Design and construction of high performance homes : building envelopes, renewable energies and integrated practice 9780415615280, 0415615283

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Design and Construction of High-Performance Homes

Both professionals and students are increasingly committed to achieving highperformance metrics in the design, construction and operation of residential buildings. This book responds to this demand by offering a comprehensive guide which features: • architectural innovations in building skin technologies which make lighter more transparent buildings high performing; • energy-free architectural design principles and advances in building-integrated photovoltaics; • essential engineering principles, controls and approaches to simulation for achieving net zero; • the advantages of integrated design in residential construction and the challenges and opportunities it engenders; • detailed case studies of innovative homes which have incorporated low-energy design solutions, new materials, alternative building assemblies, digital fabrication, integrated engineering systems and operational controls. Divided into four parts, the book discusses the requisite AEC (Architecture, Engineering and Construction) knowledge needed when building a high-performance home. It also communicates this information across four case studies, which provide the reader with a thorough overview of all aspects to be considered in the design and construction of sustainable homes. With contributions from experts in the field, the book provides a well-rounded and multi-faceted approach. This book is essential reading for students and professionals in design, architecture, engineering (civil, mechanical and electrical), construction and energy management.

Franca Trubiano is a Registered Architect (O.A.Q., Int. Assoc. AIA) and Assistant Professor at Penn Design, University of Pennsylvania, where she received her doctoral degree and conducts research in construction technology, emerging materials, tectonic theory, integrated design and architectural ecologies.

Design and Construction of High-Performance Homes Building Envelopes, Renewable Energies and Integrated Practice

Edited by

Franca Trubiano

First published 2013 by Routledge 2 Park Square, Milton Park, Abingdon, Oxon OX14 4RN Simultaneously published in the USA and Canada by Routledge 711 Third Avenue, New York, NY 10017 Routledge is an imprint of the Taylor & Francis Group, an informa business © 2013 selection and editorial Franca Trubiano; individual chapters, the contributors The right of the editor to be identified as the author of the editorial material, and of the authors for their individual chapters, has been asserted in accordance with sections 77 and 78 of the Copyright, Designs and Patents Act 1988. Every effort has been made to contact and acknowledge copyright owners. The publishers would be grateful to hear from any copyright holder who is not acknowledged here and will undertake to rectify any errors or omissions in future printings or editions of the book. All rights reserved. No part of this book may be reprinted or reproduced or utilized in any form or by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying and recording, or in any information storage or retrieval system, without permission in writing from the publishers. Trademark notice : Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging in Publication Data Trubiano, Franca. Design and construction of high-performance homes: building envelopes, renewable energies, and integrated practice / Franca Trubiano.   p. cm. Includes index. 1. Ecological houses—Design and construction. I. Title. II. Title: Building envelopes, renewable energies, and integrated practice.   TH4860.T78 2012   728'.047—dc23   2011041919 ISBN: 978-0-415-61528-0 (pbk) Designed and typeset by Alex Lazarou

Contents

Contributors Acknowledgments

PART 0



0.1





0.2



vii ix

Introduction

High-Performance Homes: Metrics, Ethics and Design

3

franca trubiano

Household Power: How Much is Enough?

23

william w. braham

PART 1

Building Envelopes, New Materials and Architectural Design

35

1.1

Energy-Free Architectural Design: The Case of Passivhaus and Double-Skin Façades

37



franca trubiano

1.2

Translucent Building Skins: Advancing the Technology of Light Transmission



franca trubiano

1.3

Responsive Building Envelopes: Characteristics and Evolving Paradigms



k at h y v e l i k o v



1.4

+

55

75

geoffrey thün

Nanomaterial + Super-Insulator = Aerogel

93



franca trubiano

PART 2

Renewable Energies, Building Systems and Simulations

105

The Design Integration of Renewable Energies

107



2.1





2.2





2.3





2.4



franca trubiano

+

t. russell gentry

Systems-Integrated Photovoltaics (SIPVs)

127

jeffrey r. s. brownson

Building Systems, Controls and Automation

139

t. russell gentry

Building Performance and Computational Simulation yun kyu yi

163



v

PART 3 Integrated Practice and Residential Construction



3.1





3.2

Integrated Project Delivery: Contracting for High Performance r ya n e . s m i t h

+

Energy and the Integrative Design Process: Defining the Team of Experts lisa d. iulo

3.3

The Construction of Affordable Low-Energy Prefabricated Housing in Denmark



anne beim



3.4





4.1



4.2





4.3





4.4



193 203

kasper sánchez vibæk

From Modeling to Making: Parametric Design and Digital Fabrication

217

t r i s ta n a l - h a d d a d

PART 4 High-Performance Homes: Case Studies



181

jörg rügemer



+

179

Lumenhaus© and the Eclipsis Sun Control System© r o b e r t d u n ay , j o s e p h w h e e l e r

+

233 235

robert p. schubert

Project Icarus: Optimizing Light and Energy in the Design of a Translucent Roof

249

franca trubiano

North House: Climate-Responsive Envelope and Control System geoffrey thün

+

265

k at h y v e l i k o v

Modular Building: Three Scales/Three Strategies

283

lisa d. iulo



Image credits Index

vi

296 297

c ontributo r s

Tristan Al-Haddad is an Assistant Professor in the School of Architecture at the Georgia Institute of Tech­ nology. His research and teaching is focused on the application of digital technology in the design and fabri­ cation of geometrically complex structures. In addition to his academic research, he is also a working designer and visual artist. His work has been exhibited in many ven­ ues including the High Museum of Art in Atlanta and the Center for Architecture in Manhattan. He was a Fulbright Scholar and Artadia Artist awardee in 2009. Anne Beim is a Professor of Architectural Technology at the Royal Danish Academy of Fine Arts (RDAFA) School of Architecture, from where she holds a PhD in Archi­ tecture. She teaches courses in architectural technology and tectonics in the graduate and undergraduate pro­ grams, and supervises research.   William W. Braham, FAIA, is an Associate Professor of Architecture at the University of Pennsylvania, where he is Director of the Master of Environmental Building Design. He received an engineering degree from Prince­ ton University and an M. Arch and Ph.D. Arch from the University of Pennsylvania, where he has taught since 1988. At Penn he teaches graduate courses on ecology, technology, and design.  Jeffrey R. S. Brownson is a faculty member in the John and Willie Leone Family Department of Energy & Mineral Engineering, College of Earth & Mineral Sciences, at the Pennsylvania State University. He served as the Director of the Natural Fusion team at Penn State for the Solar Decathlon 2009. His research team achieves a unique integration of disciplines: materials research, integrative solar system design, and energy systems simulations for analysis of new technologies. Robert Dunay, FAIA, is an ACSA Distinguished Profes­ sor, and three-time recipient of Design Intelligence’s Most Admired Educator. As Director of the Center for Design Research at Virginia Tech, he is chief protagonist exploit­ ing the territories of opportunity that reside between dis­ ciplines. His research concerns the integration of energy

performance in buildings and architectural quality as demonstrated in the 2002, 2005 and 2010 Solar Decath­ lon Competitions, culminating with Lumenhaus ©. T. Russell Gentry is an Associate Professor in the School of Architecture at the Georgia Institute of Technology and a registered professional engineer. His research focuses on the development and performance assess­ ment of building materials and systems, on the environ­ mental impact of buildings, and on the representation of design and fabrication knowledge in computational environments. Lisa D. Iulo is an Assistant Professor of Architecture at the Pennsylvania State University and a Registered Architect, Professional Planner, and LEED Accredited Professional (LEED AP). Her work has been recognized in research and practice related to residential green build­ ing practices and affordable housing, energy efficiency, and strategies for the implementation of renewable energy at the building and community scale. Robert P. Schubert is a Professor and member of the College of Architecture and Urban Studies at Virginia Polytechnic Institute and State University.  His research is in the area of energy and building design with an emphasis on promoting architectural solutions that mini­ mize the dependence on non-renewable energy sources and environmental degrading processes. Ryan E. Smith and Jörg Rügemer are Directors of an interdisciplinary design and engineering research group called the Integrated Technology in Architecture Center (ITAC) at the University of Utah. They research, write, teach and speak on the integrated paradigm, and develop processes and products that lead to sustainable and energy-efficient design and construction. Their work has been funded by federal, public and private organiza­ tions. They are recipients of the ACSA Collaborative Prac­ tice Award (2006), ACSA Creative Achievement Award (2009, 2011) and the ARCC Research Award (2011) for their innovative industry collaborative teaching, research and outreach.

vii

Geoffrey Thün is an Associate Professor and Kathy Velikov is an Assistant Professor at the University of Michigan Taubman College of Architecture and Urban Planning. They are principals of the research-based practice RVTR. Their design work, research and writing focuses on built environments and landscapes that are shaped and mediated by advanced materials, technologies and energies, within the context of complex ecological, economic, and social systems. Franca Trubiano is a Registered Architect (O.A.Q.) and Assistant Professor at the University of Pennsylvania with research areas in construction technology, mater­ials, tectonic theory, and architectural ecologies. She is a member of the DOE-sponsored Greater Philadelphia Innovation Cluster in the Retrofit of Energy-Efficient Buildings and Co PI of a research project on Integrated Practice. In 2006, while an Assistant Professor at the Georgia Institute of Technology, she was lead architecture faculty and co-recipient of a DOE/NREL Solar Decathlon Grant to design, build and operate a zero-energy house on the Natural Mall in Washington DC. The house won the BP Green Award for innovation. She holds degrees from the University of Pennsylvania and McGill University. Kasper Sánchez Vibæk has been an architectural researcher at the Royal Danish Academy of Fine Arts (RDAFA) School of Architecture since 2004. He received a PhD on Systems in Architecture in 2011. He also holds a Master of Architecture degree with a supplementary degree in sociology.

viii

Joseph Wheeler is an Associate Professor of Architecture at Virginia Tech School of Architecture + Design and a Co Director of the Virginia Tech Center for Design Research. He pursues professional research in environmental and sustainable design and assumes leadership positions in the implementation of design theory and ideas. Recent awards include a National AIA Honor Award for Architecture, the NCARB Prize for creative collaboration between the academy and the profession, the Virginia Society AIA Research Prize, and the Xcaliber University Prize for Excellence in Outreach. Yun Kyu Yi is an Assistant Professor at the University of Pennsylvania where he teaches environmental and sustainable technology and computational building simulation. He is a member of the TC Chan Center for Building Simulation and Energy Studies at Penn and has lectured at several universities. His research includes performance-driven design processes and the integration of simulation domains and decision making. At the Chan Center, his most recent project is developing measurements for different sustainable building criteria by performance-based rather than prescriptive measures.

 

ac k n o wledgme nts

There are many to thank for their support and contributions to this work. Some have offered their expertise and some their sound advice. Routledge editors Fran Ford and Laura Williamson guided the process in a spirit of great mutuality and collaboration. Contributing authors participated with much enthusiasm and commitment and to them I am most grateful. Architects graciously responded to my invitation to publish their creative work and the book is a better publication for featuring the highperformance homes they’ve designed and built. I benefitted from the technical know-how of various industry representatives including Kevin Lechwar from PPG Industries, Jocelyn O’Shea as Associate Director
for Vector Foiltec Ltd, and Michael Hindle from the PHIUS (Passive House Institute, US). To my colleagues Ruchi Choudhary, T. Russell Gentry and Godfried Augenbroe who first initiated me to the subject and who patiently answered all of my questions during our early collaborative adventures, I am most thankful. Many of my colleagues at the University of Pennsylvania including Dean Marilyn Taylor, Architecture Chairs William Braham and David Leatherbarrow, Undergraduate Chair Richard Wesley, Winka Dubbeldam, Lindsay Falck, Annette Fierro, Ali Malkawi, Cathrine Veikos, Yun Kyu Yi and Raffaella Fabiani Giannetto, supported this project in various ways, and for this I am very grateful. Architecture students, who participated in seminars on high performance, materials and energy, contributed valuable observations, questions, and challenges to the book and its thesis. To my friend Joanna Merwood who offered her editing wisdom and to doctoral student Eric Bellin who administered with diligence and rigor many of my editorial functions, I am truly appreciative. To Yves Gauthier, whose strength and affection continues to guide me in project after project, I offer my deepest gratitude.

ix

Part 0

Introduction



0.1







0.2



High-Performance Homes: Metrics, Ethics and Design

3

franca trubiano

Household Power: How Much is Enough? william w. braham

23

Chapter 0.1

High-Performance Homes: Metrics, Ethics and Design franca trubiano

1.0  Defining high performance From racecars to computers, the phrase ‘high performance’ is used to describe objects, buildings, environments, industrial processes and even human organizations. In fact, so frequently and widely is the term employed one would think it has lost much of its specificity and/or relevance. A most ubiquitous term in architecture, it is used to qualify the design, construction, and operation of mater­ ials, products, building systems, entire buildings, and even construction delivery methods.1 Yet when describing the home, there exists no more incongruous a phrase. Many reject the mere thought of living environments being subject to the qualifier ‘high performance’; to their rationalization, analysis and evaluation. Surely, reducing the home to a series of numerical measures poorly captures the fullness of dwelling. The most personal of building programs is ill suited for the scientific method. And yet, we hold no such reservations for environments in which we conduct business, save lives and educate. In fact, we seek the most advanced expression of technology for vehicles, buses and trains that transport us to and from the home, while shunning the same for spaces wherein families are raised. Why has the detached single-family house been reticent to acknowledge technological change? Why has the housing industry been recalcitrant in altering its methods of construction, failing to integrate the benefits of new materials and improved construction methods developed during the past six decades of continued industrialization?2 During the past thirty years of unchecked home building in the United States, which, albeit, came to an end during the global financial crisis of 2008, little substantive research was conducted in the technological advancement of single-family homes. The housing industry remains fragmented and uninterested in advancing the technology of building. A substantial lag in technology continues to burden homebuilders, as they too are reluctant to incorporate scientific advances in the design, construction and operations of the home. Moreover, the industry overlooks most opportunities to alter its consumptive and wasteful procedures, rejecting all responsibility for producing living environments which have

CHAPTER 0.1: High-Performance Homes ~ Trubiano

3

a modicum of performance integrity. Surely, this modus operandi is untenable in a world of diminished material and energy resources. Alongside their rejection of advancements in building science, representations of ‘home’ are predominantly focused on building elements that support a language of cultural tradition, even when the language is without functional veracity. Single-family homes are identified with notions of comfort, handicraft, and small town life more akin to rural life in the nineteenth century than to the realities of the twenty-first. And notwithstanding the social, economic and political origins of the North American middle class, the image of the single-family home sought by most remains aligned with the trappings of a genteel bourgeois life; limited only by lot size and the requirement of modern commutes. Can the home, therefore, ever become a viable site for the embodiment and representation of ‘high performance’? Can its design and construction point to a possible integration of dwelling and technology in a manner that is both sustainable and ethical? The search for answers to these questions is challenged by the lack of an agreed definition of ‘high performance’. For some, the term is loosely associated with sustainable design practices that result in ‘green’ buildings and carbonneutral designs. For others, it is aligned with the specific gains of prefabrication and new materials. And for others still, ‘high performance’ describes building systems that operate more efficiently by using less energy for supplying light, air and heat. Rarely are these positions reconciled in one all encompassing definition of high performance, at the center of which is the equal importance of metrics, ethics and design.

1.1  Metrics The field of high performance is predicated on metrics, measurements, certifications and benchmarks. Data and numerical measures of all kinds are used to establish expectations as well as to evaluate outcomes. Building simulations completed during the design stage of a project and energy audits conducted during the building’s operations result in a wealth of comparative figures. The virtual analysis of a building prior to its construction by energy, lighting and ventilation experts is a practice essential to high-performance design, as is the quantitative assessment of a building and its systems carried out according to consensusbased methods.3 At present, the energy expended and materials consumed during the construction and operation of a building, are of most interest. The impact of nonrenewable fossil fuels, the embodied energy of materials, carbon emissions resulting from building construction, operations and decommissioning are all featured in performance calculations. A number of significant institutional standards already exist for evaluating the performance of buildings. The most prominent include LEED (Leadership in Energy and Environmental Design), BREEAM (BRE Environmental Assessment Method) and Green Globes; all of which are highly participatory assessment programs for designers, builders and occupants committed to knowledge building, information sharing and technology transfers. In

4

PART 0 : Introduction

the United States, the Home Energy Rating System (HERS) focuses on the design of homes. Administered by the Residential Energy Services Network (RESNET), it is responsible for certifying the cadre of professionals known as home energy raters. These experts in the field of energy-responsive building design are trained to evaluate residential environments for the effectiveness of their construction techniques, material choices and systems design. Barely two decades since instituting the first of these environmental rating systems, a more informed group of practitioners is now conversant with the tools used in designing the building infrastructure of a more sustainable planet. Moreover, a growing number of organizations and industry partners are dedicated to the growth and dissemination of ‘high-performance’ metrics. The National Institute of Building Science in the United States is dedicated to the delivery of ‘a successful high-performance building by applying an integrated design and team approach to the project during the planning and programming phases’.4 They promote the Whole Building Design Guide in which a building and its systems are conceived as wholly interdependent and their integration sought for improved performance. Eleven governmental agencies participate in its goals, including the Department of Energy (DOE) and the General Services Administration (GSA), who are committed to implementing the Federal ‘High Performance and Sustainable Building’ (HPSB) Requirements. Alongside these efforts are research initiatives in material science, building envelope design and building systems engineering. Publications such as the Journal of Advanced and High Performance Materials, the Journal of Building Enclosure Design and High Performing Buildings attest to the large number of design and engineering professionals working in the field. And the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has, in collaboration with other industry partners, established the ‘High Performance Building Design Professional Certification’ program which trains building experts in the field of ‘high-performance’ systems evaluation.5 Typically, for these participants, the phrase ‘high performance’ is synonymous with ‘net-zero energy’.6 A high-performance building wisely manages energy expenditures to reduce the operational energy needed to supply its thermal and power needs to nearly zero. To this end, emphasis is placed on implementing design and construction strategies that eliminate the need for ‘artificial’ environmental systems. The building’s site, orientation, footprint, extents, sectional profile, material choices and construction details can all contribute to achieving the metric of net-zero energy. And where architectural strategies fail to attain the netzero benchmark, alternative forms of renewable energy, such as solar thermal, solar electric or wind, are introduced. A building, which consumes ‘zero’ amounts of non-renewable energy, is surely well performing. And yet, this is only partially true. The definition of a ‘high-performance’ building may include, but is not limited to, an account of the energy it consumes. Vastly more expansive a characterization of high performance is required for naming the qualitative measures of excellence and innovation so important to its definition.

CHAPTER 0.1: High-Performance Homes ~ Trubiano

5

1.2  Ethics Much of our contemporary language of performance is focused on the physical definition of the building; an object that responds to climatic conditions given the availability of material and energy resources. Rarely, however, are questions of equity, human behavior, and quality of life positioned at the center of what we intend by high performance. If a building saves energy it is assumed to be of benefit to its occupants. This, however, may not necessarily be the case. Office buildings designed to save energy during the early 1980s also succeeded in making their inhabitants sick when their air change frequency was decreased to reduce the amount of fresh air requiring conditioning.7 Schools designed to reduce thermal heat load also reduced the amount of natural daylight of use to young students who subsequently faired poorly in their academic endeavors. Many similar examples exist of the negative consequences resulting from the pursuit of ‘high performance’. In response, new theoretical models have been devised in which human values are posited alongside the more traditional numerical values of high performance. In Cradle to Cradle, by William McDonough and Michael Braungart, the definition of sustainability is clearly predicated on the triangulation of Ecology, Economy and Equity.8 Cultural values are unambiguously promoted in their ‘triple bottom line’ approach to sustainability. Factors aligned with justice are as important as those associated with cost, for only in this way can a true measure of sustainability be identified for all building-related processes. Job creation, access to food and transportation, and the health of our built environments are issues much larger in scope than those generated by any one house or any one client and should be addressed when considering the importance of social equity and public policy.9 ‘High-performance’ outcomes are also a function of human desire. Building environments designed to operate at optimal efficiencies often fail miserably when faced with the uncertainty of occupant behavior. Pre-sets for building systems are often overridden and even sabotaged by unsatisfied occupants. And post-occupancy evaluations have struggled with how best to capture and quantify the wide range of human preferences that condition the way in which inhabitants use a building.10 In Sibyl Moholy-Nagy’s text from 1955, ‘Environment and Anonymous Architecture’, a simple yet effective, interpretation of how human habitats can teach us important lessons about performance, beyond the dictates of measure and proof, is articulated. Herein, Moholy-Nagy addressed the modern challenge facing many architects when designing single-family homes in decentralized and suburban America. She reminded her readers that while ‘tradition is the deposit and tyranny of IDEAS; bruach or observance is the acknowledgement of past PERFORMANCE’ (emphasis Moholy-Nagy).11 Committed to the self-evident truths of anonymous architecture from the Lake Dwellers of the Alps, the Cavete Lodges of the Pueblo farmers, and the early religious buildings in Ephrata Pennsylvania, Moholy-Nagy chose the German word brauch to speak of that particular form of knowledge that results from use and habit. Access to building-related customs successfully organized vernacular building activities for hundreds of years and for Moholy-Nagy this was a valuable avenue for understanding ‘performance’.

6

PART 0 : Introduction

So stated, the definition of ‘performance’ could be expanded to include considerations beyond the metrics of building and those in excess of design intentionality. As described by David Leatherbarrow in his text ‘Architecture’s Unscripted Performance’, a building’s performance is more than the sum of its design and construction techniques and more than the idea and practices it represents.12 For to believe otherwise, ‘at risk in such an approach is architecture’s perfect rationality, for it will be seen that performances or events depend in part on conditions that cannot be rationalized’.13 Buildings do, in fact, behave in ways that are less than objective, and are used for functions and in ways they were not designed for. They are the settings for actions whose exact unfolding is difficult to predict.14 A building’s performance can never be entirely known or measured and this is surely the case in what concerns the natural and environmental actions to which it is subject. Leatherbarrow reminds us once more, that buildings are by definition never inert or static. Constantly given to resisting the forces of nature, they struggle against their own entropy, their own demise. Processes of degradation, ruination and weathering that accompany the life of a building are always in opposition to the range of engineered performances for which the building was designed.15 And it is this most unavoidable and unpredictable event in the life of a building that holds ethical consequences for high-performance homes.

1.3  Design Only by competent design may the increasing problems of a multiplying society be resolved in physically adequate manner; that only by design may sufficiently more be done with less.16 The search for an agreed to definition of ‘high performance’ began as early as the 1970s when its tenets were associated with the drive for ‘energy conservation’. In 1977, in the midst of the first ‘energy’ crisis to hit the United States, Richard Stein called his fellow architects to action.17 In Architecture and Energy: Conserving Energy through Rational Design, Stein developed a comprehensive and convincing argument for recognizing that problems of energy conservation were, in fact, problems of design. After all, it was by design that office buildings were transformed into sealed artificial environments requiring tremendous inputs of air-conditioning energy; it was by design that post-war developments favored the growth of suburban sprawl; it was by design that tall buildings were conceived with building façades inarticulate as to their solar orientation; and it was by design that the profession had relegated all knowledge of vernacular strategies for energy-free architectural design to the dark recesses of history.18 Hence, it was only by design that radical change could be effected to our highly energyconsumptive building culture. Stein’s analysis is as relevant today as it was then. He identified the planned obsolescence of building products and equipment as highly problematic, citing the necessity for life-cycle assessments. He noted the substitution of natural materials with petro-chemicals, as vinyl replaced rubber, plastics replaced wood and polyesters replaced natural fibers. He even asserted that architectural design

CHAPTER 0.1: High-Performance Homes ~ Trubiano

7

as practiced in 1977, rarely invested building form and geometry with productive environmental constraints. New buildings poorly capitalized on the use of traditional practices that ensured temperate environments without mechanical means. Stein noted how typical buildings, and even more critically, typical homes, had exponentially increased their end use of electrical power since the Second World War by drastically increasing heating, air conditioning and plug-in loads.19 He cited the largely wasteful initiative launched by power companies in the early 1970s to have residential customers shift their home heating to electricity, an ill conceived enterprise given the highly inefficient process of converting fossil fuels into electricity for producing thermal heat. In this early work, Stein had comprehensively surveyed the factors contributing to the lack of wholesale acceptance of energy conservation measures including those in the law, advertising, public policy, mortgage lending guidelines and building codes.20 And yet, notwithstanding all of the aforementioned associated factors, the inadequate energy performance of most buildings remained a function of design. More than four decades later, this is still the case. Then as now, a robust definition of ‘high performance’ is one that valorizes the role of architectural design alongside that of building metrics. Evaluating the performance of a building requires both a measure of its design excellence as well as an account of the matter and energy it consumes. Design is a projective activity situated within a cultural context and a set of human desires; many of which are difficult, if not impossible, to rationalize within the metrics favored by the sciences. And yet, it must continue to exert a significant influence in expanding the definition of ‘high performance’.

2.0  High-performance design and the single-family home Single-family homes, and the lifestyles they support, continue to burden the world’s energy resources. In developed countries, and most particularly in the United States, homes have increased in size during each decade since the end of the Second World War. According to the American Census Bureau, in 2009 new homes were 40 percent larger than in 1980 while the size of the average household decreased by two percent over the same period.21 Individually, homes represent the smallest square footage of any building type, but cumulatively they surpass all others in total square footage built. No more consumptive a model exists for the depletion of land, the wasteful implementation of building services and the sprawl of transportation infrastructures.22 Sadly, the energy-consuming detached single-family home has enthralled so many, in so many parts of the world, regardless of cultural or socio-economic background. Rethinking the single-family home represents, therefore, a unique opportunity to address the question of ‘high performance’. Radical new design solutions are required for mitigating the waste, consumption and obsolescence of the present paradigm. What is sought is a rigorous and robust science of ‘design’ for single-family homes. This book is dedicated to this pursuit, encompassing the fields of architectural design, building engineering and construction management.

8

PART 0 : Introduction

2.1  Towards a science of housing An integrated solution was first sought to this question, immediately following the Second World War when architects who had overseen the industrialization of vast sectors of the American economy called for a drastic realignment of design goals for single-family housing. In 1947, C. Theodore Larson – Harvard Graduate, technical editor at Architectural Forum, former project planner for the United States Housing Authority and technical consultant for the Kilgore Subcommittee on War Mobilization – proposed the first working definition of housing ‘performance’.23 In ‘Toward a Science of Housing’, Larson argued the United States had fallen behind technologically in the materials and methods with which homes were designed and built, stating, ‘the production of a house must be viewed as a single integrated process that extends all the way back to the original sources of supply’.24 Larson saw great promise in the use of new materials, such as porcelain enamels, ceramic surfaced steel plates, stressed skin panels, and composites made of glue resin and corrugated paper. He recommended their immediate adoption. He believed ‘a single multipurpose material … should be able to cut the cost of the house shell at least in half. The net effect would be to reduce the total capital cost of house and land by approximately 30 percent’.25 Given his wartime experience, Larson promoted prefabrication as a vastly more efficient means of production for advancing the science of housing and he recognized the need to consolidate building and municipal services to eliminate waste: ‘If our sanitary equipment were more efficiently designed, the average American home could get all the water it needed by merely condensing it out of the atmosphere as part of the air-conditioning system’.26 Larson had equally visionary ideas when he advocated the adoption of performance-based building standards. Familiar with the wartime need for more nimble standards and codes, he recognized the benefit of greater flexibility when setting the performance metrics of building materials, components or construction processes, particularly those made possible by new engineering technologies. Prescriptive codes, whose rules of thumb had been designed for traditional materials, were limiting in the face of new inventions and in their place Larson imagined an entirely new set of evaluation mechanisms. In setting up desirable standards of performance, the task essentially is to predetermine the range of functions a house should serve and then to prescribe the necessary behavior as a control over the development of new materials and structural systems. … This is in itself a research task of unlimited scope, for the performance standards will constantly change as new advances in science and technology open up new potentials.27 His use of the language of ‘performance’ was prophetic, even if we have yet to incorporate its true promise in the writing of our own building codes. And yet Larson did not align the home’s performance exclusively with the language of deflections, stresses and gauges. At the core of his thesis was a reminder that new building technologies should transform what he called ‘the shape of things’.

