Research Journal: Vol. 02.01

research journal

2010 / VOL 02.01

RESEARCH JOURNAL 2010 / VOL 02.01

Editors:

Ajla Aksamija, Ph.D., LEED® AP BD+C, CDT and Kalpana Kuttaiah, Associate AIA, LEED® AP BD+C

Journal Design & Layout:

Kalpana Kuttaiah, Associate AIA, LEED® AP BD+C

Cover Design:

Mimi Day, AIGA

Acknowledgements:

With much APPRECIATION to everyone who contributed in many ways to the research work and articles published in this journal.

We would like to extend our VERY SPECIAL THANKS to: Emily Gartland.

Perkins and Will is an interdisciplinary design practice offering services in the areas of Architecture, Interior Design, Branded Environments, Planning + Strategies and Urban Design.

Copyright 2010 Perkins and Will All rights reserved.

2010 / VOL 02.01

RESEARCH JOURNAL / VOL 02.01

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TABLE OF CONTENTS

JOURNAL OVERVIEW

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EDITORIAL

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01. CELL WALL: Resolving Geometrical Complexities in the Shanghai Nature Museum Iconic Wall Marius Ronnett, AIA, LEED® AP BD+C Abul Abdulla, Associate AIA, LEED® AP BD+C ..................................................................... Page 7 02. THE EFFECT OF HEAT FLOW AND MOISTURE ON THE EXTERIOR ENCLOSURE: Working with Standards and Modeling Software to Make More Intelligent Exterior Enclosure Decisions Charles Sejud, AIA, LEED® AP BD+C Jean-Claude Lesaca, LEED® AP BD+C ..................................................................... Page 22 03. HYGROSCOPIC CLIMATIC MODULATED BOUNDARIES: A Strategy for Differentiated Performance Using a Natural Circulative and Energy Captive Building Envelope in Hot and Moisture Rich Laden Air Environments Marionyt Tyrone Marshall, Associate AIA, NOMA, ACADIA, LEED® AP BD+C ........................ Page 41 04. COMPARATIVE ANALYSIS OF FLOORING MATERIALS: Environmental and Economic Performance Ajla Aksamija, Ph.D., LEED® AP BD+C, CDT ..................................................................... Page 55 05. URBAN WASTEWATER: A Renewable, Reliable Water Resource for Urban Farming Geeti Silwal, AICP, LEED® AP .................................................................... Page 67

PEER REVIEWERS

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AUTHORS

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JOURNAL OVERVIEW The Perkins and Will Research Journal is a peer-reviewed research journal, dedicated to documenting and presenting practice-related research associated with buildings and their environs. The aim of this journal is to capture and document research questions and methodologies that arise prior, during and after the design process. Original research articles and case studies have been incorporated into this publication. The unique aspect of this journal is that it conveys practice-oriented research projects aimed at supporting our design teams.

This is the third issue of the Perkins and Will Research Journal. We welcome contributions for future issues.

RESEARCH AT PERKINS AND WILL Research is systematic investigation into existing knowledge in order to discover or revise facts or add to knowledge about a certain topic. In architectural design, we take an existing condition and improve upon it with our design solutions. During the design process we constantly gather and evaluate information from different sources and apply it in novel ways to solve our design problems, thus creating new information and knowledge.

An important part of the research process is documentation and communication. We are sharing combined efforts and findings of Perkins and Will researchers within this journal.

Perkins and Will engages in the following areas of research: • Market-sector related research • Biomimicry and restoration of ecological systems • Sustainable design • Strategies for operational efficiency • Advanced building technology and performance • Design process benchmarking • Policy research • Carbon and energy analysis • Organizational behavior

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EDITORIAL The Perkins and Will Research Journal documents research relating to architectural and design practice. Architectural design requires immense amounts of information for inspiration, creation, and construction of buildings. Considerations for sustainability, innovation and high-performance designs lead the way of our practice, where research is an integral part of the process. The themes included in this issue illustrate types of projects and inquiries undertaken at Perkins and Will and capture research questions, methodologies and results of these inquiries.

This issue of Perkins and Will Research Journal contains five articles that focus on diverse topics including: design of complex curtain wall geometry; effects of heat flow and moisture analysis for exterior enclosures; comparative environmental and economic analysis of flooring materials; characteristics and potential functioning of hygroscopic building envelope; and utilization of wastewater for urban farming.

“Cell Wall: Resolving Geometrical Complexities in the Shanghai Nature Museum Iconic Wall” documents the research process for the design of a curtain wall with a complex, organic geometry. The article discusses problems and issues associated with transformation of organic geometry for the building envelope into a physical, fully-functional system that is able to withstand structural loads and environmental conditions.

“The Effect of Heat Flow and Moisture on the Exterior Enclosure: Working with Standards and Modeling Software on the Exterior Enclosure” article describes heat flow and moisture transfer through a building’s exterior wall assemblies. Methods and criteria that can assist analysis and the design process are discussed, such as guidelines established by the ASHRAE Standard 160. Also, analysis tool for simulation of transient hygrothermal behavior is discussed as well as utilization of this tool in simulating performance of three different wall assemblies in a cold climate.

“Hygroscopic Climatic Modulated Boundaries: A Strategy for Differentiated Performance Using a Natural Circulative and Energy Captive Building Envelope in Hot and Moisture Rich Laden Air Environments” discusses potential characteristics of a passive-active building envelope system in hot and humid climates. The article discusses theoretical functioning of a system that extracts water from vapor and uses hygroscopic solution for dehumidification.

“Comparative Analysis of Flooring Materials: Environmental and Economic Performance” is an article that analyzes life cycle assessment for a selected group of flooring materials; linoleum, vinyl composition tile (VCT), nylon carpet tile, composite marble tile, ceramic tile, terrazzo, cork and rubber, where they are compared and examined for both environmental and economic factors.

“Urban Wastewater: A Renewable, Reliable Water Resource for Urban Farming” investigates developments of a closed-loop system that localizes wastewater treatment for food production within urban settings. The article presents case studies and inferences made from literature reviews on the topic.

Ajla Aksamija, PhD, LEED® AP BD+C, CDT Kalpana Kuttaiah, Associate AIA, LEED® AP BD+C

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Cell Wall: Resolving Geometrical Complexities

01.

CELL WALL: Resolving Geometrical Complexities in the Shanghai Nature Museum Iconic Wall

Marius Ronnett, AIA, LEED® AP BD+C, marius.ronnett@perkinswill.com Abul Abdullah, Associate AIA, LEED® AP BD+C, abul.abdullah@perkinswill.com

ABSTRACT The “Cell Wall” is the iconic feature of the Shanghai Nature Museum and the main design feature from the initial competition phase. It is comprised of three layers, each with its own unique geometrical pattern and organic form, organized in an elliptical cone shape envelope of the atrium. At the core is the main layer, the structural cell layer, which emphasizes the organic cells as structural building blocks of nature. It is part of the building structure and carries the weight of the museum roof as well as supporting the 33.5 meter (109 feet) vertical span of the curtain-wall. An inner layer, which is the waterproof envelope of the building, is formed by the glass and aluminum mullion curtain-wall. The outer layer is a solar screen that emulates the cellular building block of all life forms and the traditional Chinese window screens.

The intent of this article is to document the original research done for this particular project in resolving complex organic geometries set to a full scale building. While there is a wealth of theoretical research on the subject of mesh structures, there are very few built examples where these mesh geometries fully function as structural building elements and are built to architectural scale. To that extent, a historical approach to problem-solving was of little use and an innovative, original approach was sought.

This article discusses the unique design of the “Cell Wall” system in terms of its complex geometry, design process and construction details. It explores geometric solutions for the wall, researched by trial and error, in terms of achieving the seemingly random organic patterns of the wall within the constraints of readily-available rectilinear building materials, structural realities in designing to full architectural scale and limitations of fabrication methods. It tracks its development from concept design to construction drawings through all different options and their variations to the ultimate modular solution.

KEYWORDS: random organic patterns, tessellated patterns, polygonal mesh structures, solar sun-screens, triangular mesh window systems, voronoi shell structures

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1.0 INTRODUCTION

Due to advances in construction technologies and direct interface with 3D computer modeling, architectural projects have, in the past decade, achieved a complexity that was not before economically feasible. The new Shanghai Nature Museum is such an example. The project, a 44,500 square meter (479,000 square feet) new facility, was won through an international competition by Perkins and Will. As the main museum identity, a dramatic central atrium was incorporated as an organizing feature of the museum and clad in an iconic skin that resonates directly to the function of the building, an organic cell membrane symbolizing the basis of all biological life forms. It is a naturally random cell wall assembly that functions as a solar sun screen, the main building structural element and waterproof building enclosure.

The atrium enclosure, an assembly of three different distinct layers, became an exercise in geometric problem solving to address the technical requirements as well as maintaining the visual aesthetics of the winning competition design. Crucial to the project was maintaining the random organic expression of the cell based enclosure. Developing a geometric system that looked “randomly organic” while fully functioning as a building structure and envelope quickly became a main challenge for the design and technical project team.

To model the complex form and modules of the atrium, various BIM software programs were explored. The team ultimately used “Rhinoceros” for active modeling and prototyping. 3DMax was then used for image renderings of the cell wall elements as well as graphical presentation for part of the overall building model.

It is important to realize that mesh design process and construction process balances many opposing factors: geometrical form generation, functionality, structural constraints, material selection, fabrication limitations and ultimately, economical feasibility. As architects, geometry generation alone is not the endgame, only the final built architecture is.

This article documents the process and research required to resolve a very complex geometric cell wall design while maintaining the organic nature of the iconic atrium envelope within the constraints of a real project with realistic technological requirements and fabrication constraints.

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2.0 GENERAL MESH GEOMETRY CONCEPTS

From the onset, the approach to the geometrical solution for our nature museum was to generate a purely original design and innovative results expressing the unique nature of the project. Thus, historical research in mesh structures was not important to our process.

While there has been an overwhelming amount of theoretical research done on the subject of mesh structures including numerous built examples of mesh geometries as applied to skins and decorative surfaces, actual built examples of truly structural geometric mesh systems built on an architectural scale are relatively rare.

Historically, mesh designs tend to fall into a couple of broad categories including: triangle meshes, quadrilateral meshes and Voronoi diagrams.

The current architectural trend in free form design shapes is a direct result of advances in computer-based BIM integration between designers, engineers and fabricators, which has produced a wealth of built shapes based on discreet surfaces. The most direct, structurally stable and economical means to resolve these curved planar surfaces are through the use of triangle meshes.

The complexities of triangulation are, however, evident in the joint conditions where six separate arms are connecting to the same node. These triangular mesh types have been thoroughly investigated in numerous publications1. An iconic built example of this would be the Milan Expo building designed by M. Fuksas2.

An alternative way to resolve curved planar surfaces is through quadrilateral meshes, also referred to as planar quad mesh or PQ mesh for short3. Quadrilateral meshes are considered the simplest way to calculate meshes and are how computers calculate curved objects by faceting curved shapes displaying them as raster images. These quad meshes can be lighter in weight and easier to resolve in glass and steel fabrication as only four arms join at any given node. Quad meshes can also be used to resolve 3D offset surfaces, which result in conical meshes4.

A more organic looking mesh type is the Voronoi diagram5. This type of cell structure is common throughout nature and ties extensively into biomimicry concepts.

The major disadvantage in architectural applications is the infinite resulting cell forms and connecting node conditions. Voronoi diagrams can easily translate into 3D mesh structures very much like a cluster of soap bubbles. The most iconic built example of the Voronoi diagram as used in architecture is the Beijing Olympic

Cell Wall: Resolving Geometrical Complexities

Swimming Center, also referred to as the Water Cube, designed by PTW Architects.

Mitigating organic patterns with a more structured mathematical layout can also be achieved through regular pattern tessellation. These types of 2D decorative patterns can be found in Islamic wall tiles, in pavement pattern stamping formwork and the iconic decorative patterns developed by the artist M.C. Escher. While often simple and intuitive plays on geometry, they follow mathematical formulas5.

The atrium cell wall design for the Shanghai Nature Museum incorporates variations of the above methods to resolve the structural support as well as the curtain wall enclosure and solar-screen.

3.0 THE ATRIUM

The Shanghai Nature Museum uses a central atrium concept to vertically and horizontally organize the various museum spaces around it and form the nucleus and central identity of the museum. The 5-story atrium, traversing the full height of the museum, is enclosed by a curved exterior envelope system that is 33.5 meters (109 feet) high with a 164.45 meter (540 feet) linear perimeter and a surface area of 2,944 square meters (31,690 square feet). The conical-oval form of the envelope results in an angled tilt-back of the atrium envelope varying from a 9.84-degree incline to a zerodegree straight perpendicular layout at the outer edges.

Figure 1: Shanghai Nature Museum massing.

Figure 2: The atrium enclosure, section-elevation.

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As part of the winning competition, this atrium exterior envelope was expressed as an organic cell form, a direct identity to the function of the museum as well as a nod to historical Chinese window screens. The organic cells as the building blocks of all life forms being represented in the structure of the atrium wall, captured the imagination of the client and general public and became a direct cue to the major exhibits within the museum. Screens composed of abstractions of natural patterns are also abundant in traditional Chinese houses, especially garden pavilions and walls.

The atrium enclosure is composed of three separate and distinct layers: structure, curtain wall and sun screen.

At center, is the atrium structure flanked by an inner glass curtain wall layer and an outer solar screen layer.

Geometrically, these three layers form offset surfaces with a constant face-to-face distance from the controlling mesh. Structurally interconnected at the nodes, the resulting mesh geometry formed a 3D conical mesh rather than 2D planar net structures.

3.1 Structural Layer

The main feature of the atrium is the structural cell wall that spans the full 33.5 meter (109 feet) height of the atrium in an unsupported clear span. It supports the roof of the building and the full weight and lateral wind load on the envelope. The curved shape of the atrium, including the conical tilt-back condition, was fully exploited for its innate geometrical stability as a structural membrane. Preliminary structural engineering analysis confirmed the feasibility and stability of the polygonalshaped cell membrane as a self-supporting and loadbearing structural entity.

Geometrical Pattern In the beginning, various computer generated parametric design solutions were explored using hexagonal cell geometries. These resulted in solutions that generated noticeable repetitions and undesired striations in the cell pattern. Pure randomized computer generated pattern offsets produce infinite variations of cell sizes and shapes that were not practical in our application and not conducive to large scale manufacturing as required for our project. This computerized form generation approach had to be abandoned and a purely manual pattern generated solution was studied.

Figure 3: a) Competition atrium cell wall; b) Living organism tissue; c) Traditional Chinese screens.

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To achieve the desired, seemingly random and organic pattern in a conical-curved layout, a mix of hexagonal and polygonal shapes were studied. A limit of eight cell form variations was set to control the overall complexity

Cell Wall: Resolving Geometrical Complexities

Figure 4: The atrium geometry. a) Conical ellipse overall layout; b) Cell-module layering; c) Cell-module within atrium geometry.

of the construction and allow for unitizing the steel fabrication in a shop. This number of cell variations was fully vetted with the client and their construction advisors as a maximum degree of difficulty for local constructability. The maximum size of the polygonal cells themselves was set originally as 3.6 meters by 2.5 meters (11.8 feet by 8.2 feet), based on the largest size of low-e coated insulated glass available as standard production in China.

To generate an adequate level of randomness in the resulting pattern, a repetitive geometric stencil-form approach was used. This is typical of stenciled shapes in precast-preformed paving systems, which are used to generate a visually varying and apparently non-repeating random pattern. Basically a single, complex shape that is tessellated repeatedly so that the resulting patterns merge together into a seemingly random geomet-

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rical field. Such tessellation concepts were frequently exploited by M. C. Escher in his iconic art patterns as well as traditional Islamic decorative wall tiles.

Numerous cell form variations were studied, by intuitive trial and error, to arrive at a visually pleasing pattern that could be tessellated without forming a recognizable overall pattern. Since simple repetitions would always result in unintended and distracting diagonal striations, every other alternate row of the cell-module was reversed by rotating the stencil module 180 degrees. This resulted in a technically feasible limited number of construction variations, but in the random organic pattern required by the project.

Structural Solution Being a full structural support element for the building and taking full axial building load, lateral wind forces, and earthquake, the structural engineers had to be fully engaged in what we were doing architecturally.

While, as architects, we tend to see the cell wall as polygonal geometrical shapes and surfaces, structural engineers viewed this as a series of vectors connecting into asymmetrical nodes. Computer analysis was critical to model the entire mesh form as a structural membrane. The node connections became a critical structural constraint for the engineers, more so since the asymmetrical geometry generated asymmetrical structural forces of tension and compression within the same node. The inclusion of gusset plates and stiffeners at the nodes was reviewed and eliminated early on as aesthetically not desirable. The structural solution was to weld the intersecting steel tubes into a solid node to resolve the complicated structural forces flowing through them. The size of the cell shapes was not very consequential to the engineers, but the structural organization of the nodes was critical for transferring structural forces and as a fabrication feasibility. Limiting the structural grid to pentagon and hexagon polygonal shapes guaranteed that the intersecting nodes would be limited to three to four intersecting members.

Incorporating triangular cells would have increased the number of connection to the nodes, complicating steel fabrication.

Figure 5: Cell geometry. a) Computer generated parametrics; b) Random pattern; c) Manual tessellation solution.

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Once the main cell geometry was resolved, it was mocked up in the full curved layout of the atrium’s conical geometry and analyzed visually for overall effect.

While all the individual legs of the cells are straight, the curvature of the wall is achieved by the angular variations in the connecting joints. The cell structure 3D line drawing was then shared with the structural engineers in China for full analysis and engineering. A rectangu-

Cell Wall: Resolving Geometrical Complexities

Figure 6: Geometric tessellation concept of the basic cell-module.

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lar tube steel structural cross-section, 500 millimeters by 275 millimeters (19.6 inches by 10.8 inches), was chosen for buildability and structural efficiency in taking lateral wind loads over the full vertical span of the atrium. This slim visual profile also afforded less obstructed views from the atrium to the main outdoor courtyard as well as from the outside looking in.

cept” was envisioned as a basic approach to steel assembly, where basic steel cell units could be pre-constructed in the factory and shipped to the job site and assembled into individual long “planks” spanning the full height of the atrium. These planks could then be tilted up in place and connecting steel members could then be used as a “zipper” to stitch the whole assembly into the final form.

Steel fabrication methods and on-site erection concepts were also researched for constructability. A “zipper con-

Figure 7: The structure. a) Basic cell module; b) Basic cell grouping; c) Structural cells as laid out on the flattened skin of the atrium envelope.

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Cell Wall: Resolving Geometrical Complexities

Figure 8: “The Zipper Concept”. a) “The Zipper” within atrium geometry; b) Atrium wall elevation.

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3.2 Curtain-Wall Layer

Once the basic structural system and cell size was confirmed, the geometry and configuration of the curtainwall layer was tackled. Three basic solutions for the curtain-wall were explored, each adding its own geometric complexity: A. A window system integrated within the cell of the structure, as a super-sized infill-window system.

B. A window system, separate and independently formed, but bracketed from the back side of the structure facing the interior side of the atrium.

