Adaptive Thermal Comfort: Foundations and Analysis

Michael Humphreys, Fergus Nicol, Susan Roaf

• Publisher: CRC Press
• Year: 2015
• Print ISBN: 9780415691611
• eBook ISBN: 9781317658566
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Construction & Architectural Engineering
• Index: Technology & Engineering

There has been widespread dissatisfaction with accepted models for predicting the conditions that people will find thermally comfortable in buildings. These models require knowledge about clothing and activity, but can give little guidance on how to quantify them in any future situation. This has forced designers to make assumptions about people's future behaviour based on very little information and, as a result, encouraged static design indoor temperatures.

This book is the second in a three volume set covering all aspects of Adaptive Thermal Comfort. The first part narrates the development of the adaptive approach to thermal comfort from its early beginnings in the 1960s. It discusses recent work in the field and suggests ways in which it can be developed and modelled. Such models can be used to set dynamic, interactive standards for thermal comfort which will help overcome the problems inherited from the past. The second part of the volume engages with the practical and theoretical problems encountered in field studies and in their statistical analysis, providing guidance towards their resolution, so that valid conclusions may be drawn from such studies.

PART I

Foundations

1

INTRODUCTION TO ADAPTIVE BEHAVIOUR

Adaptation is at the heart of the survival of all species in the ever-changing climates of our planet. All of us, more or less consciously, are aware of adapting to weather and climate. Before we describe the beginnings of the adaptive model of thermal comfort, we explain what we mean by adaptive comfort and describe some of the experiences, both personal and research, from which the adaptive approach to thermal comfort arose.

Each of us practises a range of adaptive behaviours every day. These manifest themselves when we put on an overcoat to go outside, move into a new climate or experience extreme weather events, experiences that often awaken our thermal awareness. Toward the end of the worst winter of the twentieth century, in 1947, Michael Humphreys remembers how, as a boy of ten, he helped his mother rear hundreds of baby chicks by the Sterling solid-fuel cooker in their remote Kent farmhouse. If chicks got cold they huddled so closely together for warmth that they were in danger of crushing each other but they soon learned to put their rear ends up against the front of the stove, and then move away again when they had warmed up. This was behavioural adaptive thermal regulation in action.

He now sees the behaviour of the hill sheep near his home in rural Mid Wales, as they crowd together in places sheltered from the cold winter wind, or find a sunny place if they can. In the heat of summer both sheep and cattle seek shady places. These are all adaptive behaviours employed in thermal regulation, supplementing the body’s own defences against heat and cold. It is thought that in the wild many mammals achieve perhaps two-thirds of their thermal regulation behaviourally. Edgar Folk’s beautiful books about behavioural thermal regulation give many examples.¹

People, like other animals, have always adapted too, and when and where fuel was scarce and warmth needed they largely controlled their comfort behaviourally – that is, adaptively. The ‘Ice-man’, whose well-preserved body appeared from a melting glacier in 1991, was wearing sophisticated hay-insulated clothing while out on his hunting expedition.² This was behavioural thermal adaptation by choice of suitable clothing, an example of a conscious, intelligent, adaptive response.

British Iron Age dwellings had a wood-fuelled fire burning at the centre of the dwelling and radiating heat to the occupants, who would have moved closer to the fire to get warmer and further away to get cooler. The dwelling itself was designed in response to the outdoor conditions, its walls and roof moderating the daily swings of outdoor temperature, giving shelter from the wind and rain, and providing shade in summer. The form and nature of each building reflected the location and landscape and helped to keep occupants safe from weather and climate, so that they were not wholly dependent on the body’s built-in systems of thermal regulation. Where people differ from animals is in the greater conscious use of designed solutions, such as fire, clothing and house building and eventually adding mechanical technologies to their adaptive opportunities and strategies.

Humphreys presented a thought experiment in 1995 to explain how we might go about understanding the basics of adaptive thermal comfort.³

The popularity of the The Lord of the Rings and The Hobbit films has recently introduced many people to hobbits. Suppose we were exploring Middle Earth and encountered some hobbits.⁴ Being interested in thermal comfort, our curiosity would certainly lead us to enquire what thermal environments were best for them. Perhaps we would first enquire into the climate in those parts of Middle Earth where hobbits lived and thrived. Next we might notice that although the hobbits spent some time sitting outdoors in contented contemplation, they spent much more time in their holes. So if the opportunity arose, we would measure the thermal conditions inside a representative sample of occupied hobbit holes. We would observe which rooms they most frequented and thereby obtain a more accurate knowledge of their preferences for different micro-climates at different times of year. We might notice in what circumstances hobbits opened or closed doors and windows or stoked up the fire to control the temperature of the room they occupied and how they positioned themselves to make the best use of the heat it gave out. We would notice too what the hobbits chose to wear from their extensive stock of clothes – a choice related to, among other things, their desire for comfort. Finally, if we had learned a smattering of the hobbit tongue, we would ask whether theirs was a good hole, or whether really they might prefer one which was warmer or cooler.