CHAPTER 0.1: High-Performance Homes ~ Trubiano

9

Factory-based processes should determine both the way things were made and the way they appeared. (Figure 0.1.1) Just as the first automobiles were horseless carriages … and the first airplanes looked more like kites than ‘flying machines’, it is not surprising that the factory-built houses coming on the market are quite conventional in appearance. [But] ... houses will soon evolve into forms more consistent with the needs of contemporary living and reflecting the greater freedom in design that comes with industrialization.28 Larson cited Buckminster Fuller’s Dymaxion House, the Lakes’ Steel Corporation Quonset Hut, as well as Paul Nelson’s Suspended House as successful examples of the yet untapped design potential of performance-based design. He also identified qualitative variables necessary to his ‘Science of Housing’. Design criteria which post-war single-family homes should attend to included the health of occupants, the effect of color and form on mood and behavior, a resident’s

10

PART 0 : Introduction

0.1.1 Buckminster Fuller and the Dymaxion House model. (opposite) Dymaxion House version called the Wichita House built by William Graham in 1948

subconscious needs, and particular preferences which families have for organizing their living environment. They contribute to ‘standards of performance’ and ‘should be the objective of a comprehensive program of housing research’.29 In what was an early and visionary stanch, Larson had articulated a comprehensive strategy for rehabilitating the housing industry decades ahead of his contemporaries. This was the case once more with the celebrated Case Study Houses project.30 As chief editor of the now no longer published magazine Arts & Architecture, John Entenza had commissioned the design of eight contemporary single-family homes for Los Angeles and its environs. Charged with taking ‘the mysteries and the black magic out of the hard facts that go into the building of “house”’, the magazine promoted modern design for a middle-class consumer.31 (Figure 0.1.2) Homes were to be ‘a simple and straightforward expression of the living demand of modern-minded people’.32 At the center of this initiative was the need to define a new dwelling paradigm, attuned to the era yet responsive to its locale. The program’s opening announcement explicitly addressed the search for an altered representation of dwelling:

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… perhaps we will cling longest to the symbol of the ‘house’ as we have known it, or perhaps we will realize that in accommodating ourselves to a new world the most important step in avoiding retrogression into the old, is a willingness to understand and to accept contemporary ideas in the creation of an environment that is responsible for shaping the largest part of our living and thinking.33 Architects Charles and Ray Eames, Ralph Rapson, Richard Neutra, Pierre Koenig and Craig Ellwood each designed homes; some were built, most were not. The large portfolio of designs published in the magazine from 1945 to 1966 reveals levels of invention and situated knowledge hitherto unseen in the field of singlefamily housing. The brilliant photography of Jullius Shulman promoted a highly recognizable design aesthetic, grounded in Los Angeles and its natural environment. Even the earliest homes included exterior spaces as extensions of the interior, large projective awnings for the protection of all-glass façades, and construction details advancing the technology of building skins. By 1948, six of the homes were built and many more published, including the celebrated Eames House. By 1958, Pierre Koenig had built his Case Study House #21. (Figure 0.1.3) The Case

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0.1.2 Case Study Houses 8 (above) and 9 (opposite top) by Charles Eames and Eero Saarinen, Arts & Architecture, December 1945 0.1.3 Case Study Houses. (facing left) Eames House, Santa Monica, CA (1945–1949) Charles and Ray Eames, Architects. (facing right) Case Study House #21, Los Angeles, CA, Pierre Koenig, Architect

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Study Houses project was a moment of success for the representation of technology in design; it promoted a language of housing forms and building details respectful of place and environment, celebratory of engineered materials, and supportive of modern lifestyles.

2.2 What has happened to modern architecture? In 1948, the Museum of Modern Art (MoMA) in New York held a symposium entitled ‘What is Happening to Modern Architecture?’. Organized by HenryRussell Hitchcock and Alfred H. Barr, Jr., participants included many luminaries of modern architecture such as Marcel Breuer, Walter Gropius, Eero Saarinen, Peter Blake, Lewis Mumford, Edgar Kaufmann, and Isamu Noguchi. Sixteen years after coining of the term ‘International Style’, this event addressed mounting criticism against the ‘machine aesthetic’ of pre-war European architecture and its effect on modern architecture in the United States. The evening’s discussion had been prompted by an article published by Mumford in 1947 in the New Yorker, which acknowledged the work of architects Bernard Maybeck and William Wilson Wurster whose homes do not ‘resemble factories or museums’.34 As participants of the Bay Region Style, local to the San Francisco area at the turn of the century, their work was a ‘free yet unobtrusive expression of the terrain, the climate and the way of life on the Coast’ permitting ‘regional adaptation and modifications’.35 So noting, Mumford juxtaposed this characterization of ‘home’ with that of the ‘machine aesthetic’ and in so doing questioned the continued relevance of the latter.36 Most symposium participants were, however, committed to an architectural language consonant with ‘modernity’ even if, as noted by Peter Blake, the Industrial Revolution had little influenced the building industry.37 For George Nelson, there was ‘no contradiction … between the “machine look” and “living”’.38 Architectural expression was the question at the center of the evening’s discussion and Hitchcock was singularly concerned with the growing penchant for what in American single-family housing was referred to (by Mumford) as the ‘Bay Region Style’ and (by himself) as the ‘Cottage Style’. And yet, even while lamenting the growth of interest in the ‘Cottage Style’, for Mumford, concerns associated with the detached single-family house were far removed from those affecting architecture. After all, it was, ‘frankly not one of the important problems of architecture; … the individual, detached residence is always a good field for experiment but it is of very little statistical consequence today’.39 More than half a century later, 40 million new single-family detached homes have been built with significant statistical consequences.40 Their design and construction are important problems for architecture, particularly since the majority of this post-war building was uninspired by available technological advances and their designers and builders averse to the integration of new materials, robust industrial fabrication and intelligent building systems. This book, and the work of its contributors, is dedicated to advancing the discourse required to mitigate this condition.

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0.1.4 (top) Marcel Breuer’s House in the Museum Garden Exhibit at the Museum of Modern Art (New York), 1949. (bottom) Plas-2-Point prefabricated house, scale model, designed by Marcel Breuer, 1942/ unidentified photographer

Hitchcock had however been perceptive in recognizing that the singlefamily house was suited for experimentation.41 In the same year as the symposium, the MoMA commissioned Marcel Breuer to install a House in the Museum Garden, an affordable custom-built home of interest to the suburban commuter. The 900-square-foot, two-bedroom prototype was described as ‘truly modern’ because it succeeded in representing the contemporary family’s lifestyle.42 (Figure 0.1.4) It supported a butterfly roof, open interior planning and ample extensions to the outdoors. Notably, however, the house was advertised as not having

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been prefabricated but rather built using traditional insulated wood framing techniques ‘familiar to builders in all parts of the country’.43 This was an unobtrusive, yet remarkable claim to make, as it possibly signaled the retreat of architects from an interest in prefabricated building techniques. In 1943, Breuer had not been so conservative when he developed his prefabricated Plas-2-Point house prototype. Structurally inventive in its use of both roof and floor trusses, this house was designed to be prefabricated with inventive material technologies including a melamine resin covered Resinox plywood skin.44 (Figure 0.1.4) Sadly, this project alongside others inspired by prefabricated building techniques would have little commercial success in the post-war era, notwithstanding their commitment to advancing the technology of single-family housing.

2.3  Fuller, McHale and beyond The unbridled optimism of post-war America and the culture of exploration that pre-dated early unmanned space travel, should have favored the construction of homes as inventive as Buckminster Fuller’s Dymaxion House, conceived to maximize ‘performance output per gross energy input’.45 According to its designer, architectural performance was best directed at the structural and mechanical advantages of newly engineered materials and building systems.46 The genius of his geodesic dome was its use of small quantities of material to efficiently span large expanses, as was the optimization of the hemisphere for effective heat transfer. His ‘Standard-of-Living-Package’ and his ‘Utility-Energy-Package’ engineered artificial interior environments wherein the house’s power and water were highly integrated. In his Industrialized House, Fuller ‘tried to carry on a scientific prototyping activity to show how the house product can be designed for performance’.47 With each of his prototypes, he sought to solve the riddle of designing an environmentally appropriate high-performance home as successful for dwelling as the airplane was for flying. Industrialization of the building process was his preferred route for only in this way could one succeed in producing a highly mechanized ‘high-performance dwelling’:48 … we have continually gained in degrees of performance to be obtained per unit of investment in household mechanics. I propose that we eliminate the shrinking and ever less economic house altogether and concentrate entirely on amplification of the mechanics.49 In the decade following Fuller’s exuberant visions, the artist and sociologist John McHale wrote of the design of the modern home as the most pressing problem facing the world and its resources. Foreshadowing our century’s struggle with informal settlements and the vast migration of people in search of shelter, McHale writing in 1967, recognized the extent to which ‘even in advanced countries, housing is one of the last areas of human requirement to come under scientific design review’.50 He too lamented how industrialization had neglected the housing industry, with very little technical knowledge having been created by its members. Housing the world’s population was a problem necessitating,

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‘the fullest application of the highest scientific and technological resources’.51 To this end, McHale discounted the traditional practice of architecture and its craft based building industry, in its place supporting the engineering sciences that had placed a man on the moon. To envision the construction and operation of a ‘highperformance’ home, architects would do better to seek solutions consonant with aircraft building, as this industry had successfully incorporated levels of complexity within its own design processes.52 Moreover, the space race had solved the challenge of mechanizing environmental controls and this was an area of research McHale believed essential for a true transformation of the home. The development of high performance dwellings depends closely on … the maintenance of efficiency rated inventories of all such high performance technologies appropriate to various environ control requirements.53 In the end, McHale was committed to the introduction of rigor and innovation at all levels of the built environment. He envisioned early computer-based design tools analogous to digital fabrication and building information modeling now available in contemporary practice. He promoted systems-based thinking with ‘feedback sub-procedures’ and believed the home better suited to a ‘service approach’ rather than home ownership. No differently than service contracts now used for telephones, so too could homes gain from an organizational approach that incorporated life-cycle thinking and building system obsolescence. It is a loss for the housing industry as a whole that McHale’s technological and social visions proved to be of little consequence.

3.0  Pursuing high performance in contemporary design The chapters collected in this work are committed to the pursuit of highperformance metrics, ethics and design in the construction of innovative homes. They represent a range of topics that seek the integration of architectural design, engineering and construction. They tackle many of the same research questions first addressed during the exuberant post-war years when science and engineering promoted limitless possibilities for progress. Given the contemporary context, however, the propositions put forth are more measured and concerned with the very real consequences of not achieving the goals of ‘high performance’. The focus of Part 1 is on architectural design, for which contemporary investigations are primarily concerned with the building’s envelope; the critical interface between interior space and exterior environment. The sustained pursuit of transparent, lighter and ever more dematerialized skins has resulted in a vast concentration of design research on the subject. (Figure 0.1.5) Discussed are new materials, details and assembly types that are committed to the highest levels of performance. These include engineered nanomaterials whose energy-exchanging and thermal storing capacities are innovatively optimized at the molecular scale to service the building industry. The integration of responsive technologies that sense, offer feedback and self-adjust is also examined.

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0.1.5 Photographer’s Studio in Stoney Lake, Ontario by gh3 Architects (2009). Reinvention of the ‘glass house’ is the intellectual conceit which organizes the house’s design, material selection and environmental agenda. The north-oriented curtain wall uses advanced glazing technologies to transmit diffuse light effectively while offering the home’s inhabitants abundant views of the larger landscape. Excessive solar heat gain is mitigated by an automated blind system, white roof and vegetation

Embedding sentient devices within the building’s skin, which are dynamically responsive to the environment, holds great promise for the next generation of high-performance technologies. Their possibilities for design are discussed herein. In Part 2 the engineering of a house’s building systems is discussed, as are the energy-free architectural design principles which ensure significant performance gains before systems are introduced. Addressed are the basic tenets of this ‘vernacular’ science that continue to offer the most effective strategies for bettering the environmental quality of buildings. However, because they rarely succeed in completely eliminating the need for mechanical systems that heat, cool, ventilate and illuminate our homes, knowledge is required of the best performing building systems, controls and sensors suitable for home use; both those that generate energy and those that consume it. During the past decade, significant advances have been made in the economic feasibility of renewable energies used for single-family homes. A wider selection of integrated photovoltaics is now available, altering the otherwise exclusive market of solar electric generation and they too are discussed. Lastly, the engineering of ‘high performance’ is highly dependent on the use of simulations. The capacity to virtually model and quantify the projected behavior of building environments, prior to their construction, is the very foundation of performance-based studies. Solar exposure, lighting levels, air circulation, and energy consumption define metrics of increasing importance for ‘high-performance’ design. Moreover, the way in which a home is constructed contributes significantly to its measure of excellence; this being the subject of Part 3. During the past decade, changes to project delivery methods organizing the construction of buildings have contributed to high-performance environments. Integrated design practices encouraging interdisciplinary collaboration between architects, engineers and builders with the early identification of shared project goals, methods and outcomes have increased opportunities for better building. Moreover, following decades of advances in prefabrication and modular building techniques, the construction technology of material assemblies used in single-family homes has vastly improved. Factory-controlled building environments are common in both North America and in Europe and the energy performance gains occasioned by these alternative modes of production are discussed herein. Lastly, digital fabrication is a rapidly expanding field of design enquiry and one equally promising for the construction of homes. It has the potential to not only transform the figural expression of interior architectonic details but to occasion structural innovation. In the final four chapters, case studies are introduced demonstrating a range of inventive solutions for the design and construction of net-zero-energy singlefamily homes. They represent the integration of architectural design principles with innovative systems engineering and construction technologies; highlighting a range of operational strategies. Unique in their approach, they nevertheless share in a commitment to design innovation in the pursuit of high-performance architecture.

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Notes 1 See V. Lerum, High-Performance Building, New Jersey: John Wiley & Sons, 2008; D. Orr, Design on the Edge: The Making of a High-Performance Building, Cambridge: MIT Press, 2008; B. Kolarevic and A. Malkawi, Performative Architecture: Beyond Instrumentality, New York: Spon Press, 2005. 2 For a review of the history of modern prefabricated homes see Barry Bergdoll and Peter Christensen, Home Delivery: Fabricating the Modern Dwelling, New York: Museum of Modern Art , 2008. 3 High-performance metrics are also sought for project delivery methods. See S. Korkmaz, D. Riley, and M. Horman, ‘Piloting Evaluation Metrics for Sustainable High-Performance Building Project Delivery’ in Journal of Construction Engineering and Management, August 2010, pp. 877–884. 4 The Whole Building Design Guide is an online resource accessed at www.wbdg.org 5 See C. Miro and J. Cox, ‘Sustainable Design and the High-Performance Building,’ ASHRAE Journal, August 2000, p. 42 (8). Issues of High Performance Building are available at www. hpbmagazine.org. The Certification program was established in collaboration with the Illuminating Engineering Society of North America (IESNA), the Mechanical Contractors Association of America (MCAA), the US Green Building Council (USGBC), and the Green Building Initiative (GBI). Information available at www.ashrae.org/certification/page/1683 6 See M. Guzowski, Towards a Zero Energy Architecture: New Solar Design, London: Lawrence King Publishing, 2010. 7 M. Keeler and B. Burke, Fundamentals of Integrated Design for Sustainable Building, New Jersey: John Wiley & Sons, 2009. 8 W. McDonough and M. Braungart, Cradle to Cradle: Remaking the Way We Make Things, New York: North Point Press, 2002, pp. 149–155. 9 See ARUP engineers’ registered SPeAR® (Sustainable Project Appraisal Routine) which considers ethical factors such as Health and Well Being, Culture, Community Facilities and Equality. Available at www.arup.com/Projects/SPeAR.aspx (accessed September 10, 2011). 10 G. Zachary, ‘Low Energy Dwellings: The Contribution of Behaviours to Actual Performance’ in Building Research and Information, Vol. 38., no 5, 2010, pp. 491–508. 11 S. Moholy-Nagy, ‘Environment and Anonymous Architecture’, Perspecta, Vol. 3, 1955, pp. 2–77. See p. 77. 12 D. Leatherbarrow, ‘Architecture’s Unscripted Performance’, Performative Architecture: Beyond Instrumentality, eds. B. Kolarevic and A. Malkawi, New York: Spon Press, 2005, pp. 6–19. 13 Ibid., p. 7. 14 Ibid., pp. 11–12. 15 M. Mostafavi and D. Leatherbarrow, On Weathering: The Life of Buildings in Time, Cambridge: MIT Press, 1993. 16 B. Fuller, ‘The Cardboard House’, Perspecta, Vol. 2, 1953, pp. 28–35. See p. 30. 17 R. Stein, Architecture and Energy: Conserving Energy through Rational Design, New York: Anchor Press/Doubleday, 1977. 18 Ibid., pp. 23–47. 19 Ibid., pp. 189–195. 20 Ibid., p. 111. Real obstacles to integrated project delivery exist in New York State where the Wicks Law insists that subcontractors bid separately for each building system contract and a mechanical sub contractor cannot be a general contractor on the same job. 21 J. Barth, ‘McMansion Economics’, Los Angeles Times, November 21, 2010, Part A, p. 37. 22 US Energy Information Administration (2009), ‘Residential Energy Consumption Survey’. Available at www.eia.doe.gov/emeu/recs/ (accessed 29 July 2011). 23 C.T. Larson, ‘Toward a Science of Housing’, The Scientific Monthly, Vol. 65 , No. 4, October 1947, pp. 295–305. In 1948, Larson became a Professor of Architecture at the University of Michigan where he founded the first research lab in architecture (ARL). He had also been Associate Editor at Architectural Record in the 1930s. 24 Ibid., p. 297. 25 Ibid., p. 298.

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26 27 28 29 30

31 32 33 34 35 36 37 38 39 40 41

42 43 44 45 46 47 48 49 50 51 52 53

Ibid., p. 304. Ibid., p. 300. Ibid., p. 301. Ibid., p. 302. E. Smith, Case Study Houses, the Complete CSH Program (1945–1966), New York: Taschen, 2002, p. 15; as originally published in ‘The Case Study House Program,’ Announcement in Arts & Architecture, January 1945, p. 39. See also www. artsandarchitecture.com Arts & Architecture, op. cit., p. 20. Ibid. Ibid. L. Mumford, ‘The Sky Line: Status Quo,’ New Yorker, Oct 11, 1947, pp. 104–110. Thanks to colleague Peter Laurence who facilitated my search for this article. Ibid., p. 110. Ibid., p. 109. ‘What is Happening to Modern Architecture?’ Bulletin of the Museum of Modern Art, Vol. 15, No. 3, Spring 1948, pp. 4–20. Ibid., p. 12. Ibid., p. 9. US Census Bureau (2000) ‘Census of Housing’. Available at www.census.gov/hhes/www/ housing/census/historic/units.html (accessed 29 July 2011). Exhibition and Prototypes included; the Monsanto House of the Future, built in Disneyland in 1957; the various versions of Jean Prouvé’s Maison Tropicale from 1949–1951; the Futuro House by Matti Suuronen; and the All Plastic House of 1956 by Ionel Schein. M. Roche, ‘Truly Modern’, New York Times (1923–Current file), April 10, 1949. P. Blake, ‘The House in the Museum Garden, Marcel Breuer, Architect’, The Bulletin of the Museum of Modern Art, Vol. 16, No. 1, 1949, pp. 3–12. Bergdoll and Christensen, op. cit., p. 88. B. Fuller, ‘New Directions 3’, Perspecta, Vol. 1, Summer 1952, p. 27. Ibid., pp. 27–37. Ibid, p. 35. Fuller, op. cit., 1953, pp. 28–35. Fuller, op. cit., 1952, p. 30. J. McHale, ‘World Dwelling’, Perspecta, Vol. 11, 1967, p. 122. Ibid., p. 122. Ibid., p. 127. Ibid., p. 123.

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Chapter 0.2

Household Power: How Much is Enough? william w. braham

ABSTRACT: High-performance building design is a technique for maximizing useful power, for extracting more work from the same amount of energy—a prime goal of engineering. Yet the fact that most individual households seek to maintain and enhance acquired levels of power is rarely considered. By expanding the subject from houses to households, the question of performance is focused instead on people, who are the real engines of consumption and environmental effect. Questions about the performance of houses haven’t been fully answered until we understand the ecological impact of our complex social arrangements, which are themselves tools for increasing productivity and supporting larger populations. The reduction of consumption is an important first tactic in a wealthy and wasteful civilization, but not entirely the solution, for the ultimate goal is to arrive at a sustainable balance of population and consumption.

1.0  Consumption The language of high performance can seem a bit strained when applied to the home. By comparison to commercial buildings—offices, stores, or factories— where productive work is the point, contemporary houses are mostly sites of consumption. The last century of household technological advance has largely been dedicated to “labor-saving” in the pursuit of comfort, for which the culminating invention is the color television, now a flat-screened entertainment center connected to ever more varied forms of “on-demand” entertainment. In the decades since the 5-day, 40-hour workweek became the standard, if not the norm, the time freed from work has gone almost entirely to watching screens in their different forms.1 Houses have also grown larger, even as the average number of occupants per home has fallen and the number of screens per person has increased. We might even describe the high-performance house as the building that houses the most, biggest, or best televisions.2 Its performance metric would

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have to combine a minimization of work with a maximum capacity for leisurely consumption. The opposite of this picture of domestic leisure derives from the promises of privacy, protection, and survival also expected of houses. Recognizing the house as a refuge provides quite different terms for performance based on security and self-sufficiency. Perhaps the highest-performance houses of this type are those of survivalists, who distrust the just-in-time food and utility networks of contemporary civilization and have selected very different kinds of homes. The real estate services dedicated to marketing “survival properties” include compelling listings such as “sustainable eco-villa” or “Earth Sheltered Alternative Energy Home on Five Acres.”3 As the survivalist stereotype would suggest, most of these houses are rural retreats, though some are more readily defended urban dwellings, made, for example, of brick. Survival houses come in every variety, from plywood shacks to farmhouses to units prefabricated from shipping containers, such as the All-Terrain Cabin, the Ecopod, or the Quik House, ready for rapid deployment.4 Unlike the house of minimum work and maximum consumption, these houses are understood and purchased for their resource efficiency. Ads on SurvivalRealty.com emphasize on-site water supply, food and fuel storage, and renewable energy technologies. But make no mistake; these houses require real work, especially those that include farmable land. They have exchanged the contemporary promise of leisure time for autonomy and resilience. This comparison may seem nothing more than a contrast between two radically opposed demographic groups, between houses for the status-seeking middle class and shelters for “doomers” and “preppers,” but the difference provides a useful insight into the performance of houses. It’s not that survivalists reject all comfort, or that “McMansions” aren’t marketed as refuges of security; it’s that these two groups use such different strategies toward similar ends, and those similarities point to a different subject for performance. Houses are extensions of messy human households that operate in demanding social networks. Both these kinds of households seek to enhance their wealth and security, but according to very different ideas about the future of contemporary social and technological arrangements. I have used the term household specifically to broaden the question about the performance of houses to include people, their assets (including houses), and their many activities. Shifting the question from houses to households identifies a more promising subject for understanding consumption, one that belongs as much to the occupants as to the specifics of building construction. The ambition of high-performance building design is the reduction of consumption to slow the depletion of non-renewable resources and reduce negative effects on the environment. But is that really the effect? As economists will be quick to point out, the resources saved in the more efficient operation of a highperformance house will likely be spent anyway, whether it is to turn up the thermostat, to buy more stuff (some weapons?) or to support other household goals, such as putting children through college. High-performance buildings maximize useful power, extracting more work from the same amount of energy—a prime goal of engineering. And yet the underlying fact is that individual households seek

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to maintain and enhance their overall power. Households can do this in many ways: by increasing their different kinds of income, increasing the efficiency of their devices (cars, houses, etc.), or by tapping into higher-powered networks by changing jobs, locations, or social positions. Or, in the survivalist view, by withdrawing to safety in case those higher-powered networks collapse. Considering the household as a whole opens the question of whether it makes any sense to normalize building performance to units of area, to compare the per-square-foot consumption rates of a 1,200-square-foot house to those of a 12,000-square-foot complex, if both house the same number of people? Like the truism about guns, people are the real engine of consumption, and a higher-performance house, car, or refrigerator is a tool for enhancing or altering the way people consume. Shifting the focus to households also raises the more challenging questions about social inequity and the fact that social position is largely defined by the amount of assets controlled by a household. This may not seem like a question for architects and engineers, who are charged with designing buildings, but once we make inquiries about consumption and environmental consequences, the scope of the design project expands well beyond the building. Environmental building design demands both an account of the environmental resources (renewable and non-renewable) involved in household consumption and the place of that consumption in societies organized by wealth. The first of these accounts involves an expanded, environmental assessment of building performance, while the second requires a quite different account of consumption. Questions about the performance of houses haven’t been fully answered until we understand the ecological effect of our complex social arrangements, which are themselves tools for increasing productivity and supporting larger populations. In other words, consumption itself may not be the issue. The reduction of consumption is an important first tactic in a wealthy and wasteful civilization, but the ultimate goal is to find the right size of population, without proving the survivalists right.

2.0  Environmental performance of buildings The normalization of building energy consumption to the area of a building is a common technique for comparing different forms of construction, for example between a building made with structural insulated panels (SIPs) and a conventionally insulated frame construction. These are powerful and useful techniques, and are used in setting standards for building performance, but it is important to recognize the degree to which any building performance metric determines the design strategies it encourages by the factors it includes (or excludes). Persquare-foot measurements can clarify the relative performance of different skins and systems, but conceal effects of overall size. Equally important are the different values placed on different kinds of consumption. The survivalist household, or realtor, would include all the resources required for building operation, while the more common measures only focus on utility bills. In response, environmentally minded designers have developed more ambitious and comprehensive metrics for evaluating building performance. Net-

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zero energy and life-cycle assessment represent two different approaches, each extending the goals of building performance yet equally limited by the terms they include. A net-zero-energy design balances the amounts of purchased, nonrenewable operating energies with equivalent amounts of “free” renewable energies; a challenging goal given current technologies. However, as the authors of the recently published AIA Guide to Building Life Cycle Assessment in Practice point out, there are two components of building energy consumption, operational energies—those required to heat, cool, light, and otherwise operate the building—and “embodied” energies—those required in its manufacture, construction, and maintenance.5 As building operation is made more efficient by achieving net zero for example, the importance of embodied energies increases proportionally. Life-cycle assessment procedures extend performance accounting to include embodied energies, which expands the design task from the issue of efficient operation to the optimization of resources used in the whole supply stream of the project, from cradle-to-grave (or cradle-to-cradle). The limiting terms for current life-cycle assessment methods are the different measures of environmental impact to which they are indexed—global warming potential, acidification potential, fossil fuel depletion, ecological toxicity, etc. Each impact suggests different design strategies, once again begging the question of a more fundamental measure of environmental costs and impacts. One answer lies in the nominal value placed on the renewable energies, which are dramatically discounted in both net-zero and life-cycle metrics. Renewable resources are far from free. As ecologists have shown, the renewable resources and energies moving through the biosphere are already doing some other kind of work—supporting the ecosystems that clean, concentrate, transport, and recycle the resources used by human civilization. Every human use of resources is a diversion from some other activity, so there is an environmental cost associated with even the most evidently renewable resource, from sunlight, wind, and clean water to plant, animal, and even concentrated mineral products. A thoroughly environmental performance metric would account for all the work provided by environmental ecosystems, and consider the value of their services on the same footing as those produced by the human economy. Ecological economists have long sought ways to express environmental services in economic terms, making them “internal” to the market economy.6 However, by definition, markets establish the value of resources and services to those that would use them, not according to the work required to produce them. When a resource such as clean water is abundant, the cost is low, and only rises as it becomes scarce within a particular market (or watershed). In effect, the more work done by the biosphere to provide clean water, the lower the market value, because there is less work required of those that would use it. The cost of replacing clean water when it becomes scarce, through energy-intensive processes like distillation or osmotic filtration, is a somewhat better indicator of the work the ecosystem must do to purify and transport it, though even that is dictated by the market value of the fuels used to power the purification and transport. The alternative is to base the accounting on the work required to produce renewable and non-renewable resources alike, and to use that to measure building environmental performance.

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0.2.1 Environmental web of household types on the island nation of Bonaire by Thomas Abel. Households are distinguished by the total amount of assets they control

Over the last forty years, the systems ecologist Howard Odum and his colleagues have developed a method of environmental accounting based on the thermodynamics of the biosphere.7 Every environmental resource and process can be traced back to original environmental sources of energy, to the sun (42 percent), the geological heat of the core (43 percent), and the tidal effects of the moon (15 percent). Without those three sources and the ecosystems they engender, the earth would simply be a cold rock in space. By beginning with those sources, every natural resource or human product can be situated in a sequence of energy transformations and their value expressed as the cumulative energy expended to prepare and deliver them. This is similar to the life-cycle techniques used to account for the embodied energy in industrial processes, except it is extended to include all the work involved, not just the market value of resources or one environmental impact. It can be applied equally to natural resources, like fresh water and fossil fuels, and to human products and services. This produces a thermodynamically rigorous accounting measure that Odum and his colleagues have designated as “emergy,” with an “m,” meaning the total embodied environmental energy, and which is typically expressed in the units of “solar em-joules” (semj). (Figure 0.2.1) Like other determinations of embodied energies, the amount of emergy used up in the production of a resource depends on the specific processes

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involved. For example, in studies prepared by Odum’s colleagues, the electricity produced in a hydroelectric plant in Sweden required 80,246 solar em-joules (semj) of work per joule of electricity delivered, far from free, even though the water flow is thoroughly renewable. By contrast the electricity from a coalpowered plant in Thailand required 169,444 semj/j, nearly twice the work per unit of electricity, because of the many additional transformations required to make coal.8 In another study, the dimensional lumber used in building construction had a typical emergy intensity of 87,900,000 semj/kg of wood, while aluminum sheet requires nearly 100 times the emergy, 1,270,000,000 semj/kg of aluminum.9 These kinds of emergy intensities provide a fundamental metric for comparing resources of different kinds and qualities—operational and embodied, renewable and non-renewable, purchased and free—and a rigorous environmental metric for evaluating the performance of buildings. Emergy accounting has been used for ecosystem and resource analysis for decades, and the journal Ecological Modeling has even debated making it the common technical format for their articles; however its application to building performance is relatively recent.10 A handful of researchers and dissertations have used emergy analysis to evaluate buildings, so much more work remains to be done. The basic task of establishing emergy intensities for different materials and services builds directly on the current research for embodied energy accounting, which is developing databases of results and tools for applying them to design, such as the ATHENA® Impact Estimator and EcoCalculator.11 Emergy analysis doesn’t replace current techniques of building performance assessment, but extends and resituates their results in a larger environmental context. Unlike simple measures of efficiency, emergy accounting is a form of systems analysis, so the design standards and strategies it suggests involve whole buildings and their extended environmental interactions. There is a thermodynamic, emergy minimum for every building, but because of the systemic nature of emergy analysis, it can only be identified parametrically in the interaction among its many factors and components. The house of minimum emergy would provide a maximum amount of comfort, security, and enclosure with a minimum expenditure of environmental resources. Of course that thermodynamic minimum is never zero. A truly zero-energy house would have to be unused and unoccupied, or more accurately, never built. So, even when the highest-performance, minimum emergy house has been produced, we are still left with the challenging questions about wealth and consumption—how much is enough?—which can’t be answered by the analysis of buildings alone.

