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- Herausgeber: John Wiley & Sons
- Kategorie: Geisteswissenschaft
- Sprache: Englisch
Practical information on designing sustainable, energy-efficient building facades As energy and other natural resources are being depleted, it has become clear that technologies and strategies that allow us to maintain our satisfaction with interior environments while consuming less of these resources are major objectives of contemporary facade design. Sustainable Facades focuses on the strategies and approaches for designing sustainable, high-performance building facades, and provides technical guidance for architects and designers. This timely and useful guide presents strategies and technical guidelines for designing environmentally sensitive, energy-efficient facades based on scientific principles. It provides climate-specific approaches for minimizing energy consumption, analyzes the thermal behavior of different facade systems and materials, and illustrates with case studies how these approaches have been implemented on architectural projects. It also discusses emerging facade technologies, materials, and systems. Topics covered in this unique and indispensable guide include: * Climate-based design approaches for high-performance facades * Characteristics of sustainable facades: energy efficiency, thermal behavior, and moisture resistance * Designing for thermal comfort, lighting and glare control, and acoustic quality * Emerging technologies in facade design, including smart materials, double-skin facades, and facades as energy generators * Case studies on building orientation and facade design, tectonic sun exposure control, external shading elements, and more
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Seitenzahl: 231
Veröffentlichungsjahr: 2013
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Table of Contents
Cover
Figure Credits
Acknowledgments
Introduction
Chapter 1: Climate-Based Design Approach for Facades
Climate Classifications and Types
Climate-Specific Design Guidelines for Facades
Chapter Summary
Chapter 2: Characteristics of Sustainable Facades
Energy Efficiency
Facade Types and Materials
Materials and Properties
Thermal Behavior and Moisture Resistance
Chapter Summary
Chapter 3: Designing for Comfort
Thermal Comfort
Daylight and Glare
Acoustic Comfort and Air Quality
Chapter Summary
Chapter 4: Emerging Technologies in Facade Designs
Emerging Materials and Technologies
Facades as Energy Generators
Control Systems for Facades
Chapter Summary
Chapter 5: Case Studies
Building Orientation and Facade Design
Tectonic Sun Exposure Control
External Shading Elements
Facade Materials and Wall Assemblies
Appendix: Case Studies Index
Chapter 2
Chapter 3
Chapter 4
Chapter 5
Index
Cover image: © Benjamin Benschneider/OTTO
Cover design: Michael Rutkowski
This book is printed on acid-free paper.
Copyright © 2013 by Ajla Aksamija and Perkins+Will All rights reserved.
Published by John Wiley & Sons, Inc., Hoboken, New Jersey
Published simultaneously in Canada
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Library of Congress Cataloging-in-Publication Data:
Aksamija, Ajla.
Sustainable facades : design methods for high-performance building envelopes / Ajla Aksamija, Ph.D., Perkins+Will.
pages cm
Includes bibliographical references and index.
ISBN 978-1-118-45860-0 (cloth); ISBN 978-1-118-54964-3 (ebk); ISBN 978-1-118-54971-1 (ebk); ISBN 978-1-118-54975-9 (ebk)
1. Facades--Design and construction. 2. Exterior walls--Design and construction. 3. Sustainable design. I. Title.
TH2235.A426 2013
729'.1--dc23
2012037882
Printed in the United States of America
10 9 8 7 6 5 4 3 2 1
Figure Credits
Acknowledgments
I would like to acknowledge Bill Schmalz, RK Stewart, and Bruce Toman for their input, comments, and tremendous support during the writing of this book. Also, project team members of the featured case studies were crucial in providing the necessary documentation and comments, and I am deeply grateful for their involvement: Curt Behnke, Pat Bosch, Ryan Bragg, Alejandro Bragner, Eric Brossy de Dios, Jane Cameron, Matthew Crummey, Patrick Cunningham, Anthony Fieldman, James Giebelhausen, Patrick Glenn, Andrew Goetze, David Hansen, Scott Kirkham, Devin Kleiner, Aki Knezevic, Richard Miller, Tom Mozina, Michael Palmer, Camila Querasian, Deborah Rivers, Bryan Schabel, Dan Seng, Gary Shaw, Calvin Smith, Ron Stelmarski, Angel Suarez, Jolly Thulaseedas, Deepa Tolat, Ashwin Toney, and Mark Walsh. I would also like to thank Wajdi Abou-Izzeddine (The Dar Group) for his valued input. My research assistants, Negin Beyhaghi and Abul Abdullah, deserve special recognition for their assistance: Negin for collecting information about some of the case studies in the book, and Abul for preparation of some of the diagrams. Kathryn Bourgoine, Donna Conte, Danielle Giordano, and the Wiley production team deserve special recognition for their input during the production of this book.
