5 in. wg (125 Pa); 0 to 1.0 in. wg (250 Pa); and 0 to 5.0 in. wg (1250 Pa). There are approximately 30 available pressure ranges in this instrument.

b.

Should not be mounted on a vibrating sur− face.

c.

Should be held in same position as ?zeroed".

d.

Some should be used in the vertical position only.

11.2.6

Anemometer, Rotating Vane

11.2.6.1 Description The basic propeller or rotating vane anemometer (Fig− ure 11−7) consists of a lightweight, wind−driven wheel connected through a gear train to a set of recording dials that read the linear feet of air passing through the wheel in a measured length of time. The instrument is made in various sizes; 3 inch (75 mm), 4 inch (100 mm), and 6 inch (150 mm) sizes being the most com− mon. At low velocities, the friction drag of the mechanism is considerable. In order to compensate for this, a gear train that overspeeds is commonly used. For this rea− son, the correction is often additive at the lower range and subtractive at the upper range, with the least correction in the middle of the 200 to 2000 fpm (1 to 10 m/s) range. Most older instruments are not sensitive enough for use below 200 fpm (1 m/s). Newer instru− ments can read velocities as low as 30 fpm (0.15 m/s).

FIGURE 11-6 MAGNEHELIC GAGE

11.2.5.2

Recommended Uses

a.

Use with Pitot tube or static pressure probe as outlined under subsection 11.2.4.

b.

Use with specially constructed induction unit primary air total pressure measuring tip for primary air distribution balancing on high pressure induction systems and heat of light systems.

11.2.5.3 a.

The instrument reads in feet (m), and so a timing in− strument must be used to determine velocity. Readings are usually timed for one minute, in which case the anemometer reading (when corrected according to a calibration curve) will give the result in feet per minute or meters per minute (divide by 60 for m/s). For mod− erate velocities, it may be satisfactory to use a one−half minute timed interval, repeated as a check. A stop watch should be used to measure the timed interval, al− though a wristwatch with a sweep second hand may give satisfactory results for rough field checks. In the case of coils or filters, an uneven airflow is fre− quently found because of entrance or exit conditions. This variation is taken into account by moving the in− strument in a fixed pattern to cover the entire amount of time over all parts of the area being measured so that the varying velocities can be averaged. 11.2.6.2 a.

Measurement of supply air, return air, and ex− haust air quantities at registers and grilles.

b.

Measurement of air quantities at the faces of maximum return air dampers or openings, to− tal air across the filter or coil face areas, etc.

Limitations Readings should be made in midrange of scale.

Recommended Uses

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

11.5


c.

d.

If the opening is covered with a grille, the in− strument should touch the grille face but should not be pushed in between the bars. For a free opening without a grille, the anemome− ter should be held in the plane of the entrance edges of the opening. The anemometer must always be held in such a manner that the air− flow through the instrument is in the same di− rection as was used for calibration (usually from the back toward the dial face). The manufacturer’s recommendations must be followed very carefully when using this in− strument. A quality stopwatch shall be used to time the readings.

d.

Not very accurate on coils without using spe− cific correction factors calculated for each coil. See Appendix A.

11.2.7

Electronic Rotating Vane Anemometer

11.2.7.1

Description

A battery operated, direct digital or analog readout anemometer with interchangeable remote rotating vane heads. The digital readout of the velocity is auto− matically averaged for a fixed time period depending on the measured velocity and the type of instrument. Analog instruments are direct readout with a choice of velocity scales,Figure 11−8. 11.2.7.2

Recommended Uses

For measuring airflow velocities at grilles, coils, lami− nar flow cabinets and other terminal devices. 11.2.7.3

Limitations

a.

Battery operated.

b.

Total inlet area of rotating vane head must be in measured air flow.

FIGURE 11-7 ROTATING VANE ANEMOMETER

11.2.6.3

Limitations FIGURE 11-8 ELECTRONIC ANALOG ROTATING VANE ANEMOMETER

a.

Each reading from this instrument must be corrected by its calibration chart.

b.

The air terminal manufacturer’s specified ?k factor" (effective area) for this instrument must be used in computing air quantities.

11.2.8

Anemometer, Deflection Vane

11.2.8.1

Description

Total inlet area of instrument must be in mea− sured airflow.

The deflecting vane anemometer , Figure 11−9, oper− ates by having pressure exerted on a vane that causes

c.

11.6

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


a pointer to indicate the measured value. It is not de− pendent on air denisty because of the sensing of pres− sure differential to indicate velocities. The instrument is provided and always use with a dual−hose connec− tion between the meter and the probes, except as noted below.

11.2.8.3

Limitations

Instruments should not be used in extremely hot, cold, or contaminated air. 11.2.9 11.2.9.1

Thermal Anemometer Description

The operation of a thermal type anemometer (Figure 11−10) depends on the fact that the resistance of a heated wire will change with its temperature. The probe of this instrument is provided with a special type of wire element which is supplied with current from batteries contained in the instrument case. As air flows over the element in the probe the temperature of the element is changed from that which exists in still air, and the resistance change is indicated as a velocity on the indicating scale of the instrument. FIGURE 11-9 DEFLECTING VANE ANEMOMETER SET A deflecting vane anemometer set meets the needs of TAB work as most major air distribution device manufacturers have set up arear factors based on its use. The set consists of the meter, measuring probes, range selectors, and connecting hoses. Meters are scaled through the following velocity ranges: 0–300 fpm (0–1.5 m/s); 0–1250 fpm (0–6.25 m/s); 0–2500 fpm (0–12.5 m/s); 0–5000 fpm (0–25.0 m/s); 0–10,000 fpm (0–50 m/s). Three velocity probes are providedNCNthe lo−flow probe, the diffuser probe, and the Pitot tube. The lo− flow probe is used in conjunction with the 0–300 fpm (0–1.5 m/s) scale for measuring terminal air velocities in rooms or open spaces, and to measure face veloci− ties at ventilating hoods, spray booths, fume hoods, and the like. The lo−flow probe is directly mounted to the meter without the use of hoses. The Pitot tube is used to measure airstream velocities in ducts. 11.2.8.2 a.

b.

Recommended Uses This instrument may be used for measure− ments of air velocity through both supply and return air terminals using the proper jet and the proper air terminal ?k" factor (effective area) for the airflow calculation. Some instruments may also be used for mea− suring some lower velocities wher the instru− ment case itself is placed in the airstream.

FIGURE 11-10 11.2.9.2

THERMAL ANEMOMETER

Recommended Uses

a.

Used to measure very low air velocities such as a filter face velocity, room velocity and the velocity of hood openings.

b.

Can be used for velocity traverse in ducts to determine total airflow.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

11.7


11.2.9.3

Limitations

a.

The probe that is used with this instrument is quite directional and must be located at the proper point on the diffuser or grille as indi− cated by the manufacturer.

b.

Probes subject to fouling by dust and corro− sive air.

c.

Should not be used in flammable or explosive atmosphere.

d.

Corrections must be made for the tempera− ture of air being measured.

11.2.10

Flow Measuring Hood

11.2.10.1

Description FIGURE 11-1 1 FLOW MEASURING HOOD

The flow measuring hood ,Figure 11−11, is a device that covers the terminal air outlet device to facilitate taking air velocity or air flow. The conical or pyramid shaped hood can be used to collect all of the air dis− charged from an air terminal and guide it over flow measuring instrumentation. A velocity measuring grid and calibrated manometer in the hood will read the air− flow in cfm (L/s). The balancing hood should be tailored for the particu− lar job. The large end of the hood should be sized to fit over the complete diffuser and should have a gasket around the perimeter to prevent leakage.

11.2.11

Smoke Devices

WARNING! Before using any smoke devices, the TAB Technician must warn all people within the area so that they are aware of the use. 11.2.11.1 Description These devices generally are used for the study of air− flow and for the detection of leaks.

11.2.10.2 Recommended Uses To measure air outlet devices direction in cfm (L/s). Some digital instruments have memory, averaging, and printing capabilities.

When testing for leaks, sufficient smoke should be used to fill a volume 15 to 20 times larger than the duct or enclosure volume to be tested.

11.2.10.3 Limitations a.

b.

11.8

Smoke bombs come in various sizes with different lengths of burning time from which highly visible, non−toxic smoke readily mixes with air simplifying the observation of flow patterns.

Flow measuring hoods should not be used where the discharge velocities of the air out− lets exceed manufacturer recommendations. The hood redirects the normal pattern of air discharge which creates a slight, artificially imposed, pressure drop in the ductwork branch which can be corrected by using manufacturers backpressure compensation.

Smoke sticks and candles are convenient in that they come in different sizes and they provide an indicating stream of smoke. Some are like the puff from a ciga− rette and others smoke continuously for a few minutes to a maximum of 10 minutes. Smoke guns are valuable in tracing air currents, deter− mining the direction and velocity of airflow, and the

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


general behavior of either warm or cold air in condi− tioned rooms.

studies, hoods, filters, etc. Air motion rates below 10 fpm (0.05 m/s) can be measured with a stopwatch and distance determina− tions.

11.2.11.2 Recommended Uses a.

b.

For determining the direction and observing the velocity and pattern of airflow in room

INSTRUMENT

RECOMMENDED USES

Discharge patterns from exhaust systems, driers, hoods and stacks can be made.

LIMITATIONS

U-TUBE MANOMETER

Measuring pressure of air and gas above 1.0 in.wg (250 Pa) Measuring low manifold gas pressures

Manometer should be clean and used with correct fluid. Should not be used for readings under one inch of differential pressure.

VERTICAL INCLINED MANOMETER

Measuring pressure of air and gas above 0.02 in.wg (5 Pa) Normally used with pitot tube or static probe for determination of static, total, and velocity pressures in duct systems.

Field calibration and leveling is required before each use. For extremely low pressures, a micro manometer or some other sensitive instrument should be used for maximum accuracy.

MICROMANOMETER (ELECTRONIC)

Measuring very low pressures or velocities. Used for calibration of other instrumentation.

Because some instruments utilize a time weighted average for each reading, it is difficult to measure pressures with pulsations.

PITOT TUBE

Used with manometer for determination of total, static and velocity pressures.

Accuracy depends on uniformity of flow and completeness of duct traverse. Pitot tube and tubing must be dry, clean and free of leaks and sharp bends or obstructions.

PRESSURE GAGE (MAGNEHELIC)

Used with static probes for determination of static pressure or static pressure differential.

Readings should be made in midrange of scale. Should be “zeroed” and held in same position. Should be checked against known pressure source with each use.

ANEMOMETER ROTATING VANE (MECHANICAL AND ELECTRONIC)

Measurement of velocities at air terminals, air inlets, and filter or coil banks.

Total inlet area of rotating vane must be in measured airflow. Correction factors may apply, refer to manufacturer data.

ANEMOMETER DEFLECTING VANE

Measurement of velocities at air terminals and air inlets.

Instruments should not be used in extreme temperature or contaminated conditions.

ANEMOMETER THERMAL

Measurement of low velocities such as room air currents and airflow at hoods, troffers, and other low velocity apparatus.

Care should be taken for proper use of instrument probe. Probes are subject to fouling by dust and corrosive air. Should not be used in flammable or explosive atmosphere. Temperature corrections may apply.

FLOW MEASURING HOOD

Measurement of air distribution devices directly in CFM (L/s)

Flow measuring hoods should not be used where the discharge velocities of the terminal devices are excessive. Flow measuring hoods redirect the normal pattern of air diffusion which creates a slight, artificially imposed, pressure drop in the duct branch. Capture hood used should provide a uniform velocity profile at sensing grid or device.

Table 11-1 Airflow Measuring Instruments 11.3

PRESSURE GAGE, CALIBRATED

11.3.1

Description

The calibrated ?test gage" (Figure 11−12) shall be of a minimum?GRADE A" quality, have a Bourdon tube assembly made of stainless steel, alloy steel, monel or

bronze, and a non−reflecting white face with black let− ter graduations conforming to ANSI Specification U.S.A.S. B40−1. Test gages are usually 3−1_w inch to 6 inch (90 mm to 150 mm) diameter with bottom or back connections. Many dials are available with pressure, vacuum or compound ranges.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

11.9


11.3.1.1

Recommended Uses

Dial gages are used primarily for checking pump pres− sures; coil, chiller, and condenser pressure drops; and pressure drops across orifice plates, valves, and other flow calibrated devices. 11.3.1.2

Limitations

Some precautions in the use of Bourdon tube gages are: a.

Pressure ranges should be selected so the pressures to be measured fall in the middle two−thirds of the scale range.

b.

The gage should not be exposed to pressures greater than the maximum dial reading. Simi− larly, a compound gage should be used where exposed to vacuum.

c.

d.

11.3.2 11.3.2.1

Reduce or eliminate pressure pulsations by installing a needle valve between the gage and the system equipment or piping. Under extreme pulsating conditions install a pulsa− tion dampener or snubber (available from gage manufacturers). In using a gage, apply pressure slowly by gradually opening the gage cock or valve, to avoid severe strain and possible loss of accu− racy that sudden opening of the gage cock or valve can cause. Likewise, when removing pressure, slowly close the gage cock or valve, to avoid a sudden release of pressure.

pressure drop across a piece of equipment, a balancing device, or a flow measuring device. Normally, this re− quires two pressure measurements, one on the high pressure side and one on the low pressure side. The dif− ferential pressure, or pressure drop, is then the differ− ence between the two pressure readings.

A differential pressure gage is a dual inlet, ?Grade A" dual Bourdon tube pressure gage with a single indicat− ing pointer on the dial face which indicates the pres− sure differential existing between the two measured pressures. It can be calibrated in psi, inches wg or inch− es mercury (Pa, kPa, mm wg or mm Hg). The Differen− tial Pressure Gage will automatically read the differ− ence between two pressures.

Pressure Gage, Differential Description

In practically all cases of flow measurement, it will be necessary to measure a pressure differential, that is, a

11.10

FIGURE 11-12 CALIBRATED PRESSURE GAGES

Using a single gage, the gage is alternately valved to the high pressure side and the low pressure side to de− termine the pressure differential. Such an arrangement eliminates any problem concerning gage elevations, and virtually eliminates errors due to gage calibration.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


FUNCTION

RANGE

MINIMUM ACCURACY

CALIBRATION

TEMPERATURE MEASURING INSTRUMENT (CONTACT)

Minimum Range 0 to 240 F (-20  to 120C)

± 1% of full scale

12 months

HYDRONIC PRESSURE MEASURING INSTRUMENTS

0 to 30 SPI (0 to 200 kPa) 0 to 60 PSA (0to 400 kPa) 0 to 200 PSI 30 in. Hg to 30 PSI (-760 mm Hg to 200 kPa) 30 in. Hg to 60 PSI (-760 mm Hg to 400kPa)

± 1% of full scale ± 1% of full scale ± 1% of full scale ± 1% of full scale ± 1% of full scale ± 1% of full scale ± 1% of full scale ± 1% of full scale ± 1% of full scale

12 months 12 months 12 months 12 months 12 months 12 months 12 months 12 months 12 months

HYDRONIC DIFFERENTIAL PRESSURE INSTRUMENT

Minimum Range 0 to 36 in. wg (0 to 9 kPa)

± 1% of full scale

12 months *

* If used, mechanical/electronic instrument requires compliance with calibration dates noted.

Table 11-2 Instruments for Hydronic Balancing

INSTRUMENT PRESSURE GAGE (CALIBRATED)

RECOMMENDED USES

LIMITATIONS

Static pressure measurements of system equipment and/or piping.

Pressure gages should be selected so the pressures to be measured fall in the middle two-thirds of the scale range. Gage should not be exposed to pressures greater than or less than dial range.

PRESSURE GAGE (DIFFERENTIAL) FLOW MEASURING DEVICES

Pressures should be applied slowly to prevent severe strain and possible loss of accuracy of gage. Same as pressure gage.

Differential pressure measurements of system equipment and/or piping. Used to obtain highly accurate measurement of volume flow rates in fluid systems.

Must be used in accordance with recommendations of equipment manufacturer.

Table 11-3 Hydronic Measuring Instruments

Figure 11−13 illustrates the application of one type of gage modification that uses a single standard gage and eliminates the need for subtraction to determine differ− ential. The gage glass is calibrated to ft wg (kPa) at its outer periphery. During operation, the gage glass is left loose so it can be rotated. To measure a pressure differ− ential, the high pressure is applied to the gage by oper− ating the valve to the high pressure side, and the gage glass is then rotated so that its ?zero" is even with the gage pointer. Next, the high pressure valve is closed and the valve to the low pressure side is opened. The gage pointer will now indicate a pressure that is direct− ly equal to the pressure differential in ft wg (kPa). If the gage is of large diameter, such as 8 inches (200 mm) diameter, differential pressures can be read accurately to the order of 0.25 ft wg (750 Pa).

11.3.2.2

Recommended Uses

a.

This instrument when furnished in one of the lower differential pressure ranges, calibrated in inches of mercury (mm Hg), or inches of water (Pa), can be used with water hose flex− ible connectors for water distribution balanc− ing.

b.

This instrument, when furnished in one of the higher differential pressure ranges can be used in lieu of the two combination type high pressure gages.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

11.11


Snubber

High pressure

Low pressure (A)

Loose glass rotated to “zero” setting

Diff.pressure Ft Hd. 0

0

High pressure

Valve open

(B)

Low

High

pressure

pressure

Valve

Valve

closed

closed

Low pressure

(C)

Valve open

FIGURE 11-13 SINGLE GAGE BEING USED TO MEASURE A DIFFERENTIAL PRESSURE 11.3.2.3

Limitations

Some applications require use of a pulsation suppres− sor or needle valve. 11.4

ROTATION MEASURING INSTRUMENTS

A tachometer is an instrument used to measure the speed at which a shaft or wheel is turning. The speed is usually determined in revolutions per minute (rpm), but some have many other ranges such as rev/sec, rev/ hr, ft/sec, in./sec, cm/sec, m/min, rad/sec, and rad/min. The several types of tachometers described below vary in cost, in dependability, and in accuracy of results ob− tainable. One basic difference between the different types of tachometers is that many have digital readouts directly in revolutions per minute (rpm), while older types are primarily revolution counters that must be used with a timing device such as an accurate stop watch. 11.4.1

Tachometer, Chronometric

FIGURE 11-14 SINGLE GAGE BEING USED TO MEASURE A DIFFERENTIAL PRESSURE ter spindle will then be turning with the shaft but the instrument will not be indicating. To take a reading, the push button is pressed and then quickly released. This sets the meter hand to zero, winds the stop watch movement, and then simultaneously starts both the revolution counter and the stopwatch. After a fixed time interval, usually six seconds, the counting mech− anism is automatically uncoupled so that it no longer accumulates revolutions even though the instrument tip is still in contact with the rotating shaft. After the meter hands have stopped, the tachometer may be re− moved from the shaft and read. The meter face has two pointers and two dials, the smaller one indicating one graduation for each complete revolution of the larger pointer, and the reading will be directly in rpm (rps). Some instrument spindles must be rotating in order to be reset without damage.

11.4.1.1 Description The chronometric tachometer (Figure 11−16) com− bines a revolution counter and a stopwatch in one instrument. In using this type of tachometer, its tip is placed in contact with the rotating shaft. The tachome− 11.12

Since the timing is automatically synchronized with operation of the revolution counter, the human error that can occur when a revolution counter and separate stop watch are used, is eliminated. In general, the chro− nometric tachometer is the preferred type of instru−

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


ment when the shaft end is accessible and has a coun− tersunk hole. There are new hand tachometers capable of producing instantaneous rpm measurement readings on a dial face (Eddy−current type) or, solid state instruments with digital readout. 11.4.1.2

Recommended Uses

For determining the speed of any shaft having a coun− tersunk end. 11.4.1.3

Limitations

The shaft end must be accessible and countersunk.

FIGURE 11-15 DIFFERENTIAL PRESSURE GAGE INSTRUMENT REVOLUTION COUNTER CHRONOMETRIC TACHOMETER CONTACT TACHOMETER ELECTRONIC TACHOMETER (STROBOSCOPE) OPTICAL TACHOMETER DUAL FUNCTION TACHOMETER

RECOMMENDED USES

LIMITATIONS

Contact measurement of rotating equipment speed.

Requires direct contact of rotating shaft. Must be used in conjunction with accurate timing device.

Contact measurement of rotating equipment speed.

Requires direct contact of rotating shaft.

Contact measurement of rotating and linear speeds. Non-contact measurement of rotating equipment. Non-contact measurement of rotating equipment. Contact or non-contact measurement of rotating equipment and linear speeds.

Requires direct contact of rotating shaft or device to be measured. Readings must be started at lower end of scale to avoid reading multiples (or harmonics) of the actual rpm. Must be held close to object and at correct angle. Rotating device must use reflective markings. Same as optical tachometer.

Table 11-4 Rotation Measuring Instruments

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

11.13


11.4.2 11.4.2.1

Contact Tachometer (Digital) Description

Contact tachometers (Figure 11−17) are available in ei− ther LCD or LED displays in multi−ranges. Some have a ?memory" button to recall the last reading as well as maximum and minimum readings. In addition, most have a measuring wheel for linear speeds. 11.4.2.2

Recommended Uses

For measuring rotational speeds and linear speeds of shafts. 11.4.2.3

FIGURE 11-16 CHRONOMETRIC TACHOMETER

Limitations

Battery operated; shaft must be accessible. 11.4.3

Optical Tachometer (Photo Tachometer)

11.4.3.1

Description

The optical tachometer or photo tachometer , Figure 11−18 uses a photocell, or eye which counts the pulses as the object rotates. Then by use of a transistorized computer circuit, it produces a direct rpm (rps) reading on the instrument dial that is either digital or analog. Several features make it adaptable for use in measur− ing fan speeds. It is completely portable and is equipped with long−life batteries for its light and pow− er source. It has good accuracy and any error can be re− duced by using more than one reflective marker on the rotating device. Its calibration can be continually checked on most jobs by directing its beam to a fluo− rescent light and comparing the indicated reading against 7200 on the rpm scale. 11.4.3.2

Recommended Uses

The optical tachometer does not have to be in contact with the rotating device. It indicates instantaneous speeds, not average speedCwhether constant or changingCthereby reading the speed as it is. It is easy to useCto read rpm, one need only place a contrasting mark on the rotating device by using chalk or reflec− tive tape. It is a good instrument to use on in−line fans and other such equipment where shaft ends are not ac− cessible. It also has good application for use on equip− ment rotating at a high rate of speed. 11.14

FIGURE 11-17 DIGITAL CONTACT TACHOMETER

11.4.3.3

Limitations

Battery operated; must be held close to object and at correct angle; mark on rotating device must reflect properly. 11.4.4

Electronic Tachometer (Stroboscope)

11.4.4.1

Description

The Stroboscope is an electronic tachometer that uses an electrically flashing light. The frequency of the

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


FIGURE 11-19 STROBOSCOPE FIGURE 11-18 DIGITAL OPTICAL TACHOMETER

flashing light is electronically controlled and adjusta− ble. When the frequency of the flashing light is ad− justed to equal the frequency of the rotating machine, the machine will appear to stand still. The Stroboscope shown in Figure 11−19 does not need to make contact with the machine being checked, but need only be pointed toward the machine so that a moving part will be illuminated by the Stroboscope light and can be viewed by the operator. The light flashes are of extremely short duration, and their fre− quency is adjustable by turning a knob on the Strobos− cope. When the frequency of the light flashes is exact− ly the same as the speed of the moving part being viewed, the part will be seen distinctly only once each cycle, and the moving part will appear to stand still. The corresponding frequency, or rpm, can be read from an analog or digital scale on the instrument. 11.4.4.2

Recommended Uses

For measurement of rotation speeds when instrument contact with the rotating equipment is not feasible. 11.4.4.3

Limitations

FIGURE 11-20 MULTI-RANGE, DUAL FUNCTION (OPTICAL/CONTACT TACHOMETER)

Care must be taken to avoid reading multiples (or har− monics) of the actual rpm (rps). Readings must be started at the lower end of the scale. HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

11.15


11.4.5

11.4.5.3

Dual Function Tachometer

Limitations

11.4.5.1 Description

Battery operated.

This dual−function tachometer (Figure 11−20) pro− vides both optical and contact measurements of rota− tion and linear motions. Many allow a choice of 19 ranges depending on the application. A digital display always indicates the unit of measurement to identify the operating range. The ?memory" button may be used to recall the last, maximum, minimum, and aver− age readings. Compact size and light weight make for easy one−handed operation.

11.5

TEMPERATURE FUNCTION TACHOMETER MEASURING INSTRUMENTS

11.5.1

Thermometers, Glass Tube

11.5.1.1

Description

Mercury−filled glass thermometers (Figure 11−21) have a useful temperature range of from minus 40F to over 220F (−40C to 105C). They are available in a variety of standard temperature ranges, scale gradua− tions, and lengths.

11.4.5.2 Recommended Uses For Measurement of rotation speeds by direct contact or by counting the speed of a reflective mark. FUNCTION

RANGE

RECOMMENDED ACCURACY

RECOMMENDED CALIBRATION

ROTATION MEASURING INSTRUMENT

0 to 5000 RPM

± 2%

24 months

TEMPERATURE MEASURING (IMMERSION)

-40  to -120F (-40  to 50C)

Within ½ of Scale Division

12 months*

TEMPERATURE MEASURING (IMMERSION)

0 to 220F (-20  to 105C)

Within ½ of Scale Division

12 months*

TEMPERATURE MEASURING (AIR)

-40  to 120F (-40  to 50C)

Within ½ of Scale Division

12 months*

TEMPERATURE MEASURING (AIR)

0E to 220E F (-20E to 105E C)

Within ½ of Scale Division

12 months*

ELECTRICAL MEASURING INSTRUMENTS

0 to 600 VAC 0 to 100 Amperes 0 to 30 VDC

3% of Full Scale 3% of Full Scale 3% of Full Scale

12 months* 12 months* 12 months*

*If used, mechanical/electronic instrumentation requires compliance with calibration dates noted.

Table 11-5 Instrumentation for Air & Hydronic Balancing

11.16

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


FUNCTION AIR PRESSURE MEASURING INSTRUMENTATION

RANGE

MINIMUM ACCURACY

CALIBRATION

0 to 0.5 in. wg

± - 0.01 in. wg (2.5 Pa)

12 months *

(0 to 125 Pa)

± - 0.02 in. wg (5 Pa)

12 months *

0 to 1 in. wg

± - 0.20 in. wg (50 Pa)

12 months *

0 to 5 in. wg

± - 0.5

12 months *

in. wg (125 Pa)

(0 to 1250 Pa) 0 to 18 in. wg (0 to 4500 Pa) PITOT TUBE PITOT TUBE

18 in. (450 mm) 36 in. (900 mm)

N/A N/A

N/A N/A

AIR VELOCITY MEASURING INSTRUMENT

Minimum Range: 100 to 3000 FPM (0.5 to 15 M/S)

± 10% when used in accordance with Mfg. recommendations

12 months

HUMIDITY MEASURING INSTRUMENT

10-90% RH

2% RH, Range: 10-90% RH

12 months *

AIR VOLUME MEASURING INSTRUMENT (DIRECT READING)

Minimum Range: 0 to 1400 CFM (0 to 700 l/s)

± 5% when used in accordance with Mfg. recommendations

12 months

* If used, mechanical/electronic instrument requires compliance with calibration dates noted.

Table 11-6 Instruments for Air Balancing 11.5.1.2 a.

b.

11.5.1.3 a.

b.

Recommended Uses The complete stem immersion calibrated thermometer, as the name implies, must be used with the stem completely immersed in the fluid in which the temperature is to be measured. If complete immersion of the ther− mometer stem is not possible or practical, then a correction must be made for the amount of emergent liquid column. The thermometers calibrated for partial stem immersion are more commonly used. They are used in conjunction with thermometer test wells designed to receive them. No emer− gent stem correction is required for the partial stem immersion type. Limitations Radiation effectsCwhen the temperatures of the surrounding surfaces are substantially different from the measured fluid, there is considerable radiation effect upon the ther− mometer reading, if left unshielded or other− wise unprotected from these radiation ef− fects. Proper shielding or aspiration of the thermometer bulb and stem can minimize these radiation effects. Thermometer test wellsCare used to house the test thermometer at the desired location

and permits removal and insertion of a ther− mometer without requiring removal or loss of the fluid in the system. c.

Nuclear work and many clean rooms prohibit the use of instruments containing mercury

11.5.2

Dial Thermometers

11.5.2.1

Description

Dial thermometers are of two general types: stem type (Figure 11−22) and flexible capillary type. They are constructed with various size dial heads, 1−3_r" to 5" (45 mm to 125 mm), with stainless steel encapsulated temperature sensing element. Hermetically sealed, they are rust, dust and leak proof and are actuated by sensitive bimetallic helix coils. Some can be field cali− brated. Sensing elements range in length from 2−1_w" to 24" (60 mm to 600 mm) and are available in many temperature ranges, with and without thermometer wells. The advantage of dial thermometers is that they are more rugged and more easily read than glass−stem thermometers, and they are fairly inexpensive. Small dial thermometers of this type usually use a bimetallic temperature sensing element in the stem. Temperature changes cause a change in the bend or twist of the ele− ment, and this movement is transmitted to the pointer by a mechanical linkage.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

11.17


11.5.2.2

Recommended Uses

Useable for checking both air and water temperature in ducts and pipe thermometer wells. 11.5.2.3

Limitations

Time lag is relatively long. 11.5.3

Thermocouple Thermometers

11.5.3.1

Description

Digital thermocouple thermometers (Figure 11−23) uses a thermocouple as a sensing device and a milli− voltmeter (or potentiometer) with a scale calibrated for reading temperatures directly.

FIGURE 11-21 GLASS TUBE THERMOMETERS

The flexible capillary type dial thermometer has a rather large temperature sensing bulb which is con− nected to the instrument with a capillary tube. The in− strument contains a Bourdon tube, the same as in pres− sure gages. The temperature sensing system, consisting of the bulb, capillary tube, and Bourdon tube, is charged with either liquid or a gas. Tempera− ture changes at the bulb cause the contained liquid or gas to expand or contract, resulting in changes in the pressure exerted within the Bourdon tube. This causes the pointer to move over a graduated scale as in a pres− sure gage, except that the thermometer dial is graduat− ed in degrees. The advantage of this type thermometer is that it can be used to read the temperature in a remote location.

In using a dial thermometer, the stem or bulb must be immersed a sufficient distance to allow this part of the thermometer to reach the temperature being measu− red. Dial thermometers have a relatively long lag time, so enough time must be allowed for the thermometer to reach the temperature and the pointer to come to rest. 11.18

Electronic type thermometers have an instrument case containing items such as batteries, various switches, knobs to adjust variable resistances, and a sensitive meter. Thermocouple temperature sensing elements are remote from the instrument case, and connected to it by means of wire or cables. Electronic type ther− mometers shown in Figure 11−24 have advantages of remote−reading, good precision, and flexibility as to temperature range. Additionally, some electronic type thermometers have multiple connection points on the instrument case, and a selector switch, enabling the use of a number of temperature sensors which can be placed in different locations, and read one at a time by use of the selector switch. 11.5.3.2 a.

Recommended Uses In balancing water circuits thermallyCwhen balancing by flow measurement is not practi− cal.

FIGURE 11-22 DIAL THERMOMETER

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


FIGURE 11-24 THERMISTOR THERMOMETER

FIGURE 11-23 THERMOCOUPLE

b.

11.5.3.3

For evaluation of certain types of boilers, fur− naces, ovens, etc. Limitations

In piping applications, it should be remembered that the surface temperature of the conduit is not equal to the fluid temperature and that a relative comparison is more reliable than an absolute reliance on readings at a single circuit or terminal unit. 11.5.4 11.5.4.1

FIGURE 11-25 INFRARED DIGITAL THERMOMETER

Electronic Thermometers Description

There are many types of rugged, light weight, battery powered digital electronic thermometers that have precision accuracy with interchangeable probes and/ or sensors. Types include: resistance temperature de−

tectors (RTD), thermistors, thermocouples, and diode sensors, with either liquid crystal or LED displays. Re− sponse time and ease of use will vary from model to model, and type to type. Resistance type electronic thermometers are shown in Figure 11−23 and in Figure 11−24.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

11.19


11.5.5

PSYCHROMETER

11.5.5.1

Description

The sling psychrometer (Figure 11−28) consists of two mercury filled thermometers, one of which has a cloth wick or sock around its bulb. The two thermometers are mounted side by side on a frame fitted with a han− dle by which the device can be whirled with a steady motion through the surrounding air. The whirling mo− tion is periodically stopped to take readings of the wet and dry bulb thermometers (in that order) until such time as consecutive readings become steady. Due to evaporation, the wet bulb thermometer will indicate a lower temperature than the dry bulb thermometer, and the difference is known as the wet bulb depression.

FIGURE 11-26 RESISTANCE TEMPERATURE DETECTOR

The newest type of electric thermometers is the in− frared scanner as shown in Figure 11−25.

Accurate wet bulb readings require an air velocity of between 1000 to 1500 fpm (5 to 7.5 m/s) across the wick, or a correction must be made; therefore, an in− strument with an 18 inch (450 mm) radius should be whirled at a rate of two revolutions per second. Signifi− cant errors will result if the wick becomes dirty or dry, so a constant supply of distilled water should be used. Digital battery powered versions are available that blow the ambient air over the wetted wick. These in−

When using an infrared temperature scanner, be sure to calibrate the meter for the type of surface being measured. Shiny surfaces like polished metal will have a different energy reflectivity or emissivity than a rusted or painted surface. This will cause the meter readings to be ?off set" unless the emissivity setpoint matches the material surface conditions being scanned. 11.5.4.2

Recommended Uses

Remote probe electronic thermometers may be used for checking air or liquid temperatures either im− mersed in the fluid steam or from surfaces. Infrared scanners are excellent for uninsulated overhead pip− ing, steam traps, and very hot or cold surfaces that are difficult to access. 11.5.4.3

Limitations

Resistance type have longer response times than ther− mocouple type. Infrared scanners ?see" a larger area at a distance which may introduce errors when the item being scanned is small.

11.20

FIGURE 11-27 ELECTRONIC THERMOMETER

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


struments are accurate and they can be placed into con− fined areas where there is insufficient room to whirl a sling psychrometer. 11.5.5.2

11.5.5.3 a.

Accurate wet bulb readings require an air ve− locity of between 1000 to 1500 fpm (5 to 7.5 m/s) across the wick, or a correction must be made.

b.

Significant errors will result if the wick be− comes dirty or dry.

c.

For an 18 inch (450 mm) radius unit, the in− strument should be whirled at a rate of two revolutions per second.

Recommended Uses

The sling psychrometer can be used in determining the psychrometric properties of the conditioned spaces, return air, outdoor air, mixed air and conditioned sup− ply air. The readings taken from the sling psychrome− ter can be spotted on a standard psychrometric chart from which all other psychrometric properties of the air so measured can be determined. INSTRUMENT GLASS TUBE THERMOMETERS

RECOMMENDED USES Measurement of temperatures of air and fluids

Limitations

LIMITATIONS Ambient conditions may impact measurement of fluid temperature. Glass tube thermometers require immersion in fluid or adequate test wells. Some applications prohibit use of instruments containing mercury within the work area.

DIAL THERMOMETERS

Measurement of temperatures of air and fluids.

Ambient conditions may impact measurement of fluid temperature. Stem or bulb must be immersed a sufficient distance in fluid to record accurate measurement. Time lag of measurement is relatively long.

THERMOCOUPLE THERMOMETERS

Measurement of surface temperatures of pipes and ducts.

ELECTRONICTHERMOM- Measurement of temperatures of air and ETERS fluids. Measurement of surface temperatures of pipes and ducts. PSYCHROMETERS

Measurement of dry and wet bulb air temperatures.

Surface temperatures of piping and duct may not equal fluid temperature within due to thermal conductivity of material. Use instrument within recommended range. Use thermal probes in accordance with recommendations of manufacturer. Accurate wet bulb measurements require an air velocity between 1000 and 1500 fpm (5 to 7.5 m/s) across the wick, or a correction must be made. Dirty or dry wicks will result in significant error.

ELECTRONIC THERMO-HYGRO METER

Measurement of dry and wet bulb air temperatures and direct reading of relative humidity.

Accuracy of measurement above 90% R.H. is decreased due to swelling of the sensing element.

INFRARED

Measurement of surface temperatures of distant objects

Condition and meter must be adjusted for the finish of surface being measured

Table 11-7 Temperature Measuring Instruments 11.5.6

Electronic Thermohygrometers

11.5.6.1

Description

Unlike the psychrometer, the thermohygrometer (Fig− ure 11−30) does not utilize the cooling effect of the wet bulb to determine the moisture content in the air. A thin film capacitance sensor is used as a sensing element in many instruments. As the moisture content and tem− perature change, the resistance in the sensor changes proportionally. Read out is normally in percent rela− tive humidity. Because the instruments do not rely

upon evaporation for measurement, the need for air− flow across the wetted wick or sock is eliminated. The sensing element needs only to be held in the sampled air. Typical measuring rate is 10% to 98% RH, 32F to 140F (0C to 60C). 11.5.6.2

Recommended Uses

The thermohygrometer can be used to determine the psychrometric properties of air in much the same way as the sling psychrometer. The reading can be spotted on a standard psychrometric chart from which all other

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

11.21


psychrometric properties of the air so measured can be determined. It can be used for measuring and monitoring of areas sensitive to change in relative humidity such as clean rooms, hospitals, museums and paper storage. Contin− uous monitoring of conditions in areas sensitive to hu− midity is possible with a greater accuracy and ease of measurement. 11.5.6.3

Limitations

At relative humidities above 90%, the accuracy of the sensor is decreased due to swelling of the sensing ele− ment.

FIGURE 11-28

SLING PSYCHROMETER

11.6

ELECTRICAL MEASURING INSTRUMENTS

11.6.1

Volt-Ammeter

11.6.1.1

Description

The testing, adjusting, and balancing of mechanical systems requires the measurement of voltages and electrical currents as a routine matter. The clamp−on− type volt−ammeter with digital readout (Figure 11−31) is one of the types used for taking field electrical mea− surements. The clamp−on type volt−ammeter shown has trigger operated, clamp−on transformer jaws which permit current readings without interrupting electrical service. Most meters have several scale ranges in amperes and volts. Two voltage test leads are furnished which may be quick−connected into the bot− tom of the volt−ammeter. 11.6.1.2

Safety & Use

When using the volt−ammeter, the proper range must be selected. When in doubt, begin with the highest range for both voltage and amperage scales. Before using, be aware of the following safety precau− tions: First C be careful not to contact an open electrical cir− cuit. Hands should never be put into the electrical box− es. Do not attempt to pry wires over into position. Do not force the instrument jaws into position. These pre− cautions reduce the risk of causing a short circuit which could injure both equipment and personnel. FIGURE 11-29 DIGITAL PSYCHROMETER

11.22

Second C when taking amperage readings do not at− tach the instrument and then start the motor. Position the instrument and read it after the motor is running at full speed. The inrush current required to start a motor

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


is from three to five times higher than the load rated full nameplate current. Therefore, starting the motor with the instrument attached could damage the instru− ment. Readings may be taken at the motor leads or from the load terminals of the starter. To determine the amper− ages of single phase motors, place the clamp about one wire. When involved with three phase current, take readings on each of three wires and average the results. To measure voltage with portable test instruments, set the meter to the most suitable range, and connect the test lead probes firmly against the terminals or other surfaces of the line under test, and read the meter, mak− ing certain to read the correct scale if the meter has more than one scale. When reading single phase volt− age the leads should be applied to the two load termi− nals. The resulting single reading is the voltage of the current being applied to the motor. When reading three phase current it is necessary to ap− ply the voltmeter terminals to Pole No. 1 and Pole No. 2; then to Pole No. 2 and Pole No. 3; and finally to Pole No. 1 and Pole No. 3. This will result in three readings, each of which will likely be a little different, but which should be close to each other. If the average voltage delivered to the motor varies by more than a few volts from the nameplate rating of the motor, several things can occur. A rise in voltage may damage the motor and will cause a drop in the amper− age reading. A drop in the voltage will cause a rise in the amperage and can cause the overload protectors on the starter to ?kick out." In either case, it is advisable to promptly report high or low voltage situations. 11.6.1.3

FIGURE 11-30

THERMOHYGROMETER

digital communication technology to access and ad− just setpoints or ?variables" of a system. Digital controllers utilize programmed algorithms to perform desired functions related to a sequence of op− eration. The algorithm(s) may call for the proportional changes, such as modulation of a variable air volume

Limitations

a.

The proper range must be selected. When in doubt begin with the highest range for both voltage and amperage scales.

b.

Depending on the conditions at the point of measurement, and the size of the volt−amme− ter, access for measurements may be restricti− ve. Caution is required, particularly when taking measurements within starters.

11.7

COMMUNICATION DEVICES

11.7.1

Introduction

The advent of microprocessor based controls has created the need for individuals working within the TAB industry to become familiar with computer and

FIGURE 11-31 CLAMP-ON VOLT AMMETER

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

11.23


(PDA). To speed system trouble shooting, many brands of electronic wall thermostats also include this communication jack or data port. This is extremely helpful when balancing VAV boxes serving a specific room, since the VAV box minimum and maximum or flow rates, heating and cooling temperature setpoints, and thermostat calibrations can be checked from the same point. Unfortunately, until all automation control system manufacturers standardize their communication pro− tocols, you will need either a specific handheld device for a given system, or a copy of the manufacturer’s software installed on your own laptop computer. This software may be easy to obtain since most automation system installers realize that giving you this ability re− duces their onsite setup workload. Figure 11−32 shows a TAB technician adjusting VAV box setpoints with a laptop computer ?plugged" into the data port on a modern electronic wall thermostat.

FIGURE 11-32 ACCESSING AUTOMATION SYSTEM WITH LAPTOP COMPUTER

(VAV) terminal unit, or may perform Boolean func− tions such as starting and stopping a fan. The setpoints or ?variables" of an algorithm may be predetermined and programmed. It should be noted that the TAB tech− nician may establish setpoints and communicate them to the automation system installer, which normally is required to facilitate satisfactory system operation.

11.8

HYDRONIC FLOW MEASURING DEVICES

11.8.1

Metric Measurements

Although gallons per minute (gpm) is the common hy− dronic measurement value in U.S. units, many coun− tries have not accepted S.I. units in the metric system. Many organizations use litres per second (L/s), al− though cubic meters per second (m3/s) and cubic me− ters per hour (m3/h) are used. 11.8.2

Venturi Tube and Orifice Plate

Dedicated Communication Terminals

The venturi tube or orifice plate (Figures 11−33 and 11−34) is a specific, fixed area reduction in the path of fluid flow, installed to produce a flow restriction and a pressure drop. The pressure differential (the up− stream pressure minus the downstream pressure) is re− lated to the velocity of the fluid. The pressure differen− tial also is equated to the flow in gpm (L/s) but the pressure drop is not equal to velocity pressure drop. By accurate measurement of the pressure drop with a ma− nometer at flow rates from zero fluid velocity to a max− imum fluid velocity established by a maximum practi− cal pressure drop, a calibrated flow range may be established. The flow range may then be plotted on a graph which reads pressure drop versus flow rate (gpm or L/s) or the manometer scale may be graduated di− rectly in the flow rate values.

Most microprocessor based programmable field pan− els include a jack or ?port" that allows connecting a laptop computer or hand held personal data assistant

The diagrams in Figure 11−34 illustrate the difference between the venturi tube and an orifice plate. The ven− turi tube, because of the streamlining effect of the en−

11.7.2

Computer Terminals

Today’s building temperature control systems are mi− croprocessor based, using one or more programmable field panels to provide all of the sequence of control functions and setpoints for the HVAC systems. Al− though there is still a lack of industry standards for in− terconnect cabling and communication protocols, most automation system installations include one or more desktop computers located remotely, that can monitor each field panel and adjust setpoints and oper− ating hours for each HVAC system controlled. 11.7.3

11.24

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


ORIFICE DIAMETER

ORIFICE SIZE IDENTIFICATON

PRESSURE TAPPINGS FOR INSTRUMENT CONNECTIONS

AIR VENT HOLE; LOCATE AT TOP OF HORIZONTAL PIPE IF CARRYING WATER

DRAIN HOLE: LOCATE AT BOTTOM OF PIPE IF ORIFICE IS USED IN STEAM PIPE

ORIFICE PLATE

FLOW

ORIFICE

(A) ORIFICE PLATE

(B) ORIFICE PLATE INSTALLED BETWEEN SPECIAL FLOWMETER FLANGES FLOWMETER FLANGES

FIGURE 11-33 ORIFICE AS A MEASURING DEVICE trance and the recovery cone, produces a lower pres− sure loss for the same flow rate. The full venturi tube can be extremely accurate with no appreciable system pressure loss, but it must then be extremely long. Unless such accuracy is required, a modified version with a shortened entrance and re− covery cones may be employed. The modified tube generally provides adequate accuracy with acceptable system pressure losses (still less than the orifice plate for the same accuracy) for environmental systems.

valves. They are similar to ordinary balancing valves, but the manufacturer has provided pressure taps into the inlet and outlet; and has calibrated the device by setting up known flow quantities while measuring the resistance which results from the different valve posi− tions. These positions usually are graduated on the valve body (as a dial) and the handle has a pointer to indicate the reading. The manufacturer then publishes a chart or graph which illustrates the percentage open to the valve (the dial settings), the pressure drop and the resulting flow .

11.8.3

11.8.5

Annual Flow Indicator

The Annular Flow Indicator (Figure 11−35) is a flow sensing and indicating system that is an adaptation of the principle of the Pitot tube. The upstream sensing tube has a number of holes which face the flow and so are subjected to impact pressure (velocity pressure plus static pressure). The holes are spaced so as to be representative of equal annular areas of the pipe, in the manner of selecting Pitot tube traverse points. An equalizing tube arrangement within the upstream tube averages the pressures sensed at the various holes, and this pressure is transmitted to a pressure gage. The downstream tube is similar to a reversed impact tube, and senses a pressure equal to static pressure minus ve− locity pressure at this point; this pressure is also trans− mitted to a gage. The difference between the two pres− sures, when referred to appropriate calibration data, will indicate flow in gpm (L/s). A differential pressure gage is used to directly read the pressure differential. 11.8.4

Calibrated Balancing Valves

Calibrated balancing valves (Figure 11−36) perform dual duty as flow measuring devices and as balancing

Location Of Flow Devices

Flow measuring devices including the orifice, venturi, and other types described above, give accurate and re− liable readings only when fluid flow in the line is quite uniform and free of turbulence. Pipe fittings such as el− bows, valves, etc., create turbulence and non−unifor− mity of flow. Therefore, an essential rule is that flow measuring elements must be installed far enough away from elbows, valves and other sources of flow distur− bance to permit turbulence to subside and for flow to regain uniformity. This applies particularly to condi− tions upstream of the measuring element, and it also applies downstream except to a lesser extent. The manufacturers of flow measuring devices usually specify the lengths of straight pipe required upstream and downstream of the measuring element. Lengths are specified in numbers of pipe diameters, so that the actual required lengths will depend on the size of the pipe. Requirements will vary with the type of element and the types of fittings at the ends of the straight pipe runs, ranging from about 5 to 25 pipe diameters up− stream and 2 to 5 pipe diameters downstream, or as recommended by the manufacturer.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

11.25


MODIFIED TUBE ORIFICE PLATE

FULL VENTURI TUBE

PIPE PIPE TURBULENCE

THROAT VENA CONTRACTA

ENTRANCE CONE

RECOVERY CONE

VENTURI TUBE

ORIFICE PLATE

FIGURE 11-34 FLOW METER TYPES

FIGURE 11-35 ANNULAR FLOW INDICATOR

11.26

FIGURE 11-36 CALIBRATED BALANCING VALVE

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition


CHAPTER 12

PRELIMINARY TAB PROCEDURES


CHAPTER 12 12.1

INITIAL PLANNING

12.1.1 Organization Since testing, adjusting and balancing (TAB) of HVAC systems can best be accomplished by following sys− tematic procedures, the entire TAB process should be thoroughly organized and planned. All activities, in− cluding the organization, procurement of required test instrumentation and the actual system balancing should be scheduled as soon as practical after the con− tract has been consummated. Building space loads often vary with each change of season and space tem− perature levels are a significant factor in TAB work. This needs to be considered when scheduling the TAB work for any project. 12.1.2 Initial Reviews Preparatory work includes the planning and schedul− ing of all TAB procedures, collecting the necessary data, reviewing the data collected, studying the sys− tems to be balanced, making schematic system lay− outs, recording the published data on the test report forms, and finally, making preliminary field checks of the HVAC equipment and systems. If the initial study of the HVAC system plans and specifications by the TAB technician indicates that the systems may not be able to be balanced properly, the HVAC system de− signer should be sent a written notification containing suggestions for changes or the addition of balancing equipment (dampers or valves) that would allow cor− rective action before starting the balancing proce− dures. Occasionally, a system cannot be balanced or made to perform in accordance with the contract docu− ments regardless of the number of balancing dampers or valves that can be installed. 12.2

CONTRACT DOCUMENTS

Secure the latest contract drawings for the HVAC sys− tems making sure that they are complete including; floor plans, sections, schedules, riser diagrams, sche− matic flow diagrams, ATC schedules and interlocks, and any other detail drawing that is normally produced by the preparing engineer or agency. Obtain a complete set of specifications including all sections that pertain to the HVAC equipment, auto− matic temperature controls, motors, air outlets, sheet metal, VAV boxes, pumps, piping, valves, and any oth− er appurtenances that will be installed on the project.

PRELIMINARY TAB PROCEDURES Check to see that you have all change orders, bulletins or any other document that could have an impact on the installed project. Obtain the latest ?as built" shop drawing for the sheet metal and piping. Obtain system leakage rates for ductwork and secure leak test data reports if field testing was in fact required and performed. 12.2.1 HVAC Equipment Performance Data Performance data, including fan and pump curves, should be obtained for all HVAC equipment. Fan per− formance can only be verified by measuring the total static pressure. External static pressure values from manufacturer tables are helpful for initial system duct designs, but these table values do not include the ef− fects from connected ductwork. Fan performance data must relate to the actual job re− quirements and include items such as inlet vanes and altitude and temperature effects. Many times data is general and is not adjusted for these conditions. Fan performance also can be affected by improper de− sign of ductwork near the fan inlet and/or discharge. This phenomenon is called ?system effect", and it can− not be measured in the field. Performance of lower pressure fans can be substantially reduced by system effect. Fan curves or prototype curves can be obtained upon request. If none of these can be obtained, limited curves may be developed from tabulated catalog data. Use caution and determine if the pressures given are internal or external to the equipment and are total pres− sures or static pressure. Pump curves can be handled in a similar manner. Take particular note of equipment substitutions that might affect air and water pressure drops of heat ex− changers, cooling towers, coils and condensers. These include changes in coil size, fin spacing, fin configura− tion, number of rows, cooling coil wet or dry ratings, or number of tubes in the coil face. Data should include air and hydronic pressure differences, the direction of air and water flow (so that proper field installation checks can be made), temperature differentials, capac− ities, operating temperatures and pressures, and limit or safety temperatures and pressures. 12.2.2 Manufacturer’s Catalogs Obtain manufacturers catalogs for all HVAC equip− ment including pumps, air moving and air terminal de−

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

12.1


vices to supplement the shop drawings and submitted data where possible.

perature setpoints, operating schedules, and interlock relationships.

12.2.3 Electrical Data

Before starting any TAB work on a system controlled by an automation system, obtain copies of the written sequence of controls, and the latest printout of all equipment setpoints and operating schedules.

