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Principles of Adaptive Thermal Comfort

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Adaptive thermal comfort rests on field-study research results. ... from Singapore, Bahgdad (Iraq), Roorkee (N India) and Watford (near London, UK) ... – PowerPoint PPT presentation

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Title: Principles of Adaptive Thermal Comfort


1
Principles 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

4
Bedfords 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

5
Bedfords 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

7
Continued
  • From the environmental measurements he
    calculated-
  • Air temperature (ta)
  • Mean radiant temperature (tw)
  • Air speed (v)
  • Relative Humidity

8
Continued
  • Physiological measurements included
  • Forehead temperature
  • Palm temperature
  • Mean surface temperature of clothed body
  • Foot temperature

9
Bedfords 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.

10
Using an electric adding machine
11
Some 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.

12
Others 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.

13
Charles 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

14
Charles 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)

15
Charles 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

16
Charles 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)

17
Charles 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

18
1966-69 BRE data-logging project
19
Close-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.

21
Mean 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

23
The 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)

24
Thermal comfort as a self-regulating system
Ferguss diagram
Source Nicol Humphreys 1972
25
A 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?

26
The 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

27
Continued-
  • 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

28
Continued-
  • 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)

29
The data represented over 200,000 comfort-votes
30
The 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

31
The 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)

32
Neutral temperature is correlated with the mean
temperature
Source Humphreys 1975
33
Subjective warmth was unresponsive to the mean
temperature
Source Humphreys 1975
34
The 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)

35
neutral temperature related to outdoor temperature
Source Humphreys 1978
36
Clothing 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

37
BRE 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

38
Percentage of children in shirt-sleeves against
room temperature, c1969
39
Primary children, clothing and comfort
Source Humphreys 1978
40
Clothing air temperature shopping streets and
zoo park
Source Humphreys 1977
41
Bedclothes and bedroom temperature
Source Humphreys 1977
42
What 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)

43
After 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

44
Adaptive 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

45
The 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

46
Adaptation 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

47
ASHRAE 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.

48
de 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

49
de Dear Database, buildings with 100
observations. Mean room temperature and the
temperatures for comfort (neutrality) are
correlated (r0.94)
(my analysis)
50
Indoor neutral temperatures and daily mean
outdoor temperatures for the de Dear database
(my analysis)
51
Explaining 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

53
The Adaptive Principle-
  • If a change occurs that produces discomfort,
    people will tend to act to restore their comfort.
  • (The return towards comfort is pleasurable)

54
Thermal 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)

55
Consequences 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

56
Types of adaptation
  • It is useful to classify the different kinds
    of adaptation that may occur
  • Physiological
  • Behavioural
  • Psychological

57
Physiological adaptations
  • To coldness
  • Vaso-constriction
  • Shivering
  • Eating more
  • Cold acclimatisation?
  • To warmth
  • Vaso-dilatation
  • Sweating
  • Eating less
  • Heat acclimatisation

58
Some 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

59
Psychological 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

60
Behavioural adaptation
  • The next slides illustrate some behavioural
    adaptations

61
Even Pandas think adaptively
62
And so do children
63
Clothing behaviour
  • The next slides illustrate changes in clothing as
    a means of achieving comfort

64
Comfort in the UK winter at about 15oC
(1906) Notice the heavy indoor clothing
65
Mens clothing was also heavy (mens club,
London, 1906)
66
Ice Hotel in Lapland, 1995. Comfortable at
-7oC?
67
Thermal hospitality! its a little chilly, so
Ive put an extra dog on your bed.
68
You can show your status without a business suit
69
Warm clothing can be smart too.
70
Window-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.

71
Example window opening behaviour, Aberdeen
Oxford (UK)
Source H Rijal 2007
72
Constraints
  • 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.

73
Constraints
  • The next slides illustrate the presence of
    some constraints on adaptation

74
Clothing is for display as well as for thermal
comfort. This may constrain thermal adaptation
75
Dress is partially constrained by the social
occasion (a wedding in Germany)
76
Posture may be constrained by the task
77
Window-opening may be constrained by noise and
fumes Oxford Coach Station (UK)
78
This office shows good adaptive opportunity
79
An office with poor adaptive opportunity
80
Successful adaptation
  • If the combined effect of the various actions is
    sufficient, comfort will be achieved
  • The next slides show successful combinations of
    adaptive actions

81
Adaptation need not be a conscious act
Photograph by Ruth Roberts
82
Basis 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

83
Problems 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

84
Adaptation 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

85
Mean comfort vote (red) and mean PMV (green)
against mean operative temperature, all recent
survey data (ngt20)
(Fitted to a cubic regression model)
86
Mean 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
87
summary 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

88
summary 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

89
summary 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

90
Concluding comments
  • The Nicol self- regulating system should be seen
    within the context of climate and culture
  • This is illustrated in my final slide

91
The context of the Nicol self-regulating system
climate
society culture
92
The end
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