C. An orthogonal cable-net wall with point-supported glass running independently behind the structural cell system.

Ultimately, for constructability and visual cohesiveness with the overall geometry of the cell structure, option B was chosen.

Structure, by its nature, is a vector-based geometry and in our case, the main structural cell frame has its nodes aligned along the curved conical plane of the atrium geometry. Curtain-walls are planar-faced surface geometries and reconciling the nodes of the structural cells in the same polygonal shape of the structure would have resulted in warped glass surfaces. Thus, for the window geometry to resolve itself in the curved and conical layout of the atrium within the framework of the structural nodes, the windows had to be triangulated so that they formed a seamless fold.

Triangular meshes have inherent geometrical complexities as they converge on a node. The connecting nodes had to contend with five to six intersecting members, some at rather acute angles. Despite this complexity, extensive studies showed the triangulation to work most effectively in navigating the curved geometry.

Figure 9: The curtain wall layer. a) Basic curtain wall cell-module; b) Basic cell grouping; c) Curtain wall cells as laid out on the flattened skin of the atrium envelope.

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Cell Wall: Resolving Geometrical Complexities

For constructability, the curtain wall was conceived as a series of factory-unitized triangular aluminum windows bolted together at the intersecting nodes. Each structural polygon shape was divided into three or four triangular pieces for a total of twenty six unique triangular shapes. The window assemblies were then pointsupported via brackets from the structural super-cells at the geometrical nodes. Due to the layout of the glasswall within the atrium envelope sandwich, the windows would have to be installed, maintained and replaced from the interior side of the atrium.

lated polygonal cell geometry had to be developed for proper sun-shading function. Since the all glass atrium wall is slightly tilting back and facing south, east and west, the density and size of the screen geometry had to be carefully studied for actual solar-shading performance while maintaining the visual aesthetic required to connect the interior and exterior spaces. The sunscreen is floated outward from the structure, breaking down the mass of the structural cells with a lacier screen polygonal grid, a miniaturized variation of the structural cells.

3.3 Sun-Screen Layer

The screen itself was conceived as a series of simple rectangular aluminum tubes and can be easily factory fabricated into the custom cell shapes required. Larger cell groupings could then be transported to the project site and erected in place.

The geometrical solution of the exterior sun-screen was a take-off from the Voronoi module of the structural wall, and like the curtain wall, was pinned at the central nodes of the structure. A denser pattern of the tessel-

Figure 10: The sun-screen layer. a) Basic cell-module; b) Basic cell grouping; c) Sun-screen cells as laid out on the flattened skin of the atrium envelope.

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Figure 11: a) The 3 atrium layer’s cell-module overlap.

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Cell Wall: Resolving Geometrical Complexities

Figure 11: b) Atrium sandwich section.

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Figure 12: The interior view of the atrium.

Figure 13: The exterior view of the atrium wall and museum entry.

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Cell Wall: Resolving Geometrical Complexities

4.0 CONCLUSIONS

Complex geometrical envelope systems require the active involvement of technical and design teams to tackle possible solutions simultaneously, thus constantly adding balance to the process. Inevitably, numerous deadend solutions would be pursued and vetted quickly so as not to distract from the project schedule and project deliverables. Technical buildability and the design aesthetics needed to be constantly evaluated so as not to stray into unrealistic expectations. This dictated that the right blend of talents be fully engaged from the beginning of the project.

Designing cell structures to full building scale and with active real-world structural and economic constraints proved a lot more challenging than initially anticipated.

While these systems can be relatively easily generated as patterns and decorations in a virtual computer world, executing them to the scales of real architecture produces innumerable constraints and dead-end solutions. Feasibility considerations had to be constantly applied to keep the design process real. Structural realities of overall span and incurred axial and lateral static forces produce unanticipated stresses when dealing with asymmetrical cell geometries.

Solving complex architectural conditions and geometries was simplified when simple achievable elements were considered. Since the Shanghai Nature Museum is a real project with a real design/construction schedule and budget, innovative applications of existing technology had to be incorporated. Incorporating readily available rectilinear construction elements and combining them in complex layouts was crucial in delivering a buildable design within economic realities.

Actively using 3D computer BIM models was crucial to the project in order to understand the visual design implications as well as to quickly ascertain where the actual technical complexities were. Quick 3D studies also exposed weaknesses in proposed solutions in a timely manner. Being able to share the computer model with the local Chinese engineers also guaranteed that we were all looking at the same geometry and structural data. The 3D models also became the basic visual tool to explain the atrium enclosure to the clients in China as well as to the client’s engineers and construction experts.

Acknowledgments

Exterior envelope team: Ralph Johnson, Bryan Schabel, Marius Ronnett, Ian Bush, Abul Abdullah, Hemant Thombre, Michael Tumminello, Leila Kanar and Kyle Knudson. Special acknowledgement to Todd Snapp, for his initial studies of computer-generated algorithms as a possible solution to the cell geometry.

REFERENCES

[1] Pottmann, H., Liu, Y., Wallner, J. Bobenko, A. and Wang, W., (2007). “Geometry of Multi-layer Freeform Structures for Architecture”, ACM Transactions on Graphics (TOG): Proceedings of ACM SIGGRAPH 2007, Vol. 26, No. 3.

[2] Pottmann, H., Brell-Cokcan, S. and Wallner, J., (2007). “Discrete Surfaces for Architectural Design”, In Chenin, P., Lyche, T., Schumaker, L. (eds.), Curves and Surface Design: Avignon 2006, Brentwood, TN: Nashboro Press.

[3] Pottmann, H., Schiftner, A., Bo, P., Schmiedhofer, H., Wang, W., Baldassini, N. and Wallner, J. (2008).

“Freeform Surfaces from Single Curved Panels”, ACM Transactions on Graphics (TOG): Proceedings of ACM SIGGRAPH 2008, Vol. 27, No. 3.

[4] Liu, Y., Pottmann, H., Wallner, J. Yang, Y. and Wang, W., (2006). “Geometric Modeling with Conical Meshes and Developable Surfaces”, ACM Transactions on Graphics (TOG): Proceedings of ACM SIGGRAPH 2006, Vol. 25, No. 3, pp. 681-689.

[5] Pottman, H., Asperl, A., Hofer, M. and Kilian, A., (2007). Architectural Geometry, Exton, PA: Bentley Institute Press.

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02.

THE EFFECT OF HEAT FLOW AND MOISTURE ON THE EXTERIOR ENCLOSURE: Working with Standards and Modeling Software to Make More Intelligent Exterior Enclosure Decisions

Charles Sejud, AIA, LEED® AP BD+C, charles.sejud@perkinswill.com Jean-Claude Lesaca, LEED® AP BD+C, jean-claude.lesaca@perkinswill.com ABSTRACT This article describes the importance of the effect of heat flow and moisture on the building’s exterior enclosure.

It provides a basic understanding of the concerns of why understanding heat flow and moisture is important to the design of exterior walls, its basic physics and traditional, yet obsolete solutions. It provides a technique for making intelligent exterior enclosure decisions regarding condensation using ASHRAE Standard 160 guidelines to specify performance-based design criteria. Also, it discusses the application of these criteria to computer software that uses the Transient Hygrothermal Behavior Method.

ASHRAE Standard 160 can be used to establish and/or calculate the criteria for temperature, relative humidity and air pressure that may affect moisture (vapor) diffusion in wall assemblies, selecting analytical procedures and establishing evaluation criteria for the results of those analytical procedures. The Transient Hygrothermal Behavior Method can use the criteria established in ASHRAE Standard 160 to calculate the transfer of heat and moisture diffusion over time. WUFI (Wärme und Feuchte Instationär - Transient Heat and Moisture) is an analytical procedural software program that can be used in conjunction with ASHRAE Standard 160 evaluation criteria.

The WUFI program allows realistic calculations of the Transient Hygrothermal Behavior of multi-layer building components exposed to natural climate conditions. ASHRAE Standard 160 and WUFI can be used in an iterative process and to find solutions where vapor pressure exceeds vapor saturation pressure. Essentially, WUFI, along with the criteria of ASHRAE Standard 160, can help the designer find appropriate solutions to prevent internal condensation, provide appropriate insulation and locate suitable positions for air barriers.

KEYWORDS: heat flow, moisture analysis, exterior building envelope DEFINITIONS: Air Barrier System- An assembly of materials that provides a complete barrier to air leakage through the building enclosure.

Condensation- The act or process of reducing a gas or vapor to a liquid or solid form.

Heating Climate- The determination of when the quantitative indices of heating degree days (the demand for energy needed to heat a building) exceeds the cooling degree days.

Hydraulic transport- Movement of material produced by the flow of water.

Hygrothermal- Of or pertaining to both humidity and temperature; combined moisture and heat.

Permeance, Perms- A measurement of the ability of a material to retard the diffusion of water vapor at 73.4°F/ / 23°C) in response to an applied vapor pressure gradient. A permeance (a perm measurement unit) is the number of grains of water vapor that pass through a square foot of material per hour at a differential vapor pressure equal to one inch of mercury.

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The Effect Of Heat Flow And Moisture On The Exterior Enclosure

R-Value- A measure of the capacity of a material, such as insulation, to impede heat flow with increasing values indicating a greater capacity (The inverse of U-value).

Vapor Retarder– A material that delays or impedes the progress of gaseous particles of water by diffusion U-Value- A measure of heat transmission through a material for a given thickness (The inverse of R-Value).

1.0 INTRODUCTION

The water hollowed the stone, The wind dispersed the water, The stone stopped the wind.

Water and wind and stone.

Octavio Paz, A Draft of Shadows1, 2.

There has been an increased interest in the sustainability and durability of our constructed environment beginning with the onset of the oil crisis of the early 1970’s. By the late 1970’s, the issues revolved around conserving and reducing the demand of natural resources. By the early 1990’s, the National Resource Defense Council spearheaded the Leadership in Energy and Environmental Design (LEED) system with the U.S. Green Building Council (USGBC) and industry design, engineering and construction leaders. USGBC’s LEED system along with allied organizations such as The American Society of Heating, Refrigerating and AirConditioning Engineers (ASHRAE), not only created standards and metrics to address the demand of natural resources, but expanded the idea of environmental design by including issues such as indoor air quality and water efficiency. By the mid-1990’s, these groups had reinforced LEED’s goals and also added their own values, such as durability, to the concept of sustainable design. When we think of the durability of materials, we typically think of the effect that weather, primarily wind and rain, has on its appearance and performance.

These readily observed forces affect the appearance and, therefore, the aesthetics of a building through patina, weathering, staining and erosion1. However, these same forces, water as vapor and wind as pressure differentials, can also work less visibly within our structures and assemblies resulting in durability issues that affect the life building performance.

By 1990, the design and engineering professions began addressing the need to mitigate the effect that these invisible forces have on the construction assemblies.

In 1996, ASHRAE created a chair for the Prevention of Moisture Damage with the sole purpose of creating more durable environments. As early as 1999, they formed a committee and incorporated ideas to mitigate mold growth and improve the health of building occupants by eliminating or mitigating moisture damage

through climate, construction type and system operations3. By the mid-2000’s, the American construction industry began moving away from prescriptive codes and standards to a more performance-based design.

ASHRAE created Standard 160 to address criteria that can be used in analyzing systems while ASTM International created a standard, ASTM E-241, for limiting water-induced damage to buildings4. Soon, designers will no longer be allowed to simply use rules-of-thumb such as a vapor barrier belongs on the warm side of the insulation. The design team will be required to analyze the effect of heat flow and moisture on building systems and design to the parameters of program, site and construction assemblies.

This article provides an explanation of how heat flow and moisture affect exterior wall assemblies as well as basic concepts regarding moisture and vapor control.

Finally, this article explains ASHRAE 160 Standard Criteria for Moisture-Control Design Analysis in Buildings and the Transient Hygrothermal Behavior Method as tools for analyzing and designing wall assemblies.

2.0 EFFECTS OF HEAT FLOW AND MOISTURE ON EXTERIOR WALL ASSEMBLIES

With the increased need for more energy-efficient environments, buildings are being designed with increased insulation and barriers to limit air infiltration. There is a vigorous debate about whether the search for these solutions has created an environment that has allowed for potential condensation problems to occur within and around wall assemblies through hygrothermal processes3, 5. In lieu of answering the question of whether or not energy efficiency is causing water mitigation problems, we are taking the spirit of ASHRAE 160 in defining issues regarding heat flow and moisture, how to analyze the data and how to apply the resultant information. Current codes do not adequately address either a prescriptive or performance-based solution for solving condensation issues. For instance, the International Building Code 2009 (IBC) only requires the use of a vapor retarder in certain attic spaces, roof and wood or light-gauge steel frame construction and permits the use of vapor retarders in other assemblies6. Where the code requires a vapor retarder, the requirements are prescriptive; the code tells you what you must do.

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Where vapor retarders are permitted, the code offers no assistance in their location within the wall assembly.

Their need and application is the designer’s responsibility.

The sole purpose of a vapor retarder is to delay or impede the progress of water vapor to the adjoining area.

If the water is being stored or built-up in an area, the effects of this water need to be investigated. Currently, IBC addresses the need to protect against condensation and drain water that has infiltrated the exterior wall assembly, but does not address how to analyze and execute such concerns. The code limits its discussion to the requirement only. Therefore, the exterior wall designer must understand how heat flow and vapor diffusion are occurring within the wall assembly and how to place the vapor retarder, if needed, in the proper location within that assembly.

The most effective way of eliminating vapor transmission through the exterior wall is to provide a solid and continuous air-barrier system around the perimeter of the building. Since air contains vapor, limiting the transference of air substantially limits the movement of vapor7 (see Figure 1). In order to be a recognized air barrier system, the system must comply with ASTM E 2178 Standard Test Method for the Air Permeance of Building Materials. These systems come in a variety of materials, such as rigid, flexible and fluid-applied8.

Figure 1: Air leakage.

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So, why do we need to address vapor diffusion if an air barrier is preventing the majority of vapor transmission? While air barriers must have a low degree of air permeance, their vapor permeance can vary widely and they may need to be used in conjunction with vapor retarders. Each building material has its own vapor permeability. When combined as a wall or roof assembly, the materials may let vapor move through the assembly or delay its progress through diffusion. Vapor’s location and movement needs to be examined to determine any potentially deleterious effects. The most common problem with vapor transmission occurs when vapor molecules condense into liquid water, a historical enemy of the built environment. When vapor is allowed to condense uncontrolled in a concealed wall assembly, the effects, such as corrosion of metals and increased bacterial and fungal growth, can be serious. These adverse effects can negatively impact the long-term durability of the materials and indoor air quality. However, vapor transfer can be delayed through an assembly by the use of vapor retarders, which delay the progress of gaseous particles of water by diffusion. The location within the wall assembly of these air barriers and vapor retarders will have an effect on the performance, cost and aesthetics of the building. The need for and location of the vapor retarders must be investigated, established and any potential adverse affects addressed in the building design.

The Effect Of Heat Flow And Moisture On The Exterior Enclosure

In addition, not only will the diffusion of air and vapor significantly affect the performance of the exterior wall, but so will the combination of heat and moisture movement in exterior wall assemblies. Heat flow is the natural movement of heat from a material at a higher temperature to one that is lower9. Heat flow and moisture migration have traditionally been looked at as separate design criteria. The Transient Hygrothermal Behavior Method allows for these two criteria to be analyzed together and can lead to better and more efficient design considerations. The combined analysis of looking at heat flow and moisture migration coupled with time allows the designer to see how external heat sources, temperature gradients through materials and the limitation or diffusion of moisture affect the assembly at the same time. These forces are particularly evident in the effects of moisture on building insulation components3.

The performance of insulation or any material depends not only on the material’s heat conductivity (U-value), but also the moisture content of the material. Strong evidence has been scientifically recorded that shows certain moisture-laden insulation materials perform at much lower rates than the manufacturers’ published dry-state R-Values (heat resistance)10. This reduction in the R-value can result in additional energy consumption and reduced thermal comfort of the building’s occupants. These consequences, along with rust and microbial growth, have a direct relationship to the wall assemblies’ thermal resistance, latent moisture content, vapor and air barrier locations as it relates to internal and external climate conditions11, 12. Therefore, in variable environments it becomes important to review the heat-flow in different seasons and weather conditions to understand how the insulation will perform and affect the performance of the exterior wall assembly.

2.1 Basic Concepts Regarding Moisture and Vapor Control

To be able to understand these complex building assemblies and make intelligent decisions regarding moisture and vapor control, it is necessary to understand the basic concepts of insulating materials, air barrier systems and vapor retarders and their relationship to humidity, temperature and condensation. Moisture content in the air, otherwise known as vapor, can travel through materials in two ways: through air movement and through diffusion. When vapor is not allowed to easily flow from one atmosphere to another, it can be trapped in areas and can lead to condensation. Condensation is the process by which matter transitions from a gas (or vapor) phase into a liquid phase. This can happen when the amount of vapor contained in the air meets its satu-

ration point or the ability of the air to hold water in a gaseous state. The factors that relate to the saturation point or dew point are related to thermal temperature of the area in question and the relative humidity of the area in question under constant pressure. A general concept in the transfer of vapor and condensation is that cool air can hold less water than warm air.

The designer must be aware if and where the vapor in the wall assembly is being impeded or the conditions are created that may have a harmful effect. It has been already discussed that the majority of this vapor can be stopped by using air barriers assemblies. These air barriers also have vapor permeability ratings that relate directly to their proper placement. Seven U.S. states have already adopted conservation codes with requirements for air infiltration and four states have pending codes8.

In addition, model energy codes such as the 2009 ICC International Energy Conservation Code are requiring the need for increased insulating values of exterior wall assemblies. These current design requirements require the designer to understand the wall assemblies vapor permeability, temperature and relative humidity gradients and how they affect their design.

Traditionally, the vapor retarder is placed on the warm side of the insulation. In theory, this impedes moisture/ vapor from condensing against adjacent substrates where typical weather conditions meet the dew point.

When the ability of a material to hold water ceases (vapor content reaches vapor saturation) and temperature gradients meet the dew-point temperature, vapor will condense into water causing a need for a design resolution (see Figure 2). For example, in heating-dominated climate such as Chicago, Illinois, the vapor retarder is typically placed on the interior side of thermal mass to prevent the warm, relatively moist interior climate from diffusing to the cold, relatively dry climate of the exterior. In a humid cooling climate such as Miami, Florida, the opposite would be the typical practice.

If we were to look closer at those conditions and study them over the course of a year, we might find conflicts in the design approach. For instance, Chicago is also known for its short season of humid cooling climate during the late summer months; it has traditionally been assumed that this duration was too short and the risk of condensation too small to worry about. In other cases, the interior climate has been adjusted to suit a particular need such as low humidity in a rare book library, or the use of a space can result in high humidity, as in a natatorium. Or, perhaps a material can be technically considered a vapor retarder such as certain interior wall

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Figure 2a: Assembly diagram.

2.70 (Hg in.)

2.70 (Hg in.)

Interior Temp: 70 F @ 30% RH

Exterior Temp: 93 F @ 71% RH

vapour saturation

Exterior Temp: 93 F @ 71% RH

Interior Temp: 70 F @ 30% RH

vapour saturation

1.50 (Hg in.)