Look for changes of horsepower ratings as a result of equipment substitutions. Note voltage variations such as 230 volt indicated on a nameplate instead of the 208 volt specified. Note phase substitutions, especially on packaged equipment, such as single phase on the nameplate instead of three phase specified. Often these changes can be discovered from the shop draw− ings or submittals. Motor data not available from shop drawings should be obtained in the field. Motor starters, sizes, locations, and thermal overload protection ratings should be checked against horse− power, phase and voltage for substitutions. Coordinate this information with the electrical drawings and with the electrical contractor to verify that the specified electrical service is being installed to each piece of HVAC equipment. 12.2.4 Air Distribution Devices Manufacturer’s recommendations on device testing is available in most cases. Effective Areas (K factors) usually can be obtained for all air grilles, registers, and diffuser devices for the velocity measuring instrument recommended. In addition to air pattern adjustment and sound data. Manufacturer’s Data and Test Proce− dures should be obtained for all other rated or adjust− able air handling devices, such as variable air volume boxes, constant volume regulators, static pressure con− trol dampers and all other similar equipment. Air pressure drop data across louvers, filter banks, sound traps, remote coils and other devices in the air distribution system should be obtained. Note if louvers are provided with screening; filter pressure drop data is for clean, partially dirty, or dirty filters; if sound trap pressure drops are certified and can be confirmed, and if all pressure drops for substituted equipment are within design limitations. 12.2.5 Automatic Temperature Control (ATC) And Energy Management System (EMS) Diagrams With the phase out of pneumatic control systems by microprocessor based programmable controls, it is no longer possible to determine the sequence of controls or control setpoints by visually looking into a control cabinet. Computer chips in microprocessor controls now contain all of the control logic, equipment tem− 12.2

12.2.6 Maintenance, Operating And Start-Up Obtain operating and maintenance manuals for all equipment if available for review. 12.3

SYSTEM REVIEW AND ANALYSIS

After all preliminary data has been collected, a study of each HVAC system may be performed. Two basic reasons for the importance of system review and anal− ysis are (1) to isolate any discrepancies in the data or drawings that may prevent the proper balancing and performance of a system, and (2) to establish the best approach for testing and balancing. The design engi− neer, architect, and owner may want to review what procedures will be employed during the actual testing and balancing of their systems. This also offers an ex− cellent opportunity to present any discrepancies found during the system review and analysis. 12.3.1 System Components And Types Review all available plans, specifications and equip− ment data noting such things as the types and locations of the areas served, types of system, types of compo− nents used such as fans, pumps, boilers, chillers, coils, and VAV boxes. Note such things as primary and sec− ondary systems, interlocked or interconnected sys− tems, possible tie−ins to existing systems and the loca− tion of motor control centers, breakers, and other electrical equipment. Review the equipment sched− ules, the temperature control drawings and carefully note the operating sequence of control for each system. Review the most current set of plans, notes, sections, and details and check for possible additional fans or other equipment that may not be listed in the equip− ment schedules. 12.3.2 System Schematic Drawings It is recommended that drawings or a schematic layout of each HVAC duct system be prepared as shown in Figure 12−1. You can color code an extra set of the original design drawings if you do not normally gener− ate your own plans. A similar drawing should be made for all complex piping systems. All dampers, regulat−

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


-400 CFM EA. (200 l/s) 1200 CFM (600 l/s) 800 fpm (4 m/s)

2

1

-200 CFM EA. (100 l/s)

3

4

20"  12" (500  300 mm) FD

10

6

1800 CFM (900 l/s) VD

VD

5

FD

VD

20"  12" (500  300 mm)

1200 CFM (600 l/s) 800 fpm (4 m/s)

7

8

9

1800 CFM (900 l/s) 1200 fpm (6 m/s) 18"  12" (450  300 mm)

-200 CFM EA.(100 l/s)

3rd FL. -400 CFM EA.(200 l/s) 2400 CFM (1200 l/s) 1200 CFM (600 l/s) 11 12 13 1200 fpm (6 m/s) 800 fpm (4 m/s)

-200 CFM EA.(100 l/s)

28"  12" (700  300 mm)

14

20"  12" (500  300 mm) VD PT FD

15

FD 20

16

1800 CFM (900 l/s) VD

VD PT 1200 CFM (600 l/s) 20”  12” (500  300 mm) 800 fpm (4 m/s)

17

19

18

3600 CFM (1800 l/s) 1200 fpm (6 m/s)

-200 CFM EA.(100 l/s)

2nd FL. -400 CFM EA.(200 l/s) 4800 CFM (2400 l/s) 1200 CFM (600 l/s) 21 800 fpm (4 m/s) 1425 fpm (7.2 m/s)

22

36"  13" (900  325 mm) 23

-200 CFM EA.(100 l/s) 24

30"  18" 20"  12" (750  250 mm) (500  300 mm) VD FD VD

25

26

28

29

1800 CFM (900 l/s)

VD

20"  12" 1200 CFM (600 l/s) PT(500  200 mm) 800 fpm (4 m/s)

27

-200 CFM EA.(100 l/s)

1st FL. 7200 CFM (3600 l/s) 1600 fpm (8 m/s) 30"  26" (750  650 mm)

FD

S. FAN NO.1

FILTER

COOLING COIL

PT

35"  20" (875  500 mm) OUTDOOR AIR LOUVER

VD ATC ATC

EXHAUST LOUVER

5400 CFM (2700 l/s) 1200 fpm (6 m/s)

PREHEAT COIL

ATC PREHEAT COIL

ATC - Temp. Control Damper FD - Fire Damper VD - Volume Damper PT - Pilot Tube Traverse Point

30

5400 CFM (2700 l/s) PT

5400 CFM (2700 l/s)

R.A. FAN NO. 1

FIGURE 12-1 SCHEMATIC DUCT SYSTEM LAYOUT

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

12.3


ing devices, terminal units, supply outlets, return and exhaust inlets should be indicated on these plans. Note all air intakes and exhaust air and relief air louvers where applicable.

cess doors, light fixtures with troffers, wall openings, architectural louvers, door louvers or door undercut− ting. Also note: a.

Location of volume dampers and balancing valves required to balance systems.

b.

System features which may contribute to an unbalanced condition.

c.

Required test report forms.

d.

Instrumentation required.

12.3.3 Study Of Systems And Data

e.

The purpose of this study is to find discrepancies in the submittal data or drawings and to establish the best testing and balancing approach. The following items should be verified.

ATC and EMS sequence of operation, and ability to index (set) system configuration as required.

f.

Sequence and time of the year of balancing the systems.

Be sure your drawing set includes any changes in the HVAC system that was made during construction. For rapid identification and for reporting purposes, all out− lets should be numbered similar to that shown in Fig− ure 12−1. The same applies when there are many fan coil or heating units in hydronic systems. Add general notes indicating thermostat locations and other special conditions needed by the TAB team in the field.

12.3.3.5

12.3.3.1 Performance data for all equipment. Correcting fac− tors if required (such as altitude and temperature). 12.3.3.2 Notify the general contractor of any concerns related to access requirements to take measurements and to adjust volume dampers and balancing valves (are ceil− ing access doors and other openings large enough).

Total quantity of fluid flow for all terminal units or de− vices compared to the designated total fan or pump ca− pacities. Identify the best locations to obtain duct and piping flow measurements. 12.3.3.6 Location and function of all devices which might im− pact the system or change the system operation, in− cluding:

12.3.3.3

a.

smoke and fire dampers

Identify all air filtration requirements including:

b.

automatic control dampers

a.

filter locations

c.

static pressure dampers

b.

special duty filters

d.

automatic control valves

c.

air filters in place

e.

flow control devices

d.

requirements for prefilters

f.

air vents (hydronic systems) and provisions for make−up water

e.

will systems be balanced with temporary fil− ters or will they be balanced with an artificial pressure drop across filter bank to simulate special duty filters.

g.

strainers and filters

h.

safety devices.

12.3.3.4

12.4

Note special requirements to be provided by other con− tractors that must be completed prior to doing the test− ing and balancing work, such as ceiling plenums, ac−

It is recommended that an agenda be prepared and sub− mitted on jobs, prior to balancing the HVAC systems. The agenda should include a preliminary reporting of

12.4

THE AGENDA

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


any discrepancies that would prevent the proper bal− ancing of the project. The agenda should include brief descriptions about the systems and their operation. It should include all proposed balancing procedures and note any items excluded. To be effective, agendas should be submitted early in the process and with ade− quate time for review by the owner/engineer.

Look for obvious static and head pressure discrepan− cies. Review the scheduled pressure drops of compo− nents and compare to the fan and pump capacities for each system. If a fan is undersized, the system design− er, purchaser or owner should be notified.

12.4.1 Balancing Devices

Examine the ATC and EMS control system diagrams to determine how to set the HVAC system components (ATC and EMS dampers, terminal boxes, etc.) and whether full heating or cooling is required for testing. Also consider any possible sequences that may result in an unbalanced system operation.

Review the project drawings, schematics, and details to insure that all necessary balancing devices such as volume dampers and balancing valves are provided to facilitate the balancing procedure. Identify additional dampers or any devices necessary to properly balance the systems. Report any balancing devices that may be inaccessible. 12.4.2 System Capacity Review Check that the total flow requirements of all system terminal units equals the design fan or pump capaci− ties. If a diversity procedure is applicable it should be established and clearly defined in the agenda.

12.4.3 Sequence Of Operation

12.4.4 TAB Instrument Selection Review Chapter 11CTAB Instruments to select the in− struments that are best suited for the TAB work to be done. Select instruments that will give the measure− ments required in the least amount of time and provide the accuracies required. Prepare a list of all instru− ments to be used and include the accuracy informa− tion. 12.4.5 Report Forms Select the report forms based upon tests to be con− ducted and record design data obtained from the sys− tem drawings, plans, and submittals. Perform all cal− culations that are possible to do before the actual TAB work is started. This can save many field labor hours. If terminal airflows are to be determined by velocity readings, calculate the terminal velocities using the manufacturer’s ?K" factors. 12.5

PLANNING FIELD TAB PROCEDURES

12.5.1 Scheduling Prepare a schedule and plan of attack for the TAB work. Review the job progress schedule and know when the systems are expected to be ready for balanc− ing.

FIGURE 12-2 INSTRUMENTS SELECTED FOR A SPECIFIC JOB

It is recommended to estimate the amount of time that it will take to perform the TAB work and notify all contractors involved that there will be a specific period of time needed to perform the work after the job is complete and ready for balancing. Indicate items that must be completed such as all doors, windows, ceil− ings, thermostats, diffusers and registers, and that all controls are in automatic operation.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

12.5


If partial occupancy is planned, find out which sec− tions of the building will be needed. Determine if it is possible to perform the TAB work for this area only.

equipped with thermal overload protection of the proper size. 12.6.1.4 Power

12.5.2 Field Readiness Check Contact supervisors of the other trades involved to in− quire about what work is complete and operable. Also, ask about special conditions such as prior use of equip− ment for temporary heat. Typical pre−balance check lists can be found in the Ap− pendix which may be used by installing contractors to verify that the building and the building systems are ready for the TAB work to begin. 12.6

Check availability of electrical power to all equipment needed for TAB work and verify the compatibility of voltage and phase. 12.6.1.5 Dampers a.

Confirm the operation of all unit and related dampers and their sequence of operation (in− cludes fire and smoke dampers). Proper damper position during startup and TAB work is very critical. If dampers are closed, restricting the airflow, serious damage can be done to casings, housing and ductwork. It is generally best to work with an automatic tem− perature control (ATC) technician during bal− ancing to ensure that all ATC dampers are positioned properly.

b.

All dampers should be in a position to ensure the desired path for air to travel through the correct components of the system and not cause a choked or blocked condition.

c.

Where separate minimum and maximum O. A.. dampers are used, the minimum damper should be opened 100 percent. Where a single O.A. damper is used in conjunction with a minimum position controller, the damper should be opened approximately to the per− centage of minimum outside airflow. If the system uses 100 percent outside air, the damper will have to be fully open. (Note: Don’t leave O.A. dampers open when the unit is not in use, especially during cold weather when freeze−ups may occur.)

d.

Return air dampers should be opened 100%.

e.

Exhaust air dampers may require opening to a percentage equal to the minimum outside air damper setting. This is where minimum relief or exhaust air is specified.

f.

Face and bypass dampers should be set so that the airflow is through the coil. Multi−zone dampers should be set so the air will flow through the cooling coil if sized for 100% full flow. Confirm that the coils are sized for an airflow equal to the fan design. Occasionally coils are sized for less airflow than the fan. In this case, the bypass damper should be left open an amount equal to the excess fan air−

PRELIMINARY FIELD PROCEDURES

After completing initial planning, systematically fol− low the steps listed below. Note that the responsibilities will be different if the TAB firm is also the installing contractor. If the TAB technician is only doing TAB work, the installing con− tractor has responsibility for assuring satisfactory startup procedures have been achieved. 12.6.1 HVAC Equipment 12.6.1.1 HVAC Units Confirm that all HVAC unit fans have been checked and that: a.

equipment matches the test report data such as model number, make, arrangement, class, etc.

b.

test report forms have had data entered that must be obtained from the field.

Secure and review system ready to balance check list from start up contractor, manufacturer or installing contractor. 12.6.1.2 Airflow Check the airflow pattern from the outside air louvers/ dampers and the return/exhaust air dampers through to the supply air fan discharge (and mixing dampers if present). 12.6.1.3 Electrical Locate all start−stop, disconnect switches, electrical interlocks and motor starters. Motor starters must be 12.6

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


flow so that the total airflow will not be re− stricted. g.

h.

Fire and smoke dampers must be in the open position. More complex systems use a variety of damper configurations, particularly where multiple fans and sequences are involved. In this case, the sequence of operation must be studied and dampers must be open or closed accordingly. Vortex and other fan limiting dampers are often used with variable air volume (VAV) systems. It is safest to start the systems with these dampers throttled somewhat and then open them up slowly, observing the static pressure and amperage accordingly.

e.

12.6.2 Duct System Checks 12.6.2.1 Field Review Walk each duct system from the supply air or exhaust air to the last terminal. Check that: a.

the ductwork is complete and if any areas of construction are incomplete.

b.

all terminals, boxes, reheat coils, etc. are installed.

c.

there are no missing air zone partitions, ceil− ing plenums, or windows.

d.

the system really is ready for balancing. (This is important because the TAB technician often is pressured by the owner, general con− tractors, mechanical contractors, or system designer to start the TAB work before the building and/or the systems are ready.)

12.6.1.6 GENERAL a.

b.

c.

Check for any type of temporary blockage over the outside air inlet opening and the ex− haust air discharge openings, (such as poly− ethylene, cardboard or plywood), that may have been placed during construction. Look for any other types of debris or blockage in both the outside air and the return air duct sys− tems. Check the entire unit and the internal compo− nents for proper leak sealing. Leaks will cause whistling, possible moisture carryover and short circuiting of the air. Particularly check around pipes and panel holes. Have the leaks sealed. If the system has spray systems, they should be clean and operating.

12.6.1.7 Filters a.

b.

Confirm that the correct size and type of fil− ters are installed for the TAB work. If the permanent filters are to be used, con− firm that they are the correct size and type of filter by comparing them with the submitted data.

c.

Check the filters for cleanliness and pressure drop. If they aren’t clean, have them replaced before starting TAB work.

d.

Confirm that the filters and filter frames are properly installed and are airtight. Any leaks must be corrected.

If the unit has been running with no filters or very dirty filters, be alerted for possible dirty or clogged coils, etc.

12.6.2.2 Terminal Devices a.

Check that terminal boxes, VAV boxes and mixing boxes are installed and accessible, and that the thermostat controls are energized and operate. Thermostats must be installed and operable.

CAUTION: Some boxes are furnished with normally closed dampers. Starting a complete system with closed terminal box dampers will result in excessive system static pressures and possible duct system dam− age. 12.6.2.3 Openings Check that any required openings between partitions, etc. have been installed and are open. 12.6.2.4 Test Holes a.

Pitot tube test holes must be located in the field to confirm that they will be accessible. Confirm that the actual duct installation matches the plans and that adequate straight sections of duct work are available for the tests. Look for obstructions that will hamper swinging the Pitot tube, such as pipes, ceiling supports, lights, etc. Pitot tube test holes must be sealed or capped when not being used.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

12.7


b.

If the duct is to be externally insulated, any insulation removed for the test will have to be replaced and re−sealed.

c.

If the Pitot tube test holes and caps have al− ready been installed by others, confirm that they are in the correct ducts and at satisfacto− ry locations.

12.8

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


CHAPTER 13

GENERAL AIR SYSTEMS TAB PROCEDURES


CHAPTER 13 13.1

GENERAL AIR SYSTEM TAB PROCEDURES

BASIC FAN TESTING PROCEDURES

Chapter 12CPreliminary TAB Procedures covered the preparation work that must be done prior to the actual testing, adjusting, and balancing of the HVAC systems on the job. Confirm that these preliminary procedures have been completed and check lists prepared. Do not attempt to balance a system before installation has been completed and the system is ready to be balanced.

trols so that the air returned from the individual rooms or areas supplied by the fan is returned via the related return air system. Normally this will involve opening an outside air damper to the minimum position, open− ing the return air damper, and closing exhaust air and relief air dampers. (If the supply system is associated with a return air system and/or an independent exhaust system, make sure all systems are operating and all re− lated dampers are set properly for the TAB work.) 13.3

13.1.1

FAN TESTING

Preparation

The following balancing procedures are basic to all types of air systems.

Perform the following tests and adjustments prior to beginning the air balancing. 1.

Confirm that every item affecting the airflow of a duct system is ready for the TAB work, such as doors and windows being closed, ceiling tiles (return air ple− nums) in place, etc.

Record nameplate data on fan, motor, and air handling cabinet.

2.

Record and measure fan and motor sheaves indicating number and size of belts along with center to center distances.

Establish the conditions for the maximum demand system airflow.

3.

Test and record actual operating fan rpm.

13.2

SYSTEM STARTUP

4.

Measure and record actual running amper− age.

13.2.1

Fan Check

After verifying all control dampers are open, start all related systems, returns, and exhaust fans and take pre− liminary fan static pressure readings. 13.2.2

Damper Check

Be sure each automatic damper is being controlled au− tomatically and is in the correct position. There will be some effect on the airflow if these dampers are hun− ting. This is undesirable while doing air balancing. Therefore, the dampers or their controls should be blocked out to keep them in the desired position. All dampers should be set for a full flow cooling condition. 13.2.3

Damper Setting

If a supply fan is connected to a return air system and an outside air intake, set all system dampers and con−

Fan Volume

Determine the volume of air being moved by the sup− ply fan at design rpm by one or more of the acceptable methods, such as: a.

Pitot tube traverse of the main duct or the ducts leaving fan discharge, if good location available.

b.

Velocity readings across coils, filters, and/or dampers on the intake side of the fan.

c.

Where impossible to take good Pitot tube tra− verses of duct system, use total sum of termi− nal device air volume readings.

d.

Fan curves or fan performance charts. In or− der to determine fan performance using a fan curve or performance rating chart, it is neces− sary to take amperage and voltage readings. In addition, a static pressure reading across the fan must be recorded.

Flow/Pressure Check

Confirm that all related system fans serving each area within the space being balanced are operating. If they are not, pressure differences and infiltration or ex− filtration may adversely influence the balancing. Posi− tive and negative pressure zones should be identified at this time. 13.2.4

13.3.1

With rpm, brake power and static pressure, the fan manufacturer’s data sheets may be used to determine the airflow predicted by the manufacturer. Fan perfor− mance can deviate from the fan curves, if system effect or other system installation defects are present.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

13.1


The total fan air flow should be equal to the outlet CFM plus the allowable transmission losses (leakage) as described in SMACNA’S HVAC Air Duct Leakage Test Manual. Appendix ?A" and an additional 5% for balancing effects. 13.3.2

Fan Adjustments

If there are no obvious deficiencies and the airflow is high, the fan can be slowed by adjusting the drives or making drive changes. When the airflow is low, the fan speed should be increased. First determine if there is adequate fan motor capacity available. The new air− flow−fan power relationship can be determined by use of the fan laws found in Chapter 5CFans. The fan curves are a better reference, if available. If any siz− able upward change is made, the fan manufacturer’s data should be checked for the maximum allowable rpm for this fan and its bearings. If fan power and static pressure data are available and the fan speed can be in− creased, adjust the drives accordingly to obtain the de− sired airflow. Although any fan or pump powered from a variable frequency drive (VFD) can have its speed changed by adjusting the VFD minimum and maximum setpoints, this method should only be used for minor speed correction. The primary purpose of the VFD is to allow short term reduction of fan or pump speeds during peri− ods of reduced system loads, and not for balancing a duct or piping loop system. If changes are made to drive pulleys and belts to achieve the correct system flows after initial VFD setup, the VFD setpoints will need to be adjusted to reflect these pulley and belt changes. 13.3.3

Fan Drive Changes

When new HVAC systems do not perform as designed, new drives and motors are often required. The finan− cial responsibility for these items do not belong to the TAB technician, but the balancing readings will have a lot to do with determining responsibility. Be sure to include the necessary data together with explanations about how and where the readings were taken. The above steps should also be used for any return air or ex− haust air fan associated with the HVAC system in ques− tion. 13.3.4

Fan Amperage

Always recheck the amperage whenever any rpm change or major damper setting change is made. 13.2

13.3.5

Fan Static Pressures

Subsequent to the adjustments of the fan and obtaining the desired air flow, static pressure readings should be taken at the fan suction and fan discharge to obtain the current total fan static pressure reading. This data along with the actual running amperage should be re− corded. Many fan rooms are also return air or outside air ple− nums. When taking readings in these rooms, it will be necessary to reference the manometer or anemometer to the atmosphere. This is accomplished by running a length of hose from the opposite port of the instrument to the outside or atmosphere. Take advantage of exist− ing possible openings available for static pressure (SP) readings such as access doors, handles, bolt holes etc. that may be removed to get the SP probe into the air− stream. If none are available, new ones will have to be drilled. Be sure to close or cap them when finished. 13.4

DEFICIENCY REVIEW

If the fan volume is not within specified range of the design capacity, determine the reason by reviewing all system conditions, procedures and recorded data. Check and record the air pressure drop across filters, coils, eliminators, sound traps, etc. to see if excessive loss is occurring. Particularly study duct and casing conditions at the fan inlet and outlet for system effect. 13.5

RETURN AND OUTSIDE AIR SETTINGS

If the fan system you are adjusting has return and out− side air components and no dedicated return, exhaust, or spill air fan it will be necessary to adjust the associ− ated dampers to achieve the proper air flow for each. With the supply fan being set up to the proper air flow as described above it will be essential to take total air readings for the return, outside air, and spill air portion of the system. Total air readings may be taken by: 1.

Duct traverse readings.

2.

Compilation of individual air inlet readings.

3.

By mathematical calculation from previous− ly taken readings (supply minus return equal outside air)

4.

By temperature calculations involving sup− ply air temperature, return air temperature, mixed air temperature, and outside air tem− perature.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


If volume dampers are provided for each component of the system they should be used for balancing. If dampers are not provided it may be necessary to coor− dinate with the control contractor to limit the stroke or adjustment of the automatically operated damper. Upon completion of the above, it is required to check the supply air reading to see if these adjustments ad− versely affected the total air of the system. If the ad− justments were severe enough to cause a considerable change in total air flow, all of the above steps must be repeated until proper supply, return, outside, exhaust, and spill air quantities are achieved. After proper air quantities have been achieved in the minimum outside air mode of operation it will be nec− essary to check the 100% outside air mode of opera− tion. The automatic dampers should be indexed to the 100% OA Mode of operation and the operating amper− age; static pressure should be checked to see if sub− stantial deviations occur in total performance. If air flow is increased adjust the volume damper for the out− side air or restrict the operation of the automatically operated damper. If the air flow substantially decreased it may be neces− sary to review the system to determine if the 100% OA Mode of operation is the mode with the highest system pressure drop. If this is the case the previous readings will have to be taken over in the reverse order and the AC unit adjusted accordingly. In other words, the sys− tem would be set up for 100% OA and then checked for minimum OA operation with adjustments being made in the minimum mode. 13.6

ANALYSIS OF MEASUREMENTS

If the Pitot tube traverse readings are taken at a good location and the readings are reasonably steady and uniform, these readings are going to give the most ac− curate field measurement of the system airflow and should be used accordingly. When the readings are not steady and uniform, they should be used in conjunc− tion with the other test data and the fan curves to make a determination. The fan curve and fan speed data, when used with the calculated brake horsepower, will give the most accurate field readings that can be relied on heavily. Static pressures will be the least accurate field readings along with airflow readings, depending on how and where they were taken. But with a com− bination of these readings, one should be able to make a reasonable determination of the performance of the fan.

13.6.1

Accuracy

Don’t be surprised when all of this data doesn’t fall into place on the correct fan curve. Field readings are not that accurate, and fan curves do not reflect installed conditions (fans are tested in a laboratory un− der ideal conditions). Accurate HVAC system airflow readings should be taken with a wet cooling coil. If this is not possible, allow for some loss of airflow. 13.7

RECORDING DATA

Record the as balanced state of the system on report forms for all terminals and duct apparatus 13.7.1

Control Verification

Verify the action of all fan control dampers, shut down controls, and airflow safety controls. 13.7.2

Report Forms

Prepare the report forms and submit as required (see Chapter 16 TAB Report Forms). 13.8

PROPORTIONAL BALANCING (RATIO) METHOD

13.8.1

Basic Procedures

Perform the initial air systems TAB work as described under section 13−1CBasic Air Systems Testing Proce− dures. 13.8.2

Farthest Branch

Select the supply air duct branch farthest from the fan. All terminal units or outlets should be numbered on a schematic drawing. (For example, see Figure 13−1, outlets number 4 to 9.) 13.8.3

Branch Duct Readings

Preferably using a direct reading flow hood, record the measured airflow Qm from each of the terminal outlets on the selected branch duct. 13.9

PERCENTAGE OF DESIGN AIRFLOW

Calculate the percentage (X%) of design airflow Qd for each outlet (Qm /Qd =X%). For example, 250 cfm (125 L/s) measured airflow divided by 200 cfm (100 L/s) design airflow equals 125%.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

13.3


The outlets are renumbered in their degree of percent− age of design from the lowest to the highest as shown in the following example (based on Figure 13−1):

Design Q4

Meas. Qm

Outlet No.

cfm

L/s

cfm

L/s

%

6

200

100

150

150

75

9

200

100

160

160

80

5

200

100

170

170

85

8

200

100

180

180

90

7

200

100

200

200

100

4

200

100

210

210

105

should be verified by measurement, and these two out− lets (6 and 9) should be in balance. 13.9.2

Outlet number 5, which is the next lowest percentage of design, is adjusted down to about 160 cfm (80 L/s). Outlets 6 and 9 should then come up to near 160 cfm (80 L/s) and number 9 should be measured to verify this. Outlet numbers 6, 9 and 5 should all be basically in balance. 13.9.3

First Step

The branch damper for outlet number 6, the lowest percentage of design, is not adjusted. The damper for outlet number 9, the next lowest percentage of design, is adjusted until the airflow volume decreases to about 155 cfm (77 L/s). Outlet number 6 airflow volume should then come up to about 155 cfm (77 L/s). This

1

2

Next Step

This procedure is followed, proportionally balancing the next highest percentage of design outlet to the pre− vious one balanced. This should bring all outlets bal− anced earlier into balance with it. 13.9.4

13.9.1

Second Step

Second Branch

Using Figure 13−5, the three (3) outlets numbered 1 to 3 would be proportional balanced to each other in the same manner. The two branches then could be propor− tional balanced using the same procedures used with the terminals. 13.9.5

Varying Airflows

If a branch duct has outlets with varying airflows, the percentage of design is calculated for each and the

3

400 CFM EA. (200 L/s) VD

200 CFM EA. (100 L/s) 20"  12" (500  300 mm)

4

5

6

VD 20"  12"

VD

8 200 CFM EA. (100 L/s)

FIGURE 13-1 SAMPLE SUPPLY AIR DUCT (PART)

13.4

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

9


same procedures are used, balancing to the percentage of design airflow for each.

branch that is very low in capacity to make sure that no blockage exists.

13.9.6

NOTE: Zone traverse readings are not required on VAV CAV systems or systems that use terminal type boxes for volume control.

Completion

Upon completion of proportional balancing of all out− lets and branches, recheck the supply air fan capacity to the final Qm /Qd percentage. If measured airflow (Qm ) is lower than design airflow (Qd ) , the fan airflow volume must be increased to the design airflow (Qd ) and all outlets should increase proportionally to their design airflow (Qd ). Continue the TAB work by following steps for the Stepwise Method. 13.10

SYSTEM AIRFLOW

13.10.1

Systems Coordination

Make a preliminary survey, spot checking air circula− tion in various rooms. With knowledge of the supply, return or exhaust fan volumes and data from the sur− vey, determine if the return air or exhaust air system should be balanced before the supply air system is ba− lanced. In continuation of this procedural outline, the assumption is made that the supply air system balance is not restrained by the exhaust air system or the return air system. However, if such a restraint exists, the ex− haust air system or the return air system should be bal− anced prior to continuing with the supply air system. 13.11

BASIC OUTLET BALANCING PROCEDURES

Balancing air systems may be accomplished in various ways. Regardless of method, the objectives remain the same. The system will be considered balanced when the value of the air quantity of each inlet or outlet de− vice is measured and found to be within the specified limits of the design air quantities (unless there are rea− sons beyond the control of the TAB technician).

13.12.2

Static Pressure Measurements

Adjust the volume damper on each branch that is high on airflow. Monitor the static pressure (SP) at a point downstream of the balancing damper. Slowly close the damper until the SP comes down to the new required SP determined by the equation SP2 /SP1 = (airflow2 /airflow1 ) 2 This should give approximately the correct airflow for this zone. This procedure should be used on each zone with high airflow, usually starting with the highest one first. Then remeasure the SP in all of the zones. There usually will be some interaction between the zones. Some of the adjusted zones may need adjusting again. The zones that were low in airflow should have in− creased, and now some of these may be high and may themselves need adjusting. After the zones are ad− justed to the new calculated SP, proceed to the terminal units. 13.12.3

Zone Balance

There will be instances where a branch damper will need adjusting but there won’t be any satisfactory location for a Pitot tube traverse. In this instance, it will be necessary to take airflow readings at all of the terminals in the zone and total them. Use this total, take a reference SP as detailed earlier, and then pro− ceed to balance the zone. 13.12.4

Terminal Balance

a.

Stepwise method,

Measure and record the airflow at each terminal in the system. In making adjustments, adjust volume damp− ers instead of face dampers (if installed) or the damp− ers at the air terminals.

b.

Proportional Balancing (Ratio) method.

13.12.5

13.12

STEPWISE METHOD

13.12.1

Pitot Tube Traverse

Starting at the main supply duct closest to the fan, or with the highest percentage of required flow, make Pi− tot tube traverses on all main supply and major branch ducts to determine the air distribution. Investigate any

Ak Factors

Using the appropriate instruments and procedures as delineated earlier, measure and record a preliminary reading at each terminal unit. This is a good time to confirm that the size and type of terminal device installed is what was specified. If not, the Ak factor will surely be different. Unless a direct reading hood for airflow is being used, be absolutely sure that the manufacturer’s published Ak factor and measurement

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

13.5


procedures are being used. Many hours have been wasted searching for a problem when the wrong Ak factor was used. Direct reading hoods eliminate the need for Ak factors and special procedures.

balance. An additional pass will probably be necessary to fine−tune the system. Mark all dampers at the point of final adjustment for ease of resetting in the event of tampering. 13.13

FAN ADJUSTMENT

Verify the fan capacity and operating conditions again and make a final adjustment to the fan drive, if neces− sary. 13.14

WET COIL CONDITIONS

If the supply system was tested with dry coil surfaces and is designed for dehumidification, the total air quantity should be rechecked under wet coil condi− tions. 13.15

AIRFLOW TOTALS

After testing and recording all of the terminal units, to− tal the readings on a zone or branch basis. Compare the totals to the comparable zone duct traverse reading and the required airflow. The total airflow for the terminal units should be close to the traverse reading for the zone or branch. The terminal unit total usually will be a little lower due to allowable duct leakage. The accu− racy of a good Pitot tube traverse is usually consider− ably better than most terminal readings. If significant variations are found between traverse readings and time readings, further investigation of ducts may be re− quired. 13.16 FIGURE 13-2 TYPICAL AIR DIFFUSER CFM MEASUREMENT

13.12.6

High Airflow Terminals

Review the readings and start adjusting the terminals that are highest on airflow. On the first adjusting pass through the system, it usually helps to throttle these terminals to about ten percent under design airflow. This will allow for the possible buildup as other termi− nals are adjusted. 13.12.7

Adjusting Passes

After adjusting the high airflow volume terminals, proceed to make another pass through the entire zone or system. Adjust each terminal to the specified air− flow, assuming that sufficient air is available. After two adjusting passes, most systems should be in good 13.6

EXHAUST FANS

Using the methods outlined above, determine the vol− ume of air being handled by a return air fan, if used, and/or if a central exhaust fan system is used. Also de− termine the airflow being handled by the exhaust fan. If several exhaust fans, such as power roof ventilators, are related to a particular supply air system, it general− ly is not necessary to measure the airflow of each such exhaust fan until after the supply air system is bal− anced. 13.17

FAN DRIVE ADJUSTMENT

If the measured airflow of the supply air fan, central return air fan or central exhaust air fan varies more than the specified design plus allowable leakage, ad− just the drive of each fan to obtain the approximate re− quired airflow. Record the fan suction static pressure, fan discharge static pressure, amperage and air volume measurements. Confirm that the fan motor is not over− loaded.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


13.18

DAMPER ADJUSTMENTS

After balancing the return air system and the associat− ed supply air system, the return air damper should be closed; the relief air dampers should be 100 percent open and the return air fan, if used, static pressure and system airflow should be checked again. If it is neces− sary to increase the system static pressure and thereby reduce the fan airflow, adjust the exhaust air damper to a maximum position less than 100 percent open. Re− check the supply fan airflow with the outside air damp− er in the full open position. 13.19

DUCT TRAVERSES

The most accurate and accepted field test of airflow is by a Pitot tube traverse of the duct being tested. 13.19.1

Airflow Measurements

There will be instances when a total of the outlet read− ings will be the only field readings available for the system total airflow. Fan curves can be used when oth− er required data can be obtained, such as SP, rpm, and bhp. Experience has shown, however, that often all of the field readings will not fall into place on the fan and

system curves. Therefore, it is best to make Pitot tube traverses whenever possible and use them in conjunc− tion with the other test data and fan and system curves to tell what actually is happening. 13.19.2

Tranverse Locations

The accuracy of a Pitot tube traverse is determined by the availability of a satisfactory location to perform the traverse. Reasonably uniform airflow through the duct is necessary. Ideally, there should be six to ten di− ameters of straight duct upstream from the test loca− tion. Realistically, this condition will not be found very often in the field, therefore, use the best locations available. Avoid getting close to elbows, offsets, tran− sitions or anything else in the duct that is creating tur− bulence. 13.20

SYSTEM DEFICIENCIES

13.20.1

Fan Airflow

Compare the actual results of the above tests with the specified performance of the fan. If the fan airflow is not near design, try to identify the reason for the differ− ence. Determine if the pressure drops across the duct system components (such as coils, filters, sound atten− uators, eliminator blades, etc.) agree with the manufacturer’s ratings. Observe the duct system con− figurations at the inlet and discharge of the fans. Compare these with the contract drawings. Notice if any radical changes were made to the duct system lay− out during installation. If any corrections are needed, report this to the appropriate persons. 13.21

FUME HOOD EXHAUST BALANCING PROCEDURES

13.21.1

Balancing Criteria

For each fume hood, verify by Pitot tube traverse that the airflow is between 90% and 100% of design. (The design airflow is the volume of exhaust that produces the required face velocity at sash opening, i.e., FV area). For each laboratory hood balance, the supply airflow should be between 90% and 100% of design. Avoid any direct velocity from the ceiling diffuser to− ward the fume hoods. Verify airflow measurements by establishing correction factors from Pitot tube traver− ses. Balance the general exhaust system airflow to be− tween 100% and 110% of design. When flow hoods are used to establish general exhaust, care should be taken when reading multiple grilles that the flow hood does not add restriction, forcing the air to another grille. FIGURE 13-3 MEASURING EXHAUST AIR VELOCITY ON LAB EXHAUST HOOD WITH SASH HEIGHT

13.21.2

Verify Face Velocities

After the correct airflow for the hood has been estab− lished and all exhaust and supply air systems have

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

13.7


been balanced, verify that the face velocities do not fall below the design face velocity at any one point. Face velocities shall be taken at equal areas over the cross section of the sash opening. The face velocities shall be measured using an instrument accurate to 25 fpm. It is imperative that all face velocities be read in the same plane and the instrument be mounted on a stand. Make a sketch of the tested hood, indicating each ve− locity, the sash opening (height, width, and area), the position of the internal baffles, the traversed cfm, the laboratory room number, and exhaust system number. After the face velocities have been determined to be within the limits established here, use a titanium tetra− chloride swab and traverse the face of the hood to ob− serve smoke flows into the hood to determine that no reverse flows are present. 13.21.3

Data Label For Hood

A sticker or label indicating the inspection test result as shown in Figure 13−4 may be requested to be placed on the side of the hood, at the maximum sash height measured, indicating the following:

COMPANY NAME Height of sash (in inches [mm]) Average velocity:

fpm

Highest velocity:

fpm

Lowest velocity:

fpm

Person performing the test: Date of test: FIGURE 13-4 EXAMPLE OF EXHAUST HOOD AIR BALANCE LABEL 13.22

DUST COLLECTION AND EXHAUST BALANCING PROCEDURES

13.22.1

Balancing Criteria

Since most dust collection systems include some form of equipment to remove all or most of the dust particles contained in the exhaust air prior to flow through the exhaust fan, these systems are balanced differently from kitchen hood or lab exhaust systems. The follow− ing guidelines and Figure 13−5 used with permission from the Industrial Ventilation Handbook, 24th Edi− tion. 13.8

13.22.2

New Installation

Sufficient data should be taken on completion of every installation to verify that exhaust volumes, distribu− tion and system balance are in agreement with design data; and that contaminant control is effective. As a first step, a sketch of the system, indicating size, length and relative location of all ducts, fittings, and associat− ed system components should be made. This sketch will serve as a guide in selection of measuring points and very often will bring to light incorrect installation and poor design features. Physical system changes which may occur at a later date (addition of branches, alteration of hoods or ductwork) are easily noted if such a sketch is available as a permanent record. Initial air measurements should include cfm (velocity) and static pressure measurements in each branch and in the main. Static pressure measurements (throat suc− tion) at each exhaust opening, static and total pressure measurements at both fan inlet and outlet, and pressure measurements at collection equipment inlet and outlet (differential pressure) should also be taken. Measure− ment data will indicate any variation from design data, identify where balancing is still needed to obtain re− quired flow distribution and to verify that transport ve− locities in branches and main are ample to convey the material handled. Where imbalance is found, it is ad− visable to again take pressure readings after the system has been balanced. All air measurements and location of measuring points should be recorded to serve as a basis for future checks designed to spot any variations in exhaust volumes from original values. 13.22.3

Testing of Ventilation Systems

Hood design checks should verify that the contami− nant source is hooded as completely as possible with− out interfering with the operation. Air analysis will vary with contaminant: sampling at operator’s breath− ing zone should be completed where toxic materials are involved, with only observation for visual escape− ment where non−toxic and nuisance materials are ex− hausted. Figure 13−5 is an example of an exhaust system with recommended testing points. Obviously, selection of testing points will be dictated by the system under con− sideration and rarely will it be possible to attain perfect results. However, with judicious selection of measur− ing stations to avoid excessively turbulent flow and with proper attention to calibration, alignment, and positioning of instruments, measurements approach− ing the accuracy of design calculations are possible.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


D 5 D MIN.

E

B

B B

C

A

A A A

POINT A B

C

MEASUREMENT HOOD STATIC PRESSURE

LOCATION OF MEASUREMENT DISTANCE FROM HOOD 3 PIPE ∅’S-FLANGED OR PLAIN HOOD 1 ∅-T APERED HOOD VELOCITY AND BRANCH AND MAINS-PREFERABLY 7.5 STATIC PRESSURE ∅’S STRAIGHT RUN DOWNSTREAM FROM NEAREST AIR DISTURBANCE ( EL,ENTRY, ETC..) CENTERLINE VP SMALL DUCTS LOCATION AS ABOVE. CENTERLINE VELOCITY READING ONLY.

D

STATIC,VELOCITY AND TOTAL PRESSURES

E

STATIC PRESSURE INLET AND OUTLET OF COLLECTOR DIFFERENTIAL PRESSURE

INLET AND OUTLET OF FAN-ANY TWO OF THREE READINGS AT EACH LOCATION

MEASUREMENT USE 1. ESTIMATE FLOW: Q=4005CeA SPh 2. CHECK POINT FOR HOOD AND SYSTEM PERFORMANCE. 1. TRANSPORT VELOCITY 2. EXHAUST VOLUME: Q=VA 3. SP AS SYSTEM CHECK POINT ROUND DUCT ONLY. USE ON SMALL DUCTS WHERE TRANSVERSE IMPRACTICAL OR WHERE APPROXIMATE VOLUME WANTED. 1. FAN STATIC AND TOTAL PRESSURES FSP= SP0 – SP1 – VP1 TP= SP0 - S P1+ VP0 - VP1 2. MOTOR SIZE OR GFM ESTIMATE CFM  TP BHP= 6356  ME OF FAN 3. SP AS SYSTEM CHECK POINT 1. COMPARE PRESSURE DROP WITH NORMAL OPERATING RANGE 2. CHECKPOINTS FOR MAINTENANCE. READINGS ABOVE OR BELOW NORMAL INDICATE PLUGGING, WEAR OR DAMAGE TO COLLECTOR ELEMENTS, NEED OF CLEANING

IN ADDITION TO THE ABOVE, FACE VELOCITY (HOOD FACE) AND CAPTURE VELOCITY (POINT OF CONTAMINANT DISPERSION) MEASUREMENTS ARE USUALLY MADE TO DEFINE HOOD PERFORMANCE. OBSERVATION OF AIR FLOWS SURROUNDING EXHAUST OPENINGS MAY BE VISUALLY AUGMENTED BY USE OF SMOKE GENERATORS, TRAILS, AND STREAMERS.

FIGURE 13-5 SAMPLE DUST COLLECTION EXHAUST SYSTEM

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

13.9


13.22.4

Existing Installations

For most existing installations, elaborate air sampling studies are seldom needed at frequent intervals. Unless the process is changed, the hoods or enclosures altered, or the method of materials handling revised, the haz− ard should remain controlled as long as the exhaust system functions properly.

ing, or accumulation on rotor or casing that would obstruct air flow. 2.

Reduced performance caused by defects in the exhaust piping, such as accumulations in branch or main ducts due to insufficient con− veying velocities, condensation of oil or wa− ter vapors on duct walls, adhesive character− istics of material exhausted or leakage losses caused by loose clean−out doors, broken joints, holes worn in duct (most frequent in elbows), poor connection to exhauster inlet, or accumulations in ducts or on fan blades.

3.

Losses in suction can also be attributed to additional exhaust points added to the system (sometimes systems are designed for future connections and more air than required is handled by present branches until future con− nections are made) or change of setting of blast gates in branch lines. Blast gates adjust the air distribution between the various bran− ches. Tampering with the blast gates can seri− ously affect such distribution and therefore gates should be locked in place immediately after the system has been installed and its ef− fectiveness checked.

4.

Reduced exhaust volume may also be caused by an increased pressure loss through the dust collector due to lack of maintenance, improp− er operation, or wear. These items will vary with the collector design. Refer to operation and maintenance instructions furnished with the collector or consult the equipment manufacturer.

The tools required under most cases for a routine check on the performance of an exhaust system are a manom− eter (U−gage) or an inclined gage, depending on the static pressure values involved. While hood suction readings have rightfully fallen into a state of ill repute as a means of measuring air flow, they do offer a quick and accurate method of measur− ing relative air flow. If the hood suction is known while an exhaust system is functioning properly, its contin− ued effectiveness can be assured so long as the hood suction does not reduce from its original value. Any change from the original hood suction can only indi− cate a change in velocity in the branch and consequent− ly a change in air volume removed from the hood. This relation will be true unless (1) the hood design has been changed which would affect the ease of exhausting the air volume (entrance loss), (2) there are obstructions or accumulations in hood or branch ahead of the point of hood suction reading, or (3) the system has been al− tered or extended. Restrictions of cross−sectional area will reduce the air volume, although hood suction may even increase, dependent on location and degree of ac− cumulation. The hood suction method can more readily be dele− gated to a less skilled technician than the Pitot tube where care must be exercised in reading velocity pres− sures in the correct location with the tube paralleling the flow of air. U−gages have been standard plant equipment long enough to eliminate any feeling of un− certainty in their use. Since pressure readings vary with the square of the ve− locity or volume in question, a slight change is magni− fied by comparison of gage readings. For example, an indicated reduction in static pressure readings of 19 to 30 percent would reflect a volume (or velocity) de− crease of 10 to 15 percent. A marked reduction in hood suction can often be traced to one or more of the following items: 1.

13.10

Reduced performance by the exhaust fan caused by belt slippage, wear on rotor or cas−

13.22.5

Check-Out Procedure

The following check−out procedure may be used on systems which were designed to balance without the aid of blast gates. It is intended as an initial check on the design computations and contractor’s construction in new systems, but it may be used also for existing systems when design calculations are available or can be recomputed. It does not detect poor choices of de− sign criteria such as low conveying or capture veloci− ties and consequently will not reveal inadequate con− trol due to this type of error. Agreement with design within ± 10% is considered acceptable. a.

Measure flow in duct on inlet side of fan with a Pitot traverse. If flow is too low, proceed to step 1.a; if correct, go to step d. 1.

Check fan size against plan

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


b.

c.

d.

e.

f.

g.

h.

2.

Check fan speed and direction of rota− tion against design

3.

Check fan inlet and outlet configuration against plan

If a discrepancy is found and corrected, return to step a. If not, measure fan inlet and outlet static pressures and compute the fan static pressure. Using the fan table, check flow, fan static pressure, and rpm. If agreement is ac− ceptable although at some other operating point than specified, fan is satisfactory and trouble is elsewhere in system. Proceed to step c.

sary corrections and return to step a. If loss is less than anticipated, proceed to step h.1. i.

If errors are found, correct and return to step a. If no errors can be detected, recheck design against plan, recalculate and return to step a with new expected design parameters.

j.

Measure control velocities at all hoods where possible. If control is inadequate, redesign or modify hood.

k.

The above process should be repeated until all defects are corrected and the hood static pressures and control velocities are in reason− able agreement with design. The actual hood static pressures should then be recorded for use in periodic system checks. A file should be prepared containing the following docu− ments:

If fan inlet static pressure is greater (more negative) than calculated in design, proceed to step d. If fan outlet static pressure is greater (more positive) than design, proceed to step h. Measure hood static pressure on each hood and check against design. If too high on any hood, proceed to step e; if too low, go to step f. If correct, go to step j. After all hood construction errors and ob− structions have been corrected, if hood static pressures are correct, return to step a; if too low, proceed to step f. Measure static pressure at various junctions in ducts and compare with design calcula− tions. If too high at a junction, proceed up− stream until static pressures are too low and isolate the trouble. In an area where losses ex− ceed design: 1.

Check angle of entries to junctions against plan

2.

Check radius of elbows against plan

3.

Check duct diameters against plan

4.

Check duct for obstructions

1.

System plan

2.

Design calculations

3.

Fan rating table

4.

Hood static pressures after check−out

5.

Maintenance schedule

6.

Hood static pressure measurement log

7.

Periodic maintenance log

The following equipment will be adequate to perform the tests required for this check−out procedure: a.

Pitot tubesCvarious lengths

b.

Pressure gagesCinclined manometer or Magnehelic

c.

Rotational speed measuring deviceCrevolu− tion counter or stroboscope

d.

Air velocity meterClow range (Velometer or thermal anemometer)

e.

Diameter tape

After correcting all construction details which deviate from specifications, return to No. 1.

13.23

Measure pressure differential across air cleaning device and check against manufac− turer’s data. If loss is excessive, make neces−

It is often necessary in connection with the evaluation and control of air pollution to determine the velocity

AIR FLOW MEASUREMENTS ON DISCHARGE STACKS

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

13.11


and quantity of air in discharge stacks. These measure− ments are of importance for the following reasons: 1.

It is necessary to know the volume of air com− ing from a discharge stack to select the proper size of air−cleaning equipment.

2.

The measurement of the quantity of air dis− charged is necessary in conjunction with stack−sampling data in determining the total quantity of contaminant coming from the stack per unit time.

3.

The linear velocity in the discharge stack is necessary for accurate stack−sampling tech− nique. The collection of a representative dust sample requires that the velocity in the sam− pling nozzle and the air stream be nearly equal. This is known as sampling under isoki− netic conditions.

13.23.1

Difficulties Encountered In Measuring Stack Flows Or Density

The general procedures and instrumentation for the measurement of airflow have been perviously address− es. However, special problems connected with airflow measurement in discharge stacks necessitate a some− what more detailed discussion. Some of the special problems are: 1.

Measurement of airflows in highly contami− nated air which may contain corrosive gases, dusts, fumes, or mists.

2.

Measurement of airflows at high temperate− ness.

3.

Measurements of airflow in high concentra− tions of water vapor and mist.

4.

Measurement of airflow where the velocity is very low.

5.

Measurement of the airflow in locations of turbulence and non−uniform airflow, i.e., dis− charge of cupolas, locations near bends or en− largements.

6.

13.12

Measurement of airflow in connection with isokinetic sampling where the velocity is constantly changing.

13.23.2

Corrections For Temperature And Moisture

Air velocities in discharge stacks are sometimes mea− sured at elevated air temperature or moisture content. If these factors are ignored there can be serious errors introduced in the measurement of actual duct velocity for isokinetic sampling and the determination of the actual or standard air volume flowing in the system. Refer to Industrial Ventilation Handbook, 24th Edi− tion for additional examples and correction factor cal− culating procedures. 13.24

INDUSTRIAL VENTILATION

For lower velocities, the swinging−vane anemometer previously described can be used if conditions are not too severe. The instrument can be purchased with a special duct filter which allows its use in light duct loadings. It can be used in temperatures up to 1000F if the jet is exposed to the high temperature gases only for a very short period of time (30 seconds or less). it cannot be used in corrosive gases. If the very low ve− locity jet is used, a hole over 1" in diameter must be cut into the duct or stack For very low velocities, anemometers utilizing the heated thermocouple principle can be used under spe− cial conditions. In most cases, these anemometers can− not be used in high temperatures above 300F (149C). One manufacturer claims that the exposed materials in the thermocouple probe have been se− lected for non−corrosiveness and that the probe can be inserted into corrosive gases. In most stack work, it is necessary to make a traverse as previously described. Center−line readings only, may lead to serious error. This is true in cupolas where the depth of charge may greatly vary the velocity across the cross−sectional area of the stack and in loca− tions near bends, duct collectors, etc. In stack−sampling work where a match of velocities is required, the null method is sometimes used. This method uses two static tubes or inverted impact tubes, one located within the sampling nozzle and the other in the air stream. Each is connected to opposite legs of the same manometer, and the sampling rate is adjusted so the manometer reading is zero. 13.25

SELECTION OF INSTRUMENTS

The selection of the proper instrument will depend on the range of airflow to which the instrument is sensi− tive, its vulnerability to high temperatures, corrosive gases and contaminated atmospheres, its portability

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


and ruggedness, and its size of measuring probe rela− tive to the available sampling hole in the stack. In many cases, conditions for airflow measurement are so severe that it is difficult to select an instrument. Generally speaking, the Pitot tube is the most service− able instrument as it has no moving parts and it is rugged and will stand high temperatures and corrosive atmospheres when it is made of stainless steel. It is subject to plugging, however, when it is used in a dusty

atmosphere. In many cases, it is difficult to set up an inclined manometer in the field because many read− ings are made from ladders, scaffolds, and difficult places. This greatly limits the lower range of the Pitot tube. A mechanical gage has been used in place of the liquid U−tube manometer. This gage is estimated to be accurate to 0.02" of water, however, the gage should be frequently calibrated against an inclined U−tube manometer.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

13.13


THIS PAGE INTENTIONALLY LEFT BLANK

13.14

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition


CHAPTER 14

TAB PROCEDURES FOR SPECIFIC AIR SYSTEMS


CHAPTER 14 14.1

TAB PROCEDURES FOR SPECIFIC AIR SYSTEMS

INTRODUCTION

reduced airflow or turn down systems. They further can be connected to single or dual supply air ducts, have constant or variable airflow on the primary side of the VAV boxes with variable air flow on the secon− dary or distribution side. The variable airflow rate can be from 100 percent to 0 percent of full flow. Figure 14−1 is a system layout for a typical VAV system.

The TAB procedures for basic air systems found in Chapter 13 General Air System TAB Procedures are the foundation for the testing, adjusting, and balancing of any air distribution system. There are, however, cer− tain different or additional procedures that should be used when balancing other than single duct, constant volume air systems.

14.2.1.2 Terminal Units

Even though some of the duct systems addressed in this section are considered obsolete by the HVAC in− dustry, TAB firms may encounter them when re−bal− ancing or retrofitting systems in older buildings.

VAV terminal units (VAV boxes) can also be classified as pressure independent and pressure dependent. A pressure independent device has a volume regulator which will maintain the proper airflow regardless of the terminal inlet static pressure. A pressure dependent device will allow the airflow to vary in accordance with the inlet static pressure.

Procedures will follow for:



Variable air volume (VAV) systems



Multi−zone systems



Dual duct systems



Induction unit systems



Process exhaust air systems

14.2.1.3 Diversity Factor

14.2

VARIABLE AIR VOLUME (VAV) SYSTEMS

14.2.1

Characteristics Of VAV Systems

Usually, VAV systems are designed with a diversity factor which means that the supply fan airflow (cfm or L/s) capacity is less than the sum of the airflows of all the terminal devices. If the diversity factor is not giv− en, it can be approximated by dividing the supply air fan maximum airflow by the sum of the airflows of all VAV terminal units and converting the decimal num− ber to a percentage.

14.2.1.1 Categories There are many types of VAV systems but they can fall into two basic categories: (1) by−pass systems and (2)

OUTDOOR AIR INTAKE

OUTDOOR AIR DAMPERS

POSSIBLE PRE-HEA T COIL

HEATING COIL

FILTERS

RETURN AIR DAMPER

COOLING COIL

PRIMARY AIR DUCT S.P. CONTROLLER

SUPPLY FAN WITH S.P. CONTROL VAV TERMINAL UNITS

EXHAUST AIR LOUVER

EXHAUST AIR DAMPER

OPTIONAL RETURN AIR FAN RETURN AIR SYSTEM

T

T

FIGURE 14-1 TYPICAL VARIABLE AIR VOLUME (VAV) SYSTEM HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

14.1


POSSIBLE PRE-HEA T COIL

OUTDOOR AIR INTAKE

HIGH STATIC LIMIT AND SIGNAL DETECTOR

COOLING COIL

CONTROLLER

FILTERS STATIC PRESSURE TRANSMITTER

O.A. OUTDOOR AIR DAMPERS

DM RETURN AIR DAMPER

RELIEF AIR LOUVER

RELIEF AIR DAMPER

RETURN AIR FAN WITH INLET VANES

SUPPLY AIR FAN WITH INLET VANES

DM

RETURN AIR SYSTEM

VAV SUPPLY SYSTEM

FIGURE 14-2 OPEN LOOP FAN VOLUME CONTROL 14.2.2

Primary Air Volume Control

The supply air fan installation for a VAV system is sim− ilar to that for constant volume systems except that the fan air volume must be varied. Inlet or discharge dampers and variable speed drives or motors may be used to control the system airflow. A static pressure sensor, usually located about two−thirds of the way from the fan to the end of the duct system, senses the supply air duct static pressure and sends a signal back to the apparatus controlling the fan airflow volume. Verify that the controls are set to maintain a constant static pressure at the sensor location, as the system air− flow varies. Systems with combination return/exhaust air fans re− quire special attention by the TAB technician. Build− ing pressure will vary if the return air fan volume does not vary closely with the supply air fan volume. The three common methods used are: building static con− trol, open loop control, and closed loop control. 14.2.2.1 Building Static Control Building static control senses differential pressures between a typical room and outdoors, and increases the volume of air handled by the return/exhaust air fan as building pressure increases. 14.2

14.2.2.2 Open Loop Control Open loop control uses an adjustable span and start point on the supply air and return air fan controls to se− quence the return air fan operation with the supply air fan (Figure 14−2). This system requires close attention by the TAB technician. If the system load varies signif− icantly among major zones the supply air fan serves, resistance in the return air system may not vary in di− rect proportion to resistance in the supply air system. Open loop control does not sense the effect of resist− ance variance between the supply air and return air systems, and building pressures may vary when major load variation occurs. 14.2.2.3 Closed Loop Control The closed loop control senses changes in the volume of air the supply air fan delivers and uses a controller having a second input proportional to the return air fan flow to reset the return air fan (Figure 14−3). Square root factors should be applied where flow is measured as velocity pressure, enabling comparison of linea− rized signals. Controlling flow eliminates the effects of different fan or vane characteristics. The controller can be set to maintain the difference in the airflow re− quired between the supply and return air fan to main− tain building pressurization and accommodate auxilia− ry exhaust systems. If this difference is also the

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


14.2.3

minimum amount of outside air the system requires, the flow controller on the fans will maintain the mini− mum ventilation rate regardless of variations in out− side air and return air damper characteristics. Multiple point Pitot tubes or flow measuring stations should be used to sense velocity pressure at the fans on VAV sys− tems, since the velocity profile will vary with flow; single−point Pitot tubes will give inaccurate readings of total airflow. The calibration of these flow stations should be verified by the TAB technician.