Lastly, I would like to acknowledge Zlatan and Nur Aksamija for their undivided love and support.
Introduction
Buildings, as the largest users of energy in our society, are also our greatest opportunity for energy conservation and protection of the environment. The rapidly growing world energy use has raised global concerns over continued depletion of energy resources and their negative environmental impacts. Current predictions show that this growing trend will continue.
The facade is one of the most significant contributors to the energy budget and the comfort parameters of any building. As energy and other natural resources continue to be depleted, it has become clear that technologies and strategies that allow us to maintain our satisfaction with the interior environment while consuming fewer of these resources are major objectives for contemporary facade designs.
This book focuses on the strategies and approaches for designing sustainable, high-performance building facades, and provides technical guidance for architects and designers. Building facades act as barriers between the interior and exterior environment. To provide building occupants with a comfortable and safe environment, a facade must fulfill many functions, such as:
Provision of views to the outside
Resistance of forces from wind loads
Bearing its own weight
Implementation of daylighting strategies to minimize use of artificial lighting
Protection from solar heat gain
Protection from noise
Resistance to rainwater and moisture penetration
Control of physical environmental factors (heat, light, sounds) must be considered during the design process, as must design strategies that improve occupant comfort (thermal, visual, acoustic, and air quality). Therefore, sustainable facades must block adverse external environmental effects and maintain internal comfort conditions with minimum energy consumption. The location and climate thus are crucial factors in selecting appropriate design strategies for sustainable facades.
Strategies and technical guidelines for designing environmentally sensitive, energy-efficient facades based on scientific principles are the basis of this book (such as climate-specific approaches for minimizing energy consumption, thermal behavior of different facade systems, and materials and their properties), which illustrates with case studies how these approaches have been implemented on real-life architectural projects. It also discusses emerging facade technologies, materials, and systems.
Chapter 1
Climate-Based Design Approach for Facades
Building facades perform two functions: first, they are the barriers that separate a building’s interior from the external environment; and second, more than any other component, they create the image of the building. High-performance sustainable facades can be defined as exterior enclosures that use the least possible amount of energy to maintain a comfortable interior environment, which promotes the health and productivity of the building’s occupants. This means that sustainable facades are not simply barriers between interior and exterior; rather, they are building systems that create comfortable spaces by actively responding to the building’s external environment, and significantly reduce buildings’ energy consumption.
Figure 1-1 Energy use breakdown for commercial buildings (Adapted from DOE, 2012).
Average energy use for commercial buildings is shown in Figure 1-1. Heating, cooling, lighting, and ventilating interior spaces account for more than half of the energy use. The performance of the building facade can significantly affect the energy consumed by these building systems.
Designers of sustainable facades should use the specific characteristics of a building’s location and climate, as well as its program requirements and site constraints, to create high-performance building envelopes that reduce the building’s energy needs. Climate-specific guidelines must be considered during the design process. Strategies that work best in hot and arid climates are different from those that work in temperate or hot and humid regions.
In this chapter, we look at the different ways of classifying climates, and the characteristics of each climate zone. We also discuss some of the factors that must be considered when designing high-performance sustainable facades, based on climatic environmental characteristics.
Climate Classifications and Types
Climate encompasses the sum of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particles, and other meteorological characteristics over extended periods of time. Climate is affected, in varying degrees, by latitude, terrain, and altitude, as well as by nearby mountain ranges or bodies of water. In the United States, for example, the coastal regions of the Pacific Northwest are at the same latitudes as the northern Great Plains. However, due to the tempering effects of ocean currents, its coastal winters are mild compared to the harsh winters on the northern plains. The effects of the Gulf Stream, an ocean current in the northern hemisphere, are responsible for moderating the climate of western Europe. Therefore, countries such as the United Kingdom and France have relatively warm winters, although they are positioned along the same latitude as Canada.
The Koppen Climate Classification System was one of the first methods to categorize different climates. It consists of five major climate groups, each of which is further divided into one or more subgroups. The five primary groups are labeled by the letters A through E, and the subgroups by two- and three-letter codes to designate relative temperature, average precipitation, and (where relevant) native vegetation. The entire world can be classified using this system, as shown in Figure 1-2. Table 1-1 summarizes the basic characteristics of all Koppen climate groups and subgroups, and indicates representative locations.
