VISION ISSUE TEN | WINTER 2020
Designing a Safe Electrical System What Is a Short Circuit and What Causes an Arc Flash? Two forms of electrical circuit protection devices are commonly used in electrical systems: the fuse and the circuit breaker. Both fuses and circuit breakers are manufactured to accommodate up to a predetermined electrical current, 20A for example, without opening the circuit. Once electrical current rises above 20A, both devices will open the circuit ceasing the flow of electricity. The scenario described above is of an overload situation; however, the same occurs during a short circuit. A short circuit is the unintentional flow of electricity through a low impedance path. An example of such an event is a phase leg making unintentional contact with a neutral, ground, or other phase leg conductor. Because the impedance on a short circuit is so low, the current is typically hundreds of times higher, or more, than what a circuit breaker experiences during an overload condition. Both the electrical equipment and the circuit breakers or fuses must be rated to withstand short circuit current and to open upon a fault. If a short circuit is allowed to continue without intervention from a circuit breaker or fuse, the energy produced can be large enough to conduct through the air to ground, resulting in a dangerous arc flash explosion. Key Design Considerations The main goal in designing an electrical system to clear short circuit faults is to keep the electrical system safe and avoid dangerous conditions. Improperly sized equipment and devices can lead to costly repairs, or worse, fatalities. Images 1 and 2 illustrate the possible effects of a short circuit condition between two phase legs of a switchboard; the resulting current was enough to melt the metal enclosure.
Further, had someone been nearby when the short circuit occurred, the resulting arc flash could have seriously wounded the person. Image 2
By coordinating with the electrical utility company in the design phase of projects, the maximum available fault (short circuit) current from the utility company’s transformer can be determined. This is the largest current that any electrical equipment will see after the transformer. The farther the equipment is away from the transformer, the lower the fault current typically will be; however, it is important to note that any motor will contribute to the fault current, provided it is not controlled by a Variable Frequency Drive (VFD) or similar device. ALL TEXT ©2020 KOHLER RONAN, LLC
From the maximum available fault current, motor sizes, conductor sizes, and conductor lengths, the short circuit current at all the equipment in the electrical distribution system can be calculated. Informed decisions can be made on what the Short Circuit Current Rating (SCCR) of the equipment should be to safely withstand a short circuit condition, and also what the Ampere Interrupting Capacity (AIC) of the fuses or circuit breakers should be in order to clear a fault. Similarly, the required Personal Protective Equipment (PPE) can be determined and a label affixed to the electrical equipment. Necessary Device Coordination Once circuit breakers or fuse ratings are selected, calculations should be performed to know which device will clear a fault first in an electrical system. The goal is for the device nearest a fault to clear before the devices upstream, in order to limit the amount of electrical circuits that are opened as a result of the fault. Often, this is accomplished through the use of electronically adjustable circuit breakers that allow for the intentional delay in opening circuit breakers, so the one farthest downstream can open first. What Role Does Existing Electrical Systems Play? When a project is intended to reuse existing electrical equipment, it is important for the design engineer to consider whether or not continued on page 3
IN THIS ISSUE Fire Pump Basics
Benefits of Commisioning Revit® Corner
What’s Wrong With This Picture? Project Highlight
Do You Know Your Fire Pump Basics? Fire pumps within fire protection systems may be required because of the simple adage “supply and demand.” A building’s fire protection water demand is created by two common systems: fire sprinklers and/or fire standpipes. Whether a building has either one, or both, of these systems is dictated by applicable building and fire codes. In any case, both of these fire protection systems create a waterflow demand which includes both pressure (psi) and gallons per minute (gpm) demand. Fire Sprinkler and Standpipe Demand Fire sprinkler demand is outlined in NFPA 13. The gpm demand for fire sprinklers is based on the type of system installed (wet, dry, etc.); the occupancy, which determines the density over a certain square footage; plus any outside hose demand allowing for fire department use. The pound per square inch (psi) demand for a fire