1.50 (Hg in.) vapour content

vapour content

0 (Hg in.)

0 (Hg in.)

Condensation w/ no Vapor Barrier

Figure 2b: One-dimensional steady state heat transfer diagram.

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Condensation w/ Vapor Barrier

The Effect Of Heat Flow And Moisture On The Exterior Enclosure

Start moisture design

Exterior Wall Assembly

Assign material properties

Select initial conditions known per ASHRAE 160

Select outdoor conditions

Select exposure conditions

Humdity + Temperture Range

Change in HVAC design

Perform analysis

Acceptable performance

No

Yes No

Add initial drying procedure?

Yes

Change in construction design?

Yes

Report results No

Figure 3: ASHRAE 160 Supplemental workflow diagram.

coverings. Therefore, the design needs to prevent the potential trapping of moisture within the assembly. In all these cases, how does one assess the risk of adding a vapor retarder to the assembly and determine its location in the assembly?

tionär - Transient Heat and Moisture) software, developed by Fraunhofer Institute for Building Physics (IBP).

In order to help analyze the exterior wall assembly, we will investigate two recent trends in the building sciences for the determination of criteria and analysis of moisture-control design. The first is ASHRAE Standard 160 Criteria for Moisture-Control Design Analysis in Buildings, which provides set of criteria for the assemblies design, selection of analytical procedures and criteria for analyzing the results. The second is the Transient Hygrothermal Behavior Method that uses a ten-year data base of weather information to analyze, not only the potential for condensation at a given time, but also to see the potential influences that heat flow and building exposure can have on the assembly. This method can only be understood effectively through software programs such as WUFI (Wärme und Feuchte Insta-

ASHRAE Standard 160 Criteria for Moisture-Control Design Analysis in Buildings, has been established as a performance-based tool for setting criteria for setting design parameters, selecting analytical procedures and moisture performance evaluations of building enclosures3, 5, 13. This standard can be used with a variety of different analytical tools including computer-based moisture analysis tools by establishing much of the criteria that has been discussed earlier. A reason for establishing the standard is to allow the design and construction industry to have a consistent set of underlying assumptions. This allows the professions to base their analysis on the appropriate design loads operating on the building above grade by establishing minimum attributes. It must be mentioned that the standard does

2.2 ASHRAE Standard 160 Criteria for Moisture- Control Design Analysis in Buildings

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not address the needs of thermal comfort, air quality or bulk water issues such as rainwater, plumbing leaks or floods—these issues must be addressed elsewhere and they are not the focus of this article. The standard, along with its appendices, provides guidelines for moisture-control design procedure allowing for the hypothetical testing of materials and climate situations based on actual weather data or ASHRAE standard climate data (see Figure 3).

By following the standard, the first set of criteria is establishing design parameters or loads. ASHRAE has chosen to base their 10 percent safety factor on an international consensus of 10 percent failure13. The design loads that ASHRAE Standard 160 establishes are the initial moisture content of building materials, indoor design temperature, indoor design humidity, optional design air pressure differentials and flows, and moisture design weather data.

One design criterion that is now beginning to be acknowledged as important in the analysis is initial moisture content of building materials. Most materials have embodied water content. Some materials have such a large content that vapor eventually diffuses into the general wall assembly. These materials are concrete, wood and wet-spray cellulose insulation. These materials release their water content into the wall assembly.

In concrete, it is the concrete curing. In wood, it is the material drying out its natural saps. In wet-spray insulation, it is the drying of the added water required to spray the insulation. It also takes into consideration the water content that may be absorbed or imbedded from the construction process, such as rain or storage. In Standard 160, ASHRAE has decided that this is a criterion that needs to be in a wall assembly design and has established each material, except concrete, to have an equilibrium water content of 80 percent. This criterion is called EMC80. Concrete is assumed to have an equilibrium water content of 90 percent or EMC90.

The standard states if no special measures are taken to mitigate the imbedded water content of a material, the established EMC water must be taken at twice the standard level.

The next design criteria are internal loads and are interior design temperature and interior design humidity.

Indoor air temperature is the project specification as required by code, regulation or law. If it is not established, ASHRAE provides calculations based on heating, cooling and averaging the outdoor air temperature.

ASHRAE allows for the designed relative humidity if it is controlled by the building’s heating, ventilation and air conditioner (HVAC) system. If the HVAC system does

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not control humidity or does not exist, the interior design humidity can be figured in three ways. The first method, the simplified method, considers humidity level for buildings without an air-conditioning system.

However, the values are primarily based on variables from northern Europe because the primary leadership and research has been developed by German building scientists. These variables are not scientific, but are primarily a correlation between exterior and interior relative humidity13. These non-scientific values can be higher than assumed especially in dry-climates. The next method, the intermediate level allows for more exact calculation of the criterion. However, the building must have a dehumidification or air-conditioning system. Other variables include residential versus nonresidential and ventilated versus non-ventilated buildings. The last method is full parametric method and is more sophisticated, but needs ventilation software and weather data.

The last set of design criteria that exterior wall assemblies need to consider per ASHRAE Standard 160 include external loads and water loads from the exterior environment. These are rain, air pressures and flow.

The rain criterion needs to consider ten-year minimum weather data, which needs to include dry-bulb air temperature, total solar insolation on a horizontal surface, average wind speed and direction, rainfall, cloud index and a choice of vapor pressure, dew-point, wetbulb temperature, relative humidity or humidity ratio. The air pressure and flow criteria can completely dominate the criteria set of water vapor diffusion. Since the method of verifying this data set is not readily available, ASHRAE decided to make this criterion optional. If chosen to include as a factor, the standard does guide air tightness, minimum air pressures and pressure direction.

ASHRAE does point out that this portion of the standard is elusive and still under review.

ASHRAE considers two performance criteria for analyzing the results of exterior wall designs. These criteria are for mold and corrosion. The mold criterion is based on IEA Annex 14 from 1991. The criteria for avoiding mold growth are a 30-day running average surface relative humidity of less than 80 percentage running between 5o-40o C (41o -104o F), a 7-day running average surface relative humidity of less than 98 percent when the temperature is between 5o-41o C (41o -104o F) and 24-hour running average surface relative humidity of less than 100 percent when the temperature is between 5o-40o C (41o-104o F). ASHRAE does acknowledge that the performance criteria are general and that some bacterial growth exists at lower humidities and/or tem-

The Effect Of Heat Flow And Moisture On The Exterior Enclosure

peratures. The corrosion criterion allows for the analysis to be material specific if known. However, if not known the default should be a relative humidity less than 80 percent for an average 30-day period.

But how does one use ASHRAE Standard 160’s criteria for both design and performance? ASHRAE Standard 160 also sets criteria for selecting analytical tools that can use the design data and will give the output to analyze the data. The analytical procedures and tools need to be transient or time-oriented in nature and have the following minimum requirements: energy transport, material properties as a function of water content, water transport including capillary transport, moisture disposition on surfaces, storage in materials, vapor diffusion and water leakage. If the exterior wall includes a ventilated cavity, the process must include temperature and surface relative humidity, average temperature for each material layer and average moisture content of each layer. Acceptable analytical procedures are incorporated in the German software program, WUFI software (Wärme und Feuchte Instationär - Transient Heat and Moisture), and is discussed in the next section along with how ASHRAE Standard 160’s criteria is incorporaed.

2.3 Transient Hygrothermal Behavior Method

WUFI (Wärme und Feuchte Instationär - Transient Heat and Moisture) is a software program that produces computational modeling of the dynamic movement of heat and moisture transportation through wall assemblies.

Beyond the steady-state concepts applied with dew point assessment, WUFI analysis provides a more realistic calculation of the transient hygrothermal behavior of the exterior wall assembly by realistically simulating heat and moisture performance based on historical weather data for specific climatic regions and building orientation. WUFI offers an hour-by-hour overview of the complex and dynamic moisture transport phenomena occurring within construction assemblies during a specified period of time and highlights basic principles and interactions present during moisture transport. The program takes into account various properties such as permeability, moisture storage capacity of assembly and thermal conductivity, which affect the heat and moisture movement within the wall. WUFI results include temperature and relative humidity values within the wall, and solar load and rain load as a function of time.

WUFI is capable of performing a dynamic analysis over accelerated time, typically a minimum 10-year weather cycle. During this cycle, the temperature, moisture content, relative humidity, dew-point, heat fluxes and vapor drive within the wall are observed concurrently to deter-

mine any deleterious effects. WUFI analysis generates graphic diagrams showing a momentary snapshot of how the wall assembly is performing.

Based on the ASHRAE Standard 160, WUFI offers the designers of an exterior wall assembly the tools needed to generate a performance-based design evaluation.

Per ASHRAE Standard 160, “The purpose of this standard is to specify performance-based design criteria for predicting, mitigating or reducing moisture damage to the building envelope, materials, components, systems and furnishings, depending on climate, construction type and HVAC system operation”5.

The ASHRAE standard specifies the minimum time required for analytical procedures, depending on the building design and other parameters. For instance, if the construction is a pre-cast concrete wall, the analytical procedure should be able to handle water absorption and redistribution in the pre-cast concrete. In contrast, where a wall assembly does not contain hygroscopic materials and is airtight, a simple vapor diffusion analysis may be sufficient. The standard also defines design input values or “design moisture loads,” primarily by prescribing default values in case the designer does not have actual design specifications. These include interior as well as exterior (such as rain and humidity) loads.

WUFI can calculate interior relative humidity RH levels using the ASHRAE 160 Standard Method. Finally, the standard describes how the results from the analysis should be interpreted. It provides criteria to determine if the building component is likely to perform satisfactorily or not. Some of the criteria that can be modeled in WUFI include the RH levels and the time an assembly’s RH is over 80 percent. These conditions could lead to interior component corrosion and potentially create an environment that fosters mold growth. The analysis also calculates the total amount of water retained in individual wall components and uses the result to determine if the insulation is not drying out over the specified length of time.

While different air barrier products may display similar wall performance results when modeled with WUFI, their actual, real-world performance characteristics may vary in practice due to the nature of the product or application methods (see Figure 1 for air leakage as an example).

WUFI is available as a free research and education version from the Oak Ridge National Laboratory Buildings Technology Center (http://www.ornl.gov/sci/btc/apps/ moisture/ibpe_sof161.htm).

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2.4 Sample WUFI Analysis

For the WUFI test case, we looked at a pre-cast concrete panel assembly for use in a 10-story office building in Minneapolis. We used the WUFI Pro 4.0 IBP version of the program to determine the optimal location of the vapor barrier. Three test case wall assemblies where chosen for the analysis. The first case is the precast panel assembly without a vapor barrier, the second case is the same assembly with a vapor barrier located on the cold side of the insulation and the third case is the assembly with a vapor barrier located on the warm side of the insulation.

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When performing the WUFI calculations, we followed the ASHRAE 160 Supplemental Workflow Diagram (Figure 2) in setting up the test case parameters: • Start moisture design • Exterior wall assembly: Case 1, 2 and 3 • Assign material properties • Select initial conditions per ASHRAE 160 • Select outdoor conditions • Select exposure conditions • Humidity and temperature range • Perform analysis • Acceptable performance • Report results

Figure 4a: Case 1 - component assembly.

Figure 4b: Case 2 - component assembly.

The Case 1 assembly design is composed of the following materials:

The Case 2 assembly design is composed of the following materials:

Pre-cast concrete panel, 5.41 inch thick Air layer, 1 inch thick Insulation Owens Corning CW8 Unfaced, 3.5 inch thick Air layer, 3-1/2” metal stud Gypsum board, 5/8 inch thick See Figure 4a

Pre-cast concrete panel, 5.41 inch thick Air layer, 1 inch thick Insulation Owens Corning CW8 Unfaced, 3.5 inch thick Air layer, 3-1/2” metal stud Gypsum board, 5/8 inch thick See Figure 4b

The Effect Of Heat Flow And Moisture On The Exterior Enclosure

As noted, the test case project is located in a cold climate, the basic wall assembly is the same for each case the only variable that changes is the addition of a vapor barrier and its location inside the wall assembly (Case 1: no vapor barrier in the wall assembly; Case 2: a vapor barrier on the cold side of the wall assembly; Case 3: a vapor barrier on the warm side of the wall assembly).

We assigned the material properties using basic materials with known hydrological properties in the WUFI material database. Per the ASHRAE 160 requirements we assigned an 80 percent RH level at the beginning of each test to simulate the higher moisture content in

building materials during initial construction.

The outdoor conditions are based on actual weather data files available with the WUFI software. Per the ASHRAE 160 Standard, a ten year analysis using the weather files are required. For the test case analysis we performed a ten year calculation to validate our results, but we limited our graphs to show one year worth of data in order to simplify the legibility of the graphs.

WUFI calculates the building exposure conditions. For our test case we oriented our structure facing north.

Based on the actual weather and climate data for Minneapolis, using the WUFI software we did a rain analysis to determine how much wind driven rain is impacting the north face of our test building.

The humidity and temperature for the test cases are set at an indoor design temperature of 21o C (70o F). The indoor design humidity is set at 70 percent RH. These are based on the ASHRAE 160 requirements.

During the analysis of each test case, the temperature, moisture content, relative humidity, dew-point, heat fluxes and vapor drive within the wall are observed concurrently to determine any deleterious effects. Results are shown in Figures 5, 6 and 7.

Figure 4c: Case 3 - component assembly.

The Case 3 assembly design is composed of the following materials: Pre-cast concrete panel, 5.41 inch thick Air layer, 1 inch thick Insulation Owens Corning CW8 Unfaced, 3.5 inch thick Vapor retarder (1 perm rating) Air layer, 3-1/2� metal stud Gypsum board, 5/8 inch thick See Figure 4c

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Figure 5a: Case 1 - Results for water content.

Figure 5b: Case 1 - Results for water content.

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The Effect Of Heat Flow And Moisture On The Exterior Enclosure

Figure 5c: Case 1 - Results for temperature and relative humidity.

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Figure 6a: Case 2 - Results for water content.

Figure 6b: Case 2 - Results for water content.

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The Effect Of Heat Flow And Moisture On The Exterior Enclosure

Figure 6c: Case 2 - Results for temperature and relative humidity.

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Figure 7a: Case 3 - Results for water content.

Figure 7b: Case 3 - Results for water content.

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The Effect Of Heat Flow And Moisture On The Exterior Enclosure

Figure 7c: Case 3 - Results for temperature and relative humidity.

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2.5 Discussion of WUFI Analysis Results

Per the ASHRAE 160 Standard, the performance of the design assembly must meet moisture performance evaluation criteria. These criteria apply to all materials and surfaces except the exterior surface of the building envelope. The basic requirements are: • Conditions necessary to minimize mold growth • Corrosion, based on RH levels above 80 percent over a sustained period of time The WUFI program generates water content (lbs/ft3) for each material in the test case wall assemblies (see Figures 5a, 6a and 7a). As noted in the standard, we ignore the exterior surface in this analysis (the pre-cast concrete panel). The vapor retarder does not absorb any water and the air layer can show water accumulation at the boundary conditions next to adjacent materials. The most critical component in each test case is the insulation and interior gypsum board.

The WUFI results show if the insulation is absorbing water, which is important since it could greatly impact the actual R-value. Since the proposed building is in Minneapolis, it is important to get the optimal R-value from the insulation. Looking at the water content graph for the Owens Corning CW8 unfaced insulation data output, we see that in the Case 1 assembly (Figure 5a), the insulation has achieved a steady state in the moisture balance. In Case 2 (Figure 6a), we observe an increase in the amount of water being absorbed in the insulation.

This would have a negative impact to the R-values. In Case 3 (Figure 7a), the insulation layer is observed to be drying out over the course of the year.

We also have to take into account the effect of humidity and temperature inside each case assembly. Looking at Case 1 (Figure 5c) humidity and temperature levels, we can observe that at monitor position (MP) 3, at the boundary between the back of the pre-cast and the 1-inch air cavity, humidity levels are observed from 100 percent RH in the cold months to 75 percent RH in the summer. There is also a significant amount of water (0.75 lbs/ft3) recorded that could result in condensation forming on the back of the concrete pre-cast panels.

MP 4 is at the mid-point of the Owens Corning CW8 insulation layer.

At Case 2 (Figure 6c), we observe that there is less humidity at MP 3 than in Case 1, but there are sustained humidity levels in excess of 80 percent RH at MP 4.

Based on the water content at MP 4, this would have a negative impact on the insulation R-value as previously noted.

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At MP-3 in Case 3 (Figure 7c), we observe more fluctuations in the RH levels at the back of the pre-cast.

However, at MP 4 (within the insulation), the RH levels range from 45 percent to just a bit above 75 percent in the summer months. There is very little water accumulating in the insulation layer based on the water content graph (Figures 5a and 5b).

Based on the total water content graphs and the RH levels inside the wall cavity, our best performance comes from the test Case 3. The graphs indicate that we are not retaining water inside the wall assembly.

The last chart (Figure 8) shows profile views across each case wall assembly. Each profile is a view through the test assembly for any given day—in this case, February 25, 2011, the last date for the WUFI study. The plot lines show where the vapor drive through the wall assembly is meeting resistance, caused by the physical material properties or by the application of a vapor barrier. This profile is for one day’s result, but the WUFI software is able to generate an animation that shows, for each 24-hour over the course of the WUFI analysis period (for this study, a year) when the test case wall assembly has reached its dynamic steady state where the amount of vapor accumulation is stable and is not decreasing or increasing.

Based on the above observations, we can see that Case 3 is the optimal design for our test exterior wall assembly. There are still issues with the amount of water vapor accumulating in the outer air cavity that need to be addressed by the design team. There are other options the design team could study, such as providing a water-repelling treatment on the exterior pre-cast concrete face to reduce the amount of water absorbed in the concrete. Each proposed concept can then be re-evaluated with a new WUFI analysis.

3.0 CONCLUSION

The demands on the design team to understand the performance of the exterior wall assembly is becoming more important with the advent of more stringent requirements. Heat flow and moisture content in exterior walls are becoming major design factors. Using old rules of thumb and metrics may no longer be advisable if the reasons behind them are not clearly understood and a better understanding of the design can be garnered from recent standards and procedures.

In addition, there has been an increased requirement to maintain an exterior enclosure that conserves energy by increasing insulation values and providing complete

The Effect Of Heat Flow And Moisture On The Exterior Enclosure

Figure 8: Profile chart for Case 1, 2 and 3.

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air barrier systems. These changes in our assemblies require examination on the heat flow and the movement of moisture in the wall assembly. The exterior wall needs to be designed to prevent corrosion and degradation of materials, maximize performance abilities of building materials and contribute to good indoor air quality including avoiding mold or bacterial growth.

Traditional steady-state diagrams have been used successfully in the past to verify exterior wall performance.

However, the current and future use of more progressive exterior wall assemblies, new materials and variable climate control is creating a wider assortment of factors than traditional steady state diagrams can compute. For projects that require more complex analysis, the industry is moving towards standards that allow these calculations to be easily performed by the design team. New standards, such as ASHRAE 160 Criteria for Moisture-Control Design Analysis in Buildings establishes procedure for the design and performance of exterior walls while it also establishes criteria for selecting analytical procedures. New software applications, such as WUFI (Wärme und Feuchte Instationär - Transient Heat and Moisture), have been developed to assist the design team to collect data regarding the exterior wall.