14.2.3.1 Initial Procedures Prior to beginning the TAB work, verify that the tem− perature control contractor’s sequence of operation compliments the terminal unit or VAV box manufac− turer’s factory installed control system. Inspect prima− ry air ducts to ensure adequate entry conditions. 14.2.3.2 Preliminary And Initial Procedures All initial procedures as outlined in the preceeding chapter apply until you get to the total air and traverse readings. The curse of a balancer in performing his work is that ?he must be finished before he starts". This is the most difficult part to understand when you un− dertake the balancing of a system with numerous vari− VAV or constant air volume boxes (CAV).

14.2.2.4 Static Pressure Sensor

The system designer should locate the static pressure sensor on the drawings, as it depends to some extent on the type of VAV terminal unit used. Pressure depen− dent units without controllers may be near the static pressure midpoint of the duct run to ensure minimum pressure variation in the system. Where pressure inde− pendent units are installed, pressure controllers may be at the end of the duct run with the highest static pres− sure loss to ensure maximum fan horsepower savings while maintaining the minimum required pressure at the last terminal unit. However, as the flow through the various parts of a large system varies, so does the static pressure losses. Some field adjustment or relocation may be required.

Each type of system VAV, CAV, dual duct, pressure de− pendent, pressure independent, diversified, and non− diversified system has appurtenances that have to be adjusted individually before you can ascertain the total system performance. Terminal boxes have numerous operating parts and settings. To assume that they all work and are installed is incorrect. Therefore, separate balancing procedure for each type of application is included herewith. In many cases you have to balance the end items before you attempt of balance the main system.

RETURN AIR FAN WITH INLET VANES

RELIEF AIR DAMPER

RELIEF AIR LOUVER

L

RETURN AIR DAMPER

General TAB Procedures

RECEIVER CONTROLLER

RELIEF AIR SYSTEM FLOW MEASURING STATIONS

H

VELOCITY PRESSURE TRANSMITTER

FILTERS

COOLING COIL H

L

O.A.

OUTSIDE AIR INTAKE

OUTSIDE AIR DAMPERS

STATIC PRESSURE TRANSMITTER

HIGH STATIC LIMIT SUPPLY AIR FAN WITH INLET VANES

SIGNAL SELECTOR

CONTROLLER

FIGURE 14-3 CLOSED LOOP FAN VOLUME CONTROL

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

14.3


Pressure Independent VAV System Balancing Procedures

Pressure dependent VAV boxes or terminal units have no automatic volume controller to regulate the airflow as the inlet static pressure to the box changes. The air− flow delivered by the box for any given condition will change at any time the inlet static pressure changes. Since the airflow delivered is dependent on the inlet static pressure furnished, the VAV boxes are consid− ered pressure dependent.

DESIGN FAN OPERATING POINT

FAN OPERATING POINT AT REDUCED AIR FLOW AND SPEED

STATIC PRESSURE in.wg (Pa)

14.2.4

DESIGN P FOR VAV TERMINAL UNIT

P FOR TERMINAL UNIT AT REDUCED AIRFLOW

FAN CURVES

SYSTEM CURVE

These VAV boxes must have an inlet balancing damper in addition to an automatic temperature control (ATC) damper. The ATC damper may have limiters to pro− vide for adjustments of the minimum and maximum position. The TAB technician must realize that every change in damper setting, either manual or automatic, is going to affect the airflow in the system as shown in Figures 14−4 and 14−5.

REDUCED

DESIGN

AIRFLOW-CFM (L/S)

FIGURE 14-5 FAN AND SYSTEM CURVES, VARIABLE SPEED FAN

FAN OPERATING POINT AT REDUCED AIRFLOW

ADDITIONAL P TO BE OVERCOME BY DISCHARGE DAMPER OR TERMINAL UNIT

STATIC PRESSURE in.wg(Pa)

c.

Adjust the inlet dampers to each box to obtain the design airflow and verify the operation of the VAV box.

d.

With box set at maximum balance individual outlets to design CFM.

e.

Turn box to minimum and adjust minimum stops if providedCif no stops are provided box will go to ?o" flow. Note: If box has flow sensor or voltage coils for measuring flow, reading should be taken and recorded.

f.

Repeat steps C through E until all boxes and air outlets are balanced to project specified allowances (+/– 10%).

g.

Revisit the fan and confirm all final air read− ings, static pressure readings, component unit pressure drops, and operating amperage.

h.

If the system has a static pressure controller, check and provide the required reading to the control contractor.

DESIGN FAN OPERATING POINT DESIGN P FOR VAV TERMINAL UNIT

P FOR TERMINAL UNIT AT REDUCED AIRFLOW SYSTEM CURVE

CONSTANT SPEED FAN CURVE

REDUCED

DESIGN

AIRFLOW - CFM (L/S)

FIGURE 14-4 FAN AND SYSTEM CURVES, CONSTANT SPEED FAN

14.2.5

BALANCING NON-DIVERSITY SYSTEMS

Non−diversity systems are balanced similar to constant volume systems. a.

Put all of the VAV boxes and the supply air fan in a full flow condition.

b.

Test and adjust the fan to design airflow using methods previously described.

14.4



Turn all boxes to their minimum setting except the box with the longest equiva− lent run of duct (this may be the box fur− thest from the fan or the box that you had the most difficulty in achieving design flow through). This box should be in− dexed to maximum flow.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


i.



Take total air reading at the box or the outlets (whichever is most convenient or accessible). The flow should be above design CFM.



Have the controls contractor reduce the volume control device (VFD, Vortex, Spill Damper or Discharge Damper until design flow is achieved at the box being monitored.



With the box at design obtain the actual static pressure reading at the static pres− sure sensor and advise the control con− tractor of the required setting. Record this reading appropriately in the balanc− ing data sheets.

b.

Test and adjust the supply air fan to deliver the design airflow with the variable airflow control device set at maximum. This device may be an inlet damper, discharge damper, variable speed drive, or variable speed motor.

c.

After the fan has been set to its operational design flow, start at the boxes that have been indexed to their minimum flow and set the ac− tual minimum flow. These boxes will not be balanced at this time, but only have the mini− mum total flow set so that proper total air flow will be available at the ends of the sys− tem.

d.

Starting at the supply air fan end of the sys− tem, adjust the inlet damper of each VAV box to provide the correct airflow for that box, and then balance its downstream terminal outlets. Do this to each VAV box that has the correct airflow available with the system in this condition. These VAV boxes and their as− sociated outlets are now balanced. Adjust the minimum airflow requirements at this time.

e.

If the boxes have flow measuring devices they should be recorded at this time. If no measuring devices are provided, it may be advisable to take proper static pressure read− ings at the box so that resetting can be done without rebalancing all the outlets on the box.

f.

After the boxes that have been indexed to maximum have been balanced on both maxi− mum and minimum flow, the remaining boxes should be indexed to their maximum position and the proper number of balanced boxes should be indexed to their minimum position.

Confirm total air flow and performance on 100% OA Mode of operation.

14.2.5.1 Balancing Diversity Systems Diversity systems can be the most difficult VAV sys− tems to balance satisfactorily. Any procedure used will be a compromise, and shortcomings will appear some− where in the system under certain operating condi− tions. To eliminate possible misunderstandings later, an agenda with the proposed balancing procedures should be submitted and approved by the system de− signer or authorized persons before the TAB work is started. This practice is recommended for all jobs, but it is critical on jobs with these particular systems. Generally, pressure dependent diversity systems are balanced as follows: a.

Put the system into a mode where it will re− quire approximately the same airflow as the maximum HVAC fan design airflow by plac− ing the required number of VAV boxes in a minimum airflow position. And, leaving the required boxes at their maximum setting, sys− tem total should equal the required CFM for the boxes indexed to maximum plus the boxes indicated to minimum. Stagger the boxes so that the boxes at the beginning of the duct runs are at their minimum position and the boxes furthest from the fan are at the maximum position.

NOTE: The total boxes indexed to minimum and max− imum should be equal to the total air flow required at the fan. g.

Under this mode of operation the fan parame− ters should be checked to insure that the pre− vious balancing and the new operating mode did not adversely affect the system total. If this is the case, resetting of the fan may be re− quired at this time.

h.

Balance the remaining boxes as outlined in paragraph ?D" of this section until all boxes are balanced.

i.

Revisit the fan and confirm all final air read− ings, static pressure readings, component unit pressure drops, and operating amperage.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

14.5


j.

If the system has a static pressure controller, check and provide the required reading to the control contractor.



Turn all boxes to their minimum set− ting except the box with the longest equivalent run of duct (this may be the box furthest from the fan or the box that you had the most difficulty in achieving design flow through). This box should be indexed to maximum flow.



Take total air reading at the box or the outlets (whichever is most convenient or accessible). The flow should be above design CFM.



Have the controls contractor reduce the volume control device (VFD, Vortex, Spill Damper, or Discharge Damper until design flow is achieved at the box being monitored.



With the box at design, obtain the actu− al static pressure reading at the static pressure sensor and advise the control contractor of the required setting. Re− cord this reading appropriately in the balancing data sheets.

At the conclusion of the balancing, the static pressure set up will be identical as described earlier in this manual. However, you must remember to set the static pressure for the true design CFM and not the diversi− fied CFM. 14.2.6

Pressure Independent VAV System Balancing Procedures

14.2.6.1 Inlet Pressures Pressure independent VAV boxes have the ability to maintain a constant maximum and minimum airflow as long as the box inlet static pressure is within the de− sign range of the VAV box. The manufacturer’s pub− lished data provides the static pressure operating range and the minimum static pressure drop across each ter− minal unit for a given airflow. Use this data to verify that adequate pressure is available for the terminal unit to function properly. The objective of balancing pres− sure independent VAV boxes is the same, regardless of the type of controls used. They must be adjusted to de− liver the specified maximum and minimum airflows. 14.2.6.2 VAV Downstream System

k.

Confirm total air flow and performance on 100% OA Mode of operation.

14.2.5.2 Proportional Balancing Of Diversifed Pressure Dependent Systems Pressure dependent systems with diversity may be bal− anced as previously outlined in section 14.2.5.1 of this manual if you attribute CFM proportionally to the out− lets in the same proportion as the diversity factor.

For simplification, consider each pressure indepen− dent VAV box and its associated downstream ductwork to be a separate supply air duct system. If there is ade− quate static pressure and airflow available at the box inlet, the box and its associated outlets can be bal− anced. 14.2.6.3 TAB Procedures After the fan systems have been adjusted in accor− dance with previous procedures, the VAV system should be tested, adjusted, and balanced using the fol− lowing procedures: a.

This method of balancing will guarantee proportional air flow to all outlets under varying system operating parameters.

If a diversity factor was used in equipment selection, set the number of units meeting this factor in the full cooling mode and the re− maining terminals in the fully closed posi− tion. Distribute the closed boxes throughout the system. If this procedure tends to over cool the building, the system supply air tem− perature should be raised.

The diversity factor is the percent of the fan total as compared to the outlet total. A fan that is scheduled for 8000 CFM and has a connected outlet total of 10,000 has a diversity factor of 20% (8000/10,000 CFM). Once the diversity factor has been established, all out− let CFM’s are reduced by the diversity factor. The fac− tored outlet total will equal the fan or system total. 14.6

Determine if the system designer has taken into account a diversity factor when selecting the equipment by comparing the fan design airflow with the total airflow of the terminal units shown on the drawings.

b.

Set outside air dampers to the minimum posi− tion and exhaust and/or return air dampers to a position that simulates full load.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


c.

Index and verify that the fan volume control is set for maximum flow. Observe the amper− age of the fan motor for possible overload.

Three common methods are available for verification that the box is delivering the correct total air flow: 1.

Most boxes have taps in the lines going from the flow measuring device (cross flow sensor, volume probe, etc.) to the controller or regu− lator on the box. Connect a differential static pressure gage to these taps and measure the actual flow differential using the manufactur− ers curves or charts determine the actual box CFM flow. Field testing, however, has proven this method is not always accurate. Often the inlet duct configuration and the type of sensor will affect the signal sent to the controller. Remember the flow stations are velocity av− eraging devices and, as such, depend upon uniform flow not irregular flow. (You cannot average velocity pressures to obtain CFM as they are a square root function.)

2.

Pitot tube traverse may be used if the flow tap is not provided or if the inlet condition at the box is poor. The traverse should only be taken if there is a better location upstream of the box. It serves no purpose to traverse in a poor run of duct or in the same poor inlet condition at the box.

3.

Total compilation of the individual air outlets is the most desirable since this is an actual measure of the air being delivered to the con− ditioned space. This procedure accounts for system transmission losses that are inherent in all duct installations.

g.

After the outlets are balanced, set the VAV box for a minimum airflow. Check the total airflow and adjust the minimum setting on the box, when required, following the manufacturer’s recommendations. It is not unusual, however, for the terminals to be slightly out of balance in the minimum posi− tion. The VAV box and its associated outlets are now in balance and they should stay in balance as long as the inlet static pressure to the box stays within the design static pressure range given by the manufacturer.

If the unit is operating above amperage it will be necessary to reduce flow by adjusting the volume control devices (VFD, Vortex, Dis− charge Damper or Bypass Relief Damper). It is not necessary or required to perform fan or motor sheave adjustments at this time. At this stage of the balancing, it is required to have sufficient static pressure to be able to adjust the VAV boxes and maintain the fan operation by insuring that the fan motor is not over am− perage and running safely.

d.

e.

If the static pressure controller is operational, it is advisable to set the static pressure to a value that will maintain fan operation and ad− equate pressure to perform a box−by−box bal− ancing procedure. If the controller is not op− erational, it will be necessary to lock the volume control device in such a position that static pressure can be maintained without do− ing damage to the duct system.

Because of terminal unit pressure indepen− dent characteristics, it is possible to balance all of the boxes on a system, even if the sys− tem pressure is low. When there is inadequate static pressure, index adjacent boxes into the minimum airflow position to increase the static pressure to simulate design conditions.

Adjust the static pressure regulating control− ler until the static pressure is at the point re− quired in item d. above. Usually boxes and outlets of a system can be completely bal− anced to their design maximum and mini− mum regardless of fan capacity. This method of simulating or providing adequate static pressure also applies to balancing systems with diversity.

f.

With the VAV box set at the maximum flow rate, measure the total airflow being deliv− ered. If necessary, adjust the controller or reg− ulator to deliver the specified airflow follow− ing the manufacturer’s recommended procedures. When the total airflow is correct, balance the outlets.

After the successful balancing of the VAV box, all pertinent information concerning the balanced condition should be recorded and inserted into the proper VAV commissioning sheet including; box size, type, address, DES maximum CFM, DES minimum CFM, actual maximum CFM, actual minimum CFM, flow sensor pressure drop maximum and mini− mum, coefficient, DC voltage, pick up, gain,

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

14.7


h.

i.

j.

k.

l.

14.2.7

or any other distinguishing operating param− eters that would aid in restoring settings if they are disturbed, erased, or tampered with.

valve with actuator, and an air discharge. When the VAV box is pressure independent, a primary air veloc− ity sensor and controller also will be included.

Upon the successful completion of balancing all the boxes, it is now the proper time to as− certain the system total design operating parameters. In either diversified or non−di− versified systems, place all boxes in the max− imum air flow position. Note: In the diversi− fied system we still want to determine if the unit can go over amperage if all the boxes call for maximum flow (chiller failure, excessive− ly high demand day, etc.)

14.2.8.1 Balancing Procedures

Perform total air and fan set up as described in the General Balancing Procedure section of this manual. Once the total supply return and outside air have been established it is now time to bal− ance the return system, if applicable.

b.

Index the VAV box to maximum (cooling) position. Some boxes may have to be set to the minimum position first.

c.

Test total airflow delivered by the VAV box using one of the following methods:

Pressure Dependent VAV System Balancing Procedures

Turndown (Shutoff) VAV Boxes

The basic components of a turndown VAV box consist of a plenum box with a primary air inlet, damper, or air



Inlet velocity sensor (where furnished).



Total of air being delivered from the outlets.



Pitot tube traverse of box inlet or dis− charge.

14.2.8.2 Airflow Adjustment Adjust total airflow using components provided as fol− lows: a.

Pressure Independent:



If the system has a static pressure controller, provide the control contractor with the re− quired setting and readings.

These VAV boxes may have an inlet balancing damper in addition to an automatic temperature control (ATC) damper. The ATC damper may have limiters to pro− vide for adjustments of the minimum and maximum position. The TAB technician must realize that every change in damper setting, either manual or automatic, is going to affect the airflow in the system.

14.8

Verify fan and control operation.

With all boxes at maximum set the return air damper and minimum outside air damper to their approximate design position with the aid and cooperation of the control contractor.

Pressure dependent VAV boxes or terminal units have no automatic volume controller to regulate the airflow as the inlet static pressure to the box changes. The air− flow delivered by the box for any given condition will change at any time the inlet static pressure changes. Since the airflow delivered is dependent on the inlet static pressure furnished, the VAV boxes are consid− ered pressure dependent.

14.2.8

a.

b.

Adjust the controller to achieve design maximum airflow. Index the VAV box to minimum (heating) and adjust the controller to achieve design minimum airflow.

Pressure Dependent:

Adjust maximum airflow by using one of the fol− lowing:



Adjust the stops or limiting devices on the actuator operated damper in the VAV box.



Adjust the manual volume damper in the primary air inlet or VAV box dis− charge.



Index the VAV box to the minimum position. Adjust minimum airflow us− ing stops or position limiting devices on the actuator operated damper in the VAV box.

14.2.8.3 Downstream Ductwork After the total airflow is adjusted, index the VAV box to maximum (cooling) position and balance down− stream duct system terminal outlets.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


14.2.9

Fan Powered VAV Boxes

air load requirement. Series type VAV boxes include a primary air velocity sensor and controller.

Fan powered VAV boxes are VAV boxes that contain individual supply air fans. The variations of operating sequences are numerous and it is imperative that the manufacturer’s data be reviewed. Identify the fan powered VAV box application as either a series or par− allel type. Supplemental Heat Section

Plenum Inlet

After the initial preliminary balancing procedures have been performed, the series fan powered VAV boxes shall be adjusted, tested, and balanced using the following procedures: a.

through f.: Either repeat the procedures for pressure independent or refer to them as be− ing the same.

g.

In order to properly set up and balance a se− ries type box, it is mandatory to establish and confirm the induced air portion of the box. Under most scenarios the primary air is equal to the secondary air (VAV fan CFM). In other cases the primary air is less than the secon− dary air and air is induced through the induct air opening at the box. We never want prima− ry air to exceed the secondary air and exfil− trate out the induced air opening. This would lower the ceiling temperature and cause ex− cess air quantities to be produced by the pri− mary air fan.

Unit Discharge

Primary Air Valve

Fan Motor Plenum Inlet

FIGURE 14-6 SERIES FAN POWERED VAV UNIT

Unit Discharge

Our first step is to attach a streamer or mylar filament to the induced air opening to visual− ly check the air flow path through the induced air opening.

Supplemental Heat Section

h. Primary Air Valve Plenum Inlet Fan Motor

Index the VAV box to its maximum air flow and confirm that the VAV fan is ?on" and run− ning. At this time you may wish to set up to the manufacture’s air flow ports and set the primary air flow to approximate design flow.

FIGURE 14-7 PARALLEL FAN POWERED VAV UNIT

14.2.9.1 Series S Type, Balancing Procedures (Pressure Independent) A constant volume fan−powered induction type VAV box mixes primary air with induced air by using a con− tinuously operating fan located in the VAV box dis− charge (see Figure 14−7). It provides a relatively constant volume of air to the space and comes either with or without an auxiliary heating coil. As more or less cold primary air flows through the unit, ceiling plenum return air is induced to mix with the primary air, providing enough total airflow for a constant dis− charge. To avoid short circuiting of primary air through the fan terminal into the return air plenum, a balancing device permits the discharge to be adjusted so that total air delivery equals the maximum primary

FIGURE 14-8 PAPER STRIP AT VAV BOX RETURN BEFORE BALANCING

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

14.9


i.

j.

Verify total flow at the outlets by reading the individual air outlet or by traverse, which ever is most convenient at this time. Check the actual fan speed of the VAV fan. Before you proceed with further fan adjustments, note the position of the streamer located on the induction opening: 1.

If the streamer is blowing out it will be necessary to reduce the primary flow before proceeding.

2.

If the streamer is pulling in severely, it will be necessary to increase the prima− ry air flow before proceeding.

With the plenum set as described above, pro− ceed to adjust the fan speed to obtain proper total air at the outlets. (Solid state speed con− trols, multi−position switches, or wiring selection.)

NOTE: You do not want to set up the VAV fan with a pressurized mixed air plenum or a starving plenum. It should almost be equal, but not perfect at this time. k.

Balance all the outlets to within the design al− lowable tolerances. This procedure estab− lishes the actual total CFM for the box.

l.

With the box balanced for design total flow, it is now time to neutralize or balance the pri− mary air side. Noting the position of the streamer, utilize the controller or DDC sys− tem adjust to make the streamer neutral or pull slightly into the mixed air plenum. (Nev− er have primary air escape from the mixed air plenum.)

o.

Repeat these steps on all boxes until com− plete, then perform fan data and return air balancing.

14.2.9.2 Parallel Type, Balancing Procedures (Pressure Independent Or Dependent) Parallel flow VAV box components include a plenum box with a discharge outlet, return air inlet with a fan, and a primary air inlet (see Figure 14−8). Primary air enters through an actuated air valve or damper. Return (secondary) air is induced into the plenum by the fan, which is usually equipped with a backdraft damper. When full cooling is no longer needed, the primary air begins to decrease. At a predetermined setpoint, the fan comes on and return air is mixed with the primary air. On full heating, primary air may be completely shut off. Consult project specifications for the specific se− quence specified. Most parallel VAV boxes are pres− sure independent and include a primary air velocity sensor and controller. Heating coils may be provided at the return inlet or at the VAV box discharge.

m. When the plenum is neutralized it may be necessary to reset and recheck the fan speed and outlets to see if any adverse effect were encountered by adjusting the primary flow. Repeat the above steps until the outlets are at design and the plenum is neutral. n.

14.10

After successfully balancing the box, record all pertinent operating parameters: VAV box type, size, address, DES primary maximum and minimum CFM, fan DES CFM, actual primary maximum and minimum CFM, coef− ficient, DC volts, pick−up, gain flow sensor PD maximum and minimum, and/or any oth− er relevant operating conditions.

FIGURE 14-9 PAPER STRIP AT VAV BOX AFTER BALANCING

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


After the initial preliminary balancing procedures have been performed as described in this manual, the parallel fan powered VAV boxes shall be adjusted, tested, and balanced using the following procedures: a.

through g: Either repeat the procedures for Pressure Independent or refer to them as be− ing the same.

h.

After successfully setting the maximum set− ting index the box to its minimum setting. Based upon the control sequence you will have at least two operating scenarios: 1.

2.

ume of air to the zone. Bypass VAV terminal units gen− erally are used on smaller systems. To balance the bypass VAV system, the same tech− niques as discussed above for Pressure Independent VAV and Pressure Dependent VAV systems are used except that the supply fan does not have airflow or stat− ic pressure controls. a.

Follow the procedures a. through d. as de− scribed in the Pressure Dependent Non−Di− versified Balancing section of this manual.

b.

Turn the box to its minimum flow (by−pass) position. In this mode you may be required to obtain two separate readings:

There is minimum cooling setpoint and the fan is off. In this mode you have to set the minimum in the same fashion as the pressure independent style boxes prior to proceeding to the full heating mode. TThere is a minimum primary air flow for heating and the fan is on. In this case, the air flow for the fan may be equal to or less than the design air flow for the maximum primary air side of the box. The primary minimum air flow may be zero at this point or another minimum setting (Heating Minimum).

The amount of air that is bypassed to the return duct or to the return plenum.

d.

Measurement of the bypass air may be deter− mined by either of three methods:

The actual primary air flow can only be determined by reading the manufac− ture’s flow sensors or by traversing the inlet to the box on the primary duct. The remaining procedures for fan operating parameters, total supply air, return air, out− side air and setup of the static pressure con− troller are the same as described in the Pres− sure Independent Balancing Procedures, sections j. – n.

In the bypass VAV system, the supply fan supplies a constant volume of air at all load conditions and the terminal device diverts air from the supply outlets to the return plenum, thus reducing or varying the vol−

2.

With the box indexed for minimum flow, ad− just the stops or control device to obtain the required minimum flow to the conditioned space. The CFM can only be read by total out− let compilation or by traverse of the supply duct on the downstream side of the box.

Rebalancing of the outlets is not done.

14.2.10 Bypass VAV Boxes

The minimum supply air CFM deliv− ered to the conditioned space.

c.

In this scenario, you would set the fan speed to obtain the required actual air flow by outlet compilation or traverse reading.

i.

1.

1.

Direct reading of the discharge opening at the box.

2.

By calculating the difference between the total air flow entering the box less the actual air flow as measured on the downstream side of the box.

3.

If the bypass portion of the box is ducted to the return duct a traverse of this duct will be required. If direct measurement cannot be made you may be able to calculate CFM being delivered by the box by monitoring ad− jacent boxed or total air flow in the main ducts.

e.

For non−ducted bypass boxes measure the amount of bypass air and adjust the volume control device on the box. If the box does not have a volume limiting device on the bypass it will be required to have the installing con− tractor provide a damper or blank off to simu−

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

14.11


late the full flow condition through the box. If the bypass flow is low there are no adjust− ments required. f.

Recheck the minimum flow to the occupied space to insure that the total flow has been maintained. Repeat steps d. and e. if neces− sary.

g.

For bypass boxes with ducted returns, the by− pass balancing is very critical. Even if the correct amount of air is bypassed by the box, there is a potential for positive air flow in the return duct thus causing air flow to be sup− plied through the return outlets and over cool− ing the conditioned space A volume damper in the bypass duct is man− datory for proper balancing of this type duct configuration.

Study the manufacturer’s data before attempting to do the TAB work, because many operating sequences are available. Balancing will consist of setting the primary airflow, both maximum and minimum. The discharge air is a total of the primary air and the induced air. Some boxes have adjustments for the induction damp− er setting. After the box is set, the downstream air out− lets can be balanced in the conventional manner. Induction type boxes are balanced the same manner as pressure independent boxes both diversified and non− diversified. The only difference is that if a minimum amount of in− duced air is required at full flow we must calculate this flow by comparing the primary air flow (as measured by the manufacture’s flow sensor or by a traverse read− ing of primary air) with the total air flow (as measured at the box discharge or outlet total).

Cooling Range

h.

The remaining procedures for fan operating parameters, total supply air, return air, out− side air are the same as previously described with the exception of the return air balancing of bypass boxes that have ducted bypass duct− work. All VAV boxes must be indexed to full flow when balancing the returns to avoid bypass air going into the return ducts.

14.2.11

Induction VAV Boxes

Induction VAV boxes use primary air from a central fan system to create a low pressure area within the box by discharging the primary air at high velocities into a plenum. This low pressure area usually is separated from a ceiling return air plenum by an automatic dam− per. The induced air from the ceiling is mixed with the primary air, so that the actual airflow being discharged from the box is considerably more than the primary air airflow. Most of these induction boxes are designed for VAV operation, but a few are constant volume boxes. 14.12

Heating Range

Max.

Fan Airflow

AIRFLOW

Balance the bypass by traversing and set the volume damper to obtain the proper CFM. After obtaining the proper CFM you must measure the static pressure in the duct down− stream of the volume damper to insure that it is slightly negative. If the reading is not nega− tive, you must adjust the volume damper in the duct until you obtain a negative reading. Go to Step I) and complete the box set up.

Dead Band

Min. Hot

SPACE TEMPERATURE

Cold

FIGURE 14-10 CONSTANT FAN VAV BOX 14.2.12 Combination Systems System applications may incorporate independent VAV boxes and pressure dependent VAV boxes on the same system, either with or without diversity. Balanc− ing procedures will have to be tailored to each job, but it is recommended that the pressure independent boxes are balanced first, since once they are balanced, they will not be affected by changing static pressures as the rest of the system is being balanced. If a system has many pressure dependent boxes, they may consume most of the system airflow and static pressure on the initial system start up, since they will be wide open. Either set some of these boxes to a mini− mum airflow position or partially close the inlet damp− ers on some boxes to build up the static pressure in the system. After setting all of the pressure independent VAV boxes, use the procedures detailed previously for pressure dependent systems and balance the down− stream air outlets.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


Cooling Range

Heating Range

AIRFLOW

Max.

Dea d Band

since the mixing dampers are not capable of control− ling the total airflow quantity. Some units will not have a heating coil, but will just bypass the return air/out− side air mixture when cooling is not needed. 14.3.2 Fan Airflow

Min. Hot

SPACE TEMPERATURE

Cold

FIGURE 14-11 INTERMITTENT FAN VAV BOX (PARALLEL) CYCLE 14.2.12.1 System Powered System powered boxes are powered by the HVAC duct system inlet static pressure and/or velocity pressure. System powered boxes usually have a higher required minimum inlet static pressure than non−system pow− ered boxes. Although the higher static pressure may not be needed for the airflow quantity, it will be needed to operate the controls. Since most system powered boxes are normally open, it is possible to have a VAV box that is delivering the designed amount of air, but the controls will not operate due to low system static pressure at the VAV box inlet. With a high diversity factor, it is possible to have the HVAC duct system not develop sufficient pressure to activate the VAV box control systems upon startup, as a lack of static pressure leaves all of the boxes wide open. With a system of wide open boxes, static pres− sure cannot build up until some of the boxes are either manually or automatically closed to allow the rest of the VAV boxes to start controlling and begin to close down. 14.3

MULTI-ZONE SYSTEMS

14.3.1

Description

A multi−zone unit (Figure 14−12) uses one fan that can blow air through two paths, usually a cooling coil and a heating coil or a perforated plate, before being dis− charged from the HVAC unit. After the air passes through each coil into a cold air plenum or a hot air (or neutral) plenum, the air then passes through mixing dampers into two or more zone ducts serving various spaces. Each zone duct must have a manual volume damper that is used to balance the airflow to each zone. These balancing dampers definitely are required,

Diversity

Multi−zone systems normally are balanced with all the zones in the full cooling position. There are, however, exceptions. The cooling coil may be designed for less air than the fan delivers and the total system requires, because the building normally will not need full cool− ing in all zones at the same time. This diversity is caused by the sun load of the spaces changing from east to west during the day. It will be necessary to check the manufacturer’s data to determine if the cool− ing coil is sized for full airflow or if a diversity factor has been used. If there is a diversity, set enough zones into full cooling to equal the design airflow of the coil. The remaining air will then go through the heating coil or by the bypass. 14.3.3

Normal Operations

During normal operations, there will be some varia− tion in airflow as each zone satisfies its individual re− quirements. It is also not uncommon for the system to move less air when it is in the heating mode. 14.3.4

Balancing

If the cooling coil is sized for the full fan airflow, put all zones into full cooling by setting each zone thermo− stat to its lowest point. The system is then balanced (similar to any low pressure, constant volume system detailed earlier) as outlined below: a.

Adjust and set the fan; put the system into full flow through the cooling coil with allowance for diversity.

b.

Make a Pitot tube traverse of each zone and total the results.

c.

Make any required fan adjustments to obtain the design total airflow.

d.

Adjust each zone damper to obtain the proper airflow in each zone. This should be done by making a traverse if possible. This type of system usually cannot be balanced satisfacto− rily without zone balancing dampers. If they are not shown on the construction drawings, the TAB technician should notify the proper people to have them installed.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

14.13


e.

Once each zone has the correct airflow, the terminals can be balanced by using the pre− viously described methods.

14.4

INDUCTION UNIT SYSTEMS

14.4.1

Preliminary Procedures

typical basketball or football inflation pin connected to rubber tubing connected to the static pressure gage). The opening on the probe should be on the side to take static pres− sure and not total pressure. c.

Induction unit systems (Figure 14−14) use high or me− dium pressure fans to supply primary air to the induc− tion units. Since they usually are located around the perimeter of the building, it is common practice to run many risers up and down the building and feed the units from a common header duct from the risers. As these systems use high or medium pressure, take extra precautions to avoid building up excessive system pressures and causing damage. 14.4.2

TAB Procedures

Airflow readings at the induction units are taken by reading the static pressure at one of the nozzles and comparing it to the manufacturer’s published data. The design static pressure and airflow will be shown on the manufacturer’s submittal data for the various size units on the job. a.

b.

Adjust the primary air fan using previously described methods for constant volume sys− tems. With a new or wide open system, allow for a 10 percent reduction in airflow while balancing. Proceed with the first pass to test and adjust each induction unit working from the supply fan outward. Using an appropriate static pres− sure gage insert a probe into the nozzle of the induction unit and read the static pressure (an acceptable probe for taking such reading is a

EXHAUST AIR LOUVER

EXHAUST AIR DAMPER

14.5

Compare the static pressure reading to the manufacturer’s values and determine the ac− tual CFM delivery of the unit. If the unit is above design flow, throttle until the required static pressure is achieved. (It is suggested to adjust this reading to the low side of accept− able air flow to allow for some system build− up as the rest of the system is balanced.) If the unit is low on flow, adjust the damper to in− sure that the damper is open and functioning. It will be advisable to check inlet static pres− sure to the unit prior to adjusting the damper to make sure sufficient static pressure is available to balance the unit. DUAL DUCT SYSTEMS

Dual duct systems (see Figure 14−13) use both a hot air duct and a cold air duct to supply air to mixing boxes. Mixing boxes may operate in a constant air volume mode or in a VAV mode. They are usually pressure in− dependent, but they may be either system powered or have external control systems. 14.5.1

Constant Volume Systems

Each mixing box has a thermostatically controlled mixing damper to satisfy the space temperature requi− rements. A mixture of the hot and cold air is controlled to maintain a constant airflow to the space. Constant volume dual duct mixing boxes maintain a constant volume of air to the conditioned space regard− less of which duct is supplying the air. This control

POSSIBLE RETURN AIR FAN RETURN AIR SYSTEM

RETURN AIR DAMPER

ZONE 4

OUTDOOR AIR INTAKE FILTERS

OUTDOOR AIR DAMPER

HEATING COIL

ZONE3 ZONE 2 ZONE MIXING DAMPERS

SUPPLY AIR FAN

COOLING COIL

ZONE 1

SUPPLY AIR SYSTEMS

POSSIBLE PRE-HEAT COIL

FIGURE 14-12 MULTI-ZONE SYSTEM 14.14

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


may be accomplished by a mechanical volume regula− tor located within the box.

Like the multi−zone system, most designers size the cooling coil for the full connected load of the outlets. If, however, the coil is not sized for full flow it will be necessary to index the proper number of boxes to cool− ing and heating in order to obtain total flow reading in the final stages of the procedures.

Since these boxes are pressure independent and the system is non−diversified, the procedures are the same as outlined previously. The only difference in this type of system is that you have two controls to set values for, the hot deck and cold deck, and both may have a maximum and mini− mum value.

Since the system is constant volume, it will be neces− sary to check the static pressures at the longest equiva− lent run of duct.

It is also required to check and verify that the hot and cold deck dampers respond properly especially when there is a common volume regulator.

At the conclusion of the balancing procedure, this is to properly obtain system total flow at the lowest possible static pressure.

EXHAUST AIR LOUVER

RETURN AIR FAN (OPTIONAL)

EXHAUST AIR DAMPER

RETURN AIR DAMPER

SUPPLY AIR FAN

HEATING COIL

OUTDOOR AIR INTAKE RETURN AIR SYSTEM

FILTERS

OUTDOOR AIR DAMPER

COOLING COIL

POSSIBLE PRE-HEAT COIL

T ZONE 1

T

SUPPLY DUCT TO ZONE 2

SUPPLY DUCT TO ZONE 1

MIXING DAMPERS

SUPPLY DUCT SYSTEM (COLD)

SUPPLY DUCT SYSTEM (HOT)

ZONE 2

FIGURE 14-13 DUAL DUCT SYSTEM

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

14.15


14.5.2

Variable Air Volume Systems

Each mixing box is thermostatically controlled to sat− isfy the space and temperature requirements. As the box airflow changes from cold to hot, the quantity of the hot air discharged is increased as the cold air is re− duced or shut off. The available sequences are numer− ous and it is imperative that the TAB technician review the operating sequence for the individual box being balanced.

b.

Proceed with additional passes until all units are balanced to acceptable air flow and static pressure tolerances.

c.

Some systems use the primary air source to power controls and move a secondary damp− er for adjusting room temperature. In such case, it is important to maintain the manufac− turer’s minimum static pressure regardless of CFM tolerances.

d.

After successfully balancing all induction units, revisit the fan system and record all fi− nal operating parameters as described in the Procedures For Conventional Systems.

Testing and adjusting is similar to a dual duct constant volume system except that VAV capability is incorpo− rated and will have to be taken into account. 14.6 NOTE: If static pressures on the first units read vary greatly from design, it may be necessary to check indi− vidual risers to ensure that air flow is available to all risers. Most induction units have the same static pres− sure for each exposure. It is advisable to start balanc− ing those units with the lowest required static pressure first.

a.

After the first pass, depending on the extent of adjustment, it may be advisable to check the fan system to see if total operating param− eters have been affected. If variation occurs re−adjust the fan to obtain the required flow.

OUTDOOR AIR INTAKE

POSSIBLE PRE-HEA T COIL

HEATING COIL

RETURN AIR DAMPER

OUTDOOR AIR DAMPER

EXHAUST AIR LOUVER

FILTERS

EXHAUST AIR DAMPER

POSSIBLE RETURN AIR FAN

SPECIAL EXHAUST AIR SYSTEMS

Exhaust air systems are found in various types of venti− lating systems and are encountered in all types of of− fice buildings, factories, institutions, schools, hospi− tals, arenas, restaurants, and labs. Many of these systems utilize hoods to effectively re− move fumes, odors, grease or any contaminant that is required to be exhausted. In order to properly remove any particulate, fume or odor, it is necessary to achieve the proper capture velocity at the hood opening. It is, therefore, incumbent upon the design professional and the hood manufacturer to properly design the air flow and hood dimensions for effective removal of the con− taminant that is to be exhausted. Local codes and ordi−

HIGH VELOCITY PRIMARY AIR SYSTEM

COOLING COIL

T

SUPPLY FAN

SECONDARY WATER COIL

T

INDUCTION UNITS

FIGURE 14-14 INDUCTION UNIT SYSTEM

14.16

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

INDUCED AIR


nances will also play an important part in the design phase of hood selection and operation. 14.7

PROCESS EXHAUST AIR SYSTEMS

Exhaust air systems with hoods are found in various types of ventilating systems. Hoods in restaurants and institutions are the type most frequently encountered in HVAC work. Most kitchen hoods are designed for a face velocity of about 100 feet per minute (0.5 m/s) at the hood entrance. Capture velocity is necessary to insure entrainment of steam and grease laden vapors from the equipment below. Some municipalities have ordinances setting minimum requirements for face or hood perimeter velocities at kitchen hoods, and further require that an authorized representative be present at the time of the balancing work. 14.7.1

Kitchen Exhaust/Makeup Air Systems

14.7.1.1 Test Instruments Kitchen makeup air systems must be in operation when the balancing takes place. Sometimes make−up is achieved by means of relief grilles from adjoining areas. The thermal anemometer is a good instrument for measuring these low face velocities. Some swing− ing vane anemometers (Velometer) can be used at ve− locities under 100 fpm (0.5 m/s) using the low flow probe. A Pitot tube used with a micromanometer also can be used. When making a Pitot tube traverse of the duct from the hood, be sure to correct for air density if elevated temperatures are present or predicted. 14.7.1.2 Ducts Most kitchen hood exhaust ducts are made of heavy gage metal, and are covered with a thick fire resistant insulation. A Pitot tube traverse of the duct is the most accurate way to test, but the test holes will need to be plugged with moisture tight, fire resistant metal plugs or caps, and often, holes are not allowed. Avoid putting holes in the bottom of the duct where moisture or grease can accumulate and/or leak out. If possible, put the test holes in the side of a riser. Never use plastic or rubber test plugs in a kitchen exhaust duct. Also, be aware that even if the correct airflow is obtained by the Pitot tube traverse, the hood face velocity may not be sufficient to satisfy local ordinances. In this case speed up the fan if the system designer approves and the fan/ drive components can accommodate the increase.

14.7.1.3 Filters Velocity readings across grease filters are not usually reliable. Accurate free area correction data is not usu− ally available and it would be influenced by the condi− tion of the filters. 14.7.2

Fume Hoods

14.7.2.1 General Fume hoods frequently are found in laboratory build− ings, hospitals and clean rooms. See the NEBB Proce− dural Standards for Certified Testing of Clean Rooms for additional information. As experiments are con− ducted in confined areas, the hoods are designed to prevent the escape of toxic or noxious fumes. Make up air must be provided from the HVAC system or from a separate system that some hoods have built in to minimize the loss of conditioned air from the laborato− ry. These systems also must be accurately balanced. 14.7.2.2 Working Tests When toxic experiments will be performed by the oc− cupants, when permissible, a smoke candle test should be made to ensure that vapors do not escape. Often the whole room is designed to be under a negative pres− sure, so the room also should be smoke tested, if per− missible. Some of the more sophisticated hoods have a built in exhaust fan working in series with the system exhaust fan. 14.7.2.3 Face Velocities Some fume hoods are designed to exhaust the same amount of air with the work door open or closed. Many fume hoods are variable volume and maintain a constant face velocity at the hood opening as the hood door is raised or lowered. The airflow varies to main− tain the same velocity through the opening, no matter how far the door is open. Face velocity testing should be done with the door wide open, unless otherwise spe− cified. Readings are best taken with a thermal anemometer and should be taken in equal area rectan− gles similar to a traverse. Be sure to keep well out of the airstream. 14.7.2.4 Smoke Test A hand held smoke generator should be used to insure that the entire face of the hood is drawing air into the hood. Be sure that air is not swirling and escaping back out of the hood. A 30−second smoke candle should be set off in the hood also. This will insure that the hood will contain the exhaust fumes without escaping back into the space.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

14.17


14.7.2.5 Balancing Fume hoods are used mostly in laboratories. When balancing laboratories, carefully study the drawings, noting the airflow and pressure differentials between different areas and rooms. Balancing is critical in these areas and will require precise readings and adjust− ments to obtain the correct positive and negative pres− sure relationship between spaces. Even with airflow readings within acceptable tolerances, some adjust− ments may have to be made to the airflows to obtain the correct pressures. If there is any question, consult with the system designer or the laboratory operator. 14.7.3

Industrial Exhaust Hoods And Equipment

14.7.3.1 General

A digital or thermal anemometer is a very valuable in− strument for this type of work as the probe is small enough to get into obstructed places. But here again, review the equipment manufacturer’s data, as the pro− cedures for setting up and testing the equipment often may be available.

14.7.3.3 Material Handling Procedures

Industrial exhaust air systems with hoods fall into two categories. One group, similar in many respects to lab− oratory fume hoods, is used over vats such as dip tanks and plating tanks. Exhaust hoods are often placed at one end above the tank and make up air hoods are placed at the opposite end. This permits vapors to be swept from the tank surface but still leaves the top open for overhead handling equipment. Often an ex− haust duct will be connected direct to a piece of equip− ment with no external hood. Other times, hoods may be used just to remove heat from equipment. Heat re− covery systems also are being used more frequently. Here again, make up air becomes critical and air densi− ty must be corrected in calculations. 14.7.3.2 Exhaust Air Procedures The balancing procedure is basically the same as any other exhaust air system. A Pitot tube traverse of the

14.18

exhaust air duct is the preferred method where possi− ble. The differences are mainly in how to test the vari− ous inlet openings. If an inlet opening velocity must be measured, obtain the free area opening by measuring it and then calculate what the velocity should be. Quite often this will not be possible due to irregular shapes and/or obstructions.

A second group of industrial exhaust air systems is used to remove and convey solid materials. Sawdust, wood chips, paper trimmings, etc., are transported at high velocities through these exhaust systems. These systems must be balanced so that velocities do not fall below predetermined transport velocities below which the materials would drop out.

Balancing of these systems is done with blast gates which are installed in lieu of dampers and are used to temporarily shut off unused branches. In addition to velocity readings, static pressure readings of the pres− sure differential between the room and the hood should be recorded in a convenient reference point at each hood or intake device. This will permit easy future checks designed to spot any deviation in exhaust vol− umes from original volumes.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


CHAPTER 15

HYDRONIC SYSTEM TAB PROCEDURES


CHAPTER 15 15.1

15.1.1

HYDRONIC SYSTEM MEASUREMENT METHODS Basic Balancing Methods

The best possible method for flow measurement of hy− dronic systems cannot be determined without review− ing the systems. There are five basic methods avail− able for measuring the flow quantity in a piping system: a. b. c. d. e. f.

with flow meters with calibrated balancing valves using the equipment pressure loss by heat transfer using pump curves ultrasonic, Doppler

It is preferable to balance hydronic systems by direct flow measurement. This balance approach is very ac− curate because it eliminates compounding errors introduced by the temperature difference procedures. Balance by direct flow measurement allows the pump to be matched to the actual system requirements (pump impeller trim). Proper instrumentation and good preplanning is needed. Water flow instrumenta− tion must be installed during construction of the piping system; they can consist of all or a combination of the following: a. b. c. d.

HYDRONIC SYSTEM TAB PROCEDURES 15.1.2

Using Flow Meters

A flow meter usually is deemed to be the most reliable method for measuring the system flow. Flow meters usually are permanently installed in the hydronic pip− ing system and are used for the measurement and ad− justment of flow to pumps, to primary heat exchange equipment, at each zone, and at terminal units. Flow meters such as the venturi, orifice, and Annubar types, require the use of a differential pressure gage and flow charts provided by the manufacturer to calculate the system flow. Always verify that installation of the flow meters is in accordance with recommended practices given by the manufacturer. There must be adequate amounts of straight sections of piping upstream and downstream from the flow meter to prevent erroneous readings affecting final system balance. NOTE: Verify that the pressure units of the differen− tial pressure gage and the pressure units found on the flow charts provided by the manufacturer are identic− al. If pressure units are not the same, (i.e. psi, in. wg, ft wg, Pa, kPa, mm. wg, m 3h) pressure conversions will be required.

System components used as flow metersC control valves, terminal units, chillers, etc. Flow metersCventuri, orifice plate, and Pitot tube Pumps Flow limiting devices and balancing devices

System circumstance often dictates a combination of flow and temperature balance. In many cases, it may not be economically sound or even necessary to install flow indicating devices at every terminal. For exam− ple, in reheat, induction, and radiation systems, tem− perature readings can be used to set the flow. Branch piping and risers should still be set with primary flow measuring devices. The water balance is undertaken using all the pressure measuring methods available and verified by total heat transfer using air and water temperature readings. The pressure readings provide the necessary accuracy for a good balance, only if veri− fied by a heat balance.

FIGURE 15-1 HYDRONIC FLOW MEASUREMENT

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

15.1


15.1.3

Using Combination Valve/Flow Meters

A self−adjusting valve/flow meter as shown in Figure 15−1 utilizes internal mechanisms that constantly change internal orifice openings to compensate for varying system differential pressures while maintain− ing a pre−set flow rate. An external adjustment is avail− able on some models. Pressure taps, providing mea− surement of valve differential pressure, allow measurements of the system flow.

Calibrated balancing valve/flow meters are field ad− justable devices. Pressure loss of the valve is measured similar to that of a flow meter. A chart or graph, pro− vided by the valve manufacturer, indicates actual flow rates at various valve positions and differential pres− sures. Unlike a flow meter, the flow coefficient of a calibrated balancing valve/flow meter changes with adjustment of the valve. Always be aware of the actual valve position when calculating the system flow.

An ultrasonic flow meter as shown in Figure 15−3, can be located remotely from the strap−on external pipe flow sensor shown in Figure 15−2. Note that the pipe insulation was removed so the sensor makes direct contact with the external pipe surface.

FIGURE 15-3 ULTRASONIC FLOW METER

15.1.4

Equipment Pressure Loss Method

Actual system flow rates may be established by using HVAC equipment pressure loss calculations, provided the following two items are available: a.

certified data from the equipment manufac− turer indicating rated flow and pressure losses;

b.

and an accurate means for determining the actual equipment pressure losses.

When the design criteria of the equipment and the ac− tual pressure loss is known, the flow rate may be calcu− lated by using the following equation: flow 2  flow 1 DP 2DP1

15.1.5

Heat Transfer Method

Approximate flow rates may be established at heating and cooling terminal units by using both air and hy− dronic measured heat transfer data and the proper equations. Although the equations used are slightly different, both are based upon the First Law of Ther− modynamics (heat transfer). Each determines the total heat transfer rate of the terminal unit at the time of test− ing, and then the flow rate is calculated based upon the fluid heat transfer rate (water temperature difference). See section 2.1 Heat Flow for the correct equations. FIGURE 15-2 EXTERNAL ULTRASONIC FLOW SENSOR ON PIPE WITH INSULATION REMOVED

15.2

15.1.6

Using Pump Curves

Flow may be established at circulating pumps through a series of differential pressure testing and pump curve

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


analysis. When circulating pumps are installed in se− ries with any item of HVAC equipment, the equipment flow rate may be assumed to be equal to that of the pump. 15.2

BASIC HYDRONIC SYSTEM PROCEDURES

Chapter 12CPreliminary TAB Procedures outlined the preparation work that must be done prior to the ac− tual testing, adjusting, and balancing of the HVAC sys− tems. Confirm that these preliminary procedures have been completed and check lists prepared. Do not at− tempt to balance a hydronic system before the installa− tion has been completed and all of the air systems have been balanced.

15.2.2

System Balancing Procedures

15.2.2.1

System Startup

Place the systems into operation, check that all air has been vented from the piping systems and allow flow conditions to stabilize. Verify that the system com− pression tank(s) and automatic water fill valve are op− erating properly. 15.2.2.2

Record the operating voltage and amperage of the pump(s) and compare these with nameplate ratings and thermal overload heater ratings. Verify the speed of each pump. 15.2.2.3

15.2.1

Related Systems

Confirm that all necessary electrical systems, temper− ature control systems, all related hydronic piping cir− cuits, and all related duct systems are functional and that any necessary compensation for seasonal effects have been made. 15.2.1.2

Hydronic Systems Ready

Verify that all hydronic systems have been cleaned, flushed, refilled, and vented, as required. 15.2.1.3

Valves Set

Verify that all manual valves are open, or preset as re− quired and all temperature control (automatic) valves are in a normal or desired position. 15.2.1.4

Control Devices

Verify that all automatically controlled devices in the piping or duct systems will not adversely affect the balancing procedures. 15.2.1.5

Flow Measurements

Preliminary Procedures

The following balancing procedures are basic to all types of hydronic distribution systems: 15.2.1.1

Pump Amperage

Static Head

With the pump(s) off, observe and record system static pressure (head) at the pump(s).

If flow meters or calibrated balancing valves are installed, which would allow the flow rate of the pump circuit(s) to be measured, perform the necessary work and record the data. 15.2.2.4

Zero Flow Readings

With the pump(s) running, slowly close the balancing cock fully in the pump discharge piping and record the shutoff−discharge and suction pressures found at the pump gage connections. Do not fully close any valves in the discharge piping of a positive displacement pump. Severe damage may occur. 15.2.2.5

Pump Curve Verification

Using pump shut−off head, determine and verify each actual pump operating curve and the size of each im− peller. Compare this data with the submittal data cur− ves. If the test point falls on the design curve, proceed to the next step; if not, plot a new curve parallel to the other curves on the chart, from zero flow to maximum flow. Make sure the test readings were taken correctly before plotting a new curve. Preferably one gage should be used to read differential pressure. It is impor− tant that gage readings should be corrected to the cen− ter line elevation of the pump. 15.2.2.6

SYSTEM FLOW

Open the discharge balancing cock slowly to the fully open position; record the discharge pressure, suction pressure, and total head. Using the total head, read the system water flow from the corrected pump curve es− tablished in step 15.2.2.5. Verify the data with that from flow meters and calibrated balancing valves, if used (see step 15.2.2.3).

