Title: Principles of Adaptive Thermal Comfort
1Principles of Adaptive Thermal Comfort
- Michael A Humphreys
- Oxford Brookes University
-
- Regents Park College
- University of Oxford
2- Adaptive thermal comfort rests on field-study
research results. This is because adaptive
behaviour is best studied in the normal habitat. - Early field studies date from the 1930s.
- The pattern was laid down by Thomas Bedford,
who published his report in 1936. - We now briefly review his study-
3- Dr Thomas Bedford
- The warmth factor in comfort at work
- MRC Industrial Health Board,
- Report 76, 1936
4Bedfords field-study
- Workers in light industry
- 12 factories
- Colder seasons of the year
- Some 3085 interviews (mostly women)
- At each interview-
- Subjective responses were obtained
- Temperature of hand, foot, etc
- Thermal environmental measurements
5Bedfords interview method-
- Do you feel comfortably warm?
- If yes are you really quite comfortable, or
would you rather have the room slightly warmer or
slightly cooler? - If no are you feeling too warm or too cool?
- If too warm just definitely too warm, or much
too warm? - If too cool just definitely too cool, or much
too cool?
6- The Bedford Scale-
- Much too warm
- Too warm
- Comfortably warm
- Comfortable
- Comfortably cool
- Too cool
- Much too cool
7Continued
- From the environmental measurements he
calculated- - Air temperature (ta)
- Mean radiant temperature (tw)
- Air speed (v)
- Relative Humidity
8Continued
- Physiological measurements included
- Forehead temperature
- Palm temperature
- Mean surface temperature of clothed body
- Foot temperature
9Bedfords analytical methods-
- Bedford was the first to use multivariate
statistical analysis in a thermal comfort survey. - All the calculations were done by hand or by
using mechanical adding machines.
10Using an electric adding machine
11Some results-
- He derived equivalent temperature (et) by
multiple regression- - et 0.522ta 0.478tw 0.01474vv(100-ta)
- He found the optimum temperature for comfort was
- 65oF (18oC)
- the temperatures are degrees Fahrenheit,
- and the air speed is in feet/minute.
12Others followed Bedfords lead
- Many field studies of thermal comfort were
conducted worldwide in the following years, using
the basic pattern pioneered by Bedford. - Few were as comprehensive, and few as thoroughly
analysed.
13Charles G Webb
- I want to say a little about Charles Webb, whom I
regard as the originator of the adaptive approach
to thermal comfort - Professor Fergus Nicol and I were both
researchers in Charless research unit
14Charles G Webb
- Physicist and field-study comfort researcher at
UK Building Research Station - Charles obtained data from Singapore, Bahgdad
(Iraq), Roorkee (N India) and Watford (near
London, UK) - He favoured longitudinal experimental designs
(each respondent provided data over many days)
15Charles G Webb
- Charles noticed that his respondents were
comfortable at the mean conditions they
experienced, whether in Singapore, North India,
Iraq or England. - This suggested that they had adapted to the mean
conditions they had experienced
16Charles G Webb
- Charles initiated the first application of
electronic data-logging and computer processing
to comfort surveys (c1965) - We look briefly at this project-
- (Charles retired before its completion)
17Charles G Webb
- The next two slides show the data-logging monitor
unit. - It automatically recorded
- ventilated wet and dry bulb temperatures,
- the temperatures of a heated and an unheated
globe - The comfort-vote of the respondent
181966-69 BRE data-logging project
19Close-up of instrument note the miniature 50mm
globes and the automated response-scales
Source Humphreys Nicol 1970
20- The next slide shows the relationship between the
new English data and Charless other sets of
data. It also shows Bedfords result. - Notice how little the mean warmth sensation (the
mean comfort vote) depends on the mean room
temperature.