Figure 1-2 Koppen Climate Classification System (Adapted from Peel et al., 2007).
Table 1-1: Koppen Climate Classification System.
Although the Koppen Classification System can be used to classify climate and environmental conditions for any location in the world, its complexity makes it difficult for designers to use when relating local climate to energy-reduction design strategies. The International Energy Conservation Code (IECC), in conjunction with the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), has developed a climate classification system for the United States that is easier for designers to use. The IECC climate map provides a simplified, consistent approach based on widely accepted descriptions of world climates, as well as the number of cooling and heating degree days for each location. This classification system divides the United States into eight temperature-based climate zones (labeled by numbers 1 to 8), and three subzones based on humidity levels (labeled by letters A, B, and C).
The eight climate zones are:
Zone 1: very hot
Zone 2: hot
Zone 3: warm
Zone 4: mixed
Zone 5: cool
Zone 6: cold
Zone 7: very cold
Zone 8: subarctic
The three subcategories based on the location’s humidity are:
A: humid
B: dry
C: marine
Every location in the United States has an associated IECC climate zone and humidity subcategory, as seen in Figure 1-3. The IECC and ASHRAE standards, and the energy codes that are based on them, use this classification system.
Although the IECC climate classification system is useful for designers, and is referred to frequently throughout this book, it has some limitations. The IECC system does not recognize local microclimates. For example, the entire Chicago metropolitan region falls within climate zone 5A. However, the microclimate within a mile of Lake Michigan is different from an inland location such as O’Hare International Airport (one of the weather stations where Chicago weather data are collected). Another example is the city of Los Angeles, which is located in climate zone 3B. However, the microclimate near the Pacific Ocean shore is significantly different from the microclimate of the San Fernando Valley, which is 600 or more feet above sea level and entirely surrounded by hills. For buildings in urban areas, designers should research local microclimate conditions, which may vary from the IECC climate zone description.
Figure 1-3 Climate classification for the United States.
Energy performance modeling for buildings is typically based on historical weather data, which are collected over a specific time period, such as thirty years. Temperature, relative humidity, wind speeds, precipitation, and solar radiation data are collected and statistically analyzed to identify typical weather patterns that can be used to predict heating and cooling loads when used in performance modeling. In addition to historic weather data, predictive climate models are currently being developed, which can be used to predict future conditions for a specific location (Lawrence and Chase, 2010). Predictive climate models account for climate changes, impacts of existing and projected greenhouse gas emissions, and slight increases in temperatures. Predicted weather data can be used instead of historical data for modeling a building’s energy consumption, thus taking into account these future changes in climate and their effects on energy consumption.
Climate-Specific Design Guidelines for Facades
Environmental Considerations and Design Criteria
For most buildings, the facade affects the building’s energy budget and the comfort of its occupants more than any other system. To provide occupants with a comfortable and safe environment, a facade must fulfill many functions, such as providing views to the outside, resisting wind loads, supporting its own dead-load weight, allowing daylight to interior spaces, blocking unwanted solar heat gain, protecting occupants from outside noise and temperature extremes, and resisting air and water penetration (Aksamija, 2009).
Designers need to consider the external environment, building orientation, space dimensions, and occupants’ comfort expectations. Table 1-2 shows how air temperature, solar radiation, humidity, wind velocity, noise, ground reflectivity, and dimension and location of external obstacles (e.g., buildings, topography, or plantings) can affect thermal, visual, and acoustic comfort. The relative importance of these criteria will affect design decisions, such as the properties of opaque materials (thickness, density, conduction, reflectivity) and transparent (glazing) materials (thickness, number of layers, heat transmission, light absorption, reflection).
Table 1-2: Environmental conditions and properties of facade elements that affect thermal, visual, and acoustic comfort.
Design Strategies and Climate
Different design strategies are required for different climatic zones. Basic methods for designing high-performance building facades include:
Orienting and developing geometry and massing of the building to respond to solar position
Providing solar shading to control cooling loads and improve thermal comfort
Using natural ventilation to reduce cooling loads and enhance air quality
Minimizing energy used for artificial lighting and mechanical cooling and heating by optimizing exterior wall insulation and the use of daylighting
In choosing design strategies, we need to consider the conditions of the climate zone to minimize their impacts and reduce energy consumption. In Table 1-3, we see how design strategies are affected by climate types (Aksamija, 2010). Heating-dominated climates (zones 5 through 8) benefit from collection of solar radiation, passive heating, heat storage, improved insulation to reduce heating demand, and the use of daylighting to reduce lighting demand. In cooling-dominated climates (zones 1 through 3), protection from sun and direct solar radiation becomes more important. In mixed climates (zone 4), combined strategies that balance solar exposure and access to daylight should be implemented.In some cases, localized climate conditions, or microclimates, may be different from the generalized conditions of that climate zone. Designers need to respond to the specific characteristics of a building site.