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

15.3


15.2.2.7

Pump Flow Adjustments

If the total head is higher than the design total head, the water flow will be lower than designed. If the total head is less than design, water flow will be greater. If greater, the pump discharge pressure should be in− creased by partially closing the balancing cock until the system water flow is approximately 110 percent of design. Record the pressures and the water flow. Check pump motor, voltage, and amperage and record. This data should still be within the motor nameplate ratings. Start any secondary system pumps and re− adjust the balancing cock in the primary circuit pump discharge piping, if necessary. Again record all read− ings. See section 15.6 of this chapter for the balancing of primary−secondary systems. 15.2.2.8

15.2.2.12 High Flow Units Make another adjustment to the balancing valves on all units which have readings more than 10 percent above design flow in order to increase the flow through those units with less than design flow. 15.2.2.13 Unit Balancing Repeat this process until the actual fluid flow through each piece of equipment is within plus or minus 10 per− cent of the design flow. 15.2.2.14 Pump Check Make a final check of the pressures and the flow of all pump and equipment; of the voltage and amperage of pump motors; and record the data.

Initial System Adjustments 15.2.2.15 Bypass Valves

If orifice plates, venturi meters, or other flow measur− ing or control devices have been provided in the piping system branches, an initial recording of the flow dis− tribution throughout the system should be made with− out making any adjustments. After studying the sys− tem, adjust the distribution branches or risers to achieve balanced circuits as outlined above. Vent air from low flow circuits. Then proceed with the balanc− ing of terminal units on each branch. 15.2.2.9

Equipment Pressure Drops

Before adjusting any balancing valves at equipment (i.e. chillers, boilers, hot water exchangers, hot water coils, chilled water coils, etc.), take a complete set of pressure drop readings through all equipment and compare this with submittal data readings. Determine which are high and which are low in water flow. Vent air from low flow circuits or units and retake readings. 15.2.2.10 Preliminary Adjustments Make a preliminary adjustment to the balancing valves on all units with high water flow, setting each about 10 percent higher than the design flow rate. 15.2.2.11 Pump Measurements Take another complete set of pressure, voltage, and ampere readings on all pumps in the system. If system total flow has fallen below design flow, open the bal− ancing cock at each pump discharge to bring the flow at each pump within 105 to 110 percent of the design reading (if pump capacity permits). 15.4

Where three−way automatic valves are used, set all by− pass line balancing valves to restrict the bypassed wa− ter to 90 percent of the maximum demand through coils, heat exchangers and other terminal units. 15.2.2.16 Operating Ranges After all TAB work has been completed and the sys− tems are operating within plus or minus 10 percent of design flow, mark or score all balancing valves, gages, and thermometers at final set points and/or range of operation. 15.2.2.17 Safety Controls Verify the action of all water flow safety and shut− down controls. 15.2.2.18 Report Forms Prepare all TAB report forms (Chapter 16) and submit as required. 15.3

PIPING SYSTEM BALANCING

Many systems use combinations of the piping applica− tions outlined below. As it is necessary to apply bal− ancing procedures correctly, a procedure (or system) may be required to be broken down into several steps that correspond to the source, outlet, and piping. All of the balancing procedures outlined below have two things in common: a.

Balancing of a forced circulation system starts at the pump. Pump testing and adjust−

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


ment, as described in section 15.2, must be done prior to any adjustments to system pip− ing or terminal units. b.

System terminal units are maintained in the full flow position (i.e. control valves open to coil and closed to bypass) during the entire balancing procedure.

15.3.1

One-Pipe Systems

15.3.1.1

Series Loop

Upon adjustment of the source flow rate, balancing of a series loop is accomplished with the use of one bal− ancing device located in the loop. Balancing valves are normally located at the end (return) of a series loop piping arrangement. Adjustment of more than one de− vice within a loop will directly affect the flow and heat transfer of other terminals in the loop. Total loop flow is the primary concern in the adjustment of series loop systems. 15.3.1.2

One-Pipe (Monoflow)

Upon adjustment of the source flow rate, balancing of a one−pipe (single main) system is initiated with the first terminal unit supplied by the source. Adjustment of individual terminal unit flow rates may be accom− plished by any of the acceptable methods utilizing a balancing device normally located in the return pip− ing. Adjustment of the system continues sequentially from the first to the last terminal unit served. 15.3.2

Two-Pipe Systems

15.3.2.1

Direct-Return

Upon adjustment of the source flow rate, balancing of a two−pipe, direct−return system is initiated with the first terminal unit supplied by the source. Adjustment of terminal unit flow rates may be accomplished by any of the acceptable methods as outlined in the pre− vious subsection. Adjustment of system terminal units continues sequentially from the first to the last termi− nal unit served. Several passes of the system terminal units may be required to achieve balanced conditions. Therefore, on the first pass it is recommended that flow to the first 1_e section of the system should be ad− justed 10 percent below the design requirements. The reasoning for this is that the system differential pres− sure will increase as terminal unit flow rates are adjus− ted. On the second pass of balancing, flow rates for the first section of terminal units usually will have in− creased, but they should remain within acceptable tol− erances.

15.3.2.2

Reverse-Return

Adjustment and balancing of two−pipe reverse−return systems is usually much easier due to the inherent equal system pressure differential resulting from the piping arrangement. For example, a properly sized re− verse−return piping system serving ten terminal units of identical capacity and resistance may require ad− justment to the total system flow rate only. Flow will then be equally distributed to the terminals as a result of the piping application. However, many reverse− return systems do not contain identical terminal units. A review of the terminal units with specific attention to unit resistance should be made. Adjust the terminal flow rates starting with the units of least resistance and work toward the units with the greatest resistance. 15.3.3

Three-Pipe Systems (SummerWinter)

Due to the nature of this unusual piping application, the heating and cooling water systems may be viewed as diversity operations. In other words, the required terminal unit flow rate may vary with actual load conditions. Balancing should be performed on a sys− tem in a maximum load condition. Therefore, source and terminal unit adjustment should be accomplished with all terminal units (or as many as stipulated by di− versity procedure) in the wide−open position. Although connected to one another, the cooling and heating piping systems should be balanced as indepen− dently as possible with the given system conditions. Be aware that incorrect piping of automatic tempera− ture control valves or improper system pressurization may result in extreme difficulties while performing the balancing procedures. Crossed piping and/or incorrect valve applications are another common installation problem. 15.3.4

Four-Pipe Systems (SummerWinter)

Typical four−pipe systems are simply two independent two−pipe systems and should be addressed accor− dingly. Four−pipe systems may also be seen as the heart of ?summer−winter systems". They are reviewed in the following section 15.5. 15.4

BALANCING SPECIFIC SYSTEMS

The basic steps previously outlined in section 15.2 form the foundation for balancing any hydronic dis− tribution system. In this subsection, additional or spe− cial balancing procedures are outlined for use in bal− ancing specific types of hydronic distribution systems.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

15.5


All equipment such as boilers, chillers, compressors, etc., shall be started by, and operated under, the super− vision of the responsible contractor or the designated authority. 15.4.1

Chilled and/or Hot Water Equipment

15.4.1.1

Equipment Pressures Differences

15.4.1.5

Coils

When units or systems have multiple coil sections, ad− just the water flow to the design water pressure drop across each coil. A less accurate method of balancing multiple coil sections involves reading the water tem− peratures at each coil section with insertion thermom− eters and adjusting the balancing valves until uniform temperatures are obtained. 15.4.1.6

Flow through chillers, HVAC unit coils, and heat ex− changers should be measured by using flow meters or calibrated balancing valves if installed. Otherwise use the equipment manufacturer’s certified pressure drop tables and curves or use the pressure drop characteris− tics of automatic control valves. If three−way control valves are used, measure the pressure difference with full flow both through the coil or unit and the bypass. Set the bypass line balancing cock to maintain a constant pressure with the control valve in either posi− tion. 15.4.1.2

Unit Measurements

When fan−coil units or induction units are used with a direct return piping system, flow measurements for each unit should be made, either by using calibrated balancing valves, by taking pressure readings across each coil, from pressure readings across each automat− ic water valve, or (as a last resort) from water or air temperature readings. 15.4.1.3

Reverse Returns

When a reverse return piping system is installed, a flow measurement should be made at each set of risers to make sure that all units are getting the water flow to provide a fairly uniform water temperature drop. All automatic water valves must be open and coils must have the rated airflow when measurements are being made. 15.4.1.4

Temperature Differences

After all of the fan−coil type units have been put into operation with all automatic valves fully open and full flow through the coils, take the entering and leaving water temperatures of all chillers, boilers, heat ex− changers and coils. Record and compare with design conditions. 15.6

Complete the TAB procedures by recording the re− quired data on TAB report forms (Chapter 16) for sub− mittal. 15.4.2

Cooling Tower Systems

15.4.2.1

Tower Conditions

With the system off, confirm that the water level in the tower basin is at the correct level and that the piping system has been cleaned and flushed. On towers with variable pitch fan blades, verify that the setting of the blades is correct for the test conditions. Verify that all dampers are open and that all fan motors are ready to operate. 15.4.2.2

Pumps

With pump(s) off, observe and record the system static pressure at the pump(s). 15.4.2.3

System Startup

Place the system into operation and allow the flow conditions to stabilize. Check the operation of the wa− ter makeup valve and blow down. 15.4.2.4

Amperages

Record the operating voltage and amperage of all fan and pump motors and compare these with nameplate ratings and thermal overload heater ratings. 15.4.2.5

Pump Speed

Record the speed of each pump and verify with sub− mittals. 15.4.2.6

Zero Flow Readings

With the pump(s) running, slowly close the balancing cock in each pump discharge line and record shutoff discharge and suction pressures at the pump gage con− nections. Do not use this method if a positive dis−

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


placement pump(s) is used. Using the shutoff head, determine (and verify) the actual pump operating curve and the size of each impeller. Compare this data with the submittal data curves. If the test point falls on the design curve, proceed to the next step; if not, plot a new curve parallel with other curves on the chart, from zero flow to maximum flow. Make sure the test readings were taken correctly before plotting a new curve. Preferably a single gage should be used to read differential pressure. It is important that gage readings be corrected to center line elevation of the pump.

15.4.2.12 Tower Airflow

15.4.2.7

15.4.2.14 Condenser Controls

Tower Water Flow

Establish a uniform water distribution within the tower where possible, and check for clogged outlets or spray nozzles. Check for vortex conditions at the tower con− denser water suction connection. 15.4.2.8

Condensers

Record the inlet and outlet pressures of the condens− er(s) and check against the manufacturer’s design pressure difference. 15.4.2.9

Three-W ay Control Valve

When a three−way control valve is used in the condens− er water piping at the tower, measure the pressure dif− ference with full water flow going both through the tower and/or through the bypass line. Set the bypass line balancing cock to maintain a constant pressure at the pump discharge with the control valve in either position.

If the cooling tower has a ducted inlet or outlet, make a Pitot tube traverse of the duct to verify the airflow. 15.4.2.13 Refrigeration System After operation stabilizes under a normal cooling load, measure and record the condenser water inlet and out− let temperatures. Observe and record the percent of load on the compressor where possible.

After setting the three−way control valve (to control head pressure) in the condenser water line (step 15.4.2.9), verify and record that it operates to maintain the correct head pressure by varying the flow at the tower. On units that have a fan cycling control, verify that the fan cycles to maintain design condenser water temperature. If fan inlet or outlet damper controls are used, verify that the dampers modulate to maintain the design condenser water temperature leaving the tower. 15.4.2.15 Pump Adjustments Make another complete set of pressure, voltage and ampere readings at the pump(s). If the pump(s) capac− ity has fallen below design flow, open the balancing cock(s) at the pump discharge to bring flow within 5 to 10 percent of the design reading, if possible. 15.4.2.16 Final Measurements Make final measurements of all pump, fan and equip− ment data, and record on the TAB report forms.

15.4.2.10 Tower Fan(s) 15.4.2.17 Operating Ranges Start the tower fan(s) and check rotation, gear box, belts and sheave alignment. Measure and record fan motor amperes, voltage, phase and speed. 15.4.2.11 Temperature Readings

After all balancing work has been completed and the system is operating within plus or minus 10 percent of design flow, mark or score all balancing valves, gages, and thermometers at final set points and/or range of operation.

Take inlet and outlet dry bulb and wet bulb air temper− ature readings. Take test readings continually with a minimum of time lapse between readings. Note wind velocity and direction at the time of the test.

15.4.2.18 Safety Controls

Take inlet air temperature readings between 3 and 5 feet (0.9 and 1.5 m) from the tower at all inlets. These readings shall be taken halfway between the base and the top of the inlet and then averaged.

15.4.2.19 Report Forms

Verify the action of all water flow safety and shutdown controls.

Prepare all TAB report forms (Chapter 16) and submit as required.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

15.7


15.4.3

Boilers

15.4.3.8

15.4.3.1

Boiler Conditions

Follow the basic TAB procedures for hot water sys− tems.

Verify that the boiler(s) and/or system has been cleaned, flushed, and started; that all safety and oper− ating controls have been tested, adjusted and set; and that the burner(s) is operating properly and at full ca− pacity. 15.4.3.2

a.

Boiler feed pump(s) or makeup water sys− tem(s) and compression tank operation.

b.

Boiler, burner and pump nameplate data.

c.

Boiler control settings (operating pressures and temperatures).

e.

Water flow rates and inlet and outlet tempera− tures (hot water boilers). Steam boiler water level proper and steady.

15.4.3.3

System Venting

On initial runs, hot water systems normally require additional air venting. Confirm that automatic air vents are operating and vent air manually as required. 15.4.3.4

Steam Traps

Prepare TAB report forms (Chapter 16) and submit as required. 15.4.4

Heat Exchangers/Converters

15.4.4.1

Water Flow

Determine the water flow through the heat exchanger for all circuits using flow meters or calibrated balanc− ing valves. If the measured differential pressure must be used, the flow data can be obtained from the manufacturer’s submittal data curves or tables. Adjust the flow to design conditions and record the data. 15.4.4.2

Control Valves

Confirm that all automatic temperature control valves and steam pressure reducing valves in the system have the proper setting or mode of operation for the TAB work. 15.4.3.6

Strainers

15.4.4.3

15.4.3.7

Steam Distribution

15.4.4.4

15.8

Safety Valves

Record safety valve settings. Strainers

Confirm that all pipe strainers are clean. 15.4.4.6

Steam Traps

Check the operation of any steam traps. 15.4.4.7

Air Vents

Check all automatic air vents; manually vent air from hydronic piping as required. TAB Procedures

Follow the basic procedures for hot water or steam sys− tem TAB work for items not mentioned above. 15.4.4.9

The distribution of steam systems is set by the piping design, layout and pressures; therefore, no field bal− ancing is required.

Control Data

Measure and record the inlet steam pressure when used; check the setting and/or operation of any auto− matic temperature control valves, self contained con− trol valves, or pressure reducing valves. Record the data.

15.4.4.8

Confirm that all pipe strainers are clean.

Temperature Measurements

Take inlet and outlet water temperature readings; check against design data and record.

15.4.4.5 Coil and main drip steam traps can be checked for proper operation with a surface contact thermometer. 15.4.3.5

Report Forms

System Conditions

With the boiler(s) operating under normal conditions, check the following:

d.

15.4.3.9

Hot Water Procedures

Report Forms

Prepare TAB report forms (Chapter 16) and submit as required.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


15.5

VARIABLE VOLUME FLOW

15.5.1

Heating Systems at Reduced Flow Rates

code, does not allow the temperature increase safety factor to be applied.

The typical heating only hydronic system often oper− ates satisfactory at reduced flow because of the water flow/heat transfer relationship, as shown in Figure 15−4. 100

PERCENT OF DESIGN HEAT TRANSFER

90

15.5.1.2

Flow Variation

The previous comments apply to allowable flow varia− tion for heating terminal units selected for a 20F (11C) temperature drop (∆t) and the general order of 200F (93C) supply water temperature. Changes in design supply water temperature and design tempera− ture drop affect permissible flow variation. When 90 percent terminal capacity is acceptable for a system application, the flow variation can be approximated, as shown in Figure 15−5.

80

15.5.1.3

70 60

Heating Tolerance

Note that heating system tolerance to unbalance de− creases with increases in the design ∆t and with de− creases in supply water temperature. As a general rule, however, system tolerance to flow rates less than de− sign is important.

50 40 30

15.5.2

20

Cooling Systems at Reduced Flow Rates

10

0

10

20

30 40 50 60 70 80 PERCENT OF DESIGN FLOW RATE

90

100

FIGURE 15-4 EFFECTS OF FLOW VARIATION ON HEAT TRANSFER 20_F (11_C) ∆t AT 200_F (93_C) 15.5.1.1

Heat Transfer Rates

A decrease in terminal unit flow rate to 50 percent of design requirement still allows about 90 percent of heat transfer capability. The reason for the relative in− sensitivity to changing flow rates is that the governing coefficient for heat transfer is the air side coefficient. A change in internal or water side coefficient with flow rates does not materially affect the overall heat transfer coefficient. This means that (1) load ability for water− to−air terminals is basically established by the mean air−to−water temperature difference, (2) a high order of design temperature difference exists between the air being heated and mean water temperature in the coil (a substantial change in mean water temperature is necessary before terminal load ability is measurably changed), and (3) a substantial change in the mean wa− ter temperature (load ability) requires a very substan− tial change in water flow rate. A reduction in terminal heating capacity caused by an inadequate flow rate often can be overcome by simply raising the system supply water temperature. Designing near the upper temperature limits, 250F (121C) for low pressure

Chilled water terminal units are much less tolerant to flow variation. This is illustrated in Figure 15−5, which compares chilled and heating terminals for flow reduc− tion that will establish 90 percent of design heat trans− fer capacity. PERCENT OF DESIGN FLOW

0

100 50 45 40

90 80

140

220 260 300

180

70 60 50 40

CONVERSION FACTOR: C=(F-32)/1.8 C=degF/1.8

30 20 10 0 0

10

20

30

40

50

60

70

80

90

100

DESIGN T

FIGURE 15-5 PERCENT VARIATION TO MAINTAIN 90% TERMINAL HEAT TRANSFER 15.5.2.1

Dual-T emperature Units

Many dual−temperature changeover systems are com− pleted and first started during the heating season. Rea− sonably adequate heating ability in all terminals may suggest that the system is balanced adequately. As shown in Figure 15−5, 40 percent of design flow through the terminal provides 90 percent terminal de− sign heating with about 140F (60C) supply water and a 10 F (5.6C) ∆t. Increased supply water tem−

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

15.9


The majority of dual−temperature systems establish a decreased flow during the cooling season because of the introduction of chiller pressure drop against the distribution pump. The flow reduction can reach 25 percent, meaning that during chiller operation, a ter− minal that original heated satisfactorily could receive only 30 percent of the originally defined design flow rate. 15.5.2.3

Mandatory TAB Work

Under these circumstances, TAB work will become mandatory during spring chilled water startup. Bal− ancing procedures therefore must be related to the least tolerant system application or the cooling season. The procedures follow below under section 15.7.

100 90

TOTAL HEAT

80

SENSIBLE HEAT

100

70

90 60 50 40 30

80 70 60 50 40

100 80

% LATENT

Increased System Pressure

% SENSIBLE

15.5.2.2

75F (23.9C) DB, 65F (18.3C) WB]. Deviation from the curves shown is to be expected with changes in inlet water temperature, temperature rise, air veloc− ity, and DB and WB conditions. Figure 15−4 should be considered only as a general representation of variable change, not as a fact that applies to all chilled water ap− plications.

% TOTAL HEAT TRANSFER

perature establishes the same heat transfer at terminal flow rates of less than 40 percent design.

30

20

20 10

10

0

15.5.2.4

HEAT TRANSFER RATES

% Design

Other Load

Load Type

90% Load Sensible

Total

Latent

Sensible

65

90

84

58

Total

75

95

90

65

Latent

90

98

95

90

Order of %

Flow at

Table 15-1 Load-Flow Variations

Dual temperature systems are designed to chilled flow requirements and often operate on a 10F (5.6C) temperature drop as full−load heating. The basic curve applies to catalog ratings for lower dry bulb temperatures, provided a consistent entering air moisture content or vapor pressure is maintained [e.g., 15.10

20 40 60 PERCENT DESIGN FLOW

80

100

CONVERSION FACTOR: C=degF/1.8

20 15 10 0

The general change for chilled water heat transfer with changes in water flow rate is shown in Figure 15−6. The curves shown are based on ARI rating points: 45F (7.2C) inlet water at a 10F (5.6C) rise with air at 80F (26.7C) DB and 67F (19.4C) WB.

60 40 20 0

TEMP. RISE

The major reason for lessened tolerance of chilled wa− ter terminals to decreased flow is that the air−to−water temperature difference is much less than that with the heating cycle.

LATENT HEAT

0

20

40

60

80

100

FIGURE 15-6 CHILLED WATER TERMINAL FLOW VERSUS HEAT TRANSFER

If the chilled water terminal is matched to the load, the load variation to 90 percent design can be interpreted to three flow variations, as shown in Table 15−1. Note that load−flow variation for Figure 15−5 is stated for to− tal load. Table 15−1 and Figure 15−6 illustrate that the first loss with reduced chilled terminal flow rate is latent cap− ability. Table 15−1 defines that permissible flow varia− tion from design will be related to the following ap− plication requirements: (1) when high latent capability is needed, operational terminal flow rate must substantially meet design flow and (2) the ap− plication where sensible load control is predominant provides for a much wider terminal flow tolerance. 15.5.3

Variable Speed Pump Curves

Figure 15−7 shows pump curves from 50 percent to 100 percent capacity using a variable speed drive. Several efficient plot points A, B and C are used as system

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


curve start points to describe variable speed pump op− eration curves. The intersection of the percent base speed pump curves with the system ?control curve" can be determined as points 1 through 5 in Figure 15−7. Each intersection point states a pump, flow, head, and efficiency point. These points, in combination with variable speed drive efficiency, permit an indication of the power draw for the pump drive combination at the flow points illustrated.

Procedures

When circulating pump and terminal unit capacities are within acceptable tolerances, terminal unit balanc− ing may be performed in accordance with procedures stipulated by the piping configuration of the system. Units isolated for the initial balancing procedure are then balanced to design flow rates. Specific units and procedures involved in the diversity balancing procedure should be delineated in an agenda for approval prior to initiating field testing.

1

POWER

15.5.4.2

2 3

15.6

PRIMARY-SECONDAR Y SYSTEMS

15.6.1

Primary Loop

4 5

50%

% EFF

60%

70%

A

75%

77%

B

50% EFF CURVE

70%

79%

C

1750 RPM (100% SYNCHRONOUS)

77%

90%

“CONTROL CURVE” 1

80% HEAD

DIFFERENTIAL PRESSURE CONTROL RANGE 2

70% 60%

3 4

50% 5

DISTRIBUTION PIPING HEAD LOSS CURVE (HIGH HEAD LOSS SYSTEM)

FLOW RATE

FIGURE 15-7 PUMP WITH VARIABLE SPEED DRIVE

15.5.4

Balancing Variable Volume Systems

15.5.4.1

Characteristics

Variable volume systems have the following charac− teristics: a.

A system diversity is usually present (re− quired terminal flow rate exceeds pump and primary heat exchange unit).

b.

Two−way control valves are utilized at termi− nal units creating a variable system flow rate or pressure differential.

c.

Some form of differential pressure control (such as variable speed pumping) normally is used to maintain system differential pressure requirements.

Primary−secondary systems (Figure 15−8) may appear to be too complex when first reviewed, but a proper system analysis will result in a relatively simple bal− ancing procedure. First, address the primary loop. The source (primary pump) may supply outlets (primary bridges) in any of the possible piping arrangements de− scribed previously. The duty of the primary pump is to supply proper circulation to the primary bridges and return water back to the source. Initial balancing should therefore be restricted to the primary loop and its components. Note that secondary systems should be in full flow operation during primary loop balanc− ing. 15.6.2

Secondary Loops

Upon adjustment of primary pump flow rate, primary bridge piping is adjusted using a procedure applicable to the piping arrangement of the loop. When primary loop flow rates have been adjusted to design quanti− ties, testing of the secondary systems may begin. Test− ing of each secondary system should be accomplished independently with procedures applicable to the pip− ing arrangement of the secondary loop. 15.7

SUMMER-WINTER SYSTEMS

Characteristics of summer−winter piping applications (Figure 15−9) as stated above in section 15.5 Variable Volume Flow dictate that initial system testing and bal− ancing be accomplished in the cooling mode of opera− tion. 15.7.1

Cooling Mode

Design terminal unit cooling flow rates are usually much greater than that required for heating. As the ter− minal unit may only be adjusted to satisfy one flow

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

15.11


15.7.2

rate, that flow rate must be the greatest required, nor− mally that of the cooling application. The system pip− ing should be analyzed and set to accommodate the re− quirements of summer operation prior to pump testing. Insure that no bypasses are open and that summer−win− ter changeover valves (manual or automatic) are func− tional and open to the cooling mode of operation. Pro− ceed to test and balance the pump(s) required for the chilled water operation. Upon completion of the ad− justments to the circulation pump(s), test and balance the terminal units of the system in accordance with recommended procedures outlined for the piping ap− plication.

Heating Mode

Upon completion of system balancing in the cooling mode of operation, switch the system operation over to the heating mode. Balance applicable pumps and equipment unique to the hot water piping without dis− turbing the valve settings accomplished during the summer mode balancing procedure. 15.7.3

Alternative Mode

If necessary, balancing of summer−winter systems may be accomplished in the winter mode of operation provided system pump and terminal units are set to de− sign chilled water flow rates.

Control Valves

Terminal Unit

3-W ay control Valve for secondary circuit

Common Flow

Secondary Pump

Common Flow Secondary Pump

B

C

D

Balance Cock

Boiler or Chiller

E

F A

Primary Pump

FIGURE 15-8 EXAMPLE OF PRIMARY AND SECONDARY PUMPING CIRCUITS

15.12

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


By-pass valve Control valve Check valve

Boiler Flow control valves

Zone1

Zone 2

Air flow

Air flow

Chiller Compr. Tank By-pass valve Air separator

FIGURE 15-9 SUMMER-WINTER SYSTEMS

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition

15.13


THIS PAGE INTENTIONALLY LEFT BLANK

15.14

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition


CHAPTER 16

TAB REPORT FORMS


CHAPTER 16 16.1

PREPARING TAB REPORT FORMS

The proper use of the TAB Report Forms by SMACNA contractors, both as work sheets and as a final report of operating conditions, will provide the best method of ensuring that testing, adjusting, and balancing is be− ing correctly, systematically, and effectively per− formed. As described in Chapter 12CPreliminary TAB Proce− dures, design and manufacturer’s data should be en− tered on applicable report forms during the initial plan− ning stages for TAB. This step coupled with proper instruction of the TAB team by the use of these forms as work sheets will facilitate production and enhance the final results. Accuracy in preparing the final report forms is impor− tant for several reasons: a.

They provide a permanent record of system operating conditions after the last adjust− ments have been made.

b.

They confirm that the prescribed TAB proce− dures have been executed.

c.

They will serve as a handy reference that can be used by the owner for maintenance.

d.

They provide the system designer with a sys− tem operational check and would serve as an aid in diagnosing problem areas.

16.2

DESCRIPTION OF USE

The following is a brief explanation of the use of each report form and of any entries which may not be self− explanatory. The TAB Report Forms are designed for multiple use, therefore it is not necessary to enter data in all blank spaces or at each designated item. 16.2.1 System Diagram—TAB 1-02 This report form is to be used primarily for a schematic layout of air distribution systems, but it may be used for hydronic systems as well. A single line system dia− gram is highly recommended to insure systematic and efficient procedures. Figure 12.1 in Chapter 12 depicts a typical system diagram. Be sure to show quantities of outside air, return air and relief air, sizes and airflow for main ducts, sizes and airflow of outlets and inlets, and all dampers, regulating devices and terminal units. All outlets should be numbered before filling out form TAB 9−02CAir Outlet Test Report (or TAB 9A−02, 9B−02 and 9C−02). The use of this form is not mandato−

TAB REPORT FORMS ry and, if appropriate, a larger (similar) diagram sheet or computer printout diagram may be used. 16.2.2 Air Apparatus Test Report TAB 2-02 The performance of air handling apparatus with coils is to be reported on this report form. In addition, there is space for other information which will be of benefit to the design engineer, the maintenance engineer, and the TAB technician. Motor voltage and amperage for three phase motors should be reported for all three legs (T1, T2, T3). If the design engineer did not specify a de− sign quantity for any item in the test data section, place an X in the slot for the design quantity and record the actual quantity. However, if the equipment manufac− turer furnished ratings, enter them in the design co− lumns. If motor ratings differ from submitted data, provide an explanation at the bottom of the page. 16.2.3 Apparatus Coil Test Report TAB 3-02 This report form is to be used for recording perfor− mance of chilled water, hot water, steam, or DX coils, and for run−around heat recovery systems. The perfor− mance of as many as four coils (or two run−around sys− tems) can be shown on the same sheet. 16.2.4 Gas/Oil Fired Heat Apparatus Test Report—TAB 4-02 Data for gas or oil fired devices such as unit heaters, duct furnaces, etc. should be recorded on this report form. This report is not intended to be used in lieu of a factory start−up equipment report, but could be used as a supplement. All available design data should be reported. The ?HP/RPM, F. L. AMPS/S.F. (Service Factor), Drive Data" information could apply to the burner motor, burner fan motor, unit air fan motor, etc. depending on the application or equipment. Therefore, designate the motor of the recorded data. 16.2.5 Electronic Coil/Duct Heater Test Report—TAB 5-02 This report form is to be used for electric furnaces, or for electric coils installed in built−up units or in branch ducts. ?Min. Air Vel." is the manufacturers recom− mended minimum airflow velocity. 16.2.6 Fan Test Report—TAB 6-02 This report form is to be used with supply air, return air, or exhaust air fans. Since housings for various types of fans may have many different shapes and ar− rangements, not all entry blanks will be needed for testing a particular fan. The performance of up to three fans may be reported on this sheet.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

16.1


16.2.7 Rectangular Duct Traverse Report— TAB 7-02

on the test report form is acceptable based on the prior− ity assigned in Chapter 14.

This report form is to be used as a work sheet for re− cording the results of a Pitot tube traverse in a rectan− gular duct. It is recommended that the velocity pres− sures be recorded in one−half of each of the spaces provided and converted to velocities in the other half of each space at a later time. The velocities shall be av− eraged (not the velocity pressures).

16.2.11 Packaged Chiller Test Report— TAB 12-02

Instructions for making a traverse are shown on the re− verse side of the form (next page in manual). 16.2.8 Round Duct Traverse Report— TAB 8-02 Record the results of a Pitot tube traverse in a round duct on this work sheet type report form. Spaces shown are for velocity pressures and velocities taken at points across two diameters of the duct. Instructions for mak− ing the traverse are shown on the reverse side (next page in manual). 16.2.9 Air Outlet Test Report (Includes TAB 9A-02, TAB 9B-02 AND TAB 9C-02) As these report forms can be used as both work sheets and final report forms, the TAB technician is encour− aged to record all readings on these test report forms. However, it is not necessary to record preliminary ve− locity readings on the final forms unless specified by the design engineer. If more than one set of prelimi− nary readings is necessary or required, the data can be entered in the blank column between Preliminary and Final. The outlet number refers to numbers similar to those assigned on the schematic layout of Figure 12.1 which should be drawn on form TAB 1−02. The mini− mum columns on TAB 9C−02 are for the recom− mended minimum settings of VAV boxes. If the final adjusted airflow of any outlet varies by more than ± 10 percent from the design airflow, a note should be placed in the remarks section indicating the amount of variance. The remarks section at the bottom of the sheet should be used to provide known or poten− tial reasons for such deviation. 16.2.10 Terminal Unit Coil Check Report— TAB 11-02 This report form is used as a work sheet to check the water coil of terminal units. Any of the three methods for determining water flow or heat transfer indicated 16.2

Use this report form as a check sheet to record the con− trol settings and the entering and leaving conditions at the chiller. Since the TAB technician is not responsible for start−up or the proper operation of the machine, this form does not attempt to indicate the performance or efficiency of the machine except as may be determined by the design engineer from the data contained therein. The SMACNA TAB 12−02 report form or the equip− ment manufacturer’s form should be substantially completed and verified by the manufacturers’ repre− sentatives and/or the installing contractor before the HVAC distribution systems are balanced. Temperature and pressure readings of the chiller unit evaporator and condenser should be entered during the TAB proce− dures. 16.2.12 Package Rooftop/Heat Pump/Air Conditioning Unit Test Report— TAB 13-02 Test data from package units of all types is to be re− corded on this report form, with most of the data being furnished and verified by the installing contractor. If the unit has components other than the evaporator fan, DX coil, compressor, and condenser fan(s), use an ap− propriate test report form such as: Form TAB 3−02 for water or steam coils Form TAB 4−02 for direct fired heaters Form TAB 5−02 for electric coils Form TAB 6−02 for return air fans 16.2.13 Compressor and/or Condenser Test Report—TAB 14-02 The same comments apply to this report form as for form TAB 12−02. This form may also be used to have the installing contractor record data for the refrigerant side of unitary systems, bare compressors, separate air cooled condensers, or separate water cooled condens− ers. 16.2.14 Cooling Tower or Evaporative Condenser Test Report—TAB 15-02 This report form should be substantially completed and verified by the installing contractor before the sys−

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


tem is balanced. The pump data section is to be used for the recirculating pump in evaporative condensers, not the system pump used with cooling towers (use form TAB 17−02CPump Test Report). 16.2.15 Heat Exchanger/Converter Test Report—TAB 16-02 This report form is designed to record final conditions for up to three steam or hot water heat exchangers. 16.2.16 Pump Test Report—TAB 17-02 Final data on each pump performance must be re− corded on this form. The actual impeller diameter entry is that indicated by plotting the head curve or by actual field measurement where possible. Net positive suction heat (NPSH) is an important item for pumps in open circuits and for pumps handling fluids at elevated temperatures. 16.2.17 Balance Valve/Flow Meter Test Report—TAB 18-02 This new report form is used for recording data from balance valves or flow meters in hydronic systems.

16.2.18 Boiler Test Report—TAB 19-02 This report form may be used by the installing contrac− tor to substantially verify the data on this test report, particularly when factory start−up services are invol− ved. A flue gas analysis is beyond the scope of TAB procedures, but data could be added in the ?remarks" section if available and required by the design engi− neer. 16.2.19 Instrument Calibration Report— TAB 20-02 This report form is to be used for recording the applica− tion and date of the most recent calibration test or cal− ibration for each instrument used in the testing, adjust− ing, and balancing work. o determine the average air velocity in square or rec− tangular ducts, a Pitot tube traverse must be made to measure the velocities at the center points of equal areas over the cross section of the duct. The number of equal areas should not be less than 15, but need not be more than 64. The maximum distance between center points, for less than 64 readings, should not be more than 6 inches (150 mm). The readings closest to the ductwalls should be taken at one−half of this distance. For maximum accuracy, the velocity corresponding to each velocity pressure measured must be determined and then averaged.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

16.3


TAB 1-02 Copyright, SMACNA 2002

Page

of

TAB Report Forms SYSTEM DIAGRAM PROJECT LOCATION

16.4

SYSTEM UNIT DATE

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition


TAB 2-02 Copyright, SMACNA 2002

Page

of

AIR APPARATUS TEST REPORT PROJECT

SYSTEM UNIT

LOCATION

DATE

UNIT DATA

MOTOR DATA

Make/Model No.

Make/Frame

Type/Size

HP (W) RPM

Serial Number

Volts/Phase/Hertz

Arr./Class

F.L. Amps/S.F.

Discharge

Sheave

Sheave

Sheave Diam/Bore

Sheave Diam/Bore

Sheave Distance

No. Belts/Make/Size No. Filters/Type/Size

TEST DATA

DESIGN

ACTUAL

TEST DATA

Total CFM (L/s)

Discharge S.P.

Total S.P.

Suction S.P.

Fan RPM

Reheat Coil S.P.

DESIGN

ACTUAL

Cooling Coil S.P. Motor Volts

Preheat Coil S.P.

Motor Amps T1/T2/T3

Filters S.P.

Outside Air CFM (L/s) Return Air CFM (L/s)

Vortex Damp. Position Out Air Damp. Position

REMARKS: TEST DATE

READINGS BY

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition

16.5


TAB 3-02 Copyright, SMACNA 2002

Page

of

APPARATUS COIL TEST REPORT

PROJECT

COIL DATA

COIL NO.

COIL NO.

COIL NO.

COIL NO.

System Number Location Coil Type No. Row-Fins/in. (mm) Manufacturer Model Number Face Area, Ft.2 (m2)

TEST DATA

DESIGN

ACTUAL

DESIGN

ACTUAL

DESIGN

ACTUAL

DESIGN

Air Qty., CFM (L/s) Air Vel., FPM (m/s) Press. Drop, in. (Pa) Out. Air DB/WB Ret. Air DB/WB Ent. Air DB/WB Lvg. Air DB/WB Air T Water Flow, GPM (L/s) Press. Drop, PSI (kPa) Ent. Water Temp. Lvg. Water Temp. Water T Exp. Valve/Refrig. Refrig. Suction Press. Refrig. Suction Temp. Inlet Steam Press.

REMARKS: TEST DATE

16.6

READINGS BY

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition

ACTUAL


TAB 4-02 Copyright, SMACNA 2002

Page

of

GAS/OIL FIRED HEAT APPARATUS TEST REPORT

PROJECT

UNIT DATA

UNIT NO.

UNIT NO.

UNIT NO.

UNIT NO.

System Location Make/Model Type/Size Serial Number Type Fuel/Input Output Ignition Type Burner Control Volts/Phase/Hertz HP (W)/RPM F.L. Amps/S.F. Drive Data

TEST DATA

DESIGN

ACTUAL

DESIGN

ACTUAL

DESIGN

ACTUAL

DESIGN

ACTUAL

CFM (L/s) Ent./Lvg. Air Temp Air Temp. T Ent. Lvg. Air Press. Air Press. P Low Fire Input High Fire Input Manifold Press High Limit Setting Operating Set Point

REMARKS: TEST DATE

READINGS BY

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition

16.7


TAB 5-02 Copyright, SMACNA 2002

Page

of

ELECTRIC COIL/DUCT HEATER TEST REPORT

PROJECT

COIL DATA

COIL NO.

COIL NO.

COIL NO.

COIL NO.

System Number Location Coil Type Stages Manufacturer Model Number Face Area, Ft.2 (m2) TEST DATA

DESIGN

ACTUAL

DESIGN

ACTUAL

DESIGN

ACTUAL

DESIGN

Air Qty., CFM (L/s) Min. Air Vel., FPM (m/s) Press.Drop, In. wg (Pa) KW Phase Ent. Air DB/WB Lvg. Air DB/WB Air T Volts (T1-T 2) Volts (T2-T 3) Volts (T3-T 1) Amps (T1) Amps (T2) Amps (T3) Limit-Cutout Time Limit-Cutout Temp. Flow Switch Check

REMARKS: TEST DATE

16.8

READINGS BY

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition

ACTUAL


TAB 6-02 Copyright, SMACNA 2002

Page

of

FAN TEST REPORT

PROJECT

FAN DATA

FAN NO.

FAN NO.

FAN NO.

Location Service Manufacturer Model Number Serial Number Class Motor Make/Frame Motor HP (W) / RPM Volts/Phase/Hertz F.L. Amps/S.F. Motor Sheave Make Motor Sheave Diam./Bore No. Belts/Make/Size Sheave Distance

TEST DATA

DESIGN

ACTUAL

DESIGN

ACTUAL

DESIGN

ACTUAL

CFM (L/s) Fan RPM Total S.P. Suction Total S.P.—Discharge Total S.P. Amperage T1/T2/T3 Voltage

REMARKS: TEST DATE

READINGS BY

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

16.9


TAB 7-02 Copyright, SMACNA 2002

Page

of

RECTANGULAR DUCT TRAVERSE REPORT PROJECT

SYSTEM UNIT

LOCATION/ZONE

SERVICE

ALTITUDE

DENSITY

CORR. FACTOR

DUCT S.P.

REQUIRED F

Air Temp

(C) Size

DISTANCE FROM BOTTOM

Area

POSITION

1

2

3

ACTUAL

SCFM (sL/s)

SCFM (sL/s)

FPM (m/s)

FPM (m/s)

CFM (L/s)

CFM (L/s)

4

5

6

7

8

9

10

11

1 2 3 4 5 6 7 8 9 10 11 12 13 DISTANCE FROM DUCT EDGE VELOCITY SUB-T OTALS NOTE: Take readings with air blowing toward the observer.

REMARKS: TEST DATE

16.10

READINGS BY

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition

12

13


TAB 7-02 (Cont.) Copyright, SMACNA 2002

Page

of

INSTRUCTIONS

METHOD No.1 (EQUAL AREA) To determine the average air velocity in square or rectangular ducts, a Pitot tube traverse must be made to measure the velocities at the center points of equal areas over the cross section of the duct. The number of equal areas should not be less than 15, but need not be more than 64. The maximum distance between center points, for less than 64 readings, should not be more than 6 inches (150 mm). The readings closest to the ductwalls should be taken at one-half of this distance. For maximum accuracy, the velocity corresponding to each velocity pressure measured must be determined and then averaged.

METHOD No.2 (LOG)

NO. OF POINTS OR TRAVERSE LINES

POSITION RELATIVE TO INNER WALL

5

0.074, 0.238, 0.500, 0.712, 0.926

6

0.061, 0.235, 0.437, 0.563, 0.765, 0.939

7

0.053, 0.203, 0.366, 0.500, 0.634, 0.797, 0.947

LOG TCHEBYCHEFF RULE FOR RECTANGULAR DUCTS

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition

16.11


TAB 8-02 Copyright, SMACNA 2002

Page

of

ROUND DUCT TRAVERSE REPORT PROJECT

SYSTEM UNIT

LOCATION/ZONE

SERVICE

ALTITUDE

DENSITY

DUCT S.P.

Air Temp

Size

Area

CORR. FACTOR

REQUIRED F (C)

ACTUAL

SCFM (sL/s)

SCFM (sL/s)

FPM (m/s)

FPM (m/s)

CFM (L/s)

CFM (L/s)

(SEE PREVIOUS PAGE FOR INSTRUCTIONS)

Vert. Subtotal Horiz. Subtotal Total No. of points Average

REMARKS: TEST DATE

16.12

READINGS BY

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition


TAB 8-02 (Cont.) Copyright, SMACNA 2002

Page

of

INSTRUCTIONS

Fig. 1 shows the locations for Pitot tube tip making a 10-point traverse across one circular pipe diameter. In making two traverse cross s zones of equal area. the pipe diameter, readings are taken at right angles to each other. The traverse points shown represent 5 annular TABLE 1 Distances of Pitot Tube Tip from Pipe Center

DUCT DIAMETER Point 1

Point 2

inches

mm

Readings in one diam.

inches

mm

3 4 5 6 7 8 9 10 12 14 16 18 20 22 24 26 28 30 32 34 36

75 100 125 150 175 200 225 250 300 350 400 450 500 550 600 650 700 750 800 850 900

6 6 6 6 6 6 6 8 8 10 10 10 10 10 10 10 10 10 10 10 10

0.612 0.812 1.021 1.225 1.429 1.633 1.837 1.768 2.122 2.214 2.530 2.846 3.162 3.479 3.795 4.111 4.427 4.743 5.060 5.376 5.692

15.3 20.4 25.5 30.6 35.7 40.8 45.9 44.2 53.0 55.3 63.2 71.1 79.1 87.0 94.9 102.8 110.7 118.6 126.5 134.4 142.3

inches 1.061 1.414 1.768 2.121 2.475 2.828 3.182 3.062 3.674 3.834 4.382 4.929 5.477 6.025 6.573 7.120 7.668 8.216 8.764 9.311 9.859

mm 26.5 35.4 44.2 53.0 61.9 70.7 79.5 76.6 91.1 95.8 109.5 123.2 136.9 150.6 164.3 178.0 191.7 205.4 219.0 232.7 246.4

Point 3

Point 4

Point 5

inches

mm

inches

mm

inches

mm

1.369 1.826 2.282 2.738 3.195 3.651 4.108 3.950 4.740 4.950 5.657 6.364 7.077 7.778 8.485 9.192 9.900 10.607 11.314 12.021 12.728

34.2 45.6 57.1 68.5 80.0 91.3 102.7 98.8 118.6 123.7 141.4 159.1 176.8 194.4 212.1 229.8 247.5 265.1 282.8 300.5 318.2

4.677 5.612 5.857 6.693 7.530 8.367 9.213 10.040 10.877 11.713 12.550 13.387 14.233 15.060

116.9 140.3 146.4 167.3 188.2 209.1 230.1 251.0 171.9 292.8 313.7 334.6 355.6 376.5

6.641 7.589 8.538 9.487 10.435 11.384 12.222 13.282 14.230 15.179 16.128 17.176

166.0 189.7 213.4 237.2 260.9 284.6 308.3 332.0 355.7 379.4 403.2 426.9

For distances of traverse points from pipe center for pipe diameters other than those given in Table 1, use constants in Table 2. TABLE 2 Constants To Be Multiplied By Pipe Diameter For Distances of Pitot Tube Tip From Pipe Center

Readings in One Diameter

6 8 10

Point 1

Point 2

Point 3

Point 4

Point 5

0.2041 0.1768 0.1581

0.3535 0.3062 0.2738

0.4564 0.3953 0.3535

0.4677 0.4183

0.4743

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;˘ Third Edition

16.13


TAB 9A-02 Copyright, SMACNA 2002

Page

of

AIR OUTLET TEST REPORT

PROJECT

SYSTEM

OUTLET MANUFACTURER

TEST APPARATUS

OUTLET

AREA SERVED NO.

TYPE

SIZE

DESIGN AK

VEL

FLOW

PRELIMINARY VEL

FLOW

FINAL VEL

FLOW

REMARKS: TEST DATE

16.14

READINGS BY

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition

PERCENT OF DESIGN


TAB 9B-02 Copyright, SMACNA 2002

Page

of

AIR OUTLET TEST REPORT (Flow Hood) PROJECT

SYSTEM

OUTLET MANUFACTURER

TEST APPARATUS

OUTLET AREA SERVED

NO.

TYPE

SIZE

DESIGN

PRELIMINARY

FINAL

AIRFLOW CFM (L/s)

AIRFLOW CFM (L/s)

AIRFLOW CFM (L/s)

PERCENT OF DESIGN

REMARKS: TEST DATE

READINGS BY

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition

16.15


TAB 9C-02 Copyright, SMACNA 2002

Page

of

VAV AIR OUTLET TEST REPORT

PROJECT

SYSTEM

OUTLET MANUFACTURER

TEST APPARATUS

MAXIMUM DESIGN AREA SERVED

FPM (m/s)

CFM (L/s)

MAXIMUM FINAL VEL

FLOW

MINIMUM DESIGN AIRFLOW

ACTUAL AIRFLOW

REMARKS: TEST DATE

16.16

READINGS BY

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition


TAB 10-02 Copyright, SMACNA 2002

Page

of

TERMINAL BOX TEST REPORT

PROJECT

SYSTEM

OUTLET MANUFACTURER

TEST APPARATUS

BOX AREA SERVED

NO.

MAXIMUM SIZE

DESIGN CFM (L/s)

ACTUAL SETPOINT

MINIMUM ACTUAL CFM (L/s)

DESIGN CFM (L/s)

ACTUAL SETPOINT

ACTUAL CFM (L/s)

REMARKS: TEST DATE

READINGS BY

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16.17


TAB 11-02 Copyright, SMACNA 2002

Page

of

TERMINAL UNIT COIL CHECK REPORT

PROJECT SYSTEM

MANUFACTURER ALTERNATE NO.1

ROOM NO.

RISER NO.

UNIT SIZE

DESIGN DESIGN ENT. GPM P PRES.

LVG. PRES.

ALTERNATE NO.2

DESIGN T

EWT

LWT

ALTERNATE NO.3

DESIGN EAT T

LAT

NOTE: USE ONE OF THE ABOVE ALTERNATE METHODS

REMARKS:

TEST DATE

16.18

WATER SUPPLY TEMP.

OUT. AIR TEMP.

READINGS BY

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition

P

T


TAB 12-02 Copyright, SMACNA 2002

Page

of

PACKAGED CHILLER TEST REPORT

PROJECT

UNIT

LOCATION MANUF.

MODEL

CAPACITY

REFRIG.

EVAPORATOR

DESIGN

SERIAL NO. STARTER ACTUAL

Evaporator Press./Temp. Ent./Lvg. Water Press.

CONDENSER

DESIGN

ACTUAL

Condenser Press./Temp. xxxxx

Ent./Lvg. Water Press.

Water Press. P

Water Press. P

Ent./Lvg. Water Temp. Water Temp. T

Ent./Lvg. Water Temp.

GPM (L/s)

GPM (L/s)

COMPRESSOR

HEATER SIZE

xxxxx

Water Temp. T

DESIGN

ACTUAL

REFRIGERATION

Make/Model

Oil Level Checked

Serial Number

Oil Failure Sw. Diff.

Suction Press./Temp.

Refrig.Level Checked

Dischg. Press./Temp.

Relief Valve Setting

Oil Press./Temp.

Unloader Set Points

Voltage

% Cylinders Unloaded

Amps T1/T2/T3

Purge Operation Checked

KW Input

Bearing Temperature

Crankcase Htr. Amps

Vane Position

Ch. W. Control Setting

Demand Limit

Cond. W. Control Setting

Low Temp. Cutout Setting

DESIGN

ACTUAL

xxxxx

xxxxx

L.P. Cutout Setting H.P. Cutout Setting

REMARKS: TEST DATE

READINGS BY

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16.19


TAB 13-02 Copyright, SMACNA 2002

Page

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PACKAGE ROOFTOP/HEAT PUMP/ AIR CONDITIONING UNIT TEST REPORT PROJECT

SYSTEM/UNIT

LOCATION

UNIT DATA

MOTOR DATA

Make/Model Number

Make/Frame

Type/Size

HP (W)/RPM

Serial Number

Volts/Phase/Hertz

Type Filters/Size

F.L. Amps/S.F.

Fan Sheave Make

Make Sheave

Fan Sheave Diam./Bore

Sheave Diam./Bore

No. Belts/Make/Size

Sheave Distance

Type Heating Section*

TEST DATA EVAPORATOR

DESIGN

ACTUAL

TEST DATA CONDENSER

Total CFM (L/s)

Refrigerant/Lbs (kg)

Total S.P.

Compr. Mfr./Number

Discharge S.P.

Low Amb. Control

Suction S.P.

Compr. Model/Ser. Number

Out. Air CFM (L/s)

Suction Press./Temp.

Out. Air DB/WB

Cond. Press./Temp.

Ret. Air CFM (L/s)

Crankcase Htr. Amps

Ret. Air DB/WB

Compr. Volts

Ent. Air DB/WB

Compr.Amps T1/T2/T3

Lvg. Air DB/WB

L.P./H.P. Cutout Setting

Fan RPM

No. of Fans/Fan RPM

DESIGN

Cond. Fan HP (W)/CFM (L/s) Voltage Amperage T1/T2/T3 *Use TAB 4-02 or TAB 5-02 for heating section test report

REMARKS: TEST DATE

16.20

READINGS BY

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition

ACTUAL


TAB 14-02 Copyright, SMACNA 2002

Page

of

COMPRESSOR AND/OR CONDENSER TEST REPORT

PROJECT UNIT DATA

UNIT NO.

UNIT NO.

UNIT NO.

LOCATION Unit Manufacturer Unit Model/Ser.Number Compressor Manufacturer Compr. Model/Ser. Number Refrigerant/Lbs. (kg) Low Amb. Control TEST DATA

DESIGN

ACTUAL

DESIGN

ACTUAL

DESIGN

ACTUAL

Suction Press./Temp. Cond. Press./Temp. Oil Press./Temp. Voltage Amps T1/T2/T3 KW Input Crankcase Htr. Amps No.Fans/Fan RPM/CFM (L/s) Fan Motor Make/Frame/H.P. (W) Fan Motor Volts/Amps Duct Inlet/Outlet S.P. Ent./Lvg. Air D.B. Cond. Wtr. Temp. In/Out Cond. Wtr. Press. In/Out Control Setting Unloader Set Points L.P./H.P. Cutout Setting

REMARKS: TEST DATE

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16.21


TAB 15-02 Copyright, SMACNA 2002

Page

of

COOLING TOWER OR EVAPORATIVE CONDENSER TEST REPORT PROJECT LOCATION MANUF.

SYSTEM MODEL

NOM. CAPACITY

REFRIG.

SERIAL NO. WATER TREAT.

FAN DATA

PUMP DATA

No. of Fan Motors

Make/Model

Motor Make/Frame

Pump Serial No.

Motor HP (W)/RPM

Motor Make/Frame

Volts/Phase/Hertz

Motor HP (W)/RPM

Motor Sheave Diam./Bore

Volts/Phase/Hertz

Fan Sheave Diam./Bore

GPM (L/s)

Sheave Distance No. Belts/Make Size

AIR DATA

DESIGN

ACTUAL

Duct CFM (L/s)

WATER DATA

Duct Inlet S.P.

Ent./Lvg. Water Press. Water Press. P

Duct Outlet S.P.

Ent./Lvg. Water Temp.

Avg. Ent. W.B.

Water Temp. T

Avg. Lvg. W.B.

GPM (L/s)

Ambient W.B.

Bleed GPM (L/s)

DESIGN

Fan RPM Voltage

Voltage

Amperage T1/T2/T3

Amperage T1/T2/T3

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ACTUAL


TAB 16-02 Copyright, SMACNA 2002

Page

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HEAT EXCHANGER/CONVERTER TEST REPORT

PROJECT

MANUFACTURER

UNIT DATA

UNIT NO.

UNIT NO.

UNIT NO.