3.0  Households It is fitting that the word ecology was derived from the Greek word for house, oikos, and it is to systems ecology that we must turn to really situate household consumption. The term ecology was originally coined to identify the role of the environment in the evolution of life, and ecology has in turn revealed the degree to which life has shaped that environment to its own ends. Houses, too, can be understood as part of the ecology of human consumption, shaped in their

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occupants’ struggle for wealth and security and directly furthering, even symbolizing, their prosperity. Human societies have continued to evolve ever more complex arrangements that support ever-larger populations at higher rates of consumption. It is the success story of human civilization, and it is also the characteristic story of any biological population, which expands to the limits of available resources. The particular explosion of human wealth and population in recent centuries has resulted from two factors: the increasing ingenuity and efficiency of our technologies, which have enabled us to extract more value from resources, and the discovery of resources well beyond the basic solar income that limited the size and wealth of earlier human societies. While the environmental debate often focuses on the limiting nature of those factors—will resources like oil really run out, and why can’t we come up with even better technologies?—the more important story concerns the competition for resources itself and the spectacular growth in complexity of both biological life and human societies. One lesson of systems ecology is the deeply evolutionary nature of ecosystems, and the competition for useful power that drives them. The story is less easily told because its subject involves the dynamics of populations and generations rather than heroic tales of individuals. No individual decided that human population should grow into the billions, even though many groups have sought to outgrow their neighbors. The narrative about human consumption is less a morality tale about greed, than the collective effect of many, incremental acts of ingenuity and household efficiency. The collective results of those many acts, however, are not random or chaotic. The basic proposition of systems ecology is that ecosystems, including human society, are self-organizing and do so to increase their total power and prosperity.12 In other words, social self-organization is a process of selecting those households suited to prosper, not just those that are strong or wealthy, but those that also reinforce the larger systems in which they operate. Odum called it the maximum power principle and it applies to whole ecosystems, not just individ­ uals.13 The middle-class household of maximum consumption and the survivalist retreat will succeed (or not) as parts of the larger social systems in which they are situated. Both kinds of households develop from the access to massive power and resources of the last two centuries. As long as those resources continue to be available, households that are well-positioned in current social hierarchies can prosper, but if those flows falter, then not only will survivalist households do well (or at least better), but the rest of the households will either become survivalists too, or disappear. The message is not really about competition, but about the many kinds of interaction and cooperation required for larger populations to survive at all, and the degree to which contemporary social arrangements themselves constitute a technique for maximizing the flow of power and resources. The second part of Odum’s maximum power principle concerns the success of complex hierarchies of energy transformation, which succeed by the amplification of production and the recycling of waste. This is typically illustrated by the richly hierarchical food networks in climax forests—green plants, herbivores, and carnivores—but the same principle applies to social and economic systems. The high-performance house belongs to a hierarchical social system that has evolved to increase the flow of resources. The specialization of roles

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and the differentiation of rewards for those roles characterize the evolution of human culture, from tribes based on hunting, to the towns and cities supported by agriculture, to the national, and now global, political arrangements made possible by tapping the stored potential of fossil fuels. It isn’t that new technologies and energy sources directly cause new social arrangements, or that a particular path of cultural evolution is somehow inevitable, but that the arrangements which increase human power persist. (Figure 0.2.2) When human consumption is considered in a broader social context, the distinction between residential and commercial buildings seems less obvious. After all, the same people are using both kinds of buildings, “living” in one kind and “working” in the other (and driving their cars between the two). This is another version of what I think of as the “footprint problem.” In the methods for determining the responsibility for carbon emissions that have been codified by the World Resources Institute, emissions are divided into “scopes” of influence or responsibility, meaning the degrees of control exerted by the entity whose footprint is being calculated.14 If you burn a fuel in your furnace, that is scope 1, if the electric company burns the fuel in their plant, that is scope 2, because you can decide whether or not to use the electricity, but not how it is burned. Scope 3 emissions are even more removed from direct influence or control, involving, for example, the emissions released in the manufacturing and delivery of products that you choose to buy (or not). This is an accounting technique developed to reduce double counting, but the carbon footprints of individuals still overlap messily with the footprints created for companies or institutions. Was that trip voluntary or for work? Didn’t the food you ate at home actually contribute to the work you did at the office? The confusion derives from the deep assumption that consumption is an activity of individuals in households, while production is a separate activity of business entities. That assumption has been criticized by the ecological anthropologist Thomas Abel, who has argued that since consumption and production are the work of the same individuals, the conventional economic model should be unified in a more comprehensive description centered on households.15 His ambition is to reveal the ecological basis of social organization, and understand the limits that the ecosystem places on economic activity. The result is a more complete accounting of the resources commanded by households, including not just immediate assets like houses and cars, but everything owned or controlled by its members. His critical insight is that the different kinds of business firms are nothing more than a facilitation of the exchanges and interactions among different kinds of households. Ultimately the wages and profits of businesses flow to individuals in households, and form the basis of socioeconomic differences. Houses that live on wages paid in exchange for labor differ in their capacity for consumption from those households supported on the profits from ownership. The immediate conclusion of Abel’s consolidated ecosystem model is that the consumption we are trying to regulate depends on the socioeconomic class of the household. Wealthier households own more and consume more. This is not a surprising observation in itself, but it turns our question on its head. Should the answer to “how much is enough” be different for different classes of households, or should all households be held to the same standard? This is well

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0.2.2 Thomas Abel’s socioeconomic hierarchy of households distinguished by total amount of assets controlled

beyond the regular work of designers and shows the kinds of issues concealed by current performance standards. It places the regulation of high-performance houses among other political discussions about freedom, equity, and efficiency. How great a difference in wealth is fair, and when does it become the concern of society generally to regulate or restrict it? The income tax code, for example, is already progressive, with higher rates for wealthier households, even as the degree of difference in rates is debated and adjusted. That debate typically focuses on individual achievement and the rights of individuals to keep what they have earned, but the ecosystem model of the economy argues that it is the whole economy and ecosystem which make such wealth possible. Up to a point, the differences in wealth based on the specialization and hierarchy of roles increase the flows or resources, but beyond that point, excessive concentrations of wealth only reduce the efficacy of the whole system. The more complete conclusion would recognize that socioeconomic classes and their membership are far from fixed, and that even the debates about equity and the constant shifting of wealth among households constitute part of the restless process of self-organization to increase overall wealth. Perhaps the simplest statement would be that it’s not really about houses (or cars or shopping bags), it’s about people and their ever-expanding presence in the biosphere. Efficiency gains of all kinds, including higher-performance houses, are ultimately tactics for shifting resources to facilitate growth. A household (or city or country) that voluntarily renounces high levels of consumption effectively gives the available resources to other, higher-level consumers, whose population will then increase. In these dynamics, are humans really any different than other biological populations that simply grow until the available resources have all been consumed and their population declines or collapses? The final lesson of systems

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ecology is that these cycles of growth and decline are themselves a result of the blind drive of self-organization (“the invisible hand of the market”), which pushes populations to constantly test the limits of their ecosystems. Human households only differ from other forms of life in their ability to ask the question, “how much is enough?”

Notes 1 S. de Grazia, Of Time, Work, and Leisure, New York: The Twentieth Century Fund, 1962. J. P. Robinson and G. Godbey, Time for Life: The Surprising Ways Americans Use Their Time, University Park, PA: The Pennsylvania State University Press, 1997. 2 That definition isn’t as accurate as it was only a decade or two ago as screens have been introduced into numerous other settings—food courts, hospital rooms, and shoe stores— precisely to make them seem more home-like. 3 J. Edwards (2008) SurvivalRealty.com. Available at: www.survivalrealty.com (accessed 30 January 2011). 4 Bark Design Collective (2009) All-Terrain Cabin, Open Architecture Network. Available at: http://openarchitecturenetwork.org/projects/6400 (accessed 30 January 2011). A. Kalkin (2004) Quik House, Kalkin & Co. Available at: www.quik-build.com/quikHouse/QH_main.htm (accessed 30 January 2011). 5 C. Bayer et al., AIA Guide to Building Life Cycle Assessment in Practice, Washington, DC: American Institute of Architects, 2010. 6 H. E. Daly and J. Farley, Ecological Economics: Principles and Applications, Second Edition, New York: Island Press, 2010. 7 T. Abel, “Emergy, Sociocultural Hierarchy, and Cultural Evolution,” EMERGY SYNTHESIS 4: Theory and Applications of the Emergy Methodology, Proceedings, Fourth Biennial Emergy Conference, Gainesville, Florida, 2007. H. T. Odum, Environmental Accounting: EMERGY and Environmental Decision Making, New York: John Wiley & Sons, 1996. 8 Odum, op. cit., Appendix C: Transformities. 9 V. Buranakarn, Emergy Indices and Ratios for Sustainable Material Cycles and Recycle Options: Evaluation of Recycling and Reuse of Building Materials using the Emergy Analysis Method, Unpublished PhD Dissertation, University of Florida, 1998. M. T. Brown and V. Buranakarn, “Emergy Indices and Ratios for Sustainable Material Cycles and Recycle Options,” Resources, Conservation and Recycling 38, 2003, pp. 1–22. 10 S. Maud, “A DirectScience: The Synthesis of ScienceDirect and EmSim,” Ecological Modeling 203, 2007, pp. 518–520. 11 Athena Sustainable Materials Institute (2009) Athena Institute. Available at: www. athenasmi.org/ (accessed 30 January 2011). 12 In 1922, the biophysicist Alfred Lotka argued that “the fundamental object of contention in the life-struggle, in the evolution of the organic world, is available energy. In accord with this observation is the principle that, in the struggle for existence, the advantage must go to those organisms whose energy-capturing devices are most efficient in directing available energy into channels favorable to the preservation of the species.” A. J. Lotka, “Contribution to the Energetics of Evolution,” Proceedings National Academy of Science 8, 1922, pp. 147–151. A. J. Lotka, “Natural Selection as a Physical Principle,” Proceedings National Academy of Science 8, 1922, pp. 151–154. 13 C. Hall, Maximum Power: The Ideas and Applications of H. T. Odum, Niwot, CO: University Press of Colorado, 1995. 14 The World Resources Institute (WRI) and World Business Council for Sustainable Development have jointly developed the Greenhouse Gas Protocol Initiative: GHG Protocol (2011) Greenhouse Gas Protocol Initiative. Available at: www.ghgprotocol.org (accessed 30 January 2011). For a discussion of “Scopes” of emissions, see for example their publication: J. Ranganathan et al., A Corporate Accounting and Reporting Standard, The Greenhouse Gas Protocol, 2004.

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15 T. Abel, “Systems Diagrams for Visualizing Macroeconomics,” Ecological Modeling 178, 2004, pp. 189–194. The consolidated ecosystem model is illustrated in his earlier work, “Understanding Complex Human Ecosystems: The Case of Ecotourism on Bonaire,” Conservation Ecology 7, 2003, p. 10. Available at: www.consecol.org/vol7/iss3/art10 (accessed 30 January 2011).

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Part 1

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Energy-Free Architectural Design: The Case of Passivhaus and Double-Skin Façades



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Translucent Building Skins: Advancing the Technology of Light Transmission



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Responsive Building Envelopes: Characteristics and Evolving Paradigms



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Chapter 1.1

Energy-Free Architectural Design: The Case of Passivhaus and DoubleSkin Façades franca trubiano

ABSTRACT: Climate-responsive design has been practiced in traditional cultures since the beginning of recorded history. Its energy-free architectural design principles seek to maintain a building and its interior environment within a balanced comfort range without additional inputs of non-renewable energy. With global interest in low-energy high-performance buildings, energy-free design principles are increasingly promoted for a range of climates and for many parts of the world. The Passivhaus movement and the interest in ‘double-skin façades’ are two contemporary examples of highly adaptable envelope-based strategies which successfully integrate the benefits of energy-free design. Albeit vastly different in their approaches, both offer important lessons for achieving high-performance measures alongside excellence in design.

1.0  Defining the practice In coining the term ‘energy-free architectural design’ this chapter renames one of the most commonly used monikers associated with sustainable architecture: ‘passive design’ and/or ‘passive solar architecture’.1 The term ‘passive’ had been used to describe the opposite of ‘active’ building’s systems, and it so being, has been associated with climate-specific architectural strategies not requiring of additional inputs of energy for their effectiveness. Given, however, the vastly successful solutions made possible by its highly productive principles, energy-free architectural design is a more appropriate phrase for identifying the tenets of a continually maturing and developing building science dedicated to the saving of energy and the enrichment of architectural experience. The phrase in no way suggests its principles are unencumbered by energy considerations,

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but rather benefit from the workings of energy at no additional net costs to the environment. Energy-free architectural design remains one of the most cost-effective means for achieving highly-performing buildings. Its principles of climateresponsive design have been tried and tested for thousands of years. Carefully considered at the very beginning of the design process, they reduce, if not eliminate, a building’s energy load while imparting to the home an architectural language consonant with the building’s geography. Recent interest in low-energy high-performance buildings has evidenced a return to its tenets, particularly those with easy applicability in varied climates, cultures and parts of the world. And contrary to its own history, contemporary initiatives seek the translation of their material and operational details across a broader spectrum of environmental conditions. In general, the field of energy-free architectural design seeks the following ecological goal: maintenance of a building’s thermal, ventilation and lighting environment within a balanced comfort range (both qualitatively and quantitatively) such that radically reduced amounts of additional energy (non-renewable or otherwise) are required, regardless of the external forces acting upon the building (be they temperature, humidity, wind, rain or solar radiation).2 Among its most often applied principles are those contributing to the proper selection of a site, to a building’s location and orientation, and to the interior layout of the building’s program spaces. A site’s topography, vegetation and access to sun, air and water define its potential for power generation, light transmission, thermal heating and ventilation cooling.3 A building’s orientation can be used to minimize excessive heat gains or to channel the thermal benefits of solar heat. The layout of a home, in plan and section, can be optimized to protect against wintery winds or to encourage exposure to refreshing breezes.4 These, and similar strategies, have been well documented for their adaptability on most building sites.

1.1  Beginnings of energy-free design principles Climate-responsive design has been practiced in traditional cultures since the beginning of recorded history. Its clearly recognizable principles, including the proper alignment of a city’s grid for maximum natural ventilation and the avoidance of marshes and overly humid sites for the founding of a town, were recorded as early as the first century AD.5 Its lessons are as effective today as they were then. Wind towers and adobe mud bricks continue to be used in hot and dry climates, while trombe walls and thermal mass are celebrated as low-energy solutions for retaining thermal heat in cold environments.6 During the twentieth century, a wide array of indigenous strategies were studied and codified by architects and cultural historians. In House Form and Culture (1969), Amos Rapaport wrote of the cultural function of climate, environment and geography. Sun, water, air and temperature affected the form of vernacular buildings crafted by skilled villagers throughout the world. And as keepers of a cultural practice of intelligent building, villagers were always highly attentive to a site and its local climate.7 In Architecture Without Architects, Bernard Rudofsky

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wrote of the many original building practices, which independent of architectural intention, were knowing of the thermal benefits of channeling air (as in the bad-gir wind scoop of Pakistan) and of living in carved-out dwellings (as in the hollowed out underground buildings of the loess belt of China).8 Little was codified, however, prior to the publication of key works that communicated the principles of energy-free architectural design to a professional audience. The first was William Atkinson’s The Orientation of Buildings, or Planning of Sunlight, published in 1912.9 As an architect from Boston who worked on the design of hospitals, Atkinson planned buildings as a function of solar exposure. Addressing quality of life issues in many congested urban cities with tall buildings, he promoted their exposure to direct solar radiation to ensure the health of its inhabitants. He studied the sun’s movement (with sun-path diagrams) teaching architects how to calculate the location and orientation of buildings to avoid an abundance of shadows. In 1933, this was once again the subject of a publication by the Royal Institute of British Architects (RIBA). The Orientation of Buildings was a detailed guide for integrating daylight in design introducing architects and town planners to the merit of heliodons, sunshine gauges and pinhole photography.10 By the late 1950s, the sun and its movement had become the subject of detailed analytical studies by Victor and Aladar Olgyay, who in their first publication Solar Control and Shading Devices of 1957, promoted its study as an element of design.11 They offered practicing architects building-science-related knowledge for the composition of façades truly responsive to sunlight. With the publication in 1963 of Design with Climate: Bioclimatic Approach to Architectural Regionalism, the Olgyays promoted the regional character of human shelter, comfort, bioclimatic charts, microclimates, the heat transmission of materials and the use of graphical and mechanical tools for determining the sun’s path. By the mid-twentieth century, the sun’s movement and its control were transformed into an easily recognizable architectural motif by celebrated architects. Le Corbusier introduced the brise soleil at l’Unite d’Habitation in Marseilles (1947–1952), the Dominican Monastery of La Tourette (1953–1957) and in his retrofit of the façade at Cité Refuge—l’Armée du Salut (1952). When Richard Neutra rebuilt his VDL II home and office in Los Angeles in 1966, full-height operable vertical sunshades of great elegance were prominently integrated in the entrance façade. In these and countless similar projects, the shading device had become a veritable emblem of solar-responsive design. In the area of applied research, Hungarian-born chemist Maria Telkes conducted early studies in the use of sunlight for the heating of homes. In 1940, as researcher at the Massachusetts Institute of Technology with the Solar Energy Conversion Project, Telkes experimented with thermoelectric devices and other inventive mechanisms for the storage of heat energy. (Figure 1.1.1) In 1949, alongside architect Eleanor Raymond and patron Amelia Peabody, she built an early experimental solar house in Dover, Massachusetts, demonstrating the virtue of integrating sophisticated forms of technology within the single-family house.12 A fully glazed solar heat collector was installed on the second floor of the southern façade. It measured 75 feet long and in combination with sodium sulfate decahydrate (Glauber’s salts), an early phase change material, the architectural device stored solar heat energy. Using a set of fans, hot air was drawn from the

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collector to the Glauber’s salts; when prompted by a drop in temperature, the stored energy was thereafter rereleased and distributed throughout the house using fans.13 Decades later, the field was transformed when harnessing sunlight was explicitly aligned with its capacity to generate energy. In 1969, Baruch Givoni in Man, Climate and Architecture comprehensively codified building-related design variables, such as building materials, wall details, room profiles and building orientation, whose energy performance was contingent upon the effects of light, heat, air and moisture.14 Less than a decade later, during the energy crisis of the mid 1970s, power-saving strategies were sought for the building of new homes such that climatically appropriate energy-free architectural principles were now translated into the science of ‘passive solar design.’ In the United States, Ed Mazria organized many of its most basic principles in his Passive Solar Energy Book, introducing the language of degree-days, thermal storage and direct and indirect gains to an architectural audience.15 The question remains, however, why the promise of energy-free design principles was not fulfilled during this earlier period of great need, extensive research and proven principles? A possible answer can be found in the following observation made by Bruce Anderson in Solar Building Architecture. While engineers were responsible for developing the science and technology of ‘active’ systems, architects were focused on finding a recognizable iconography for ‘passive’ building design, and builders were involved in the actual construction of energy conservation strategies. Only in the very best of circumstances did collaborative activities take place amongst all participants.16 Hence, called upon once again to devise innovative solutions for reducing the operating energy of homes, a far more integrated approach is required to achieve the true promise of energy-free architectural design in the twenty-first century. To this end, this chapter discusses two widely different approaches. The first acknowledges the Passivhaus movement and its endorsement of super-

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1.1.1 Maria Telkes and MIT Solar House. (Left) Exterior of MIT Solar House in Dover, Massachusetts (1949). (Right) Maria Telkes and Eleanor Raymond, Architect in front of MIT Solar House

insulated building enclosures for minimizing the need for energy-consuming building systems. This initiative by engineers, designers and builders has had a catalytic effect on the residential industry in countries where its tenets have achieved social if not political acceptance. Its architectural guidelines are explicit, quantitatively rigorous, verifiable, and adaptable in many regions of the world. The second approach to advancing the science of energy-free architectural design introduces the construction of ‘double-skin façades’ whose technological prowess holds great promise for high-performance homes. Invented for use primarily in large-scale office environments, this envelope-centered technology is being investigated for possible transfer in the thermal operation of single-family homes, an example of which will be described.

2.0  Passivhaus The Passivhaus movement represents an international group of design, construction and engineering professionals actively dedicated to the advancement of energy-free architectural design principles. Certified building professionals implement sophisticated, yet low-technology, high-performance measures for energy-efficient buildings. The group’s members include the Passivhaus Institut and its certified international chapters as well as the International Passive House Association. Together they promote the Passive House Building Energy Standard, a performance-based certification program that evaluates the energy savings of single-family homes, multi-family housing and small-scale commercial and institutional buildings.17 (Figure 1.1.2) The Passivhaus Institut is a research-based group of engineers, mathematicians and physicists founded in 1996 in Darmstadt, Germany by Wolfgang Feist. Its origins are in the Passivhaus concept, co-formulated in 1988 by Feist and Bo Adamson (Lund University), whose five tenets are as follows: all homes should be super-insulated, designed with minimal thermal bridges, built to be air tight, glazed with highly insulated window assemblies and operated using heat recovery ventilators. The main hypothesis being that homes located in northern temperate climate zones, with greater heating than cooling demands, could forgo artificially supplied energy for the purposes of heating if designed to maximize solar heat gains. Once solar heat energy is transmitted to the interior, homes built to Passivhaus standards retain their thermal comfort by using heat recovery ventilators for introducing fresh air with a minimal loss of energy. Proof of concept first was the construction in 1991 of the first Passivhaus project built in Kranichstein, Darmstadt. This multi-family residence was designed and built employing each of the five tenets described above. Direct southern exposure maximized desired heat gains in primary living spaces; it was detailed using 10 to 18 inches (250–450 mm) of polystyrene and blown-in mineral wool insulation for the basement, roof and exterior walls; the windows were triple-pane krypton-filled insulated frames; and air-to-air heat recovery ventilators were used with 80 percent efficiency. The fresh air intake for each home was located on the northern face of the building with the air ducted below ground

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1.1.2 Certified Passivhaus in Neuenhagen, Berlin. This two-bedroom home designed by ArchitekturWerkstatt Vallentin and completed in 2010 measures 153 square meters. Its principal glazed façade is oriented south to maximize solar exposure for the winter months and inset sufficiently to protect against excessive solar heat gain. The south-facing balcony also protects the ground floor from excessive solar exposure and the envelope’s construction includes a highly insulated timber frame, triple-glazed windows and an air-tight skin. (Client – Ottmann GmbH & Co. Südhausbau KG)

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for preheating before traveling to the heat exchanger. The housing complex included an unconditioned north-facing glass atrium that performed as a thermal buffer. Once completed, extensive monitoring began with results confirming the merit of the idea and the attainability of its goals. As published by the Institut, the inaugural Passivhaus uses 88 percent less energy than a typical German home.18 By 1998, the Passive Housing Planning Package (PHPP) was developed to guide certified practitioners in designing to Passivhaus standards. The 2007 version of the PHPP is a sophisticated software package available for both residential and non-residential buildings, for new construction and renovations. Validated against 300 projects, the tool facilitates calculation of thermal conductivity values, internal heat gains, energy balance, ventilation rates, total energy demands, and electricity demands from fans and other plug-in loads. It can be used during the design process to parametrically model the effect of external walls, windows, ventilation rates, solar absorption of external materials, and internal loads on energy use.19 Tens of thousands of buildings have already been built using the standard, mostly in Central Europe where the climate is optimal. Yet many of its tenets are just as effective in cooling dominated environments that depend on air conditioning for thermal comfort. Highly insulated building skins, minimized thermal bridging, air tightness and energy recovery ventilators are necessary for minimizing the consumption of energy in hot and humid climates. And where abundant solar radiation can be found, the Institut promotes the use of low-tech solar hot water collectors to further offset energy consumption. The worldwide popularity of Passivhaus has resulted in the founding of international chapters including the Passive House Institute US (PHIUS) and Passivhaus UK managed by the Building Research Establishment (BRE).20 They offer access to a wide array of services including certification of consultants and buildings, thermal modeling, and the testing and monitoring of homes and equipment. The certification process endorses designer/consultants and building inspector/certifiers involved in the delivery of buildings, as well as actual building components tested for performance, including wall and construction systems, glazing, doors, and curtain-wall systems. Certified designers can be found in over 35 different countries including Latvia, United Arab Emirates and Bulgaria. In the United States, nearly 200 PHIUS consultants help with the decision-making process during the early design phase of a project, during construction as well as during post-construction monitoring. Consultants verify homes to ensure they are built air tight and without thermal bridging; details necessary for achieving the Passive House Building Energy Standard and for securing official certification. Hundreds of successful Passivhaus homes have been built, including the first Passivhaus certified in London, UK by bere:architects. (Figure 1.1.3) Located in Camden, the two-bedroom, two-storey home is 118 square meters and, in keeping with Passivhaus standards, built using a heavily insulated exterior envelope made of 3-meter-tall retaining walls and prefabricated timber frames. It features glazed openings to the south for maximizing winter solar heat gains. It is cool in the summer and warm in the winter. The PHPP was employed in siting the house and in establishing the amount and location of fenestration. Triple-

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1.1.3 (facing) Certified Passivhaus, bere:architects, Camden, London 1.1.4 (top) Certified Passivhaus, KEY Architects, Kamakura, Japan

glazed windows were used alongside automatic retractable shades for protecting against summer solar exposure. It employs a highly efficient energy recovery ventilator (ERV) that contributes directly to the home’s 90 percent reduction in energy consumption over a typical London residence. In desiring to implement larger ecological strategies, rainwater is harvested and a solar thermal panel is used for supplying the house’s domestic hot water needs. Urban landscaping strategies include a green roof and south-facing green wall. And as noted by bere:architects, the project surpasses the minimum standards of the UK Building Regulations Part L 2006 by 70 percent as well as being compliant with the UK 2016 definition for zero-carbon homes. The firm’s commitment to the Passivhaus program continues, having just completed a 6-Month Post-Construction and Initial Occupation Study and initiating a 24-Month In-Use Performance and Post-Occupancy Evaluation, both of which were funded by the UK’s Technology Strategy Board. In autumn 2009, the very first Japanese certified Passivhaus was built in Kamakura city, Kanagawa prefecture, Japan, by KEY Architects. (Figure 1.1.4) The two-storey home was designed to integrate within its setting as well as to promote the tenets of energy-efficient design. To this end, it was clad with locally sourced cedar, detailed with an abundance of insulation, glazed with triple-pane windows from Germany and built according to the best practices for achieving air tightness. Light wood-frame techniques were used for the house’s main structure and wood fibers were used for insulation. Its particular invention lay in updating Passivhaus standards for the Japanese climate, being a great deal more humid than the temperate climate of Europe. Unconventionally, this house used a vapor barrier/retarder that allows the air moisture to travel in both directions across the wall, avoiding the very real possibility of condensation in the building envelope. In so doing, this Passivhaus demonstrates the program’s capacity to accommodate to local conditions.

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Architects C. F. Møller completed Villa Alstrup in 2010 in Hjerting, Esbjerg, Denmark to the same high standards. (Figure 1.1.5) The four-bedroom, 311-square-meter house was designed to take advantage of passive solar heating for free winter heating. Its compact building volume minimizes heat loss to the exterior, as do the insulated windows and integrated shading. The building’s cross-section clearly identifies the house as designed according to the principles of Passivhaus. The southern exposure is carefully profiled for solar heat gain during the winter season while the northern façade, roof and basement perimeter walls are highly insulated (400–600 mm) and barely fenestrated. The floors to the south of the house are designed for maximizing the benefits of thermal mass. And the house is host to three forms of renewable energy technology including a ground-heat exchanger, photovoltaic solar electric power and solar hot water collectors. Villa Alstrup has passed post-construction inspections and is in the process of being Passivhaus certified. These, and other such projects demonstrate the design potential of adopting Passivhaus standards, be they in Japan, Denmark or the UK; with certification primarily a function of the compactness of the building’s volume and the detailing of its skin. The construction of the roof, exterior walls and foundations directly impacts the home’s energy equation. Their materials, detailing and craftsmanship affect the efficacy of the overall standard. Said otherwise, maximum insulation and minimal air leakage are of greatest value when building a Passivhaus. Recommended operable openings are limited to those used for controlled ventilation, such as the air intake used to transport limited amounts of outside air to the heat exchanger. These principles do, however, inadequately address the human desire for operable windows, privilege the use of highly engineered insulation materials for the building’s exterior finish (to minimize thermal bridging) and limit the amount of fenestration permissible on façades other than the south. These are clearly limitations and notwithstanding well-documented successes of the Passivhaus standard, alternative solutions are required when increased operability of the building envelope and increased levels of light transmission are desired.

3.0  Double-skin façades

1.1.5 Villa Alstrup, C. F. Møller Architects, Esbjerg, Denmark

A well-constructed building envelope maximizes the benefits of energy-free architectural design.21 The potential for reducing, if not eliminating, the need for extraneous energy, while maintaining thermal comfort, resides in the rigorous design of a façade that channels light, reduces heat loss and mitigates air transfer. Its materials, construction details, glazing type and aperture design can be calibrated for the highest level of solar, thermal and ventilation performance. This design activity is a veritable sub-science of building technology with many resources available to those interested in exploiting its potential for architectural invention and sound environmental design.22 The ‘double-skin façade’ is the latest innovation in the field occasioning serious study and discussion. Used extensively in curtain walls for commercial buildings throughout the world, its commercialization represents a new type of

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exterior skin, engineered to optimize a building’s energy equation.23 Albeit few attempts have been made to introduce this integrated building technology in the construction of single-family homes, prototypes with the greatest promise are currently being designed and built. It is a form of technology that operates beyond the divide of ‘active building systems’ and ‘passive design principles’. It is predicated on fully integrating a building’s envelope with its building systems. Given the goal of maximizing the energy reduction potential of both, its three main functions are sunlight control, thermal heating and/or cooling and natural ventilation. Intelligently designed, a double-skin façade can increase access to daylight, convert sunlight into heat energy, recover heat energy for re-use in other parts of the building, facilitate the ventilation of interior spaces, and mitigate the infiltration risk of outside air.24 The exact details of any double-skin façade are contingent on the climate in which it will operate, yet in all instances it is built of an inner and outer layer, four surfaces, and an air cavity.25 Key to its energy-dependent functionality is the width of the air cavity. Designed to be as narrow as six inches or as wide as three feet, it is engineered to operate in conjunction with the building’s ventilation, heating and electrical systems. To this end, the cavity can incorporate shading devices, heat exchange mechanisms, thermal controls and ventilation ducts, automated or otherwise; the particular combination of which is dependent upon the building’s energy goals and the geographical context.