sprinkler system can be determined by assessing: 1. The required minimum pressure at the most remote sprinkler head (usually 7 psi) 2. Any friction loss through the piping (fittings, backflow preventer, etc.) 3. The elevation at the most remote sprinklers An approximate sprinkler demand within a 5-story office building could be in the area of 50 psi at 400 gpm. Fire standpipe demand, similar to fire sprinkler demand, is dictated by NFPA 14. The gpm demand for fire standpipes requires 250 gpm at the most remote outlet, 250 gpm at the next remote outlet, and so on, up to a maximum of 1,000 gpm for fully sprinklered buildings. The pressure demand for fire standpipes includes providing 100 psi in CT and 65 psi in NYC at the most remote outlet, assessing friction loss through the piping (fittings, backflow preventer, etc.), and accounting for the elevation at the outlet. An approximate standpipe demand within a 5-story building with three rated stairwells could be in the area of 150 psi at 1000 gpm. Available Water Supply The “supply” part of the old adage simply refers to the available water which could be provided by an existing underground
water main within the street, or, a gravity or pressure tank which could be located on the roof. If, of course, the project were in a rural area and lacking an existing, available water supply, both a tank and a pump would be required. The more common scenario, however, is the underground street water main in an urban area. A waterflow test needs to be conducted to document the psi and gpm available. The waterflow test yields a static psi, a residual psi, and an overall gpm. A typical waterflow test within urban areas could be 50 psi static and 49 psi residual at 500 gpm. These results when compared to the above demand (sprinkler or standpipe) will determine whether or not a fire pump and/or tank is required. Of course a safety margin should be included. Architectural Concerns Given the scenario above, a room large enough to accommodate a diesel or electric driven fire pump, along with all associated equipment (fire pump controller, jockey pump controller, backflow preventer, riser check valve, and/or dry pipe valve assemblies) would be required. A typical fire pump room would measure approximately 15 feet by 10 feet. If an electric driven fire pump assembly were utilized, then a back-up generator would also be required. The fire pump room requires a 1-hour fire rating. Depending on the edition of NFPA 20 adopted by the local building code, it may not be permitted for the fire pump
to house other mechanical equipment. Fire sprinklers, standpipes, and fire pumps are critical life safety systems that protect occupants. Governed by codes and industry standards, these fire protection systems are solely designed to protect life and property. Statistically, their inclusion in buildings has shown overwhelmingly positive results. Owners, architects, and engineers should consider installing these systems (in accordance with NFPA) regardless of being required by code. More importantly, continued maintenance of existing fire protection systems is critical to their operation, as is employing a reputable contractor to perform the required inspections (as outlined in NFPA 25) to ensure that systems function properly should an unfortunate incident occur. Electric Fire Pump Assembly
Diesel Fire Pump Assembly
AIA Registered Provider Kohler Ronan is a registered provider of AIA Continuing Education Credits. Our professionals have prepared several presentations on relevant and timely industry topics. We would be pleased to visit your offices and share these presentations. To learn more, or to schedule a visit, please contact Joe Lembo at 203.778.1017 or via email at firstname.lastname@example.org.
NYSERDA Approved Provider Kohler Ronan is an approved Technical Consultant for the New York State Energy Research & Development Authority’s (NYSERDA) Commercial New Construction Program. Under this program, we will provide technical support in the form of energy modeling and controls commissioning to assess and determine appropriate energy efficiency opportunities for New Construction and Substantial Renovation Projects. For details, please email Madhav Munshi at email@example.com.
“Safe Electical Systems” continued from page 1
the fault current at the existing equipment is being affected by the design of other trades. If not considered, the equipment may no longer be properly sized for a short circuit condition, resulting in a violation of the National Electric Code (NEC). An example scenario is the addition of HVAC units to an existing mechanical system. Calculations must be performed to see if the new units will contribute to a fault condition, which potentially could turn a simple project with limited electrical scope into a much larger project requiring the replacement of electrical equipment or devices.