Location Service Rating, Btuh (W) Model Number Serial Number TEST DATA

DESIGN

ACTUAL

DESIGN

ACTUAL

DESIGN

ACTUAL

STEAM Pressure,PSI (kPa) Flow, Lbs./Hr. (kg/s) PRIMARY WATER Ent./Lvg. Temp. Temp. T Ent./Lvg. Press. Press. P GPM (L/s) SECONDARY WATER Ent./Lvg. Temp. Temp. T Ent./Lvg. Press. Press. P GPM (L/s) Control Set Point Exchanger Circuiting

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TAB 17-02 Copyright, SMACNA 2002

Page

of

PUMP TEST REPORT

PROJECT DATA

MANUFACTURER PUMP NO.

PUMP NO.

PUMP NO.

PUMP NO.

DESIGN Location Service Model Number Serial Number GPM (L/s) / Head—ft (m) Req. NPSH Pump RPM Impeller Diam. Motor Mfr./Frame Motor HP (W)/RPM Volts/Phase/Hertz F.L. Amps/S.F. Seal Type ACTUAL Pump Off-Press. Valve Shut Diff. Act. Impeller Diam. Valve Open Diff. Valve Open GPM (L/s) Final Dischg. Press. Final Suction Press. Final P Final GPM (L/s) Voltage Amperage T1/T2/T3

REMARKS: TEST DATE

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TAB 18-02 Copyright, SMACNA 2002

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BALANCING VALVE/FLOW METER TEST REPORT

PROJECT

SYSTEM/UNIT

LOCATION

SERVICE OR DESIGNATION

SIZE

MODEL

DESIGN GPM (L/s)

ACTUAL VALVE SETPOINT (DEGREE)

ACTUAL VALVE P.D.

ACTUAL GPM (L/s)

NOTES

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TAB 19-02 Copyright, SMACNA 2002

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BOILER TEST REPORT

PROJECT UNIT DATA

UNIT NO.

UNIT NO.

UNIT NO.

Location Manufacturer Model Number Serial Number Type/Size Fuel/Input No. of Passes Ignition Type Burner Control Volts/Phase/Hertz TEST DATA

DESIGN

ACTUAL

DESIGN

ACTUAL

DESIGN

ACTUAL

Operating Press./Temp. Ent./Lvg./Temp. No. Safety Valves/Size Safety Valve Setting High Limit Setting Operating Contr. Setting High Fire Set Point Low Fire Set Point Voltage Amperage T1/T2/T3 Draft Fan Volts/Amps Manifold Press. Output—MBH (kW) Safety Controls—Check

REMARKS: TEST DATE

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TAB 20-02 Copyright, SMACNA 2002

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INSTRUMENT CALIBRATION REPORT

PROJECT INSTRUMENT/SERIAL NO.

APPLICATION

DATES OF USE

CALIBRATION TEST DATE

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THIS PAGE INTENTIONALLY LEFT BLANK

16.28

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition


APPENDIX A

DUCT DESIGN TABLES & CHARTS


APPENDIX A

DUCT DESIGN TABLES & CHARTS

10

5

2

1

0.6 0.5 FRICTION LOSS, in. of water/100 ft

0.2

0.1 0.08

0.05

0.02

0.01 50

100

200

500

1000

2000

5000

20,000

10000

AIR QUALITY. cfm at 0.075 lb/ft3

50,000

100,000

400,000

3

FIGURE A-1 DUCT FRICTION LOSS CHART (I-P)

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition

A.1


FIGURE A-2 DUCT FRICTION LOSS CHART (SI)

A.2

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition


Duct Material Uncoated carbon steel, clean (Moody 1944) (0.00015 ft) (0.05 mm)

Roughness Category

Absolute Roughness Îľ1 ft

mm

Smooth

0.0001

0.03

Medium Smooth

0.0003

0.09

PVC plastic pipe (Swim 1982) (0.0003 to 0.00015 ft) (0.01 to 0.05 mm) Aluminum (Hutchinson 1953) (0.00015 to 0.0002 ft) (0.04 to 0.06 mm) Galvanized steel, longitudinal seams, 4 ft (1200 mm) joints (Griggs 1987) (0.00016 to 0.00032 ft) (0.05 to 0.1 mm) Galvanized steel, spiral seam with 1, 2, and 3ribs, 12 ft (3600 mm) joints (Jones 1979, Griggs 1987) (0.00018 to 0.00038 ft) (0.05 to 0.12 mm) Hot-dipped galvanized steel, longitudinal seams, 2.5ft (760 mm) joints (Wright 1945) (0.0005 ft) (0.15 mm)

(New Duct Friction Loss Chart) Old Average

0.0005

0.15

Medium Rough

0.003

0.9

Rough

0.01

3.0

Fibrous glass duct, rigid Fibrous glass duct liner, air side with facing material (Swim 1978) (0.005 ft) (1.5 mm) Fibrous glass duct liner, air side spray coated (Swim 1978) (0.015 ft) (4.5 mm) Flexible duct, metallic, (0.004 to 0.007 ft (1.2 to 2.1 mm) when fully extended) Flexible duct, all types of fabric and wire (0.0035 to 0.015 ft (1.0 to 4.6 mm) when fully extended) Concrete (Moody 1944) (0.001 to 0.01 ft) (0.3 to 3.0 mm)

Table A-1 Duct Material Roughness Factors

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;˘ Third Edition

A.3


2.6 Duct diameter inches (mm) 2.5 5 (125) 2.4 5 (125) 8 (200) 2.3 12 (300) 2.2 20 (500)

2.1

2.0

40 (1000) 60 (1500)

1.9 Correction Factor

100 (2500) 1.8

1.7 5 (125) 8 (200)

1.6

12 (300) 20 (500) 1.5 40 (1000) 100 (2500)

1.4

1.3

1.2

(ALL SIZES)

1.1

(ALL SIZES)

1.0

100 (2500)

0.9

5 (125) 0.8 100 (.5)

200 (1.0)

300 (1.5)

400 500 600 (2) (2.5) (3)

800 1000 (4) (5)

2000 (10)

3000 (15)

4000 5000 (20) (25)

Velocity-fpm (m/s)

FIGURE A-3 DUCT FRICTION LOSS CORRECTION FACTORS

A.4

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition


Side Rectangular Duct

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

8.0

9.0

10.0

11.0

12.0

13.0

14.0

15.0

16.0

3.0

3.8

4.0

4.2

4.4

4.6

4.7

4.9

5.1

5.2

5.5

5.7

6.0

6.2

6.4

6.6

6.8

7.0

3.5

4.1

4.3

4.6

4.8

5.0

5.2

5.3

5.5

5.7

6.0

6.3

6.5

6.8

7.0

7.2

7.5

7.7

4.0

4.4

4.6

4.9

5.1

5.3

5.5

5.7

5.9

6.1

6.4

6.7

7.0

7.3

7.6

7.8

8.1

8.3

4.5

4.6

4.9

5.2

5.4

5.7

5.9

6.1

6.3

6.5

6.9

7.2

7.5

7.8

8.1

8.4

8.6

8.8

5.0

4.9

5.2

5.5

5.7

6.0

6.2

6.4

6.7

6.9

7.3

7.6

8.0

8.3

8.6

8.9

9.1

9.4

5.5

5.1

5.4

5.7

6.0

6.3

6.5

6.8

7.0

7.2

7.6

8.0

8.4

8.7

9.0

9.3

9.6

9.9

Side Rectangular Duct 6 7 8 9 10

6

7

8

9

10

6.6 7.1 7.6 8.0 8.4

7.7 8.2 8.7 9.1

8.7 9.3 9.8

9.8 10.4

10.9

11 12 13 14 15

8.8 9.1 9.5 9.8 10.1

9.5 9.9 10.3 10.7 11.0

10.2 10.7 11.1 11.5 11.8

10.9 11.3 11.8 12.2 12.6

16 17 18 19 20

10.4 10.7 11.0 11.2 11.5

11.3 11.6 11.9 12.2 12.5

12.2 12.5 12.9 13.2 13.5

22 24 26 28 30

12.0 12.4 12.8 13.2 13.6

13.0 13.5 14.0 14.5 14.9

32 34 36 38 40

14.0 14.4 14.7 15.0 15.3

42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90 92 96

13

14

15

16

17

18

19

20

22

24

26

28

30

Side Rectangular Duct 6 7 8 9 10

11

12

11.5 12.0 12.4 12.9 13.3

12.0 12.6 13.1 13.5 14.0

13.1 13.7 14.2 14.6

14.2 14.7 15.3

15.3 15.8

16.4

13.0 13.4 13.7 14.1 14.4

13.7 14.1 14.5 14.9 15.2

14.4 14.9 15.3 15.7 16.0

15.1 15.6 16.0 16.4 16.8

15.7 16.2 16.7 17.1 17.5

16.4 16.8 17.3 17.8 18.2

16.9 17.4 17.9 18.4 18.9

17.5 18.0 18.5 19.0 19.5

18.6 19.1 19.6 20.1

19.7 20.2 20.7

20.8 21.3

21.9

14.1 14.6 15.1 15.6 16.1

15.0 15.6 16.2 16.7 17.2

15.9 16.5 17.1 17.7 18.3

16.8 17.4 18.1 18.7 19.3

17.6 18.3 19.0 19.6 20.2

18.3 19.1 19.8 20.5 21.1

19.1 19.9 20.6 21.3 22.0

19.8 20.6 214 22.1 22.9

20.4 21.3 22.1 22.9 23.7

21.1 22.0 22.9 23.7 24.4

21.7 22.7 23.5 24.4 25.2

22.3 23.3 24.2 25.1 25.9

22.9 23.9 24.9 25.8 26.6

24.0 25.1 26.1 27.1 28.0

26.2 27.3 28.3 29.3

28.4 29.5 30.5

30.6 31.7

32.8

22 24 26 28 30

15.3 15.7 16.1 16.5 16.8

16.5 17.0 17.4 17.8 18.2

17.7 18.2 18.6 19.0 19.5

18.8 19.3 19.8 20.2 20.7

19.8 20.4 20.9 21.4 21.8

20.8 21.4 21.9 22.4 22.9

21.8 22.4 22.9 23.5 24.0

22.7 23.3 23.9 24.5 25.0

23.5 24.2 24.8 25.4 26.0

24.4 25.1 25.7 26.4 27.0

25.2 25.9 26.6 27.2 27.9

26.0 26.7 27.4 28.1 28.8

26.7 27.5 28.2 28.9 29.6

27.5 28.3 29.0 29.8 30.5

28.9 29.7 30.5 31.3 32.1

30.2 31.0 32.0 32.8 33.6

31.5 32.4 33.3 34.2 35.1

32.7 33.7 34.6 35.6 36.4

33.9 34.9 35.9 36.8 37.8

32 34 36 38 40

15.6 15.9 16.2 16.5 16.8

17.1 17.5 17.8 18.1 18.4

18.5 18.9 19.3 19.6 19.9

19.9 20.3 20.6 21.0 21.4

21.1 21.5 21.9 22.3 22.7

22.3 22.7 23.2 23.6 24.0

23.4 23.9 24.4 24.8 25.2

24.5 25.0 25.5 26.0 26.4

25.6 26.1 26.6 27.1 27.6

26.6 27.1 27.7 28.2 28.7

27.6 28.1 28.7 29.2 29.8

28.5 29.1 29.7 30.2 30.8

29.4 30.0 30.6 31.2 31.8

30.3 30.9 31.6 32.2 32.8

31.2 31.8 32.5 33.1 33.7

32.8 33.5 34.2 34.9 35.5

34.4 35.1 35.9 36.6 37.2

35.9 36.7 37.4 38.2 38.9

37.3 38.1 38.9 39.7 40.5

38.7 39.5 40.4 41.2 42.0

42 44 46 48 50

17.1 17.3 17.6 17.8 18.1

18.7 19.0 19.3 19.5 19.8

20.2 20.6 20.9 21.2 21.5

21.7 22.0 22.4 22.7 23.0

23.1 23.5 23.8 24.2 24.5

24.4 24.8 25.2 25.5 25.9

25.7 26.1 26.5 26.9 27.3

26.9 27.3 27.7 28.2 28.6

28.0 28.5 28.9 29.4 29.8

29.2 29.7 30.1 30.6 31.0

30.3 30.8 31.2 31.7 32.2

31.3 31.8 32.3 32.8 33.3

32.3 32.9 33.4 33.9 34.4

33.3 33.9 34.4 35.0 35.5

34.3 34.9 35.4 36.0 36.5

36.2 36.8 37.4 38.0 38.5

37.9 38.6 39.2 39.8 40.4

39.6 40.3 41.0 41.6 42.3

41.2 41.9 42.7 43.3 44.0

42.8 43.5 44.3 45.0 45.7

52 54 56 58 60

20.1 20.3 20.6 20.8 21.1

21.7 22.0 22.3 22.6 22.6

23.3 23.6 23.9 24.2 24.5

24.8 25.1 25.5 25.8 26.1

26.3 26.6 26.9 27.3 27.6

27.6 28.0 28.4 28.7 29.1

28.9 29.3 29.7 30.1 30.4

30.2 30.6 31.0 31.4 31.8

31.5 31.9 32.3 32.7 33.1

32.6 33.1 33.5 33.9 34.4

33.8 34.3 34.7 35.2 35.6

34.9 35.4 35.9 36.3 36.8

36.0 36.5 37.0 37.5 37.9

37.1 37.6 38.1 38.6 39.1

39.1 39.6 40.2 40.7 41.2

41.0 41.6 42.2 42.8 43.3

42.9 43.5 44.1 44.7 45.3

44.7 45.3 46.0 46.6 47.2

46.4 47.1 47.7 48.4 49.0

62 64 66 68 70

23.1 23.3 23.6 23.8 24.1

24.8 25.1 25.3 25.6 25.8

26.4 26.7 27.0 27.3 27.5

27.9 28.2 28.5 28.8 29.1

29.4 29.7 30.0 30.4 30.7

30.8 31.2 31.5 31.8 32.2

32.2 32.5 32.9 33.3 33.6

33.5 33.9 34.3 34.6 35.0

34.8 35.2 35.6 36.0 36.3

36.0 36.4 36.8 37.2 37.6

37.2 37.7 38.1 38.5 38.9

38.4 38.8 39.3 39.7 40.2

39.5 40.0 40.5 40.9 41.4

41.7 42.2 42.7 43.2 43.7

43.8 44.4 44.9 45.4 45.9

45.8 46.4 47.0 47.5 48.0

47.8 48.4 48.9 49.5 50.1

49.6 50.3 50.9 51.4 52.0

72 74 76 78 80

26.1 26.4 26.6 26.9 27.1

27.8 28.1 28.3 28.6 28.9

29.4 29.7 30.0 30.3 30.6

31.0 31.3 31.6 31.9 32.2

32.5 32.8 33.1 33.4 33.8

34.0 34.3 34.6 34.9 35.3

35.4 35.7 36.1 36.4 36.7

36.7 37.1 37.4 37.8 38.2

38.0 38.4 38.8 39.2 39.5

39.3 39.7 40.1 40.5 40.9

40.6 41.0 41.4 41.8 42.2

41.8 42.2 42.6 43.1 43.5

44.1 44.6 45.0 45.5 45.9

46.4 46.9 47.3 47.8 48.3

48.5 49.0 49.6 50.0 50.5

50.6 51.1 51.7 52.2 52.7

52.6 53.2 53.7 54.3 54.8

82 84 86 88 90

29.1 29.6

30.8 31.4

32.5 33.0

34.1 34.7

35.6 36.2

37.1 37.7

38.5 39.2

39.9 40.6

41.3 42.0

42.6 43.3

43.9 44.7

46.4 47.2

48.7 49.6

51.0 52.0

53.2 54.2

55.3 56.4

92 96

11 12 13 14 15 16 17 18 19 20

Table A-2 Circulation Equivalents of Rectangular Ducts for Equal Friction and Capacity (I-P) (2) Dimensions in Inches

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition

A.5


Side Rectangular Duct 32 34 36 38 40

32 35.0 36.1 37.1 38.1 39.0

34

36

38

40

37.2 38.2 39.3 40.3

39.4 40.4 41.5

41.5 42.6

43.7

42 44 46 48 50

40.0 40.9 41.8 42.6 43.6

41.3 42.2 43.1 44.0 44.9

42.5 43.5 44.4 45.3 46.2

43.7 44.7 45.7 46.6 47.5

52 54 56 58 60

44.3 45.1 45.8 46.6 47.3

45.7 46.5 47.3 48.1 48.9

47.1 48.0 48.8 49.6 50.4

62 64 66 68 70

48.0 48.7 49.4 50.1 50.8

49.6 50.4 51.1 51.8 52.5

72 74 76 78 80

51.4 52.1 52.7 53.3 539

82 84 86 88 90 92 94 96

46

48

50

52

56

60

64

68

72

76

80

84

88

42

44

44.8 45.8 46.9 47.9 48.8

45.9 47.0 48.0 49.1 50.0

48.1 49.2 50.2 51.2

50.3 51.4 52.4

52.5 53.6

54.7

48.4 49.3 50.2 51.0 51.9

49.7 50.7 51.6 52.4 53.3

51.0 52.0 52.9 53.8 54.7

52.2 53.2 54.2 55.1 60.0

53.4 54.4 55.4 56.4 57.3

54.6 55.6 56.6 57.6 58.6

55.7 56.8 57.8 58.8 59.8

56.8 57.9 59.0 60.0 61.0

61.2 62.3 63.4

65.6

51.2 51.9 52.7 53.4 54.1

52.7 53.5 54.2 55.0 55.7

54.1 54.9 55.7 56.5 57.3

55.5 56.4 57.2 58.0 58.8

56.9 57.8 58.6 59.4 60.3

58.2 59.1 60.0 60.8 61.7

59.5 60.4 61.3 62.2 63.1

60.8 61.7 62.6 63.6 64.4

62.0 63.0 63.9 64.9 65.8

64.4 65.4 66.4 67.4 68.3

66.7 67.7 68.8 69.8 70.8

70.0 71.0 72.1 73.2

74.3 75.4

53.2 53.8 54.5 55.1 55.8

54.8 55.5 56.2 56.9 57.5

56.5 57.2 57.9 58.6 59.3

58.0 58.8 59.5 60.2 60.9

59.6 60.3 61.1 61.8 62.6

61.1 61.9 62.6 63.4 64.1

62.5 63.3 64.1 64.9 65.7

63.9 64.8 65.6 66.4 67.2

65.3 66.2 67.0 67.9 68.7

66.7 67.5 68.4 69.3 70.1

69.3 70.2 71.1 72.0 72.9

71.8 72.7 73.7 74.6 75.4

74.2 75.2 76.2 77.1 78.1

76.5 77.5 78.6 79.6 80.6

78.7 79.8 80.9 81.9 82.9

83.1 84.2 85.2

87.5

54.5 55.1 55.7 56.3 56.8

56.4 57.0 57.6 58.2 58.8

58.2 58.8 59.4 60.1 60.7

59.9 60.6 61.2 61.9 62.5

61.6 62.3 63.0 63.6 64.3

63.3 64.0 64.7 65.4 66.0

64.9 65.6 66.3 67.0 67.7

66.5 67.2 67.9 68.7 69.4

68.0 68.7 69.5 70.2 71.0

69.5 70.3 71.0 71.8 72.6

70.9 71.7 72.5 73.3 74.1

73.7 74.6 75.4 76.3 77.1

76.4 77.3 78.2 79.1 79.9

79.0 80.0 80.9 81.8 82.7

81.5 82.5 83.5 84.4 85.3

84.0 85.0 85.9 86.9 87.9

86.3 87.3 88.3 89.3 90.3

88.5 89.6 90.7 91.7 92.7

91.8 92.9 94.0 95.0

96.2 97.3

82 84 86 88 90

57.4 57.9 58A

59.3 59.9 60.5

61.3 61.9 62.4

63.1 63.7 64.3

64.9 65.6 66.2

66.7 67.3 68.0

68.4 69.1 69.7

70.1 70.8 71.5

71.7 72.4 73.1

73.3 74.0 74.8

74.9 75.6 76.3

77.9 78.7 79.4

80.8 81.6 82.4

83.5 84.4 85.3

86.2 87.1 88.0

88.8 89.7 90.7

91.3 92.3 93.2

93.7 94.7 95.7

96.1 97.1 981

98.4 99.4 100.5

92 94 96

42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80

Table A-2 Circulation Equivalents of Rectangular Ducts for Equal Friction and Capacity (I-P) (2) Dimensions in Inches (continued) Equation for Circular Equivalent of a Rectangular Duct: De = 1.30 [(ab)0.625 / (a+b)0.250] where a = length of one side of rectangular duct, inches. b = length of adjacent side of rectangular duct, inches. De = circular equivalent of rectangular duct for equal friction and capacity, inches.

A.6

Side Rectangular Duct 32 34 36 38 40

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;˘ Third Edition


Side RectangularDuct

100

125

150

100 125 150 175 200

109 122 133 143 152

137 150 161 172

164 177 189

191 204

219

225 250 275 300 350

161 169 176 183 195

181 190 199 207 222

200 210 220 229 245

216 228 238 248 267

232 244 256 266 286

246 259 272 283 305

273 287 299 322

301 314 339

328 354

383

400 450 500 550 600

207 217 227 236 245

235 247 258 269 279

260 274 287 299 310

283 299 313 326 339

305 321 337 352 365

325 343 360 375 390

343 363 381 398 414

361 382 401 419 436

378 400 420 439 457

409 433 455 477 496

437 464 488 511 533

492 518 543 567

547 573 598

601 628

656

650 700 750 800 900

253 261 268 275 289

289 298 306 314 330

321 331 341 350 367

351 362 373 383 402

378 391 402 414 435

404 418 430 442 465

429 443 457 470 494

452 467 482 496 522

474 490 506 520 548

515 533 550 567 597

553 573 592 609 643

589 610 630 649 686

622 644 666 687 726

653 677 700 722 763

683 708 732 755 799

711 737 763 787 833

765 792 818 866

820 847 897

875 927

984

650 700 750 800 900

1000 1100 1200 1300 1400

301 313 324 334 344

344 358 370 382 394

384 399 413 426 439

420 437 453 468 482

454 473 490 506 522

486 506 525 543 559

517 538 558 577 595

546 569 590 610 629

574 598 620 642 662

626 652 677 701 724

674 703 731 757 781

719 751 780 808 835

762 795 827 857 886

802 838 872 904 934

840 878 914 948 980

876 916 954 990 1024

911 953 993 1031 1066

941 988 1030 1069 1077

976 1022 1066 1107 1146

1037 1086 1133 1177 1220

1000 1100 1200 1300 1400

1500 1600 1700 1800 1900

353 362 371 379 387

404 415 425 434 444

452 463 475 485 496

495 508 521 533 544

536 551 564 577 590

575 591 605 619 633

612 629 644 660 674

648 665 682 698 713

681 700 718 735 751

745 766 785 804 823

805 827 849 869 889

860 885 908 930 952

913 939 964 988 1012

963 991 1018 1043 1068

1011 1041 1069 1096 1122

1057 1088 1118 1146 1174

1100 1133 1164 1195 1224

1143 1177 1209 1241 1271

1183 1219 1253 1286 1318

1260 1298 1335 1371 1405

1500 1600 1700 1800 1900

2000 2100 2200 2300 2400

395 402 410 417 424

453 461 470 478 486

506 516 525 534 543

555 566 577 587 597

602 614 625 636 647

646 659 671 683 695

688 702 715 728 740

728 743 757 771 784

767 782 797 812 826

840 857 874 890 905

908 927 945 963 980

973 993 1013 1031 1050

1034 1055 1076 1097 1116

1092 1115 1137 1159 1180

1147 1172 1195 1218 1241

1200 1226 1251 1275 1299

1252 1279 1305 1330 1355

1301 1329 1356 1383 1409

1348 1378 1406 1434 1461

1438 1470 1501 1532 1561

2000 2100 2200 2300 2400

2500 2600 2700 2800 2900

430 437 443 450 456

494 501 509 516 523

552 560 569 577 585

606 616 625 634 643

658 668 678 688 697

706 717 728 738 749

753 764 776 787 798

797 810 822 834 845

840 853 866 879 891

920 935 950 964 977

996 1012 1028 1043 1058

1068 1085 1102 1119 1135

1136 1154 1173 1190 1208

1200 1220 1240 1259 1277

1262 1283 1304 1324 1344

1322 1344 1366 1387 1408

1379 1402 1425 1447 1469

1434 1459 1483 1506 1529

1488 1513 1538 1562 1586

1589 1617 1644 1670 1696

2500 2600 2700 2800 2900

Side Rectangular Duct

100

125

150

175

200

225

250

275

300

350

400

450

500

550

600

650

700

750

800

900

Side Rectangular Duct

175

200

225

250

275

300

350

400

450

500

550

600

650

700

750

800

900

Side Rectangular Duct 100 125 150 175 200 225 250 275 300 350 400 450 500 550 600

Table A-3 Circular Equivalents of Rectangular Ducts for Equal Friction and Capacity (SI) (2) Dimensions in mm

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition

A.7


Side RectangularDuct

1000

1100

1000 1100 1200 1300 1400

1093 1143 1196 1244 1289

1202 1256 1306 1354

1312 1365 1416

1421 1530

1500 1600 1700 1800 1900

1332 1373 1413 1451 1488

1400 1444 1486 1527 1566

1464 1511 1555 1598 1640

1526 1574 1621 1667 1710

1584 1635 1684 1732 1778

1640 1693 1745 1794 1842

1749 1803 1854 1904

1858 1912 1964

1968 2021

2077

2000 2100 2200 2300 2400

1523 1558 1591 1623 1655

1604 1640 1676 1710 1744

1680 1719 1756 1793 1828

1753 1793 1833 1871 1909

1822 1865 1906 1947 1986

1889 1933 1977 2019 2060

1952 1999 2044 2088 2131

2014 2063 2110 2155 2200

2073 2124 2173 2220 2266

2131 2183 2233 2283 2330

2186 2240 2292 2343 2393

2296 2350 2402 2453

2405 2459 2511

2514 2568

2624

2500 2600 2700 2800 2900

1685 1715 1744 1772 1800

1776 1808 1839 1869 1898

1862 1896 1929 1961 1992

1945 1980 2015 2048 2081

2024 2061 2097 2133 2167

2100 2139 2177 2214 2250

2173 2213 2253 2292 2329

2243 2285 2327 2367 2406

2311 2355 2398 2439 2480

2377 2422 2466 2510 2552

2441 2487 2533 2578 2621

2502 2551 2598 2644 2689

2562 2612 2661 2708 2755

2621 2672 2722 2771 2819

2678 2730 2782 2832 2881

Side Rectangular Duct

1000

1100

1200

1300

1400

1500

1800

1900

2000

1200

1300

1400

1500

1600

1700

1800

1900

2000

2100

2200

2300

2400

2500

2600

2700

2800

1000 1100 1200 1300 1400

1600

1700

1500 1600 1700 1800 1900

2100

2200

2300

2400

2000 2100 2200 2300 2400

2733 2787 2840 2891 2941 2500

2842 2896 2949 3001

2952 3006 3058

3061 3115

3170

2600 2700

2800

2900

Table A-3 Circular Equivalents of Rectangular Ducts for Equal Friction and Capacity (SI) (2) Dimensions in mm (continued) Equation for Circular Equivalent of a Rectangular Duct: De = 1.30 [(ab)0.625 / (a+b)0.250] where a = length of one side of rectangular duct, mm. b = length of adjacent side of rectangular duct, mm. De = circular equivalent of rectangular duct for equal friction and capacity, mm.

A.8

2900

Side Rectangular Duct

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;˘ Third Edition

2500 2600 2700 2800 2900 Side Rectangular Duct


Velocity fpm

Velocity Pressure in. wg

Velocity fpm

Velocity Pressure in. wg

Velocity fpm

Velocity Pressure in. wg

300 350 400 450 500

0.01 0.01 0.01 0.01 0.02

2050 2100 2150 2200 2250

0.26 0.27 0.29 0.30 0.32

3800 3850 3900 3950 4000

0.90 0.92 0.95 0.97 1.00

5550 5600 5650 5700 5750

550 600 650 700 750

0.02 0.02 0.03 0.03 0.04

2300 2350 2400 2450 2500

0.33 0.34 0.36 0.37 0.39

4050 4100 4150 4200 4250

1.02 1.05 1.07 1.10 1.13

800 850 900 950 1000

0.04 0.05 0.05 0.06 0.06

2550 2600 2650 2700 2750

0.41 0.42 0.44 0.45 0.47

4300 4350 4400 4450 4500

1050 1100 1150 1200 1250

0.07 0.08 0.08 0.09 0.10

2800 2850 2900 2950 3000

0.49 0.51 0.52 0.54 0.56

1300 1350 1400 1450 1500

0.11 0.11 0.12 0.13 0.14

3050 3100 3150 3200 3250

1550 1600 1650 1700 1750

0.15 0.16 0.17 0.18 0.19

1800 1850 1900 1950 2000

0.20 0.21 0.22 0.24 0.25

Velocity fpm

Velocity Pressure in. wg

1.92 1.95 1.99 2.02 2.06

7300 7350 7400 7450 7500

3.32 3.37 3.41 3.46 3.51

5800 5850 5900 5950 6000

2.10 2.13 2.17 2.21 2.24

7550 7600 7650 7700 7750

3.55 3.60 3.65 3.70 3.74

1.15 1.18 1.21 1.23 1.26

6050 6100 6150 6200 6250

2.28 2.32 2.36 2.40 2.43

7800 7850 7900 7950 8000

3.79 3.84 3.89 3.94 3.99

4550 4600 4650 4700 4750

1.29 1.32 1.35 1.38 1.41

6300 6350 6400 6450 6500

2.47 2.51 2.55 2.59 2.63

8050 8100 8150 8200 8250

4.04 4.09 4.14 4.19 4.24

0.58 0.60 0.62 0.64 0.66

4800 4850 4900 4950 5000

1.44 1.47 1.50 1.53 1.56

6550 6600 6650 6700 6750

2.67 2.71 2.76 2.80 2.84

8300 8350 8400 8450 8500

4.29 4.35 4.40 4.45 4.50

3300 3350 3400 3450 3500

0.68 0.70 0.72 0.74 0.76

5050 5100 5150 5200 5250

1.59 1.62 1.65 1.69 1.72

6800 6850 6900 6950 7000

2.88 2.92 2.97 3.01 3.05

8550 8600 8650 8700 8750

4.56 4.61 4.66 4.72 4.77

3550 3600 3650 3700 3750

0.79 0.81 0.83 0.85 0.88

5300 5350 5400 5450 5500

1.75 1.78 1.82 1.85 1.89

7050 7100 7150 7200 7250

3.10 3.14 3.19 3.23 3.28

8800 8850 8900 8950 9000

4.83 4.88 4.94 4.99 5.05

Velocity  4005 V p (or) V p 

Velocity Pressure in. wg

Velocity fpm

Velocity

4005

2

Table A-4 Velocities/Velocity Pressures (I-P)

PRESSURE LOSS CORRECTION FACTOR

4 3

2

1 0 10 20 30 PERCENT OF COMPRESSION LENGTH

FIGURE A-4 VELOCITIES/VELOCITY PRESSURES (I-P) HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition

A.9


Velocity (m/s) 1.0 1.2 1.4 1.6 1.8

Velocity Pressure (Pa) 0.6 0.9 1.2 1.5 2.0

Velocity (m/s) 10.0 10.2 10.4 10.6 10.8

Velocity Pressure (Pa) 60 63 65 68 70

Velocity (m/s) 19.0 19.2 19.4 19.6 19.8

Velocity Pressure (Pa) 217 222 227 231 236

Velocity (m/s) 28.0 28.2 28.4 28.6 28.8

Velocity Pressure (Pa) 472 479 486 493 499

Velocity (m/s) 37.0 37.2 37.4 37.6 37.8

Velocity Pressure (Pa) 824 833 842 851 860

2.0 2.2 2.4 2.6 2.8

2.4 2.9 3.5 4.1 4.7

11.0 11.2 11.4 11.6 11.8

73 76 78 81 84

20.0 20.2 20.4 20.6 20.8

241 246 251 256 261

29.0 29.2 29.4 29.6 29.8

506 513” 521 528 535

38.0 38.2 38.4 38.6 38.8

870 879 888 897 907

3.0 3.2 3.4 3.6 3.8

5.4 6.2 7.0 7.8 8.7

12.0 12.2 12.4 12.6 12.8

87 90 93 96 99

21.0 21.2 21.4 21.6 21.8

266 271 276 281 286

30.0 30.2 30.4 30.6 30.8

542 549 557 564 571

39.0 39.2 39.4 39.6 39.8

916 925 935 944 954

4.0 4.2 4.4 4.6 4.8

9.6 10.6 11.7 12.7 13.9

13.0 13.2 13.4 13.6 13.8

102 105 108 111 115

22.0 22.2 22.4 22.6 22.8

291 297 302 308 313

31.0 31.2 31.4 31.6 31.8

579 586 594 601 609

40.0 40.2 40.4 40.6 40.8

963 973 983 993 1002

5.0 5.2 5.4 5.6 5.8

15.1 16.3 17.6 18.9 20.3

14.0 14.2 14.4 14.6 14.8

118 121 125 128 132

23.0 23.2 23.4 23.6 23.8

319 324 330 335 341

32.0 32.2 32.4 32.6 32.8

617 624 632 640 648

41.0 41.2 41.4 41.6 41.8

1012 1022 1032 1042 1052

6.0 6.2 6.4 6.6 6.8

21.7 23.1 24.7 26.2 27.8

15.0 15.2 15.4 15.6 15.8

135 139 143 147 150

24.0 24.2 24.4 24.6 24.8

347 353 359 364 370

33.0 33.2 33.4 33.6 33.8

656 664 672 680 688

42.0 42.2 42.4 42.6 42.8

1062 1072 1083 1093 1103

7.0 7.2 7.4 7.6 7.8

29.5 31.2 33.0 34.8 36.6

16.0 16.2 16.4 16.6 16.8

154 158 162 166 170

25.0 25.2 25.4 25.6 25.8

376 382 389 395 401

34.0 34.2 34.4 34.6 34.8

696 704 713 721 729

43.0 43.2 43.4 43.6 43.8

1113 1124 1134 1145 1155

8.0 8.2 8.4 8.6 8.8

38.5 40.5 42.5 44.5 46.6

17.0 17.2 17.4 17.6 17.8

174 178 182 187 191

26.0 26.2 26.4 26.6 26.8

407 413 420 426 433

35.0 35.2 35.4 35.6 35.8

738 746 755 763 772

44.0 44.2 44.4 44.6 44.8

1166 1176 1187 1198 1209

9.0 9.2 9.4 9.6 9.8

48.8 51.0 53.2 55.5. 57.8

18.0 18.2 18.4 18.6 18.8

195 199 204 208 213

27.0 27.2 27.4 27.6 27.8

439 446 452 459 465

36.0 36.2 36.4 36.6 36.8

780 789 798 807 815

45.0 45.2 45.4 45.6 45.8

1219 1230 1241 1252 1263

Table A-5 Velocities/Velocity Pressures (SI) Degrees 10 20 30 40 50 60

Radians 0.175 0.349 0.524 0.698 0.873 1.05

Degrees 70 80 90 135 180 360

Radians 1.22 1.40 1.57 (π/2) 2.36 3.14 (π) 6.28 (2π)

Table A-6 Angular Conversion

A.10

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


C

Vs / Vc

75% Regain

90% Regain

0.95 .91 .87 .83 .80

0.03 .04 .06 .08 .09

0.01 .02 .02 .03 .04

0.77 .74 .71 .69 .67

0.10 .11 .12 .13 .14

0.04 .04 .05 .05 .06

0.65 .63 .61 .59 .57

0.15 .15 .16 .16 .17

0.06 .06 .06 .07 .07

0.56 .54 .53 .51 .50

0.18 .18 .18 .18 .19

0.07 .07 .07 .07 .08

Vs = Downstream Velocity; Vc = Upstream Velocity

200°F 93°C 100°F 150°F 38°C 66°C AIR TEMPERATURE

2440 m 8.000 ft.

STANDARD AIR

07

08

09

10

11

12

-50 °F -46 °C

0

610 m 2.000 ft.

0°F -18 °C

50°F 10°C

1220 m 4.000 ft.

1830 m 6.000 ft.

ELEVATION

3050 m 10.000 ft.

250°F 121°C

3660 m 4270 m 12.000 ft. 14.000 ft.

300°F 149°C

Table A-7 Loss Coefficients for Straight-Through Flow

CORRECTION FACTOR 1K. OR K.1

FIGURE A-5 AIR DENSITY FRICTION CHART CORRECTION FACTORS NOTE: When an air distribution system is designed to operate above 2000 feet (610 m) altitude, below 32_ F (0_C), or above 1200_ F (490_ C) temperature, the duct friction loss obtained must be corrected for the air

density. The actual air flow (cfm or L/s) is used to find the duct friction loss which is multiplied by the correc− tion factor or factors from the above chart to obtain the actual friction loss.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

A.11


FACE AREA, FT2 (m2) PER LOUVER

30 (3)

INTAKE

20 (2)

EXHAUST

10 (1)

0 0

2000 (1000)

4000 (2000)

8000 (4000)

6000 (3000)

12000 (6000)

10000 (5000)

FIGURE A-6 LOUVER VELOCITY

Parameters Used Above Minimum Free Area (48 Inch Square Test Section) Water Penetration, oz/ft2, 15 min. Maximum Static Pressure Drop, in. wg (Pa)

Intake Louver

Exhaust Louver

45%

45%

Negligible (Less than 0.2)

Not Applicable

0.15 (37)

0.25 (62)

Table A-8 Recommended Criteria for Louver Sizing

A.12

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition


DUCT ELEMENT LOUVERS A. Intake: 1. 7,000 cfm (3500 L/s) and greater 2. Less than 7,000 cfm (3500 L/s) B. Exhaust: 1. 5,000 cfm (2500 L/s) and greater 2. Less than 5,000 cfm (2500 L/s) FILTERS A. Fibrous Media Unit Filters: 1. Viscous Impingement 2. Dry Type 3. HEPA B. Renewable Media Filters: 1. Moving Curtain Viscous Impingement 2. Moving Curtain Dry−media C. Electronic Air Cleaners: 1. Ionizing Plate−Type HEATING COILS A. Steam and Hot Water

B. Electric: 1. Open Wire 2. Finned Tubular COOLING OR DEHUMIDIFYING COILS A. Without Eliminators B. With Eliminators AIR WASHERS A. Spray−Type B. Cell−Type C. High Velocity Spray−Type

ACTUAL FACE VELOCITY, fpm (m/s)

400 (2.0) See Fig. 16−6 500 (2.5) See Fig. 16−6

250–700 (1.2–3.5) Up to 750 (3.5) 250 (1.2) 500 (2.5) 200 (1.0) 300–500 (1.5–2.5) 500–600 (2.5–3.0) (Most common) 200 (1.0) min., 1,500 (7.5) max. Refer to Mfg. Data Refer to Mfg. Data 500–600 (2.5–3.0) 600–800 (3.0–4.0) 300–700 (1.5–3.5) Refer to Mfg. Data Refer to Mfg. Data

Table A-9 Typical Design Velocities for Duct Components

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

A.13


FITTING LOSS COEFFICIENT TABLES A. ELBOW, SMOOTH RADIUS (DIE STAMPED), ROUND

Coefficients for 90 Elbows: (See Note 1) R/D

0.5

0.75

1.0

1.5

2.0

2.5

C

0.71

0.33

0.22

0.15

0.13

0.12

q

Note 1: For angles other than 90° multiply by the following factors: 

0

20°

30°

45°

60°

75°

90°

110°

130°

150°

180°

K

0

0.31

0.45

0.60

0.78

0.90

1.00

1.13

1.20

1.28

1.40

B. ELBOW, ROUND, 3 TO 5 PIECE — 90_

Coefficient C

q  90°

No. of Pieces

0.5

0.75

1.0

1.5

2.0

5 4 3

— — 0.98

0.46 0.50 0.54

0.33 0.37 0.42

0.24 0.27 0.34

0.19 0.24 0.33



20°

30°

45°

60°

75°

90°

C

0.08

0.16

0.34

0.55

0.81

1.2

R/D

q

C. ELBOW, ROUND, MITERED

Coefficient C D

NOTE: Fitting loss (TP) = C

Vp. Use the velocity pressure (Vp ) of the upstream section.

Table A-10 Elbow Loss Coefficients A.14

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


D. ELBOW, RECTANGULAR, MITERED Coeffiecient C H/W

θ 20 30 45 60 75 90

0.25

0.5

0.08 0.18 0.38 0.60 0.89 1.3

0.08 0.17 0.37 0.59 0.87 1.3

0.75 0.08 0.17 0.36 0.57 0.84 1.2

1.0

1.5

2.0

4.0

6.0

8.0

0.07 0.16 0.34 0.55 0.81 1.2

0.07 0.15 0.33 0.52 0.77 1.1

0.07 0.15 0.31 0.49 0.73 1.1

0.06 0.13 0.27 0.43 0.63 0.92

0.05 0.12 0.25 0.39 0.58 0.85

0.05 0.11 0.24 0.38 0.57 0.83

θ

E. ELBOW, RECTANGULAR, SMOOTH RADIUS WITHOUT VANES

θ

Coeffiecient for 90 elbows (See Note 1) Coefficient C H/W R/W 0.5 0.75 1.0 1.5 2.0

0.25

0.5

0.75

1.5 0.57 0.27 0.22 0.20

1.4 0.52 0.25 0.20 0.18

1.3 0.48 0.23 0.19 0.16

1.0 1.2 0.44 0.21 0.17 0.15

Note 1: For angles other than 90 multiply by the following factors: q 0 20 30 45 60 75 K

0

0.31

0.45

NOTE: Fitting loss (TP) = C

0.60

0.78

0.90

1.5

2.0

3.0

4.0

5.0

6.0

8.0

1.1 0.40 0.19 0.15 0.14

1.0 0.39 0.18 0.14 0.13

1.0 0.39 0.18 0.14 0.13

1.1 0.40 0.19 0.15 0.14

1.1 0.42 0.20 0.16 0.14

1.2 0.43 0.27 0.17 0.15

1.2 0.44 0.21 0.17 0.15

90

110

130

150

180

1.00

1.13

1.20

1.28

1.40

Vp. Use the velocity pressure (Vp ) of the upstream section.

Table A-10 Elbow Loss Coefficients (continued) HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

A.15


F. ELBOW, RECTANGULAR, MITERED WITH TURNING VANES

S R AIR FLOW

Loss Coefficients (C) for Single Thickness Vanes Dimensions, Inches (mm) Velocity, fpm (m/s)

H

1000

1500

2000

2500

R

S

(5)

(7.5)

(10)

(12.5)

2.0 (50)

1.5 (38)

0.24

0.23

0.22

0.20

4.5 (114)

3.25 (83)

0.26

0.24

0.23

0.22

S

W R

Loss Coefficients (C) for Double Thickness Vanes Velocity, fpm (m/s) Dimensions, Inches (mm) 1000

1500

2000

2500

S

(5)

(7.5)

(10)

(12.5)

1.5 (38)

0.43

0.42

0.41

0.40

0.53

0.52

0.50

0.49

0.27

0.25

0.24

0.23

R 2.0 (50) 2.0 (50)

2.25(56)

4.5 (114)

3.25 (83)

Note 1: For angles other than 90 multiply by the following factors: 0 20 30 45 60 75 q

90

110

130

150

180

K

1.00

1.13

1.20

1.28

1.40

0

0.31

0.45

NOTE: Fitting loss (TP) = C

0.60

0.78

0.90

Vp. Use the velocity pressure (Vp ) of the upstream section.

Table A-10 Elbow Loss Coefficients (continued) A.16

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition


A. TRANSITION, ROUND, CONICAL Use Vp of the upstream section

q Re = 8.56 DV where: D = Upstream Diameter (inches) V = Upstream Velocity (fpm)

Whenq  180°

Re

Coefficient C (See Note 2) q

A1/A

20°

30°

45°

60°

90°

120°

180°

0.5  105

2 4 6 10 16

0.14 0.23 0.27 0.29 0.31

16°

0.19 0.30 0.33 0.38 0.38

0.32 0.46 0.48 0.59 0.60

0.33 0.61 0.66 0.76 0.84

0.33 0.68 0.77 0.80 0.88

0.32 0.64 0.74 0.83 0.88

0.31 0.63 0.73 0.84 0.88

0.30 0.62 0.72 0.83 0.88

2  105

2 4 6 10 16

0.07 0.15 0.19 0.20 0.21

0.12 0.18 0.28 0.24 0.28

0.23 0.36 0.44 0.43 0.52

0.28 0.55 0.90 0.76 0.76

0.27 0.59 0.70 0.80 0.87

0.27 0.59 0.71 0.81 0.87

0.27 0.58 0.71 0.81 0.87

0.26 0.57 0.69 0.81 087

 6  105

2 4 6 10 16

0.05 0.17 0.16 0.21 0.21

0.07 0.24 0.29 0.33 0.34

0.12 0.38 0.46 0.52 0.56

0.27 0.51 0.60 0.60 0.72

0.27 0.56 0.69 0.76 0.79

0.27 0.58 0.71 0.83 0.85

0.27 0.58 0.70 0.84 0.87

0.27 0.57 0.70 0.83 0.89

B. TRANSITION, RECTANGULAR, PYRAMIDAL Use Vp of the upstream section

q q Note 2: A = Area ( Entering airstream) A1 = Area (Leaving airstream)

Whenq  180°

A1/A 2 4 6 10

Coefficient C (See Note 2) q 16°

20°

30°

45°

60°

90°

120°

180°

0.18 0.36 0.42 0.42

0.22 0.43 0.47 0.49

0.25 0.50 0.58 0.59

0.29 0.56 0.68 0.70

0.31 0.61 0.72 0.80

0.32 0.63 0.76 0.87

0.33 0.63 0.76 0.85

0.30 0.63 0.75 0.86

Table A-11 Transition Loss Coefficients HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition

A.17


C. CONTRACTION, ROUND AND RECTANGULAR, GRADUAL TO ABRUPT Use the velocity pressure (Vp) of the downstream section

q

q q

Whenq  180°

A1/A 2 4 6 10

Coefficient C (See Note 3)  10°

15°–40°

50°–60°

90°

120°

150°

180°

0.05 0.05 0.05 0.05

0.05 0.04 0.04 0.05

0.06 0.07 0.07 0.08

0.12 0.17 0.18 0.19

0.18 0.27 0.28 0.29

0.24 0.35 0.36 0.37

0.26 0.41 0.42 0.43

Note 3: A = Area ( Entering airstream). A1 = Area (Leaving airstream)

Table A-11 Transition Loss Coefficients (continued) A.18

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


A. TEE, 45°, ENTRY, RECTANGULAR MAIN AND BRANCH Use Vp of the upstream section

Branch, Coefficient C (See Note 4) Qb/Qc

Vb/Vc

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.2

0.91

0.4

0.81

0.79

0.6

0.77

0.72

0.70

0.8

0.78

0.73

0.69

0.66

1.0

0.78

0.98

0.85

0.79

0.74

1.2

0.90

1.11

1.16

1.23

1.03

0.86

1.4

1.19

1.22

1.26

1.29

1.54

1.25

0.92

1.6

1.35

1.42

1.55

1.59

1.63

1.50

1.31

1.8

1.44

1.50

1.75

1.74

1.72

2.24

1.63

For Main Loss Coefficient (C) see below.

B. TEE, RECTANGULAR MAIN TO ROUND BRANCH Use Vp of the upstream section

Vb/Vc

Branch, Coefficient C (See Note 4) Qb/Qc 0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.2

1.00

0.4

1.01

1.07

0.6

1.14

1.10

1.08

0.8

1.18

1.31

1.12

1.13

1.0

1.30

1.38

1.20

1.23

1.26

1.2

1.46

1.58

1.45

1.31

1.39

1.48

1.4

1.70

1.82

1.65

1.51

1.56

1.64

1.71

1.6

1.93

2.06

2.00

1.85

1.70

1.76

1.80

1.8

2.06

2.17

2.20

2.13

2.06

1.98

1.99

For Main Loss Coefficient (C) see below.

C. TEE, RECTANGULAR MAIN AND BRANCH Use Vp of the upstream section Vb/Vc

Branch, Coefficient C (See Note 4) Qb/Qc 0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.2

1.03

0.4

1.04

1.01

0.6

1.11

1.03

1.05

0.8

1.16

1.21

1.17

1.12

1.0

1.38

1.40

1.30

1.36

1.27

1.2

1.52

1.61

1.68

191

1.47

1.66

1.4

1.79

2.01

1.90

2.31

2.28

2.20

1.95

1.6

2.07

2.28

2.13

2.71

2.99

2.81

2.09

1.8

2.32

2.54

2.64

3.09

3.72

3.48

2.21

For Main Loss Coefficient (C) see below.

Note 4: A = Area ( sq. in.). Q= airflow (cfm). V= Velocity (fpm)

Table A-12 Rectangular Branch Connection Loss Coefficients HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

A.19


D. TEE, RECTANGULAR MAIN AND BRANCH WITH EXTRACTOR Use Vp of the upstream section

Branch, Coefficient C (See Note 4) Qb/Qc

Vb/Vc

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.2

1.03

0.4

1.04

1.01

0.6

1.11

1.03

1.05

0.8

1.16

1.21

1.17

1.12

1.0

1.38

1.40

1.30

1.36

1.27

1.2

1.52

1.61

1.68

191

1.47

1.66

1.4

1.79

2.01

1.90

2.31

2.28

2.20

1.95

1.6

2.07

2.28

2.13

2.71

2.99

2.81

2.09

1.8

2.32

2.54

2.64

3.09

3.72

3.48

2.21

For Main Loss Coefficient (C) see below.

E. WYE, RECTANGULAR Use Vp of the upstream section

R  1.0 W 90 Branch

Ab/As

Ab/Ac

0.25 0.33 0.5 0.67 1.0 1.0 1.33 2.0

0.25 0.25 0.5 0.5 0.5 1.0 1.0 1.0

Ab/As

Ab/Ac

0.25 0.33 0.5 0.67 1.0 1.0 1.33 2.0

0.25 0.25 0.5 0.5 0.5 1.0 1.0 1.0

Branch, Coefficient C (See Note 4) Qb/Qc 0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.55 0.35 0.62 0.52 0.44 0.67 0.70 0.60

0.50 0.35 0.48 0.40 0.38 0.55 0.60 0.52

0.60 0.50 0.40 0.32 0.38 0.46 0.51 0.43

0.85 0.80 0.40 0.30 0.41 0.37 0.42 0.33

1.2 1.3 0.48 0.34 0.52 0.32 0.34 0.24

1.8 2.0 0.60 0.44 0.68 0.29 0.28 0.17

3.1 2.8 0.78 0.62 0.92 0.29 0.26 0.15

Main, Coefficient C (See Note 4) Qb/Qc 0.1

0.2

0.3

0.4

0.5

0.6

0.7

-0 .1 0.08 -0 .3 0.04 0.72 -0 .02 0.10 0.62

- .03 0 - .06 - .02 0.48 - .04 0 0.38

- .01 - .02 - .05 - .04 0.28 - .04 0.01 0.23

0.05 - .01 0 - .03 0.13 - .01 - .03 0.13

0.13 0.02 0.06 -.01 0.05 0.06 -.01 0.08

0.21 0.08 0.12 0.04 0.04 0.13 0.03 0.05

0.29 0.16 0.19 0.12 0.09 0.22 0.10 0.06

Main Duct Loss Coefficient for Above Fittings Vb / Vc

0.2

C

0.03

Main Coefficeient C (See Note 4) 0.4 0.6 0.8 1.0 0.04

0.07

0.12

0.13

1.2

1.4

1.6

1.8

0.14

0.27

0.30

0.25

Note 4: A = Area ( sq. in.). Q= airflow (cfm). V= Velocity (fpm)

Table A-12 Rectangular Branch Connection Loss Coefficients (continued) A.20

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition


F. CONVERGING TEE, 45° ENTRY BRANCH TO RECTANGULAR MAIN Use Vp of the downstream section When:

Ab/As

As/Ac

As/As

0.5

1.0

0.5

Branch, Coefficient C (See Note 4) Qb/Qc

Vc

0.1

0.2

0.3

0.4

0.5

0.6

0.7

< 1200 fpm

-0.83

-0.68

-0.30

0.28

0.55

1.03

1.50

> 1200 fpm

-0.72

-0.52

-0.23

0.34

0.76

1.14

1.83

For Main Loss Coefficient (C) see below.

G. CONVERGING TEE, ROUND BRANCH TO RECTANGULAR MAIN Use Vp of the downstream section When:

Ab/As

As/Ac

Ab/Ac

0.5

1.0

0.5

Branch, Coefficient C (See Note 4) Qb/Qc

Vc

0.1

0.2

0.3

0.4

0.5

0.6

0.7

< 1200 fpm

-0.63

-0.55

-0.13

0.23

0.78

1.30

1.93

> 1200 fpm

-0.49

-0.21

-0.23

0.60

1.27

2.06

2.75

For Main Loss Coefficient (C) see below.

H. CONVERGING TEE, RECTANGULAR MAIN AND BRANCH Use Vp of the downstream section When:

Ab/As

As/Ac

As/Ac

0.5

1.0

0.5

Vc

Branch, Coefficient C (See Note 4) Qb/Qc 0.1

0.2

0.3

0.4

0.5

0.6

0.7

< 1200 fpm

-0.75

-0.53

-0.03

0.33

1.03

1.10

2.15

> 1200 fpm

-0.69

-0.21

-0.23

0.67

1.17

1.66

2.67

For Main Loss Coefficient (C) see below.