3.1  Daylight transmission, solar shading and thermal buffers The controlled transmission of daylight to the interior of a space is an energy-free architectural design principle easily introduced when engineering a double-skin façade. Extending the use of daylight for ambient and/or task lighting in the home, all the while having access to mechanisms which control its transmission, is a sure means for reducing artificial illumination and its accompanying consumption of energy. The transparency and/or translucency of each material layer, the window to wall ratios, the size of window openings, the solar heat gain coefficient, the visible transmittance, and the use of spectrally advanced films can be optimized for light transmission and energy performance. Additionally solar shading devices such as fixed and/or movable awnings, louvers, shades and/or blinds are used for controlling the envelope’s ratio of light to heat energy.26 In cooling dominated climates, maximizing daylight transmission requires the careful balance of luminance and energy levels by orchestrating the closure of shading devices on a daily basis. Vastly more effective is the use of doubleskin façades in heating dominated climates where they are used to maximize solar heat gain. In a manner analogous to a greenhouse, solar rays transmitted to the interior of the cavity are converted into heat energy.27 Captured between two layers of glass, this form of energy conversion increases the amount of heat available for thermal comfort, as it protects the inside air from extreme exterior temperatures.

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3.2  Heat transfer and heat recovery As noted, solar rays can be used to strategically heat the air in a double-skin façade, be it transparent or otherwise. If kept at rest, the air can serve as a thermal blanket. When encouraged to circulate, it can be used for a number of energysaving purposes. The heat energy in the air cavity can be encouraged to move to the top of the chamber or to ducts for further distribution by a form of convection called thermosiphoning. This induced air movement (enhanced by using darkly colored surfaces, metal absorbers and thermal chimneys) promotes the collection, storage and subsequent diffusion of heat energy. The captured energy can be transferred to storage devices (such as phase change materials or water), ducted to other areas of the house, or extracted by heat recovery units. In all three cases, the cavity of the double-skin assembly is connected to ducting and recovery devices. Alternatively, the exterior layer is not limited to being made of glass. It can also be made of dark metals which, when heated, heat the air in the cavity by conductance and radiation. Once collected in the cavity, the heat energy can be stored, diffused or recovered. A recent example of which is the western façade of the new National Renewable Energy Laboratory (NREL) Research Support Facility in Golden, Colorado, whose metal skin heats the air contained within a chamber and transports the heated air to a series of serpentine concrete walls located in the building’s basement.28

3.3  Trombe walls All materials that come into contact with sunlight absorb energy as a function of their reflectivity, opacity and density; a characteristic of heat governed by the principle of thermal mass. The large heat capacity and absorption potential of stone, brick, concrete and adobe can be employed to productive ends in both hot arid and cold climates. In the thermal lag of these materials—the time required for the heat to be absorbed by the mass and thereafter reradiated—the surrounding air is cooled. When temperature differentials are large enough for the stored heat to be reradiated, the process is reversed.29 Thermal mass mitigates the temperature extremes that accompany direct and indirect solar heat gains and when combined with a layer of glass, the result is a double-skin façade called a trombe wall. In its simplest manifestation, the interior surface of the thermal mass can be used to reradiate its heat energy to the inside of the room. More dynamically, using a form of thermosiphoning described here above, heat is allowed to build up in the space between the mass and the glass and thereafter ducted, collected, or recovered.30 Hence, the use of a trombe wall in a double-skin façade offers yet another opportunity for offsetting energy loads using energy-free architectural design principles.

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3.4  Natural ventilation Double-skin façades are ideal mechanisms for orchestrating a building’s natural ventilation. Air exchanges are required for maintaining the health of indoor environments. As with a regular window, introducing openings in both the exterior and interior layers of the assembly, allows for exterior air, whose temperature and humidity are within the comfort range, to be introduced to the interior of the home. In addition, the cavity of a double-skin façade can be ventilated in such a way that it contributes to cooling the home’s interior. Without further energy inputs, and with the proper coordination of operable windows and vents, nighttime flushing of hot indoor air can be achieved; as can the flushing of air in northfacing skins using solar chimneys which draw air from the bottom of the cavity. This form of energy-free cooling is essential for maintaining thermal comfort in hot-dry and hot-humid climates and for facilitating air changes without the expenditure of mechanical energy.

3.5  Prototyping a double-skin façade A double-skin façade of note is the very first prototype to be built and operated in the design of a net-zero solar-powered home.31 (Fig.1.1.6) Built by a team of researchers at the University of Tennessee, the Living Light House has been designed with both south- and north-facing building envelopes that operate as a double-skin façade. The façades are made of an outermost layer of single-pane glass and an inner layer of 2-inch quadruple-paned insulated glazing. The inner unit has two internal layers of mylar film and three argon-filled cavities; for a thermal resistance value of 11. Between the two layers of single glass and quadruple glass is a solar shading device that can be programmed for optimal seasonal operations. The component key to the façade’s performance is the energy recovery ventilator (ERV), integrated in the operation of its air exchange. As with the use of an ERV in the Passivhaus concept, this house’s ERV captures heat energy for efficient reuse during the winter and summer. What is new, however, is the capture of energy from both the main living space and the north and south cavities in the double-skin façade. During the summer, the cool air from the already conditioned interior living space is recovered; during the winter, the heat energy from the already heated interior living space is recovered. Additionally, during the winter, the southern façade preheats the air inside the cavity and this ‘free’ thermal energy is thereafter used to offset the heating load for the building. In the summer, ambient exterior air is made to move from the colder northern façade and exhausted through the warmer southern façade. Hence, the ventilation mode for the summer is from the north façade to the south; the ventilation mode for the winter is from the south façade to the north. This is the first of, hopefully, many more prototypes aimed at engineering the integration of the building’s envelope alongside that of its larger building systems. Double-skin façades are a resource whose energy-saving potentials have yet to be fully explored in the context of high-performance homes and this project makes a welcome contribution to the discussion.

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1.1.6 Prototype of the University of Tennessee, Living Light House, double-skin façade

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4.0  Conclusion The recent interest in low-energy high-performance buildings has promoted energy-free architectural design principles that are easily applicable in multiple climates and in many parts of the world. Both the Passivhaus movement and the current fascination with double-skin façades are exemplary of the ambition to develop envelope-based strategies for low-energy design, easily adaptable within a global context. The former has defined its principles of high insulation, no air infiltration and heat recovery, by perfecting the construction practices of singlefamily housing, while the latter continues to adapt the technologies of thermal gain, solar shading and heat recovery, developed in commercial curtain walls, to the scale of the house. While vastly different in approach, they offer important opportunities for attaining high measures of performance alongside excellence in design.

Acknowledgments The author acknowledges the valuable comments and insight offered by Michael Hindle, a certified Passive House Consultant and Acting Chair of the Mid-Atlantic Passive House Alliance.

Notes 1 E. Paul, Passive Solar Energy, Design and Materials, Park Ridge, New Jersey: Noyes Data Corporation, 1979; E. Dean, Energy Principles in Architectural Design, Sacramento, CA: California Energy Commission, 1981; B. Anderson, ed., Solar Building Architecture, Cambridge, MA: MIT Press, 1990; J. Balcomb, Ed., Passive Solar Building, Cambridge, MA: MIT Press, 1992; T. Johnson, ‘Performance of Passively Heated Buildings’, Journal of Architectural Education, Vol. 30, no. 3, Energy and Architecture, February 1977, pp. 16–20. 2 See N. Lechner, Heating, Cooling and Lighting: Sustainable Design Methods for Architects, New Jersey: John Wiley & Sons, 2009, Chapters 7, 9 and 11; P. Steadman, Energy, Environment and Building, Cambridge: Cambridge University Press, 1975; E. Dean, op. cit. 3 K. L. Haggard, D. A. Bainbridge and R. Aljilani, Passive Solar Architecture: Pocket Reference, Earthscan, 2009, pp. 17–19; E. Mazria, Passive Solar Energy Book: A Complete Guide to Passive Solar Home, Green House and Building Design, Emmaus, PA: Rodale Press, 1979. 4 Haggard et al., op. cit., pp. 21–22, 51–52. 5 Vitruvius, On Architecture, Loeb Series, Harvard University Press, 1933, Book 1, Chapters IV and VI; see also D. Lord, ‘Power Applied to Purpose: Towards a Synthesis of Climate, Energy and Comfort’, Journal of Architectural Education, Vol. 37, No. 3/4, Summer 1984, pp. 38–42. 6 S. Newburgh, ‘Rediscovering Energy-Conscious Architecture’, Technology Review, August/ September, 1980, pp. 68–78. 7 A. Rapaport, House Form and Culture, Englewood Cliffs, NJ: Prentice Hall Inc, 1969, p. 86. See also R. Stein, ‘A History of Comfort with Low Technology’, in Architecture and Energy: Conserving Energy through Rational Design, Garden City, New York: Anchor Press/ Doubleday, 1977, pp. 23–47. 8 B. Rudofsky, Architecture Without Architects: An Introduction to Non-Pedigreed Architecture, Museum of Modern Art, New York, 1964; see also P. Oliver, Dwellings, London: Phaidon, 2003.

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9 W. Atkinson, The Orientation of Buildings, or Planning of Sunlight, New York: John Wiley & Sons, 1912. Cited in B. Anderson, ed., op. cit., p. 4. 10 The Orientation of Buildings, being the Report with Appendices of the RIBA Joint Committee on the Orientation of Buildings, Royal Institute of British Architects, 1933. 11 V. and A. Olgyay, Solar Control and Shading Devices, Princeton, NJ: Princeton University Press, 1957; and V. and A. Olgyay, Design with Climate: Bioclimatic Approach to Architectural Regionalism, Princeton, NJ: Princeton University Press, 1963. 12 K. Butti and J. Perlin, A Golden Thread: 2500 Years of Solar Architecture and Technology, Palo Alto, CA: Cheshire Books, 1980, pp. 211–214. Another team of researchers at MIT built three solar homes in 1939, 1947 and 1949. See MIT (2009) ‘Architects & Buildings: Solar Houses’. Available at: http://libraries.mit.edu/guides/subjects/architecture/architects/ solar/solardover.html (accessed 29 July 2011). Albert Dietz continued this work in the 1950s with his development of both passive and active systems. 13 Butti and Perlin, op. cit., p. 213. 14 B. Givoni, Man, Climate and Architecture, Second edition, London: Applied Sciences Publishers, 1976. 15 Mazria, op. cit.; see also the work of his contemporaries; S. Yannas, Solar Energy and Housing Design, 2 Vols., London: Architectural Association Publications, 1994; D. Balcomb, Passive Solar Heating Analysis: A Design Manual and Passive Solar Building, Cambridge, MA: MIT Press, 1992; B. Anderson, Solar Building Architecture, in the series Solar Heat Technologies: Fundamentals and Applications, Cambridge, MA: MIT Press, 1990; D. Watson and R. Glover, Solar Control Workbook – US Department of Energy Passive Solar, Curriculum Project, Yale University, School of Architecture, 1981; and J. Paul (ed.), Passive Solar Design and Materials, Park Ridge, NJ: Noyes Data Corporation, 1979. 16 B. Anderson, ‘Introduction’, in Solar Building Architecture, Cambridge, MA: MIT Press, 1990, pp. 6–7. 17 Passivhaus Institut (2011). Available at: www.passiv.de (accessed 31 July 2011); IPHA (2011). Available at: www.passivehouse-international.org (accessed 31 July 2011); Passivhaus Institut (2011) ‘International Passive House Conference 2011’. Available at: www.passivhaustagung.de/fuenfzehnte/englisch/index_eng.html (accessed 31 July 2011). 18 Passivhaus Institut (2006) ‘15th Anniversary of the Darmstadt-Kranichstein Passive House’. Available at: www.passivhaustagung.de/Kran/First_Passive_House_Kranichstein_en.html (accessed 31 July 2011). 19 W. Feist, ‘First Steps: What Can Be a Passive House in Your Region with Your Climate?’, Darmstadt: Passivhaus Institut, p. 6. 20 PHIUS (2011). Available at: www.passivehouse.us/passiveHouse/PHIUSHome.html (accessed 31 July 2011); Passivhaus UK (2011). Available at: www.passivhaus.org.uk (accessed 31 July 2011). 21 D. Prowler and D. Kelbaugh, ‘Building Envelopes’ in B. Anderson, ed., op. cit., pp. 77–146. 22 Ibid.; see also V. Knaack, T. Klein, T. Bilow and T. Auer, Facades: Principle of Construction, Basel: Birkhäuser, 2007; A. Compagno, Intelligent Glass Facades: Material, Practice, Design, Basel: Birkhäuser, 1999; J. Carmody, S. Selkowitz, E. S. Lee, D. Arasteh and T. Willmert, Window Systems for High Performance Buildings, New York: W.W. Norton & Company, 2004; S. Murray, Contemporary Curtain Wall Architecture, New York: Princeton Architectural Press, 2009. 23 Leading manufacturers of double-skin façades include the Permasteelisa Group, Schuco and Gartnerer. Double-skin façades have been criticized for their excessive material requirements and their, as of yet, largely unproven claims of energy reductions. For a review of early skins in North America see Terri Boake (2007) ‘The Tectonics of the Double Skin: Green Building or Just More Hi-Tech Hi-Jinx?’. Available at: www.architecture. uwaterloo.ca/faculty_projects/terri/ds/tectonic.pdf (accessed 14 August 2011). 24 Compagno, op. cit.; Carmody et al., op. cit. 25 R. Banham, Architecture of the Well-Tempered Environment, Chicago: University of Chicago Press, 1984, pp. 143–162. See Banham’s description of Le Corbusier’s early attempts at designing and constructing a double-skin façade in collaboration with the French company St. Gobain. 26 Lechner, op. cit., Chapter 9.

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27 Ibid., Chapter 7; see also Dean, op. cit., p. 8–12. 28 Available at: http://buildipedia.com/go-green/green-energy-technologies/nrels-researchsupport-facilities-strive-for-net-zero-energy? (accessed 10 September 2011). 29 Ibid., Chapter 10. 30 Ibid., Lechner, Chapter 7, pp. 158–159; and Mazria, op. cit., pp. 44–50, 166–170. 31 The house was built and operated as part of the 2011 Solar Decathlon Competition, with principal researchers Edgar Stach and James Rose from the College of Architecture and Design at the University of Tennessee, and Bill Miller from the College of Engineering and Mechanical Engineering at the University of Tennessee. Available at: http://livinglightutk.com (accessed 10 September 2011).

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Chapter 1.2

Translucent Building Skins: Advancing the Technology of Light Transmission franca trubiano

ABSTRACT: Building envelopes contribute to both the qualitative and quantitative measure of a building’s sustainability. The choice of their materials and construction technologies play a crucial role in the energy equation of any building. This is particularly the case for singlefamily homes whose building envelope contributes to a significantly higher percentage of surface area to volume ratio. Paradoxically, designers and their clients are committed to the construction of ever more immaterial and transparent building envelopes. Constructing skins lighter and thinner than ever before is a near-global fascination, resulting, at times, in negative consequences for the energy performance of a building. And yet, this chapter discusses high-performance, lightweight and light-transmissive material assemblies used in innovative architectural envelopes that positively contribute to a building’s energy balance. Featured are technologies such as glass-fiber-reinforced plastics, translucent polymer fluoroethylene sheets and thin films, conducive to both high levels of performance and the purposeful diffusion of daylight.

1.0  < Matter = > transparency A predilection for ever lighter and more transparent building envelopes has been a preoccupation of designers from the early days of architectural modernism and is virtually synonymous with twentieth-century architecture.1 Architects Mies van der Rohe and Phillip Johnson articulated a vision for living with nature founded on the near-complete elimination of all physical and material impediments to its enjoyment. The Farnsworth House of 1951 and the Glass House of 1949 are emblematic of this desire for experiencing the immaterial. (Figure 1.2.1)

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Floor-to-ceiling glass panes line the perimeter of each home, liberating the building envelope to perform its singular function: visually connecting interior space to exterior landscape. Or so it would appear. Upon closer examination of Johnson’s Glass House, for example, it has been observed to be equally engaged with exchanges in thermal energy. Having dematerialized all of the house’s vertical surfaces, Johnson paradoxically created a narrative centered on heat and its displacement. Reyner Banham claimed as much in his characterization of the home as an enclosure defined not by its perimeter walls but by its fireplace and extended floor, elements key to the conditioning of its interior.2 So transparent had the home become that in ‘the recent scorching fall, the sun reaching in through the bare trees created such a greenhouse effect that parts of the interior were acutely uncomfortable—the house would have been better off without its glass walls.’3 These residential projects were not, however, the first to characterize our longing for dwelling within the glass crystal. (Figure 1.2.2) Two of the earliest all-glass houses were built by 1934 by George Fred Keck, of Keck + Keck, on the occasion of the Chicago International Exposition A Century of Progress.4 The conceptual framework for transparent living was first articulated in his House of Tomorrow (1933) and Crystal House (1934). A dodecahedron and cube respectively, both homes were exceptional structures, of bolted steel plates and trusses entirely skinned in floor-to-ceiling fixed storefront glass panes. Their façades were wholly transparent yet outfitted with a range of solar control devices including interior louvers, black-out roller shades and sheer curtains.5 These early homes both absorbed an abundance of light as well as rejected its harmful extremes. In nearly four decades of practice following their construction, the Keck brothers went on to design dozens of innovative solar houses, most of which featured highly articulate glass façades of their invention.6 Following the Second World War, architectural innovation was equally committed to dematerializing the physical substance of which building assemblies and their components were made. Construction processes and details, particularly those associated with building skins, privileged materials light in weight

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1.2.1 Philip Johnson, Glass House (1949). Views of the interior space framing the distant landscape, during summer and fall

1.2.2 George Fred Keck, Keck + Keck, Crystal House (1934). (Top) Exterior view of the home during the day. (Bottom) Exterior view of the home during the evening

and thin in section. Building parts previously made of one material, were now engineered and assembled using a number of different sources and suppliers. Envelopes were transformed from load-bearing masonry walls, still common at the turn of the twentieth century, to aluminum and glass curtain walls ubiquitous by the 1970s. The exponential growth of synthetic polymers made the use of composites all the more commonplace. And this tendency has only accelerated

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1.2.3 KieranTimberlake Associates, Cellophane House™ (2007–2008)

1.2.4 Werner Sobek Engineer, House R128, Stuttgart, Germany

given our present-day focus on highly sophisticated operable double-skin façades built of thousands of parts. This brief and partial account serves but to more fully situate our own predilection for building with evermore-transparent materials; the fascination continues unabated.7 Increasingly, light transmission is used to articulate the character of buildings, and in particular the character of homes; this is evident in a number of

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early twenty-first-century projects. Both KieranTimberlake’s Cellophane House™ and Werner Sobek’s House R128 are defined by expanses of near-total transparency with living environments candidly bared to exterior landscapes. (Figures 1.2.3 and 1.2.4) And yet, both are carefully calibrated settings for the intelligent integration of innovative energy solutions.8 Undoubtedly, preference for lighter, light-transmissive envelopes has direct consequences for the energy performance of a building. Technologically advanced buildings are often the poorest performing, routinely condemned for not addressing their elevated levels of embodied energy and the energy required in maintaining their interiors temperate. In this regard, building envelopes are often to blame.

2.0  >Transparency = > energy The performance of a building’s envelope is fundamental in defining the building’s overall energy profile; this, being all the more critical for the energy equation of single-family homes. The smaller a building volume, the greater the ratio of the envelope’s surface area to its volume, and thus, the greater the effect of the envelope is on the overall performance of the building.9 Given the size of a typical home, its overall energy equation is vastly more affected by its building envelope than by internal loads from refrigerators, stoves, dishwashers, hot water heaters and other plug-ins. Fifty percent of the energy consumed in a house is due to its skin.10 How, therefore, does one reconcile this evidence with the knowledge that during the past century architectural design has been singularly focused on dematerializing the protective envelope so intensely invested in the building’s energy performance? The answer lies in the availability of inexpensive energy. Both the House of Tomorrow and the Crystal House were technologically advanced for their time, but both were highly dependent on infinite energy reserves for powering their central heating and air-conditioning systems. Seeking material and spatial transparency by such means is no longer a sustainable practice; a truth well known by the older Keck brothers when they redirected their efforts to the design and construction of energy-free façades incorporating operable windows, architectural shades, and ventilated louvers.11

3.0  Material science and the lightness of building with plastics In seeking sustainably appropriate levels of architectural transparency, the intelligent control of light, quantitatively and qualitatively is paramount. Building skins can be designed to both facilitate light transmission and to protect against excessive heat gain. Sunlight is absorbed, directed, distributed and even rejected from the surface of an envelope by the informed use of light shelves, louvers, plenums, shading devices, thin films, gases, and coatings. In fact, significant energy and monetary savings can result from designing interior environments with an

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abundance of diffuse natural lighting. Translucent materials can be used to facilitate the transmission of ambient light useful in completing many tasks. Moreover, the controlled transmission of direct light can be used to support the workings of thermal mass with notable energy benefits; whether achieved using traditional materials with high heat capacities, water and radiant heating, or by incorporating the latest variety of phase change materials. Yet, when building envelopes are constructed with thinner, lighter and ever less material, additional technologies are required to ensure adequate levels of performance. The risk of uncontrolled solar heat gain increases with the use of unmitigated transparency. Glass and metals have low specific heat capacities and inhibit the advantages of thermal mass. Probability of air infiltration greatly increases when a larger number of individual parts are used for a singular building product. And the recyclability of certain materials is diminished, if not entirely lost, when composites such as glass-fiber-reinforced plastics are incorporated into building assemblies. These challenges should not, however, deter designers from seeking opportunities in the vast array of innovative products that engage our current interest in the lightweight and the light transmissive. Advances in material science have profoundly altered the nature of architectural design, with laboratory centered research resulting in a host of new materials.12 Having displaced nature, the mater­ial scientist is the progenitor of emerging products whose intrinsic and extrinsic properties outperform traditional materials. With a particular focus on plastics, this chapter asserts that in adopting highly engineered composites, transparent polymers, and advanced glazing assemblies, the promise of architectural translucency can be fulfilled without compromise in energy accountability. Glass-fiber-reinforced plastics, fluoroethylene sheets, and thin films are building products with superior performance metrics in spite of their thinness and proclivity to light transmission.

3.1  Glass-fiber-reinforced plastics (GFRP) Plastic composites have been commercially available for well over four decades, most commonly marketed as laminates and reinforced plastics. Made of a resin matrix and reinforced with fibers of various materials, the latter are of particular interest to this chapter. Engineered to high levels of performance, and known more generally as fiber-reinforced plastics (FRP), these materials are championed for their capacity to be shaped into complex three-dimensional profiles, for their high strength-to-weight ratio and for their exceptional light transmission. In the 1950s, reinforced plastics were frequently employed for non-orthogonal shell structures such as the 1957 Monsanto House of the Future, designed by Hamilton and Goody. This early example featured a structural exterior envelope made of a double-curvature shell with an inner sandwich core of paper honeycombs and an outer skin of fiber-reinforced plastic.13 Cantilevered from its central structural core, this highly celebrated exhibition home was the visual and tectonic embodiment of the lightness made possible with plastics.14 In 1959, Albert Dietz of the Massachusetts Institute of Technology built ninety large-scale glass-fiber-

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1.2.5 Archi-Tectonics, Winka Dubbeldam, glass-fiberreinforced plastic (GFRP) façade prototype

reinforced plastic (GFRP) parasols for the American Pavilion at the National Exhibition in Moscow.15 They were made with an epoxy/polyester matrix and, as a thermoset plastic, were easily cured in a mold at room temperature. During the curing process GFRPs undergo an exothermic chemical reaction without need for external energy inputs and when cured they are low thermal conductors, both variables which make them low-energy-intensive materials. With a minimum of applied pressure, GFRP can register a wide array of curves limited only by the material employed in making the mold. In a recent project by Winka Dubbeldam of Archi-Tectonics, the material is used in the design of a multi-storey façade for the new garden/roof deck of a townhome in Chelsea, New York. (Figure 1.2.5) The mold needed for forming the GFRP can be prototyped using a CNC milling machine that has the capacity to mill objects as wide as 20 feet. Once the mold has been digitally fabricated, the GFRP panels are thermoset to the required dimension. Of all the polymers used in the building industry, these are most typically exploited for the quasi-structural capacity of their glass fibers which contribute both the needed strength and stiffness. Microscopic in dimension, the glass fibers are less than one thousandth of an inch thick yet add a final strength in excess of 250,000 psi to the plastic composite.16 This results in the lightest of materials; GFRPs are resistant across their proportionately thin sections but lighter in weight than load-bearing materials such as concrete and steel.17 When necessary, glass fibers can be substituted by carbon fibers that are 30 percent stronger in tensile strength. And most recently, aramide fibers have been used where high-impact resistance is desired.18

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The structural capacity of GFRPs is undeniable. Important research in GFRPs is being conducted under the guidance of Jan Knippers at the University of Stuttgart’s Institute of Building Structures and Structural Design.19 The first GFRP bridge with a 27-meter span was built in Freidberg, Germany in 2007. However, the same lab is also involved in prototyping a composite glass and GFRP façade system. First installed at the glasstec 2002 trade fair in Dusseldorf, Germany, the structural yet translucent Glass Cube was engineered to achieve high levels of performance by combining the high tensile strength of the GFRP with the transparency of glass panels. Given its capacity for light transmission, GFRP is of interest to architectural designers as well. (Figure 1.2.6) Architect Shigeru Ban used it to great advantage when he built the highly ethereal Naked House in Kawagoe, Japan in 2000. Constructed using two-storey-high wood framing, the house is an articulated essay on architectural translucency. The exterior skin of the façade’s 400mm-wide assembly was built using two layers of corrugated GFRP. The distinctive quality of the house’s ambient interior light was a result of this material choice and that of its insulation.20 Needing to identify a form of insulation as translucent as the skin occasioned the use of a custom detail

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1.2.6 Shigeru Ban, Naked House, Kawagoe, Japan (2000). Interior views of light diffusion by the house’s glass-fiberreinforced plastic walls

1.2.7 Museum of Paper Art, Shizuoka, Japan (2001). Views of glass-fiber-reinforced plastic building envelope

in which the insulation was fabricated with white polymer fibers.21 The result is a highly translucent yet effective thermal envelope. But a year later, Ban once again used GFRPs for the exterior skin of his Museum of Paper Art built in Shizuoka, Japan. (Figure 1.2.7) This time they were deployed in an equally ingenious number of ways. Whether fixed to the building’s structure, installed in large operable louvers the scale of the façade, or integrated in a three-storey operable garage door, GFRPs were used to the benefit of both the thermal and architectural goals of the building.22

3.2 Ethylene-tetrafluoroethylene (ETFE) Sheet-based plastics are employed with ever-greater frequency in provocative architectural projects. Ethylene-tetrafluoroethylene (ETFE) is one such polymerized material used in the construction of innovative building envelopes with ever-greater frequency since the beginning of the twenty-first century. Nearly transparent in appearance and measured at the scale of microns, its perceptual and phenomenal characteristics make of it a highly lyrical material. Ethereal, lightweight and balloon-like in appearance, ETFE evokes the playful terrains of the child’s imagination. Membrane-like in its structural expression, it suggests earlier utopias dreamt up by Buckminster Fuller and Frei Otto. ETFE is increasingly the focus of material science research with its supporters intent on bettering the energy responsiveness of this most unlikely of building materials.23 Manufactured from the isometric halide mineral fluorite, fluoroethylene was first patented by Dupont in 1945. In the 1970s, Herbert Fitz, while at the German company Hoechst AG, invented the particular form of ETFE tested in solar thermal installations and thereafter manufactured in sheets for commercial use in green houses.24 Given its natural proclivity for light transmission, it was and

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continues to be very effective where solar heat gains are desirable. By the late 1990s, it resurfaced as a material of great interest to architects for use in the form of pneumatic pillows.25 ETFE is typically substituted for glass in building envelopes. Polymerized from its raw materials in the form of resin pellets and heated to its melting temperature (270°C/380°F), ETFE can be molded, extruded or blown into a range of products.26 Thin films used in architectural membranes result from the extrusion process. They are engineered to desired levels of transparency or translucency, with matt or glossy finishes, and in thicknesses that range from 50 to 250 microns (0.05 to 0.25mm).27 Foils are manufactured by a number of patented processes, including the Texlon® Foil System devised by Stefan Lehnert of Vector Foiltec Ltd.28 Structurally capable of withstanding very high stresses (with a 400 percent strain to failure ratio), it is decidedly resilient to tears parallel to the direction of the sheet. Its strength increases as a function of its installation. When the material is mounted in its frame and tensioned (mechanically or by air pressure), it increases its resistance to wind loads by undergoing a ‘molecular realignment’.29 And notwithstanding its susceptibility to punctures prior to installation, ETFE is a self-healing material with perforations easily repaired using transparent ETFE tape. A singular layer of ETFE can be used and secured using mechanical fasteners. Maintaining the sheet at its required tension involves periodic review of the installation, with some manufacturers recommending a maximum sheet span of only two meters. Thomas Herzog employed this method in 2002 at the DBU Conference and Exhibition Pavilion in Osnabrück, where the ETFE was used primarily as a rain screen in curved single-span roofs independent of the thermal envelope.30 The building’s interior wood structure supported a flat glass plate, above which a set of horizontal louvers were used to modify the amount of light transmitted by the uppermost barrel-vaulted ETFE layer.31 In 2004, the Gerontology Technology Center in Bad Tolz was also built using a mechanically