Together the criteria developed by ASHRAE Standard 160 and software such as WUFI coupled with the iterative process alluded to in Standard 160 can be used to create more intelligent design decisions in relationship to heat flow and moisture migration. Through industry demands and leadership, the increased performance of exterior wall in corrosion resistance, insulation values and enhanced indoor air quality will increase the longevity and value of the built environment.

Acknowledgments

The authors would like to acknowledge Reginald Curtis for help with generating the graphics in this paper.

REFERENCES

[1] Mostavi M. and Leatherbarrow D., (1993). On Weathering: The Life of Buildings in Time, Cambridge, MA: The MIT Press.

[2] Paz, O., (1991). The Collected Poems of Octavio Paz: 1957-1987, New York, NY: New Directions Publishing Corporation.

[3] Shipp, P., (2006). ASHRAE Standard 160P: Design Criteria for Moisture Control in Buildings. Libertyville, IL: USG Research & Technology Innovation Center.

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[4] ASTM International, (2000). E 241-00 Standard Guide for Limiting Water-Induced Damage to Buildings.

[5] ASHRAE, (2009). ASHRAE Standard 160 Criteria for Moisture-Control Design Analysis in Buildings.

[6] International Building Code, (2009). The 2009 International Building Code, Washington, DC: International Code Council.

[7] Brock, L., (2005). Designing the Exterior Wall: An Architectural Guide to the Vertical Envelope, Hoboken, NJ: John Wiley & Sons, Inc. [8] American Air Barrier Association, (2009). “About Air Barriers”, Retrieved on 2/2010 from http://www.airbarrier.org/about/index_e.php [9] Lechner, N., (2001). Heating, Cooling, Lighting: Design Methods for Architects, New York, NY: John Wiley & Sons, Inc. [10] Fraunhofer Institute for Building Physics (IBP), (2010). “Moisture Transport In Building Materials: Computer Simulation with the WUFI Model”, Retreived on 2/2010 from http://www.wufipro.com [11] Banham, R., (1969). The Architecture of the WellTempered Environment, Chicago, IL: University of Chicago Press.

[12] ASTM International, (2003). ASTM E 2178-03 Standard Test Method for the Air Permeance of Building Materials.

[13] TenWolde, Anton., (2008). “ASHRAE Standard 160 P-Criteria for Moisture Control Design Analysis in Buildings”, ASHRAE Transactions, pp. 167-171.

Hygroscopic Climatic Modulated Boundaries

03.

HYGROSCOPIC CLIMATIC MODULATED BOUNDARIES:

A Strategy for Differentiated Performance Using a Natural Circulative and Energy Captive Building Envelope in Hot and Moisture Rich Laden Air Environments

Marionyt Tyrone Marshall, Associate AIA, NOMA, ACADIA, LEED® AP BD+C, tyrone.marshall@perkinswill.com

ABSTRACT The operation and construction of buildings account for almost half of the energy use in the United States. To meet global climate change targets, energy consumption of buildings in the long term must be reduced as well as carbon dioxide emissions. This article explores a theoretical building envelope that generates energy and produces water by drawing water vapor out of the air to deliver new sources of water; it lowers indoor humidity in hot and humid climates.

The design in this model considers materiality, surface area and environmental conditions to influence building form. The case in this article considers materials and systems application in the design of the building envelope. The hygroscopic building envelope design strategically senses varying conditions of concentration and density of moisture laden air to provide visual indications of its performance. It is a building skin that emulates biological processes by creating pressure differences and transferring energy in various forms.

KEYWORDS: biomimetics, building envelope, building façade, computational design, computational control, humidity, hygroscopic, renewable resources

1.0 INTRODUCTION

This article discusses the adaptive properties of a hygroscopic building envelope. The hygroscopic building envelope is a biomimetic skin where all of the components for dehumidifying air and harvesting energy and water are placed within the building façade. Energy use in buildings and production of green house gases contributes to global climate change. Reducing energy usage in building operations is inspiration for rethinking how a building envelope might function for a climate that requires both cooling and dehumidification.

Current energy consumption of buildings is forty-eight percent of all energy consumed in the United States1.

Figure 1 shows the percentage of all energy usage in the United States in relation to operation and construction of buildings. Out of the forty-eight percent of energy used for operations, eight percent is embodied in the energy associated with building construction including the manufacture and transport of building materials to the site. The use of fossil fuels for building operations contributes directly to the production of carbon dioxide1.

Figure 1: United States energy consumption, adapted from1.

In hot and humid climates this problem increases due to the demands on HVAC systems that must cool and dehumidify interior spaces for comfort. Unfortunately, conventional HVAC systems do all of these things at the expense of additional building energy use and consequently produce more carbon dioxide.

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Figure 2: Diagram of hygroscopic building envelope.

A hygroscopic building envelope that harvests water from humid air must use a hygroscopic brine solution.

A hygroscopic material is a solution that will readily absorb water from the atmosphere2. A basic salt such as sodium chloride can be dissolved in water to create a hygroscopic brine solution. For the hygroscopic process to work, the solution of sodium chloride and water is exposed to the air. The hygroscopic solution readily absorbs moisture in the air through the attraction of strong ionic bonds of negative ions of the brine to positive ions of hydrogen in water vapor. Strong ionic bonds of a saturated salt solution attract to polar water molecules.

This characteristic is unlike a desiccant, which changes state from a solid when absorbing water from its surroundings to produce a solution. A solid desiccant drying agent is limited in its capacity to capture water. It is not able to regenerate itself and repeat the cycle.

A hygroscopic brine solution can absorb water and then be heated to release and harvest the excess water. The process cycle for a hygroscopic brine solution must first interact with a stream of air containing water vapor. The hygroscopic brine solution absorbs water vapor from the passing outside air that can be heated, evaporated and condensed as a new source of water. The water vapor is removed from the outside air, humidifying it in a natural manner.

Figure 2 depicts the workings of a hygroscopic climatic modulated boundary. The diagram shows a theoretical placement of the hygroscopic building envelope between the ‘outside’ and the ‘inside’ environment. The

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‘outside’ represents exterior climatic conditions. The ‘inside’ represents the building interior. The building façade contains all of the components for harvesting water and energy from sun and wind. The hygroscopic building envelope uses a solution to interact with exterior hot, humid air to absorb water and dehumidifies the air for use in interior spaces to satisfy comfort requirements. The building façade is a filter that air from the outside must pass through and, in the process, collects water and energy allowing dehumidified air to pass through to the interior. Induced pressure changes in the hygroscopic building envelope circulate air from outside to the inside. A hygroscopic building envelope can be understood in three layers as shown in Figure 3. Harvesting of energy from the sun and dehumidification of outside air occurs at layer one. Dehumidified air from layer one enters layer two where it is cooled by the HVAC system in the building interior spaces. Convection currents mix cool dehumidified air with warm interior space air in layer two. Openings in the hygroscopic building façade at layers one and three create pressure changes to circulate warm air through layer two as shown in Figure 3. The third layer of the hygroscopic building façade harvests wind energy from natural cross ventilation as shown in Figure 3. The hygroscopic building envelope system reduces the need for conventional air conditioning systems to dehumidify interior air. The HVAC system is only needed to cool interior air. The HVAC system can be smaller in size.

The HVAC system for cooling filtered dehumidified air in the interior spaces can be accomplished by a conventional air conditioning system or an active chilled beam

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Figure 3: Section showing layering of the hygroscopic building envelope.

system. Active chilled beam systems reduce building energy usage much better than a conventional HVAC system.

A strategy for water and energy harvesting opportunities unique to hot and humid climates is prevalent in areas such as the Gulf Coast region. This climate type is similar to conditions in areas such as the Mid-Atlantic Coast climate, Mississippi Valley and the southern portions of Appalachia in the United States. The Koppen map shown in Figure 4 shows the global distribution of this climate type characterized by hot, humid summers and cool winters with significant amounts of precipitation year round4. These are areas specifically suited by climatic conditions for the building envelope boundary approach described in this article. It should be noted that areas of rising usage of fossil fuels and water occurs in these zones such as the eastern seaboard of China, Australia and South America.

Figure 4: Koppen map of humid subtropical climate Cfa4.

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2.0 PAST RESEARCH: BIOMIMETICS, POTENTIAL COMPONENTS OF HYGROSCOPIC ENVELOPE AND APPLICATION

The hygroscopic building envelope draws upon past research from biomimetics in understanding water transport in desert reptiles, a water absorption system in desert climates, liquid desiccant systems, advanced photovoltaic cells design and color changing additives to substances that absorb water readily. Biomimetics application in the hygroscopic building envelope model inspires natural methods for moving water and air through the building faรงade. Examples for this process can be found in understanding how water moves through channels beneath the scales of desert reptiles and air through a building in Zimbabwe. Liquid desiccant systems have a long history of industrial use, but have not had success with use in commercial buildings. Liquid desiccant systems can be effective at removing water vapor from moisture laden air as well as adding water vapor to dry air. At this time, most uses of a liquid desiccant system exhaust air and water to the outside air and consequently, do not take advantage of harvesting the condensate for other uses. The work in advanced photovoltaic cells fibers can potentially allow for a higher level of integration into a hygroscopic building faรงade to heighten energy conversion and collection. Color changing additives to the hygroscopic substances may provide an interesting visual aesthetic that can be related to saturation and concentration. The hygroscopic building envelope essentially rethinks how these ideas and processes can advance the design of building facades.

2.1 Biomimetic Inspired Design

Biomimetics is an understanding of biological and natural systems for modern design was originally coined

by Otto H. Schmitt in 19695. A hygroscopic climatic boundary references the evolution of the Australian thorny devil and Texas horned lizards (Moloch horridus and Phrynosoma cornutum) in understanding their ability to harvest water in dry climates. The method of water transport through tubes offers a viable adaptation in understanding how water may be harvested in hot and humid climates. In another case, the behavior of Zimbabwe termites that regulates interior temperature in large mounds influences the design of the Eastgate Centre in Zimbabwe by the architect Mike Pearce with Arup engineers6. The termites store fungus for the purpose of food keeping in the mound interior at a constant 87o F while the outside temperate can be 35o-104o F6.

They do this by constantly opening and closing heat-

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ing and cooling vents throughout the mound over the course of a day6. Temperature differences due to termite activity inside the mound create currents to pull air from the bottom wet wall enclosures where it can vent through a channel at the top of the mound6. The Eastgate Centre is a naturally ventilated concrete thermal mass structure that creates temperature differences in its interior pulling air through floors and offices to chimneys at the top to maintain internal temperatures within comfortable levels without air conditioning. At night, the structure releases heat absorbed from the day cooling interior spaces for the next day.

2.2 Water Uptake and Rain Harvesting in Australian Thorny Devil (Moloch horridus) and Texas Horned Lizard (Phrynosoma cornutum) The Australian Thorny Devil (Moloch horridus) and the Texas Horned Lizard (Phrynosoma cornutum) survive in their desert climate by rapid water absorption through tubes below their scales. Water is absorbed through partially closed tubes that can expand to hold more water. The tubes are recessed below the hinge and joint of their scales. The tubes form a network of channels below the skin and cover their entire body. The semitubular channels at the base of scale hinges expand to store water for long periods of time7. The tubes create capillary forces drawing water into hinge-joint channels.

Small fractures or protrusions in the channels increase surface area to attract water and heighten the hygroscopic effect7. The reptiles develop negative pressure using jaw and tongue movements to create a suction that pulls water into their mouths for drinking.

2.3 Water from Humidity

The Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB based in Stuttgart with Logos Innovationen is developing a system to capture water vapor in air for conversion to drinkable water. The site for the project will be the Negev Desert of Israel where the average humidity is about sixty-four percent8. The system will feature a tower to circulate a hygroscopic brine solution to absorb water vapor from the air and drain the captured water down to a tank under vacuum pressure8.

Heat from thermal solar collectors and power from photovoltaic solar collectors will release the water from the brine8. A pump will circulate the regenerated brine to absorb water again8. While this system is in development for desert conditions, the technology and premise is suitable for hot and humid climates to remove water vapor and lesson the energy requirements from building operation with air conditioning equipment.

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2.4 Color-Changing Desiccant

Silica gels are usually transparent, but gradually turn hazy or milky when moisture is absorbed. Sorbead India has produced an additive that allows silica gels to have intense initial colors that change hue in response to the amount of moisture absorbed9. The granular or bead shaped silica gel by Sorbead India uses interlocking cavities to increase its surface area for attracting and trapping water molecules9. The beads are infused with chemicals like cobalt chloride to change color9. The color change intensifies as water is absorbed. It also fades as water is removed from the desiccant during regeneration. Color change properties in the working fluid of the hygroscopic building envelope can allow building inhabitants to understand the process of water absorption and observe the changing architectural aesthetic and performance so that unseen climatic processes become visible.

2.5 Flexible Solar Cells

Highly absorptive and flexible silicon solar cell wires developed by researchers at the California Institute of Technology and the University of Illinois at UrbanaChampaign can be thin and transparent to be useful in windows of buildings10. The small wires, which are about 1 micron in diameter, use less material than current photovoltaic solar cells11. Researchers at the California Institute of Technology and University of Illinois at Urbana-Champaign are developing lighter solar cells that use one percent of material needed to make con-

ventional solar cells for about the same energy conversion output.

2.6 LEAFHouse 2007 Solar Decathlon University of Maryland

The University of Maryland LEAFHouse project, “Leading Everyone to an Abundant Future”, demonstrated a regenerative liquid desiccant in a water wall system at the 2007 Solar Decathlon in Washington, D.C. LEAFHouse uses a number of sustainable technologies such as photovoltaic panels, solar hot water, light dimming system, greywater recycling, rainwater collection, energy recovery ventilator and radiant floor. The liquid desiccant water wall is used to control humidity and is placed within the interior of the main room. The system uses concentrated calcium chloride mixed with water to lower the vapor pressure of the solution below the vapor pressure of the main room. Calcium chloride is a highly absorptive salt mixed into the waterfall wall to capture moisture from the air12. Any increase in the room’s water vapor will be absorbed by the liquid desiccant when it is in contact with air at the waterfall area. The liquid desiccant system can reverse itself if the room’s humidity level decreases. The amount of surface area that the waterfall wall exposes to the interior of the room heightens the vapor transfer from the interior room to the liquid desiccant. Heat from solar water collectors regenerates the liquid desiccant system. The liquid desiccant is heated and the excess water is evaporated to the outside12. The system removes water from the air using

Figure 5: Simple diagram section of LEAFHouse liquid waterfall wall system.

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little energy and requiring air conditioning equipment for cooling the interior spaces12. A video of the liquid desiccant wall system can be viewed online13. Figure 5 is a conceptual diagram that shows the position of the liquid waterfall wall to the outside of the LEAFHouse and the interior space of the room where the wall is installed. The LEAFHouse uses a liquid water vapor absorbing medium to moderate interior humidity conditions. It is a practical demonstration of potential systems that reduce the intensive energy requirements of air conditioning equipment in hot and humid climates.

2.7 Eighty-Year History of Open Absorption Systems

Open absorption systems closely resemble current approaches to liquid desiccant systems for dehumidification and energy reduction in hot and humid climates. It is a process that is nearly eighty years in development from the work of Edmund Altenkirch and Francis Bichowsky14. Open absorption systems are used in industrial applications useful in handling latent loads, leaving sensible loads to traditional air conditioning systems14.

In this model, the liquid desiccant is a system-dominant approach for removing latent heat from hot and humid climates. The advantage of the open absorption systems over conventional air handling conditioning systems is that they can work in lower supply temperatures and use energy from alternate thermal energy sources such as solar photovoltaic, effluents of co-generation plants and heat from urban waste in district heating plants14. Open absorption systems are simple to build and operate, but susceptible to corrosion when metallic components come in contact with liquid desiccants

such as lithium chloride and oxygen14. Table 1 shows the benefits of using liquid desiccant systems for increasing comfort, lowering energy demands, improving indoor air quality and maintaining clean indoor spaces.

Liquid desiccant systems have a potential to be used in commercial HVAC systems for applications that favor a ratio of latent load to total cooling loads greater than thirty percent such as dry air laboratory spaces, computer rooms, libraries, museums and in spaces with typical indoor air quality problems such as schools, hospitals, offices, meeting halls, and dormitories15. Currently liquid desiccants are used in industrial dehumidifiers because of the cost to use these systems with lithium-based desiccants16.

3.0 CHARACTERISTICS OF HYGROSCOPIC ENVELOPE

Why is a hygroscopic building envelope different than conventional HVAC or liquid desiccant system? The United States uses more energy than any other nation in the world by more than 21 percent18. The commercial sector in the United States uses the same energy to heat and cool spaces as it uses for lighting18. Consequently, much of the water used by commercial buildings is to heat and cool spaces, irrigate landscaping and use in toilets and sinks19. In conventional HVAC systems, condensate vapor that forms in the air as it passes over cold refrigerant coils drains to the sanitary sewer system. In a liquid desiccant system, the excess water is exhausted to outside air. A potential water reduction and building operations costs opportunity is lost in both of these processes. The hygroscopic building envelope impacts energy used for cooling spaces in hot

Table 1: Benefits of dehumidification with desiccants, adapted from15.

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Increased Comfort

Desiccant unit independently controls humidity. Conventional cooling system controls temperature.

Lower Peak Electric Demand

Alternate energy sources such as natural gas, steam and heat recovery for use in cooling latent cooling loads.

Heat Recovery Options

Engine driven chillers, cogenerators, steam condensate.

Dry Duct Systems

Conventional systems allow humid air and dust in ducting allows fungus growth, bacteria growth and reduction in indoor air quality.

CFC Free

Desiccant systems do not use CFC’s for moisture removal.

Improved Indoor Air Quality

Appropriate levels of fresh air to reduce levels of air borne bacteria.

Reduced Building Maintenance

Reduces building maintenance by decreasing high humidity levels for remediation of mold and mildew, corrosion, replacement of wall and window coverings and carpeting.

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and humid climates—where it matters most in the United States. This impacts both energy use and water use.

The hygroscopic building envelope will reuse the water harvested from water vapor in the outside air. The harvested water can be filtered to provide water for sinks and toilets, irrigation and grey water. There is an opportunity to provide pure potable water. The hygroscopic building envelope will also harvest sun and wind energy.

The function of an innovative building envelope for hot and humid climates is based upon the following characteristics: site topography, site orientation, energy and water harvesting, use of hygroscopic brine solutions and a computational control system.

3.1 Site Topography Influences Hygroscopic Effect

Site topography influences the performance of the hygroscopic effect. The hygroscopic building envelope must be vertically located as high as possible with respect to the ground. Figure 6 shows a building situated on the higher elevations of a site in a hot and humid climate. By locating a structure higher in elevation, there is a reasonable decrease in pressure and temperature.

Figure 6: Site plan and site section versus saturation temperature and pressure23.

A decrease in temperature and pressure reduces the capacity of air to absorb more water vapor. The water vapor condenses from the air as water with a change in latent heat to sensible heat lost to the environment.

A common response in hot and humid environments is to raise a structure above the ground. At ground, the air is warmer and pressure and temperature increase.