Main Duct Loss Coefficient for Above Fittings Main Coefficeient C (See Note 4) 0.2 0.4 0.6 Vb / Vc C

0.03

0.04

0.07

0.8

1.0

1.2

1.4

1.6

1.8

0.12

0.13

0.14

0.27

0.30

0.25

Note 4: A = Area ( sq. in.). Q= airflow (cfm). V= Velocity (fpm)

Table A-12 Rectangular Branch Connection Loss Coefficients (continued) HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

A.21


I. CONVERGING WYE, RECTANGULAR Use Vp of the downstream section Branch, Coefficient C (See Note 4)

R  1.0 W

Ab/As

Ab/Ac

0.25 0.33 0.5 0.67 1.0 1.0 1.33 2.0

0.25 0.25 0.5 0.5 0.5 1.0 1.0 1.0

Qb/Qc 0.1

0.2

0.3

0.4

0.5

0.6

0.7

-0 .50 -1 .2 -0 .50 -1 .0 -2 .2 -0 .60 -1 .2 -2 .1

0 -0 .40 -0 .20 -0 .60 -1 .5 -0 .30 -0 .80 -1 .4

0.50 0.40 0 -0 .20 -0 .95 -0 .10 -0 .40 -0 .90

1.2 1.6 0.25 0.10 -0 .50 -0 .04 -0 .20 -0 .5

2.2 3.0 0.45 0.30 0 0.13 0 - .20

3.7 4.8 0.70 0.60 0.40 0.21 0.16 0

5.8 6.8 1.0 1.0 0.80 0.29 0.24 0.20

Main, Coefficient C (See Note 4) AS/AC 0.75 1.0 0.75 0.5 1.0 0.75 0.5

Qb/Qc

Ab/AC

0.1

025 0.5 0.5 0.5 1.0 1.0 1.0

0.2

30 0.17 0.27 1.2 0.18 0.75 0.80

0.3

30 0.16 0.35 1.1 0.24 0.36 0.87

0.20 0.10 0.32 0.90 0.27 0.38 0.80

0.4

0.5

0.6

0.7

-0.10 0 0.25 0.65 0.26 0.35 0.68

-0.45 -0.08 0.12 0.35 0.23 0.27 0.55

-0.92 -0.18 -0.03 0 0.18 0.18 0.40

-1.5 -.027 -0.23 -0.40 0.10 0.05 0.25

J. TEE, RECTANGULAR MAIN TO CONICAL BRANCH Use Vp of the upstream section

Vb/Vc

0.40

C

0.80

Branch, Coefficient C (See note 4) 0.50 0.75 1.0 1.3 0.83

0.90

1.0

1.1

1.5 1.4

Main Duct Loss Coefficient for Above Fittings Main Coefficeient C (See Note 4) Vb / Vc 0.2 0.4 0.6 C

0.03

0.04

0.07

0.8

1.0

1.2

1.4

1.6

1.8

0.12

0.13

0.14

0.27

0.30

0.25

Note 4: A = Area ( sq. in.). Q= airflow (cfm). V= Velocity (fpm)

Table A-12 Rectangular Branch Connection Loss Coefficients (continued) A.22

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition


A. TEE OR WYE, 30_ DEGREES TO 90_, ROUND Diverging FittingsCUse the Vp of the upstream section. Converging FittingsCUse the Vp of the downstream section. Wye  = 30 Ab/Ac q

0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1

Branch, Coefficient C (See note 5) Qb/Qc 0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.75 0.72 0.69 0.65 0.59 0.55 0.40 0.28

0.55 0.51 0.46 0.41 0.33 0.28 0.26 1.5

0.40 0.36 0.31 0.26 0.21 0.24 0.58 —

0.28 0.25 0.21 0.19 0.20 0.38 1.3 —

0.21 0.18 0.17 0.18 0.27 0.76 2.5 —

0.16 0.15 0.16 0.22 0.40 1.3 — —

0.15 0.16 0.20 0.32 0.62 2.0 — —

Wye  = 45 As/Ac 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1

Branch, Coefficient C (See note 5) Qb/Qc 0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.78 0.77 0.74 0.71 0.66 0.66 0.56 0.60

0.62 0.59 0.56 0.52 0.47 0.48 0.56 2.1

0.49 0.47 0.44 0.41 0.40 0.52 1.0 —

0.40 0.38 0.37 0.38 0.43 0.73 1.8 —

0.34 0.34 0.35 0.40 0.54 1.2 — —

0.31 0.32 0.36 0.45 0.69 1.8 — —

0.32 0.35 0.43 0.59 0.95 2.7 — —

Wye  = 60 Ab/Ac 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1

Branch, Coefficient C (See note 5) Qb/Qc 0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.83 0.82 0.81 0.79 0.76 0.80 0.77 1.0

0.71 0.69 0.68 0.66 0.65 0.75 0.96 2.9

0.62 0.61 0.60 0.61 0.65 0.89 1.6 —

0.56 0.56 0.58 0.62 0.74 1.2 2.5 —

0.52 0.54 0.58 0.68 0.89 1.8 — —

0.50 0.54 0.61 0.76 1.1 2.6 — —

0.53 0.60 0.72 0.94 1.4 3.5 — —

Wye  = 90 Ab/Ac 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1

Branch, Coefficient C (See note 5) Qb/Qc 0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.95 0.95 0.96 0.97 0.99 1.1 1.3 2.1

0.92 0.94 0.97 1.0 1.1 1.4 1.9 —

0.92 0.95 1.0 1.1 1.3 1.8 2.9 —

0.93 0.98 1.1 1.2 1.5 2.3 — —

0.94 1.0 1.1 1.4 1.7 — — —

0.95 1.1 1.2 1.5 2.0 — — —

1.1 1.2 1.4 1.8 2.4 — — —

Note 5: A = Area (sq. in.). Q = Airflow (cfm). V = Velocity (fpm)

Table A-13 Round Branch Connection Loss Coefficients HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

A.23


B. 90_ CONICAL TEE, ROUND Diverging FittingsCUse the Vp of the upstream section. Converging FittingsCUse the Vp of the downstream section.

Vb/Vc

0

0.2

0.4

Branch, Coefficient C (See Note 5) 0.6 0.8 1.0 1.2 1.4

1.6

C

1.0

0.85

0.74

0.62

0.32

0.52

0.42

0.36

0.32

For Main Loss Coefficient (C) see below.

C. 45_ CONICAL WYE, ROUND Diverging FittingsCUse the Vp of the upstream section. Converging FittingsCUse the Vp of the downstream section.

Vb/Vc

0

0.2

0.4

0.6

C

1.0

0.84

0.61

0.41

Branch, Coefficient C (See Note 5) 0.8 1.0 1.2 1.4 0.27

0.17

0.12

0.12

1.6

1.8

2.0

0.14

0.18

0.27

For Main Loss Coefficient (C) see below.

Diverging Fitting Main Duct Loss Coefficients

Vs / Vc

0

0.1

0.2

C

0.35

0.28

0.22

Main, Coefficient C (See note 5) 0.3 0.4 0.5 0.17

0.13

0.09

Note 5: A = Area (sq. in.). Q = Airflow (cfm). V = Velocity (fpm)

Table A-13 Round Branch Connection Loss Coefficients (continued) A.24

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition

0.6

0.8

0.06

0.02


D. CONVERGING WYE, ROUND Diverging FittingsCUse the Vp of the upstream section. Converging FittingsCUse the Vp of the downstream section.

Vb/Vc

45

Branch, Coefficient C (See Note 5) Ab/Ac 0.1

0.2

0.3

0.4

0.6

0.8

1.0

0.4

-0.56

-0.44

-0.35

-0.28

-0.15

-0.04

0.05

0.5

-0.48

-0.37

-0.28

-0.21

-0.09

0.02

0.11

0.6

-0.38

-0.27

-0.19

-0.12

0

0.10

0.18

0.7

-0.26

-0.16

-0.08

-0.01

0.10

0.20

0.28

0.8

-0.21

-0.02

0.05

0.12

0.23

0.32

0.40

0.9

0.04

0.13

0.21

0.27

0.37

0.46

053

1.0

0.22

0.31

0.38

0.44

0.53

0.62

0.69

1.5

1.4

1.5

1.5

1.6

1.7

1.7

1.8

2.0

3.1

3.2

3.2

3.2

3.3

3.3

3.3

2.5

5.3

5.3

5.3

5.4

5.4

5.4

5.4

3.0

8.0

8.0

8.0

8.0

8.0

8.0

8.0

Vb/Vc

Main Coefficient C Ab/Ac 0.1

0.2

0.3

0.4

0.6

0.8

1.0

0.1

-8.6

-4.1

-2.5

-1.7

-0.97

-0.58

-0.34

0.2

-6.7

-3.1

-1.9

-1.3

-0.67

-0.36

-0.18

0.3

-5.0

-2.2

-1.3

-0.88

-0.42

-0.19

-0.05

0.4

-3.5

-1.5

-0.88

-0.55

-0.21

-0.05

0.05

0.5

-2.3

-0.95

-0.51

-0.28

-0.06

0.06

0.13

0.6

-1.3

-0.50

-0.22

-0.09

0.05

0.12

0.17

0.7

-0.63

-0.18

-0.03

0.04

0.12

0.16

0.18

0.8

-0.18

0.01

0.07

0.10

0.13

0.15

0.17

0.9

0.03

0.07

0.08

0.09

0.10

0.11

0.13

1.0

-0.01

0

0

0.10

0.02

0.04

0.05

Note 5: A = Area (sq. in.). Q = Airflow (cfm). V = Velocity (fpm)

Table A-13 Round Branch Connection Loss Coefficients (continued) HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition

A.25


E. CONVERGING TEE, 90_, ROUND Diverging FittingsCUse the Vp of the upstream section. Converging FittingsCUse the Vp of the downstream section. Branch, Coefficient C (See Note 5) Ab/Ac

Ob/Qc

90°

0.1

0.2

0.3

0.4

0.6

0.8

0.1

0.40

-0 .37

-0 .51

-0 .46

-0 .50

-0 .51

0.2

3.8

0.72

0.17

-0 .02

-0 .14

-0 .18

0.3

9.2

2.3

1.0

0.44

0.21

0.11

0.4

16

4.3

2.1

0.94

0.54

0.40

0.5

26

6.8

3.2

1.1

0.66

0.49

0.6

37

9.7

4.7

1.6

0.92

0.69

0.7

43

13

6.3

2.1

1.2

0.88

0.8

65

17

7.9

2.7

1.5

1.1

0.9

82

21

9.7

3.4

1.8

1.2

1.0

101

26

4.0

2.1

1.4

12

F. CONVERGING WYE, CONICAL ROUND Diverging FittingsCUse the Vp of the upstream section. Converging FittingsCUse the Vp of the downstream section.

Ab

Main, Coefficient C (See Note 5) Qb/Qs

As/Ac

Ab/Ac

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0.3

0.2 0.3

-2.4 -2.8

-0.01 -1.2

2.0 0.12

3.8 1.1

5.3 1.9

6.6 2.6

7.8 3.2

8.9 3.7

9.8 4.2

0.4

0.2 0.3 0.4

-1.2 -1.6 -1.8

0.93 -0.27 -0.72

2.8 0.81 0.07

4.5 1.7 0.66

5.9 2.4 1.1

7.2 3.0 1.5

8.4 3.6 1.8

9.5 4.1 2.1

10 4.5 2.3

0.5

0.2 0.3 0.4 0.5

-.046 -.094 -1.1 -1.2

1.5 0.25 -0.24 -0.38

3.3 1.2 0.42 0.18

4.9 2.0 0.92 0.58

6.4 2.7 1.3 0.88

7.7 3.3 1.6 1.1

8.8 3.8 1.9 1.3

9.9 4.2 2.1 1.5

11 4.7 2.3 1.6

0.6

0.2 0.3 0.4 0.5 0.6

-0.55 -1.1 -1.2 -1.3 -1.3

1.3 0 -0.48 -0.62 -0.69

3.1 0.88 0.10 -0.14 -0.26

4.4 1.6 0.54 0.21 0.04

6.1 2.3 0.89 0.47 0.26

7.4 2.8 1.2 0.68 0.42

6.6 3.3 1.4 0.85 0.57

9.6 3.7 1.6 0.99 0.66

11 4.1 1.8 1.1 0.75

0.8

0.2 0.3 0.4 0.5 0.6 0.7 0.8

0.06 -0.52 -0.67 -0.73 -0.75 -0.77 -0.78

1.8 0.35 -0.05 -0.19 -0.27 -0.31 -0.34

3.5 1.1 0.43 0.18 0.05 -0.02 -0.07

5.1 1.7 0.80 0.46 0.28 0.18 0.12

6.5 2.3 1.1 0.68 0.45 0.32 0.24

7.8 2.8 1.4 0.85 0.58 0.43 0.33

8.9 3.2 1.6 0.99 0.68 0.50 0.39

10 3.6 1.8 1.1 0.76 0.56 0.44

11 3.9 1.9 1.2 0.83 0.61 0.47

0.2 0.3 0.4 0.5 0.6 0.8 1.0

— — — — — — —

2.1 0.54 0.21 0.05 -0.02 -0.10 -0.14

3.7 1.2 0.62 0.37 0.23 0.11 0.05

5.2 1.8 0.96 0.60 0.42 0.24 0.16

6.6 2.3 1.2 0.79 0.55 0.33 0.23

7.8 2.7 1.5 0.93 0.66 0.39 0.27

9.0 3.1 1.7 1.1 0.73 0.43 0.29

11 3.7 2.0 1.2 0.80 0.46 0.30

11 3.7 2.0 1.2 0.85 0.47 0.30

Qb

Qs As 45°

Qc Ac

1.0

Converging Fitting Main Duct Loss Coefficients Main, Coefficient C (See note 5) Qb/Qc 0.1 0.2 0.3 0.4 0.5 0.6 0.7 C

0.16

0.27

0.38

0.46

0.53

0.57

0.59

0.8

0.9

0.60

0.59

Note 5: A = Area (sq. in.). Q = Airflow (cfm). V = Velocity (fpm)

Table A-13 Round Branch Connection Loss Coefficients (continued) A.26

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


A. DAMPER, BUTTERFLY, THIN PLATE, ROUND Use Vp of the upstream section

q



0

10

Coefficient C 20 30

40

50

60

C

0.20

0.52

1.5

11

29

108

4.5

0 is full open

B. DAMPER, BUTTERFLY, THIN PLATE, RECTANGULAR Use Vp of the upstream section

q



0

10

Coefficient C 20 30

40

50

60

C

0.04

0.33

1.2

9.0

26

70

3.3

0 is full open

C. DAMPER, RECTANGULAR, PARALLEL BLADES Use Vp of the upstream section

Coefficient C  L/R

q Damper blades with crimped leaf edges and 1/4” metal damper frame

0.3 0.4 0.5 0.6 0.8 1.0 1.5

80°

70°

60°

50°

40°

30°

20°

10°

0° Fully open

116 152 188 245 284 361 576

32 38 45 45 55 65 102

14 16 18 21 22 24 28

9.0 9.0 9.0 9.0 9.0 10 10

5.0 6.0 6.0 5.4 5.4 5.4 5.4

2.3 2.4 2.4 2.4 2.5 2.6 2.7

1.4 1.5 1.5 1.5 1.5 1.6 1.6

0.79 0.85 0.92 0.92 0.92 1.0 1.0

0.52 0.52 0.52 0.52 0.52 0.52 0.52

NW L  R 2(H  W)

where: N W L R H

is number of damper blades is duct dimension parallel to blade axis is sum of damper blade lengths is perimeter of duct is duct dimension on perpendicular to blade axis

Table A-14 Miscellaneous Fitting Coefficients HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

A.27


D. DAMPER, RECTANGULAR, OPPOSED BLADES Use Vp of the upstream section

Coefficient C  80°

70°

60°

50°

40°

30°

20°

10°

0° Fully open

807 915 1045 1121 1299 1521 1654

284 332 377 411 495 547 677

73 100 122 148 188 245 361

21 28 33 38 54 65 107

9.0 11 13 14 18 21 28

4.1 5.0 5.4 6.0 6.6 7.3 9.0

2.1 2.2 2.3 2.3 2.4 2.7 3.2

0.85 0.92 1.0 1.0 1.1 1.2 1.4

0.52 0.52 0.52 0.52 0.52 0.52 0.52

L/R

H

q

0.3 0.4 0.5 0.6 0.8 1.0 1.5

where:

NW L  R 2(H  W)

Damper blades with crimped leaf edges and 1/4â&#x20AC;? metal damper frame

N W L R H

is number of damper blades is duct dimension parallel to blade axis is sum of damper blade lengths is perimeter of duct is duct dimension on perpendicular to blade axis

E. PERFORATED PLATE IN DUCT, THICK, ROUND AND RECTANGULAR Use Vp of the upstream section

Coefficient C n t/D

0.20

0.25

0.30

0.40

0.50

0.60

0.70

0.80

0.90

0.015

52

30

18

8.2

4.0

2.0

0.97

0.42

0.13

0.2

48

28

17

7.7

3.8

1.9

0.91

0.40

0.13

0.4

46

27

17

7.4

3.6

1.8

0.88

0.39

0.13

42 where:

24 15 t = plate thickness

6.6

3.2

1.6

0.80

0.36

0.13

0.6 t/D  0.015

n

Ap A

d

= duameter of perforated holes

n = free area ratio of plate Ap = total flow area of perforated plate A = area of duct

Table A-14 Miscellaneous Fitting Coefficients (continued) A.28

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;˘ Third Edition


F. RECTANGULAR DUCT WITH 4-90_ MITERED ELLS TO AVOID OBSTRUCTION Use Vp of the upstream section

Coefficient C 1.0 L/H Ratio 0.5

1.5

2

Single Blade Turning Vanes

0.86

0.83

0.77

Double Blade Turning Vanes

1.85

2.84

2.91

“S” type Splitter Vanes

0.61

0.65

No Vanes - Up to 1200 fpm

0.88

5.26

6.92

7.56

No Vanes - Over 1200 fpm

1.26

6.22

8.82

9.24

Where:

W/H = 1.0 to 3.0 B

= 12” to 24”

G. RECTANGULAR DUCT, DEPRESSED TO AVOID AN OBSTRUCTION Use Vp of the upstream section

Coefficient C L/H W/H

12”

0.125

0.15

0.25

0.30

1.0

0.26

0.30

0.33

0.35

0.4

0.10

0.14

0.22

0.30

15

H. ROUND DUCT, DEPRESSED TO AVOID AN OBSTRUCTION Use Vp of the upstream section

30

12”

When: L/D = 0.33 C = 0.24

Table A-14 Miscellaneous Fitting Coefficients (continued) HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

A.29


I. EXIT, ABRUPT, ROUND AND RECTANGULAR, WITH OR WITHOUT A WALL Use Vp of the upstream section

C = 1.0 With Screen: Cs = 1 + (C from Table K) WALL (OPTIONAL)

J. DUCT MOUNTED IN WALL, ROUND AND RECTANGULAR Use Vp of the upstream section Coefficient C L/D t/D 0

0.02 0.05 Rectangular : D 

2HW (H  W)

0

0.002

0.01

0.05

0.2

0.5

1.0

0.50 0.50 0.50

0.57 0.51 0.50

0.68 0.52 0.50

0.80 0.55 0.50

0.92 0.66 0.50

1.0 0.72 0.50

1.0 0.72 0.50

With Screen or Perforated Plate: a. Sharp Edge (t/De  0.05): Cs = 1 + C1 b. Thick Edge (t/De  0.05): Cs = C + C1 where: Cs is new coefficient C is from above table C1 is from Table K (screen) or Table E (perforated plate)

K. SCREEN IN DUCT, ROUND AND RECTANGULAR Use Vp of the upstream section

n

0.30

0.40

0.50

0.55

C

6.2

3.0

1.7

1.3

Coefficient C 0.60 0.65 0.97

0.75

0.70

0.75

0.80

0.90

0.58

0.44

0.32

0.14

Table A-14 Miscellaneous Fitting Coefficients (continued) A.30

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition


HVAC EQUATIONS (I-P) Air Equations (I-P) a.

V p

V Vp d P

= = = =

T

=

Velocity (fpm) Velocity Pressure (in. wg) Density (lb/cu ft) Absolute Static Pressure (in. Hg) (Barometric pressure + static pressure) Absolute Temperature (460 + F)

Q (sens.) = 1.08 × cfm × ∆t

Q Cp d ∆t

= = = =

Heat Flow (Btu/hr) Specific Heat (Btu/lb × F) Density (lb/cu ft) Temperature Difference (F)

Q (lat.) = 4750 × cfm × ∆W (lb.)

∆W =

Humidity Ratio (lb or gr H2O/lb dry air)

V  1096

d or for standard air (d = 0.075 lb/cu ft): V  4005 V p to solve for d: d  1.325 b.

Pb T

Q (sens.) = 60 × Cp × d × cfm × ∆t

or for standard air (Cp = 0.24 Btu/lb × F):

c.

Q (lat.) = 0.67 × cfm × ∆W (gr.) d.

Q (total) = 4.5 × cfm × ∆h

∆h =

Enthalpy Difference (Btu/lb dry air)

e.

Q = A × U × ∆t

A U

= =

Area of Surface (sq ft) Heat Transfer Coefficient (Btu/sq ft × hr × F)

f.

R  1 U

R

=

Sum of Thermal Resistance (sq ft × hr × F / Btu)

g.

P1

P V R T M

= = = = =

Absolute Pressure (lb/sq ft) Total Volume (cu ft) Gas Constant Absolute Temperature (460 + F = R) Mass (lb)

h.

TP = Vp + SP

V1 V  P 2 2  RM T1 T2

V

4005

2

TP = Vp = SP =

Total Pressure (in. wg) Velocity Pressure (in. wg) Static Pressure (in. wg)

i.

Vp 

j.

V  Vm

V = Vm = d =

Velocity (fpm) Measured Velocity (fpm) Density (lb/cu ft)

k.

cfm = A × V

A

=

Area of Duct cross section (sq ft)

l.

TP = C × Vp

C

=

Duct Fitting Loss Coefficient

d(otherthanstandard)  0.075(d  std.air)

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

A.31


Fan Equations (I-P) cfm 2 rpm a.  rpm2 1 cfm 1

2

b.

P2 rpm  rpm2 P1 1

c.

bhp 2 rpm  rpm2 1 bhp 1

d.

rpm d2  rpm2 1 d1

e.

rpmfan Pitchdiam.motorpulley  rpmmotor Pitchdiam.fanpulley

3

2

Pump Equations (I-P) gpm rpm a. gpm 2  rpm2 1 1 gpm 2 D2 b. gpm  1 D1 H2 rpm2 2 c.  rpm H1 1

d. e. f.

cfm = rpm =

Cubic feet per minute Revolutions per minute

P

Static or Total Pressure (in. wg)

=

bhp =

Brake horsepower

d

Density (lb/cu ft)

=

rpm =

Revolutions per minute

D

=

Impeller diameter

H

=

Head (ft wg)

2

H2 D2  D1 h1 bhp 2 rpm  rpm2 1 bhp 1 3 bhp 2 D2  D1 bhp 1

bhp =

Brake horsepower

3

Hydronic Equivalents (I-P) a.

One gallon water = 8.33 pounds

b.

Specific heat (Cp ) water = 1.00 Btu/lb ⋅ F (@68F)

c.

Specific heat (Cp ) water vapor = 0.45 Btu/lb ⋅ F (@68F)

d.

One ft of water = 0.433 psi

e.

One psi = 2.3 ft wg = 2.04 in. Hg

f.

One cu ft of water = 62.4 lb = 7.49 gal.

g.

One in. of mercury (Hg) = 13.6 in. wg = 1.13 ft. wg

h.

Atmospheric Pressure = 29.92 in. Hg = 14.696 psi

A.32

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


Hydronic Equations (I-P) a.

Q  500  gpm  Dt

b.

DP 2 gpm  gpm2 1 DP 1

c.

gpm

DP  C

2

2

v

d. e. f.

gpm  H  Sp.Gr. 3960 gpm  H  Sp.Gr. whp bhp   Ep 3960  E p whp  100 Ep  (inpercent) bhp whp 

g.

NPSHA  P a Ps 

h.

V h  f L 2 D 2g

V2  P vp 2g

Q = gpm = ∆t =

Heat Flow (Btu/hr) Gallons per minute Temperature Difference (F)

∆P = Cv =

Pressure difference (F) Valve constant (dimensionless)

whp = gpm = bhp = H = Sp.Gr.= Ep =

Water horsepower Gallons per minute Brake horsepower Head (ft wg) Specific gravity (use 1.0 for water) Efficiency of pump

NPSHA Pa = Ps = g =

= Net positive suction head available Atm. pressure (use 34 ft wg) Pressure at pump centerline (ft wg) Gravity acceleration (32.2 ft/sec2)

h f L D V

Head Loss (ft) Friction factor (dimensionless) Length of pipe (ft) Internal diameter (ft) Velocity (ft/sec)

= = = = =

Electric Equations (I-P) a. b.

I  E  P.F.  Eff. (Single Phase) 746 I  E  P.F.  Eff.  1.73 Bhp  (Three Phase) 746 Bhp 

c.

E  IR

d.

P  EI

e.

F.L.Amps  Voltage *  ActualF.L.Amps ActualVoltage

NOTE: * refers to Nameplate ratings. Water Temperature F

60F

150F

200F

250F

300F

340F

Ft. head differential per inch Hg. differential

1.046

1.07

1.09

1.11

1.15

1.165

Table A-15 Converting Pressure In Inches of Mercury to Feet of Water at Various Water Temperatures

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

A.33


Altitude (ft)

Sea Level

Barometer (in. Hg)

29.92

28.86

(in. wg)

407.5

392.8

−40°

1.26

1.22

1.15

40°

1000

2000

3000

4000

5000

6000

7000

8000

9000

10,000

27.82

26.82

25.84

24.90

23.98

23.09

22.22

21.39

20.58

378.6

365.0

351.7

338.9

326.4

314.3

302.1

291.1

280.1

1.17

1.13

1.09

1.05

1.01

0.97

0.93

0.90

0.87

1.11

1.07

1.03

0.99

0.95

0.91

0.89

0.85

0.82

0.79

1.06

1.02

0.99

0.95

0.92

0.88

0.85

0.82

0.79

0.76

0.73

Air Temp. °F

70°

1.00

0.96

0.93

0.89

0.86

0.83

0.80

0.77

0.74

0.71

0.69

100°

0.95

0.92

0.88

0.85

0.81

0.78

0.75

0.73

0.70

0.68

0.65

150°

0.87

0.84

0.81

0.78

0.75

0.72

0.69

0.67

0.65

0.62

0.60

200°

0.80

0.77

0.74

0.71

0.69

0.66

0.64

0.62

0.60

0.57

0.55

250°

0.75

0.72

0.70

0.67

0.64

0.62

0.60

0.58

0.56

0.58

0.51

300°

0.70

0.67

0.65

0.62

0.60

0.58

0.56

0.54

0.52

0.50

0.48

350°

0.65

0.62

0.60

0.58

0.56

0.54

0.52

0.51

0.49

0.47

0.45

400°

0.62

0.60

0.57

0.55

0.53

0.51

0.49

0.48

0.46

0.44

0.42

450°

0.58

0.56

0.54

0.52

0.50

0.48

0.46

0.45

0.43

0.42

0.40

500°

0.55

0.53

0.51

0.49

0.47

0.45

0.44

0.43

0.41

0.39

0.38

550°

0.53

0.51

0.49

0.47

0.45

0.44

0.42

0.41

0.39

0.38

0.36

600°

0.50

0.48

0.46

0.45

0.43

0.41

0.40

0.39

0.37

0.35

0.34

700°

0.46

0.44

0.43

0.41

0.39

0.38

0.37

0.35

0.34

0.33

0.32

800°

0.42

0.40

0.39

0.37

0.36

0.35

0.33

0.32

0.31

0.30

0.29

900°

0.39

0.37

0.36

0.35

0.33

0.32

0.31

0.30

0.29

0.28

0.27

1000°

0.36

0.35

0.33

0.32

0.31

0.30

0.29

0.28

0.27

0.26

0.25

Standard Air Density, Sea Level, 70°F = 0.0 75 lb/cu ft at 29. 92 in. Hg

Table A-16 Air Density Correction Factors (I-P)

A.34

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


HVAC EQUATIONS (SI) Air Equations (SI) a.

V  1.414

Vd

p

or for standard air (d = 1.204 kg/m3): V  1.66V p

V Vp d Pb

= = = =

T

=

Velocity (m/s) Velocity Pressure (pascals or Pa) Density (kg/m3) Absolute Static Pressure (kPa) (Barometric pressure + static pressure) Absolute Temp. (273 + C = K)

Q Cp d L/s

= = = =

Heat Flow (watts or kilowatts) Specific Heat (kJ/kg ⋅ C) Density (kg/m3) Airflow (liters per second)

To solve for d: P d  3.48 b T b.

Q  C p  d  Ls  Dt

or for standard air (CP = 1.005 kJ/kg ⋅ C) Q(sens.)  1.23  Ls  Dt (in watts) Q(sens.)  1.23  m3s  Dt (in kilowatts)

t = m3/s =

Temperature Difference (C) Airflow (cubic meters per second)

c.

Q(lat.)  3.0  Ls  DW

W=

Humidity Ratio (g H2O/kg dry air)

d.

Q(totalheat)  1.20  Ls  Dh

h =

Enthalpy Diff. (kJ/kg dry air)

e.

Q  A  U  Dt

A U

= =

Area of Surface (m2) Heat Transfer Coefficient (W/m2 ⋅ C)

f.

R  1 U

R

=

Sum of Thermal Resistances (m2 ⋅ C/W)

g.

P 1V 1 PV   2 2  RM T1 T2

P V T R M

= = = = =

Absolute Pressure (kPa) Total Volume (m3) Absolute Temp. (273 + C = K) Gas Constant Mass (kg)

h.

TP  V P  SP

TP = Vp = SP =

Total Pressure (Pa) Velocity Pressure (Pa) Static Pressure (Pa)

V p  d  V 2  0.602V2 2 d(otherthanstandard) V  V m 1.204(d  std.air)

d = V = Vm =

Density (kg/m3) Velocity (m/s) Measured Velocity (m/s)

A C

Area of duct cross section (m2) Duct Fitting Loss Coefficient

i. j.



k.

Ls  1000  A  V

l.

TP  C  VP



= =

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

A.35


Fan Equations (SI) Ls 2 m3s rads 2 revs 2 a.   3 2    Ls 1 m s 1 rads 1 revs 1

2

b.

rads 2 P2   P1 rads 1

c.

rads 2 kW 2   kW 1 rads 1

d.

rads 2 d2   d1 rads 1

e.

rads(fan) Pitchdiam.motorpulley   Pitch.diam.fanpulley rads(motor)

3

2

Pump Equations (SI) Ls 2 m3s rads 2 revs 2 a.   3 2    Ls 1 m s 1 rads 1 revs 1 m 3s 2 d2 b.   d1 m 3s 1

c.

rads 2 H2   H1 rads 1

d.

H2 D2   H1 D1

e.

rads 2 BP 2   BP 1 rads 1

2

2

L/s = Liters per second m3/s = Cubic meters per second rad/s = Radians per second rev/s = Revolutions per second P = Static or Total Pressure (Pa) kW = Kilowatts d = Density (kg/m3) NOTE: m3/h = Cubic meters per hour (is used in lieu of m3/s in some countries.)

L/s = Liters per second m3/s = Cubic meters per second rad/s = Radians per second rev/s = Revolutions per second D = Impeller diameter H = Head (kPa) BP. = Brake horsepower NOTE: m3/h = Cubic meters per hour (is used in lieu of m3/s in some countries.)

3

Hydronic Equations (SI) a.

Q  4190  m3s  Dt

2

b.

m3s 2 DP 2   DP 1 m3s 1

c.

m 3s Ls DP    Cv Cv

2

Q

Ls 2   Ls 1

2

2

WP(kW)  9.81  m3s  H(m)  Sp.8 Gr. Ls  H(Pa)  Sp.8 Gr. or WP(W)  1002

=

Heat flow (kilowatts)

t = m3/s =

Temperature difference (C) Cubic meters per second (used for large volumes)

L/s =

Liters per second

P = Cv =

Pressure diff. (Pa or kPa) Valve constant (dimensionless)

d.

e.

BP  WP Ep

f.

E p  WP  100 (inpercent) BP

A.36

WP = Water power (kW or W) m3/s = Cubic meters per second H = Head (Pa or m) L/s = Liters per second Sp.Gr. = Specific gravity (use 1.0 for water) BP = Ep =

Brake power (kW) Efficiency of Pump

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;˘ Third Edition


g.

NPSHA  P a Ps  V  P vp 2g

NPSHA = Net positive suction head available Pa = Atm. press (Pa) (Std. Atm. press. = 101,325 Pa) Ps = Pressure at pump centerline (Pa) V 2 = Velocity head at point P (m) s 2g Pvp = Absolute vapor pressure (Pa)

h.

h  f  L  V D 2g

h g f L D V

= = = = = =

Head loss (m) Gravity acceleration (9.807 m/s2) Friction factor (dimensionless) Length of pipe (m) Internal diameter (m) Velocity (m/s)

I  E  P.F.  Eff. (Single Phase) 1000 I  E  P.F.  Eff.  1.73 kW  1000 (Three Phase)

kW I E P.F. R P.

= = = = = =

Kilowatts Amps (A) Volts (V) Power factor ohms (Ω) watts (W)

a. b.

2

2

kW 

c.

E  IR

d.

P  EI F.L.Amps *  Voltage *   ActualF.L.Amps ActualVoltage

e.

NOTE: * Refers to Nameplate Ratings

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

A.37


Altitude (m) Barometer (kPa) Air Temp °C 0° 20° 50° 75° 100° 125° 150° 175° 200° 225° 250° 275° 300° 325° 350° 375° 400° 425° 450° 475° 500° 525°

Sea Level 101.3

250 98.3

500 96.3

750 93.2

1000 90.2

1250 88.2

1500 85.1

1750 83.1

2000 80.0

2500 76.0

3000 71.9

1.08 1.00 0.91 0.85 0.79 0.74 0.70 0.66 0.62 0.59 0.56 0.54 0.51 0.49 0.47 0.46 0.44 0.42 0.41 0.39 0.38 0.37

1.05 0.97 0.89 0.82 0.77 0.72 0.68 0.64 0.61 0.58 0.55 0.52 0.50 0.48 0.46 0.44 0.43 0.41 0.40 0.38 0.37 0.36

1.02 0.95 0.86 0.80 0.75 0.70 0.66 0.62 0.59 0.56 0.53 0.51 0.49 0.47 0.45 0.43 0.41 0.40 0.38 0.37 0.36 0.35

0.99 0.92 0.84 0.78 0.72 0.68 0.64 0.62 0.57 0.54 0.52 0.49 0.47 0.45 0.43 0.42 0.40 0.39 0.37 0.36 0.35 0.34

0.96 0.89 0.81 0.75 0.70 0.66 0.62 0.59 0.56 0.53 0.50 0.48 0.46 0.44 0.42 0.41 0.39 0.38 0.36 0.35 0.34 0.33

0.93 0.87 0.79 0.73 0.68 0.64 0.60 0.57 0.54 0.51 0.49 0.47 0.45 0.43 0.41 0.39 0.38 0.37 0.35 0.34 0.33 0.32

0.91 0.84 0.77 0.71 0.66 0.62 0.59 0.55 0.52 0.50 0.47 0.45 0.43 0.41 0.40 0.38 0.37 0.35 0.34 0.33 0.32 0.31

0.88 0.82 0.75 0.69 0.65 0.60 0.57 0.54 0.51 0.48 0.46 0.44 0.42 0.40 0.39 0.37 0.36 0.34 0.33 0.32 0.31 0.30

0.86 0.79 0.72 0.67 0.63 0.59 0.55 0.52 0.49 0.47 0.45 0.43 0.41 0.39 0.38 0.36 0.35 0.33 0.32 0.31 0.30 0.29

0.81 0.75 0.68 0.63 0.59 0.55 0.52 0.44 0.47 0.44 0.42 0.40 0.38 0.37 0.35 0.34 0.33 0.32 0.31 0.29 0.28 0.27

0.76 0.71 0.64 0.60 0.56 0.52 0.49 0.46 0.44 0.42 0.40 0.38 0.36 0.35 0.33 0.32 0.31 0.30 0.29 0.28 0.27 0.26

Table A-17 Air Density Correction Factors (SI)

A.38

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


SI UNITS AND EQUIVALENTS

UNIT ampere candela Celsius coulomb farad henry hertz joule kelvin

SYMBOL A cd °C C F H Hz J K

QUANTITY Electric current Luminous intensity Temperature Electric charge Electric capacitance Electric inductance Frequency Energy, work, heat Thermodynamic y temperature

kilogram liter lumens lux meter mole newton ohm pascal

kg L lm lx m mol N Ω Pa

Mass Liquid volume Luminous flux Illuminance Length Amount of substance Force Electrical resistance Pressure, stress

radian second siemens steradian volt watt

rad s S sr v w

Plane angle Time Electric conductance Solid angle Electric potential Power, heat flow

EQUIVALENT OR RELATIONSHIP Same as I−P 1 cd/m2 = 0.292 ft. lamberts °F = 1.8 °C + 32° Same as I−P Same as I−P Same as I−P Same as cycles per second 1 J = 0.7376 ft−lb = 0.000948 Btu °K = °C + 273.15°  °F  459.67 1.8 1 kg = 2.2046 lb 1 L = 1.056 qt = 0.264 gal 1 lm/m2 = 0.0929 ft candles 1 lx = 0.0929 ft candles 1 m = 3.281 ft C 1 N = kg • m/s2 = 0.2248 lb (force) Same as I−P 1 Pa = N/m2 = 0.000145 psi = 0.004022 in.wg 1 rad = 57.29° Same as I−P C C Same as I−P 1 W = J/s = 3.4122 Btu/hr 1 W = 0.000284 tons of refrigeration

Table A-18 SI Units (Basic and Derived)

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

A.39


QUANTITY acceleration angular velocity area atmospheric pressure density density, air density, water duct friction loss enthalpy gravity heat flow length (normal) linear velocity mass flow rate moment of inertia power pressure specific heatCair (Cp ) specific specific specific thermal

heatCair (Cv ) heatCwater volume conductivity

volume flow rate

SYMBOL m/s2 rad/s m2 C kg/m 3 C C Pa/m kJ/kg W m m/s kg/s kg⋅m2 W kPa Pa C C C m3/kg W mm/m2⋅°C m3/s L/s C C m3/h

UNIT meters per second squared radians per second square meter 101.325 kPa kilograms per cubic meter 1.2 kg/m3 1000 kg/m3 pascals per meter kilojoule per kilogram 9.8067 m/s2 watt meter meters per second kilograms per second kilograms × square meter watt kilopascal (1000 pascals) pascal 1000 J/kg °C 717 J/kg °C 4190 J/kg °C cubic meters per kilogram watt millimeter per square meter °C cubic meters per second liters per second 1 m3/s = 1000 L/s 1 mL = liters/1000 cubic meters per hour

I−P RELATIONSHIP 1 = 3.281 ft/sec2 1 rad/sec = 9.549 rpm = 0.159 rps 1 m2 = 10.76 ft2 29.92 in Hg = 14.696 psi 1 kg/m3 = 0.0624 lb/ft3 0.075 lb/ft3 62.4 lb/ft3 1 Pa/m = 0.1224 in.wg/100 ft 1 kJ/kg = 0.4299 Btu/lb dry air 32.2 ft/sec2 1 W = 3.412 Btu/hr 1 m = 3.281 ft = 39.37 in. 1 m/s = 196.9 fpm 1 kg/s = 7936.6 lb/hr 1 kg⋅m2 = 23.73 lb ft2 1 W = 0.00134 hp 1 kPa = 0.296 in Hg = 0.145 psi 1 Pa = 0.004015 in.wg 1000 J/kg °C = 1 kJ/kg °C = 0.2388 Btu/lb °F 0.17 Btu/lb °F 1.0 Btu/lb °F 1 m3/kg = 16.019 ft3/lb 1 W mm/m2 ⋅°C = 0.0069 Btuh in/ft2 °F 1 m3/s = 2118.88 cfm (air) 1 L/s = 2.12 cfm (air) 1 m3/s = 15,850 gpm (water) 1 mL/s = 1.05 gph (water) 1 m3/h = 0.588 cfm (air) 1 m3/h = 4.4 gpm (water) m/s2

Table A-19 SI Equivalents

A.40

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


L w  Lp  10 log10

4prQ  A4   10.5dB

L p  Lw  10 log10

4prQ  A4   10.5dB

2

2

R  Sa or R  A 1a 1a

Lp = Sound pressure level, dB re 0.0002 microbar Lw = Sound power level, dB re 10−12 watt r = Distance from the sound source, feet A%orNSα= Total sabins in the room Q = Directivity factor R = Room constant α = Absorption coefficient of the surface treat− ment S = Surface area in square feet a = Average sabin absorption coefficient for the room D V f

= = =

Characteristic dimension, in. Velocity, fpm Octave band center frequency, Hz

Octave Band Sound Power Level = F  G  HindBre10 12watts

F G H

= = =

Function (Use with charts) Function (Use with charts) Function (Use with charts)

L WB  LWD  TL  10 log 10 S A

LWB = LWD = TL = S = A =

Sound power level breakout Sound power level in duct Transmission loss of duct wall Radiating surface area of duct wall (sqNft) Cross−sectional area of duct component (sqNft)

L w  Lp  10 log10 A  10dB

Lw = Lp = A =

Sound power level that enters duct Sound pressure level in source room Opening in duct (sq ft.)

lc f

λ c f

Wavelength in feet Speed of sound, 1125 fps Cycles per second, hertz

L w  10 log W W ref

Lw = W = Wref =

Sound power level, dB Acoustic power output of noise source 10−12 watt

Lp = P = Pref =

Sound power level in dB rms sound pressure Ref. rms sound pressure

Strouhal Number N str 

fD 5 V

= = =

dBre10 12watt  dBre1013watt  10 L p  20 log P Pref

D 

C1 C2 C   ... n T1 T2 Tn

Cn = Tn =

Actual duration of exposure, hours Noise exposure limit

B f 

RPM  No.ofBlades 60

Bf =

Blade frequency

Lw Kw Q P

Est sound power level, dB re 10−12 watt Specific sound power level Volume flow rate, cfm Pressure, in. wg

L w  Kw  10 log Q  20 log P

= = = =

Table A-20 Sound Design Equations

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

A.41


NR  TL  10 log S  10 log A

TL = S A

= =

The transmission loss of the partition separating the two spaces The surface area of the partition (sq ft) Total of the sound absorptive materials in the receiving room (sq ft sabins)

TL  20 log M  20 log F  33dB

M = F =

Mass of construction (lb/sq ft) Frequency (hertz)

D  0.5 A

D A

Distance (in feet) from the noise source Total absorption in room (sq ft sabins)

A2 A1 Noise Reduction in dB

NR, dB  10 log NR =

L P1  LP2  20 log D 1  20 log D 2

= =

A1 =

Total absorption (Sabins, sq ft) in the room before adding the sound absorption

LP1 = LP2 = D1 =

Sound pressure level at position #1 Sound pressure level at position #2 Distance (in ft) from noise source to position #1 Distance (in ft) from noise source to position #2

D2 = L p  Lw  20 log D  0.5dB

D

a  (AntilogL a20)105

a = La =

Acceleration in meters/sec2 (g = 9.8 m/s2) Acceleration level in dB re 10−5 (m/s2)

v  (AntilogL v20)108

v

Velocity in meters/sec (1 g@ 100 Hz = 0.015 m/s) Velocity level in dB re 10−8 (m/s)

=

=

Lv = d  (AntilogL d20)1011

d

=

Ld =

Distance (in ft) from the point source to the point where sound pressure is measured

Displacement in meters (1g@100 Hz = 0.0249 mm) Displacement level in dB re 10−11 (meters)

Table A-20 Sound Design Equations (continued)

A.42

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


FITTING EQUIVALENTS (WATER) Velocity, ft/s 1 2 3 4 5 6 7 8 9 10

1_w

3_r

1

11_r

I1_w

2

21_w

1.2 1.4 1.5 1.5 1.6 1.7 1.7 1.7 1.8 1.8

1.7 1.9 2.0 2.1 2.2 2.3 2.3 2.4 2.4 2.5

2.2 2.5 2.7 2.8 2.9 3.0 3.0 3.1 3.2 3.2

3.0 3.3 3.6 3.7 3.9 4.0 4.1 4.2 4.3 4.3

3.5 3.9 4.2 4.4 4.5 4.7 4.8 4.9 5.0 5.1

4.5 5.1 5.4 5.6 5.9 6.0 6.2 6.3 6.4 6.5

5.4 6.0 6.4 6.7 7.0 7.2 7.4 7.5 7.7 7.8

Pipe Size 3 31_w 6.7 7.5 8.0 8.3 8.7 8.9 9.1 9.3 9.5 9.7

7.7 8.6 9.2 9.6 10.0 10.3 10.5 10.8 11.0 11.2

4

5

6

8

10

12

8.6 9.5 10.2 10.6 11.1 11.4 11.7 11.9 12.2 12.4

10.5 11.7 12.5 13.1 13.6 14.0 14.3 14.6 14.9 15.2

12.2 13.7 14.6 15.2 15.8 16.3 16.7 17.1 17.4 17.7

15.4 17.3 18.4 19.2 19.8 20.5 21.0 21.5 21.9 22.2

18.7 20.8 22.3 23.2 24.2 24.9 25.5 26.1 26.6 27.0

22.2 24.8 26.5 27.6 28.8 29.6 30.3 31.0 31.6 32.0

Table A-21 Equivalent Length in Feet of Pipe for 90_ Elbows Pipe Size, mm

Velocity, m/s 0.33

15

20

25

32

40

50

65

75

100

125

150

200

250

300

0.4

0.5

0.7

0.9

1.1

1.4

1.6

2.0

2.6

3.2

3.7

4.7

5.7

6.8

0.67

0.4

0.6

0.8

1.0

1.2

1.5

1.8

2.3

2.9

3.6

4.2

5.3

6.3

7.6

1.00

0.5

0.6

0.8

1.1

1.3

1.6

1.9

2.5

3.1

3.8

4.5

5.6

6.8

8.0

1.33

0.5

0.6

0.8

1.1

1.3

1.7

2.0

2.5

3.2

4.0

4.6

5.8

7.1

8.4

1.67

0.5

0.7

0.9

1.2

1.4

1.8

2.1

2.6

3.4

4.1

4.8

6.0

7.4

8.8

2.00

0.5

0.7

0.9

1.2

1.4

1.8

2.2

2.7

3.5

4.3

5.0

6.2

7.6

9.0

2.33

0.5

0.7

0.9

1.2

1.5

1.9

2.2

2.8

3.6

4.4

5.1

6.4

7.8

9.2

2.67

0.5

0.7

0.9

1.3

1.5

1.9

2.3

2.8

3.6

4.5

5.2

6.5

8.0

9.4

3.00

0.5

0.7

0.9

1.3

1.5

1.9

2.3

2.9

3.7

4.5

5.3

6.7

8.1

9.6

3.33

0.5

0.8

0.9

1.3

1.5

1.9

2.4

3.0

3.8

4.6

5.4

6.8

8.2

9.8

Table A-22 Equivalent Length in Meters of Pipe for 90_ Elbows Iron Pipe

Fitting

Copper Tubing

Elbow. 90

1.0

1.0

Elbow, 45

0.7

0.7

Elbow. 90 long turn

0.5

0.5

Elbow. welded, 90

0.5

0.5

Reduced coupling

0.5

0.4

Open return bend

1.0

1.0

Angle Radiator valve

2.0

3.0

Radiator or convector

3.0

4.0

Boiler or heater

3.0

4.0

Open gate valve

0.5

0.7

Open globe valve

12.0

17.0

Table A-23 Iron and Copper Elbow Equivalents FIGURE A-7 ELBOW EQUIVALENTS OF TEES AT VARIOUS FLOW CONDITIONS

HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;¢ Third Edition

A.43


PROPERTIES OF STEAM

Pressure Gage psi Vacuum 25 in. Hg 9.56 in. Hg 0 2 5 15 50 100 150 200

Absolute psia

Saturation Temperature F

2.4 10 14.7 16.7 19.7 29.7 64.7 114.7 164.7 214.7

134 193 212 218 227 250 298 338 366 388

Specific Volume ft3/lb

Enthalpy Btu/lb

Liquid Vf

Steam Vg

Liquid hf

0.0163 0.0166

146.4 38.4 26.8 23.8 20.4 13.9 6.7 3.9 2.8 2.1

101 161 180 187 195 218 267 309 339 362

0.0167 0.0168 0.0168 0.0170 0.0174 0.0179 0.0182 0.0185

Evap. hfg

Steam hg

1018 982 970 966 961 946 912 881 857 837

1119 1143 1150 1153 1156 1164 1179 1190 1196 1179

Table A-24 Properties of Saturated Steam (I-P)

Specific Volume L/kg Pressure, kPa 19.9 47.4 101.00 199.00 362 618 1003 1555

Enthalpy, kJ/kg

Saturation Temperature °C

Liquid Vf

Steam Vg

Liquid hf

Evap. hfg

Steam hg

60 80 100 120 140 160 180 200

1.02 1.03 1.04 1.06 1.08 1.10 1.13 1.16

7669 3405 1672 891 508 307 194 127

251 335 419 504 589 676 763 852

2358 2308 2256 2202 2144 2082 2015 1941

2609 2643 2775 2706 2733 2758 2778 2793

Table A-25 Properties of Saturated Steam (SI)

A.44

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


STEAM PIPING (I-P)

Pressure DropCpsi per 100 Ft in Length

Nom. Pipe Size, in. 3_r 1 11_r 11_w

1_qy psi (1 oz)

1_i psi (2 oz)

1_r psi (4 oz)

1_w psi (8 oz)

3_r psi (12 oz)

1 psi

2 psi

Sat. press psig

Sat. press. psig

Sat. press psig

Sat. press psig

Sat. press. psig

Sat. press. psig

Sat. press. psig

3.5

12

3.5

12

3.5

12

3.5

12

3.5

12

3.5

12

3.5

12

9 17 36 56

11 21 45 70

14 26 53 84

16 31 66 100

20 37 78 120

24 46 96 147

29 54 111 174

35 66 138 210

36 68 140 218

43 82 170 260

42 81 162 246

50 95 200 304

60 114 232 360

73 137 280 430

2 21_w 3 31_w

108 174 318 462

134 215 380 550

162 258 465 670

194 310 550 800

234 378 660 990

285 460 810 1218

336 540 960 1410

410 660 1160 1700

420 680 1190 1740

510 820 1430 2100

480 780 1380 2000

590 950 1670 2420

710 1150 1950 2950

850 1370 2400 3450

4 5 6 8

640 1200 1920 3900

800 1430 2300 4800

950 1680 2820 5570

1160 2100 3350 7000

1410 2440 3960 8100

1690 3000 4850

1980 3570 5700

2400 4250 5700

2450 4380 7000

3000 5250 8600

2880 5100 8400

3460 6100

4200 7500

4900 8600

10,000

11,900

14,200

10,000

11,400

14,300

14,500

17,700

16,500

20,500

24,000

29,500

10 12

7200

8800

10,200

12,600

15,000

18,200

21,000

26,000

26,200

32,000

30,000

37,000

42,700

52,000

11.400

13,700

16,500

19,500

23,400

28,400

33,000

40,000

41,000

49,500

48,000

57,500

67,800

81,000

Table A-26 Steam Piping (I-P) Flow Rate of Steam in Schedule 40 Pipe at Initial Saturation Pressure of 3.5 and 12 psig (Flow Rate expressed in Pounds per Hour)

Pitch of Pipe Pipe Size, in.

1_r in.

1_w in.

1 1_w in.

1 in.

Capa− city

Max. Vel.

Capa− city

Max. Vel.

Capa− city

3.2 6.8 11.8 19.8 42.9

8 9 11 12 15

4.1 9.0 15.9 25.9 54.0

11 12 13 16 18

5.7 11.7 19.9 33.0 68.8

Max. Vel.

Capa− city

2 in.

Max. Vel.

Capa− city

3 in.

Max. Vel.

4 in.

Capa− city

Max. Vel.

Capa− city

8.3 17.3 31.3 46.8 99.6

17 22 25 26 32

9.9 19.2 33.4 50.8 102.4

5 in.

Max. Vel.

Capa− city

Max. Vel.

22 10.5 24 20.5 26 38.1 28 59.2 32 115.0

22 25 31 33 33

Capacity Expressed in Pounds Per Hour

3_r 1 11_r 11_w 2

13 15 17 19 24

6.4 12.8 24.6 37.4 83.3

14 17 20 22 27

7.1 14.8 27.0 42.0 92.9

16 19 22 24 30

Table A-27 Comparative Capacity of Steam Lines at Various Pitches for Steam and Condensate Flowing in Opposite Directions (Pitch of Pipe in Inches per 10 Feet – Velocity in Feet per Second) HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

A.45


Initial Steam Pressure, psig

Total Pressure Drop in Steam Supply Piping, psi

Pressure Drop Per 100 Ft, psi

Subatmos, or vacuum return 0 1 2 5 10 15 30 50 100 150

2–4 oz. 1_w oz. 2 oz. 2 oz. 4 oz. 8 oz.