1.2.8 Gerontology Technology Center, Bad Tolz by Hightex/ Solarnext

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fastened ETFE rain screen; this time, however, in a double-curvature façade.32 Decidedly suitable for smaller spans with lower bearing capacities, mechanically fastened single-leaf ETFE skins are nonetheless significant for the tectonic and environmental merit of a building.33 (Figure 1.2.8) Most typically, however, ETFE is designed to function within pneumatic assemblies, wherein inflated pillows are held in tension by small amounts of pumped air. Bound within custom-extruded aluminum frames, a minimum of two layers are required to create a pillow that maintains its sectional stability with the use of air pressure. The average pressure used to maintain a pillow’s stability is a matter of design; ranging from 200 to 600 Pascals (Pa). The chosen air pressure affects the pillow’s engineering including its geometry and load distribution. The maximum allowable deviation in the inflated panel section is between 10 to 15 percent of its span and maintaining the pillow pressurized is essential as it contributes to thermal and wind resistance.34 The pillow’s cross-section is re-engineered with every new application; its variables carefully calibrated for the particular building site, climate and program. Its section may vary from two to five foils; the greater the number of foils, the greater the number of surfaces available for augmenting the overall thermal responsiveness of the envelope. Increasingly ETFE is engineered to optimize its remarkable capacity for light transmission, thermal insulation and solar shading. Foils can be manufactured with high levels of light transmission, typically 90 to 95 percent across each layer. Even when multiple layers are used in the construction of a pillow, such as a three-layered section (exterior layer of 200μm material thickness, center layer 100μm, and inner layer 200μm), the amount of light transmitted is still 70 percent.35 Each layer also contributes to the thermal resistance of the assembly, with published heat transmission (U) values in the range 5.1 to 6.0 W/m²K for one layer, 2.94 to 3.5 W/m²K for a pillow of two layers and 1.96 to 2.0 W/m²K for three-layered membranes.36 Because air is contained between the pillows, an increase in thermal resistance results. In facilitating solar shading, patterns are printed on each ETFE layer to augment its ability to reject heat gain from radiation, whether using a preestablished pattern or a custom design. Within any one pillow, foil surfaces can be independently customized, with one foil achieving 100 percent coverage while another fritted only to 65 percent. As such, each layer in the ETFE assembly can be individually calibrated to a desired measure of light and heat transmission. The printing is accomplished using fluoro polymer ink (whether transparent or opaque) and varying the amount of pigment in the paint can control the amount of light transmitted. As noted by Vector Foiltec Ltd, a leading manufacturer and supplier of ETFE, by controlling the ratio of light transmission through the foil, ‘visual effects and solar shading can be achieved while retaining the visual transparency of the envelope’.37 Each layer can be designed to fulfill a range of ‘solar shading [requirements], enabling the [architect] to optimize the aesthetic and environmental performance of the building envelope’.38 It is micron-scale engineering of the foils that facilitates the attainment of these performance goals. This has precisely the case at the Pasadena Art Center, whose ETFE surface pattern was designed by Bruce Mau. Here, the three-layer assembly of Texlon® Foils produced a variable skin that moves synchronically

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such that two layers open and close at the same time to alter the pillow’s light transmission. (Figure 1.2.9) Early success of pneumatically pressurized ETFE pillows was insured by their use in high-profile architectural projects, including the exterior envelopes of the Rocket Tower (2001) research center in Leicester, UK and those of the Eden Project environmental center in Cornwall, UK, both by Nicholas Grimshaw & Partners. In the former, the vertical tower is structured with steel circular columns and beams with ETFE pillows ‘stacked’ horizontally about the building’s circular plan. In the latter, eight self-supporting quasi-geodesic domes are organized in hexagonal frames of varying dimensions, some of which contain ETFE pillows 9 meters in diameter and 2 meters in section. In both instances, the pillows define the thermal envelope and as such are directly implicated in the building’s energy equation. However, at the Allianz Arena football stadium, built in 2005 in Munich, Germany by architects Herzog & de Meuron, the ETFE is used primarily as a light diffuser for daylight and ornamental LED lighting. (Figure 1.2.10) Nearly 3,000 pneumatic cushions are arrayed across the building skin of this 60,000-capacity stadium. The pillows are translucent, transparent and/or fritted for light control. The foil, 200 microns thick, is tensioned into lozenge-shaped modules and held in place by structural steel members exterior to the building’s thermal glass envelope. The Beijing National Aquatics Center, completed for the 2008 Olympic Games, used 4,000 separate three-layer/four-ply pillows of 200-micron-thick

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1.2.9 Pasadena Art Center, California by Vector Foiltec Ltd

1.2.10 Herzog & de Meuron Architects, Allianz Arena in Munich, Germany (2005)

sheets covering a million square feet of wall and roof surface. As noted by ARUP, the building’s engineers, the increased daylight transmission made possible by the translucent ETFE results in a 55 percent saving in artificial lighting and a 20 percent harvesting of the solar heat that falls upon the building.39 The ETFE surfaces are calibrated with a fritted pattern that transmits as little as 10 percent or as much as 90 percent of the light. Unlike all other ETFE envelopes previously built, it is composed of two entirely separate structures, each of which contains ETFE pillows. In the wall section, the exterior layer is separated from the interior layer by a distance of 12 feet, while the roof cavity is 25 feet deep.

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Most recently, Behnisch Architeckten adopted the material for the façade design of their Unilever Headquarters in Hamburg, Germany. (Figure 1.2.11) Using Texlon® Foil they introduced a single layer of ETFE to reduce the wind force exerted on the building from the particular configuration of the site. Positioned more than a meter outboard of the glass façade, the mechanically fastened ETFE is supported by an aluminum and steel frame with compression bars to keep the foil at its required tension. This particular installation speaks to the sails typical of the port of Hamburg; an appropriate reference given the interest in sailing of Vector Foiltec Ltd’s founder Stefan Lehnert, an interest said to have contributed to his promotion of the material. ETFE is clearly a material whose performance can be engineered to respond to a range of climatic demands, be they thermal, solar, or ventilationrelated. Alongside those who recognize its measurable reductions in embodied energy and weight (with 1 percent the weight of glass), are those who promote its easy recyclability.40 This polymer continues to be successfully deployed in a range of environmental contexts, with its greatest potential residing in its yetto-be confirmed ability to integrate photovoltaic arrays and actively generate energy. A fact which must be addressed, however, is that notwithstanding its ability to encapsulate air within its layers and to facilitate the greenhouse effect,

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1.2.11 Unilever Headquarters, Hamburg, Germany by Vector Foiltec Ltd

1.2.12 Project Icarus, net-zero-solarpowered prototype house (2007). (Left) Detailed view of ETFE and aerogel thermal roof panel. (Right) Interior view of hybrid steel and wood structure supporting ETFE and aerogel roof panels

ETFE has a somewhat limited thermal resistance because of its micron-scale thickness. Worthy of study, therefore, is the possibility of combining ETFE with a supra-insulator. When paired with aerogel, a nano-sized translucent granule that is comprised of more than 90 percent air, the thermal conductivity of ETFE is significantly reduced. (Figure 1.2.12) The thermal resistance achieved when so coupled with insulation is akin to that of an advanced insulated glazing unit. And in Chapter 4.2, a single-family home whose roof was entirely built using ETFE and aerogel sandwich panels is described in greater detail.

3.3  Thin films and thermochromic glass For well over two decades, the addition of thin films to glazing units of all types and sizes has drastically improved the energy profile of many buildings.41 Participating in the building’s light and heat management, this family of polymers controls light transmittance and solar heat gains and in so doing contributes to increased levels of thermal performance. Most typically, thin films are added to a glass substrate. The earliest versions of ‘tinted films’ were separate sheets attached to the surface of the glass after the glass was cured.42 These installations proved to be far less effective, however, than simply tinting the surface of the actual glass pane when in the process of producing the glass itself. Far better results were achieved with the later ‘reflective coatings’ whose solar heat gain coefficients (SHGC) were reduced by increasing the amount of light reflected from the surface of the glass. Reflective coatings were made of metal oxide layers, produced in various colors including silver, gold and bronze. The thickness of the deposited oxide controlled the amount of reflected light. While popularly used

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in the mid 1980s, reflective coatings inhibited the transmission of much of the visible light spectrum hindering the beneficial diffusion of light. Vastly more effective is the current use of thin-film technology called low-emissivity (low-E) coatings, which reduces the amount of thermal energy absorbed by the glass, and in turn reduces the amount of heat energy re-emitted by the glass to the interior of the room.43 The genius of low-E coatings is that they are ‘spectrally selective’ and in being so are engineered to only transmit light energy to the interior of the building; that is, the portion of the light spectrum free of thermal energy (long-wave infrared radiation). By rejecting the spectrum’s short-wave heat radiation, low-E coatings allow for the passage of light without its associated solar heat gain resulting in lower effective U values for Insulated Glazing Units (IGU). Light-responsive glazing units are defining a rapidly expanding territory for research and commercialization. Three products are being advanced for highperformance installations: thermochromic, photochromic and electrochromic films. Thermochromic films register the effects of heat, photochromic films are activated by light, while electrochromic films are triggered by electric current.44 In each, adding a film or other like substance to the surface of the IGU renders an otherwise transparent window translucent or opaque. This ability to alter a window’s light transmission is essential for its thermal performance. One thermochromic low-emissivity window is identified, by its manufacturer, as a highly sustainable product because of its capacity to transmit light, while reject heat.45 It controls heat transfer using a so-called ‘insulating’ gel in the air space of the IGU, which modifies its molecular structure to be either ‘transparent’ or translucent. When the amount of light is insufficient to result in damaging solar heat gains, the window and its gel molecules (water and specially designed polymers) remain transparent allowing for visibility across the window. However, when the temperature reaches a set point (assigned by the designer for a particular climate and a building’s energy equation) the polymer molecules within the IGU section become translucent and prohibit the transmission of light and solar heat. This energy-free response greatly diminishes the transfer of unwanted heat gains to the inside of the space. Set points can be engineered for temperatures between 68°F and 104°F and gels can be fixed in thicknesses of 5/16 of an inch.46 These products are highly recommended for use in skylights, which are sensitive to solar heat gains but not required to offer views to the outside. To similar effect, electrochromic glazing uses liquid crystal technology, for rendering an otherwise transparent window translucent with the application of an electric current. The use of highly transmissive materials continues to be a viable option for high-performance homes when they are coupled with these and other forms of smart thin films. With the ability to calibrate the light to heat equation, architects and their clients are no longer bound to choose between either transparent building envelopes or highly insulated opaque enclosures. Selectively engineering the behavior of light and its various wavelengths renders possible the coexistence of glass walls with energy-efficient buildings.

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4.0  Conclusion If architectural design continues to be singularly focused on dematerializing the protective skin so intensely invested in the building’s energy performance, strategies and solutions will be required; most critically, during a time of limited resources. A truly committed interpretation of high performance is one charged with critical tools and material knowledge that encourages informed decision making. Building envelopes of highly engineered materials with advanced energy capacities, can effectively mitigate our desire for transparency. And the materials discussed herein represent but a sampling of those available to contemporary designers. Predicated on the purposeful diffusion of daylight, material technologies such as these hold the greatest promise for the future of high-performance buildings.

Acknowledgments The author acknowledges the valuable comments and insight offered by Jocelyn O’Shea, Associate Director at Vector Foiltec Ltd (London).

Notes 1 Seminal early studies on the role of the environment on architectural design include, V. Olgyay and A. Olgyay, Design with Climate: Bioclimatic Approach to Architecture, Princeton, NJ: Princeton University Press, 1963; and M. Frau, Solar Control and Shading Devices, Princeton, NJ: Princeton University Press, 1957; M. Frey and J. Drew, Tropical Architecture in the Dry and Humid Zones, New York: B.T. Batsford Ltd, 1956; B. Givoni, Man, Climate and Architecture, London: Applied Science Publishers Ltd, 1969. For a discussion of the larger political, cultural and social implications of architectural transparency see A. Fierro, The Glass State: The Technology of the Spectacle, Paris 1981–1998, Cambridge, MA: MIT Press, 2002. 2 R. Banham, ‘A Home is Not a House’, Art in America, Issue 2, April 1965; N. Whiteley, Reyner Banham: Historian of the Immediate Future, Cambridge, MA: MIT Press, 2003, pp. 204–205. 3 Banham, op. cit., p. 79. 4 G. F. Keck, House of Tomorrow: America’s First Glass House, B. R. Graham,1933; T. Slade, ‘The “Crystal House” of 1934’, Journal of the Society of Architectural Historians, Vol. 29, No. 4, December 1970, pp. 350–353. 5 R. Boyce, Keck + Keck, New York: Princeton Architectural Press, 1993, pp. 50, 72. 6 Ibid. 7 See M. Bell and J. Kim (eds), Engineered Transparency: The Technical, Visual and Spatial Effects of Glass, New York: Princeton Architectural Press, 2009. 8 See L. Ryker, Off the Grid: Modern Homes and Alternative Energy, Gibbs Smith Publisher, 2005, pp. 122–131: B. Bergdoll and P. Christensen, Home Delivery: Fabricating the Modern Dwelling, New York, The Museum of Modern Art, 2008, pp. 224–233. 9 Acknowledged by Don Prowler and Douglas Kelbaugh, ‘small buildings with load bearing envelopes tend to be skinload–dominated’. See D. Prowler and D. Kelbaugh, ‘Building Envelopes’ in Solar Heat Technologies: Fundamentals and Applications, Cambridge, MA: MIT Press, 1990, p. 80. 10 In commercial buildings, the envelope typically contributes 15 percent of the energy demand. See Prowler and Kelbaugh, op. cit., p. 90. See also K. L. Haggard, D. A. Bainbridge

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11

12

13

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15 16 17 18 19

20 21 22 23 24 25 26 27

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29 30 31

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and R. Aljilani, Passive Solar Architecture: Pocket Reference, International Solar Energy Society, Earthscan, 2010, p. 13. See D. Postel, ‘Architettura residenziale: per una poetica del comfort modernista’, Domus, Vol. 757, No. 02, 1994, pp. 36–42. See also Boyce, op. cit., pp. 71–72. By the mid 1950s the Keck brothers had built more than a dozen homes using passive solar design principles. They employed a wide repertoire of techniques including: calculating direct solar radiation to orient the building to its site, thermal mass studies for the design of concrete floors, developing prototypes for external horizontal blinds, the use of insulated glass units with two panes of glass (developed in 1935 by the Libby Owens Ford Glass Company), creation of thermal roof buffers using flat roofs with 1” water ponds. In the Cahn House, the all-glass southern façade was protected by a large cantilevered awning whereas in the Johnson House of 1938, the southern-facing glass façade was designed with air inlets to channel cool air through the heating system. A. Ritter, Smart Materials in Architecture, Interior Architecture and Design, Basel: Birkhäuser, 2007; M. Addington and D. Schodek, Smart Materials and Technologies, Boston, MA: Architectural Press, 2005; F. Kaltenbach, In Detail: Translucent Materials: Glass, Plastics, Metals, Basel: Birkhäuser, 2004. J. Knippers, J. Cremers, M. Gabler and J. Leinhard, Construction Manual for Polymers and Membranes, Basel; Birkhäuser, 2011, p. 13; A. Dietz, Plastics for Architects and Builders, Cambridge, MA: MIT Press, 1969, pp. 16–17; S. Jeska, Transparent Plastics Design and Technology, Basel: Birkhäuser, 2008, pp. 11–12. See also Alison and Peter Smithson’s 1956 House of the Future built in the UK as a temporary pavilion inspired by the potential form-making capacities of plastic. See Beatrice Colomina’s article ‘Unbreathed Air 1956’ in Alison and Peter Smithson: From the House of the Future to a House of Today, 010 Publishers: Rotterdam, 2004, p. 30. See also Frederick Kiesler’s all-plastic house of 1933, Space House, designed for Modernage Furniture Company of New York. It, however, was never built, only modeled. See also Jeska, op. cit., p. 9. A. Dietz, op. cit., pp. 18–19. Ibid., p. 100. Ibid., p. 104. See also F. Kaltenbach, ‘Structural Glass: GRP, Glass Composite Systems’, in Kaltenbach (ed.), op. cit., pp. 36–38. Kaltenbach, op. cit. J. Knippers and M. Gabler, ‘New Concepts for Advanced Composite Bridges: The Freidberg Bridge in Germany’. Available at: www.khing.de/upload/pap_0185ee870203.pdf (accessed September 30, 2011). Jeska, op. cit., pp. 70–72. C. Schittich (ed.), Building Skins, Basel: Birkhäuser, 2006, p. 134. Ibid., pp. 104–107. A. LeCuyer, ETFE: Technology and Design, Basel: Birkhäuser, 2008, pp. 32–40. This information was communicated to the author by Jocelyn O’Shea, Associate Director at Vector Foiltec Ltd (London). K. Moritz and R. Barthel, ‘Building with ETFE Sheeting’ in Kaltenbach (ed.), op. cit., p. 70. Ibid., p. 72; and Lecuyer, op. cit. Lecuyer, op. cit. According to Vector Foiltec Ltd, in the thin-film industry, thicknesses of less than one micron are common for surface coatings and sheets as thin as 12 microns are available for the single-ply use of ETFE. S. Lehnert, ‘Intelligent Roof Systems: Foil Cushions’, in The Design of Membrane and Lightweight Structures, Marijke Mollaert (ed.), VUB Brussels University Press, 2002, pp. 125–132. Ibid. Jeska, op. cit., pp. 116–121. See also C. Schittich, In Detail: Solar Architecture: Strategies, Visions, Concepts, Basel: Birkhäuser, 2003, pp. 108–111. The project was engineered by Barthel & Maus along with the ZAE Bayern group. See project description in K. M. Koch (ed.), Membrane Structures, Prestel, 2004, pp. 162–165 and T. Herzog, ‘Building with Membranes: Perspectives and Options for the Future’, in Koch (ed.), op. cit., pp. 246–251. Jeska, op cit., p. 130.

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33 Ibid., p. 72. 34 Moritz and Barthel, op. cit., p. 70. 35 See Hightex/Solarnext. Available at: http://hightexworld.com/images/pdf/hightex_etfefoil_properties%20e.pdf (accessed September 10, 2011). 36 Ibid., and see also Lehnert, op. cit., p. 128. 37 See Vector Foiltec Ltd. Available at: www.vector-foiltec.com/en/products/the-texlon-system. html (accessed September 10, 2011). 38 Ibid. 39 See ARUP (2011) ‘National Aquatics Center (Water Cube)’. Available at: www.arup.com/ Projects/Chinese_National_Aquatics_Center.aspx (accessed 8 August 2011); and J. Gonchar ‘Inside Beijing’s Big Box of Blue Bubbles’ in McGraw Hill Construction, July 2008. 40 Lecuyer, op. cit. 41 J. Paul (ed.), Passive Solar Energy: Design and Materials, Park Ridge, NJ: Noyes Data Corporation, 1979, pp. 15–58. 42 J. Carmody et al., Window Systems for High Performance Buildings, New York: Norton, 2004, p. 87. 43 Ibid., p. 88. 44 Ritter and Addington, op. cit. 45 Suntek (2011) ‘Low-E Cloud Gel Window System’. Available at: www.sunteklp.com/18. php (accessed August 14, 2011). The product works because of a long-chain polymer that is ‘invisible’ when dissolved in water. When heated to a set temperature, it alters its molecular structure making it big enough for light to fall upon it and to hinder light transmission. See also M. Saeli, C. Piccirillo et al. ‘Nano-Composite Thermochromic Thin Films and Their Applications in Energy-Efficient Glazing’. Solar Energy Materials & Solar Cells, 2009; M. Saeli, C. Piccirillo et al. ‘Energy Modeling Studies of Thermochromic Glazing’ in Energy and Buildings, 2010. 46 Suntek (2011), op. cit.

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Chapter 1.3

Responsive Building Envelopes: Characteristics and Evolving Paradigms k at h y v e l i k o v + g e o f f r e y t h ü n

ABSTRACT: A new generation of high-performance envelopes have contributed to the emergence of sophisticated assemblies combining real-time environmental response, advanced materials, dynamic automation with embedded microprocessors, wireless sensors and actuators, and design-for-manufacture techniques. This practice has fundamentally transformed the way in which architects approach building design with a shift in emphasis from form to performance, from structure to envelope. In the realm of high-performance buildings, the envelope has become the primary site of innovative research and development.1 Borrowing a set of terms from the discipline of biology now commonplace in architectural design, this chapter articulates a conceptual paradigm and working vocabulary for the development of high-performance building skins that are smart, intelligent, interactive and responsive.

1.0  Redefining the responsive environment An expanded understanding of building performance acknowledges that all forces acting on buildings (climate, energies, information, human agents) are not static and fixed, but rather mutable and transient. This has serious consequences for the building envelope whose design must transcend its role as mere protective wrapper separating inside from outside.2 Building façades are increasingly developed as complex systems of material assemblies attuned to climate and energy optimization. With ever greater frequency, they are equipped with new performative materials, sensors, actuators and computerized intelligence that support automated dynamic operations and functionalities, such as regulating a building’s light, air and sound transmission, thermal transfer, and interior air quality. This façade-based equipment assists and even at times replaces functionalities otherwise performed by traditional building systems. As the building component most directly exposed to sun and wind, the envelope

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is also the most effective site for innovations in energy savings and alternative energy generation. The evolution of the building envelope as a focus of design innovation in the twentieth century parallels advancements in envelope engineering and building science, as well as developments in computer engineering, cybernetics and artificial intelligence (Figure 1.3.1). Additionally, new technologies, smart materials and distributed systems have spurred the introduction of biological models for understanding the behavior and design of building systems and their controls. A descriptive lexicon has emerged that employs decidedly biological terminology in conceptualizing architectural design. For example, we frequently encounter the term “building skin” in reference to the building’s exterior envelope. Michael Wigginton and Jude Harris, in their book Intelligent Skins, argue that the use of the term “skin” is more than merely a metaphor; the building’s envelope can be considered quite literally as a complex membrane capable of energy, material and information exchanges. It can be designed to operate “as part of a holistic building metabolism and morphology, and will often be connected to other parts of the building, including sensors, actuators and command wires from the building management system.”3 This contemporary understanding of the building skin has fundamentally changed the way in which architects approach building design, having shifted questions of performance away from the traditional formal and physical properties of building envelopes to reposition the discourse within a more expansive definition of how they behave. These new parameters have resulted in increased architectural collaboration with the disciplines of mechanical and electrical engineering, computing and the physical and social sciences. However, as argued by Michelle Addington and Daniel Schodek in their seminal book Smart Materials and Technologies for the Architecture and Design Professions, relative to the aforementioned disciplines, architecture has evolved without a common language, problem solving methodology or common basis of knowledge, and this often hampers the design process. The blurring of boundaries between

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1.3.1 Contextual timeline of responsive building envelope development

disciplines has given rise to a near crisis in the definition of their respective roles, responsibilities and professional accountability.4 Even within the discipline of architecture, terms such as “smart”, “intelligent”, “interactive”, “adaptive” or “responsive” have been used loosely and interchangeably, creating confusion as to their specific meaning and their conceptual relationship to building performance and design. In response, this chapter frames a provisional lexicon of descriptive, behavioral and methodological terms to assist designers in navigating the field of high-performance skins that incorporate materially innovative and feedbackbased systems. It offers a brief overview of current advances in this nascent and rapidly evolving field and articulates a broader conceptual territory for the term “responsive”; one that empowers an operational definition of building ecology and that functions through the combined and co-evolutionary agency of building, technology, inhabitant and environment.

2.0  Smart Within the design disciplines, the term “smart” has most frequently been used in reference to materials and surfaces.5 Addington and Schodek identify “smart materials” as systems possessing “embedded technological functions” that involve specific environmental responses, operating either through internal physical property changes or through external energy exchanges.6 They define the characteristics of smart materials as: “immediacy” (real-time response), “transiency” (responsive to more than one environmental state), “self-actuation” (internal intelligence), “selectivity” (a response is discrete and predictable) and “directness” (a response is local to the activating events).7 Smart surfaces and materials can play a significant role in intelligent, adaptive and responsive envel­ opes because of these intrinsic properties. Examples of smart materials used in high-performance building skins include aerogel (the synthetic low-density translucent material used in window glazing), phase change materials such as micro-

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encapsulated wax, salt hydrates, thermochromic polymer films, and buildingintegrated photovoltaics. One of the most significant characteristics of smart materials is that they have the ability to transform their physical properties and/or shape, or to exchange energy without requiring an external source of power. Hence, they are extremely attractive to building designers who aim to increase functionality and performance while at the same time reducing energy use. Doris Sung, principal of DO|SU Studio Architecture and faculty member at the University of Southern California, is experimenting with the use of thermobimetals for creating selfsupporting building skins that are able to open their pores to self-ventilate without the use of external energy sources (Figure 1.3.2).8 Laminated metals with differential thermal coefficients deform unevenly when exposed to temperature set points, inducing tension and causing movement in the thermobimetal. When the heat source is removed, the bimetal returns to its original shape. The use of electro active polymers for kinetic skins is also at the forefront of research in the field, given their speed of response, large potential for active deformation and resilience. Manuel Kretzer and students from the Swiss Federal Institute of Technology Zurich (ETH) have developed a prototype dynamic skin called ShapeShift; a layered, self-supporting unit made of elastomeric films which deforms when electrically charged (Figure 1.3.3).9 Moreover, architects Soo-in Yang and David Benjamin are developing a new smart material called Living Glass which is comprised of arrays of polymer “gills” interfaced with sensors. The system opens and closes as a function of both human presence and carbon dioxide levels and is designed to control the air quality of a room.10

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1.3.2 Smart Thermobimetal SelfVentilating Skin: installation of prototype and details of skin performance under different temperatures, 2010

1.3.3 ShapeShift prototype, consisting of 36 individual EAP elements, as exhibited at the Gallery StarkArt in Zurich, September 2010

1.3.4 Smart envelope comprised of ETFE-encased solar-activated shading diaphragm developed for the Media-TIC Building in Barcelona, Cloud 9 Architects, 2011

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While many of these systems are still in the research and development phase, a recent example of a smart skin installed in a completed building is that of the Media-TIC Building, constructed in Barcelona in 2011 and designed by Cloud 9 Architects and envelope specialists Vector Foiltec Ltd. The envelope features a pillow cladding system made of the polymer ETFE with encased shading foil diaphragms whose pneumatic mechanisms are automatically activated by light sensors that respond to the presence of solar energy (Figure 1.3.4). While smart materials offer many advantages for high-performance building envelopes, their performance is often tightly bracketed within a specific range of climatic conditions and predictable reactions. However, in a high-performance building skin that is required to be intelligent or responsive, it is often necessary to accommodate much broader variation in conditions and performance criteria. The skin may be required to facilitate more complex building system communications, to respond to occupant requests, and to adapt and learn over time. As such, smart materials are often incorporated in complex building skins with sophisticated thermal management systems – a pairing that would render them “intelligent”.

3.0  Intelligent The term “intelligent” has been used extensively in the construction industry since building automation and telecommunications became more pervasive in the 1960s and 1970s, gaining widespread currency in the 1980s when it referred to the programmable zones of a building’s heating, ventilation and air-conditioning (HVAC) systems. Many countries have intelligent building (IB) institutes, each of which contributes a slightly different approach to defining the characteristics of IBs.11 Relative to building skins, the term “intelligent” implies a higher order of organization and performance than “smart”. In the broadest sense, the goal of an intelligent building skin is to optimize the building’s systems relative to climate, energy balance and human comfort, typically based on predictive models. This is often accomplished through building automation and physically adaptive elements such as louvers, sunshades, operable vents or smart material assemblies. Brian Atkin, in his book Intelligent Buildings, defines intelligent buildings as those that “know” what the environmental conditions are both outside and inside, that “decide” how to provide a convenient and comfortable environment for occupants, and that “respond” promptly to occupant requests.12 This is typically achieved using a variety of sensing apparatus that communicate with building control systems to optimize interior conditions, including computational protocols (for both the envelope and HVAC equipment) capable of re-balancing the system based on occupant adjustments. For their part, Addington and Schodek describe the term “intelligent” using these three characterizations: environmental characterizations (surrounding environments, use environments), cognition characterizations (information systems, expert systems, artificial intelligence) and implementation characterizations (methods of operation and control).13 The widespread availability and use of mechanical conditioning equipment during the post-war era was certainly a factor in the development of intelligent

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1.3.5 (overleaf) Buckminster Fuller’s façade for the United States Pavilion at the 1967 Montreal Expo, illustrating canvas sunshades in variable positions

buildings. This mechanically regulated environment released the building envel­ ope from its primary role as thermal barrier, calling into question its very necessity – an observation eloquently developed by Reyner Banham and Francois Dellagret in their 1969 article “A Home is Not a House”.14 The use of mechanical systems for interior climate regulation resulted in buildings designed with ever increasing amounts of glass, which in turn necessitated variable shading and ventilation as an integral part of the envelope. As buildings often follow on the heels of advancements in the automotive and household appliance industries, the rise of automation was another factor which led to the development of intelligent building envelopes.15 One of the first automated climate-adaptive envelopes was Buckminster Fuller’s façade for the United States Pavilion built for the 1967 Montreal Expo (Figure 1.3.5). The skin of this geodesic dome was made of a transparent cladding of acrylic panels, with interior canvas sunshades controlled by a computer program that would adjust their position relative to the movement of the sun.16 The ability for a building envelope to change and adapt its configuration relative to the sun (either by blocking its rays to prevent overheating and/or glare, or by allowing them to penetrate for passive heat gain and/or daylighting), has been a primary source of formal and technological innovations in intelligent building skins. The Terrence Donnelley Centre for Cellular and Biomolecular Research at the University of Toronto, completed in 2006 by architectsAlliance/Behnisch Architekten, has a south-facing double-skin façade with intelligently controlled internal blinds and ventilation louvers that together manage light, heat gain and natural ventilation in this energy-efficient all-glass building (Figure 1.3.6). So pervasive is the field, engineering firm Buro Happold, in collaboration with deployable structures innovator Chuck Hoberman, have established an intelligent surfaces unit called the Adaptive Buildings Initiative (ABI). This design unit has developed a number of kinetic shading and cladding systems, including the Strata™ System, which consists of automated modular kinetic units that can retract into a slender profile (Figure 1.3.7). The Strata™ System was the basis for the HelioTrace Façade, developed in collaboration with SOM and the Permasteelisa Group, that improves envelope performance relative to daylight and glare while reducing solar heat gain by as much as 81 percent.17 Although a significant amount of research and development in intelligent building envelopes occurs in the commercial building sector, where building automation and advanced technologies have had faster and more widespread adoption, residential buildings have also engaged the question of intelligent building skins. An early home featuring automated curtains and controllable windows, which opened and closed as a function of data received from internal and external climate conditions, was the TRON-Concept Intelligent House. The prototype developed by Ken Sakamura from the University of Tokyo, operated as a “living lab” for research in domestic automated environments from 1989 to 1993.18 More recently, the home built by Technische Universität (TU) Darmstadt for the 2007 US Solar Decathlon Competition incorporated an exterior building skin comprised of computer-controlled wooden louvers with integrated photovoltaic panels that generated power while shielding the interior of the house from the sun (Figure 1.3.8).