The capacity of air to absorb water vapor is increased.

The change of water vapor in the air from sensible heat to latent heat also increases. The hygroscopic building envelope can also be used with strategies to ventilate the underside of a lightweight overall building structure.

Site topography can lower the temperature of outside air reducing the demand on mechanical systems that only cool in a hygroscopic building envelope. This can greatly reduce energy requirements in the operation of a building.

3.2 Site and Building Orientation Affects Hygroscopic Effect

Buildings should provide natural ventilation whenever possible and promote passive strategies in conjunction with active strategies when required as a secondary system based on renewable energy sources20. The hygroscopic building envelope makes use of natural ventilation to promote air exchange with inside and outside air.

The hygroscopic building envelope does not use energy intensive mechanical systems. It is a building envelope that uses pressure differences and selective environmental interactions to transfer energy in various forms.

Tuning building form to site and climate is a process to orient the building to achieve maximum sun and wind energy harvesting at layers one and three (see Figure 3). The hygroscopic building envelope creates pressure differences at the windward and leeward side of a building to move air and water using natural phenomenon.

The red dashed line in Figure 8 is the location of layer one, which is the windward facing hygroscopic building boundary. The green dashed line at layer three is the location of integrated wind driven generators that receives air pulled through the building on the leeward side of the building. The orientation in the plan diagram in Figure 7 can be for a location where wind direction and speed are dominantly from the south west. Rather than orient the building to face the wind perpendicularly, the building is oriented to allow air to flow diagonally through openings in layer one. The dehumidified air is now in layer two where it is being cooled by HVAC system to mix with interior spaces. Warmer air is pulled through the building by negative suction at the leeward side as shown in Figure 7 at layer three.

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Figure 7: Simple building plan of hygroscopic climatic modulated boundary23.

Figure 8: Hygroscopic building envelope system diagram of layer one.

3.3 Design of the Building Form Influences Hygroscopic Effect

The design of building form that uses a hygroscopic building envelope can take advantage of natural phenomenon such as wind energy. Wind flows through the site and over the building to create controlled pressure

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changes for improved natural cross ventilation. The flow of air over building surfaces can be modulated. A metaphor for understanding this method is to understand the process of using wind tunnels to streamline the design and form of automobiles to reduce wind drag and heighten performance. Sculpting the overall building

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form and its façade to heighten the hygroscopic effect of natural cross ventilation in a hygroscopic building envelope is a new kind of performance measurement for advanced building façade development. Shaping varying aperture sizes at layer one introduces Venturi effect that can channel air from the exterior to interior building spaces and increase air pressure and velocity. The Venturi apertures at layer one increase natural cross ventilation to penetrate to the interior at layer two. The use of pressure changes to create natural cross ventilation is not a new idea. Building façade development using Venturi effect pressure differences has been used for the GSW Headquarters in Berlin designed by Sauerbruch & Hutton Architects, with engineering by Arup in 2002. The GSW Headquarters uses its building skin similar to the metaphor of a living organism that breathes by taking in air using operable flaps to change form in adapting to gradient environmental conditions22. It is naturally ventilated for seventy percent of the year22. Natural ventilation is accomplished by moving air in low wind conditions through single-glazed skin on the east façade, an inner double-glazed west façade and out through the top of a thermal flue, irrespective of the wind direction22. Ventilation is induced by the automatic control of dampers that maintains balanced air changes to building interior. Natural ventilation in the GSW Headquarters must switch to mechanical ventilation during extreme seasonal conditions; it requires windows to be closed. The fans installed within the building façade operate from fully open to completely closed to automatically compensate for increase or decrease in wind flow at the windward side of the building. The hygroscopic building façade at layer two enhances this idea pioneered by the GSW Headquarters by harvesting wind at the leeward side for energy generation. In layer three of the hygroscopic building envelope, required air changes for fresh air are balanced by constant pressure in the interior spaces by building façade fans at the leeward side of the building.

3.4 Hygroscopic Building Envelope Functioning

Humidity is a measure of water vapor in a gaseous state such as air3. As more water vapor mixes with air molecules, it lowers the ability of the air to accept additional water vapor3. Relative humidity is a ratio that compares the actual amount of water vapor in the air with the capacity of the air at a specific saturation temperature and pressure3. Relative humidity is inversely proportional to the saturation temperature and pressure such that when either temperature or pressure decreases or increases, relative humidity will, in the opposite direction, increase or decrease3. As saturation temperature and pressure rise, relative humidity will lower. The property of humidity in response to temperature and pressure

can be a natural phenomenon that has advantages in a hygroscopic building envelope.

Figure 8 is a system diagram of layer one showing detail of the hygroscopic climatic modulated building envelope where outside air is dehumidified. It would work by using a hygroscopic brine solution to remove the latent heat from air moisture from exterior conditions in a hot and humid climate. The humid air is dehumidified and can be delivered to a conventional HVAC system. It is preferred to use a chilled beam system.

The chilled beam system works by utilizing chilled water and air movement to remove sensible heat from the interior space23. A hygroscopic building envelope and a chilled beam system can work together to dehumidify and cool interior air for comfort in a hot and humid climate to realize significant energy reductions. Figure 8 shows other characteristics of the hygroscopic building envelope system such as delivering the water collected from water vapor to potable water for building use.

Other theoretical characteristics are energy production through solar and wind collection by using photovoltaic solar collectors at layer one and small building façade wind generators at layer three of the hygroscopic building envelope model. The individual characteristics of the boundary condition work as a system to reduce the reliance upon more energy intensive means to maintain habitable conditions in hot and humid climates.

3.5 Hygroscopic Brine Solution

Saturated salt solutions can reduce the amount of water vapor available for evaporation by reducing the temperature and pressure of air volume24. A hygroscopic brine solution absorbs moisture from the air to change thermal comfort from a humid condition to a naturally dehumidified condition. Natural dehumidification by a hygroscopic brine solution can make it possible to require air conditioning for cooling purposes only. It can reduce energy consumption in the operation of a building. Figure 9 depicts regeneration cycle of the hygroscopic brine solution that occurs within the hygroscopic building envelope. Water vapor from hot and humid climates is absorbed by a hygroscopic brine solution.

Absorption is made possible because of the low water content of the hygroscopic solution. The hygroscopic solution moves through the building envelope to absorb water vapor through the thermal driving pressure in response to the solution’s temperature change and a pump if more flow is necessary. The hygroscopic brine solution contains more water content. The solution then flows downward where it can be heated and the excess water evaporated. The excess water is evaporated and condensed as potable water for use in the building.

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Figure 9: Hygroscopic brine solution regeneration diagram.

3.6 Hygroscopic Brine Solution Transport

In a biomimetic response similar to that of the Australian Thorny Devil and the Texas Horned Lizard, openings in the hygroscopic building faรงade at layer one provide areas available for water absorption through direct contact below the upper layers of a building boundary through very small, thin and breathable micro water transport tubes. A natural convective flow of hygroscopic brine with warm high water content and cooler low water content circulates through the transport tube system.

A pump can derive power from solar photovoltaic conversion at layer one to circulate recharged hygroscopic

brine solution to increase rate of flow, if necessary. The hygroscopic brine solution transport is circulated by a thermal driving pressure through the micro tubes where water is absorbed, drained, collected, regenerated and sent back up through the system at layer one. Figure 10 is a simple building section diagram of how this system may function in context. The building structure is elevated above grade. The red dashed line is located at the windward facing hygroscopic building faรงade and represents layer one. The green dashed line is the location of the wind driven generators on the leeward facing hygroscopic building faรงade side where air is exhausted

Figure 10: Simple building section of hygroscopic climatic modulated boundary23.

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at layer three by natural cross ventilation. The material properties of the hygroscopic brine in its capillary water transport structures with thin walls must allow air and light to pass from the exterior to the interior. Air must interact with the hygroscopic building envelope to diffuse and separate out the water vapor. The subtle change in local pressure and air flow drives fluid through the capillary tubes of hygroscopic brine solution. At one scale, the small bundles of very small tube structures transport hygroscopic brine solution and water. At another scale, the surface area of these very small water transport tubes as bundles provide enough mass where needed to develop necessary insulation properties. The capillary water transport structures act as a membrane that can pass air and collect water from outside air.

4.0 COMPUTATIONAL CONTROL ALGORITHM 4.1 Sensing

The hygroscopic building envelope can sense and respond. It can sense information that has been gathered and passed through analysis using a mixture of hardware and software. Driven by the varied, differential, gradient and dynamic conditions of the exterior environment of hot and humid climate, the hygroscopic building envelope responds to these conditions by altering the absorption characteristics of the hygroscopic brine solution. It can use the pump to provide more flow to areas of the building envelope that have more water vapor from the outside air. The flow of hygroscopic brine solution at layer one is not uniformly constant throughout the building envelope. The system pulls more water vapor from the air and into solution by raising the salinity to reduce pressure and temperature locally at specific areas.

4.2 Computational Control System

Computational control can gather environmental data.

External environmental forces such as wind pressure can act as an environmental tectonic instrument. Pressure changes sensitive to environmental conditions with changes in moisture in outside air become dynamic data. The selection of an environmental factor such as wind pressure acting on the windward side of a building and influencing the opening and closing of flaps at layer three of the hygroscopic building envelope is important in the environmental data. This is meaningful data to a computational control system and is a metaphor to understand how the relationship of respective weight and selection of factors work to enable a response condition25.

4.3 Integration of Materials and Technology

Computational parameters for a hygroscopic building envelope establish a set of conditions for changes in water vapor detected over time. Building envelope surface area performs as a distributed material system for water harvesting. Water harvesting uses a capillary transport sensing tube system, generative air circulation and integrated solar cells in an experimental fiber form. Controls within the material system respond to varying environmental conditions for the production of water, energy and air movement. Since most experiences of energy in buildings is automatic and opaque to the user, the automation of controls in a sealed environment independent of ability to sense changes in the external environment is mostly ignored26. The exterior is isolated in such a manner that the interior of a space is regulated in functions of cooling and heating through thermostats26.

There is no direct contact between the user and the energy use or resources except for the occasional climate control equipment or bill or malfunction of equipment26.

A color change property in the hygroscopic brine solution is visible to both the building occupant and the observer from the exterior of the hygroscopic boundary.

The experience of the hygroscopic boundary working fluid in operation is dynamic and real-time response to the environment. The material color change properties of the hygroscopic brine solution is a subtle modulation architectural aesthetic. Change color is due to a change in saturation and density of air moisture. The response indicates more hygroscopic brine recharge volume to absorb moisture in the air intake from the exterior and eventual reclamation by the hygroscopic building envelope system. Building form generation is due to the use of digital technologies that augment site climatic design with parameters based on air and moisture concentrations. Building form is a reflection of local incident air flow and pressure modulations upon the building envelope at any point with dynamic sensing.

5.0 CONCLUSION

This article has allowed the author to understand the characteristics of a hygroscopic building envelope, how it functions, design possibilities within the hygroscopic building envelope model, the importance of the past work and to define potential properties. The model is a strategy for dehumidifying air using natural phenomenon in hot and humid climates. The hygroscopic building envelope is explored. A computational control system is explored for regulation of hygroscopic brine to correspond with uneven environmental conditions. Design for the hygroscopic building faรงade is explored with

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a visual feedback of color change to express environmental conditions of humidity percentage and working of the system in real time.

The characteristics of a hygroscopic building envelope are processes of energy transfer, solar and wind collection and water harvesting. The hygroscopic climatic modulated boundary can meet the challenge to use passive and sustainable practices that modify an often undesirable condition found in hot and humid climates.

Research in the extraction of water from water vapor in the air and biological processes for water transport provide a theoretical strategy for understanding how a hygroscopic building envelope might be designed in a hot and humid climate to reduce energy consumption in buildings.

The hygroscopic boundary is an idea to understand how it works as a passive-active envelope. It does not stop at the exterior, nor does it end at the edge of the interior of a building. It modulates as a more open, functional system from the building exterior to the interior. The hygroscopic boundary captures moisture and heat and

produces water and electricity. The integrated building envelope system differs from conventional systems because it does not depend primarily on the supplying or removing of energy through mechanically dominant active means based on fossil fuels.

In summary, all of these activities in combination with site characteristics appropriate to hot and humid climates can create a condition that results in a lowering of dependence on air conditioning equipment for dehumidification. Instead of air conditioning equipment, a chilled beam system can be used for cooling an interior space by removing sensible heat. Lower energy by the use of passive cooling from chilled beam systems and small amounts of renewable energy from the motion of very small embedded wind driven generators in building surfaces could provide enhanced air circulation.

The dynamic mixture of air moisture, wind speed, pressure and temperature allow for an architectural design to work in a range of constantly changing environmental conditions by using material and system elements27.

The climatic conditions are specifically for hot and hu-

Table 2: Hygroscopic building envelope proposed benefits.

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Increased Comfort via Envelope Dominant System

Independent control of humidity and temperature because hygroscopic building envelope controls humidity while conventional system or active chilled beam systems controls temperature.

Lower Peak Electric Demand

Switch latent cooling to alternate energy sources such as thermodynamic transformation in entropy energy recovery, fiber solar photovoltaic system, air flow pressure and driven wind generators, steam, and heat recovery.

Heat Recovery

Heat recovery from latent heat to sensible heat energy transformation.

No Duct Systems

Hygroscopic building envelope has the potential to eliminate ducts as dry air is delivered to the interior space for active sensible cooling system.

Increased Latent Loads and Levels of Outside Air

Hygroscopic building envelope can use computational control system to increase necessary concentration of hygroscopic solution and thermal driving pressure to meet increase in total cooling and latent loads from increasing levels of outside air.

CFC Free

Hygroscopic brine solution does not use CFC’s for moisture removal.

Improved Indoor Air Quality

Hygroscopic building envelope uses natural ventilation as well as a computational control system for increasing ventilation through renewable sources to potentially improve indoor air quality. The hygroscopic brine solution uses a salt that naturally inhibits microbiological growth by maintaining lower humidity levels. Lower humidity in building interior spaces prevents moisture, mildew and rot in building materials.

Renewable Resource Collector

Hygroscopic building envelope renews and collects both water and energy for reuse.

Hygroscopic Climatic Modulated Boundaries

mid conditions, which have an abundance of air moisture. The building envelope reduces energy requirements needed to dehumidify and cool interior spaces in hot and humid climates. Hygroscopic brine solution absorbs water vapor and responds with color change to exhibit itself as a real-time architectural aesthetic of exterior outside conditions. There is a potential to use wind driven generators and thin and flexible solar collecting photovoltaic fibers for onsite energy generation that supports the hygroscopic process. Table 2 shows various potential benefits of the hygroscopic climatic modulated boundary model for contributions to better interior air quality, renewable resources and its effects on the environment.

There are few potential issues that must be dealt with when considering the hygroscopic building envelope model such as corrosion, component consolidation, realization of the model, cost and construction and the development of key technologies for commercial use. Possible hygroscopic brine solutions use lithium chloride and calcium chloride as the most effective. In the presence of oxygen, hygroscopic solutions containing lithium chloride are corrosive when in contact with metallic components. Issues with corroded metallic components have been experienced in liquid desiccant systems used in industrial applications and have yet to be available for widespread use in commercial HVAC systems. Calcium chloride, when mixed with water, heats up tremendously and can burn human skin. Sodium chloride mixed with water is the safest and can be used, but is not as effective as calcium chloride. The hygroscopic building envelope favors the use of sodium chloride and emerging natural high strength organic bio-plastics for the transport system.

The hygroscopic brine solution must contact incoming air from the outside while it is still liquid and flow within the building envelope. The hygroscopic building envelope must deliver relatively dry air to the interior for a system like active chilled beams to avoid the issue of condensate forming on these systems. The realization of the hygroscopic building envelope involves the design and prototyping of a working model to understand and solve problems for potential commercial use. The cost of the components, design of the computational control and hygroscopic brine liquid transport systems must be understood.

REFERENCES

[1] Architecture 2030, (2010) The Building Sector: A Hidden Culprit, Retrieved on 2/2010 from http://www. architecture2030.org/current_situation/building_sector. html.

[2] Wikipedia, (2010). Hygroscopy, Retrieved on 2/2010 from http://en.wikipedia.org/wiki/Hygroscopy.

[3] USA Today, (2010). Understanding Humidity, Retrieved on 2/2010 from http://www.usatoday.com/ weather/whumdef.htm.

[4] Wikipedia, (2010). Humid Subtropical Climate, Retrieved on 2/2010 from http://en.wikipedia.org/wiki/Humid_subtropical_climate.

[5] Wikipedia, (2010). Bionics, Retrieved on 2/2010 from http://en.wikipedia.org/wiki/Bionics.

[6] Doan, A., (2007). “Green Building in Zimbabwe Modeled After Termite Mounds”, Retrieved on April 02, 2010 from http://www.inhabitat.com/2007/12/10/ building-modelled-on-termites-eastgate-centre-in-zimbabwe/.

[7] Jones, D., (2008). “Desert Lizards Get a Skinful”, Retrieved on 2/2010 from http://www.australasianscience.com.au/bi2008/298lizards.pdf.

[8] Fraunhofer-Gesellschaft, (2009). “Drinking Water from Air Humidity”, Fraunhofer Research News, Fraunhofer-Gesellschaft Press and Public Relations.

[9] _____ (2010). “Color-Changing Desiccant”, Retrieved on 2/2010 from https://www.inventables.com/ technologies/color-changing-desiccant.

[10] ____ (2010). “Caltech Researchers Create Highly Absorbing, Flexible Solar Cells with Silicon Wire Arrays”, Retrieved on 2/2010 from http://media.caltech.edu/ press_releases/13325.

[11] Steenhuysen, J., (2010). “A New Wire Twist on Silicon Solar Cells”, Retrieved on 2/2010 from http://www. reuters.com/article/idUSTRE61D1TK20100214.

[12] _____ (2007). “Liquid Desiccant Waterfall”, Retrieved on 2/2010 from http://solarteam.org/page. php?id=641.

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[13] ____ (2007). “Liquid Desiccant Wall”, Retrieved on 2/2010 from http://www.youtube.com/ watch?v=EtFd2NEj9yw.

[14] Conde-Petit, M., (2007). “Liquid Desiccant-Based Air-Conditioning Systems – LDACS”, Proceedings of the 1st European Conference on Polygeneration, Retrieved April 2, 2010 from http://six6.region-stuttgart. de/sixcms/media.php/773/19_Conde_M.pdf.

[15] Desiccant Cooling Technology Resource Guide, (1999). Retrieved April 2, 2010 from http://www.wbdg. org/ccb/COOL/maindct1.pdf.

[16] Lowenstein, A., (2008). “Review of Liquid Desiccant Technology for HVAC Applications”, Retrieved April 02, 2010 from http://www.thefreelibrary.com/Review of liquid desiccant technology for HVAC applications.a0201618274.

[17] USA Today, (2010). “Understanding Air Density and its Effects”, Retrieved on 2/2010 from http://www. usatoday.com/weather/wdensity.htm.

[18] U.S. Department of Energy, (2009). 2009 Buildings Energy Data Book. Retrieved April 24, 2010, from http://buildingsdatabook.eren.doe.gov/docs/DataBooks/2009_BEDB_Updated.pdf [19] Center for Sustainable Systems, University of Michigan, (2009). “Commercial Buildings Factsheet”, (Pub. No. CSS05-05).