1–2 psi 1 oz. 1–4 oz. 8 oz. 11_w psi 3 psi

1 psi 2 psi 2–5 psi 2–5 psi 2–10 psi

4 psi 5–10 psi 10–15 psi 15–25 psi 25–30 psi

Table A-28 Pressure Drops In Common Use for Sizing Steam Pipe (For Corresponding Initial Steam Pressure)

Length in Feet to be Added to Run Size of Pipe Inches 1_w 3_r 1 1 1_r 1 1_w 2 2 1_w 3 3 1_w 4 5 6 8 10 12

Standard Elbow

Side Out− let Teeb

Gate Valve 2

Globe Valve 2

Angle Valve 2

1.3 1.8 2.2 3.0

3 4 5 6

0.3 0.4 0.5 0.6

14 18 23 29

7 10 12 15

3.5 4.3 5.0 6.5

7 8 11 13

0.8 1.0 1.1 1.4

34 46 54 66

18 22 27 34

8 9 11 13

15 18 22 27

1.6 1.9 2.2 2.8

80 92 112 136

40 45 56 67

17 21 27

35 45 53

3.7 4.6 5.5

180 230 270

92 112 132

Table A-29 Length in Feet of Pipe to be Added to Actual Length of Run — Owing to Fittings — to Obtain Equivalent Length

A.46

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


Capacity in Pounds per Hour Two Pipe Systems Nominal Pipe Size, Size Inches A

One−Pipe Systems

Condensate Flowing Against Steam Vertical

Horizontal

Ba

Ca

Supply Risers Up−Feed Db

Radiator Valves and Vertical Connections E

Radiator and Riser Runouts Fc

3_r 1 1 1_r 1 1_w 2

8 14 31 48 97

7 14 27 42 93

6 11 20 38 72

C 7 16 23 42

7 7 16 16 23

2 1_w 3 3 1_w 4 5

159 282 387 511 1,050

132 200 288 425 788

116 200 286 380 C

C C C C C

42 65 119 186 278

1,800 3,750 7,000 11,500 22,000

1,400 3,000 5,700 9,500 19,000

C C C C C

C C C C C

545 C C C

6 8 10 12 16

NOTE: Steam at an average pressure of 1 psig is used as a basis of calculating capacities. a Do

not use Column B for pressure drops of less than 1_qy ft. of equivalent run.

not use Column D for pressure drops of less than 1_wr psi per 100 ft. of equivalent run except on sizes 3 in. and over. b Do

c Pitch of horizontal runouts to risers and radiators should be not less than 1_w in. per ft.

Where this pitch cannot be obtained, runouts over 8 ft. in length should be one pipe size larger than called for in this table.

Table A-30 Steam Pipe Capacities for Low Pressure Systems (For Use on One-Pipe Systems or Two-Pipe Systems in which Condensate Flows Against the Steam Flow)

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

A.47


1_er psi or 1_w oz Drop per 100 ft Pipe Size Inch− es G

1_wr psi or 2_e oz Drop per 100 ft

1_qy psi or 1 oz Drop per 100 ft

Wet

Dry

Vac.

Wet

Dry

Vac.

H

I

J

K

L

M

1_i psi or 2 oz Drop per 100 ft

1_r psi or 4 oz Drop per 100 ft

Wet

Dry

Vac.

Wet

Dry

Vac.

Wet

Dry

Vac.

N

O

P

Q

R

S

T

U

V

Return Main 3_r

C

C

C

C

C

42

C

C

100

C

C

142

C

C

200

1

125

62

C

145

71

143

175

80

175

250

103

249

350

115

350

11_r

213

130

C

248

149

244

300

168

300

425

217

426

600

241

600

11_w

338

206

C

393

236

388

475

265

475

675

340

674

950

378

950

700

470

C

810

535

815

1,000

575

1,000

1,400

740

1,420

2,000

825

2,000

21_w

2

1,180

760

C

1,580

868

1,360

1,680

950

1,680

2,350

1,230

2,380

3,350

1,360

3,350

3

1,880

1,460

C

2,130

1,560

2,180

2,680

1,750

2,680

3,750

2,250

3,800

5,350

2,500

5,350

31_w

2,750

1,970

C

3,300

2,200

3,250

4,000

2,500

4,000

5,500

3,230

5,680

8,000

3,580

8,000

4

3,880

2,930

C

4,580

3,350

4,500

5,500

3,750

5,500

7,750

4,830

7,810 11,000

5,380 11,000

5

C

C

C

C

C

7,880

C

C

9,680

C

C 13,700

C

C 19,400

6

C

C

C

C

C 12,600

C

C 15,500

C

C 22,000

C

C 31,000

Table A-31 Return Main and Riser Capacities for Low-Pressure Systems—Pounds per Hour (Reference to this table will be made by column letter G through V)

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HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


STEAM PIPING (SI) Pressure Drop—Pa/m

Nom. Pipe Size mm 20 25 32 40

14 Pa/m

28 Pa/m

58 Pa/m

113 Pa/m

170 Pa/m

225 Pa/m

450 Pa/m

Sat. press. kPa

Sat. press. kPa

Sat. press. kPa

Sat. press. kPa

Sat. press. kPa

Sat. press. kPa

Sat. press. kPa

25 4 8 16 25

85 5 10 20 32

25 6 12 24 38

85 7 14 30 45

25 9 17 35 54

85 11 21 44 67

25 13 24 50 79

85 16 30 63 95

25 16 31 64 99

85 20 37 77 118

25 19 37 73 112

85 23 43 91 138

25 27 52 105 163

85 33 62 127 195

50 65 80 90

49 79 144 210

61 98 172 249

73 117 211 304

88 141 249 363

106 171 299 449

129 209 367 552

152 245 435 640

186 299 526 771

191 308 540 789

231 372 649 953

218 354 626 907

268 431 758 1100

322 522 885 1340

386 621 1090 1560

100 125 150 200

290 544 871 1770

363 649 1040 2180

431 762 1280 2530

526 953 1520 3180

640 1110 1800 3670

767 1360 2200 4540

898 1620 2590 5170

1090 1930 2590 6490

1110 1990 3180 6580

1360 2380 3900 8030

1310 2310 3910 7480

1570 2770 4540 9300

1910 3400 5400

2220 3900 6440

10,900

13,400

250 300

3270 5170

3990 6210

4630 7480

5720 8850

6800

8260

9530

11,800

11,900

14,500

13,600

16,800

19,400

23,600

10,600

12,900

15,000

18,100

18,600

22,500

21,800

26,100

30,800

36,000

Table A-32 Flow Rate in kg/h of Steam in Schedule 40 Pipe at Initial Saturation Pressure of 15 and 85 kPa Above Atmospheric Pitch of Pipe

20

40

80

120

170

250

350

420

Pipe Size mm

Capa− city kg/h

Max Vel. m/s

Capa− city kg/h

Max Vel. m/s

Capa− city kg/h

Max Vel. m/s

Capa− city kg/h

Max Vel. m/s

Capa− city kg/h

Max Vel. m/s

Capa− city kg/h

Max Vel. m/s

Capa− city kg/h

Max Vel. m/s

Capa− city kg/h

Max Vel. m/s

20

1.5

2.4

1.9

3.4

2.6

4.0

2.9

4.3

3.2

4.9

3.8

5.2

4.5

6.7

4.8

6.7

25

3.1

2.7

4.1

3.7

5.3

4.6

5.8

5.2

6.7

5.8

7.8

6.7

8.7

7.3

9.3

7.6

32

5.4

3.4

6.8

4.3

9.0

5.2

11.2

6.1

12.2

6.7

14.2

7.6

15.2

7.9

17.3

9.4

40

9.0

3.7

11.7

4.9

15.0

5.8

17.0

6.7

19.1

7.3

15.1

7.9

23.0

8.5

26.9

10.1

50

19.5

4.6

24.5

5.5

31.2

7.3

37.8

8.2

42.1

9.1

45.2

9.8

46.4

9.8

52.2

10.1

Capacity in kg/h, Velocity in m/s

Table A-33 Comparative Capacity of Steam Lines at Various Pitches for Steam and Condensate Flowing in Opposite Directions

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

A.49


Length in Meters to be Added to Run Size of Pipe mm 15 20 25 32

Standard Elbow 0.4 0.5 0.7 0.9

Side Outlet Teeb 1 1 1 2

Gate Valve 0.1 0.1 0.1 0.2

Globe Valve 4 5 7 9

Angle Valve a 2 3 4 5

40 50 65 80

1.1 1.3 1.5 1.9

2 2 3 4

0.2 0.3 0.3 0.4

10 14 16 20

6 8 8 10

100 125 150

2.7 3.3 4.0

5 7 8

0.5 0.7 0.9

28 34 41

14 17 20

200 250 300 350

5.2 6.4 8.2 9.1

11 14 16 19

1.1 1.4 1.7 1.9

55 70 82 94

28 34 40 46

NOTE:

a Valve

in full open position.

b Valve

given only to a tee used to divert the flow in the main to the last riser.

Table A-34 Equivalent Length of Fittings to be Added to Pipe Run

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HVAC SYSTEMS Testing, Adjusting & Balancing â&#x20AC;˘ Third Edition


Capacity, kg/h Two−Pipe Systems Nominal Pipe Size, mm A

One−Pipe System

Condensate Flowing Against Steam

Supply Risers Up−feed Db

Radiator Valves and Vertical Connections E

Radiator and Riser Runouts Fc

Vertical

Horizontal

Ba

Ca

20 25 32 40 50

4 6 14 22 44

3 6 12 19 42

3 5 9 17 33

C 3 7 10 19

3 3 7 7 10

65 80 90 100 125

72 128 176 232 476

60 91 131 193 357

53 91 130 172 C

C C C C C

19 29 54 84 126

150 200 250 300 400

816 1700 3180 5220 9980

635 1360 2590 4310 8620

C C C C C

C C C C C

247 C C C C

NOTE: Steam at an average pressure of 7 kPa above atmospheric is used as a basis of calculating capacities. a Do

not use Column B for pressure drops of less than 13 Pa/m of equivalent run.

b Do not use Column D for pressure drops of less than 9 Pa/m of equivalent run except on sizes 88 mm and over. c Pitch of horizontal runouts to risers and radiators should not be less than 40 mm/m. Where this pitch cannot be obtained, runouts over 2.5 m in length should be one pipe size larger than called for in this table.

Table A-35 Steam Pipe Capacities for Low-Pressure Systems (For Use on One-Pipe Systems or Two-Pipe Systems in which Condensate Flows Against the Steam Flow)

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

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7 Pa/m

9 Pa/m

14 Pa/m

28 Pa/m

57 Pa/m

Pipe Size, mm

Wet

Dry

Vac.

Wet

Dry

Vac.

Wet

Dry

Vac.

Wet

Dry

Vac.

Wet

Dry

Vac.

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

20 25 32 40 50

C 57 97 153 318

C 28 59 93 213

C C C C C

C 66 112 178 367

C 32 68 107 243

19 65 111 176 370

Return Main C C 79 36 136 76 215 120 454 261

45 79 136 215 454

C 113 193 306 635

C 47 98 154 336

64 113 193 306 644

C 159 272 431 907

C 52 109 171 374

91 159 272 431 907

65 80 90 100 125 150

535 853 1,125 1,760 C C

345 662 894 1,330 C C

C C C C C C

717 967 1,500 2,080 C C

394 708 998 1,520 C C

616 989 1,400 2,040 3,570 5,720

762 1,220 1,810 2,490 4,390 7,030

1,070 1,700 2,490 3,520 C C

558 1,020 1,470 2,190 C C

1,080 1,720 2,580 3,540 6,210 9,980

762 1,220 1,810 2,490 C C

431 794 1,130 1,700 C C

1,520 617 1,520 2,430 1,130 2,430 3,630 1,620 3,630 4,990 2,440 4,990 C C 8,800 C C 14,100

Riser 20 25 32 40 50

C C C C C

22 51 112 170 340

C C C C C

C C C C C

22 51 112 170 340

65 111 176 370 616

C C C C C

22 51 112 170 340

79 136 215 454 762

C C C C C

22 51 112 170 340

113 193 306 644 1,080

C C C C C

65 70 80 100 125

C C C C C

C C C C C

C C C C C

C C C C C

C C C C C

989 1,470 2,030 3,570 5,720

C C C C C

C C C C C

1,220 1,810 2,490 4,390 7,030

C C C C C

C C C C C

1,720 2,580 3,540 6,210 9,980

C C C C C

Table A-36 Return Main and Riser Capacities for Low-Pressure Systems — kg/h

A.52

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

22 51 112 170 340

159 272 431 907 1,520

C 2,430 C 3,630 C 4,990 C 8,800 C 14,100


Sample Specification for Testing, Adjusting and Balancing The minimum requirements for testing, adjusting and balancing (TAB) of heating, ventilating and air conditioning (HVAC) distribution systems shall be as follows: 1.

The TAB Contractor shall review and become thoroughly familiar with the basic duct and piping installation layout prior to ceiling and wall installation. Prior to any closing−in of ductwork and piping, verify that all fittings, dampers, control devices, test devices and valves are properly located and installed.

2.

Examine each air and hydronic distribution system to see that is is free from obstructions. Confirm that all dampers, registers and valves are operating and in a set or full open position; that moving equipment is lubri− cated and functioning properly; and that the required filters are clean and installed. Request that the installing contractor perform any adjustments necessary for proper functioning of the system.

3.

The TAB Contractor shall use test instruments that have been calibrated within a time period recommended by the manufacturer or in the SMACNA HVAC SYSTEMS Testing, Adjusting and Balancing manual, and that they have been checked for accuracy prior to the start of the testing, adjusting and balancing activity.

4.

Verify that all equipment performs as specified. Adjust variable type drives, column dampers, control damp− ers, balancing valves and control valves as required by the TAB work.

5.

Adjust each register, diffuser and terminal unit to handle and properly distribute the design airflow within 10N% of the specified quantities.

6.

Adjust all balancing equipment so that each heating/cooling coil is furnished with the design fluid within 10N% of the specified quantities.

7.

Document the results of all testing on SMACNA TAB Report Forms and submit specified copies for approval and record.

8.

All TAB work shall be performed in accordance with the methods and the procedures described in the SMACNA HVAC SYSTEMS Testing, Adjusting and Balancing manual.

9.

The TAB Contractor shall become familiar with and comply with the provisions of all national, state, and local codes, ordinances, and safety acts that affect the TAB work.

10. HVAC systems utilizing microprocessor temperature controls, variable speed fans and pumps, and variable air terminal boxes should have the control system contractor on site during all primary system TAB work to provide any software programming or setpoint modifications required.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

A.53


REFERENCES Publications from the following sources can be used as reference material to supplement the information con− tained in this manual. The members of the SMACNA Duct Design Committee express their thanks and ap− preciation to these firms for allowing selected text, fig− ures and tables to be used in this manual. 1.

Alnor Instrument Company

2. AMCA Fan Application Manuals C Air Move− ment and Control Association, Inc.

A.54

3. ASHRAE Handbooks C American Society of Heating, Refrigeration and Air Conditioning Engi− neers 4.

Bell and Gossett, Fluid Handling Division, ITT

5. Carrier System Design Manuals C Carrier Cor− poration 6. Fans and Their Application in Air Condition− ingCTrane Company 7. Products of Environmental Elements Corporation C Titus Corporation

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


GLOSSARY


GLOSSARY −A− A−Scale − A filtering system that has characteristics which roughly match the response characteristics of the human ear at low sound levels (below 55 dB Sound Pressure Level, but frequently used to gauge levels to 85 dB). A−scale measurements are often referred to as dB(A). Absolute Filter − Obsolete term (See HEPA filter) Absolute Pressure − Air at standard conditions 70F (20C ) air at sea level with a barometric pressure of 29.92 in.Hg. (760 mm Hg) exerts a pressure of 14.696 psi (101.325 kPa). This is the pressure in a system when the pressure gauge reads zero. So the absolute pressure of a system is the gauge pressure in pounds per square inch (kPa) added to the atmospheric pres− sure of 14.696 psi (use 14.7 psi in environmental sys− tem work) and the symbol is ?psia." Add 101.325 kPa to the gauge pressure for metric units. Absorbent − A material which, due to an affinity for certain substances, extracts one or more such sub− stances from a liquid or gaseous medium with which it contacts and which changes physically or chemical− ly, or both, during the process. Calcium chloride is an example of a solid absorbent, while solutions of lithi− um chloride, lithium bromide, and ethylene glycols are liquid absorbents.

Absorption Unit − Is a factory tested assembly of component parts producing refrigeration for comfort cooling by the application of heat. This definition shall apply to those absorption units which also produce comfort heating. Acceleration − The time rate of change of velocity, i.e., the derivative of velocity; with respect to time. Acceleration Due to Gravity − The rate of increase in velocity of a body falling freely in a vacuum. Its val− ue varies with latitude and elevation. The International Standard is 32.174 ft. per second per second (9.807 m/ s/s). Acceptance Test − A test made upon completion of fabrication, receipt, installation or modification of a component unit or system to verify that it meets the re− quirements specified. Accuracy − The extent to which the value of a quantity indicated by an instrument under test agrees with an accepted value of the quantity. Actuator − A controlled motor, relay or solenoid in which the electric energy is converted into a rotary, lin− ear, or switching action. An actuator can effect a change in the controlled variable by operating the final control elements a number of times. Valves and damp− ers are examples of mechanisms which can be con− trolled by actuators.

Absorber Surface − The surface of the collector plate which absorbs solar energy and transfers it to the col− lector plate.

Adiabatic Process − A thermodynamic process during which no heat is added to, or taken from, a substance or system.

Absorptance − The ratio of the amount of radiation ab− sorbed by a surface to the amount of radiation incident upon it.

Adjustable Differential − A means of changing the difference between the control cut−in and cutout points.

Absorption − A process whereby a material extracts one or more substances present in an atmosphere or mixture of gases or liquids accompanied by the materi− al’s physical and/or chemical changes.

Adsorbent − A material which has the ability to cause molecules of gases, liquids, or solids to adhere to its in− ternal surfaces without changing the adsorbent physi− cally or chemically. Certain solid materials, such as silica gel and activated alumina, have this properly.

Absorption Coefficient − For a surface, the ratio of the sound energy absorbed by a surface of a medium (or material) exposed to a sound field (or to sound radi− ation) divided by the sound energy incident on the sur− face. The conditions under which measurements of ab− sorption coefficients are made must be stated explicitly. The absorption coefficient is a function of both angle of incidence and frequency. Tables of ab− sorption coefficients usually list the absorption coeffi− cients at various frequencies, the values being those obtained by averaging over all angles of incidence.

Adsorption − The action, associated with the surface adherence, of a material in extracting one or more sub− stances present in an atmosphere or mixture of gases and liquids, unaccompanied by physical or chemical change. Commercial adsorbent materials have enor− mous internal surfaces. Aerodynamic Noise − Also called generated noise, self−generated noise; is a noise of aerodynamic origin in a moving fluid arising from flow instabilities. In

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

G.1


duct systems, aerodynamic noise is caused by airflow through elbows, dampers, branch wyes, pressure re− duction devices, silencers and other duct components. Air, Ambient − Generally speaking, the air surround− ing an object. Airborne Noise − Noise which reaches the observer by transmission through air. Air, Dry − Air without contained water vapor; air only. Air, Outdoor − Air taken from outdoors and, therefore, not previously circulated through the system. Air, Outside − External air, atmosphere exterior to re− frigerated or conditioned space; ambient (surround− ing) air. Air, Recirculated − Return air passed through the con− ditioner before being again supplied to the conditioned space. Air, Reheating of − In an air conditioning system, the final step in treatment, in the event the temperature is too low. Air, Return − Air returned from conditioned or refrig− erated space. Air, Saturated − Moist air in which the partial pressure of the water vapor is equal to the vapor pressure of wa− ter at the existing temperature. This occurs when dry air and saturated water vapor coexist at the same dry− bulb temperature. Air, Standard − Dry air at a pressure of 29.92 in.Hg (760 mm Hg) at 70F (20C) temperature and with a specific volume of 13.33 ft.3/lb (0.8305 m3/kg). Air Change Rate − The number of times the total air volume of a defined space is replaced in a given unit of time. Ordinarily computed by dividing the total vol− ume of the subject space (in cubic feet) into the total volume of air exhausted from the space per unit of time. Air Changes − A method of expressing the amount of air leakage into or out of a building or room in terms of the number of building volumes or room volumes exchanged. Air Conditioner, Unitary − An evaporator, compres− sor, and condenser combination; designed in one or G.2

more assemblies, the separate parts designed to be as− sembled together. Air Conditioning, Comfort − The process of treating air so as to control simultaneously its temperature, hu− midity, cleanliness and distribution to meet the com− fort requirements of the occupants of the conditioned space. Air Conditioning Unit − An assembly of equipment for the treatment of air so as to control, simultaneously, its temperature, humidity, cleanliness and distribution to meet the requirements of a conditioned space. Air Cooler − A factory−encased assembly of elements whereby the temperature of air passing through the de− vice is reduced. Air Diffuser − A circular, square, or rectangular air distribution outlet, generally located in the ceiling and comprised of deflecting members discharging supply air in various directions and planes, and arranged to promote mixing of primary air with secondary room air. Air Gap − An air gap in a potable water distribution system is the unobstructed vertical distance through the free atmosphere between the lowest opening from any pipe or faucet supplying water to a tank, plumbing fixture or other device and the floor level rim of the re− ceptacle. Air Shower − A relatively small, isolated ?chamber" normally located at the main entrance of a cleanroom to remove particulate from personnel and garments by high velocity air. Air, Supply − That air delivered to the conditioned space and used for ventilation, heating, cooling, hu− midification or dehumidification. Air, Transfer − The movement of indoor air from one space to another. Air, Ventilation − That portion of supply air which is outdoor air plus any recirculated air that has been treated for the purpose of maintaining acceptable in− door air quality. Air Washer − A water spray system or device for cleaning, humidifying, or dehumidifying the air. Airborne Sound − Sound which reaches the point of interest by radiation through the air. Airlock − An area between the entrance to the clean− room and the entry from an outside area. The airlock

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


receives the same clean, filtered air as the cleanroom, and is designed to prevent contaminated air in the out− side area from flowing into the cleanroom. (Also re− ferred to as ?Ante−Room.")

bulb temperature of the entering air. In a conduction heat exchanger device, the temperature difference be− tween the leaving treated fluid and the entering work− ing fluid.

Algae − A minute fresh water plant growth which forms a scum on the surfaces of recirculated water ap− paratus, interfering with fluid flow and heat transfer.

Area − Generally used to designate a portion of a build− ing at a given level of protection or contamination con− trol, as set off from adjoining portions of different con− tamination levels. Used somewhat interchangeably with ?space" or ?zone."

Alternating Current (AC) − A source of power for an electrical circuit which periodically reverses the po− larity of its charge. Ambient − The existing surrounding environmental conditions (Temperature, Relative Humidity, Pres− sure, etc...) of a particular area of consideration. Ampacity − A wire’s ability to carry current safely, without undue heating. The term formerly used to de− scribe this characteristic was current−capacity of the wire. Amperage − The flow of current in an electrical circuit measured in ?amperes," abbreviated ?amps" (A). Amplitude of Ground Surface Temperature Varia− tion − Peak Annual fluctuation of ground surface tem− perature about a mean value. Anemometer − An instrument for measuring the ve− locity of a fluid. Anemometer, Shielded Hot−Wire − An instrument for measuring air velocities based on the convective cool− ing effect of airflow on a heated wire. Instruments of this type are specifically designed for low air speeds, ranging from about 25 to 300 feet per minute (0.12 to 1.5 m/s). Anticipating Control − One which, by artificial means, is activated sooner than it would be without such means, to produce a smaller differential of the controlled property. Heat and cool anticipators are commonly used in thermostats. Anticipators − A small heater element in two−position temperature controllers which deliberately cause false indications of temperature in the controller in an at− tempt to minimize the override of the differential and smooth out the temperature variation in the controlled space. Approach − In an evaporative cooling device, the dif− ference between the average temperature of the circu− lating water leaving the device and the average wet−

As−Built Facility − A cleanroom which is complete and operating, with all services connected and func− tioning, but has no production equipment or operating personnel within the facility. As−Found Data − Data comparing the response of an instrument to known standards as determined without adjustment after the instrument is made operational. Aspect Ratio − In air distribution outlets, the ratio of the length of the core opening of a grille, face, or regis− ter to the width. In rectangular ducts, the ratio of the width to the depth. Aspiration − Production of movement in a fluid by suction created by fluid velocity. At−Rest Facility − A cleanroom which is complete and has the production equipment installed, but has no per− sonnel within the facility. Attenuation − The transmission loss or reduction in magnitude of a signal between two points in a trans− mission system. Autumnal Equinox (See Also Vernal Equinox) − The position of the sun midway between its lowest and highest altitude during the autumn; it occurs Septem− ber 21. Auxiliary Contacts − A set of contacts that perform a secondary function, usual in relation to the operation of a set of primary contacts. Averaging Element − A thermostat sensing element which will respond to the average duct temperature. Azimuth Angle (Solar) − The angular direction of the sun with respect to true south. −B− Backflow − The unintentional reversal of flow in a po− table water distribution system which may result in the transport of foreign materials or substances into the other branches of the distribution system.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

G.3


Background Noise − Sound other than the signal wanted. In room acoustics, it is the irreducible noise level measured in the absence of any building occu− pants when all of the known sound sources have been turned off.

Bypass − A pipe or duct, usually controlled by valve or damper, for conveying a fluid around an element of a system.

Barometer − Instrument for measuring atmospheric pressure.

Calibration − Comparison of a measurement standard or instrument of unknown accuracy with another stan− dard or instrument of known accuracy to detect, corre− late, report, or eliminate by adjustment, any variation in the accuracy of the unknown standard or instrument.

Basic Principles − Essential theory and understanding of operation. Bimetallic Element − One formed of two metals hav− ing different coefficients of thermal expansion such as are used in temperature indicating and controlling de− vices. Boiling Point − The temperature at which the vapor pressure of a liquid equals the absolute external pres− sure of the liquid−vapor interface. Branch Circuit − Wiring between the last overcurrent device and the branch circuit outlets. Breakout Noise − The transmission or radiation of noise through some part of the duct system to an occu− pied space in the building. British Thermal Unit (Btu) − The Btu is defined as the heat required to raise the temperature of a pound of wa− ter from 59F to 60F. Btuh − Number of Btu’s transferred during a period of one hour. Bulb − The name given to the temperature sensing de− vice located in the fluid for which control or indication is provided. The bulb may be liquid−filled, gas−filled, or gas−and−liquid filled. Changes in temperature pro− duce pressure changes within the bulb which are trans− mitted to the controller. Building Envelope − The elements of a building which enclose conditioned spaces through which energy may be transferred to or from the exterior. Bus Bar − A heavy, rigid metallic conductor which car− ries a large current and makes a common connection between several circuits. Bus bars are usually uninsu− lated and located where the electrical service enters a building; that is, in the main distribution cabinet. Bus Duct − An assembly of heavy bars of copper or aluminum that acts as a conductor of large capacity. G.4

−C−

Calibration, Field − Calibration test performed in the field in accordance with the manufacturer’s recom− mended and/or accepted industry practices. Calibration, On−Line − Calibration performed using the reference system built into the instrument, in ac− cordance with manufacturer’s recommendations and/ or accepted industry standards. Capacitance − The property of an electric current that permits the storage of electrical energy in an electro− static field and the release of that energy at a later time. Capacitor (condenser) − An electrical device that will store an electric charge used to produce a power factor change. Capacity, Latent − The available refrigerating capac− ity of an air conditioner for removing latent heat from the space to be conditioned. Capillary − The name given to the thin tube attached to the bulb which transmits the bulb pressure changes to the controller or indicator. The cross sectional area of the capillary is extremely small compared to the cross section of the bulb so that the capillary, which is usually outside of the controlled fluid, will introduce the smallest possible error in the signal being trans− mitted from the bulb. Capillary Tube − The capillary tube is a metering de− vice made from a thin tube approximately 2 to 20 feet (0.6 to 6 m) long and from 0.025 to 0.090 inches (0.6 mm to 2.3 mm) in diameter which feeds liquid directly to the evaporator. Usually limited to systems of 1 ton or less, it performs all of the functions of the thermal expansion valve when properly sized. Cathodic Protection − The process of providing cor− rosion protection against electrolytic reactions that could be deleterious to the performance of the pro− tected material or component. Ceiling Outlet − A round, square, rectangular or linear air diffuser located in the ceiling which provides a hor−

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


izontal distribution pattern of primary and secondary air over the occupied zone and induces low velocity secondary air motion through the occupied zone. Celsius (Formerly Centigrade) − A thermometric scale in which the freezing point of water is called 0C and its boiling point 100C at normal atmospheric pressure (101.325 kPa). Certificate of Compliance (Conformance) − A writ− ten statement, signed by a qualified party, attesting that the items or services are in accordance with speci− fied requirements, and accompanied by additional in− formation to substantiate the statement. Certification − The process of validation required to obtain a certificate of compliance. Certification Agency − A company providing on−site, field certification services for profit or gain. Change of State − Change from one phase, such as sol− id, liquid or gas, to another. Changeover − The process of switching an air condi− tioning system from heating to cooling, or vice versa. Channel − Term used to describe output of a load man− agement system. Usually corresponds to a specific relay. Chemical Compatibility − The ability of materials and components in contact with each other to resist mutual chemical degradation, such as that caused by electrolytic action.

Clearing a Fault − Eliminating a fault condition by some means. Generally taken to mean operation of the over−circuit device that opens the circuit and clears the fault. Clo Value − A numerical representation of a clothing ensemble’s thermal resistance. 1Clo  0.88°F  ft 2  hrBtu (0.155°C  m 2W) Coanda Effect − The diversion of the normal fluid flow path from a jet by its attachment to an adjacent surface (wall or ceiling) caused by a low pressure re− gion between the fluid flow path and the surface. Coefficient of Discharge − For an air diffuser, the ratio of net area or effective area of vena contracta of an orificed airstream to the tree area of the opening. Coefficient of Expansion − The change in length per unit length or the change in volume per unit volume, per degree. change in temperature. Coefficient of Performance (COP), Heat Pump − The ratio of the compressor heating effect (heat pump) to the rate of energy input to the shaft of the compres− sor, in consistent units, in a complete heat pump, under designated operating conditions. Coil − A cooling or heating element made of pipe or tubing. Cold Deck − The cooling section of a mixed air zoning system. Collector Azimuth − The horizontal angle between true south and a line which is perpendicular to the plane of the collector that is projected on a horizontal plane.

Circuit − An electrical arrangement requiring a source of voltage, a closed loop of wiring, an electric load and some means for opening and closing it.

Collector Plate − The component of a solar collector which transfers the heat from solar energy to a circulat− ing fluid.

Circuit Breaker − A switch−type mechanism that opens automatically when it senses an overload (ex− cess current).

Collector (Solar) − An assembly of components in− tended to capture usable solar energy. Combustion − The act or process of burning.

Cleanroom − A specially constructed room in which the air supply, air distribution, filtration of air supply, materials of construction, and operating procedures are regulated to control airborne particle concentra− tions to meet appropriate cleanliness levels as defined by Federal Standard 209E. Clean Zone − A defined space in which the concentra− tion of airborne particles is controlled to specified lim− its.

Comfort Chart − A chart showing effective tempera− ture with dry−bulb temperatures and humidities (and sometimes air motion) by which the effects of various air conditions on human comfort may be compared. Comfort Cooling − Refrigeration for comfort as op− posed to refrigeration for storage or manufacture. Comfort Zone − (average) the range of effective tem− peratures over which the majority (50 percent or more)

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

G.5


of adults feels comfortable − (extreme) the range of ef− fective temperatures over which one or more adults feel comfortable. Commissioning Plan − A documented, systematic process to ready new building systems for active ser− vice. Common Neutral − A neutral conductor that is com− mon to, or serves, more than one circuit. Compressibility − The ease which a fluid may be re− duced in volume by the application of pressure, de− pends upon the state of the fluid as well as the type of fluid itself. In TAB work, consider that water may not be compressed. Air is a compressible gas, but that fac− tor is usually not considered during normal testing and balancing procedures. Compressor − The pump which provides the pressure differential to cause fluid to flow and in the pumping process increases pressure of the refrigerant to the high side condition. The compressor is the separation be− tween low side and high side. Concentration − The quantity of one constituent dis− persed in a defined amount of another. Concentrator − A reflective surface or refracting lens for directing insolation onto the absorber surface. Condensate − The liquid formed by condensation of a vapor. In steam heating, water condensed from steam; in air conditioning, water extracted from air, as by con− densation on the cooling coil of a refrigeration ma− chine. Condensation − Process of changing a vapor into liq− uid by extracting heat. Condensation of steam or water vapor is effected in either steam condensers or dehu− midifying coils, and the resulting water is called con− densate. Condenser − The heat exchanger in which the heat ab− sorbed by the evaporator and some of the heat of com− pression introduced by the compressor are removed from the system. The gaseous refrigerant changes to a liquid, again taking advantage of the relatively large heat transfer by the change of state in the condensing process. Condenser − ElectricalCsee ?capacitor". Condensing Unit, Refrigerant − An assembly of re− frigerating components designed to compress and liq− G.6

uify a specific refrigerant, consisting of one or more refrigerant compressors, refrigerant condensers, liq− uid receivers (when required) and regularly furnished accessories. Conditioned Space − Space within a building which is provided with heated and/or cooled air or surfaces and, where required, with humidification or dehumidifica− tion means so as to maintain a space condition falling within the ?comfort zone." Conditions, Standard − A set of physical, chemical, or other parameters of a substance or system which de− fines an accepted reference state or forms a basis for comparison. Conductance, Electrical − The reciprocal (opposite) of resistance and is the current carrying ability of any wire or electrical component. Resistance is the ability to oppose the flow of current. Conductance, Surface Film − Time rate of heat flow per unit area under steady conditions between a sur− face and a fluid for unit temperature difference be− tween the surface and fluid. Conductance, Thermal − Time rate of heat flow through a body (frequently per unit area) from one of its bounding surfaces to the other for a unit tempera− ture difference between the two surfaces, under steady conditions. Conductivity, Thermal − The time rate of heat flow through unit area and unit thickness of a homogeneous material under steady conditions when a unit tempera− ture gradient is maintained in the direction perpendic− ular to area. Materials are considered homogeneous when the value of the thermal conductivity is not af− fected by variation in thickness or in size of sample within the range normally used in construction. Conductor, Thermal − A material which readily transmits heat by means of conduction. Conduit − A round cross−section electrical raceway, of metal or plastic. Connected Load − The sum of all loads on a circuit. Connection in Parallel − System whereby flow is di− vided among two or more channels from a common starting point or header. Connection in Series − System whereby flow through two or more channels is in a single path entering each succeeding channel only after leaving the first or pre− vious channel.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


Contamination − The presence of any unwanted sub− stance, material or energy which adversely affects a product or procedure in a cleanroom. Contactor − Electromagnetic switching device. Contaminant − An unwanted airborne constituent that may be reduced acceptability of the air. Control − A device for regulation of a system or com− ponent in normal operation, manual or automatic. If automatic, the implication is that it is responsive to changes of pressure, temperature or other property whose magnitude is to be regulated. Control Diagram (ladder diagram) − A diagram that shows the control scheme only. Power wiring is not shown. The control items are shown between two ver− tical lines; hence, the nameCladder diagram. Control Point − The value of the controlled variable which the controller operates to maintain. Controlled Area − An air conditioned work space or room in which the particle concentration is lower than normal air conditioned spaces. A controlled area is not to be classified as a cleanroom, but some special filtra− tion is required.

Cooling, Evaporative − Involves the adiabatic ex− change of heat between air and water spray or wetted surface. The water assumes the wet−bulb temperature of the air, which remains constant during its traverse of the exchanger. Cooling, Regenerative − Process of utilizing heat which must be rejected or absorbed in one part of the cycle to function usefully in another part of the cycle by heat transfer. Cooling Coil − An arrangement of pipe or tubing which transfers heat from air to a refrigerant or brine. Cooling Effect, Sensible − Difference between the to− tal cooling effect and the dehumidifying effect, usual− ly in watts (Btuh). Cooling Effect, Total − Difference between the total enthalpy of the dry air and water vapor mixture enter− ing the cooler per hour and the total enthalpy of the dry air and water vapor mixture leaving the cooler per hour, expressed in watts (Btuh). Cooling Range − In a water cooling device, the differ− ence between the average temperatures of the water entering and leaving the device. Core Area − The total plane area of that portion of a grille, included within lines tangent to the outer edges of the openings through which air can pass.

Controlled Device − One which receives the con− verted signal from the transmission system and trans− lates it into the appropriate action in the environmental system. For example − a valve opens or closes to regu− late fluid flow in the system.

Corresponding Values − Simultaneous values of vari− ous properties of a fluid, such as pressure, volume, temperature, etc., for a given condition of fluid.

Controller − An instrument which receives the signal from the sensing device and translates that signal into the appropriate corrective measure. The correction is then sent to the system controlled devices through the transmission system.

Counterflow − In heat exchange between two fluids, opposite direction of flow, coldest portion of one meet− ing coldest portion of the other.

Convection − Transfer of heat by movement of fluid. Convection, Forced − Convection resulting from forced circulation of a fluid, as by a fan, jet or pump. Convection, Natural − Circulation of gas or liquid (usually air or water) due to differences in density re− sulting from temperature changes. Conventional Flow (Nonlaminar Flow) Cleanroom − A cleanroom with non−uniform or mixed patterns and velocities.

Corrosive − Having chemically destructive effect on metals (occasionally on other materials).

Critical Surface − The surface of the work part to be protected from particulate contamination. Critical Velocity − The velocity above which fluid flow is turbulent. Cross Connection − Any physical connection or ar− rangement between two otherwise separate piping sys− tems, one of which contains potable water and the oth− er either water of unknown or questionable safety or steam, gas, chemicals, or other substances whereby there may be a flow from one system to the other, the direction of flow depending on the pressure differen− tial between the two systems.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

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Crossflow − Horizontal airflow. Crystal Formation, Zone of Maximum − Tempera− ture range in freezing in which most freezing takes place, i.e., about 25F to 30F (−4C to −1C) for wa− ter.

The referenced power for sound power level is 10−12 watts. In noise control work, the decibel notation is used to indicate the magnitude of sound pressure and sound power.

Curb Box − Access to an underground valve at the street curb. It controls water service to a house or building.

Combining Decibels − In sound survey work, it is fre− quently necessary to combine sound pressure level readings. An example would be to evaluate the effect of adding a noise source in a room where the noise lev− el is already considered borderline. Since the decibel scale is logarithmic, decibel values cannot be added directly. The correct procedure is to convert the deci− bels to intensity ratios, add the intensity ratios, and re− convert this sum into decibels.

Current (I) − The electric flow in an electric circuit, which is expressed in amperes (amps). Cycle − A complete course of operation of working fluid back to a starting point, measured in thermody− namic terms (functions). Also in general for any re− peated process on any system. Cycle, Reversible − Theoretical thermodynamic cycle, composed of a series of reversible processes, which can be completely reversed. −D− DWV − Drainage, waste and vent. Dalton’s Law of Partial Pressure − Each constituent of a mixture of gases behaves thermodynamically as if it alone occupied the space. The sum of the individu− al pressures of the constituents equals the total pres− sure of the mixture. Damper − A device to vary the volume of air passing through an airoutlet, air inlet or duct. Deadband − In HVAC, a temperature range in which neither heating nor cooling is turned on; in load man− agement, a kilowatt range in which loads are neither shed nor restored.

Degree Day − A unit, based upon temperature differ− ence and time, used in estimating fuel consumption and specifying nominal heating load of a building in winter. For any one day, when the mean temperature is less than 65F (18C), there exist as many degree days as there are Fahrenheit degrees difference in tem− perature between the mean temperature for the day and 65F (18C). Dehumidification − The condensation of water vapor from air by cooling below the dewpoint or removal of water vapor from air by chemical or physical methods. Dehumidifier − (1) an air cooler or washer used for lowering the moisture content of the air passing through it; (2) an absorption or adsorption device for removing moisture from air. Dehydration − (1) removal of water vapor from air by the use of absorbing or adsorbing materials, (2) remov− al of water from stored goods. Delta Service − An arrangement of the utility trans− formers. Commonly shown ?."

Decay Rate − The rate at which the sound pressure lev− el in an enclosed space decreases after the sound source has stopped. it is measured in decibels per sec− ond.

Demand − The probable maximum rate of water flow as determined by the number of water supply fixture units.

Decibel (dB) − The unit ?bel" is used in telecommu− nication engineering as a dimensionless unit for the logarithmic ratio of two power quantities. The decibel is one−tenth of a bel.

Demand Charge − The part of an electric bill based on kW demand and the demand interval, expressed in dol− lars per kilowatt. Demand charges offset construction and maintenance of a utility’s need for a large generat− ing capacity.

Therefore, L  10 log 10

G.8



sound power reference power



Demand Control − A device which controls the kW demand level by shedding loads when the kW demand exceeds a predetermined set point.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


Demand Interval − The period of time during which kW demand is monitored by a utility service, usually 15 or 30 minutes long. Demand Load − The actual amount of load on a circuit at any time. The sum of all the loads which are ON. Equal to the connected load minus the loads that are OFF. Demand Reading − Highest or maximum demand for electricity an individual customer registers in a given interval, example, 15 minute interval. The metered de− mand reading sets the demand charge for the month. Density − The ratio of the mass of a specimen of a sub− stance to the volume of the specimen. The mass of a unit volume of a substance. When weight can be used without confusion, as synonymous with mass, density is the weight per unit volume. Desiccant − Any absorbent or adsorbent, liquid or sol− id, that will remove water or water vapor from a mate− rial. In a refrigeration circuit, the desiccant should be insoluble in the refrigerant. Design Working Pressure − The maximum allowable working pressure for which a specific part of a system is designed. Dewpoint, Apparatus − That temperature which would result if the psychrometric process occurring in a dehumidifier, humidifier or surface−cooler were car− ried to the saturation condition of the leaving air while maintaining the same ratio of sensible to total heat load in the process. Dewpoint Depression − The difference between dry bulb and dewpoint temperatures. Dewpoint Temperature − (tdp) The temperature at which moist air becomes saturated (100% relative hu− midity) with water vapor when cooled at constant pres− sure.

Diffuse Sound Field − A diffuse sound field is a space in which at every point the flow of sound energy in all directions is equally probable. (It is often assumed that in a diffuse field, the sound pressure level, averaged through time, is everywhere the same.) Diffuser − A circular, square, or rectangular air dis− tribution outlet, generally located in the ceiling and comprised of deflecting members discharging supply air in various directions and planes, and arranged to promote mixing of primary air with secondary room air. Direct Acting − Instruments that increase control pres− sure as the controlled variable (such as temperature or pressure) increases; while reverse acting instruments increase control pressure as the controlled variable de− creases. Direct Current (DC) − A source of power for an elec− trical circuit which does not reverse the polarity of its charge. Direct Field − The sound in a region in which all or most of the sound arrives directly from the source without reflection. Directivity Factor − The ratio of the sound pressure squared at some fixed distance and direction divided by the mean−squared sound pressure at the same dis− tance averaged over all directions from the source. Discharge Stop Valve − The manual service valve at the leaving connection of the compressor. Discrete Logic − Electronic circuitry composed of standard transistors, resistors, capacitors, etc., as compared to microprocessor circuits where the logic is condensed on a single chip (integrated circuit). Domestic Hot Water − Potable hot water as distin− guished from hot water used for house heating.

Dielectric Fitting − An insulating or nonconducting fitting used to isolate electrochemically dissimilar ma− terials.

D.O.P. (Dioctyl Phthalate) − An aerosol generated by blowing air through liquid dioctyl phthalate. Thermal− ly generated D.O.P. is an aerosol generated by con− densing vapor that has been evaporated from liquid (D.O.P.) by heat. The aerosol mean particle diameter is between 0.2 and 0.4 micron with a maximum geo− metric standard deviation of 1.3.

Differential − The difference between the points where a controller turns ?on" and ?off." If a thermostat turns a furnace on at 68F (20C) and the differential is 2F (1C), the burner will be turned off at 70F (21C).

D.O.P. Aerosol Generator, Air Operated − A device for producing a D.O.P. aerosol, operated by com− pressed air at room temperature, equipped with Laskin nozzles to produce a heterogeneous D.O.P. test aero− sol.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

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D.O.P. Aerosol Generator, Pressurized Gas−Ther− mal − A device for producing D.O.P. aerosol, operated by pressurized gas and equipped with heating means. Downflow − Vertical airflow (from ceiling to floor). Draft − a) A current of air, when referring to the pres− sure difference which causes a current of air or gases to flow through a flue, chimney, heater, or space; or b) to a localized effect caused by one or more factors of high air velocity, low ambient temperature, or direc− tion of air flow,whereby more heat is withdrawn from a person’s skin than is normally dissipated. Drier − A manufactured device containing a desiccant placed in the refrigerant circuit. Its primary purpose is to collect and hold within the desiccant, all water in the system in excess of the amount which can be tolerated in the circulating refrigerant. Drift − Term used to describe the difference between the set point and the actual operating or control point. Drip − A pipe, or a steam trap and a pipe considered as a unit, which conducts condensation from the steam side of a piping system to the water or return side of the system. Drop − The vertical distance that the lower edge of a horizontally projected airstream drops between the outlet and the end of its throw. Dry Bulb, Room − The dry bulb temperature of the conditioned room or space. Dry Bulb Temperature − The temperature of a gas or mixture of gases registered by an accurate thermome− ter after correction for radiation. The dry bulb repre− sents the measure of sensible heat, or the intensity of heat. Dry Bulb Temperature, Adjusted (tadb) − The average of the air temperature (ta) and the mean radiant tem− perature (tr) at a given location. The adjusted dry bulb temperature (tadb) is approximately equivalent to op− erative temperature (to) at air motions less than 80 fpm (0.4 m/s) when tr is less than 120F (49C).

Dynamic Discharge Head − Static discharge head plus friction head plus velocity head. Dynamic Insertion Loss − The dynamic insertion loss of a silencer, duct lining, or other attenuating device is in the performance measured in accordance with ASTM E 477 when handling the rated airflow. it is the reduction in sound pressure level, expressed in deci− bels, due solely to the placement of the sound attenuat− ing device in the duct system. Dynamic Suction Head − Positive static suction head minus friction head and minus velocity head. Dynamic Suction Lift − The sum of suction lift and ve− locity head at the pump suction when the source is be− low pump centerline. −E− Economizer − A system of dampers, temperature and humidity sensors, and motors which maximizes the use of outdoor air for cooling. Effect, Humidifying − Latent heat of water vaporiza− tion at the average evaporating temperature times the number of pounds (kilograms) of water evaporated per hour in Btuh (watts). Effect, Sun − Solar energy transmitted into space through windows and building materials. Effect, Total Cooling − The difference between the to− tal enthalpy of the dry air and water vapor mixture en− tering a unit per hour and the total enthalpy of the dry air and water vapor (and water) mixture leaving the unit per hour, expressed in Btu per hour (watts). Effective Area − The net area of an outlet or inlet de− vice through which air can pass, equal to the free area times the coefficient of discharge. Effectiveness (Efficiency) − The ratio of the actual amount of heat transferred by a heat recovery device to the maximum heat transfer possible between the air− streams (sensible heat/sensible heat, sensible heat/to− tal heat, or total heat/total heat).

Duct − A passageway made of sheet metal or other suit− able material, not necessarily leak tight, used for con− veying air or other gas at low pressures.

Elasticity of Demand − The change of quantity of electricity (or other commodity) purchased as a result of a change in its price. Demand for electricity is ?elas− tic" when it increases or decreases in response to de− creases or increases, respectively, in the price for the electricity.

Dust − An air suspension (aerosol) or particles of any solid material, usually with particle size less than 100 microns.

Electrical Circuit − A power supply, a load, and a path for current flow are the minimum requirements for an electrical circuit.

G.10

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


Electromechanical − Converting electrical input into mechanical action. A relay in an electromechanical switch. Electro−Pneumatic (EP) Switches − Switches that open or close an air line valve from an electrical im− pulse. Electrostatic Discharge (E.S.D.) − A transfer of elec− trostatic charge between objects at different electro− static potentials caused by direct contact or induced by electrostatic field. Emissivity − The property of a surface that determines its ability to give off radiant energy. Emittance − The ratio of the radiant energy emitted by a body to the energy emitted by a black body at the same temperature. End Reflection − When a duct system opens abruptly into a large room, some of the acoustic energy at the exit of the duct is reflected upstream with the result that the amount of the acoustic energy radiated into the room is reduced. This decrease in radiated energy in− creases as the frequency decreases. Energy − Expressed in kilowatt−hours (kWh) or watt− hours (Wh), and is equal to the product of power and time. energy = power × time kilowatt−hours = kilowatts × hours watt−hours = watts × hours

Enthalpy, Specific − A term sometimes applied to en− thalpy per unit weight. Entrainment − The capture of part of the surrounding air by the airstream discharged from an outlet (some− times called secondary air motion). Entropy − The ratio of the heat added to a substance to the absolute temperature at which it is added. Entropy, Specific − A term sometimes applied to en− tropy per unit weight. Equal Friction Method − A method of duct sizing wherein the selected duct friction loss value is used constantly throughout the design of a low pressure duct system. Equivalent Duct Diameter − The equivalent duct di− ameter for a rectangular duct with sides of dimensions a and b is 4/abp. Evaporation − Change of state from liquid to vapor. Evaporative Cooling − The adiabatic exchange of heat between air and a water spray or wetted surface. The water approaches the wet bulb temperature of the air, which remains constant during its traverse of the exchanger. Evaporator − The heat exchanger in which the me− dium being cooled, usually air or water, gives up heat to the refrigerant through the exchanger transfer sur− face. The liquid refrigerant boils into a gas in the pro− cess of the heat absorption. Exfiltration − Air leakage outward through cracks and interstices and through ceilings, floors and walls of a space or building.

Energy (Consumption) Charge − That part of an elec− tric bill based on kWh consumption (expressed in cents per kWh). Energy charge covers cost of utility fuel, general operating costs, and part of the amortiza− tion of the utility’s equipment.

Extended Surface − Heat transfer surface, one or both sides of which are increased in area by the addition of fins, discs, or other means.

Energy Efficiency Ratio (EER), Cooling − The ratio of net cooling capacity in Btuh to total electric input in watts under designated operating conditions.

Face Area − The total plane area of the portion of a grille, coil, or other items bounded by a line tangent to the outer edges of the openings through which air can pass.

Engine − Prime mover; device for transforming fuel or heat energy into mechanical energy.

Face Velocity − The velocity obtained by dividing the air quantity by the component face area.

Enthalpy − The total quantity of heat energy contained in a substance, also called total heat; the sum of the sensible heat and latent heat in an exchange process.

Fahrenheit − A thermometric scale in which 32 (F) denotes freezing and 212 (F) the boiling point of wa− ter under normal pressure at sea level (14.696 psi).

−F−

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

G.11


Fail Safe − In load management, returning all loads to conventional control during a power failure. Accom− plished by a relay whose contacts are normally closed. Fan, Centrifugal − A fan rotor or wheel within a scroll type housing and including driving mechanism sup− ports for either belt drive or direct connection. Fan performance Curve − Fan performance curve re− fers to the constant speed performance curve. This is a graphical presentation of static or total pressure and power input over a range of air volume flow rate at a stated inlet density and fan speed. It may include static and mechanical efficiency curves. The range of air volume flow rate which is covered generally extends from shutoff (zero air volume flow rate) to free deliv− ery (zero fan static pressure). The pressure curves are generally referred to as the pressure−volume curves. Fan propeller − A propeller or disc type wheel within a mounting or plate and including driving mechanism supports for either belt drive or direct connection. Fan, Tubeaxial − A propeller or disc type wheel within a cylinder and including driving mechanism supports for either belt drive or direct connection. Fan, Vaneaxial − A disc type wheel within a cylinder, a set of airguide vanes located either before or after the wheel and including driving mechanism supports for either belt drive or direct connection. Fault − A short circuitCeither line to line, or line to ground. Feed Line − A pipe that supplies water to items such as a boiler or a domestic hot water tank. Filter − A device to remove solid material from a fluid. Filter−Drier − A combination device used as a strainer and moisture remover.

If this ?first" room has the same noise criterion (NC) or a lower NC value than rooms further away from the fan, it may be assumed that, if the acoustical attenua− tion of the duct system from the fan to this ?first" room satisfies the requirements for this ?first" room, it also satisfies the acoustical requirements for rooms further away from the fan. Fire Damper − A device, installed in an air distribu− tion system, designed to close automatically upon detection of heat, to interrupt migratory airflow, and to restrict the passage of flame. A combination fire and smoke damper shall meet the requirements of both. Fire Resistance Rating − The time, in minutes or hours, that materials or assemblies have withstood a fire exposure as established in accordance with the test procedures of NFPA 251, Standard Methods of Fire Tests of Building Construction and Materials. Fire Wall − A wall having adequate fire resistance and structural stability under fire conditions to accomplish the purpose of subdividing buildings to restrict the spread of fire. First Air − The air which issues directly from the HEPA filter before it passes over any work location. First Work Location − The work location nearest the downstream side of the HEPA filters in a laminar air− flow device or cleanroom. Fixed Collector − A permanently oriented collector that has no provision for seasonal adjustment or track− ing of the sun. Flame Spread Rating − The flame spread rating of a material refers to a number or classification of materi− al obtained according to NFPA 255, Method of Test of Surface Burning Characteristics of Building Materi− als.

Fin − An extended surface to increase the heat transfer area, as metal sheets attached to tubes.

Flanking (Sound) Transmission − The transmission of sound between two rooms by any indirect path of sound transmission.

Final Filter − The last stage of filtration before the air− stream enters the clean space. The performance grade of this filter determines the air quality entering the clean space.

Flat−Plate Collector − A solar collector without exter− nal concentrators or focusing devices, usually consist− ing of an absorber plate, cover plates, back and side in− sulation and a container.

First Acoustically Critical Room − Most duct system service a number of rooms. The room that has the shortest duct run from the fan is usually exposed to more fan noise than rooms further away from the fan.

Floating Action Controllers − Essentially two posi− tion type controllers which vary the position of the controlled devices but which are arranged to stop be− fore reaching a maximum or minimum position.