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1.3.6 Intelligent double-skin façade system with integral automated shading for the Terrence Donnelley Centre for Cellular and Biomolecular Research at the University of Toronto, architectsAlliance/ Behnisch Architekten, 2006

1.3.7 (top) ABI Strata™ System demonstrated in the continually transforming Emergent Surface exhibition at MoMA, 2008; (bottom) the award-winning HelioTrace Adaptive Façade system by SOM/ABI/ Permasteelisa, 2010 © Skidmore, Owings & Merrill

The biggest difference, therefore, between terms “smart” and “intelligent” is that in the case of the former functionality results from intrinsic mater­ ial properties, whereas in the latter performance is primarily controlled through computation and automation. The performance profile of intelligent envelopes is typically more variable than that of smart skins; the operation of smart skins is typically binary and more limited in control, while intelligent envelopes typically require external power to achieve their goals. Hence, when committed to overall building energy reductions, intelligent envelopes should ideally be developed with smart materials that are self-powering and self-actuating.

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1.3.8 Intelligent façade of automated wood louvers with buildingintegrated photovoltaics create a continuous façade for TU Darmstadt’s 2007 Solar Decathlon House

4.0  Interactive The term “interactive” is used less frequently with regard to building envelopes than in reference to computer-enabled artworks, installations and other such environments encouraging active public participation. The past twenty years have witnessed an explosive rise in the number and range of interactive devices used to this end; in part due to the increasing miniaturization of technology, rendering ubiquitous and inexpensive the sensing, computational and micro processing components necessary for their widespread adoption.19 However, for the purposes of this text, the most significant characterization of the term is that of an interactive system that fundamentally requires human input to initiate response. The history of ideas on human–machine systems and the concepts of feedback and circular causality can be traced to the Macy Conferences of the Cybernetics Group held between 1946 and 1953. These events included the participation of individuals seminal in the development of the field of Systems Theory such as, Gregory Bateson, Norbert Weiner, Warren McCulloch, John von Neumann, Ross Ashby and Margaret Mead.20 One of the earliest attempts to develop an interactive architectural system was Cedric Price and Joan Littlewood’s Fun Palace, a project developed in 1961, in collaboration with well-known cybernetician Gordon Pask.21 During this early phase, limited computer processing capability constrained the possibility for interactive systems to become widespread in buildings. And yet, a great deal of the conceptual and process-related groundwork in the field took place during the 1960s and 1970s via the work of Warren Brodey, Charles Eastman, Gordon Pask and MIT Media Lab founder Nicholas Negroponte.22 Early

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1.3.9 Michael Mozer’s ACHE computer architecture for the Adaptive House project

discussions were focused on regulatory feedback-based systems, or first-order cybernetics, while the development of second-order cybernetic systems (i.e. machine-based learning or conversing systems) was the goal of contemporary designers working in the field.23 According to Usman Haque, in second-order cybernetics, input and output criteria are “actively and iteratively constructed by other participants of the project, and a more productive relationship ensues between human and environment”, informing future operations of the system.24 So stated, a number of projects that have more commonly fallen under the rubric of “intelligent”, might be more appropriately identified as “interactive”. This includes the Adaptive House project by Michael C. Mozer at the University of Colorado at Boulder which, equipped with sensors and an automated building management system, is programmed to optimize energy conservation while at the same time ensure the comfort of its inhabitants.25 The home control computer “architecture” called ACHE (Adaptive Control of Human Environments) is implemented using networks that emulate neural functions, with sensors positioned to not only monitor interior climate, but also to track and record information on inhabitant actions under changing scenarios.26 As a result, the computer algorithm learns over time and begins to anticipate inhabitant preferences (Figure 1.3.9). In addition to the computerized observation of human behavior, of particular interest are advancements that have been made in the capacity to interpret gestures and actions. As opposed to more familiar human input interfaces that are keyboards and touchscreens, inhabitant preferences are “understood” via an advanced recognition-based interface. This not only foregrounds the human factor in the building–energy–environment equation, but also engages deeper questions of bodily and psychological importance when designing interactive environments and their material components.

5.0  Responsive The term “responsive” is often used interchangeably with “interactive” and “adaptive”, but most simply it is used to describe, “how natural and artificial systems can interact and adapt”.27 In 1975, Nicholas Negroponte proposed the following definition of responsive architecture in his text Soft Architecture Machines:

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The manipulative environment is a passive one, one that is moved as opposed to one that moves. In contrast, responsive … means the environment is taking an active role, initiating to a greater or lesser degree changes as a result and function of complex or simple computations … maybe a house is not a home until it can learn to laugh at your jokes.28 In a responsive milieu, one that operates under the principles of second-order cybernetics, both user and system are capable of shaping an unlimited set of performance outcomes. Rather than the designer predetermining appropriate responses to user inputs, the system measures reactions to its outputs and continually modifies its actions according to these responses. In an extreme case, buildings and environments could co-evolve and transform according to cognitive and biological models. A responsive building skin includes functionalities and performance characteristics similar to those of an “intelligent” building skin including real-time sensing, kinetic climate-adaptive elements, smart materials, automation and the ability for user override. But it also includes interactive characteristics, such as computational algorithms that allow the building system to self-adjust and learn over time, as well as the ability for inhabitants to physically manipulate elements of the building envelope to control environmental conditions.29 Learning takes place in accordance with changing environmental conditions and inhabitant preferences, such that the algorithm anticipates desirable configurations. A truly responsive building envelope, therefore, not only includes mechanisms for inhabitant sensing and feedback, but is also committed to educating both the building and its occupants. Information is provided to the building’s inhabitants so they too can learn over time and modify their actions relative to climate and energy use. In this way, both building and occupant are engaged in a continuous and evolving conversation (Figure 1.3.10).

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1.3.10 Responsive building envelope characteristics include both response input interfaces as well as learning through mechanisms that use adaptive computation based on continual sensing and information feedback

1.3.11 North House exterior shade operation: response logistics and occupant control interface logic

One such home is the North House prototype, described in detail in Chapter 4.3. It was built using a responsive envelope with computer-automated exterior shading louvers capable of continually adjusting their configuration. The energy balance of the mechanical system – based on real-time interior and exterior climate sensing and user manipulation – was continually optimized for minimum energy use. Although a building-learning algorithm for occupant preferences was not developed for this prototype, interactivity researchers at Simon Fraser University developed a human-learning environment that was a computerized interface system, called ALIS (Adaptive Living Interface System). It provided real-time energy and resource use feedback in both numerical and ambient formats, alerted users when occupant actions (such as opening the blinds on a sunny day) would compromise energy optimization, and supported a matrix of online community and social networking applications to promote energy-saving lifestyle patterns (Figure 1.3.11).

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6.0  The human factor in building performance A responsive building skin is one that facilitates co-evolutionary interaction between the building, the inhabitant and the environment in a meaningful way. One of the primary performance mandates for high-performance envelopes has been energy optimization and reduction in the use of resources. Yet research has shown that while approximately half of the energy used in the home depends on its physical characteristics and equipment, the behavior of its residents accounts for the balance.30 Ray Cole, co-founder of the Green Building Challenge, has proposed to add “inhabitant intelligence” to existing concepts of building intelligence, challenging the assumption that inhabitants understand building control options, and that they will make appropriate and intelligent choices.31 Social scientists have long recognized that motivations to consume or conserve energy are socially dependent32 and the social, political, and personal dimensions of a building’s energy consumption and resource management are as critical to address as the technical ones.33 Differences in individual behavior have been shown to produce large variations in energy consumption – in some cases as much as 300 percent – even when accounting for differences in housing types, appliances, HVAC systems, and family size.34 Moreover, in a study including extended monitoring of energy use patterns in a community of zero-energy houses in California, results showed that while the energy-efficient and energy-producing features of the buildings were effective at reducing the energy consumption, the patterns of energy use by inhabitants remained identical to those of neighbors in non-zeroenergy houses. In spite of living in high-performance sustainable buildings, residents did not change their consumption habits in any significant way.35 Motivations for saving energy may vary. However, availability of information and feedback loops are effective means for encouraging building occupants to develop more energy-conscious lifestyles and building use patterns.36 In a “responsive” design paradigm, where building, inhabitant and environment are all agents, the positive and negative feedback loops that individuals have with their built environment, the active co-evolution that they necessarily share with it, as well as the agency of both buildings and their inhabitants, are all potentially powerful tools for promoting social change. They not only increase the intelligence of building systems, but the “intelligence” of their inhabitants as well. Given residential buildings in the United States account for nearly 57 percent of building energy use,37 and that the home is a central site of habit forming behavior, residential buildings may prove to be an ideal place for advancing developments in responsive envelope systems. With emphasis on adaptability, the high-performance skin has the capacity to learn over time and in so doing can form ongoing and emergent relationships with its inhabitants. In this way, responsive envelopes can significantly impact the definition of building performance by forging a new cognitive framework for buildings, their inhabitants and the larger environment.

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Acknowledgments The authors thank Franca Trubiano and Malcolm McCullough for content and editorial feedback; Lauren Barhydt, Julie Janiski and Zain AbuSeir for research and drawing assistance.

Notes 1 Witness the recent societies and research initiatives related to high-performance façades, such as the Society of Façade Engineering (www.facadeengineeringsociety.org), the advanced work in adaptive façades by the Adaptive Buildings Initiative (Buro Happold with Hoberman and Associates, www.adaptivebuildings.com), the Center for Architecture Science and Ecology (CASE) (Rensselaer Polytechnic Institute with SOM, www.case.rpi. edu) and the work of consultants, Front Inc. (www.frontinc.com), among others. 2 B. Kolarevic and A. M. Malkawi (eds), Performative Architecture: Beyond Instrumentality, New York: Spon Press, 2005, pp. 203–212. 3 M. Wigginton and J. Harris, Intelligent Skins, Oxford: Elsevier Architectural Press, 2006 [2002], p. 3. 4 M. Addington and D. Schodek, Smart Materials and Technologies for the Architecture and Design Professions, Oxford: Elsevier Architectural Press, 2007 [2005], p. 12. 5 For the two most comprehensive publications on the matter, see Addington and Schodek, Smart Materials as well as T. Klooster, Smart Surfaces and Their Application in Architecture and Design, Berlin: Birkhäuser, 2009. 6 Addington and Schodek, op. cit., p. 9. 7 Ibid., p. 10. 8 D. K. Sung, “Skin Deep: Making Building Skins Breathe with Smart Thermobimetals”, Where Do You Stand?: Proceedings of the 2011 ACSA National Conference, A. PérezGómez, A. Cormier, and A. Pedret (eds), Washington, DC: ACSA Press, 2010, pp. 145–152. 9 ShapeShift is a collaboration between the Chair for Computer Aided Architectural Design (ETHZ) and the Swiss Federal Laboratories for Materials Science and Technology (EMPA). The team includes M. Kretzer, D. Rossi, S. Georgakopoulou, E. Augustynowicz and S. Sixt. See www.caad-eap.blogspot.com 10 The Living New York (2010) Living Glass. Available at: www.thelivingnewyork.com/lg/lg01. htm (accessed 30 January 2011). 11 A summary can be found in S. W. Wang, Intelligent Buildings and Building Automation, New York: Spon Press, 2010, pp. 1–3. 12 B. Atkin, Intelligent Buildings, Worcester: Billings & Sons, 1988, p. 1. 13 Addington and Schodek, op. cit., pp. 204–205. 14 R. Banham and F. Dellagret, “A Home is Not a House”, Art in America, Vol. 53, April 1965, pp. 70–79. 15 See S. Giedion, Mechanization Takes Command: A Contribution to Anonymous History, New York: W.W. Norton & Co., 1948 and R. Banham, Theory and Design of the First Machine Age, Cambridge, MA: MIT Press, 1980 [1960]. 16 M. J. Gorman, Buckminster Fuller: Designing for Mobility, Milan: Skira, 2006, p. 134. Unfortunately the shades seized up in a random position the first time the system was in use, and then the entire skin burned in an accidental fire in 1976. 17 Hoberman Associates and B. Happold (2010) Adaptive Buildings Initiative. Available at: www.adaptivebuildings.com (accessed 18 February 2011). 18 Wigginton and Harris, op. cit., pp. 155–158. 19 For comprehensive references to contemporary interactive design see: M. Fox and M. Kemp, Interactive Architecture, New York: Princeton Architectural Press, 2009; Klooster, op. cit.; and L. Bullivant, Responsive Environments: Architecture, Art and Design, V&A Contemporary, London: Victoria and Albert Museum, 2006. 20 S. Heims, Constructing a Social Science for Postwar America: The Cybernetics Group, 1946–1953, Cambridge, MA: MIT Press, 1993.

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21 M. L. Lobsinger, “Cybernetic Theory and the Architecture of Performance: Cedric Price’s Fun Palace”, in S. W. Goldhagen and R. Legault (eds), Anxious Modernisms: Experimentation in Post-War Architectural Culture, Cambridge, MA: MIT Press, 2000. 22 For early writings on interactive architecture see: W. Brodey, “The Design of Intelligent Environments: Soft Architecture”, Landscape, Autumn 1967, pp. 8–12; G. Pask, “Architectural Relevance of Cybernetics”, Architectural Design, September 1969, pp. 494– 496; A. Rabeneck, “Cybermation: A Useful Dream”, Architectural Design, September 1969, pp. 497–500; C. Eastman, “Adaptive-Conditional Architecture”, in N. Cross (ed.), Design Participation: Proceedings of the Design Research Society’s Conference, Manchester, September 1971, London: Academy Editions, 1972, pp. 51–57; and N. Negroponte, The Architecture Machine, Cambridge: MIT Press, 1973, and Soft Architecture Machines, Cambridge, MA: MIT Press, 1975. 23 H. Dubberly, U. Haque, and P. Pangaro, “What is Interaction? Are There Different Types?”, Interactions, Vol. 16, Issue 1, January/February 2009, pp. 69–75. 24 U. Haque, “Distinguishing Concepts: Lexicons of Interactive Art and Architecture”, 4dsocial: Interactive Design Environments, Architectural Design, Vol. 77, No. 4, 2007, pp. 26–27. 25 M. Mozer, “Lessons from an Adaptive House”, in D. Cook and D. Das (eds), Smart Environments: Technology, Protocols and Applications, Hoboken, NJ: John Wiley & Sons, 2004, pp. 273–310. 26 Ibid., p. 283. 27 P. Beesley, S. Hirosue, and J. Ruxton, Responsive Architectures: Subtle Technologies 06, Cambridge: Riverside Architectural Press, 2006, p. 3. 28 Negroponte, op. cit., pp. 132–133. 29 The sense of control inhabitants have over building systems has been shown to be a significant factor in occupant satisfaction and the ability to have more perceived control over interior environments has been shown to increase inhabitants’ tolerance for “lessthan-ideal” conditions. See N. Baker, “The Irritable Occupant: Recent Developments in Thermal Comfort Theory”, Architectural Research Quarterly, 2, Winter 1996; R. Cole and Z. Brown, “Reconciling Human and Automated Intelligence in the Provision of Occupant Comfort”, Intelligent Buildings International 1, 2009, pp. 39–55; and A. Leaman and B. Bordass, “Assessing Building Performance in Use 4: the Probe Occupant Surveys and Their Implications”, Building Research & Information, Vol. 29, No. 2, 2001, pp. 129–143. 30 K. B. Janda, “Buildings Don’t Use Energy: People Do”, in C. Demers and A. Potvin (eds), Architecture, Energy and the Occupant’s Perspective: Proceedings of the 26th Conference on Passive and Low Energy in Architecture (PLEA), Quebec, Canada: Les Presses de l’Université Laval, 2009, pp. 9–14. 31 R. J. Cole and Z. Brown, “Human and Automated Intelligence in Comfort Provisioning”, in C. Demers and A. Potvin (eds), op. cit., pp. 18–21. 32 L. Schipper et al., “Linking Life-Styles and Energy Use: A Matter of Time?” Annual Review of Energy 14 (1989), pp. 273–320; and P. C. Stern and E. Aronson (eds), Energy Use: The Human Dimension, New York: W.H. Freeman and Co., 1984. 33 Janda, op. cit., pp. 9–14. 34 Ibid., p. 11. 35 M. Keesee, “Setting a New Standard: The Zero Energy Home Experience in California”, Proceedings of Solar World Congress, International Solar Energy Society: Orlando, FL, 2005; and Janda, op. cit., p. 10. 36 See M. Chetty, D. Tran and R. E. Grinter, “Getting to Green: Understanding Resource Consumption in the Home”, in Proceedings of UbiComp ‘08, pp. 242–251; and S. Darby, “The Effectiveness of Feedback on Energy Consumption”, Oxford: Environmental Change Institute, University of Oxford, 2006. See www.eci.ox.ac.uk/research/energy/downloads/ smart-metering-report.pdf (accessed 2 May 2010). 37 US Department of Energy (2009) 2009 Buildings Energy Data Book, Table 1.2.3, pp. 1–12. Available at: http://buildingsdatabook.eren.doe.gov/Default.aspx (accessed 24 January 2011).

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Chapter 1.4

Nanomaterial + Super-Insulator = Aerogel franca trubiano

ABSTRACT: This chapter discusses the adoption of nanotech materials in the development of high-performance building envelopes and the opportunity for innovation this affords the design of residential buildings. During the past decade, advances in bio-engineering, medicine and the material sciences have altered the landscape of chemical and organic synthesis, a result of which has been increased availability of its techniques and technologies for invention in the building industry. The material properties of aerogel, a translucent insulation material with multi-functional capacities, are discussed in detail, as are the design implications of using this nanotech material in high-performance homes.

1.0  Material engineering at the nano scale In the field of material science, the term ‘nano’ identifies the scale of morphological transformations that occur at the measure of one billionth of a meter. A nanometer (nm) is excessively diminutive and impossible to register by the naked eye. And yet, every year, dozens of materials are invented and manufactured with properties engineered at this tiniest of dimensions. In the field of nanotechnology it is the material itself that is being designed and engineered rather than the architecture which contains it. Nanotech materials are synthesized and calibrated to perform at the highest degree of specificity. Yet most building products that have undergone morphological changes at the nano scale typically do not occasion a significant change in their form; notwithstanding possible changes in appearance when using smart surfaces, thermochromic, photochromic and other shape-changing materials. Hence, it will be argued that rather than having a significant effect on the visual and formal design of architecture, design at the nano scale has a substantial effect on the thermal dimension of architecture.

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2.0  Nano engineering for thermal resistance The laboratory setting within which nanotechnology takes place facilitates the selective manipulation of a material’s properties, functions and performance factors. At this scale a material’s performance can be manipulated, altered and controlled to improve properties such as thermal conductivity and the capacity to carry an electrical charge. In materials destined for building envelopes, properties are altered, modified and augmented not with the goal of bettering their structural properties, but rather with the objective of ameliorating their energy performance. This is not entirely surprising given Reyner Banham’s observations in Architecture of the Well-Tempered Environment wherein he noted three different building archetypes, each predicated on vastly differing attitudes towards building materials and their larger environment. The first two are of particular interest to this chapter. According to Banham, Western architecture was founded on the construction of buildings he termed ‘conservative’ because they were built using load-bearing masonry walls. Stable structures, with excellent acoustical properties, these buildings also afforded the workings of thermal mass, negotiating large fluctuations in outdoor temperatures by storing the sun’s heat during the day and thereafter discharging it when temperatures dropped sufficiently to favor its release.1 Banham, however, was quick to criticize these structures for being incapable of satisfactorily negotiating the extremes of heat coupled with moist and humid air. Hence, his identification of a second mode of construction, aligned with an entirely other form of climatic environmental response; the building of lightweight, adaptable and transportable skins. Modeled on fabric tents employed by nomadic cultures, possibly from North Africa, this construction logic was notable for its capacity to act ‘selectively’. Albeit rarely featured in architectural canons, this flexible and easily modifiable building method was suited for the kind of thermal responsiveness required of hot-humid and tropical climates; environments befitting ventilation and aeration. Banham lauded the spatial plasticity and environmental mediation made possible by its ‘selective’ manipulation of the building’s envelope.2 In so stating, he had devised an expanded intellectual structure within which to classify the workings of matter and climate, and, more critically for this chapter, the workings of matter and energy. While load-bearing constructions were, and are, suitable for dry temperate and cold northern climates, more adaptable methods of lightweight construction are required for far more challenging environments. This continues to be the case today and in response, this chapter proposes that nanotech methods and processes which selectively engineer material properties at the sub-molecular scale, provide productive avenues for addressing the often difficult to resolve building performance issues of concern to contemporary architecture. To this end, the material featured herein is predicated on the effective and strategic manipulation of its energy equation by simultaneously optimizing light transmission and heat resistance.

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3.0  Aerogel: air that insulates A new category of insulation materials of much interest to architects, engineers and builders is that of Translucent Insulation Materials (TIMs); a group of building products which not only facilitate the transmission of light, but ensure the resistance of heat transfer. This combination of performance properties favors the reduction of energy loads alongside an increase in usable daylight. One of the most promising TIMs is the super-insulator known as ‘aerogel’.3 A truly space-age lightweight translucent material engineered at the nano scale, aerogel resists heat transfer, transmits diffuse daylight and if desired, facilitates solar thermal radiation. It acquires its most effective properties from being, on average, made of 95 percent air; recognizably, the best insulator there is.4 The United States Department of Defense and NASA were early adopters of this ultralightweight material, first engineered for insulating space ships destined for travel beyond the earth. Its physical characteristics defy reality; barely present, nearly transparent and smaller in granules than the smallest of sand particles, it outperforms all other insulation materials by weight. Originally invented in the early 1930s at the University of Illinois by American Samuel Stephens Kistler, aerogel’s particular chemistry was further developed by its inventor while employed at Monsanto in the decades following the Second World War. The ‘super-critical drying process’ necessary for attaining the thermal performance so particular to aerogel was first perfected at this time.5 Aerogel’s performance as a building insulator, light transmitter and energyfree solar collector is conditioned by being manufactured in a highly controlled laboratory setting. While air is the largest single component in aerogel’s composition, the other 5 percent is, typically, silica. At the center of its manufacturing process is the removal of the liquid content found in the original gel of silica alcogel. The result of the ‘super-critical drying process’ is a sample rendered incredibly light and extremely low in density. Its thermal, structural and acoustical properties are a direct function of its chemical composition, particulate size and profile type; all of which are controlled by various patented methods of production.6

3.1  Commercialization of aerogel Making aerogel accessible to the building industry has been a difficult process in part because of the high costs associated with its manufacturing. Contrary to pre-twentieth-century materials, it is patented by corporations and as such, not an open-source material. The high degree of chemical synthesis required in its production has favored its use primarily in cases where it is employed sparingly, but effectively. This situation is, however, rapidly changing. At present, aerogel is manufactured commercially in monolithic and granular particulate form, with the former being hydrophilic, the latter hydrophobic.7 A number of global suppliers have integrated the material in a series of product lines. Cabot is a manufacturer of the patented aerogel process, formerly called Nanogel, and now referred to as Lumira. (Figure 1.4.1) This aerogel is made of 5 percent nano-porous silica with particulates 3mm in diameter and upon whose

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surface are found apertures, nearly 10 billion of them, the size of 20 nanometers.8 This is the unimaginably small dimension of nanotechnology in which the very operations so essential to the material’s high performance are concealed. Notwithstanding its invisibility to the naked eye, the porosity ensures the particulates optimal performance as it retains the air essential for resisting heat transfer. Most particular is Cabot’s patented formula which allows the product to be manufactured in ambient conditions, without the need for the ‘super-critical drying process’ that typically renders the material prohibitively expensive. Cabot’s aerogel has the following advertised material properties: a heat transmission value (U) of 0.7 per 25mm of thickness, a heat resistance value (R) of 8 per inch, light transmission of 80 percent per cm of thickness, acoustic insulation of 50 percent reduction at 100 Hz over air, and a weight of 70–100 kg/ m3. It is UV resistant, hydrophobic, non-combustible and non-smoking.9 In order to expand its potential uses, the material has been integrated within a series of building envelope substrates; all of which favor the transmission of light, alongside the resistance of heat. These include structural composite panels such as fiber-reinforced panels (FRP), multi-cell structural polycarbonate panels, Uchannel glass and insulated glazing units.10 Additionally, Cabot manufactures a building insulation product that uses aerogel produced in the form of a blanket. Trademarked as Thermal Wrap™, this product is more than 50 percent silica gel, with the remaining materials being polyethylene fibers and nylon. Available in thicknesses of 3.5, 6 and 8mm, its standard width is 0.56 meters. Notwithstanding its white opaque-like appearance, it has a light transmission factor of 20 percent across a thickness of 8mm. Competitor Aspen Aerogels manufactures a trademarked SpaceLoft™ blanket in 5 and 10mm thicknesses, with an advertised R value of 10.3 per inch [ft2·°F·h/(BTU·in)]; more than three times the insulation value of fiberglass batt insulation (3–4 per inch), expanded polystyrene (3.6–4.2 per inch) and cellulose loose fill insulation (3.2–3.7 per inch of thickness).11 In blanket form, it can be used in a variety of applications,

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1.4.1 Cabot Nanogel in granule form and in blanket roll

including coupled behind a roof solar collector to minimize heat gain through the roof. At the Imperial War Museum in London, UK, for example, SpaceLoft™ was strategically employed in the renovation of a below-ground barrel-vaulted ceiling whose interior space was climatically intemperate, both in summer and winter. With the addition of the aerogel blanket, the U value of the ceiling was reduced to lower than 0.2W/m2K, with a loss of only 20mm to the space’s ceiling height.12 Numerous examples exist of aerogel-based products used to optimize the insulation value of building skins of all kinds.