Table 1-3: Facade design strategies for different climate zones.
Climate type
Design strategies for sustainable facades
Heating-dominated climates Zones 5, 6, 7, 8
Solar collection and passive heating:
collection of solar heat through the building envelope
Heat storage:
storage of heat in the mass of the walls
Heat conservation:
preservation of heat within the building through improved insulation
Daylight:
use of natural light sources and increased glazed areas of the facade, use of high-performance glass, and use of light shelves to redirect light into interior spaces
Cooling-dominated climates Zones 1, 2, 3
Solar control:
protection of the facade from direct solar radiation through self-shading methods (building form) or shading devices
Reduction of external heat gains:
protection from solar heat gain by infiltration (by using well-insulated opaque facade elements) or conduction (by using shading devices)
Cooling:
use of natural ventilation where environmental characteristics and building function permit
Daylight:
use of natural light sources while minimizing solar heat gain through use of shading devices and light shelves
Mixed climates Zone 4
Solar control:
protection of facade from direct solar radiation (shading) during warm seasons
Solar collection and passive heating:
solar collection during cold seasons
Daylight:
use of natural light sources and increased glazed areas of the facade with shading devices
Many energy codes reference ASHRAE 90.1, Energy Standard for Buildings except Low-Rise Residential Buildings, which provides recommendations for building envelopes (ASHRAE, 2007). ASHRAE 90.1 is periodically updated based on increasing expectations of building performance. These recommendations are based on building location and climate zone, using the IECC climate classification system of eight zones and three subzones (Figure 1-3). If ASHRAE 90.1 has been adopted as part of the state energy or building code, then the ASHRAE recommendations become the required metrics of building performance. ASHRAE’s requirements are categorized based on the basic building function and occupancy, including: (1) nonresidential conditioned space (daytime use, higher internal loads), (2) residential conditioned space (24-hour occupancy, building envelope-dominated due to lower internal loads), and (3) nonresidential and residential semiheated space.
ASHRAE identifies four types of exterior walls:
Mass walls, generally constructed of masonry or concrete materials
Metal building walls, consisting of metal members spanning between steel structural members (not including spandrel glass or metal panels in curtain walls)
Steel-framed walls, with cavities whose exterior surfaces are separated by steel framing members (including typical steel stud walls and curtain walls)
Wood-framed and other walls
ASHRAE requirements are prescribed in three ways for all climate zones:
Minimum allowable thermal resistance (R-value) for the different exterior walls
Maximum allowable heat transfer coefficients (U-value) for the facade assembly (including the thermal bridging effects of framing members)
Maximum allowable solar heat gain coefficient (SHGC) for the glazed portions of a facade assembly
Thermal resistance (R-value) is an assembly’s or a material’s resistance to heat transfer, and is expressed in h-ft2-°F/Btu or m2-°K/W. Individual materials have specific R-values, usually listed as R-value per inch (see Chapter 2). The overall R-value of a facade assembly is calculated by adding the R-values of individual material layers. R-values are typically used to define the thermal performance of opaque areas of facades built up from multiple layers of materials.
Heat transfer coefficient (U-value) is the inverse of R-value. It measures the heat transmission through a material or a facade assembly. U-values are expressed in Btu/hr-ft2-°F or W/m2-°K, and are usually used to define thermal performance of glazed parts of facade assemblies.
The solar heat gain coefficient (SHGC) quantifies the amount of solar radiation admitted into a building’s interior through glass, and is expressed as a number between 0 and 1, with 0 meaning that no radiation is admitted and 1 meaning that no radiation is blocked.
Figure 1-4 shows ASHRAE recommendations for minimum R-values for nonresidential conditioned spaces, for each climate zone and four types of wall construction. R-values for mass walls are highly dependent on the climate, and increase from warmer to colder climates. Recommended minimum R-values for metal building walls are virtually identical for all climate types. The exception is for very cold and arctic climates, which demand significantly higher insulation. Recommended minimum R-values for steel-framed walls are the same for mixed and colder climates. Recommended minimum R-values for wood-framed walls vary depending on climate zone. In general, steel-framed and wood-framed walls require higher levels of insulation than the other wall types.