[20] Mclean, W., Silver, P. and Whitsett, D., (2008). Introduction to Architecture Technology, London, United Kingdom: Laurence King Publishing Ltd. [21] Lechner, N., (2009). Heating, Cooling, Lighting: Sustainable Design Methods for Architect, Hoboken, NJ: John Wiley & Sons, Inc. [22] Wiggington, M. and Harris, J., (2003). “Breathing in Berlin”, Architecture Week pp. E1.1-E1.2.

[23] Wikipedia, (2010). “Chilled Beam”, Retrieved March 26, 2010 from http://en.wikipedia.org/wiki/ Chilled_beam.

[24] ____ (2009). “Understanding Humidity”, Retrieved February 13, 2010 from http://www.chipsensors.com/ documents/AN001-UnderstandingHumidity.pdf.

54

[25] Ottchen, C., (2009). “The Future of Information Modelling and the End of Theory: Less is Limited, More is Different”, Architectural Design, Vol. 79, No. 2, pp.

22-27.

[26] Grondzik, W., Kwok, A., Reynolds, J. and Stein, B., (2006). Mechanical and Electrical Equipment for Buildings, 10th ed., Hoboken, NJ: John Wiley & Sons.

[27] Hensel, M. and Menges, A., (2006). “Differentiation and Performance: Multi-Performance Architectures and Modulated Environments”, Architectural Design, Vol. 76, No. 2, pp. 60-63.

Comparative Analysis of Flooring Materials

04.

COMPARATIVE ANALYSIS OF FLOORING MATERIALS: Environmental and Economic Performance

Ajla Aksamija, Ph.D., LEEDÂŽ AP BD+C, CDT ajla.aksamija@perkinswill.com ABSTRACT The environmental impact of flooring materials is the aggregate of impacts of raw material properties and composition across all stages of the product life cycle including extraction, manufacturing, packaging and transportation, use and disposal. In this analysis, linoleum, vinyl composition tile (VCT), nylon carpet tile, composite marble tile, ceramic tile, terrazzo, cork and rubber flooring are compared. Life cycle assessment is performed for these selected materials, where both environmental and economic factors are examined. It is important to understand performance of various materials when design factors are changed. Therefore, this analysis compares environmental impact when design requirements are varied and material characteristics are constant.

Past research is presented, where relative results generally agree among several studies. However, various methodologies have been utilized for lifecycle assessment with differing measurements for environmental performance, thus comparative analysis is not permissible. Economic factors have not been reported in previous studies, therefore, the primary objective of this study is to investigate environmental and economic performance of various flooring materials.

Building for Environmental and Economic Sustainability (BEES) software is utilized to measure combinatory performance of the selected materials for raw material acquisition, manufacturing process, transportation, installation, use, recycling and waste management. Three scenarios are investigated, where initially equal weights are given to both environmental and economic factors. Second case is primarily associated with economic and third with the environmental performance. Results indicate that cork, linoleum and rubber flooring materials should be considered when environmental factors are the primary concern and when both environmental and economic factors are equally weighted.

KEYWORDS: life cycle analysis, environmental performance, flooring materials 1.0 INTRODUCTION

Material selection is a crucial component of sustainable design and sustainable selection, where specification decisions are based upon numerous factors. Among a few are material properties, production, cost and effects on indoor air quality. Prioritizing materials based on their environmental impact is becoming a common practice, with the objective to minimize negative environmental impacts. However, measuring environmental impact for various building materials is relatively challenging, since complex factors and relationships must be taken into account1.

This study compares flooring materials based on environmental and economic costs to understand benefits and drawbacks of choosing certain products. Literature review presents several past studies and their results. Although general conclusions of these studies are comparable, it should be noted that yielded results vary depending on the input information and analysis methodology. In order to understand environmental performance of several flooring materials in relation to economic factors, life cycle assessment (LCA) is conducted for linoleum, vinyl composition tile, nylon carpet tile, composite marble tile, ceramic tile, terrazzo, cork and rubber flooring.

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2.0 RESEARCH CONTEXT AND PAST STUDIES

Different approaches in assessing environmental impact respond to different questions and interpretation of results must take into account analysis methodologies.

Relationships between different methodologies can be: • Consecutive, where results of one approach become input data for another approach • Complementary, where two approaches use the same basis for comparison, but yield different results since different dimensions are investigated • Competing, where two approaches use the same method for comparison and investigate the same dimensions, but yield different results since different assumptions are made during the analysis • Encompassing, where a certain approach is an integral part of another • Overlapping, where both approaches yield same results since the methodology is identical.

LCA considers cradle-to-grave impacts, where material contents, production, energy requirements, and waste are analyzed to produce a total environmental impact.

ISO 14040-14043 standards specify the methodology that should be followed, where inventory data are associated with specific environmental impact categories such as depletion of abiotic resources, global warming, ozone layer depletion, human toxicity, water toxicity, acidification, nutrification and photochemical oxidant creation2, 3, 4. Inventory analysis is typically utilized to

compare productive cycle, material preparation, raw materials, manufacturing, packaging, transportation, use and disposal for a functional unit of a material.

Building for Environmental and Economic Sustainability (BEES) software measures the environmental performance of building products using the ISO 14040 series of standards and ASTM E917-05e1 standard for measuring economic performance5. Detailed description of the model components is presented later in this article.

Several previous studies have investigated environmental impact of flooring materials and are briefly reviewed.

Potting and Block investigated environmental performance of linoleum, vinyl, wool carpet and nylon carpet6.

Impacts that were analyzed include depletion of raw materials, energy requirement for production, global warming, acidification, ozone creation, ozone depletion, eutrophication, waste production and effects on human health. Functional area of 10.76 square feet (1m2) was studied with set lifetime of 15 years for all four types of materials. Environmental profiles and results of this study are shown in Table 1. Conclusions indicated that linoleum is the most environmentally favorable material and that vinyl is the least. Differentiation between different types of carpet flooring based on environmental performance is more difficult and conclusion about preferred carpet flooring was not drawn. Authors indicated that maintenance and cost analysis were not performed and that further analysis is desirable.

Table 1: Environmental profile per functional area of different flooring materials (Source Potting and Block, 1995).

56

Impact

Linoleum

Vinyl

Wool carpet

Nylon carpet

Cumulative energy requirement (MJ) Feedstock requirement Process energy

— 40

97 103

48 109

154 175

Global warming (g of CO2 equivalents)

2600

9500

64300

13500

Eutraphication (g of phosphate equivalents)

60

2

1550

14

Acidification (g of SOx equivalents)

10

170

170

80

Ozone creation (g of ethylene equivalents)

4

18

44

17

Waste (g) Hazardous waste Non-hazardous waste

400 1500

600 2000

600 3400

650 2800

Comparative Analysis of Flooring Materials

Table 2: Environmental rating for flooring materials (Source: Altshuler et al., 2007).

Impact catergory

Sheet vinyl

VCT

Linoleum

Cork

Acidification

1

5

6

10

Eutrophication

4

8

1

10

Smog

1

5

4

10

Ozone depletion

1

5

6

7

Global climate change

1

3

6

10

Fossil fuel depletion

2

7

1

9

Ecotoxicity

1

6

4

10

Table 3: Ratings for health effects associated with flooring materials (Source: Altshuler et al., 2007).

Impact catergory

Material

Impact category Material

Cancer

1. Sheet vinyl 2. VCT 3. Linoleum 4. Cork

Total human health

Petersen and Solberg conducted an analysis for greenhouse gas emissions and associated costs of wood flooring, linoleum, vinyl, wool carpet and nylon carpet7. The focus of the study was to analyze wood products and competing materials and their effect on global warming, particularly emission of greenhouse gases (CO2, CH4 and N2O). Analyzed functional area was 10.76 square feet (1m2). Emission rates were reported in relation to avoided tons of greenhouse gases per cubic meter of flooring and the results are 0.1-1.9 for linoleum, 0.22.3 for vinyl, 0.9-2.5 for nylon carpet and 11.8-15.5 for wool carpet. Authors noted that further research is necessary to link life cycle assessment with economic modeling.

US Green Building Council conducted an investigation into the environmental and health impacts of PVC materials for buildings. Two types of PVC-based materials for flooring were analyzed (sheet vinyl and vinyl composition tile), and two alternative non-PVC materials (linoleum and cork)8. Lifecycle assessment and risk assessment were performed, where LCA was based on Environmental Protection Agency’s TRACI method9. Impact categories included several environmental aspects such as acidification, ecotoxicity, eutrophication, fossil fuel depletion; combined environmental and health

1. VCT 2. Sheet vinyl 3. Linoleum 4. Cork

effects such as ozone layer depletion and smog; and health effects. EPA TRACI method relies on normalized measures of impact categories and their risks to the environment and human health, where severity of the risk is represented by a numeric value. Based on this method, lower values indicate that a certain material poses higher risks. Results of this study are shown in Tables 2 and 3.

All of the referenced past studies agree in relative rankings of environmental performance of different flooring materials. However, economic aspects have not been reported. In order to compare economic impacts, the following section focuses on the combination of environmental and economic factors.

3.0 ENVIRONMENTAL AND ECONOMIC PERFORMANCE 3.1 Methods of Measurement

Combined environmental and economic performance analysis of different flooring materials is necessary in order to compare benefits and adverse effects. Building for Environmental and Economic Sustainability 4.0 (BEES) software, developed by the National Institute of

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Impact Categories Global warming Habitat alteration Indoor air quality Eco-toxicity Human health Air pollutants

Environmental performance

Smog Acidification Eutrophication

Score

Ozone depletion Fossil fuel depletion Water intake First cost Future costs

Economic performance

Figure 1: BEES method for measuring environmental and economic impacts.

Standards and Technology, has been utilized for comparative analysis presented in this article10, 11. BEES measures environmental performance of building materials and products based on ISO 14040 series of standards and includes all stages of the product’s life (raw material acquisition, manufacturing, transportation, installation, use, recycling and waste management).

Economic performance is measured using the ASTM E917-05e1 standard for indicating economic impacts over product’s life-cycle5. Environmental and economic performances are combined to assign an overall impact measure using the ASTM standard for Multiattribute Decision Analysis.

Figure 1 indicates how these two performance indicators are weighted to assign scores for different materials. Environmental performance is measured across all life cycle stages for twelve categories (global warming, habitat alteration, indoor air quality, eco-toxicity, human health, air pollutants, smog, acidification, eutrophication, ozone depletion, fossil fuel depletion and water intake). Economic performance considers initial costs,

58

Table 4: Relative importance weights for environmental impact categories.

Impact catergory

Relative importance weight (%)

Global warming

16

Habitat alteration

16

Indoor air quality

11

Eco-toxicity

11

Human health

11

Air pollutants

6

Smog

6

Acidification

5

Eutrophication

5

Ozone depletion

5

Fossil fuel depletion

5

Water intake

3

Comparative Analysis of Flooring Materials

ECONOMIC PERFORMANCE

Construction Installation

Operation

Renovation or Demolition

ENVIRONMENTAL PERFORMANCE Manufacturing

Raw material acquisition

Figure 2: Product life cycle in relation to economic and environmental performance.

operation, maintenance, repair and disposal. Impact categories and relative importance are following Environmental Protection Agency’s recommendations11,12.

Table 4 shows relative importance weights for environmental categories, which are used to determine the overall score of individual materials in conjunction with economic performance.

In the BEES model, economic performance is measured over a 50-year study period. This same period is used to evaluate all products, even if they have different useful lives. Product replacements are accounted for materials that have shorter lives and end-of-life inventory flows are prorated for products with longer lives.

Figure 2 indicates how environmental and economic performance is measured. Environmental impact is computed for the entire life-cycle of a product, while economic performance for purchasing, operation and life cycle of the material within the 50-year period.

3.2 Limitations of the Model

The overall performance scores do not represent absolute performance, but rather proportional or relative performance among alternatives. Also, two types of products are included in the database—generic and specific products for which manufacturing data is available. Product composition, manufacturing methods, fuel mixes, transportation practices, useful lives and costs can vary from generic to individual products and therefore, generic product group may not represent the

performance of a specific product if the material composition is radically different. The analysis discussed in this article considers generic products.

3.3 Comparison of Flooring Materials

Eight different flooring materials are investigated: • Vinyl composition tile (VCT) • Linoleum • Nylon carpet tile • Ceramic tile • Composite marble tile • Terrazzo • Cork • Rubber Data for VCT, linoleum, nylon carpet tile, ceramic tile, composite marble tile, terrazzo and cork was obtained from BEES software, while data for rubber flooring was obtained from Gunther and Langowski13, Wilke et al.14, Tagisaki and Ito15, Chau et al.16 and calculated per functional unit to correspond to respective impact categories. BEES does not contain data for rubber flooring, thus these sources were used to compute impact values for functional unit of the material.

Lifetime expectancy and durability of the flooring material varies according to the type, but are normalized in this analysis as explained in the previous section. Typically, carpets are used for about ten years, although the technical lifetime can be up to fifteen years17. VCT life-

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time is around thirty years, but it depends on the location and wear. Linoleum lifetime is typically thirty to forty years. Ceramic tile lifetime is fifty years and terrazzo and composite marble tile is up to seventy-five years18. In terms of maintenance, VCT requires stripping and surface recoating. Linoleum only requires wet or dry cleaning. Energy requirements for vacuuming carpet flooring and cork flooring can be considerable. Ceramic tile, terrazzo and composite marble tile also require cleaning and occasional sealing.

Three different scenarios are investigated, where the initial scenario considers equal distribution between environmental and economic factors. Second scenario favors economic factors with 90 percent of weight. The last scenario favors environmental factors, where 90% of weight assigned to environmental impacts.

Equal distribution presents a design scenario where environmentally conscious design considerations are balanced by economic factors. Smaller normalized scores

indicate improved performance among alternatives.

Results show that although VCT would be the most economical choice of material, cork and linoleum flooring have much better environmental performance followed by rubber flooring and nylon carpet tile. Figure 3 shows overall performance scores for economic and environmental effects with equal distribution.

Figure 4 indicates scores when primarily economic considerations are taken into account. Figure 5 shows results when environmental performance is the driving factor.

Based on these scenarios, it is evident that different requirements can impact the overall relative score.

When economic and environmental considerations are weighted equally, VCT, linoleum flooring, cork and rubber flooring are comparable based on the overall score.

When environmental performance is the driving factor, cork, linoleum, rubber flooring and terrazzo are comparable.

60

50

Score

40

30

20

10

0 VCT

Linoleum

Nylon carpet tile

Ceramic tile

Marble tile

Terrazzo

Cork

Rubber

Environmental Performance 50%

1.7

0.7

2.1

5.6

38

1.6

0.2

4.1

Economic Performance 50%

1.4

3.1

5

6.3

12.6

15.5

6.1

2.5

Figure 3: Overall normalized performance score of different flooring materials with equal economic and environmental performance.

60

Comparative Analysis of Flooring Materials

35

30

25

Score

20

15

10

5

0 VCT

Linoleum

Nylon carpet tile

Ceramic tile

Marble tile

Terrazzo

Cork

Environmental Performance 10%

0.3

0.1

0.4

1.1

7.6

0.3

0.1

5.3

Economic Performance 90%

2.5

5.6

9

11.3

22.7

27.8

11

4.5

Rubber

Figure 4: Overall performance score of different flooring materials when economic performance is the primary design requirement..

80

70

60

Score

50

40

30

20

10

0 VCT

Linoleum

Nylon carpet tile

Ceramic tile

Marble tile

Terrazzo

Cork

Environmental Performance 90%

3.1

1.3

3.8

10.1

68.4

2.9

0.4

1.7

E Economic i P Performance f 10%

03 0.3

06 0.6

1

13 1.3

25 2.5

31 3.1

12 1.2

05 0.5

Rubber

Figure 5: Overall performance score of different flooring materials when environmental performance is the primary design requirement.

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3.4 Environmental Impact Categories Data

Data for selected environmental impact categories is reviewed in order to indicate values that were used to derive environmental performance scores presented in the previous section. Since the overall environmental performance score is derived by assigning relative weights to each impact category, this section presents actual numeric values that represent specific impacts for each material type. Data is presented for global warming impact, indoor air quality, acidification and fossil fuel depletion.

Figure 6 presents global warming impact for the selected flooring materials. Cork, linoleum and rubber flooring have smaller impact than VCT. Ceramic tile, nylon carpet tile, terrazzo and composite marble tile have similar global warming impact, where majority of carbon dioxide emissions are associated with raw material acquisition and the manufacturing process.

Figure 7 indicates indoor air quality impact, where terrazzo and cork have insignificant values and linoleum, rubber flooring and nylon carpet tile have low amount of total volatile organic compounds (TVOCs). Ceramic tile and composite marble tile have higher content of

TVOCs and VCT has the highest content, which is mainly associated with the operation phase.

Figure 8 shows acidification impact, where cork and linoleum flooring are the most favorable. Composite marble tile, ceramic tile and terrazzo have moderate values, while rubber flooring and nylon carpet tile have significant impacts. Impact values are highest for raw material acquisition and the manufacturing process and less for transportation.

Fossil fuel depletion impact is presented in Figure 9, where cork, rubber flooring and linoleum have smaller values than VCT. Ceramic tile, nylon carpet tile, terrazzo and composite marble tile have high impact rates, where values are primarily associated with raw materials acquisition, manufacturing and transportation.

Embodied energy indicates the amount of energy required to extract, process, transport, install and dispose or recycle a material. Figure 10 indicates embodied energy associated with selected flooring materials, where renewable and nonrenewable fractions are expressed per functional unit.

Global warming impact 3000

2600

2687 2581

2670

2500

g CO2/Unit

2000

1500

1060 1000

882.9 576

500 341

0 VCT

Linoleum

Nylon carpet tile

Ceramic tile

Figure 6: Global warming impact for selected flooring materials.

62

Composite marble tile

Terrazzo

Cork

Rubber

Comparative Analysis of Flooring Materials

Indoor Air Quality 0.12 0.11

0.1

g TVOCs//Unit

0.08

0.06

0.037

0.04

0.037

0.02 0.009

0.008

0.0037 0 VCT

Linoleum

Nylon carpet tile

Ceramic tile

Composite marble tile

0

0

Terrazzo

Cork

Rubber

Figure 7: Indoor air quality impact.

Acidification 2000 1839.63

1800.09

1800

1600

1400 1250.89

mg H+/Unit

1200 961.4

1000

807

800

600

569.5

530.79

400 181.72

200

0 VCT

Linoleum

Nylon carpet tile

Ceramic tile

Composite marble tile

Terrazzo

Cork

Rubber

Figure 8: Acidification impact for selected flooring materials.

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Fossil Fuel Depletion 12

11.29

10 8.91

MJ/Unit

8 6 53 6.53 6

4.19 4 2.67 1.92

2

0.85 0.42 0 VCT

Linoleum

Nylon carpet tile

Ceramic tile

Composite marble tile

Terrazzo

Cork

Rubber

Figure 9: Fossil fuel depletion impact.