3.2  Research into aerogel Research has been underway for nearly two decades to accelerate the material’s adoption in building envelope products for the residential and commercial sector.13 The work of researchers at the Technical University of Denmark, in collaboration with the Swedish Company, Airglass AB and their partners at the Institute for Solar Energy at the Faunhofer Institute in Freiburg, Germany has shown great promise. They have prototyped an Evacuated Aerogel Panel system made of monolithic silica aerogel which, since 1999, has been tested in dozens of prototypes.14 Their most recent sample was the thinnest: a 0.5mm cavity of monolithic aerogel inserted within an evacuated double-pane glazing unit. The aerogel’s reported pore size is in the range of 10–100nm and the unit’s low pressure vacuum further increases its performance by reducing its thermal conductivity.15 The researchers set out to construct a glazing panel whose performance ensured both a high resistance to heat transfer (low U value and high R value), and a high degree of light transmission. They tested their aerogel prototype against commercially available triple-glazed windows and proved using computer simulations that their Evacuated Aerogel Panel system outperformed a commercial triple-glazed unit in net yearly energy savings for a typical single-family house in Denmark. In this northern climate, the thermal equation is dependent on achieving solar gain for the reduction of winter heating loads while at the same time benefiting from the added insulation.16 A second group of researchers working at ZAE Bayern (Bavarian Center for Applied Energy Research) is also focused on the commercialization of aerogel for the building industry. Since 1994, an affiliate group located in Würzburg has designed and tested a range of Transparent Insulation Materials (TIMs) for use in low-energy passive solar systems, including aerogel.17 Their work has identified specific mechanisms for controlling the level of desired light transmission in any one prototype. Early empirical tests analyzed how the nanostructure of aerogel particulates could be controlled for balancing the variables of transparency (maximum solar penetration via transparent granules) and light diffusion (acceptable levels of transmission achieved using a translucent milky granular mass). Controlling transparency minimizes heat gain; promoting light diffusion promotes heat-free light transmission. Researchers observed the shape of the granule affected the degree of transparency; fractured profiles achieved higher levels of transparency whereas regular-shaped granules resulted in assemblies that were more semi-translucent.18 In fact, fractured granules achieved levels of

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solar transmission of 90 percent for a layer of aerogel between 15 and 20mm thick. Moreover, they concluded the more transparent the sample sought, the longer it needed to be held in its gel state and the slower the required pace of its super-critical drying.19 Committed to the multi-functional characteristic of aerogel, the Würzburg group tested a building-integrated aerogel sandwich panel to evaluate three interrelated building performance variables: insulation value, daylight transmittance and solar heat gain.20 Each variable was studied in the context of a northern climate and researchers sought to quantify their performance in reducing the building’s lighting load, summer cooling load, and winter heating load. They also considered aerogel’s contribution to the psychological and physiological wellbeing of those who benefited from the light-filled rooms. The specific assembly they tested was a composite sandwich made of both acrylic and glass panels. The central core was made of a PMMA Acrylic cellular panel whose cavities were filled with silica aerogel (16mm wide). On either side were two glass layers of low-E glass sheets whose 12mm cavity was filled with argon gas. The entire assembly was 50mm thick. The U value achieved for the entire panel was less than 0.4 W/m2K. The aerogel had a 65 percent solar transmission within the 16mm PMMA section, and a solar transmission of 35 percent for the entire assembly. The prototype was installed in the façade of the Bayern research facilities in Würzburg and early recordable observations included settlement of the granules within the cavity; a serious issue given the substantial drop in thermal performance in areas where the material has been displaced. Controlling aerogel’s insulation to light transmission ratio is essential; uncontrolled transparency results in solar build-up and unwanted heat gains. Having the means to competently predict the solar transmission value of any one sample is critical for the commercial viability of the material. To this end and early on, the researchers at the Bavarian Center for Applied Energy Research experimented with electrochromic and thermochromic technologies as well as with liquid crystals to further control the light transmission of aerogels. In the first instance, they introduced an electric current through the material to change its solar irradiation (the amount of solar insolation it absorbed). This electrochromic process altered the material’s coefficient of light absorption by increasing its capacity for spectral light diffusion.21 Secondly, thermochromic means were used to control the amount of permitted light in the aerogel assembly. When a set temperature was reached, by solar radiation travelling through the sample’s polymer layers that were engineered to be heat sensitive, the material assembly changed its physical properties to reduce the amount of transmitted light and heat. This planned dispersion of light rendered the aerogel sample less transparent and thus more diffuse.22 Lastly, a final set of experiments was conducted in which the light was scattered in a controlled manner through the thickness of an aerogel sample with a liquid crystal substrate. When a small charge was sent through the substrate, the molecules realigned themselves rendering it more difficult for light to travel through the sample.23 Translucency, thermal resistance and the settlement of particulates within prototypes are important variables whose control and optimal engineering are key to the future commercial viability of aerogel. And in all instances discussed

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here above, research has greatly contributed to establishing the most effective benchmarks for attaining this goal.

3.3  Aerogel in residential design Notwithstanding nearly fifteen years of research and development, aerogel envel­ ope assemblies remain primarily custom-made products, with every new project requiring the engineering of both the substrate and infill. As noted above, when choosing a substrate, the most commercially available products include polycarbonates, insulated glass units, and fiber-reinforced composite panels. In 1994, the German architect Thomas Herzog was the first to experiment with the use of aerogel in the construction of a façade for a single-family house-studio in Bavaria. This inaugural project incorporated the translucent super-insulator in glazing units that covered the home’s three-storey front façade. During the day, the product ensured visual privacy for those within the house while making possible the transmission of abundant light. During the evening, with greater light levels on the interior, the home glowed to the outside like a beacon. Few, if any, new residential projects have experimented with the possibilities latent in this new material since this early work by Herzog.24 More recently, aerogel has been used in a series of high-performance building envelope prototypes for net-zero single-family solar-powered homes discussed in Chapters 4.1 and 4.2.25 (Figure 1.4.2) Aerogel-filled multi-wall polycarbonate panels of varying thicknesses (from 10 to 55mm) can be used in the design of sandwich assemblies with significant insulation values. The polycarbonate’s cellular cavities offer an excellent structure for containing the aerogel, inhibiting convection and minimizing the amount of settlement within the cavities. This detail was used in building the exterior skins for both Lumenhaus (2005) and Project Icarus (2007).26 (Figure 1.4.3) In the latter, an assembly of two polycarbonate panels (each 40mm wide) was built with a 19mm air gap, achieving a U value of 0.48 W/m2K across 80mm of aerogel insulation. The tubular cells of the Duogard polycarbonate panels were oriented horizontally to avoid compression and settlement of the Cabot Nanogel granules. The building envelope achieved significant levels of translucency notwithstanding the large amount of insulation contained. On average, 30 percent light transmission was attained alongside a resistance value (R) of 18. Five-footlong panels were interlocked using tongue and groove extensions molded into the edges of the polycarbonate. Eight-foot-tall panels were contained in custom horizontal and vertical aluminum extrusions with little or no air infiltration and minimal amounts of thermal bridging. Moreover, and as described in greater detail in Chapter 4.2, aerogel granules were used in the construction of the house’s 800-square-foot translucent roof. Acting as the building’s thermal envelope, a 50mm-thick aerogel sandwich panel was contained between two layers of ethylene-tetrafluoroethylene (ETFE) film and pressure fitted around a perimeter wood frame.

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1.4.2 Lumenhaus©, 2005, zero-energy solarpowered prototype. (Top) Night view of interior polycarbonate assembly, filled with Nanogel and illuminated with LED lighting. (Bottom) Night view of exterior polycarbonate building envelope assembly filled with Nanogel and illuminated with LED lighting

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4.0  Conclusion 1.4.3 Project Icarus, 2007, zero-energy solar-powered prototype. (Left) Daylight transmission to the interior across the exterior skin polycarbonate assembly, filled with Nanogel. (Right) View of exterior polycarbonate building envelope with acrylic solar shading

In all instances, skin assemblies incorporating nanomaterials and super-insulators, such as aerogel, contribute to the design of a fully integrated building envelope by fostering the coincident consideration of light transmission, thermal resistance, thermal breaks, artificial lighting and user-operated shading devices. And yet the material’s capacity to affect the nature of architectural design has yet to be fully explored, as the field requires a far greater number of examples to be built, tested and evaluated. Aerogel will surpass the scientist’s laboratory. When it does, the result will surely be more inspired designs, which triangulate the material’s capacity to insulate, transmit daylight, and contribute to the construction of a thermally balanced and habitable space.

Notes 1 R. Banham, Architecture of the Well-Tempered Environment, Chicago: University of Chicago Press, 1984, p. 23. 2 Ibid. 3 C. Buratti, ‘Transparent Insulating Materials: Experimental Data and Buildings Energy Saving Evaluation’, Wessex Institute of Technology Conference Proceedings: Energy and the Environment, 2003, pp. 231–240. 4 The highly insulating capacity of air was discovered and recorded as early as 1787 by Count Rumford in his investigation on the ‘Relative Warmth of Coverings of the Same Thickness, and Formed of the Same Substance, but of Different Densities”, in The Collected Works of Count Rumford, Vol. 5., Cambridge, MA; Harvard University Press, 1968. 5 J. M. Schultz and K. I. Jensen, ‘Evacuated Aerogel Glazings’, Vacuum, Vol. 82, 2008, p. 724.

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6 J. Fricke and G. Reichenauer, ‘Thermal, Acoustical and Structural Properties of Silica Aerogels’, Proceedings of Materials Research Society Symposium, Vol. 73, 1996, pp. 775– 783. The typical range of particle sizes this group of researchers tested was, approximately φ = (1nm), between 1 to 5nm, and 5 to 100nm. For a description of how it is manufactured see A. Beck, W. Korner, H. Scheller, S. Hauck and J. Fricke, ‘Recent Developments on Transparent Insulation Materials and Light Switching Devices for Passive Solar Energy Use’, Renewable Energy, Vol. 5, Part 1, 1994, pp. 446–453. 7 The granular particulates have the added advantage of repelling all water-based liquids with which they come into contact and as such are often used a desiccant. 8 For additional information of Cabot aerogel see www.cabot-corp.com/aerogel (accessed September 10, 2011) and Cabot Nanogel, Spec Sheet. 9 The company’s MSDS sheets do note the material off-gases dangerous carbon monoxide and carbon dioxide, yet it is non-combustible and non-flammable under normal uses. Available at: www.cabot-corp.com/wcm/msds/en-gb/AE/NGBL-EUR-EN.pdf (accessed September 10, 2011). 10 U-channel glass panels such as Profilt™ and Reglit™, as well as with double-pane insulated glazing units can achieve U values as low as 0.30 W/m2K. When combined with panels made of fiber-reinforced composite panels, such as those manufactured by Kalwall, a U value of 0.26 W/m2K is possible. 11 For insulation values of typical building materials, see N. Lechner, Heating, Cooling, Lighting: Sustainable Design Methods for Architects, Third Edition, New Jersey; John Wiley & Sons, 2009, pp. 668–669. 12 For Aspen Aerogel case study, see www.aerogel.com/markets/Case_Study_Barrel_Vault_ Ceiling_web.pdf (accessed September 10, 2011). 13 While not discussed in this chapter, research is being conducted in China. Q. Zhu, R. Duan and Y. Li, ‘Measurements of Solar Optical Properties of Transparent Insulation Materials’, Proceedings of ASME/JSME Thermal Engineering Heat Transfer Conference, Vancouver, British Columbia, 2007. 14 Schultz and Jensen, op. cit., pp. 723–729; K. I. Jensen, J. M. Schultz and F. H. Kristiansen ‘Development of Windows Based on Highly Insulating Aerogel Glazings’, Journal of Non-Crystalline Solids, Vol. 350, 2004, pp. 351–357; J. M. Schultz, K. I. Jensen and F. H. Kristiansen, ‘Super Insulating Aerogel Glazing’, Solar Energy Materials & Solar Cells, Vol. 89, 2005, pp. 275–285. 15 Schultz and Jensen, op. cit., p. 724. 16 Ibid. 17 Beck et al., op. cit., pp. 446–453; M. Reim et al. ‘Silica Aerogel Granulate Material for Thermal Insulation and Daylighting’, Solar Energy, Vol. 70, 2005, pp. 131–139; M. Reim et al., ‘Highly Insulating Aerogel Glazing for Solar Energy Usage’, Solar Energy, Vol. 72, 2002, pp. 21–29; M. Reim et al. ‘Silica – Aerogel Granulate – Structural, Optical and Thermal Properties’. Journal of Non-Crystalline Solids, Vol. 350, 2004, pp. 358–363. 18 Reim et al. , op. cit., 2004, pp. 358–363. 19 Ibid. 20 Reim et al., op. cit., 2002, pp. 21–29. 21 Reim et al., op. cit., 2005, pp. 131–139; Reim et al., op. cit., 2002, pp. 21–29. 22 Ibid.; Beck et al., op. cit., pp. 446–453. 23 Ibid. 24 I. Flagge, V. Herzog-Loibl and A. Meseure, Thomas Herzog: Architecture and Technology, Munich, London and New York: Prestel, 2002. 25 These homes were built as part of three university-based international design/build competitions sponsored by the Department of Energy (DOE) and the National Renewable Energy Laboratory (NREL) from 2005 to 2010. For more information on projects completed by Virginia Institute of Technology, see R. Dunay and J. Wheeler, ‘No Compromise: The Integration of Technology and Aesthetics’, Journal of Architectural Education (JAE), Vol. 6, No. 2, 2006, pp. 8–17. For more information on the project completed by the Georgia Institute of Technology, see F. Trubiano, ‘Responding to Light and Energy: The Design and Construction of a High-Performance Roof’. Proceedings, ACSA Material Matters Conference, 2008 and R. Choudhary, F. Augenbroe, R. Gentry and H. Hu, ‘Simulation Enhanced

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Prototyping of an Experimental Solar House’, Proceedings of Building Simulation, 2007, pp. 1690–1697. 26 For information on the product patented to this end, see ‘Translucent Daylighting by Duogard, Architectural Systems Integrating Nanogel Translucent Insulation’. Available at: www.cabot-corp.com/wcm/download/en-us/ae/Nanogel-DuoGard%20brochure%205-06.pdf (accessed September 10, 2011).

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t. russell gentry

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Building Performance and Computational Simulation yun kyu yi

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ABSTRACT: High-performance homes are conceived, built and operated to be efficient, economical and minimally consumptive of materials and energy. As discussed in previous chapters, the introduction of energy-free architectural design principles is essential for achieving these benchmarks. Properly siting the home for solar exposure and choosing materials with high thermal resistance contribute substantially to the reduction of energy demand. However, in most instances, the exigencies of contemporary living make it impossible to operate a home without external inputs of energy to meet the required loads. Thus, this chapter discusses the introduction of renewable forms of energy whose buildingbased technologies are commercially adaptable for use in the design of high-performance homes. It features instructive architectural projects which have re-imagined the way in which energy-producing systems can be inventively and productively integrated within architectural designs.

1.0  Architectural design and energy generation In more than half a century of research and practical implementation, numerous advances have been made in optimizing the use of renewable energy technologies in the design of single-family homes. Most recently, a series of architectural projects have re-imagined the way in which such technologies achieve optimal design integration. Differently than in the past, when the representational role of solar-based systems was debated and contested, the recent introduction of renewable energies in architectural design reveals a range of new strategies which broaden the acceptance of their technologies. Three main factors have contributed to this change. To begin with, solar-based renewable systems are now more typically used alongside other forms of renewable energy, such as wind and geothermal, with the result being a lessening of their overall impact on the house’s design. In addition, with the resurgence of interest in

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energy-free architectural design principles, solar electric and solar thermal systems are increasingly used only when said ‘passive’ principles are insufficient for achieving the desired level of energy load reduction. And lastly, the concentration and miniaturization of solar technologies is rendering them smaller, more diffuse and more easily integrated within the building’s details. For these reasons and others, the integration of renewable forms of energy within contemporary works of architecture continues to provide important opportunities for articulating a distinctive figural language for the design of highperformance homes. An important example of this was solarCity, an ambitious project to design high-performance low-rise buildings at the scale of an urban district.1 Built in Linz, Austria and completed in 2005, this model city was constructed using rigorous ecological principles applied at the urban, architectural and building systems scale. The project included the first social housing units constructed in Austria to Passivhaus standards. Its population of 3,000 inhabitants and 1,300 housing units benefited from the early involvement of architects Thomas Herzog, Richard Rogers and Norman Foster. As its design developed in the late 1990s, it remained committed to the smart use of renewable energy and an efficient low-energy infrastructure at the scale of the town. The integration of daylight, views and desirable solar exposures was as important as choosing the right energy mix of biomass, combined heat and power (CHP) and solar thermal/ solar electrical. The project is exemplary for many reasons but principally for its effective integration of renewable energies in the design of contemporary housing. Albeit rare for being at the scale of an entire district, much of its success remains instructive for the design of single-family homes.2 This chapter discusses the representation of energy-producing building systems in the design of environmentally sensitive homes, by suggesting an alternative narrative; one that moves beyond the traditional divide between overt expression or inconspicuous disappearance. To this end, a brief review of renewable energy technologies that contribute to operational net-zero homes is necessary.

2.0  The technology of renewable energies An important goal of many high-performance building projects is the operation of the building according to net-zero-energy principles whereby, over a given calendar year, the building’s systems generate as much energy renewably as they consume from non-renewable sources.3 The most common sources for generating renewable energy are sunlight, wind, and water and to mediate the interrupted nature of these sources, renewable energy systems are typically connected to the local electrical ‘grid’. Whether supplying energy in the form of electricity, natural gas, or steam, the grid is used as a battery from which energy is pulled when needed, or returned to when renewable energy is being generated by the house’s various systems. The introduction of energy production systems into a high-performance home should be based on a number of variables: the availability of one or more renewable sources; the cost and complexity of the conversion between the renewable source and the usable energy sink; the potential for successful

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integration of energy-generating systems within the larger building site, program and form; and the context-specific environmental benefit of the renewable energy installation. In the United States, however, achieving net zero in the operation of even small, extremely efficient homes can require the continuous production of 2–4 kW (kilowatts) of power, which typically results in systems with peak power outputs in the 5–10 kW range. Given renewable power systems can cost up to US$15 per peak watt to install, the cost of a residential-scale system for netzero operation can approach US$150,000 (€100,000). For this reason, many renewable energy installations are sized to cover only part of the house’s energy requirement, with the remainder of the energy supplied by the local electrical grid.4 This financial reality further reinforces the value of introducing energy-free architectural design strategies and addressing building enclosure design and mechanical system design before considering the addition of renewable energy generation within a project. Moreover, an often-stated goal of high-performance projects is carbon neutrality. A carbon-neutral building is one that entirely offsets its carbon emissions from both the construction and operation of the building (and perhaps even the transportation modalities of the home’s occupants). However, accomplishing carbon neutrality for most buildings requires a greater level of on-site energy generation than otherwise needed for achieving net-zero energy. Hence, it is important to assess whether carbon neutrality is a high-performance goal of a given project, for if it is, the sizing of all renewable energy equipment will be significantly more extensive.

2.1  Strategies and types Five types of renewable energy strategies are typically adopted in the design of buildings. The first four involve the conversion of energies found in nature into electricity (solar photovoltaics (PVs), wind energy, low-impact hydroelectric energy, and geothermal energy) while the last involves the direct concentration of sunlight into thermal (heat) energy. (Table 2.1.1) All building sites can take advantage of photovoltaics – the conversion of radiant energy from the sun into electricity – even those with predominantly cloudy climates and diffuse radiation (e.g., London, Seattle). However, on-site energy conversions from wind or low-impact hydro are limited to specific sites with consistent prevailing winds or streams with significant changes in elevation. In most cases, site-specific studies are required to establish the viability of these systems. The use of geothermal energy is only possible where hightemperature water or steam is available from the ground; wherein the water or steam can be used directly for heating or can be converted to electricity in a turbine.5 By contrast, solar thermal energy production requires the direct exposure to sunlight, and involves the collection and concentration of thermal energy for direct use in space heating and in domestic hot water. Other sources for local energy conversion include on-site burning of renewable fuels such as wood pellets, but the environmental impact of such systems is widely debated

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Table 2.1.1  Renewable energy sources and conversions System

Conversion

Application

Production

Cost (US$ 2011)

Photovoltaics

Electrons in light-sensitive semiconductors are excited by solar radiation and create an electric current.

Widespread potential. Best production in regions with little annual cloud cover. Works well at small scale (residential) and large scale.

Typical rigid panels produce around 200 W of electricity per square meter (W/m2) when sun is at its peak (solar irradiance of around 1000 W/m2). This equates to 20% efficiency.

Typical residential-scale systems cost around $4 per watt of peak generation, or $35,000 for a 5 kW system.

Wind turbines

Wind velocity (kinetic energy) spins an electrical turbine driven by a propeller.

Limited to regions (shorelines, plains) with consistent strong winds with average wind speeds greater than 6 m/s (12 mph).

Small-scale turbines available in the 2.5 to 5 kW range and installed on 20 to 30 m (60 to 100 ft.) poles, are suitable for stand-alone installations.

Small-scale systems installed with poles cost between $50,000 and $75,000.

Low-impact hydro Water velocity (kinetic energy) spins an electrical turbine driven by a propeller.

Limited. Must be adjacent to waterway or large body of water with significant flow and change in elevation (> 3 m (10 ft.)).

With a 3 m (10 ft.) drop, a flow of 0.25 cms (cubic meters per second) is required to generate 4 kW of electricity.

Low-impact hydro systems are site specific due to the design of dams, flumes, etc.

Geo-thermal

Steam or hot water from geothermal activity is used to spin an electrical generator.

Must be adjacent to significant geothermal activity such as geysers or volcanoes.

At this time there are no residential-scale applications of geothermal electricity.

Not applicable.

Solar thermal

Collects and concentrates solar radiation into thermal energy but does not convert it to electricity.

Widespread potential. Used for space heating and hot water production.

A typical flat-plate or evacuated-tube collector can produce 20 MJ to 40 MJ (20,000 to 40,000 BTU) of thermal energy per day.

Typical residential system for domestic hot water costs around $5,000. Systems for space heating will cost significantly more.

due to the production of smoke, particulates and carbon dioxide in the combustion process. In the end, because photovoltaics and solar thermal collectors have the greatest potential for widespread use in the design and construction of highperformance homes, a discussion of their various technologies is expanded upon here below.6

2.2  Photovoltaic systems Photovoltaic or PV systems use arrays of semiconductor modules to convert solar radiation into electricity. Typically fabricated into rigid panels, photovoltaic mater­ial can also be made into roofing shingles, flexible membranes and thin films. PV panels are wired together in series and/or parallel to raise the voltage to the level required

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by the Inverter, the device that converts the Direct Current (DC) generated by the PV array into Alternating Current (AC) used by the electrical wiring of the building. The highest-efficiency, commercially available PV panels produce around 200 watts of electricity per square meter of installed panels when the sun is at its peak.7 Photovoltaic systems for residential-scale use are installed in either on-grid (most typically) or off-grid (more rarely) applications.8 In on-grid applications, the electrical grid is used as a battery, and the PV power produced is transmitted to the grid. The consumer then receives a monthly payment for all power sent to the utility grid (usually at a favorable price given the PV is generating ‘green power’).9 The home then draws and purchases all of its required electricity from the grid; a strategy sometimes referred to as ‘dual metering’. By contrast, ‘net metering’ uses a single meter. The home consumes all of the PV power produced by its systems and only when necessary, the house’s electricity is augmented by power from the grid. In off-grid applications, the PV system is the sole supplier of all energy used to power the home’s systems, appliances and other plug-in loads. A form of energy storage for use at night (when no PV energy is produced) or during cloudy periods is almost always required; most typically in the form of batteries. Photovoltaics are typically characterized by their form, in rigid panels or flexible membranes, and by the underlying semiconductor technology used to produce the individual PV cells or modules. Detailed knowledge of semiconductor technology by end users is not essential, albeit important to recognize the implications it has on price performance of PVs. The most common photovoltaics are made of crystalline silicon, grown either as a single crystal or in a multi-crystalline state. In general, single crystalline solar cells are more expensive and have higher efficiencies. Yet, both technologies are used in making rigid PV modules, which are then interconnected to make the typical rigid PV panel. Non-crystalline or amorphous silicon is used in the making of flexible and/or transparent membrane PVs. These thin-film PVs are integrated into glazing panels or other translucent membranes such as ETFE for use as alternative roofing and wall materials. In general, however, the efficiency of these systems is well below (less than one half) that of panels made of crystalline silicone. Spectrallyselective PV systems use thin films to capture only part of the sunlight spectrum for conversion into energy, while allowing the remainder of the visible light to pass through the glass substrate into the building. These systems have been used to power greenhouses by encouraging the transmission of the solar spectrum that facilitates plant growth while the remainder of the light is captured and converted into electricity. And lastly, the so-called multi-junction PV cell is the opposite of the spectrally-selective system. It uses separate stacked sets of PV junctions, tuned to capture the entire bandwidth of solar radiation, and thus increase the efficiency of the solar radiation to electricity conversion. This technology has reached an efficiency of close to 50 percent, but its initial costs are very high. Emerging technologies such as nano-structured solar cells, advanced Copper Indium Gallium Selenide cells (CIGS cells), Plastic Solar Cells (organic or otherwise) and high-efficiency ultra-miniaturized solar concentrators are further expanding the field of solar electric energy generation.10 Discussed at the very end of this chapter is one example of the promise held by ultra-miniaturized solar concentrators in expanding the possibilities for building-integrated photovoltaics.

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2.3  Solar thermal systems Solar thermal systems collect and concentrate the heat energy available in solar radiation. The collected thermal energy is generally stored in a liquid (water or a water–glycol mix), which is then used for space heating and/or domestic hot water. The magnitude of the energy produced is related to the volume of liquid heated and the temperature difference between the liquid and ambient air. At present, a number of prototypes are being conceived that return to the use of phase change materials (PCM) for storage of the heat energy.11 In all instances, a solar thermal system consists of one or more collectors, a storage tank for holding the hot liquid, and one or more pumps to route the liquid to heat exchangers (e.g., radiators) that heat spaces or water.12 The installed cost of solar thermal systems is generally well below the cost of photovoltaic systems. However, these systems create thermal energy which must be used almost exclusively for heating, whereas electricity from photovoltaic systems can be used for far more varied purposes. Solar collectors are categorized as either flat-plate or evacuated-tube collectors. The former typically route the water over a large matte black plate that absorbs most of the energy from the sun. The plate is insulated with high-performance glazing to minimize heat losses. Evacuated-tube collectors consist of a linear array of glass vacuum tubes with solar absorbing metal sleeves. In some evacuated-tube systems the water is introduced directly into the tubes. In others, an intermediate heat pipe transfers the thermal energy from the evacuated tube up into a manifold where the heat energy is therein transferred to a liquid. Historically, flat-plate collectors have been less expensive to purchase and operate than evacuated-tube collectors, albeit with lower efficiencies. More recently, the cost of evacuated-tube collectors has decreased, rendering them more competitive. They typically produce a higher temperature gain in the heat transfer liquid; an important factor during winter months or in cold climates. In some cases, the two types of collectors can be combined such that multiple flat panels are used in series with one evacuated tube, at the end of the heat loop, used to maximize the temperature of the heat transfer liquid.

2.4  Design of systems The design of PV and solar thermal systems should be undertaken with the same attention as that given to energy-free architectural design and the design of energy-consuming systems (e.g. HVAC, appliances – see Chapter 2.3). Many homes will include the clever integration of both PV and solar thermal technologies.13 Important design variables include the peak output of the collector array(s), the location and attitude of the array relative to the home’s orientation on the site, the inverters and pumps required to transfer the collected energy, and the wiring and plumbing that affect the transfer. All aspects of the design should reflect the specific climatic realities and performance objectives (cost effectiveness, goals for net zero and carbon neutrality), as well as the architectural integration objectives, which are discussed in detail here.

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3.0  The integration of renewable energies By the mid 1970s, it would have been clearly evident in the siting, planning, building section, engineering and construction details of a solar home that it was designed to incorporate solar thermal and/or solar electric technologies. If built to harvest the sun’s energy, this was formally decipherable. South-facing glass walls indicated the adoption of principles of passive solar heat gain. Large acute roof slopes, far steeper than normal for most climatic regions, denoted the installation of power generating systems optimized for incident solar radiation. The presence of these and similar devices clearly communicated the implementation of architectural and engineering-based solar principles. However, within a few short years, this commitment to expressing the energy efficiency of buildings had its detractors, as housing communities confronted neighboring homes whose distinctive features clearly marked them as different, as other. In response, promoters of solar-powered technology devised an alternative strategy for ensuring the continued use of their products. Building-Integrated Photovoltaics (BIPVs) were engineered to be fully imbedded within the existing wood frame of most single-family homes. By replacing the exterior layer of the building envelope, these new solar collecting devices were more easily camouflaged within the roof’s profile. Most typically, asphalt roof shingles were replaced with BIPV shingles, barely recognizable by the untrained eye. As a result, the traditional image of the house could remain figurally indifferent to the introduction of highly engineered power producing equipment. And in larger-scale buildings, PVs were integrated in vertical building envelopes of all kinds including curtain walls (unitized or stick system), rain screens, specialized shading systems, and even double-skin façades.14 Yet, the adoption of BIPVs by homeowners and members of the residential building industry was no more extensive. Reasons for which are many and varied including performance limitations in available technologies and the very real cost of maintaining early systems. During the three decades for which the integration of solar technology in the design of homes was sought, neither the explicit representation of its equipment nor its near-total disguise within the building’s fabric succeeded in ensuring its wider acceptance. Most recently, however, contemporary design projects have demonstrated renewed commitment to the integration of renewable energies in the construction and operation of homes. They have done so by addressing whether the design of high-performance homes should visibly communicate their integration of renewable energies. The responses have been wide-ranging, nuanced and instructive. To begin with, and as mentioned previously, renewable energy sources used in single-family homes are more numerous than ever before. Alongside more traditional forms of solar thermal and/or solar electric, technologies such as biomass, geothermal and wind are introduced with increasing ease; each of which figures quite differently in the building’s representation. Biomass can be burnt in new high-efficiency stoves that are, nevertheless, traditional in appearance; the main components of geothermal energy are predominately invisible in being underground; and the harvesting of wind energy often takes place on sites well away from the house.

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In addition, pervasive distrust of energy-consuming mechanized building systems has occasioned the adoption of energy-free architectural design principles, with much greater frequency. Their integration reduces a building’s loads as well as the very need for generating renewable energy. To the same end, building standards and certification procedures such as those established by Passive House Institutes in North America, Britain and Europe have successfully encouraged the building of highly insulated energy-efficient homes.15 The program’s tenets promise substantial savings in operational energy by minimizing to near zero the need for engineering systems that heat, cool and ventilate. The same holds true for other certification initiatives in the United States including those by the National Association of Home Builders (NAHB) who have established the National Green Building Standards and Certification program and the Energy Star Certification & Green Building Verification.16 Even more critical, is the availability of vastly more advanced solar electric technologies that further dissimulate the appearance of solar generating technologies. The installation of PV arrays no longer requires optimization for direct southern exposure according to direct solar incidence. Solar panels are now available for use in climates whose lighting conditions do not benefit from an abundance of direct solar radiation. Flat panels optimized for diffuse radiation are being installed throughout northern Europe and particularly in Germany. And the availability of thin films engineered for optimal integration within transparent glass membranes, more easily and immediately integrate the PV within the home’s already existing fenestration patterns. Lastly, with the development of super-concentrated solar cells, dimensionally as small as the size of one’s fingertip, the figural concealment of this most recent form of renewable energy is near-certain. For these and other reasons, renewable energy technologies aimed at optimal solar, wind and geothermal performance are, at present, multi-valent, multi-dimensional and typically, embedded. They not only impact the design of a building’s energy systems, both generative and consumptive, but they also condition the design of a building’s enclosure, fenestration, material choices and construction details. And it is this unique condition of contemporary practice that is described in the following projects, both built and imagined, which advance architectural design and engineering science.