Benefits of Commissioning Commissioning is defined by the American Society of Heating, Refrigerating and AirConditioning Engineers (ASHRAE) as “a quality-oriented process for achieving, verifying, and documenting that the performance of facilities, systems and assemblies meets defined objectives and criteria.” It’s a systematic process of verifying and documenting that a facility and all its systems and assemblies are planned, designed, installed, tested, operated, and maintained to meet the OPR (Owner’s Project Requirements), a document defining performance expectations for the building’s systems and equipment. Systems
that are typically commissioned include, but are not limited to, the following: • Mechanical (including HVAC&R equipment and controls) • Plumbing (domestic hot water systems, pumps, and controls) • Electrical (including service, distribution, lighting, and controls) • Renewable energy systems Ideally, commissioning begins in early design with development of the OPR. After OPR development, design documents are reviewed for consistency with the OPR, while commissioning specifications are written for inclusion in the construction documents. Specific benefits of design phase commissioning include reducing the likelihood of change orders and/or schedule delays during the construction process. During the construction phase, submittals are reviewed and pre-functional checklists are developed for the systems and equipment being commissioned. Functional performance test procedures are written based on equipment sequences of operation and systems performance requirements as established in the OPR. Any deficiencies identified during functional performance testing are tracked in the project’s Issues Log to ensure that problems are resolved, and systems are fully functional prior to the owner’s acceptance. Construction phase commissioning may also include
additional tasks to facilitate building turnover such as development of operations and maintenance manuals, and coordination of systems demonstrations and training programs for the owner’s operations staff. Recent energy codes, such as the IECC and NYCECC, have made commissioning mandatory for buildings with over 40 tons of cooling. Green Building Rating systems such as LEED, WELL, Passive House, and Living Building Challenge also have minimum and enhanced commissioning requirements for building projects. These requirements make sense considering that research from the Department of Energy shows that commissioning is the most effective energy conservation approach for new, existing, and redeveloped buildings. The commissioning process can provide a range of benefits for building owners and facility managers. It verifies that systems are installed and functioning properly prior to owner acceptance, thus leading to higher occupant satisfaction and lower operating costs. On nearly every type of project, a successful commissioning program contributes to the performance and lifespan of a building; it helps to guarantee that all standards are achieved. Simply put, commissioning is designed to improve the energy efficiency of building systems and improve the operation and maintenance of the facility throughout its lifetime.
REVIT® CORNER REVIT COLLABORATION BIM 360 Design connects integrated project teams, allowing them to collaborate on shared Revit models. Autodesk BIM 360 is a cloud-based BIM management and collaboration solution that connects the entire project team and helps streamline BIM project review and coordination workflows. The software allows for a more complete design team collaboration effort in building engineering. BIM 360 facilitates planning, design, coordination, fabrication, installation, commissioning, and maintenance of today’s complex design projects.
Co-auther cloud-shared Revit models in the BIM 360 platform
STRUCTURAL ENGINEER BIM MANAGER
View, share, and review 2D and 3D design files in the cloud
MANAGER + ASSISTANT MECHANICAL ENGINEER CONSULTANTS
What’s Wrong With This Picture? A dual drinking fountain has one standard and one handicapwheelchair capable unit. The dual drinking fountain unit shown (Image A) has been installed backwards, with the handicap fountain installed in the higher position. Today, a bottle fill station is also typically installed to save plastic; the installation below is correct (Image B). Both the bottle fill and drinking stations are at the proper code compliant heights, allowing wheelchair clearance.
Project Highlight — David Geffen Hall at Lincoln Center Designed by Max Abromovitz in 1962, Lincoln Center’s David Geffen Hall, home to the New York Philharmonic, is slated for a transformative renovation. The goal of the renovation is to address several acoustical issues which have long plagued the space, as well as to create a more intimate experience between the audience members and the performers. Kohler Ronan is delighted to be collaborating on this cultural landmark with Tod Williams Billie Tsien Architects, Diamond Schmitt Architects, and acoustics and theater design consultants Akustiks and Fisher Dachs Associates. For our part, Kohler Ronan will look to enhance the space with a completely redesigned MEP infrastructure and system distribution, allowing for increased flexibility and versatility. The phased construction of this venue will conclude in 2024.
Rendering Courtesy of Diamond Schmitt Architects
About the Firm From our offices in Danbury, Connecticut and New York, New York, our team of approximately 70 professionals collaborates with prominent architectural firms on a wide array of regional and nationally recognized project assignments. Commissions include those for world-renowned museums, fine and performing arts centers, prestigious universities, state-of-the-art educational and healthcare facilities, luxury residences, and premier recreation establishments. Additionally, we have the privilege of designing specialty systems for landmark sites and historically significant buildings across the country. For more information, please visit our website at kohlerronan.com or connect with us on social media.
New York 171 Madison Avenue, New York, NY 10016 T 212.695.2422 Danbury 93 Lake Avenue, Danbury, CT 06810 T 203.778.1017 Connect kohlerronan.com firstname.lastname@example.org