Figure 1-4 Minimum R-value recommended by ASHRAE 90.1-2007 based on wall construction type for all climate zones.
Figure 1-5 identifies maximum U-values recommended by ASHRAE for different facade assemblies (for nonresidential conditioned buildings); like Figure 1-4, it is based on four wall types and all climate zones. The recommendations are for entire wall assemblies, including glazed and opaque areas. All wall types in colder climates require lower overall U-values. Requirements for masonry, steel-framed, and wood-framed facades tend to decrease as climates get colder. In contrast, required U-values for metal building walls fall into two clusters: very cold climates and all the others. Steel-framed walls require lower U-values than mass walls for all climate types, due to thermal bridging effects. Wood-framed walls require the lowest U-values for most climate types.
Figure 1-5 Maximum assembly U-values for exterior walls recommended by ASHRAE 90.1-2007 based on wall construction type for all climate zones.
Figure 1-6 shows ASHRAE recommendations for maximum SHGC for glazed areas of the facades. For warmer climates, lower SHGC, not exceeding 25%, is desirable, as excess solar radiation should be blocked. For colder climates, higher SHGCs can support passive solar heating, but should not exceed 45%.
Figure 1-6 Maximum SHGCs for fenestration recommended by ASHRAE 90.1-2007 for all facade types and climate zones.
Chapter Summary
This chapter discussed climate classification systems; climate-based design strategies for sustainable, high-performance facades; and energy code requirements for building envelopes. Standards prescribed by the energy codes, such as ASHRAE 90.1, only establish minimum requirements for improving energy efficiency of buildings. Sustainable facades, which use high-performance materials and glazing, and daylight harvesting strategies, shading devices, and control systems to monitor and adjust their performance, typically aim for better performance than those the energy codes prescribe. They also improve overall building envelope operation, thermal behavior, and occupants’ thermal and visual comfort.
References
Aksamija, A. (2009). “Context Based Design of Double Skin Facades: Climatic Consideration During the Design Process.” Perkins+Will Research Journal, Vol. 1, No. 1, pp. 54–69.
Aksamija, A. (2010). “Analysis and Computation: Sustainable Design in Practice.” DesignPrinciples and Practices: An International Journal, Vol. 4, No. 4, pp. 291–314.
ASHRAE. (2007). BSR/ASHRAE/IESNA 90.1-2007, Energy Standard for Buildings except Low-Rise Residential Buildings. Atlanta, GA: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.
DOE. (2012). Buildings Energy Data Book 2011. Washington, DC: Department of Energy. Retrieved from http://buildingsdatabook.eren.doe.gov/default.aspx.
Lawrence, P., and Chase, T. (2010). “Investigating the Climate Impacts of Global Land Cover Change in the Community Climate System Model.” International Journal of Climatology, Vol. 30, No. 13, pp. 2066–2087.
Peel, M., Finlayson, B., and McMahon, T. (2007). “Updated World Map of the Koppen-Geiger Climate Classification.” Hydrology and Earth System Sciences, Vol. 11, No. 5, pp. 1633–1644.
Chapter 2
Characteristics of Sustainable Facades
Highly glazed facades have been with us since the Crystal Palace was built in 1851. However, it was not until the early 1950s that building technology and postwar economic prosperity allowed the extensive use of curtain walls worldwide. For decades after that, designers placed much greater priority on aesthetics and views than on how facades can improve the energy performance of an entire building. Starting with the oil shortages of the 1970s, architects became increasingly concerned about worldwide energy resources, global climate change, and the importance of designing energy-efficient buildings and high-performance facades.
Four basic mechanisms—thermal heat transfer, solar heat gain, air leakage, and lighting loads—determine how facades affect overall building energy use. There are numerous strategies and tools designers can use to improve the performance of facades. Improved wall insulation will reduce conductive heat losses. Solar shading and high-performance glazing will control solar heat gain. Continuous air barriers and well-designed window systems will prevent air leakage. Increased daylighting of interior spaces will reduce the need for and reliance on electric lighting. In this chapter, we discuss the properties of high-performance facades and factors that influence their design.
Energy Efficiency
What are the properties of energy-efficient building facades? They include allowing daylight into a building; preventing unwanted solar heat from entering the building; storing heat within the mass of the wall; preventing heat transfer through improved insulation; preventing air or moisture from passing through the facade; and allowing natural ventilation to cool the building’s interior. As we saw in Chapter 1, these properties are highly dependent on climate, as well as a building’s function, occupancy patterns, orientation, and equipment loads.
There are essentially two types of facades:
Opaque facades,