Embodied Energy by Type 100 0.81

90

80

Renewable energy

Nonrenewable energy

70 0.04

MJ/Unit

60

50 88.14

1.1

40 1.41 63.3

30 0.42 10.34

20

37 6 37.6

2 32 2.32

30.8 10

22.33 0.18

15.3

0 VCT

Linoleum

Nylon carpet tile

Figure 10: Embodied energy for flooring materials.

64

13.94

5.21 Ceramic tile

Marble tile

Terrazzo

Cork

Rubber

Comparative Analysis of Flooring Materials

4.0 CONCLUSION

It is evident that there is not a single flooring material that has the best environmental performance across all selection criteria. Selection of flooring materials should be based on overall environmental impact, expected life-time of the material, considerations for maintenance and repair as well as performance for the particular functional application. Results of the life cycle assessment indicate that cork, linoleum and rubber flooring materials perform better than VCT for the majority of environmental impact categories. Hence, in scenarios balancing economics and environment, these flooring materials perform relatively similarly. Although VCT is the least expensive choice, environmental performance should be taken into account as well as its impact on indoor air quality. Nylon carpet tile has moderate environmental performance and higher costs over the life cycle. Terrazzo has relatively good environmental performance, but life cycle costs are high. Ceramic and composite marble tile have poor environmental performance, which is mainly associated with raw material acquisition and manufacturing process.

Results of the comparative analysis presented in this article agree with previous studies. However, they also illustrate economic performance aspects that have not been previously reported. It is evident that cork, linoleum and rubber flooring materials should be selected when environmental factors are the primary concern and when both environmental and economic factors are equally weighted. Higher life cycle cost of other material types (nylon carpet tile, terrazzo, ceramic and composite marble tile) and environmental performance should be taken into account when selecting appropriate flooring materials.

REFERENCES

[4] International Organization for Standardization, (1998). ISO/DIS 14043: Environmental Management— Life Cycle Assessment—Life Cycle Interpretation.

[5] American Society of Testing Materials, (2005).

ASTM E917-05 Standard Practice for Measuring LifeCycle Costs of Buildings and Building Systems, West Conshohocken, PA : American Society for Testing Materials.

[6] Jonsson, A., Tillman, A. M. and Svensson, T., (1997). “Life Cycle Assessment of Flooring Materials: Case Study”, Building and Environment, Vol. 32, No. 3, pp. 245-255.

[7] Petersen, A. K. and Solberg, B., (2004). “Greenhouse Gas Emissions and Costs over the Life Cycle of Wood and Alternative Flooring Materials”, Climatic Change, Vol. 64, pp. 143-167.

[8] Altshuler, K., Horst, S., Malin, N., Norris, G. and Nishioka, Y., (2007). Assessment of the Technical Basis for a PVC-Related Materials Credit for LEED, US Green Building Council: LEED Technical and Scientific Advisory Committee, Retrieved on 12/09/2008 from http:// www.usgbc.org/ShowFile.aspx?DocumentID=2372.

[9] Bare, J. C., Gloria, T. P. and Norris, G., (2006). “Development of the Method and US Normalization Database for Life Cycle Impact Assessment and Sustainability Metrics”, Environmental Science and Technology, Vol. 40, No. 16, pp. 5108-5115.

[10] Lippiat, B. C. and Boyles, A. S., (2001). “Using BEES to Select Cost-Effective Green Products”, International Journal of Life Cycle Assessment, Vol. 6, No. 2, pp. 76-80.

[1] Jonsson, A., (2000). “Tools and Methods for Environmental Assessment of Building Products—Methodological Analysis of Six Selected Approaches”, Building and Environment, Vol. 35, pp. 223-238.

[11] US Environmental Protection Agency, (2000). Toward Integrated Environmental Decision-Making, EPASAB-EC-00-011, Washington, DC: EPA Science Advisory Board.

[2] International Standards Organization, (1997). ISO/ DIS 14040: Environmental Management—Life Cycle Assessment—Principles and Framework.

[12] US Environmental Protection Agency, (1990). Reducing Risk: Setting Priorities and Strategies for Environmental Protection, EPA-SAB-EC-90-021, Washington, DC: EPA Science Advisory Board.

[3] International Standards Organization, (1998). ISO/ DIS 14042: Environmental Management—Life Cycle Assessment—Goal and Scope Definition and Inventory Analysis.

[13] Gunther, A. and Langowski, H. C., (1997). “Life Cycle Assessment Study of Resilient Floor Coverings”, International Journal of Life Cycle Assessment, Vol. 2, No. 2, pp. 73-80.

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[14] Wilke, O., Jann, O. and Brodner, D., (2004). “VOC and SVOC Emissions from Adhesives, Floor Coverings, and Complete Floor Structures”, Indoor Air, Vol. 14, No. 8, pp. 98-107.

[15] Takigasaki, K. and Kazuhide, I., (2007). “Estimation Method of Emission Rate and Effective Diffusion Coefficient using Micro Cell”, Proceedings of Clima 2007 Conference: Well Being Indoors.

[16] Chau, C. K., Yik, F. W., Hui, W. K., Liu, H. C. and Yu, H. K., (2007). “Environmental Impacts of Building Materials and Building Services Components for Commercial Buildings in Hong Kong”, Journal of Cleaner Production, Vol. 15, pp. 1840-1851.

[17] Potting, J. and Block, K., (1995). “Life Cycle Assessment of Four Types of Floor Coverings”, Journal of Cleaner Production, Vol. 3, No. 4, pp. 201-213.

[18] Building for Environmental and Economic Sustainability (BEES 4.0) Product List, National Institute of Standards and Technology.

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05.

URBAN WASTEWATER: A Renewable, Reliable Water Resource for Urban Farming Geeti Silwal, AICP, LEEDÂŽ AP, geeti.silwal@perkinswill.com ABSTRACT This article proposes a new urban ecological paradigm that values urban wastewater as a renewable, reliable, freshwater resource for urban farming. The potential benefits of time-tested solutions applied in urban settings have been largely unexplored due to lack of societal acceptance. The research presented herein investigates various aspects of closed-loop systems that localize wastewater treatment and capture the rich resource of nutrients and water, maximizing food production capabilities within urban settings. The focus is on theoretical underpinnings and general practical considerations. This includes an examination of the necessity of such a new paradigm, how closed-loop systems work, a brief risk/benefit analysis, case studies exemplifying both open- and closed-loop arrangements and a blueprint for further action. A water and nutrient closed loop design sensibility can be the foundation for healthy, self-sustained, resilient cities of the future. The article stops short of providing spatial configurations or detailed risk assessments, leaving those for further research.

KEYWORDS: urban food production, water and nutrient closed-loop systems, resource efficiency, wastewater treatment and reclamation, sustainable agriculture, wastewater-irrigated farming

Figure 1: An imagined day-in-the-life of a city fueled by and thriving on a resource-efficient, closed-loop development.

Image Credit: Charles Chiang, Perkins and Will

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1.0 INTRODUCTION

Food security and water scarcity are among the most pressing issues facing cities across the globe. Food security is defined as both economic and physical access to the food supply, sufficient in both quality and quantity, at all times regardless of climate and harvest, social level and income1. Water scarcity is the point at which, under prevailing institutional arrangements, the aggregate impact of all users impinges upon the supply or quality of water to the extent that the demand by all sectors, including the environment, cannot be satisfied fully2. Water scarcity is also defined as the condition in which annual water supplies per person drops below 1000 cubic meters2.

Our current wasteful consumption pattern is a linear flow of resources into and out of the city (Figure 2). All food is produced elsewhere and transported in to the city and all wastewater generated is pumped out to the vast water bodies outside the city. Wastewater or sewage is liquid waste discharged from homes and commercial premises to municipal sewer pipes and contains human excreta and used water. When produced mainly by households and commercial activities, it is called domestic or municipal wastewater. Municipal wastewater does not contain industrial effluents. For the purpose of discussion, this article has assumed wastewater to be municipal wastewater.

Access to fresh food for many cities is a constant challenge, while unsustainable consumption of potable water for non-potable uses is increasingly threatening our freshwater resources. With over half of the world’s population now living in cities, and those numbers consistently on the rise, urban demand for food and water will continue to escalate. As cities continue to grow, more

and more resources will be channeled into them generating more waste in the form of urban wastewater. The larger the growth in population, the larger the volume of wastewater generated. Thus, the current urban population growth trend will correlate to urban wastewater as an ever-growing resource for water as well as nutrients in it. Reliable and renewable, this supply of water and rich nutrients could be harnessed to support urban farming. Following the approach outlined herein, cities with their teeming millions could provide a solution to their own problems of food security and water scarcity.

2.0 FOOD AND WATER: THE CURRENT STATE OF AFFAIRS 2.1 Access to Fresh Food

The health of a community is closely related to access to affordable, fresh food choices. Historically, poorer neighborhoods have been underserved for fresh food.

Very often the cost of transporting fresh fruits and vegetables over long distances makes it unaffordable for communities of low income. They rely on cheaper, processed and packaged food options for their daily diet.

These neighborhoods and communities are commonly referred to as “food deserts” denoting limited access to affordable and nutritious food. Problems of obesity and diabetes abound in these communities due to forced, unhealthy food habits. The current food supply system denies these communities the basics of a healthy life.

2.2 Dwindling Freshwater Reserves

It is an oft-overlooked fact that the world’s freshwater supply is finite. Water on Earth, considered over a long span of time, has been constant. It changes its state often from liquid to vapor and to ice and back to liq-

Figure 2: Current flow of resources into and out of the city is linear and wasteful.

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uid. However, there is as much water on earth now as there was hundreds of millions of years ago. Freshwater reserves on Earth, on the other hand, are dwindling.

There is a higher percentage of salt water in our global ecosystem now. Freshwater accounts for only two and a half percent of all the water available on Earth. Twothirds of this is locked in glaciers, leaving less than one percent available to meet the water needs of all living being on Earth2.

As the population on Earth increases, the use of freshwater far exceeds the pace at which nature is able to replenish and recharge its reserves, leading to dwindling resources. In light of this, the single-use urban water consumption pattern of use and discharge is irrational in that as it puts unnecessary stress on the freshwater reserves of the planet. It is not only irresponsible, but highly inefficient to serve all city water needs with potable water, especially since on-site reclaimed water could be used to meet many of our water demands without requiring large-scale treatment facilities or long-distance transportation.

The World Water Development Report, published by the United Nations [2003], states that more than 50 percent of all countries will be facing a water crisis by 2025. Stress on our freshwater reserves has a direct relation to food production since agricultural use accounts for about 70 percent of the average global freshwater needs2. Though this pattern varies from country to country depending on the climate, population size and the economic condition, supplementing the freshwater needs of food production with alternative sources is an absolute imperative.

2.3 Vagaries of Nature

Rainfall is a primary source of irrigation in many predominantly agriculture economies. However, the amount of rainfall received by any region varies greatly from year to year, making the quantity and quality of harvest highly unpredictable. Agriculture is the first sector that gets affected in times of water shortage leading to an overall reduced food production. Given the uncertainties of nature, the world is placing a growing importance on wastewater as an alternative and reliable resource for irrigation. Australia and the arid and semi-arid countries in the Middle-East have been on the forefront of advancing cost-effective and low-energy technology for wastewater treatment and reuse in agriculture. This has helped supplement these nations’ scarce freshwater resources to ensure continuous food production while minimizing net water consumption.

2.4 Infrastructure Inadequacies

Conventionally, in the developed world, urban wastewater moves through an extensive network of hidden infrastructure to large-scale, centralized wastewater treatment facilities that remove suspended and dissolved toxins and then discharge the treated water into oceans and freshwater bodies. However, a vast number of cities in emerging economies cannot afford such an expensive network of infrastructure or do not have the resources to run and maintain it. Additionally, in many growing cities where treatment plants do exist, they do not have the capacity to treat all the wastewater generated. Most such cities provide only primary treatment, leaving most of the wastewater nutrients to be discharged into the receiving water bodies. Nitrogen and phosphorous, the primary nutrients in wastewater, so critical for plants, cause algae blooms that are harmful for marine life. The damage to marine life due to the

Figure 3: Open-loop (linear) potable water usage pattern.

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current system of untreated wastewater disposal has been colossal.

Even where extensive, responsible wastewater infrastructure exists, in many developed countries it is showing its age. Water pollution, soil contamination and spread of waterborne diseases due to leakage and spillage are increasing, costing the local government and the residents in terms of both health and wealth.

The prospect of reinstalling a new city-wide network for wastewater collection and treatment is tremendously daunting to local governments. Localized, individual fixes in the next couple of decades will cost billions of dollars. Thus, regarded in the context of long-term viability, an ecological and economical approach that advocates decentralizing the process in order to treat water locally and naturally and allow it the opportunity to be reabsorbed back in the local ecosystem emerges as the best solution. This on-site wastewater treatment and reuse mimics the closed cycle of a natural ecosystem.

As we revisit our expensive fresh food supply network, burdened system of water supply, inadequate waste disposal infrastructure and attempt to address issues of economic resilience, we ought to seek every opportunity to conserve resources and build synergies. These challenges, along with the awareness of growing urban populations and accelerating climate change, beg us to rethink the existing conventional urban systems. Having the foresight to close the water and nutrient loop within all new developments will help cities take a big leap to address the food and water crisis.

Figure 4: Closed water and nutrient loop within cities.

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3.0 NEW URBAN ECOLOGICAL PARADIGM

This article proposes a new urban ecological paradigm that regards urban wastewater as a renewable, reliable, freshwater resource for urban farming, offers a ‘value-added’ vision for the future of cities, representing as it does a truly new source of freshwater. Naturally treating urban wastewater through the adoption of less energy-intensive, nature-mimicking, methods will create a whole new urban landscape that is functional and productive. This model advocates food production in urban farms as a vital infrastructure element within cities as well as a relevant green economy building on the new freshwater resource. Land use and zoning designation for urban farms (agriculture) in dense urban environments should be as important to a city as is its open space designation. As illustrated in Figure 4, this decentralized system will regenerate the urban ecosystem, manage urban wastewater and serve as a building block for a green economy by way of urban farms.

The new urban ecological paradigm attempts to offer a global solution that, once tailored for contextual responses, could be adopted in all communities irrespective of geographic, climatic and economic differences.

4.0 RECLAIMING WATER BY NATURAL TREATMENT

An important component of the closed water and nutrient loop, natural treatment is a simple and cost-effective method that employs nature’s biological processes to reclaim clean water from wastewater. It is an energypassive procedure wherein wastewater is made to flow

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by gravity through a constructed wetland. The aquatic vegetation in the wetland absorbs the nutrients in the water. The bacteria and microorganisms in their root system transform the organic material into a cellular mass that settles at the bottom, leaving clear, filtered water at the top.

Wastewater treatment process in an ideal setting involves three steps to scrub reclaimed water to meet standards of drinking water. These are the primary, secondary and the tertiary (or advanced) stages of treatment. In the primary stage, usually a sedimentation tank, the main constituent removed from the raw sewage is the suspended solids. Secondary treatment, usually performed by the aquatic vegetation, breaks down organic material, removes pathogenic organisms (bacteria and viruses) and absorbs the nutrients (nitrogen and phosphorous). To make the water reclaimed entirely potable, a tertiary step may remove any traces of chemicals and salts that might occur.

public toilets to water street trees. Wastewater from the office toilets is collected in a septic tank that allows the solid sludge to settle down. After sedimentation of solid material, the liquid flows to an overflow water tank. Water from the overflow water tank is fed into the root zone system of a constructed reed bed. As water flows by gravity through the length of the reed bed channel, it is cleaned of all organic material by the microorganisms in the reed roots. It is filtered of all suspended particles by the layers of gravel in the reed bed. Clean water is reclaimed at the end of the reed bed and collected in a storage tank. This water is used to irrigate the fruit trees and other flowering plants in the office complex. Tests conducted of the effluent revealed water fit to be used for plant irrigation.

Water usage in toilets and kitchen – 2 kilo-liters per day Number of users – 30 Area of reed bed – 11 square meters Cost of construction – Rs 85,000 (USD 1,900), estimated Year of construction – 2009

Also referred to as a Living Machine®, the secondary wastewater treatment component could be a reed bed or a constructed freshwater or tidal-flow wetland3. These are simple to build, maintain and operate, making them competitive with conventional mechanical wastewater treatment methods. Depending on the volume of water to be treated, they could, however, require sufficiently large land area with suitable soil characteristics.

Living Machines® do not just treat wastewater. They are also opportunities for food production. Some aquatic plants that are highly beneficial in absorbing the nutrients from wastewater are grown for use as vegetables.

Common among them are water spinach, water mimosa, water cress, alfalfa and water chestnut4.

There is a wealth of information on strategies for water reclamation. For a more detailed description of the wastewater treatment process and the various types of treatment mechanisms, readers are encouraged to refer to Pescod5. Discussed below are two recently constructed small-scale demonstration projects indicative of the growing interest in and readiness to test decentralized, natural wastewater treatment process within urban settings.

4.1 Pradeep Sachdeva Design Associates (PSDA) Office Complex, Ayanagar, New Delhi, India

Constructed within an office complex in New Delhi, this ecological model of wastewater treatment was a demonstration project to test the use of reclaimed water from

Figure 5: Location and size of the reed bed within the office complex, New Delhi.

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1. About 3-feet deep channel dug out for the reed bed 2. Reed bed channel constructed as a plastered brick and

5. Reed bed plant roots wrapped with coir, a potting

mortar construction 3. River pebbles layered at the base of the reed bed 4. Crushed gravel layered as a second layer and then topped with smaller-grain pea gravel to finish the trilayered bed of the channel

6. Flowering plants like Canna, planted in the reed bed 7. Wastewater being pumped from the overflow water tank

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to the reed bed

8. Plants thriving in the reed bed after 6 months of operation

Figure 6: Demonstration of reed bed construction in New Delhi.

4.2 Eco Center at Heron’s Head Park, San Francisco

The Eco Center is an environmental education center and the first off-grid building in San Francisco. Completed in April 2010 it has on-site wastewater treatment system with all reclaimed water used to irrigate the native plants on the site. The natural treatment of wastewater is an indoor, demonstration project within the Eco Center. Large closed tanks are set up to receive the wastewater for the primary sedimentation process and for the secondary anaerobic digestion process.

Anaerobic digestion is the removal of organic material from the wastewater in absence of oxygen. Water devoid of organic material undergoes a tertiary treatment to irradiate pathogens under ultraviolet radiation light.

This water is then further polished in the constructed wetland before being piped out to irrigate a 2000 square foot area with native plants through subsurface irrigation dripfield.

This is a very recent community-designed initiative built

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in hopes of spreading the knowledge of regenerative solutions in a historically environmentally polluted neighborhood. Such small-scale projects are instrumental in building societal acceptance for reuse of wastewater.

Figures 7: Demonstration of on-site, indoor, natural wastewater treatment at the Eco Center, San Francisco.

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5.0 BENEFITS OF RECLAIMED WATER FOR URBAN FARMING

in the city environment reconnects residents with nature and provides urban dwellers some of the psychological benefits of a natural environment.