4.0  Project descriptions 4.1  zeroHouse The design of zeroHouse aims to actualize the dream of a truly self-sufficient home. Using zero non-renewable energy, producing zero organic waste and requiring zero off-site water supply, this project sets the highest standards for the construction and operation of a high-performance home. (Figure 2.1.1) Developed by architects Specht Harpman, the two-storey prefabricated prototype features a building section that clearly articulates its performance goals: large-scale rain­water collection and the generation of solar power.17 As noted by its designers, the 650-square-foot house can be sited for year-round occupation anywhere

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2.1.1 zeroHouse by Specht Harpman Architects. (top main) Perspective of house with cantilevered roof upon which flat-mounted solar electric photovoltaic cells are located; (bottom left) diagram of the structural, volumetric and programmatic integration of the house’s systems; (bottom) comprehensive systems diagram for the engineering components channeling sun, water and waste

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within 36 degree north and south latitudes given its universally adaptable fourpoint load foundation system. It is fitted with a 7 kW-capacity solar electric array and solar hot water collectors for complete energy independence. The PV system uses polycrystalline cells in rectangular frames with 14.1 percent efficiency. Inverters and lead acid batteries complete the solar electric system and a grid-tied option exists for transferring excess power to the utility grid. The solar thermal system uses flat-plate collectors and while a radiant heating option is available, the base unit is designed for forced-air heating. The house’s exoskeleton steel structure is outboard of the envelope assembly, made on the inside of structurally insulated panels (SIPs) using steel studs and closed-cell insulation foam and skinned on the outside with resin composite panels installed in a rainscreen configuration. The insulation has a thermal resistance value (R) of 58; windows are made of triple-pane, argon-filled, low-E coated glass; and exterior doors have vacuum-sealed aerogel panels. The house’s energy-producing and energyconsuming technologies can be fully automated with sensors and data loggers further contributing to its energy-saving potential. The zeroHouse prototype maximizes its capacity for solar power collection and generation and in so doing, points to the far-reaching implications of integrating renewable energy in the construction of high-performance homes. Principal amongst which are the benefits of synchronizing its energy-producing and energy-consuming systems with energy-free architectural design principles. In the four additional homes here discussed, this practice is further advanced.

4.2  Xiao Yen House Many ecological design strategies are evident in the Xiao Yen House, built in 2010, in San Francisco, California, and designed by the firm of Craig Steely Architecture. (Figure 2.1.2) The two-unit 3,500-square-foot duplex was substantially rebuilt and seismically upgraded using a steel exoskeleton structure. A green roof of native California plants, a zoned hydronic heating system with sensors monitoring both use and temperature, natural cross-ventilation, southern solar shading, and a significantly refurbished exterior skin made of old growth redwood previously used for the house’s framing, significantly contribute to the house’s performance profile. As do the balcony extensions, skylights and glass penthouse that project the house’s interiors beyond the building’s envelope and reciprocally draw distant views of the surrounding neighborhood, within. However, it is in the design of the home’s rooftop that the promised elegance of using renewable energy systems is truly captured. Contained within the design of this significant tectonic device is a 4 kW solar electric array and an evacuated-tube collector (with integrated water tanks). Both of these components are essential for meeting the house’s renewable energy demands and their importance is reflected in their roof top positioning. The choice of PV technology acknowledges the advances that have been made in the harvesting of light, both direct and indirect. The PV solar panels are bi-facial mono-crystalline plates installed near-horizontally (with a 5 percent cant) which collect direct solar radiation from above, and indirect radiation from reflected light underneath. They do so

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2.1.2 Xiao Yen House by Craig Steely Architecture. (top) View from the rooftop glass penthouse indicating location of bi-facial photovoltaics, skylight and green roof; (bottom left) view of the front façade at sunset; (bottom right) view of the front façade

with 20 percent efficiency, are grid tied and benefit from net metering. Housed, therefore, in the rooftop’s structural canopy, a structure added to safeguard the entire house against earthquakes, is a combined solar device that eloquently portrays the importance which channeling the sun’s energy represents for the house’s high-performance goals.

4.3  Mona Vale House The Mona Vale House benefits from an enchanting beachfront location, sited in a northern suburb of Sydney, New South Wales, Australia. Designed by architects CHOI ROPIHA FIGHERA, it too embraces both energy-free architectural design principles and renewable forms of energy. (Figure 2.1.3) This high-performance building was designed for maximum cross-ventilation of all rooms notwithstanding the site’s long and narrow footprint. A distinctive low-angle butterfly roof, whose clerestory facilitates the evacuation of hot air, frames the open floor plan of the main living and dining area. The building’s orientation maximizes desirable winter passive solar heat gains along its northern exposure, all the while incorporating the benefits of thermal mass. The roof of the bedroom area is used for arraying seven rows of combined solar electric and solar hot water collector panels. The first two rows are used for the photovoltaic system whose total power capacity is 2.8 kW. At present only one row is installed supplying 50 percent of the house’s energy demands. The third row is designated for flat-plate collectors that furnish the house’s domestic hot water (DHW). Four meters square of copper tubes are connected to a 300liter tank, supplying all of the summer DHW and 50 percent of what is needed in the winter, with an on-demand gas booster unit for the winter. The remaining four rows of solar thermal equipment are evacuated tubes that furnish direct thermal energy for in-floor hydronic heating of rooms. The pipes are encased in 300 mm of concrete that acts as thermal mass and is insulated against heat loss. Other high-performance features include low-energy fluorescent lighting and motion detectors as well as a water management system with a rainwater collection system that includes a 15,000-liter storage tank and grey water recycling. (Figure 2.1.4) The Mona Vale House combines energy-free architectural design principles with renewable energy technologies, and in so doing maximizes the benefits of each and provides for their integration in an architectural project that is highly consonant with both its immediate site and the larger environment.

4.4  Triangulo House and Frame House Triangulo House has an equally spectacular natural setting in San Juanillo Guanacaste, Costa Rica. Its beauty organizes the home’s internal two-storey volume, transparent façades, extensive gardens, and surrounding perimeter sundecks. (Figure 2.1.5) Designed by EcoStudio Arquitectos, this 550-square-meter house adopts energy-free architectural design principles alongside the generation of

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2.1.3 Mona Vale House by CHOI ROPIHA FIGHERA Architects. (top left and right) Sunshading details and material palette; (top center) interior view of clerestory in the dining room; (bottom) elevation of the main living area with lowsloped butterfly roof

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2.1.4 Mona Vale House by CHOI ROPIHA FIGHERA Architects. (top) Longitudinal elevation of the house with solar electric and solar thermal panels indicated on the roof; (center) view of bedroom wing with partial installation of PV and solar thermal panels; (bottom) systems diagram

2.1.5 Triangulo House by EcoStudio Arquitectos. (top) Corner view of the main living space with fully operable glass skin; (bottom) elevation drawing of the house

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2.1.6 Frame House by the marc boutin architectural collaborative. (top) House as positioned in the landscape; (center) all-glass façade facing south for maximum solar heat gain; (bottom) interior view of the house

solar thermal energy. Given its particular climate, natural ventilation was the principal design tool for reducing the house’s energy demand. When favorable, the house can be totally opened to the environment. Its 3.2-meter-tall main internal volume facilitates the convection of hot air and temperature sensors are used to regulate the extraction of intemperate air via the louvers located in the roof. The large 1.2-meter overhang surrounding the ultraviolet (UV) protected all-glass façades ensures protection of the interiors from unwanted direct solar heat gain, as well as from rainfalls typical in the area. By adopting these energy-free architectural design principles, the need for artificial cooling is substantially decreased. Solar collectors, located on the roof, are only used when needed for supplying hot water. Similarly, Frame House, located in Invermere, British Columbia, Canada and designed by the marc boutin architectural collaborative, harmonizes its renewable energy strategies with its specific climatic conditions. (Figure 2.1.6) Fully immersed in its natural environment, the house is designed to maximize solar heat gain with its large southern exposure built entirely of glass and its northern exposure predominantly opaque to protect against cold northern winter winds. Once again, it too is discreetly fitted with solar collectors for supplying the house’s hot water needs. In each of the four residences described here, cost-effective strategies for introducing renewable energy have been integrated alongside energy-free architectural design principles. And the representation of their associated technologies is a matter of integration; both apparent and dissimulated.

4.5  Integrated Concentrating (IC) Dynamic Solar Façade In a final example, the introduction of renewable energies has also occasioned the invention of new building-centered technologies specifically developed for full and direct integration within the building’s skin. (Figure 2.1.7) With the design and prototyping of the IC Dynamic Solar Façade, a return to the true promise of Building-Integrated Photovoltaics (BIPVs) has been achieved. Vertical building envelopes are decidedly productive sites for the generation of renewable energy, a premise sustained by architects and mechanical engineers at the Center for Architecture, Science and Ecology (CASE) in advancing the science of concentrated photovoltaic cells in the design of a highly sophisticated architectural building skin.18 The IC Dynamic Solar Façade is a multi-functional envel­ope that generates power, facilitates the transmission of daylight, all the while maintaining occupant views to the outside. The all-glass façade is designed as an array of transparent horizontal and vertical hexagonal cups within which Fresnel lenses concentrate the sun’s rays upon a highly efficient multi-junction PV cell, the size of a fingertip. The rows of concentric lenses are engineered to track the sun’s movement for maximum power generation, augmenting the concentrating capacity of the PV by 400 percent. The design is also capable of capturing thermal energy generated by irradiance (reflected light) with the captured heat sequestered for future water-based uses. In fact the combined electrical and thermal

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energy capacity of this building envelope renders it far more efficient than the use of mere photovoltaics, achieving an efficiency of more than 39 percent. As such, this multi-dimensional skin advances the science of BIPVs by having engineered a building façade that enhances the science of solar electric generation while enriching the quality of architectural construction, of material detailing and of the architectural space it encloses.

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2.1.7 The Integrated Concentrating (IC) Dynamic Solar Façade by CASE © CASE-RensselaerHeliOptix

5.0  Conclusion Renewable energy technology, including solar thermal and electric, when adopted for the net-zero operation of contemporary high-performance homes, is most effective when fully integrated in the design and construction of the home. No longer stand-alone features, these devices channel sunlight, wind and water by being substantially woven within the larger fabric of the building. And when fully integrated within a home’s architectural, engineering and construction details, these building technologies more effectively facilitate the attainment of the highest of performance measures.

Notes 1 M. Treberspurg, solarCity: Linz-Pichling, Wien and New York: Springer, 2008. 2 For an early multi-family project built to low-energy specifications see B. Dunster, C. Simmons and B. Gilbert, The ZEDbook: Solutions for a Shrinking World, London: Taylor & Francis, 2008. For the biggest project to date designed to zero-energy standards, see Masdar, www.masdar.ae 3 S. Pless and P. Torcellini, ‘Net-Zero Energy Buildings: A Classification System Based on Renewable Energy Supply Options’. National Renewable Energy Lab, Department of Energy, 21-page report: NREL/TP-550-44586, June 2010. 4 P. Denholm, R. M. Margolis, S. Ong, and B. Roberts, ‘Break-Even Cost for Residential Photovoltaics in the United States: Key Drivers and Sensitivities’, National Renewable Energy Lab, Department of Energy, 33-page report: NREL/TP-6A2-46909. 5 Geothermal energy should not be confused with ground-source heat pumps that use the ground as a constant temperature source for the extraction or evacuation of heat from buildings. 6 C. Schittich, In Detail: Solar Architecture: Strategies, Visions, Concepts, Basel: Birkhäuser, 2003, pp. 22–33. 7 For more information, see R. A. Messenger and J. Ventre, Photovoltaic Systems Engineering, 3rd Ed., London: CRC Press. 8 For information on sizing an off-grid installation see, H. Hu and G. Augenbroe, ‘Right Sizing an Off-Grid Solar House’, Building Simulation, 2009, pp. 17–24. 9 N. Darghouth, G. Barbose, and R. Wiser, ‘Impact of Rate Design and Net Metering on the Bill Savings from Distributed PV for Residential Customers in California’, Lawrence Berkeley National Lab, Department of Energy, 63-page report: LBNL-3276E, March 30, 2010. 10 For the new generation of solar technology innovation see, F. Krupp, Earth: The Sequel, The Race to Reinvent Energy and Stop Global Warming, Norton, 2008, pp. 15–44. For the role of nanotechnology in expanding research see C. Honsberg, A. Barnett, and D. Kirkpatrick, ‘Nanostructured Solar Cells for High Efficiency Photovoltaics’. Available at: www.eecis.udel. edu/~honsberg/Refs/Nano-Hawaii.pdf (accessed September 1, 2011). 11 See Chapter 1.1 for the early work of Maria Telkes in phase change materials (PCM). See also the City College of New York’s Solar Pod Project for the extensive use of a PCM storage tank for controlling the house’s domestic hot water. Available at: http://ccnysolardecathlon.com/engineering/hydronics (accessed October 2, 2011). 12 For more information on solar thermal systems see S. A. Mumma, ‘Over Thirty Years of Experience with Solar Thermal Water Heating’, ASHRAE Transactions, January 2011. 13 P. Norton and C. Christensen, ‘Performance Results from a Cold Climate Case Study for Affordable Zero Energy Homes’, National Renewable Energy Lab, Department of Energy, 20-page report: NREL/CP-550-42339. 14 S. Roberts and N. Guariento, Building Integrated Photovoltaics: A Handbook, Basel, Boston and Berlin: Birkhäuser, 2009.

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15 For a more detailed explanation of the tenets of Passivhaus, see Chapter 1.1. 16 For the Energy Star program see www.buildersenergyrater.com/main/nahb.php, and for the National Green Building Standard see www.nahbgreen.org/NGBS/default.aspx 17 The house is designed to purify the collected rainwater through a series of roof-mounted tanks and compost the building’s organic waste in a crawl space below the ground floor. See http://zerohouse.net/wordpress/ 18 A. Dyson, P. R. H. Stark and M. K. Jensen, ‘The Integrated Concentrating (IC) Dynamic Solar Façade’. Available at: www1.eere.energy.gov/solar/review_meeting/pdfs/sys_9_dyson_ rensselaer.pdf (accessed September 10, 2011).

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Chapter 2.2

Systems-Integrated Photovoltaics (SIPVs) jeffrey r. s. brownson

ABSTRACT: This chapter promotes the adoption of an alternative approach for the productive integration of photovoltaic technology used in high-performance residential designs. Systems-Integrated Photovoltaics (SIPVs) are a more effective method for engineering solar installations capable of generating greater levels of energy performance. Considered and developed within a whole-building system logic, SIPVs advance the field of solar technology by addressing important issues of energy production and integration not otherwise engaged in the design and construction of traditional Building-Integrated Photovoltaics (BIPVs).

1.0  Introduction Solar energy applications are conversions of light to do work found useful to society. In modern solar energy design, the role of the solar energy engineer and designer is to maximize the utility of the solar resource for the client in a given locale. Maximum utility is a classical term in engineering, although not equivalent to maximum “power” or “efficiency”, which emphasizes the effectiveness of the systems’ performance; this, given the demands and flexibility of the building owner and the solar profile of the locale in question. Solar energy conversion technologies have developed over millennia, often in response to economic or fuel constraints. In periods when fuels were easily accessible, inexpensive and unconstrained, sunlight-induced energy transfer (for sensible or latent heat change or for electricity generation) was deemed too diffuse and insufficient for performing work. However, during periods in history when access to fuel was constrained (e.g. inaccessible due to high cost or high risk), necessity resulted in the invention of solar technology solutions.1 At present, we are living in a period of constrained fuel use, in part because of social and cultural initiatives that emphasize energy independence and in part because of the over-consumption of non-renewable energies and their effect on greenhouse gases and climate change.

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Hence, we seek new answers from renewable energies such as the sun. To this end, industries connected with the manufacture of photovoltaic cells, and their accompanying systems for power conversion, have grown exponentially since 1996 at a rate of approximately 35 percent. Measuring this change in growth in terms of the time required to double the size of the industry, the PV manufacturing industry has doubled its size approximately every two years since 1996.2 (Figure 2.2.1)

1.1  Solar energy conversion systems Solar energy conversion is a systems-based field of applied research of great import for the development of effective solar installations and their operations.3 Unlike traditional energy engineering it is focused on a simultaneous assessment of systems design, local energy demand, predictive economic models for the fluctuating solar resource, and storage plans for addressing the cyclical and transient nature of solar phenomena. The design of each solar energy conversion system is the result of a variable energy resource (the sun), a given geographical locale (the intended location of the system) and a set of network relations including the people using the technologies. In order to design photovoltaic technologies relevant to each region, knowledge is required of the quantity and character of the solar resource, the surrounding climatic and environmental conditions, and the economic particulars of the installation. For example, the solar resource of the American Mid-Atlantic states is different from that of the American Southwest as measured by the intensity, spectrum, degree of scattering, and temporal behavior of the sun. Additionally, the occupants of these two regions have different expectations of comfort and energy demand. As a result, the solar resource of the Mid-Atlantic region may be

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2.2.1 Exponential rate of growth in the PV industry in terms of the estimated total potential PV power available in cells (termed peak watts, Wp). As of 2009, the global PV cell production was reported to be over 10,000 MW

2.2.2 Spectrum of solar irradiance at Earth’s surface. Note the overlap in electron downconversion (range of PV action) and optocaloric conversion (solar heating)

just as useful as that of the southwest when effectively integrated within a solar energy conversion system design. Moreover, the history of energy conversion research and its derived technologies has given rise to a partly erroneous identification of “energy” as existing either in the form of “heat” (originally regarded as a transfer of thermal energy) or “light” (originally referring only to the visible portion of the electromagnetic spectrum). Despite knowledge of infrared detectors and thermal imaging cameras, there still remains a distinction between “thermal” systems and “optical” systems. This distinction is unproductive. A blacktop parking lot surface on a hot summer day is both a thermal system (atoms vibrating) and an optical system (surface absorbing and emitting radiation). In fact, every material system can be described as both heat and light responsive, including windows, mirrors, and white surfaces.4 The assumption that thermal and optical phenomena are separate leads to inaccurate design criteria for integrative systems. In the solar energy conversion field, maintaining this separation is unacceptable for the proper design of integrative solar energy conversion systems (SECS). All SECS technologies use physical materials that interact with electromagnetic radiation (photons), and in so doing offer a new definition of “optics”. When considering the most typical light–matter interactions, radiation is always directional. Light is either emitted from a source (called “radiance”) or it is incident upon a receiving surface area (called “irradiance”) and the broadband spectrum of solar irradiance contains bands of light in the short wave (ultraviolet, visible, infrared) and long wave (also commonly called thermal radiation). In solar energy conversion, the absorbing material properties can deliver both optoelectronic conversion (as in photovoltaic action which converts light into current) and optocaloric conversion (which converts light into solar heating).5 (Figure 2.2.2)

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1.2  Photovoltaic action Photovoltaic (PV) technology is a specific form of solar conversion, encompassing systems that enable direct conversion of short-wave light (photons, solar energy) into electricity. PV action is the process of absorbing light by a semi-conductor, polymer or dye in order to generate electricity or produce electrons in a circuit. PV action is a three-step process for converting solar photons into power. It includes: 1. absorption of light (typically by a dark, opaque material); 2. generation of excited charge carriers (electrons); 3. separation of charge carriers to electrical contacts (the flow of electricity). Each step is essential for the functioning of traditional silicon technologies, non-silicon thin-film technologies, as well as emerging technologies still in early stages of development (dye-sensitized PV, quantum dot PV, or organic polymer technologies).6 The truly comparative metric for commercially available PV technologies is not the efficiency of photo-conversion, but rather the cost of conversion per peak Watt ($/Wp); with a peak Watt providing the output of power density (in units of Wp/m2) given 1000 W/m2 of artificial input light (a standard testing condition at 25°C that is representative of average solar conditions).7 (Figure 2.2.3) The difference between “efficiency” and “peak watt” is important when evaluating the difference between thin-film and silicon cell technologies. Thin-film PV modules (CdTe, CIGS, and a-Si) are typically considered to be less effective than silicon PV modules when the surface area of the structure is limited (as when the house is an off-grid application). However, as noted in Figure 2.2.3, the ratio of cost per area (cost axis) relative to the peak watt per area (efficiency axis) of different module technologies actually share common slopes ($/Wp). The steeper slopes (lower cost per peak watt) are economically desirable, as they point to less expensive solutions with higher power output. But in several scenarios (where space is not constrained), thin-film technologies are more cost effective than

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2.2.3 Comparative ratios of efficiency to cost for thin-film PVs and crystalline Si PVs (here termed “monolithic”)

silicon (or “monolithic silicon”). Thin-film PV technology tends to absorb more of the diffuse light characteristic of the mid-Atlantic States, and are configurable into unique shapes that facilitate building envelope integration. This makes the $/Wp metric for thin-film PVs (CdTe and CIGS absorber materials) desirable for both their design flexibility and performance metrics. Hence, when using the cost per area metric, a difference in the percentage of module efficiency can be offset by installing a marginally larger array of PVs. In most roofing scenarios, the available area for PV installation is not constrained, resulting in the optimal PV choice being a thin-film system that can be purchased at a low $/Wp. If available area is limited, it is advisable to use single-crystal silicon modules (sc-Si) that yield the highest W/m2 at a reasonable cost to the owner.

2.0  Building-Integrated Photovoltaics (BIPVs): their limitations During the 1980s, Building-Integrated Photovoltaics (BIPVs) were developed as products for incorporating PV directly into a building’s skin; be it on a roof or façade. By replacing an otherwise necessary portion of the building envelope, BIPVs were designed to reduce the total capital costs of a home fitted with a photovoltaic system. However, decades later, the constraints and metrics used by both designers and engineers to define and implement BIPVs remain unclear. In the United States, the general practice of incorporating PV systems within the construction of the building’s envelope places undue emphasis on the need to reduce first fixed costs (lowest installed cost) at the expense of longterm energy balance (which usually results in higher long-term value). This has resulted in an over-simplified interpretation of BIPVs amongst architects, engineers and builders. In merely replacing the façade with PV elements, the true potential of systems integration (inclusive of energy balance) is lost. For example, in wishing to decrease the solar heat gains of a roof (by decreasing the thermal load absorbed from the sun’s radiation), materials scientists have designed low-absorption, high-emittance materials that render the roof cooler by not absorbing visible and infrared radiation, the light spectrum that would otherwise increase the temperature of the roof.8 Designers can replace a standard commercial roofing membrane (e.g. tar paper) with such “cooler” roofing materials and decrease the building’s passive solar heat gains. However, when using BIPVs to increase the performance of the same building, the standard roofing material would be replaced with PV panels, most typically mounted flush with the roof in order to avoid water and air penetration into the interior. Unfortunately this material substitution only decreases the roof’s performance because PVs readily absorb visible, infrared, and thermal radiation.9 (Table 2.2.1) A significant decrease in the PV system’s photo-conversion efficiency results by effectively turning the PV module into a thermal collector, as does an increased thermal load to the building. As a single component incorporated into the roof at the expense of the larger system, the client will have effectively invested in an expensive piece of equipment to perform a function for which it was not designed.

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Table 2.2.1  Expected losses in power for photovoltaic materials, expressed as a decrease in percentage of total cell efficiency per °F Reduction %

Type

–0.12

a-Si

(amorphous silicon thin films)

–0.21

CIGS

(non-silicon thin films)

–0.26

mc-SI

(multi-crystalline silicon)

–0.31

sc-SI

(single-crystal silicon)

–0.31

CdTe

(non-silicon thin films)

In response, this chapter asserts a more integrated approach for introducing PVs into the construction and operations of a building. Consider the analogue of a building’s active air-conditioning system. An air-conditioning system is considered truly integrated when it is centralized, designed and operated as part of the larger internal and external building systems. By contrast, a single window-mounted air-conditioning unit, which does not respond to other engineering systems found in the building, is analogous to a BIPV in being a “building-integrated air conditioner”. Its cooling functionality replaces the window element and the initial fixed costs for installing the window unit appears to be less expensive than those for a centralized air system. However, the function of a window is also to allow light to enter the building and to maintain heat and humidity conditions within the home. In using a window-mounted air-conditioning unit the overall functionality of the window is reduced, as is its thermal performance. As such the total life-cycle “cost” of the window unit is more than the initial costs of installation. Similar challenges are faced by the design and engineering of BIPVs.

2.1  Decreases in PV performance: microclimate factors It is generally understood that photovoltaics decrease in performance with reduced amounts of available light from the sun.10 However, it is less readily considered that PV materials lose power performance as they become hotter. In their design and deployment, thermal regulation is needed as systems yield more power per unit irradiance (W/m2) under cooler conditions than hotter ones. Why, therefore, are they often deployed in very thermally aggressive environments? PV performance metrics rely on the net sum of received solar radiation that yields PV action (and electricity output) and the climate zone behavior of the installed PV. During hot summer months, the net sum is negatively affected by excess heat, whereas during winter months, colder temperatures cool the panels allowing them to perform significantly better than expected from simple radiation calculations.11 Thermal integration of a PV system entails design considerations for heat removal by conduction, convection, and radiative emittance. Knowledge of the

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insolation conditions of a site-specific installed PV system, including monthly values, yearly summaries, and the number of heating degree-days (HDD) is critical to the decision-making process and to designing integrative cooling requirements for optimal PV performance. The Life-Cycle Cost Analysis of PV systems indicates that the variable costs of operation and maintenance (the in-service phase following installation) are strongly dependent on the availability of heat recovery and heat removal methods for the PV modules and the calculation of embodied energy of the fuel being substituted. Without understanding this need for controlling and modulating the PV’s immediate microclimate, excessive thermal heat accumulation will yield significant performance reductions in the ability of the PV system to produce electricity.12

3.0  Systems-Integrated Photovoltaics (SIPVs): a design framework Advances in energy research have shown that systems must be optimized with respect to all components in a process of integrated design. This requirement is a cornerstone of a new working definition of Systems-Integrated Photovoltaics (SIPVs). The goal is to integrate the installation of PV panels within other systems that are essential to the building’s envelope. Beyond merely replacing materials, PVs are designed into a heat and power system that functions integratively. Using this logic, it is possible to design SIPV modules for combined functionality; involved in energy production, insulation, thermal and hygroscopic control of the envelope, and even possibly building structure. SIPV design is predicated on the understanding that the performance of photovoltaics is strongly dependent upon the local environment within which they are sited, their relationship with the supporting building structure, the lightreflective properties of surrounding materials, and the thermal properties of the immediate microclimate. The deployment of PV power in a systems-integrated design calls for the thermal regulation of the entire system to reduce the costs and increase power production over the 25+-year in-service phase of PV operation. In a solar-powered building, sufficient reductions in energy demand and losses yield important increases of possible solar energy contributions to the generation of local power or heat. Moreover, SIPV design is not limited to buildings alone; it can be used to inform the design process for freestanding structures and open enclosures (such as carports), or planned networks of smartgrid PV systems within a solar garden community. In shifting the constraints of PV design from lowest fixed costs to reduced variable operating and fuel substitution costs, we can identify more productive boundaries for evaluating the energy balance between the system and its surroundings.

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3.1  SIPVs and energy balance Total energy demand is composed of both the energy consumed for active work (electric power) and the energy losses of the building system to its surroundings (thermal waste heat). In any building, the goal is to reduce the total energy demand required for its operation. The fractional contribution of solar energy relative to the total demand from fuels is often termed the solar fraction (a number from zero to one). A solar engineer focuses on maximizing the solar utility for the client given the resource in that locale, by identifying the most useful solar fraction for a project’s systems design. Solar engineering seeks to increase the value of power gains from the solar conversion system; gains which can then contribute to the local reduction of the total energy demand.13 Moreover, PV performance metrics are based on incident solar radiation and thermal climate zone behavior during the hottest summer months (winter months tend to cool the panels to high-performance conditions). Knowledge of the coupled behavior of insolation conditions per month and the number of heating degree-days (HDD) is critical for design decisions that use integrative cooling requirements in estimating initial PV performance of SIPVs. Implementing SIPV design techniques enhances sustainable building practices by identifying zones for the thermal exchange of excess heat between PV technologies involved in solar power conversion and the overall building. In this way, the efficiencies of heat exchange are carefully designed in both the building’s physical construction and building systems operation. Engineering resources are available to address and measure this PV/building interface with energy balance simulations typically undertaken using solar engineering software such as TRNSYS (TRaNsient SYstem Simulation tool).14 The following are two examples of SIPVs designed to operate within a high-performance home.

3.1.1  Green-Roof-Integrated Photovoltaics (GRIPVs) The SIPV design framework argues that each PV system introduced within a building is coupled in a combined thermal and light relationship with the building’s structure, envelope and materials. In a prototype house built by Pennsylvania State University in 2009 on the occasion of the US Department of Energy Solar Decathlon competition, the Natural Fusion team researched the installation of PVs within a green-roof-integrated system (GRIPV). The design of the green-roof was conceived to increase the performance of the rooftop PV system, cool the home during summer months and add value to the idea of investing in both a PV system and a green-roof.15 Identifying the best way to integrate the two systems required research in the reflective spectrum of plants incorporated in the green-roof, the capacity of using roofing plants for active cooling, and how best to characterize the enhanced performance of PV modules thermally conditioned by this microclimate. Plants reflect the diffuse component of visible wavelengths to the solar panels and in return panels partially shade the plants, reducing the occurrence of scorching.16 (Figure 2.2.4) Additionally, the PV modules above the green-roof were cooled via evapotranspiration (the natural process of moisture evaporation from the leaf

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PART 2 : Renewable Energies, Building Systems and Simulations

2.2.4 Comparative differences between asphalt roof reflectance and the reflectance of four varieties of Sedum plants (which reflect some visible and most infrared radiation from 700– 1,000 nm). This is within the range of most PV cell rates of absorption (