Adaptive thermal comfort : principles and practice

The fundamental function of buildings is to provide safe and healthy shelter. For the fortunate they also provide comfort and delight. In the twentieth century comfort became a 'product' produced by machines and run on cheap energy. In a world where fossil fuels are becoming ever scarcer and more expensive, and the climate more extreme, the challenge of designing comfortable buildings today requires a new approach.

This timely book is the first in a trilogy from leaders in the field which will provide just that. It explains, in a clear and comprehensible manner, how we stay comfortable by using our bodies, minds, buildings and their systems to adapt to indoor and outdoor conditions which change with the weather and the climate. The book is in two sections. The first introduces the principles on which the theory of adaptive thermal comfort is based. The second explains how to use field studies to measure thermal comfort in practice and to analyze the data gathered.

Architects have gradually passed responsibility for building performance to service engineers who are largely trained to see comfort as the 'product', designed using simplistic comfort models. The result has contributed to a shift to buildings that use ever more energy. A growing international consensus now calls for low-energy buildings. This means designers must first produce robust, passive structures that provide occupants with many opportunities to make changes to suit their environmental needs. Ventilation using free, natural energy should be preferred and mechanical conditioning only used when the climate demands it.

This book outlines the theory of adaptive thermal comfort that is essential to understand and inform such building designs. This book should be required reading for all students, teachers and practitioners of architecture, building engineering and management - for all who have a role in producing, and occupying, twenty-first century adaptive, low-carbon, comfortable buildings.

Author Notes

Fergus Nicol has led a number of important research projects on comfort, which have influenced thinking internationally. He has authored numerous journal articles and other publications including guidance on comfort and overheating. Nicol convenes the Network for Comfort and Energy use in Buildings and organises their regular international Windsor Conferences.
Michael Humphreys is known for his pioneering work on the adaptive approach to comfort. He has been Head of Human Factors at the Building Research Establishment and a Research Professor at Oxford Brookes University, UK. His current interests are the structure and modelling of human adaptive behaviour, the interactions between aspects of the environment and their expression in standards.
Susan Roaf did her PhD on comfort and the windcatchers of Yazd and after a decade working with Nicoi and Humphreys at the Oxford Thermal Comfort Unit she is now Professor of Architectural Engineering at Heriot-Watt University in Edinburgh. She is a teacher, researcher, designer and author and editor of 13 books including Ecohouse: A Design Guide (2001) and Adapting Buildings and Cities for Climate Change (2005).

List of illustrations	p. x
Preface	p. xiv
Acknowledgements	p. xviii
List of abbreviations	p. xxi
Part I Principles: building an adaptive model	p. 1
1 Thermal comfort: why it is important	p. 3
1.1 User satisfaction	p. 3
1.2 Energy consumption	p. 5
1.3 Standards, guidelines and legislation for indoor temperature	p. 5
1.4 Adaptation	p. 6
1.5 Comfort outdoors and in intermediate spaces	p. 8
2 Thermal comfort: the underlying processes	p. 10
2.1 Physiology	p. 10
2.2 Psychophysics	p. 11
2.3 Physics	p. 12
2.4 Behaviour	p. 19
2.5 Equations for heat balance in the human body	p. 19
3 Field studies and the adaptive approach	p. 23
3.1 Field surveys of thermal comfort	p. 23
3.2 Post-occupancy surveys	p. 24
3.3 Comfort and indoor temperature: the basic adaptive relationship	p. 25
3.4 Outcomes: indoor comfort and outdoor temperature	p. 26
3.5 The basis of the adaptive model: using surveys to understand comfort	p. 28
3.6 Opening the black box	p. 30
3.7 Adaptive comfort and non-standard buildings	p. 33
3.8 The challenge of climate change	p. 35
3.9 Lessons of the adaptive model for ensuring thermal comfort	p. 36
3.10 An example: naturally ventilated office in summer	p. 39
4 The heat balance approach to defining thermal comfort	p. 44
4.1 The heat balance approach	p. 45
4.2 Problems with the analytical approach	p. 46
4.3 Differences between the results from empirical and analytical investigations	p. 41
5 Standards, guidelines and legislation for the indoor environment	p. 52
5.1 The origin and purpose of standards for indoor climate	p. 52
5.2 International comfort standards today	p. 53
5.3 Discussion of international standards	p. 57
5.4 Legislation	p. 60
5.5 Standards and productivity	p. 62
5.6 Standards and overheating in buildings	p. 63
5.7 The way forward for comfort standards	p. 64
6 Low-energy adaptive buildings	p. 57
6.1 Building design and adaptive comfort	p. 69
6.2 Historic flaws with the mechanical approach to providing comfort	p. 71
6.3 Designing more appropriate buildings	p. 73
Appendix: How to make a Nicol graph	p. 78
Part II Practice: conducting a survey in the field and analysing the results	p. 81
7 What sort of survey?	p. 83
7.1 Introduction	p. 83
7.2 The complexity of your survey	p. 84
7.3 Post occupancy evaluation of buildings (POE)	p. 86
8 Instruments and questionnaires	p. 89
8.1 Physical measures	p. 89
8.2 Personal variables	p. 100
8.3 Subjective measures	p. 103
8.4 Other subjective measures	p. 106
8.5 Thermal behaviour	p. 106
8.6 The comfort questionnaire	p. 107
Appendix: An example of a longitudinal questionnaire	p. 110
9 Conducting a field study	p. 112
9.1 Choosing a subject population and their environment	p. 112
9.2 Choosing a subject sample	p. 113
9.3 How many observations from each subject and how many subjects?	p. 115
9.4 Time sampling	p. 117
9.5 The data set	p. 117
9.6 Taking the measurements	p. 118
9.7 Lack of variation in the temperature and comfort vote	p. 123
10 Analysis and reporting of field study data	p. 125
10.1 Looking at the data	p. 125
10.2 Simple statistics	p. 132
10.3 More complex statistical methods	p. 136
10.4 Some common problems encountered and some mistakes to avoid	p. 151
10.5 Writing up your results	p. 152
List of symbols	p. 155
Glossary	p. 157
Bibliography	p. 166
Index	p. 168

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