21Mean comfort votes England, Singapore, Iraq and
North India
Source Humphreys Nicol 1970
22- Mean warmth depended on the departure from the
mean temperature rather than on the mean
temperature itself
23The Adaptive Model
- Fergus Nicol and I thought long and hard about
this result, and Fergus drew a flow-diagram
showing thermal comfort as a self-regulating
adaptive system. - He included both physiological and behavioural
adaptation (Nicol
Humphreys 1973)
24Thermal comfort as a self-regulating system
Ferguss diagram
Source Nicol Humphreys 1972
25A thermal comfort meta-analysis
- But did the total evidence from all available
field studies support this interpretation? - What if we collected together all their results?
26The available field studies were-
- 1938 Sa Brazil (Rio de Janeiro)
- 1938 Newton UK (a.c.offices)
- 1940 McConnell USA (a.c. offices)
- 1947 Rowley USA (a.c. offices)
- 1952 Ellis Aboard warships in Tropics
- 1952 Rao India (Calcutta)
- 1952 Mookerjee India (North, summer)
- 1953 Ellis Singapore (on land)
- 1953 Mookerjee India (dry tropics)
- 1954 Black UK offices
- 1955 Malhotra India (tropical)
- 1955 Ambler Nigeria
- 1955 Hickish UK Factories (summer)
- 1957 Angus UK lecture-room, winter
- 1959 Webb Singapore
27Continued-
- 1962 Hindmarsh Australia (Sydney) offices
- 1963 Goromosov USSR dwellings
- 1963 Wyndham Australia (N) manual workers
- 1965 Lane USA (Iowa) schoolchildren
- 1966 Ambler North India
- 1966 Black UK (a.c. offices)
- 1966 Grandjean Switzerland (offices, winter)
- 1967 SIB(anon) Sweden (classroom teachers)
- 1967 Ballantyne Papua (Caucasians, tropics)
- 1968 Wyon UK Hospitals (operating theatres)
- 1968 Grandjean Switz. (offices, a.c., nv,
summer) - 1969 Auliciems UK schoolchildren, winter
28Continued-
- 1970 Humphreys Nicol UK offices (year-round)
- 1971 Pepler USA teachers (a.c. n.v.)
- 1972 Pepler USA Schoolchildren (a.c.
n.v.) - 19723 Davies UK Schoolchildren (year-round)
- 1973 Auliciems UK Schoolchildren, summer
- 1973 Humphreys UK Schoolchildren (summer)
- 1973 Wanner Switzerland (a.c. offices)
- 1974 Nicol India Iraq offices,
summer (Webbs data)
29The data represented over 200,000 comfort-votes
30The meta-analysis
- From most of these studies it was possible to
find - The optimum temperature for comfort
- The sensitivity of the respondents to temperature
changes
31The meta-analysis
- If people had adapted to their normal indoor
environment, the optimum temperature for comfort
should be correlated with the mean temperature
they experienced - The next slide shows this to be true (correlation
(r) 0.95, plt0.001) The range of neutral
temperatures was too wide to be explained by the
newly available PMV equation (Fanger, 1970)
32Neutral temperature is correlated with the mean
temperature
Source Humphreys 1975
33Subjective warmth was unresponsive to the mean
temperature
Source Humphreys 1975
34The meta-analysis
- Next the data were analysed in relation to the
monthly outdoor temperatures, these being
obtained from published world meteorological
tables - We found the neutral temperatures to be strongly
related to the corresponding mean outdoor
temperatures - The strongest relation was for the free-running
mode of operation (no heating or cooling in use)
35neutral temperature related to outdoor temperature
Source Humphreys 1978
36Clothing and adaptation
- Changing the clothing is the most obvious
behavioural adaptation to temperature. - So studying clothing change should tell us more
about how people adapt to their indoor environment
37BRE field-studies 1969-77 on adaptation by
clothing changes
- Thermal comfort clothing, Secondary School
Children - Thermal comfort clothing, Primary School
Children - Clothing comfort outdoors shopping leisure
- Thermal comfort bed-clothing during sleep
38Percentage of children in shirt-sleeves against
room temperature, c1969
39Primary children, clothing and comfort
Source Humphreys 1978
40Clothing air temperature shopping streets and
zoo park
Source Humphreys 1977
41Bedclothes and bedroom temperature
Source Humphreys 1977
42What we learned about clothing adaptive behaviour
- Little adaptive change during the day