5.1 Access to Fresh and Continuous Supply of Food

5.6 New Source of Livelihood

Localizing treatment of wastewater within cities to promote urban farming serves a multitude of beneficial purposes. Notably, it brings the production of food closer to its demand. Proximity to food production reduces loss of food due to damage while in transit. Wastewaterirrigated-farming is also less dependent on nature for irrigation. As noted in Section 2.2, it has been highly valued in arid and semi-arid areas where annual rainfall alone cannot support farming. In most other regions it greatly reduces the stress on the municipal potable water supply while ensuring continuous food supply.

5.2 Ecologically Responsible Waste Management

Urban farming with wastewater is an effective and ecological waste management technique. It reclaims solid and liquid waste, both compost and wastewater and provides an effective low-cost alternative to use of fertilizers. Fertilizers are nitrates and phosphates added to soil for improved yield. The solids in the wastewater are a rich source of nutrients, mainly nitrates and phosphates, for plants. Reclaimed water used for farming reduces the need for additional chemicals and fertilizers.

Urban farming creates productive landscapes within cities that have the potential to generate a source of livelihood for many. The Parks and Recreation Departments of many cities are stretched thin trying to maintain existing park systems. There is reluctance to add new open space in times of critically low public funds since constant maintenance is resource-intensive. Urban farming provides a solution by adding productive open space within cities that could be viably managed by either a private business or a community venture.

5.7 Enhanced Aesthetic Value

The closed-loop landscape will add a new aesthetic dimension to urban developments. This integrated landscape of wetlands and urban farms could be interpretive in nature providing awareness and educating city dwellers about naural food production and water recycling processes, potentially leading to better-informed and healthier food choices and habits.

6.0 RISKS INVOLVED

Wastewater used in farming provides an opportunity to recharge our aquifers. Appropriate techniques of irrigation, like subsurface driplines, minimize water-loss due to evaporation and allow reclaimed water to percolate back into the earth, thus recharging the groundwater table.

Sustainable developments across the world have reclaimed nutrients for fertilizer, biogas for energy supply and heat to warm homes from urban wastewater.

The resulting clean water has been recycled for toilet flushing, landscape irrigation and cooling purposes for mechanical building units. Still, there is a preconceived perception of risk that weighs against the reuse of urban wastewater for food production in many developed countries. Mainly this seems to be a psychological impediment or a matter of public education and political will. However, there are some real risks to closed-loop systems if the rigorous standards established by various global regulatory agencies like the Environmental Protection Agency and the World Health Organization are not followed. Following is a brief enumeration of these possible pitfalls, which are extremely unlikely if proper procedures are employed.

5.5 Cleaner Urban Environment

6.1 Potential Health Risks

5.3 Reduced Energy Demand

By successfully reusing wastewater at its point of generation, wastewater-irrigated-farming reduces the need for extensive infrastructure that requires high levels of energy to transport wastewater (and freshwater) over long distances.

5.4 Recharged Groundwater

Urban water reclamation projects reduce greenhouse gas emissions resulting from transportation of food and water into the city. Clean, fresh air, mitigation of the heat-island effect, reduced storm run-offs and increased biodiversity all contribute to an improved microclimate and a healthy city without any additional stress on freshwater reserves. Moreover, adding plants

Using reclaimed water for urban farming has associated health risks if standardized treatment is not practiced. The biggest risk lies in the use of partially treated wastewater that may expose farm workers and consumers of food produced at these farms to pathogens6. This could very quickly lead to spread of disease. However, this risk may be entirely avoided if the treatment pro-

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cess is carried out to its conclusion before water is reintroduced for agricultural use.

6.2 Risk of Soil and Water Pollution

Untreated wastewater could also lead to a reverse effect on the urban food and water system. Land degradation, crop loss and poor quality of food are consequences of not adhering or being unaware of basic guidelines for reuse of wastewater. Use of herbicides and pesticides to increase production under these circumstances pollutes the groundwater and may find its way back into the potable water supply of the city, which would be further detrimental.

6.3 Physical Challenges

Constructed wetlands do have temperature limitations.

They function best in hot and dry climates. They are not effective in areas where water freezes during winter months.

6.4 Maintenance Issues

Maintenance of these decentralized closed-loop systems could pose a challenge, as responsibility would fall upon multiple agencies or organizations. Although the system is fairly low-maintenance, if practiced as per standards, it will require effective management and regular monitoring to keep the integrated landscape of wetland and farms functioning smoothly. Failure to do so would lead to disruptions of the food and water cycle and an unhealthy living environment.

7.0 CASE STUDIES

Over the last two decades, new urban developments have successfully used advanced technologies to reclaim water from treatment plants that far exceeds quality standards for potable water. In particular, the European countries have ecological new urban districts that aim at a closed-loop development.

Leading sustainable developments in the developed world treat their wastewater to extract heat, energy and nutrients, but do not close the water loop for producing two increasingly scarce commodities–fresh food and fresh water. Exploration for solutions in the developing world, however, reveals traditional practices that do accomplish a closed-loop water and nutrient system. The following four case studies, of both open- and closedloop systems, evaluate developments in different parts of the world against the proposed new urban ecological paradigm.

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7.1 EVA Lanxmeer, Culemborg, Netherlands

The EVA Lanxmeer district of Culemborg brings together best practices of ecological architecture and natural living environment for energy and water management. It is off the city grid for gas, water, electricity and sewage disposal. Built on an aquifer zone, this new district has all the synergistic elements of urban, rural and agrarian settlements. It integrates a site-specific wastewater facility, a small scale biogas installation. All wastewater and organic waste is fed into the system to recover gas for energy and carbon and nutrients for agricultural use.

This installation has eliminated the need to connect the site to the municipal sewage system. The clean water produced is fit to be mixed with surface water at the site, which is further purified by aquatic plant life in the surface water bodies. Also, on site is the city farm that uses the organic fertilizers generated from the composted sludge of the biogas installation.

The proposed master plan for EVA Lanxmeer includes plans for a “Sustainable Implant,” which is a vertical facility combining wastewater treatment plant, biogas installation and agricultural greenhouse in one stacked configuration7. This integrated facility will be a demonstration project to educate residents and visitors.

Evaluating against the proposed paradigm – The innovative approach to decentralized wastewater treatment and reuse of its by-products makes the biogas installation at EVA Lanxmeer a successful solution. Though it is energy-driven, it is small in footprint, eliminates transportation almost entirely and meets the stringent planning guidelines that protect the aquifer it sits atop. Even though the facilty thus far has not needed to use the reclaimed water for irrigation in the city farm, the district in its current configuration measures high against the proposed paradigm.

7.2 Hammarby Sjostad, Stockholm, Sweden

Even though Sweden has abundant freshwater reserves, it is one of the leaders in water management. Hammarby Sjostad, a new neighborhood intended to expand the inner city of Stockholm, is one project that epitomizes that leadership. Built on derelict industrial land, this development is one of the most-studied integrated energy, water and waste recycling program anywhere. It is called the Hammarby Model. Since large wastewater treatment facilities are generally located outside the city, decentralized small-scale facilities have been preferred where reuse is a high priority. Hammarby Sjostad is an exception. With an on-site, large-scale wastewater treat-

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ment plant, Hammarby has the advantageous ability to reuse to maximum benefit within the development site the enormous volume of by-products normally associated with a centralized, regional treatment facility. The treatment plant extracts heat from wastewater and circulates it back to the homes for heating. Proximity to the treatment facility results in minimum loss of heat in conveyance. Solid waste generated from the wastewater is burnt to produce biogas that powers the buses at Hammarby Sjostad and provides electricity to the houses. The residue from the natural gas production is used to produce nutrient-rich soil used in agricultural lands. The remaining clean water, which is fit to be sent back to the taps, is discharged back into the surrounding freshwater lake.

Evaluating against the proposed paradigm – Hammarby reuses its wastewater for heat generation, biogas production and producing nutrients-rich soil for crops.

However, given the abundance of water, the need to reuse its treated water within the development does not exist. Hammarby’s solution to its urban wastewater treatment is appropriate given its economic status and abundance of freshwater. However, given the high cost of running and maintaining this infrastructure, it is applicable in select few countries. Hammarby’s large scale and difficulty of reproducing results means it does not measure as high against the urban ecological paradigm as its successful and innovative installation would otherwise indicate.

7.3 City of Arad, Israel

In an extremely arid climate, Israel is profoundly challenged by water scarcity and food production constraints. However, it has confronted these difficulties with an innovative and very successful natural wastewater treatment process that allows treated water to be used safely for agriculture. Israel leads the world in water purification through cost–effective methods and reuses 70% of its water, the highest rate in any country. Tried and tested on a city scale, the city of Arad’s full-scale integrated pond and reservoir system demonstrates the successes possible in closed-loop systems.

Primarily domestic wastewater of a city of 22,000 residents is treated through an extensive layout of 3 anaerobic ponds operating in parallel, a facultative and maturation pond in series, a rock filter pond, 3 stabilization reservoirs and a large storage reservoir. The reclaimed water is used for irrigation of crops like wheat, barley, sunflower and alfalfa8.

Evaluating against the proposed paradigm – Climatic and economic needs have already made Israel a frontrunner in this new urban ecological paradigm. With very limited annual rainfall, they have had to create their own freshwater resource to ensure continuous food production. Individual projects taken together make the country as a whole a bastion of innovation in this arena and the yardstick by which we should be measuring new projects.

7.4 City of Hyderabad, India

Hyderabad has a semi-arid climate. Wastewater use in urban farming is an age-old practice in India, more out of necessity than out of environmentalism. Raw, treated or reclaimed water is and always has been used to differing degrees in the urban farms of Hyderabad. Recognizing the need for reuse of wastewater, Hyderabad has legalized some areas of urban farming by leasing out land next to sewage plants to farmers for food cultivation thereby encouraging best practices9. Even so, in many cases the quality of water does not meet the recycled water quality standards of regulatory agencies like the Environmental Protection Agency or the World Health Organization.

Deteriorating quality of wastewater is leading to soil contamination, increased salinity in the ground water and unhealthy working environments. These practices now result in poor food quality, which defeats the purpose of increasing access to fresh, healthy food. Hyderabad is, therefore, a case study that points to the limitations of this paradigm.

Evaluating against the proposed paradigm – The results at Hyderabad show that the proposed paradigm cannot be effectively implemented without the watchful eyes of the regulatory authorities in wastewater management.

8.0 CHALLENGES AHEAD

Natural systems integrated into the urban environment will successfully manage resources and provide access to fresh food in a manner both environmentally and economically regenerative. In order to achieve wide-spread acceptance and adoption of techniques for naturally treated wastewater for urban farming, a transformation of perspective must occur across a wide cross-section of groups: • Planning and public health policy makers must be educated about the potential of a synergistic approach to solving our wastewater disposal issues

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and addressing fresh food needs in the city. Lack of knowledge and the lack of urgency to conserve water have been the two main deterrents in making the requisite policy changes.

• Urban designers, architects and landscape architects should prepare themselves to help catalyze a sea-change in the sector in regard to building blocks of basic sustainability and to push innovative and aesthetically pleasing programs that meet societal and engineering standards10. Limited knowledge of the science of reusing wastewater for food production has been a major obstacle to the creation of imaginative solutions. The invaluable functional connect between a familiarity with the science and the impetus to employ it needs to be brought to the forefront in urban design practice.

• Allocating land within the heart of the city for natural treatment and food production may not make economic sense, at first glance, in the real estate sector. However, the many-fold benefits to be shared by the entire city should, in fact, influence this equation and land adjacent to such amenities will offer priceless advantages.

• Societal acceptance and support around wastewater reuse for urban farming will need wide-spread education and actual small-scale demonstration projects to build confidence in the system10. Documentation of and publicity for existing projects are, therefore, invaluable resources for advancing knowledge and use of closed-loop systems.

To transform the image of a city from ever-consuming island to urban ecological laboratory generating food and water will necessitate implementation of all of the above elements. Preserving freshwater resources while increasing food production is vital to human existence and this urban ecological paradigm will constitute a big step towards this perpetual regeneration.

9.0 CONCLUSION

Cities are a resource of a continuous supply of water and nutrients from the municipal wastewater they constantly generate. Being able to channel these resources for production of fresh food as per the guidelines specified by the various international and national regulatory agencies will effect a closed water and nutrient loop within urban developments. A closed water and nutrient loop provides a reliable, economical, regenerative solution to two pressing problems, food shortage and water scarcity. In addition, it provides an easily-adaptable program that can be accomplished at the local level. Though there are risks, both real and perceived,

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the simplicity and rationality of this response merits the further research and preparation among professionals and the development of public will that will be necessary for its implementation.

This article is a result of an ongoing study aimed at understanding the basic concepts and prevalent practices of reusing urban wastewater for food production and exploring the ecological solutions to close the water and nutrient loop in future urban developments. Spatial configuration and technical considerations for construction of these decentralized natural treatment features that would serve as water reserves to irrigate farms within urban developments will require a detailed investigation. They have not been discussed in this article, but are recommended as a subsequent research.

ACKNOWLEDGMENTS

This research was partially funded by a travel fellowship from the Perkins and Will San Francisco office, under the Associates STRETCH Program. The author would like to thank the leadership of the San Francisco office for this immensely valuable opportunity.

All information related to the Constructed Reed Bed at PSDA is reproduced with permission from the architecture and urban design office of Pradeep Sachdeva Design Associates, New Delhi, India. The author is grateful to Pradeep Sachdeva and Madhu Shankar for sharing the documentation of the construction and results of their wastewater treatment demonstration project.

REFERENCES

[1] United Nation’s Food and Agriculture Organization, (2006). “Food Security”, Policy Brief, Retrieved on 1/2010 from ftp://ftp.fao.org/es/ESA/policybriefs/ pb_02.pdf.

[2] Corcoran, E. Nellemann, C., Baker, E., Bos, R., Osborn, D. and H. Savelli, (2010). “Sick Water? The Central Role of Waste-Water Management in Sustainable Development: A Rapid Response Assessment”, Report, Retrieved on 3/2010 from http://www.grida.no/publications/rr/sickwater/.

[3] Kirksey, W., (2009). “Creating a Sustainable Water Infrastructure for the 21st Century”, Worrell Water Technologies, LLC,Retrieved on 3/2010 from http:// www.livingmachines.com/images/uploads/resources/ Final_LM_White_Paper.pdf.

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[4] Cheema, G., Smit, J., Ratta, A. and Nasr, J., (1996).

Urban Farming: Food, Jobs and Sustainable Cities, New York, NY: United Nations Development Programme.

[5] Pescod, M., (1992). “Wastewater Treatment and Use in Agriculture – FAO Irrigation and Drainage Paper 47”, Food and Agriculture Organization of the United Nations, Rome, Retrieved on 3/2010 from http://www. fao.org/docrep/T0551E/T0551E00.htm.

[6] van Veenhuizen, R., (2006). Cities Farming for the Futures: Urban Farming for Green and productive Cities, Ottawa, IDRC; Silang, Philippines: International Institute of Rural Reconstruction.

[7] van Timmeren, A., Kaptein, M. andSidler, D., (2007). “Sustainable Urban Decentralization: Case Eva Lanxmeer, Culemborg, The Netherlands”, Report, Retrieved on 4/2009 from http://www.enhr2007rotterdam. nl/documents/W19_paper_Timmeren_Kaptein_Sidler. pdf.

[8] Alcalde, L., Oron, G., Manor, Y., Gillerman, L. and Salgot, M., (2003). “Wastewater Reclamation and Reuse for Agricultural Irrigation in Arid Regions: The Experience of the City of Arad, Israel”, Report, Retrieved on 9/2009 from http://www.ipcri.org/watconf/papers/ laura.pdf.

[9] Scott, C. A., Faruqui N. and Raschid-Sally L., (2004). Wastewater Use in Irrigated Agriculture – Confronting the Livelihood and Environmental Realities, Wallingford, UK: CABI Publishing.

[10] Novotny, V. and Brown, P., (2007). Cities of the Future: Towards Integrated Sustainable Water and Landscape Management, London, UK: IWA Publishing.

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PEER REVIEWERS AJLA AKSAMIJA Perkins and Will

KAREN ALSCHULER Perkins and Will

IAN BUSH Perkins and Will

MICHAEL DRIEDGER Busby Perkins and Will

BREEZE GLAZER Perkins and Will

DAVID GREEN Perkins and Will

ROBIN GUENTHER Perkins and Will

KALPANA KUTTAIAH Perkins and Will

ZAKI MALLASI Perkins and Will

RICH NITZSCHE Perkins and Will

BRYAN SCHABEL Perkins and Will

BILL SCHMALZ Perkins and Will

CATHY SIMON Perkins and Will

SAM SPATA Perkins and Will

RK STEWART Perkins and Will

CHRIS YOUSSEF Perkins and Will

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RESEARCH JOURNAL / VOL 02.01

AUTHORS 01.

MARIUS RONNETT Marius is a project architect with more than 20 years of experience in the United States as well as in Germany. His main expertise is in bridging architectural design and building technology, with an emphasis in complex exterior building envelopes.

He is based in the Chicago office and has also lent his technical expertise to the Shanghai office.

01.

ABUL ABDULLAH Abul is a designer in the Chicago office with more than 8 years of experience. His expertise is in BIM and parametric modeling with an emphasis in complex 3D modeling, especially technical modeling to resolve constructability of enclosures and features of complex exterior building envelopes. He has also taught in architecture schools at BUET, BRAC University and Ohio State University.

02.

CHARLES SEJUD

02.

JEAN-CLAUDE LESACA

Charles is a senior project architect and senior associate at Perkins and Will.

He brings more than 15 years of experience managing large complex projects for institutional and corporate clients from both technical and administrative perspectives. He has been with Perkins and Will for more than 5 years, where he has worked on The Johns Hopkins Hospital – New Clinical Building. He has a Bachelor of Arts in Architectural Studies and Masters of Architecture with an emphasis in history and preservation from the University of Illinois at UrbanaChampaign.

Jean-Claude is a technical coordinator at Perkins and Will. He has been with Perkins and Will for more than 4 years and has worked on the New Long Beach Court Building in Long Beach California and The Johns Hopkins Hospital – New Clinical Building. He has a Bachelor of Architecture from The Southern California Institute of Architecture.

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Authors

MARIONYT TYRONE MARSHALL

03.

Tyrone is a member of Perkins and Will’s San Francisco office EDI and EDI/ Design Lab, EE / Revit Task Force, San Francisco office SDI / Green Team, a coordinator and moderator of the San Francisco Office Revit User Group and Visualization User Group, and is currently a design technology leader in the San Francisco office. He is interested in design process relating to the application of advanced computation and performative strategies in the built environment.

AJLA AKSAMIJA

04.

Ajla leads Tech Lab, an ongoing research program of the Excellence in Execution Initiative. Ajla received her PhD in architecture with an emphasis on technology and environment. She monitors the latest developments in building systems theory, materials, technology and building performance to identify areas of interests and applicability to Perkins and Will design projects. She has contributed to several books, written numerous research articles and has presented at national and international conferences.

GEETI SILWAL

05.

Geeti Silwal is a senior associate at the San Francisco office. She has more than 12 years of urban design and regional planning experience working with communities to develop visions with a strong emphasis on regenerative ecological solutions. She is the winner of the Associates Traveling Fellowship 2009 offered by the San Francisco office and of the Perkins and Will Innovation Incubator 2010 grant.

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