In the course of our enquiries, we would have learned to know a good hobbit hole when we saw one, and we would also have learned a good deal about the preferences and adaptive strategies of hobbits in their quest for comfort. So if, some time later, we were told to expect a visit from a party of hobbits, we would know how to provide accommodation comfortable for them. Various strategies suggest themselves:

• We could construct a good traditional hobbit hole for them, appropriate to the climate, having all the usual facilities for thermal control, and well-stocked with hobbit clothes. Then we could trust the hobbits to make themselves comfortable.

• We might (unless the hobbits were on a holiday visit) provide them with individually adjustable environment-controlled workstations, capable of providing the range of the thermal environments we knew hobbits liked best. Then we could trust them to adjust the workstations to suit themselves. Whether they would aim for maximum comfort or for maximum task efficiency is a question we could ask the experts in performance studies, for maximum efficiency and maximum comfort may not always coincide.

• Alternatively, we could provide a thermal environment for the visiting party, regulated according to an algorithm which estimated the best conditions for hobbits, according to time of day and season of year, based on our observations when visiting Middle Earth.

So, either we give control to the hobbits, knowing that the hole or the hardware can provide any conditions within the range hobbits like best, or (perhaps less satisfactorily since hobbits generally prefer to be in control of their own thermal environment) we give the hobbits the precise temperatures which our experience has suggested they like best.

Our observations from Middle Earth would have been more than sufficient to enable us to specify and provide comfort conditions for our guests. Observation of the habits and preferences of the hobbits and the measurement of their environments was sufficient to enable us to understand how hobbits got comfortable, and to:

• produce a ‘deemed to satisfy’ design for building thermally acceptable hobbit holes;

• identify the range of environmental adjustment which a hobbit might need;

• suggest the best daily and seasonal temperature profile for spaces occupied by hobbits.

No invasive measurements or tiresome experimental routines were necessary. An enquiry about comfort and the concurrent measurement of the thermal environment yielded all that we needed to know. This simplicity makes field study work an effective, practical method for investigating adaptive thermal comfort in the huge range of climates and cultures that exist on earth.

It is interesting to notice what we did not need to know:

• We did not need to know anything at all about the thermal physiology of hobbits, such as the diurnal cycle of their body temperature, the metabolic heat production of their various activities, whether they could sweat or shiver or pant, or whether the Dubois relation between height, weight and skin surface-area held good for hobbits.

• We did not need to know anything about the heat exchange between hobbit skin and the hole, such as the surface heat-transfer coefficients by convection or by radiation, the mean skin temperature and at what sites it is best measured, the thermal insulation of their colourful clothing ensembles, or the vapour permeability of their clothing materials.

Such knowledge would help to explain quantitatively the thermal balance of hobbits, would give us a theoretical explanation of their comfort conditions there, and might be useful in identifying potentially dangerous environments but it would not be needed to enable us to provide comfortable apartments for our hobbits. This is not surprising if we recall that achieving thermal comfort pre-dates by thousands of years the development of thermal physiology and the theory of heat exchange.

The thought-experiment illustrates what has become known as the adaptive model of thermal comfort. This adaptive approach notices that people use numerous strategies to achieve thermal comfort. They are not inert recipients of the environment, but interact with it to optimise their conditions. Among the means that people use are:

• the choice of areas of the globe suitable for habitation;

• the choice of the building site (for example, shelter from wind, shade from trees);

• the choice of design and construction of the building (for example, shape, orientation, thermal capacity, glazed area, thermal insulation);

• the choice of spaces occupied within a building at different times of day and year;

• the choice of heating or cooling systems, whether simple or sophisticated;

• the use of controls (thermostats, switches, valves, openable windows, blinds, ceiling fans);

• the choice of clothing suitable to the climate, season, indoor temperature and social setting;

• the operation of sometimes unconscious changes of posture and activity, and of any physiological acclimatisation there may be to the season of the year;

• the change of attitude to their environment, so that they are willing to experience a wider range of sensation without protest.

The adaptive approach notices that, provided there are adequate possibilities for selection and adjustment, people will act to make themselves comfortable if they wish to do so. It follows that the room temperatures that people find comfortable (‘comfort temperatures’ for short) are changeable rather than fixed. Discomfort is often caused by excessive constraints being placed on these processes of choice and adjustment, rather than solely by room temperature. Thermal comfort, then, is not to be seen primarily as a matter of the physiology of heat...

Table of contents

• Cover Page
• Half Title page
• Title Page
• Copyright Page
• Dedication
• Contents
• List of Tables
• Preface
• Acknowledgements
• Part I Foundations
• Part II Analysis
• References
• Index