- More adaptive change from day-to-day
- More still from week-to-week
- Clothing changes lag behind temperature changes
- People sometimes trade thermal comfort for
fashion (social comfort)
43After publication of the meta-analysis other
researchers explored adaptive comfort
- Ian Griffiths (UK) UK European surveys
- John Busch Surveys in Bangkok, Thailand
- Auliciems deDear Australian surveys
- Gail Schiller (Brager) team USA surveys
- These researchers found adaptation to be taking
place, sometimes to an extent inexplicable on the
PMV/PPD model
44Adaptive opportunity
- Nick Baker and Mark Standeven, working in
Cambridge, UK, linked comfort to the available
means of thermal adaptation the Adaptive
Opportunity. - If there was little Adaptive Opportunity,
discomfort was likely to occur
45The Forgiveness Factor
- Bordass Leaman (working in the UK) developed
protocols for the Post-Occupancy evaluation of
buildings. Their results showed that people who
had control over their environment were more
tolerant of it. They called this the Forgiveness
Factor - If the occupants could not control their
environment discomfort was likely to occur
46Adaptation and sociology
- Accepting the adaptive hypothesis, Elizabeth
Shove argues that comfort is a Social
Construction. Different societies, historically
and geographically, have had very different
comfort temperatures. - This suggests that societies can be encouraged to
adopt solutions that are environmentally
responsible
47ASHRAE Standard 55-2004
- de Dear and Brager (1998) did a meta-analysis of
recent high quality field studies. Their results
broadly confirmed the findings of the
meta-analyses of 1978-81, as the next slides
show. - The 2004 revision of Standard 55 used this result
to provide a graphical relation between comfort
indoors and the outdoor mean temperature.
48de Dears database of field studies
- 20,000 sets of observations, each with
- subjective vote (7 point scale)
- thermal environmental measurements
- clothing and activity records
- 9 countries
- 160 buildings
- Wide coverage of climate
49de Dear Database, buildings with 100
observations. Mean room temperature and the
temperatures for comfort (neutrality) are
correlated (r0.94)
(my analysis)
50Indoor neutral temperatures and daily mean
outdoor temperatures for the de Dear database
(my analysis)
51Explaining the adaptive model
- I will now explain the basic principles of the
adaptive model of thermal comfort, and illustrate
the main features - Fundamental is the Adaptive Principle
52- People are not passive receptors of their thermal
environment, but continually interact with it
53The Adaptive Principle-
- If a change occurs that produces discomfort,
people will tend to act to restore their comfort. - (The return towards comfort is pleasurable)
54Thermal comfort is an example of a Complex
Adaptive System
- The properties of these systems are
- Mathematical intractability
- Multiple equilibria
- If disturbed may settle at a different
equilibrium position - (Other examples of Complex Adaptive Systems
are the world climate system and the world
economic system)
55Consequences of the adaptive principle
- Except in extreme climates
- People become adjusted to the conditions they
normally experience - People must be studied in their everyday habitats
- Discomfort arises from insufficient adaptive
opportunity
56Types of adaptation
- It is useful to classify the different kinds
of adaptation that may occur - Physiological
- Behavioural
- Psychological
57Physiological adaptations
- To coldness
- Vaso-constriction
- Shivering
- Eating more
- Cold acclimatisation?
- To warmth
- Vaso-dilatation
- Sweating
- Eating less
- Heat acclimatisation
58Some behavioural adaptations
- To coldness
- Increase activity
- Increase clothing
- Close posture
- Cuddle up
- Heat the room
- Find a warmer place
- Close windows
- Avoid draughts
- Modify the building
- Emigrate
- To warmth
- Reduce activity
- Reduce clothing
- Open posture
- Separate
- Cool the room
- Find a cooler place
- Open windows
- Use a fan
- Modify the building
- Emigrate
59Psychological adaptations
- These are not yet well defined or understood.