G.12

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


Flow, Laminar − Fluid flow in which each fluid par− ticle moves in a smooth path substantially parallel to the paths followed by all other particles. Flow, Turbulent − Fluid flow in which the fluid moves transversely as well as in the direction of the tube or pipe axis. Flue − A special enclosure incorporated into a building for the removal of products of combustion to the out−of−doors. Type <A" − A flue listed for use with oil, gas, or coal burning equipment. Type <B" − A manufactured flue listed for use with gas burning equipment. Fluid − Gas, vapor, or liquid. Fluid Head − The static pressure of fluid expressed in terms of the height of a column of the fluid, or of some manometric fluid, which it would support. Fluid, Heat Transfer − Any gas, vapor, or liquid used to absorb heat from a source at a high temperature and reject it to a lower temperature substance. Fluid Dynamics − Fluid Dynamics is used to describe the condition of motion of a fluid within a system. The velocity of a fluid is based upon the cross−sectional area and the volume of a fluid passing through it. The importance of this property is that volume may be de− termined for air or water systems when the area and ve− locity are known. Fluid Statics − Fluid Statics as applied to TAB work, refers to a condition of a quantity of fluid at rest. It is the direct result of gravity and weight. Static pressure is used in both air and water testing to determine the potential for the movement of fluid within a system. Pressures in air systems are normally measured in units of inches of water (in.w.g.), millimeters of water (mm w.g.) or pascals (Pa). A pressure unit of one inch of water is equivalent to the static pressure found at the base of a column of water one inch high. Pressures in water systems are normally measured in pounds per square inch (psi) or kilopascals (kPa), but are con− verted to feet of water (ft. w.g.) or meters of water (m w.g.) for the purpose of evaluating pump and equip− ment performance.

Force − The action on a body which tends to change its relative condition as to rest or motion. Forced Circulation − Circulation of heat transfer fluid by a pump or fan. Forward Flow − Forward flow occurs when air flows and noise propagates in the same direction, as in an air conditioning supply system or in a fan discharge. Free Area − The total minimum area of the openings in the air outlet or inlet through which air can pass. Free Delivery−Type Unit − A device which takes in air and discharges it directly to the space to be treated without external elements which impose air resist− ance. Free Sound Field (Free Field) − A free sound field is a field in a homogeneous, isotropic medium free from boundaries. In practice, it is a field in which the effects of the boundaries are negligible over the region of in− terest. In the free field, the sound pressure level de− creases 6 dB for a doubling of distance from a point source. Freezing Point − Temperature at which a given liquid substance will solidify or freeze on removal of heat. Freezing point of water is 32F (C). Frequency − The number of vibrations or waves or cycles of any periodic phenomenon per second. In noise control of duct systems, our interest lies in the audible frequency range of 20 to 20,000 cycles per sec− ond. The United States has adopted the international designation of ?hertz" (Hz.) for cycles per second. Frequency Spectrum − A representation of a complex noise which has been resolved into frequency compo− nents. The most commonly used components are 1/1 octave bands and 1/3 octave bands. Friction − Friction is the resistance found at the duct and piping walls. Resistance creates a static pressure loss in systems. The primary purpose of a fan or pump is to produce a design volume of fluid at a pressure equal to the frictional resistance of the system and the other dynamic pressure losses of the components. Friction Head − The pressure in psi or feet (kPa or me− ters) of the liquid pumped which represents system re− sistance that must be overcome. Full Load Current − See Running Current.

Focusing Collector − A collector using some type of focusing device (parabolic mirror, Fresnel lens, etc.) to concentrate the insolation on an absorbing element.

Fumes − Solid particles commonly formed by the con− densation of vapors from normally solid materials

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

G.13


such as molten metals. Fumes may also be formed by sublimation, distillation, calcination, or chemical reaction wherever such processes create airborne par− ticles predominantly below one micron in size. Such solid particles sometime serve as condensation nuclei for water vapor to form smog. Functional Performance Testing − A full range of checks and tests to determine if all components of equipment, systems and subsystems function and in− terface under all conditions required by the contract documents. −G− GFI, GFCI − Ground fault (circuit) interrupterCa de− vice that senses electrical ground faults and reacts by opening the circuit.

Ground Conductor − Conductor run in an electrical system, which is deliberately connected to the ground electrode. Purpose is to provide a ground point throughout the system. Insulation colorCgreen. Also called ?green ground". Ground Fault − An unintentional connection to ground. −H− Head, Dynamic or Total − In flowing fluid, the sum of the static and velocity heads at the point of measure− ment. Head, Static − The static pressure of fluid expressed in terms of the height of a column of the fluid, or of some manometric fluid, which it would support.

Gang − One wiring device position in a box,.

Head, Velocity − In a flowing fluid, the height of the fluid or of some manometric fluid equivalent to its ve− locity pressure.

Gas − Usually a highly superheated vapor which, with− in acceptable limits of accuracy, satisfies the perfect gas laws.

Heat − The form of energy that is transferred by virtue of a temperature difference.

Gas, Inert − A gas that neither experiences nor causes chemical reaction nor undergoes a change of state in a system or process; e.g. nitrogen or helium mixed with a volatile refrigerant.

Heat, Latent − Change of enthalpy during a change of state, usually expressed in Btu per lb (kJ/kg). With pure substances, latent heat is absorbed or rejected at a constant temperature.

Gas Constant − The coefficient ?R" in the perfect gas equation − PV = MRT.

Heat, Sensible − Heat is associated with a chance in temperature, specific heat exchange of temperature; in contrast to a heat interchange in which a change of state (latent heat) occurs.

Gradual Switches − Manual adjustment devices which proportion the control condition in accordance with the position of the switch. Grains of Moisture − The unit of measurement of ac− tual moisture contained in a sample of air. (7000 grains = one pound of water). Gravity, Specific − Density compared to density of standard material; reference usually to water or to air. Grille − A louvered or perforated covering for an air passage opening which can be located on a wall, ceil− ing or flood.

Heat, Specific − The ratio of the quantity of heat re− quired to raise the temperature of a given mass of any substance one degree to the quantity required to raise the temperature of an equal mass of a standard sub− stance one degree. Heat, Total (Enthalpy) − The sum of sensible heat and latent heat between an arbitrary datum point and the temperature and state under consideration. Heat Capacity − The amount of heat necessary to raise the temperature of a given mass one degree. Numeri− cally, the mass multiplied by the specific heat.

Ground − Zero voltage, or any point connected to the earth or ?ground."

Heat Conductor − A material capable of readily con− ducting heat. The opposite of an insulator or insula− tion.

Ground Bus − A busbar in a panel or elsewhere, delib− erately connected to ground.

Heat Exchanger − A device specifically designed to transfer heat between two physically separated fluids.

G.14

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


Heat of Fusion − Latent heat involved in the change between liquid and vapor states.

rupts system operation if the monitored condition be− comes excessive.

Heat Pump − A refrigerating system employed to transfer heat into a space or substance. The condenser provides the heat while the evaporator is arranged to pick up heat from air, water, etc. By shifting the flow of air or other fluid, a heat pump system may also be used to cool the space.

High Pressure Cutout − A pressure actuated switch to protect the compressor from pressure often caused by high condenser temperatures and pressure due to foul− ing and lack of water or air.

Heat Transfer Medium − A fluid used in the transport of thermal energy. Heat Transmission − Any time−rate of heat flow; usu− ally refers to conduction, convection and radiation combined. Heat Transmission Coefficient − Any one of a num− ber of coefficients used in the calculation of heat trans− mission by conduction, convection, and radiation, through various materials and structures. Heating, Regenerative (or Cooling) − Process of uti− lizing heat, which must be rejected or absorbed in one part of the cycle, to perform a useful function in anoth− er part of the cycle by heat transfer. HEPA Filter (High Efficiency Particulate Air Fil− ter) − A throw−away extended media, dry−type filter in a rigid frame having a minimum particle−collection ef− ficiency of 99.97 percent for 0.3 micron thermally− generated dioctyl phthalate (D.O.P.) or acceptable al− ternative particles, and a maximum clean filter pressure drop of 1.0 inch water gauge (249 pascals), when tested at rated airflow capacity.

High Side − Parts of the refrigerating system subjected to condenser pressure or higher; the system from the compression side of the compressor through the con− denser to the expansion point of the evaporator. Horsepower − Unit of power in foot−pound−second system; work done at the rate of 550 ft−lb per sec, or 33,000 ft−lb per min. Hot Deck − The heating section of a multizone system. Hot Gas Bypass − The piping and manual, but more often automatic, valve used to introduce compressor discharge gas directly into the evaporator. This type of arrangement will maintain compressor operation at light loads down to zero by falsely loading the evapo− rator and compressor. Hot Gas Piping − The compressor discharge piping which carries the hot refrigerant gas from the compres− sor to the condenser. Velocities must be high enough to carry entrained oil. Humidifier − A device to add moisture to air. Humidifying Effect − The latent heat of vaporization of water at the average evaporating temperature times the weight of water evaporated per unit of time.

Heterogeneous Dioctyl Phthalate (D.O.P.) − An aerosol having the approximate light scattering mean droplet size distribution as follows −

Humidistat − A regulatory device, actuated by changes in humidity, used for the automatic control of relative humidity.

99 percent less than 3.0 micron

Humidity − Water vapor within a given space.

50 percent less than 0.7 micron

Humidity, Absolute − The weight of water vapor per unit volume.

10 percent less than 0.4 micron Hidden Demand Charge − Electric bill charges that are based on cents per kWh per kW demand contain a hidden demand charge. A low load factor for a build− ing then penalizes the energy user through this ?hid− den" charge. High Limit control − A device which normally moni− tors the condition of the controlled medium and inter−

Humidity, Percentage − The ratio of the specific hu− midity of humid air to that of saturated air at the same temperature and pressure, usually expressed as a per− centage (degree of saturation; saturation ratio). Humidity Ratio − The ratio of the mass of the water vapor to the mass of dry air contained in the sample. Humidity, Relative − The ratio of the mol fraction of water vapor present in the air, to the mol fraction of

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

G.15


water vapor present in saturated air at the same tem− perature and barometric pressure; approximately, it equals the ratio of the partial pressure or density of the water vapor in the air, to the saturation pressure or den− sity, respectively, of water vapor at the same tempera− ture.

not touching it), the ever changing magnetic field will induce a current in the second conductor.

Humidity, Specific − Weight of water vapor (steam) associated with 1 pound (kilogram) weight of dry air, also called humidity.

Inductive Loads − Loads whose voltage and current are out−of−phase. True power consumption for induc− tive loads is calculated by multiplying its voltage, cur− rent, and the power factor of the load.

Hunting − A condition which occurs when the desired condition cannot be maintained. The controller, con− trolled device and system, individually or collectively, continuously override or ?overshoot" the control point with a resulting fluctuation and loss of control of the condition to be maintained. Hydrostatic Pressure − The pressure at any point in a liquid at rest; equal to the depth of the liquid multiplied by its density. Hygroscopic − Absorptive of moisture, readily ab− sorbing and retaining moisture. −I− Impedance (Z) − The quantity in an AC circuit that is equivalent to resistance in a DC circuit, inasmuch as it relates current and voltage. It is composed of resist− ance plus a purely AC concept called reactance and is expressed, like resistance, in ohms. Impervious − Not allowing passage of a gas (air). <In" Contacts − Those relay contacts which complete circuits when the relay armature is energized. Also re− ferred to as normally open contacts. Inch of Water (in.w.g.) − A unit of pressure equal to the pressure exerted by a column of liquid water 1 inch high at a temperature of 39.2F. Incidence, Angle of − The angle at which insolation strikes a surface. Indicator − A term used to describe any device such as a thermometer or pressure gauge which is used to indi− cate the condition at a point in the system but which does to provide any controlling action or effect on the system operation. Inductance − The process when a second conductor is placed next to a conductor carrying AC current (but G.16

Induction − The capture of part of the ambient air by the jet action of the primary airstream discharging from a controlled device.

Infiltration − Outside air flowing into a building as through a wall, crack, etc. Input Override Relay − A relay that allows the duty cycle to be inhibited on specific channels because of inputs from outdoor temperature, space temperature, case temperature, time−of−day, etc. Sometimes called duty cycle control relay. Inrush Current − The current that flows the instant af− ter the switch controlling current flow to a load is closed. Also called locked rotor current. Insertion Loss − The insertion loss of an element of an acoustic transmission system is the positive or nega− tive change in acoustic power transmission that results when the element is introduced. Insolation − The total amount of solar energy reaching a surface per unit of time. Instantaneous Rate − Method for determining when load shedding should occur. Actual energy usage is measured and compared to a present kilowatt level. If the actual kilowatt level exceeds a designated set point, loads will be shed until the actual rate drops be− low the set point. Insulation, Thermal − A material having a relatively high resistance to heat flow and used principally to re− tard heat flow. Interstage Differential − In a multistage HVAC sys− tem, the change in temperature at the thermostat need− ed to turn additional heating or cooling equipment on. Isentropic − An adjective describing a reversible adia− batic process; a change taking place at constant entro− py. Isobaric − An adjective used to indicate a change tak− ing place at constant pressure. Isokinetic Sampling − Any technique for collecting airborne particulate matter in which the collection is

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


so designed that the airstream entering it has a velocity equal to that of the air passing around and outside the collector.

izontal Flow), producing a uniform and parallel air− flow. (Net filter medium face area versus gross area = 0.80.)

Isothermal − An adjective used to indicate a change taking place at constant temperature.

Laminar Flow Clean Air Device − A clean bench, clean work station, wall or ceiling hung module, or other device (except a cleanroom) which incorporates a HEPA filter(s) and motor blower(s) for the purpose of supplying laminar flow clean air to a controlled work space.

−J− Junction Box − Metal box in which tap to circuit con− ductors is made. Junction box is not an outlet, since no load is fed from it directly. −K− Kilovolt Ampere − Product of the voltage times the current. Different from kilowatts because of inductive loads in an electrical system. Abbreviated − kVA kilo− watts is equal to KVA times power factor. Kilowatt − 1000 watts. Abbreviated − kW. Kilowatt−Hour − A measure of electrical energy con− sumption, 1000 watts being consumed per hour. Ab− breviated − kWh. kW Demand − The maximum rate of electric power usage required to operate a facility during a period of time, usually a month billing period. Often called de− mand. kWh Consumption − The amount of electric energy used over a period of time; the number of kWh used per month. Often called consumption.

Langley − Standard unit of insolation measurements, 1 langley = 1 cal/sq.cm. (1 langley/min. = 221 Btuh/ sq.ft.). Laskin Nozzle − A nozzle used for the generation of a heterogeneous D.O.P. aerosol by compressed gas (as defined in Air Generated D.O.P.). Latent Heat of Fusion − The heat required to change a solid to a liquid at the same temperature, i.e., ice to water requires 144 Btu/lb (335 kJ/kg). Latent Heat of Vaporization − The amount of heat necessary to change a quantity of water to water vapor without changing either temperature or pressure (re− quires 970 Btu/lb or 2256 kJ/kg). When water is vapor− ized and passes into the air, the latent heat of vaporiza− tion passes into the air along with the vapor. Likewise, latent heat is removed when water vapor is condensed. Law of Partial Pressure, Dalton’s − Each constituent of a mixture of gases behaves thermodynamically as if it alone occupied the space. The sum of the individu− al pressures of the constituents equals the total pres− sure of the mixture.

−L− Lag − A delay in the effect of a changed condition at one point in the system, on some other condition to which it is related. Also, the delay in action of the sens− ing element of a control, due to the time required for the sensing element to reach equilibrium with the property being controlled, i.e., temperature lag, flow lag, etc. Laminar (Unidirectional) Airflow − Airflow in which the entire body of air within a confined area moves with uniform velocity along parallel flow lines. Laminar Airflow Cleanroom − A cleanroom in which the filtered air entering the room makes a single pass through the work area in a parallel airflow pattern, with a minimum of turbulent flow areas. Laminar air− flow rooms have HEPA filter coverage of at least 80 percent of the ceiling (Vertical Flow) or one wall (Hor−

Level − The logarithm of the ratio, expressed in deci− bels, of two quantities proportional to power or energy. The quantity which is the denominator of the ratio is the standard reference quantity. Light Emitting Diode − A low current and voltage light used as an indicator on load management equip− ment. Abbreviated − LED. Limit − Control applied in the line or low voltage con− trol circuit to break the circuit of conditions move out− side a preset range. In a motor, a switch which cuts off power to the motor windings when the motor reaches its full open position. Limit Control − A temperature, pressure, humidity, dew point or other control that overrides the demand control and/or duty cycler to prevent any affect on the business operation from load management, malfunc−

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

G.17


tion, or abnormal conditions. Also called load over− ride. Limited Combustible Material − A building construction material not complying with the defini− tion of noncombustible material, which in the form in which it is used, has a potential heat value not exceed− ing 3500 Btu/lb (8141 KJ/kg) (see NFPA 259, Stan− dard Test Method for Potential Heat of Building Mate− rials) and complies with one of the following paragraphs (a) or (b). Materials subject to increase in combustibility or flame spread rating beyond the lim− its herein established through the effects of age, mois− ture, or other atmospheric condition shall be consid− ered combustible. (a) Materials having a structural base of noncombus− tible material,with a surfacing not exceeding a thick− ness of 1/8 in. (3.2 mm) which has a flame spread rat− ing not greater than 50. (b) Materials, in the form and thickness used, other than as described in (a), having neither a flame spread rating greater than 25 nor evidence of continued pro− gressive combustion, and of such composition that surfaces that would be exposed by cutting through the material on any plane would have neither a flame spread rating greater than 25 nor evidence of contin− ued progressive combustion. Line Side − The side of a device electrically closest to the source of current. Line Voltage − In the control industry, the normal elec− tric supply voltages, which are usually 120 or 240 volts. Liquefaction − A change of state to liquid; generally used instead of condensation in cases of substances or− dinarily gaseous. Liquid Sight Glass − The glass ported fitting in the liq− uid line used to indicate adequate refrigerant charge. When bubbles appear in the glass, there is insufficient refrigerant in the system. Liquid Solenoid Valve − The electrically operated au− tomatic shutoff valve in the liquid piping which closes on system shutdown to close off receiver discharge when used in pump down cycle and which prevents re− frigerant migration in any system. Load − The amount of heat per unit time imposed on a refrigerant system, or the required rate of heat re− moval. G.18

Load Factor − This is a ratio expressing a customer’s average actual use of the utility’s capacity provided versus the maximum amount used. Load Management − The control of electrical loads to reduce kW demand and kWh consumption. Load Programmer − Any device which turns loads on and off on a real time, time interval, or kW demand ba− sis. Load Side − The side of a device electrically farthest from the current source. Locked Rotor Current − See ?Inrush Current". Loudness − The subjective human definition of the in− tensity of a sound. Human reaction to sound is highly dependent on the sound pressure and frequency. Loudness Level − A subjective method of rating loud− ness in which a 1000 Hz tone is varied in intensity until it is judged by listeners to be equally as loud as a given sound sample. The loudness level in ?phons" is taken as the sound pressure level, in decibels, of the 100 Hz tone. Louver − An assembly of sloping vanes intended to permit air to pass through and to inhibit transfer of wa− ter droplets. Low Limit Control − A device which normally moni− tors the condition of the controlled medium and inter− rupts system operation if the monitored condition drops below the desired minimum value. Low Side − The refrigerating system from the expan− sion point to the point where the refrigerant vapor is compressed; where the system is at or below evapo− rated pressure. Low Temperature Cutout − A pressure or tempera− ture actuated device with sensing element in the evap− orator, which will shut the system down at its control setting to prevent freezing chilled water or to prevent coil frosting. Direct expansion equipment may not use this device. Low Voltage − In the control industry, a power supply of 25 volts or less. −M− MCM − Thousand circular milCused to describe large wire sizes. Magnahelic Gauge (TM) − An instrument used to measure differential air pressure between two spaces. (Trade name of Dwyer Instruments, Inc.)

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


Manometer − An instrument for measuring pressures; especially a U−tube partially filled with a liquid, usual− ly water, mercury, or a light oil, so constructed that the amount of displacement of the liquid indicates the pressure being exerted on the instrument. Mass − The quantity of matter in a body as measured by the ratio of the force required to produce given ac− celeration, to the acceleration. Mass Law (Sound) − The law relating to the transmis− sion loss of sound barriers which says that in a part of the frequency range, the magnitude of the loss is con− trolled entirely by the mass per unit area of the barrier. The law also says that the transmission loss increases 6 decibels for each doubling of frequency or each doubling of the barrier mass per unit area. Master (Central) Control − Control of all outlets from one point. Maximum <No−Flow" Temperature − The maximum temperature that will be obtained in a component when the heat transfer fluid is not flowing through the sys− tem.

Modulating Control − A mode of automatic control in which the action of the final control element is propor− tional to the deviation, from set point of the controlled medium. Modulating Controllers − Constantly reposition themselves in proportion to the requirements of the system, theoretically being able to maintain an accu− rately constant condition. Motor Control Center − A single metal enclosed as− sembly containing a number of motor controllers and possibly other devices such as switches and control de− vices. Multidirectional Airflow − Airflow in which the air within a combined area moves in a non−uniform or tur− bulent flow. Multipole − Connections to more than 1 pole such as a 2−pole circuit breaker. Multistage Thermostat − A thermostat which con− trols auxiliary equipment for heating or cooling in re− sponse to a greater demand for heating or cooling. −N−

Media − The heat transfer material used in rotary heat exchangers, also referred to as matrix. Melting Point − For a given pressure, the temperature at which the solid and liquid phases of the substance are in equilibrium. Microbar − A unit of pressure equal to 1 dyne/cm2 (one millionth of the pressure of the atmosphere). Micro−Organism − A microscopic organism, espe− cially a bacterium, fungus, or a protozoan. Micron − A unit of measurement equal to one−mil− lionth of a meter or approximately 0.00003937 inch. (25 microns are approximately 0.001 inch). Microprocessor − A small computer used in load man− agement to analyze energy demand and consumption such that loads are turned on and off according to a pre− determined program. Mixed Airflow Cleanroom − A hybrid cleanroom consisting of a combination of laminar airflow and tur− bulent airflow within the same enclosure. Modulation − Of a control, tending to adjust by incre− ments and decrements.

Natural Ventilation − The movement of outdoor air into a space through intentionally provided openings, such as windows and doors, or though nonpowered ventilators or by infiltration. NC − Normally closed contacts of a relay. Circuits are closed when the relay is de−energized. NO − Normally open contacts of a relay. Circuits are opened when the relay is de−energized. Neutral − The circuit conductor that is normally grounded or at zero voltage difference to the ground. Nocturnal Radiation − Loss of energy by radiation to the night sky. Noise − Sound which is unpleasant or unwanted by the recipient. Noise Criteria Curves (NC Curves) − Curves that de− fine the limits which the octave band spectrum of a noise source must not exceed if a certain level of occu− pant acceptance is to be achieved. Noise Criterion (NC) Curves − Established 1/1 oc− tave band noise spectra for rating the amount of noise of an occupied space with a single number.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

G.19


Noncombustible Material − A material which, in the form in which it is used and under the conditions antic− ipated, will not ignite, burn, support combustion, or re− lease flammable vapors when subjected to fire or heat. Materials reported as noncombustible, when tested in accordance with ASTM E136, Standard Method of Test for Noncombustibility of Elementary Materials, shall be considered noncombustible materials. Normally open (or normally closed) − The position of a valve, damper, relay contacts, or switch when ex− ternal power or pressure is not being applied to the de− vice. Valves and dampers usually are returned to a ?normal" position by a spring. −O− Occupied Zone − The region within an occupied space between planes 3 and 72 inches (75 and 1800 mm) above the floor and more than 2 feet (600 mm) from the walls or fixed air conditioning equipment (see ASHRAE Standard 55−1981). Octave Band (O.B.) − A range of frequency where the highest frequency of the band is double the lowest fre− quency of the band. The band is usually specified by the center frequency. 1/1 Octave Band − A range of frequencies where the highest frequency of the band is double the lowest fre− quency band. The band is specified by the center fre− quency. The preferred octave bands are designed by the following center frequencies − 31.5, 63, 125, 250, 500, 1000, 2000, 4000, 8000, 16,000. Odor − A quality of gases, liquids or particles that stimulates the olfactory organ. Offset − Term used to describe the difference between the set point and the actual operating or control point. Ohm (R) − A measure of pure resistance in an electri− cal circuit. Ohm’s Law − The relationship between current and voltage in a circuit. It states that current is proportional to voltage and inversely proportional to resistance. Ex− pressed algebraically, in D.C. circuits I = E/R; in AC circuits I − E/Z. <On−off" Control" − A two position action which al− lows operation at either maximum or minimum condi− tion, or on or off, depending on the position of the con− troller. G.20

On−Site Field Certification − Certification at the location of usage. Opaque − Not permitting transmission of radiant ener− gy or light. Open Circuit − The condition when either deliberately or accidentally, an electrical conductor or connection is broken or open with a switch. Operating Point − The value of the controlled condi− tion at which the controller actually operates. Also called control point. Operation Facility − A cleanroom in normally opera− tion. Optimum Operative Temperature − Temperature that satisfies the greatest possible number of people at a given clothing and activity level. Out Contacts − Those relay contacts which complete circuits when the relay coil is deenergized. Also re− ferred to as normally closed contacts. Outgassing − The emission of gases by materials and components, usually during exposure to elevated tem− perature, or reduced pressure. Outlet, Ceiling − A round, square, rectangular, or lin− ear air diffuser located in the ceiling, which provides a horizontal distribution pattern of primary and secon− dary air over the occupied zone and induces low veloc− ity secondary air motion through the occupied zone. Outlet, Slotted − A long, narrow air distribution outlet, comprised of deflecting members, located in the ceil− ing sidewall, or sill, with an aspect ratio greater than 10, designed to distribute supply air in varying direc− tions and planes, and arranged to promote mixing of primary air and secondary room air. Outlet, Vaned − A register or grille equipped with ver− tical and/or horizontal adjustable vanes. Outlet Velocity − The average velocity of primary air emerging from an opening, fan or outlet, measured in the plane of the opening. Output − Capacity, duty, performance, net refrigera− tion produced by system. Outside Air Opening − Any opening used as an entry for air from outdoors. Overall Coefficient of Heat Transfer (thermal transmittance) − The time rate of heat flow through a

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


body per unit area, under steady conditions, for a unit temperature difference between the fluids on the two sides of the body. Overcurrent Device − A device such as a fuse or a cir− cuit breaker designed to protect a circuit against exces− sive current by opening the circuit. Overload − A condition of excess current; more cur− rent flowing than the circuit was designed to carry. Override − A manual or automatic action taken to by− pass the normal operation of a device or system. Oxidation − A reaction in which oxygen combined with another substance.

Particulate Matter − A general term applied to minia− ture particles of material suspended in gases or liquids. Passive Solar System − An assembly of collectors, thermal storage device(s), and transfer media which converts solar energy into thermal energy and in which no energy in addition to solar is used to accomplish the transfer of thermal energy. The prime element in a pas− sive solar system is usually some form of thermal ca− pacitance. Pass−Through Box − A double doored chamber ar− ranged to permit transfer of material and/or equipment between two confined spaces of different contamina− tion levels. Peak Demand − The greatest amount of kilowatts needed during a demand interval.

−P− Package A/C Unit − Consists of a factory made assem− bly which normally includes a cooling coil, compres− sor(s), condensing coil, and may include a heating function as well. Parallel Airflow − Unidirectional airflow, as demon− strated by introduction of an isokinetic smoke stream which exhibits a measured dispersion of not more than 14 from straight line flow. Parallel Circuit − One where all the elements are con− nected across the voltage source. Therefore, the volt− age on each element is the same but the current through each may be different. Particulate Matter − A state of matter in which solid or liquid substances exist in the form of aggregated molecules or particles. Airborne particulate matter is typically in the size range of 0.01 to 100 micrometers (microns). Particle − A very small discrete mass of solid or liquid matter, usually measured in microns.

Peak Load Pricing − A pricing principle that charges more for purchases that contribute to the peak demand and, thereby, cause the expansion of productive capac− ity when the peak demand exceeds the peak capacity (less minimum excess capacity). In the electric power industry, this means charging more for electricity bought on or near the seasonal peak of the utility or on or near the daily peak of the utility. The latter requires special meters; the former does not. Performance Factor − Ratio of the useful output ca− pacity of a system to the input required to obtain it. Units of capacity and input need not be consistent. Pert − Program, evaluation and review technique; a system of planning, scheduling, controlling and re− viewing a series of interdependent events in order to follow a proper sequence and complete a project as quickly and inexpensively as possible. Pervious − Allows passage of a gas (air). Phase − Part of an AC voltage cycle. Residential elec− trical service is 2−phase; commercial facilities are usu− ally 3−phase, AC voltage.

Particle Counter − A light scattering instrument with display or recording means to count and size discrete particles in air.

Phon − A measurement of loudness level. The loud− ness level in phons of any sound is the sound pressure level of the 1000 Hz reference tone which is equally loud to the sound being rated. The loudness of 1 sone correspondents to a loudness level of 40 phons in ac− cordance with the definition of the sone; a two fold change of loudness in sones is associated with a 10 phon change in loudness level.

Particle Size − An expression for the size of solid or liquid particles expressed as the apparent maximum linear dimension or diameter of the particle.

Photovoltaic Conversion − Use of semiconductor or other photovoltaic devices that convert solar radiation directly to electricity.

Particle Count − Concentration expressed in terms of the number of particles per unit volume of air or other gas.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

G.21


Pilot Duty Relay − A relay used for switching loads such as another relay or solenoid valve coils. The pilot duty relay contacts are located in a second control cir− cuit. Pilot duty relays are rated in volt amperes (VA). Pitch − The pitch of a sound depends primarily on its frequency. In music, sounds of higher frequencies are referred to as treble notes, while those of lower fre− quencies are referred to as bass notes. Planting Screen − Bushes or other plantings that hide a refrigerant compressor. Plenum − An air compartment connected to one or more distributing ducts. Plug−in Bus Duct − Bus duct with built in power tap off points. Tap off is made with a plug−in switch, circuit breaker, or other fitting. Pneumatic − Operated by air pressure. Pneumatic Electric (PE) Switches − Device that op− erates an electric switch from a change of air pressure. Point, Critical − Of a substance, state point at which liquid and vapor have identical properties; critical temperature, critical pressure, and critical volume are the terms given to the temperature,, pressure, and vol− ume at the critical point. Above the critical tempera− ture or pressure, there is no demarcation line between liquid and gaseous phases. Point of Duty − A statement of air volume flow rate and static or total pressure at a stated density and is used to specify the point on the system curve at which a fan is to operate. Point of Operation − Used to designate the single set fan performance values which correspond to the point of intersection of the system curve and the fan pressure volume curve. Point of Rating − A statement of fan performance val− ues which correspondent to one specific point on the fan pressure volume curve. Polarity − The direction of current flow in a DC cir− cuit. By convention, current flows from plus to minus. Electron flow is actually in the opposite direction. Pole − An electrical connection point. In a panel, the point of connection. On a device, the terminal that con− nects to the power. G.22

Potable Water − Water that is safe to drink. Potential Transformer − A voltage transformer. The voltage supplied to a primary coil induces a voltage in a secondary coil according to the ratio of the wire windings in each of the coils. Potentiometer − An electromechanical device having a terminal connected to each and to the resistive ele− ment, and a third terminal connected to the wiper con− tact. The electrical input is divided as the contact moves over the element, thus making it possible to me− chanically change the resistance. Power (P) − Expressed in watts (W) or kilowatts (kW), and is equal to − in DC circuit, P = EI and P = I2R in AC circuit, P = EI x Power factor Power Factor (pf) − A quantity that relates the volt amperes of an AC circuit to the wattage (power = volt− amperes x power factor). Power factor also is the ratio of the circuit resistance (R) to the impedance (Z) ex− pressed as a decimal between zero and one (p.f. = R/Z). When the power factor equals one, all consumed pow− er produces useful work. Power Factor Charge − A utility charge for ?poor" power factor. It is more expensive to provide power to a facility with a poor power factor (usually less than 0.8). Power Factor Correction − Installing capacitors on the utility service’s supply line to improve the power factor of the building. Power supply − The voltage and current source for an electrical circuit. A battery, a utility service, and a transformer are power supplies. Predicting Method − Method for determining when load shedding should occur. A formula is used to arrive at a preset kilowatt limit. Then the actual amount of energy accumulated during the utility’s demand inter− vals is measured. A projection is made of the actual rate of energy usage during the rest of the interval. If the predicted value exceeds the preset limit, loads will be shed. Preferred Noise Criterion (PNC) Curves − The PNC curves are a proposed modification of the older NC curves. These PNC curves have values that are about 1 dB lower than the NC curves in the four octave bands at 125, 250, 500, and 1000 Hz for the same curve rating

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


numbers. In the 63 Hz band, the permissible levels are 4 or 5 dB lower; in the highest three bands, they are 4 or 5 db lower. Prefilter − A filter, usually of lower performance grade than the final filter, that precedes the final filter. Preheating − In air conditioning, to heat the air ahead of other processes. Pressure − The normal force exerted by a homoge− neous liquid or gas, per unit of area, on the wall of its container. Pressure, Absolute − Pressure referred to that of a per− fect vacuum. It is the sum of gauge pressure and stan− dard atmospheric pressure. Pressure, Atmospheric − It is the pressure indicated by a barometer. Standard atmosphere is the pressure equivalent to 14.696 psi or 29.921 in. of mercury at 70F (101.325 kPa or 760 mm Hg at 20C). Pressure, Critical − Vapor pressure corresponding to the substance’s critical state at which the liquid and va− por have identical properties. Pressure, Gauge − Pressure above atmospheric. Pressure, Hydrostatic − The normal force per unit area that would be exerted by a moving fluid on an in− finitesimally small body immersed in it if the body were carried along with the fluid. Pressure, Partial − Portion of total gas pressure of a mixture attributable to one component. Pressure, Saturation − The saturation pressure for a pure substance for any given temperature is that pres− sure at which vapor and liquid, or vapor and solid, can coexist in stable equilibrium. Pressure, Static (SP) − The normal force per unit area that would be exerted by a moving fluid on a small body immersed in it if the body were carried along with the fluid. practically, it is the normal force per unit are at a small hole in a wall of the duct through which the fluid flows (piezometer)or on the surface of a sta− tionary tube at a point where the disturbances, created by inserting the tube, cancel. It is supposed that the thermodynamic properties of a moving fluid depend on static pressure in exactly the same manner as those of the same fluid at rest depend upon its uniform hy− drostatic pressure.

Pressure, Total (TP) − In the theory of the flow of fluids, the sum of the static pressure and the velocity pressure at the point of measurement. Also called dy− namic pressure. Pressure, Vapor − Vapor pressure denotes the lowest absolute pressure that a given liquid at a given temper− ature will remain liquid before evaporating into its gaseous form or state. Pressure, Velocity (Vp) − In moving fluid, the pressure capable of causing an equivalent velocity, if applied to move the same fluid through an orifice such that all pressure energy expended is converted into kinetic en− ergy. Pressure Drop − Pressure loss in fluid pressure, as from one end of a duct to the other, due to friction, dy− namic losses, and changes in velocity pressure. Pressure Regulator − Automatic valve between the evaporator outlet and compressor inlet that is respon− sive to pressure or temperature; it functions to throttle the vapor flow when necessary to prevent the evapora− tor pressure from falling below a present level. Primary Air − The initial airstream to an air outlet or terminal device being supplied by a fan or supply duct prior to any entrainment of ambient air. Primary Control − A device which directly or indi− rectly controls the control agent in response to needs indicated by the controller. Typically a motor, valve, relay, etc. Primary Element − The portion of the controller which first uses energy derived from the controlled medium to produce a condition representing the value of the controlled variable; for example, a thermostatic bimetal. Primary Service − High voltage service, above 600 volts. Process Hot Water − Hot water needed for manufac− turing processes over and above the domestic hot wa− ter that is for the personal use of industrial workers. Properties, Thermodynamic − Basic qualities used in defining the condition of a substance, such as tempera− ture, pressure, volume, enthalpy, entropy. Proportional Band − The range of values of a propor− tional positioning controller through which the con− trolled variables must pass to move the final control element through its full operating range. Commonly

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G.23


used equivalents are throttling range and modulating range.

Random Incidence − If an object is in a diffuse sound field, the sound is said to strike the object at random incidence.

Proportional Control − See Modulating Control. Psychrometer − An instrument for ascertaining the humidity or hygrometric state of the atmosphere.

Real Time − Time measured according to the time of day (1 PM, 2 PM, etc.) Different from the ?electronic time" of a cycling device.

Psychrometric Chart − A graphical representation of the thermodynamic properties of moist air.

Receiver − An auxiliary storage receptacle for refrig− erant when the system is pumped down and shut down.

Pull Box − A metal cabinet inserted into a conduit run for the purpose of providing a cable pulling point. Cable may be spliced in these boxes.

Reflected isolation − The portion of the total solar en− ergy reaching a surface (window, wall, collector) which has been reflected by an adjoining surface.

Pulsing Demand Meter − A meter which generates a pulse in correspondence with each revolution of a kWh meter. Pulses are recorded on paper or magnetic tape. pulse can also be the signal to demand control equip− ment.

Reflectivity − The property of a material that deter− mines its ability to reflect radiant energy.

Pure Tone − A pure tone sound that has a unique pitch and is characterized by a sinusoidal variation in sound pressure with time. The frequency spectrum of a pure tone shows a single line at a discrete frequency. Pyranometer − A measurement device to determine local values of total (direct and diffuser) insolation. Pyrometer − An instrument for measuring tempera− tures. Pyrheliometer − An instrument for measuring the ra− diant energy of the sun.

Refrigerant − The fluid used for heat transfer in a re− frigerating system, which absorbs heat at a low tem− perature and a low pressure of the fluid and rejects heat at a higher temperature and a higher pressure of the fluid, usually involving changes of state of the fluid. Regenerated Noise − Duct noise, which is generated by air turbulence in the duct or fittings. Register − A grille equipped with an integral damper or control valve. Relative Humidity (RH) − The ratio of water vapor in the air as compared to the maximum amount of water vapor that may be contained.

Raceway − Any support system, open or closed, for carrying electric wires.

Relay − An electromechanical switch that opens or closes contacts in response to some controlled action. Relay contacts can be normally open (NO) and/or nor− mally closed (NC). Relays may be electric, pneumatic, or a combination of both. PE and EP switches are re− lays.

Radiation, Acoustic − The process of turning structure borne noise into airborne (or some other fluid borne) noise.

Relay, Thermal − A switching relay in which a small heater warms a bimetal element which bends to pro− vide the switching force.

Radiation, Thermal − The transmission of heat through space by wave motion; the passage of heat from one object to another without warming the adja− cent space.

Remote Temperature Set Point − Ability to set a tem− perature control point for a space from outside the space. Often used in public areas.

−R−

Radius of Diffusion − The horizontal axial distance an airstream travels after leaving an air outlet before the maximum stream velocity is reduced to a specified ter− minal level; e.g., 200, 150 or 100 fpm (1.0, 0.75 or 0.5 m/s). G.24

Reset − A process of automatically adjusting the con− trol point of a given controller to compensate for changes in outdoor temperature. The hot deck control point is normally reset upward as the outdoor tempera− ture drops. The cold deck control point is normally re− set downward as the outdoor temperature increases.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


Reset Controllers − Two controllers operating togeth− er; one sensing condition other than that of the con− trolled space and changing the set point of the second controller, which is directly responsible for the result in the controlled space. The resetting controller is commonly called the master, and the controller being reset is commonly called the submaster (slave). Reset Ratio − The ratio of change in outdoor tempera− ture to the change in control point temperature. For ex− ample, a 2 −1 reset ratio means that the control point will increase 1 degree for every 2 degrees change in outdoor temperature. Resistance (W) − The opposition which limits the amount of current that can be produced by an applied voltage in an electrical circuit, measured in ohms. Resistance, Thermal − The reciprocal of thermal con− ductance. Resistive Loads − Electrical loads whose power factor is one. Usually contain heating elements. Resistivity, Thermal − The reciprocal of thermal con− ductivity. Respirable Particles − Respirable particles are those that penetrate into and are deposited in the non−ciliated portion of the lung. Particles greater than 10 microme− ters (microns) aerodynamic diameter are not respir− able. Return Air − Air returned from conditioned or refrig− erated space. Reverberant Sound Field − A space in which sound persists because of continuous reflections. A reverber− ant field is not necessarily diffuse. Reverberation − The persistence of sound in an en− closed space after the sound source has stopped. In a reverberation room, it is characterized by the decay or dying away of the sound. Reverberation Room − A highly sound reflective room in which special care has been taken to make the sound field as diffuse as possible. Reverberation Time − The reverberation time of an enclosed space is the number of seconds required, or that would be required were the decay rate to remain constant, for the sound pressure level to decrease by 60 decibels.

Reverse Flow − Occurs when noise propagates and air flows in opposing direction, as in a typical return air system. Riser Diagram − Electrical block type diagram show− ing connection of major items of equipment. It is also applied to signal equipment connections. Also gener− ally applied to multistory buildings for vertical hy− dronic piping and ductwork. Riser Shaft − A vertical shaft designed to house elec− tric cables, piping and ductwork. Room Absorption − The product of average absorp− tion coefficients inside a room and the total surface area. This is usually expressed in sabins. Room Criterion (RC) Curves − RC curves are similar to NC or PNC curves. However, they have a slightly different shape to approximate a well balanced, bland sounding spectrum whenever the space requirements dictate that a certain amount of background noise be maintained for masking or other purposes. Room Dry Bulb − The actual temperature of the condi− tioned room or space as measured with an accurate thermometer. Room Effect − The difference between the sound pow− er level discharge by a duct (through a diffuser or other termination device) and the sound pressure level heard by an occupant of a room is called the Room Effect. The magnitude of the room effect depends upon the amount of the absorption in the room (Sabins), the dis− tance between the termination duct and the nearest ob− server and the directivity factor of the source. Room Velocity − The residual air velocity level in the occupied zone of the conditioned space, e.g., 65, 50, 35 fpm (0.33, 0.25, 0.17 m/s). Running Current − The current that flows through a load after inrush current. Usually called full load cur− rent. −S− Sabin − The unit of acoustic absorption. One sabin is one square foot of perfect sound absorbing material. Saturation, Degree of − The ratio of the weight of wa− ter vapor associated with a pound (kilogram) of dry air saturated at the same temperature. Season Energy Efficiency Ratio (SEER) − The total quantity of heat delivered or removed by heating or

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

G.25


cooling equipment in Btu divided by the total electri− cal energy input in kilowatt hours over an entire sea− son.

Sequencer − A mechanical or electrical device that may be set to initiate a series of events and to make the vents follow in sequence.

Seasonal Performance Factor − The ratio of the total quantity of heat delivered by a heat pump, (including supplemental resistance heaters) to the total quantity of energy input (including supplementary resistance heaters) for the total annual heating hours below 65F (18C).

Sequencing Control − A control which energizes successive stages of heating or cooling equipment as its sensor detects the need for increased heating or cooling capacity. May be electronic or electromechan− ical.

Secondary Air − The air surrounding an outlet that is captured or entrained by the initial outlet discharge air− stream (furnished by a supply duct or fan). Secondary Service − Voltage service up to 600 volts. Seismic − Subject to or caused by an earthquake. Semi−Extended Plenum − A trunk duct that is ex− tended as a plenum for a fan or HVAC unit to serve multiple outlets and/or branch ducts. Sensible Heat − Sensible heat is any heat transfer that causes a change in temperature. Heating and cooling of air and water that may be measured with a thermom− eter is sensible heat. Heating or cooling coils that sim− ply increase or decrease the air temperature without a chance in moisture content are examples of sensible heat.

Series Circuit − One with all the elements connected end to end. The current is the same throughout but the voltage can be different across each element. Service Drop − The overhead service wires that serve a building. Service Switch − One to six disconnect switches or cir− cuit breakers. Purpose is to completely disconnect the building from the electric service. Set Point − The value of the controlled condition at which the instrument is set to operate. The set point in the example in ?differential" might be 691_w, the mid point of the differential. Shading Loss − The loss of collector efficiency caused by the shading of the absorber plate by collector edges or components. The shading loss usually varies with the angle of incidence of the isolation.

Sensible Heat Factor − The ratio of sensible heat to to− tal heat.

Shall (or Will) − Where shall or will is used as a provi− sion specified, that provision is mandatory if com− pliance with the standard is claimed.

Sensible Heat Ratio, Air Cooler − The ratio of sensi− ble cooling effect to total cooling effect of an air cool− er.

Shed − To deenergize a load in order to maintain a kW demand set point.

Sensing Device − A device that keeps track of the mea− sured condition and its fluctuations so that when suffi− cient variation occurs it will originate the signal to re− vise the operation of the system and offset the change. Example − a thermostat ?bulb". A sensing device may be an integral part of a controller. Sensing Element − The first system element or group of elements. The sensing element performs the initial measurement operation. Sensitivity − The ability of a control instrument to measure and act upon variations of the measured con− dition. Sensor − A sensing element. G.26

Shed Mode − A method of demand control that reduces kW demand through shedding and restoring loads. Shielded Cable − Special cable used with equipment that generates a low voltage output. Used to minimize the effects of frequency ?noise" on the output signal. Short Circuit − An electric circuit with zero load; an electrical fault. Short Cycling − Unit runs and then stops at short inter− vals; generally this excessive cycling rate is hard on the system equipment. Should (or It Is Recommended) − Term used to indi− cate provisions which are not mandatory but which are desirable as good practice.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


Single Particle Counter − An instrument for continu− ous counting of individual airborne particles larger than a given threshold size(s). The sensing means may be optical, electrical, aerodynamic, etc. Single−Phasing − The condition when one phase of a multiphase (polyphase) motor circuit is broken or opened. Motors running when this occurs may contin− ue to run but with lower power output and overheating. Smoke − The airborne solid and liquid particles and gases that evolve when a material undergoes pyrolysis or combustion. Note − chemical smoke is excluded from this definition. Smoke Barrier − A continuous membrane, either ver− tical or horizontal, such as a wall, floor, or ceiling as− sembly, that is designed and constructed to restrict the movement of smoke. Smoke Control System − A system that utilizes fans to produce pressure differences to manage smoke movement. Smoke Damper − A device to resist the passage of smoke which − (a) is arranged to operate automatically, and/or (b) is controlled by a smoke detector, and/or (c) may be capable of being positioned manually from a remote command station. A smoke damper also may be combined with a fire damper or a damper serving other functions, if its loca− tion lends itself to the multiple functions. A combina− tion fire and smoke damper shall meet the require− ments of both. Smoke Detector − A device which senses visible or in− visible particles of combustion. Smoke Developed Rating − A smoke developed rating of a material refers to a number or classification of a material obtained according to NFPA 255, Method of Test of Surface Burning Characteristics of Building Materials, which measures visible smoke. Solar Altitude − The angular elevation of the sun above the horizon. Solar Azimuth − Angle between true south and project of earth sun line on a horizontal plane.

Solar Collector − Any device which collects solar en− ergy and transforms it to another usable form of ener− gy. Solar Energy − The photon energy originating from the sun’s radiation in the wavelength region from 0.3 to 2.4 micrometers; the radiant energy of the sun, whether it be direct, diffuse or reflected radiation. Solar Time − The time of day based on the relative position of the sun with respect to a position on the earth’s surface. Solar noon is that instant on any day at which the sun reaches its maximum altitude for that day. Solenoid Air Valves − EP switches with an electro− magnetic coil in the valve top works that opens or closes the valve from normal position. A spring returns the valve to the normal position when the coil is deen− ergized. Sone − One sone is defined as the loudness of a 1000 Hz tone having a sound pressure of 40 dB. Two sones is twice as loud as the 40 dB reference sound of one sone, etc. Sorbent − See absorbent. Sound Absorption − (1) The process of dissipating or removing sound energy. (2) the property possessed by materials, objects and structures, such as rooms, of ab− sorbing sound energy. (3) The measure of the magni− tude of the absorptive property of a material, an object, or a structure, such as a room. Sound Attenuator − A device or equipment that pre− vents, reduces, or absorbs sound. Sound Power Level (Lw) − The fundamental charac− teristic of an acoustic source (fan, etc.) is its ability to radiate power. Sound power level cannot be measured directly; it must be calculated from sound pressure lev− el measurements. The sound power level of a source (Lw) is the ratio, expressed in decibels, of its sound. A considerable amount of confusion exists in the rela− tive use of sound power level and sound pressure level. An analogy may be made in that the measurement of sound pressure level is comparable to the measure− ment of temperature in a room; whereas, the sound power level is comparable to the cooling capacity of the equipment conditioning the room. The resulting temperature is a function of the cooling capacity of the equipment and the heat gains and losses of the room. In exactly the same way, the resulting sound pressure level would be a function of the sound power output of

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition

G.27


the equipment together with the sound reflective and sound absorptive properties of the room.

Fahrenheit (Celsius). The following are specific heat values at standard conditions −

Given the total sound power output of sound source and knowing the acoustical properties and dimensions of a room, it is possible to calculate the resulting sound pressure levels.

waterCC p = 1.0 Btu/lbF (4190 J/kgC)

Sound Power Level of a Source (Lw) − The ratio, ex− pressed in decibels, of its sound power to the reference sound power which by divided agreement, is either 10−13 or 10−12 watts. The reference power should al− ways be stated. Sound Power of a Source (W) − The rate at which sound energy is radiated by the source. Without quali− fication, overall sound power is meant but often sound power in a specific frequency band is indicated. Sound Pressure − Sound pressure is an alternating pressure superimposed on the barometric pressure by sound. It can be measured or expressed in several ways such as maximum sound pressure or instantaneous sound pressure. Unless such a qualifying word is used, it is the effective of root−mean−square pressure which is meant. Sound Pressure Level (Lp) − A measure of the air pressure change caused by a sound wave expressed on a decibel scale reference to a reference sound pressure of 2 x 10−5 Pa or 0.0002 microbar. Sound Transmission Class − Sound transmission class is the preferred single figure rating designed to give a preliminary estimate of the sound insulating properties of a barrier. Sound Transmission Coefficient − The sound trans− mission coefficient of a partition is the fraction of the incident sound power transmitted through it when the sound fields on both sides of the partition are diffuse. Sound Transmission Loss of a Partition (TL) − The ratio, expressed in decibels, of the incident sound pow− er on the source side of the specimen of the transmitted sound power on the receiving side when the sound fields on both sides of the specimen are diffuse. When the sound fields are not diffuse, a qualifying word is necessary, such as normal incidence sound transmission loss, or field transmission loss. Specific Heat − Specific heat (Cp) is the amount of heat energy in Btu’s (joules) required to raise the tempera− ture of one pound (kilogram) of substance one degree G.28

airCC p = 0.24 Btu/lbF (1000 J/kgC) Specification Design − A concise document defining technical requirements in sufficient detail to form the basis for a product or process. It indicates, when ap− propriate, the procedure that determines whether or not the given requirements are satisfied. Specification Performance − A concise document which details the performance requirement for a prod− uct. The performance specification includes proce− dures and/or references for testing and certification of the product. Specific Volume − The reciprocal of density and is used to determine the cubic feet (m3) of volume, if the pounds (kg) of weight are known. Both density and specific volume are affected by temperature and pres− sure. The specific volume of air under standard condi− tions is 13.33 cubic feet per pound (0.8305 m3/kg) and the specific volume of water at standard conditions is 0.016 cubic feet per pound (0.001 m3/kg). Spread − The divergence of the airstream in a horizon− tal or vertical plane after it leaves the outlet. Stage Differential − Change in temperature at the ther− mostat needed to turn heating or cooling equipment off once it is turned on. Staging Interval − The minimum time period for shed− ding or restoring two sequential loads. Stagnant Air Area − An area within a space where the air velocity is less than 25 fpm (0.12 m/s). Standard Air Density (d) − Standard air density has been set at 0.075 lb/cu. ft. In metric units, the standard air density is 1.2041 kg/m3. Standard Conditions − The standard conditions for air are at 70F, and at an atmospheric pressure of 29.92 inches mercury or 14.696 psi. For water, standard con− ditions are 68F at the same barometric conditions. In metric units, standard conditions for air are at 20C, and at an air atmospheric pressure of 760 mm Hg or 101.325 kPa. Standard Rating − A rating based on tests performed at Standard Rating Conditions.

HVAC SYSTEMS Testing, Adjusting & Balancing • Third Edition


Starter − Basic contractor with motor overloads, etc., addedCa motor starter is an adaptation of the basic contractor which includes overload relays. Starters for large motors may include reactors, step resistors, dis− connects, or other features required in a more sophisti− cated starter package. State − Refers to the form of a fluid, either liquid, gas or solid. Liquids used in environmental systems are water, thermal fluids such as ethylene glycol solutions, and refrigerants in the liquid state. Gases are steam, evaporated refrigerants and the air−water vapor mix− ture found in the atmosphere. some substances, includ− ing commonly used refrigerants, may exist in any of the three states. A simple example is water, which may be solid (ice), liquid (water), or gas (steam or water va− por). Static Head − The pressure due to the weight of a fluid above the point of measurement. Static Regain Method − A method of duct sizing wherein the duct velocities are systematically re− duced, allowing a portion of the velocity pressure to convert to static pressure off setting the duct friction losses. Static Suction Head − The positive vertical height in feet (meters) from the pump centerline to the top of the level of the liquid source. Static Suction Lift − The distance in feet (meters) be− tween the pump centerline and the source of liquid be− low the pump centerline. Step Controller − See Sequencer. Stratified Air − Unmixed air that is in thermal layers that have temperature variations of approximately five degrees or more. Structure−Borne Noise − A condition when the sound waves are being carried by a portion of the building structure. Sound waves in this state are inaudible to the human ear since they cannot carry energy to it. Air− borne sound can be created from the radiation of the structure−borne sound into the air. Subcooling − The difference between the temperature of a pure condensable fluid below saturation and the temperature at the liquid saturated state, the same pres− sure. Subcooling Specific − The difference between specif− ic enthalpies of a pure condensable fluid between liq−

uid at a given temperature below saturation and liquid at saturation, at the same pressure. Sublimation − A change of state directly from solid to gas without appearance of liquid. Suction Head − The positive pressure on the pump in− let when the source of liquid supply is above the pump centerline. Suction Lift − The combination of static suction lift and friction head in the suction piping when the source of liquid is below the pump centerline. Suction Piping − The piping which returns gaseous re− frigerant to the compressor. Sizes must be large enough t