They may include - Expecting a range of conditions
- Accepting a range of sensations
- Enjoying a variety of sensation
- Accepting behavioural adaptations
- Accepting responsibility for control
60Behavioural adaptation
- The next slides illustrate some behavioural
adaptations
61Even Pandas think adaptively
62 And so do children
63Clothing behaviour
- The next slides illustrate changes in clothing as
a means of achieving comfort
64Comfort in the UK winter at about 15oC
(1906) Notice the heavy indoor clothing
65Mens clothing was also heavy (mens club,
London, 1906)
66Ice Hotel in Lapland, 1995. Comfortable at
-7oC?
67Thermal hospitality! its a little chilly, so
Ive put an extra dog on your bed.
68You can show your status without a business suit
69Warm clothing can be smart too.
70Window-opening behaviour
- Adaptation by opening and closing windows.
- The following chart shows the proportion of
windows open in batches of UK data at different
room temperatures. - From such charts the adaptive behaviour can be
modelled and quantified.
71Example window opening behaviour, Aberdeen
Oxford (UK)
Source H Rijal 2007
72Constraints
- There may be insufficient opportunity for
adaptive action to be fully effective. It may be
constrained by (for example) - Climate
- Culture and fashion
- Work requirements
- Personality
- Insufficient adaptive opportunity leads to
discomfort.
73Constraints
- The next slides illustrate the presence of
some constraints on adaptation
74Clothing is for display as well as for thermal
comfort. This may constrain thermal adaptation
75Dress is partially constrained by the social
occasion (a wedding in Germany)
76Posture may be constrained by the task
77Window-opening may be constrained by noise and
fumes Oxford Coach Station (UK)
78This office shows good adaptive opportunity
79An office with poor adaptive opportunity
80Successful adaptation
- If the combined effect of the various actions is
sufficient, comfort will be achieved - The next slides show successful combinations of
adaptive actions
81Adaptation need not be a conscious act
Photograph by Ruth Roberts
82Basis of current standards
- Current thermal comfort standards and guidelines
ISO 7730, ASHRAE 55-2004, EN 15251, CIBSE Guides
A1 (thermal comfort) are based mainly on PMV
83Problems with PMV
- PMV requires the measurement of 6 variables some
of which (especially Met and Clo) cannot be
measured with any accuracy - Yet standards ask for accurate evaluation of PMV
(e.g. 0.2 PMV) - Values of Met and Clo must be assumed and indoor
environment is specified by narrow temperature
bands - In Naturally Ventilated Buildings PMV predicts
higher discomfort than is measured in the field
84Adaptation and PMV
- To what extent can the adaptations encountered in
field studies be explained by changes in
metabolic rate and clothing insulation within
PMV? - The next slide brings information from all
surveys I have collected to date (2006), and
compares the actual mean vote with the predicted
mean vote (PMV). - Note that PMV overestimates the warmth sensation
in warm environments
85Mean comfort vote (red) and mean PMV (green)
against mean operative temperature, all recent
survey data (ngt20)
(Fitted to a cubic regression model)
86Mean comfort vote and mean PMV mean ASHRAE vote,
all recent survey data. Each point represents a
whole batch of data (ngt20)
The practical accuracy of PMV is insufficient to
support the current standards
87summary comments
- The adaptive model shows that comfort
temperatures are variable rather than fixed - We have seen populations comfortable in rooms as
low as 17oC and as high as 35oC - Comfort temperatures in the free-running mode
depend strongly on the outdoor temperature - This suggests that a society could vary its
comfort temperatures to minimise fuel use
88summary comments
- The comfort temperature can be seen as the
current equilibrium setting of a complex adaptive
system. - Modifying the pattern of constraints acting on
the system will modify the equilibrium setting. - Gradual changes in the constraints are unlikely
to produce discomfort - Inadequate adaptive opportunity ( too much
constraint) will produce discomfort
89summary comments
- Thermal physiology and heat-exchange models are
components of the adaptive model - The PMV/PPD model underestimates the adaptive
capacity of the human population - The adaptive model does not fit easily into the
current ways of expressing standards for thermal
comfort
90Concluding comments
- The Nicol self- regulating system should be seen
within the context of climate and culture - This is illustrated in my final slide
91The context of the Nicol self-regulating system
climate
society culture
92The end