ASI2 ‐ Prof. Richard de Dear ‐ Part 1

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Urban Thermal Comfort Fundamentals

• Richard de Dear

• Professor - Building Science

• The University of Sydney Lecturer’s Photo

• ASHRAE 2010 Standard 55-2010R Thermal environmental conditions for human occupancy (American Society of Heating, Refrigerating and Air-Conditioning Engineers; Atlanta)

• Bröde, P., Krüger, E.L., Rossi, F.A., Fiala, D. 2011 Predicting urban outdoor thermal comfort by the Universal Thermal Climate Index UTCI-a case study in Southern Brazil, International Journal of Biometeorology (article in press DOI: 10.1007/s00484-011-0452-3

• de Dear, R. 2011 Revisiting an old hypothesis of human thermal perception: Alliesthesia. Building Research and Information Vol.39(2), pp.108-117

• Fiala, D., Havenith, G., Bröde, P., Kampmann, B., Jendritzky, G. 2011 UTCI-Fiala multi-node model of human heat transfer and temperature regulation, International Journal of Biometeorology (article in press DOI: 10.1007/s00484-011-0424-7)

• Lin, T.-P., de Dear, R., Hwang, R.-L. 2011 Effect of thermal adaptation on seasonal outdoor thermal comfort. International Journal of Climatology V31(2), pp.302-312

• Spagnolo, J., de Dear, R. 2003 A field study of thermal comfort in outdoor and semi-outdoor environments in subtropical Sydney Australia. Building and Environment Vol.38 (5), pp.721-738

Recommended Reading

ASI2 ‐ Prof. Richard de Dear ‐ Part 1

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• The underlying hypothesis in all of the research on this topic is that the microclimatic characteristics of outdoor urban spaces influence the way people use them, the frequency and duration of of use.

• Economic implications: - e.g. consulting job for a theme-park in humid-tropical locations.

Comfort of the queuing patrons- Comfortable urban spaces attract people, good for retail and

hospitality industries, commercial rents increase, local govt taxreceipts can increase, etc.

• Applications in urban design

• Implications for architecture and indoor energy end-use: the Bangladesh case-studyAhmed, K. S. (2003). "Comfort in urban spaces: defining the boundaries of outdoor thermal comfort for the tropical urban environments." Energy and Buildings 35(1): 103-110.

• Implications for health. Populations who are averse to the urban outdoor climate become increasingly sedentary, increasing their risk of obesity, cardiovascular and metabolic diseases

Why bother about comfort in urban outdoor settings?

• “Thermal comfort” refers to moderate thermal environments (not heat/cold stress)

• Ever since the advent of Heating, Ventilation and Air-Conditioning (HVAC) research has been conducted into what constitutes comfort

• Focus has always been built environments where thermal conditions can be engineered (fully controlled)

• Research interest in outdoor and semi-outdoor thermal comfort has only emerged in recent decades- recognition of commercial implications (e.g. recreational environments)- development of capabilities for thermal environmental control in outdoor spaces (hence the term “semi-outdoors”)

Thermal Comfort Research

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• The commonly accepted definition of “thermal comfort” comes from the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE):

“Thermal comfort refers to that condition of mind expressing satisfaction with the thermal environment”

• Most research on outdoor thermal comfort to-date has forgotten about the final step in this sequence (this presents research opportunities for you!)

• In this lecture we’ll take a look at what has been done on the physics and physiology parts of the problem, then take a look at the most interesting part… psychology of thermal comfort outdoors

Thermal Comfort Definition

Thermal environment

Thermo‐regulation

Thermal comfort

physics physiology psychology

• The basic principle borrowed from indoor thermal comfort researchers is that the human thermal climate can be described by four environmental parameters affecting the body’s energy balance:

• Air temperature (convective heat transfers)

• Mean Radiant Temperature (radiative heat transfers)

• Humidity (latent or evaporative transfers)

• Air speed (convective and latent heat transfers)

• Supplemented by two personal parameters• Clothing insulation (thermal insulation)

• Metabolic rate (internal heat production)

Physics of Thermal Comfort in Urban Outdoor Settings

Thermal environment

Thermo‐regulation

Thermal comfort

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M = metabolic heat production

The dry heat loss (R+C) represents ~70% at low Clo-values and ~60% at higher Clo-values.

The evaporative heat loss (E) represents ~25% at moderate activities

Heat Loss by Conduction (K) and Respiration (RES) are normally insignificant compared to the total heat exchange, so it is usually ignored.

W = work. Man is a poor machine. The efficiency is less than 20% even for well-trained athletes. Normally set to zero in the comfort equation.

The Human Energy Balance Parameters influencing the heat exchanges of a person

Cres + Eres

http://lumasenseinc.com/EN/products/thermal‐comfort/

• Energy released by metabolism depends on muscular activity.

• Metabolism is measured in Met units(1 Met=58.15 W/m2 body surface).

• Body surface for normal adult is 1.7 m2

• A sitting person in thermal comfort will have a heat loss of 100 W (58 W/m2)

• Average activity level for the last hour should be used when evaluating metabolic rate, due to body’s heat capacity (thermal inertia).

Measurement of the Human Heat Balance Parameters: Metabolism

http://lumasenseinc.com/EN/products/thermal‐comfort/

0.8 Met

1 Met

8 Met

4 Met

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• The Mean Radiant Temperature is that uniform temperature of an imaginary black enclosure resulting in same net energy exchange by radiation from the person, as the actual environment.

• In indoor settings this we only have long‐wave fluxes, but in outdoor settings there are short‐wave fluxes as well

Measurement of the Human Heat Balance Parameters: Mean Radiant Temperature

Actual room

Imaginary room

RR’t

1

t2

tr

t3

t4

Heat exchange by radiation:R=R’

http://lumasenseinc.com/EN/products/thermal‐comfort/

Thorsson, S., et al. (2007). "Different methods for estimating the mean radianttemperature in an outdoor urban setting." International Journal of Climatology27: 1983‐1993. 

Compared three different methods for the measuring/modelling the Tmrt in an outdoor urban setting:

(a) Integral radiation measurements. Calculations of Tmrt based on angle factors for a (rotationally symmetric) standing or walking person, or a sphere

(b) 38 mm flat grey globe thermometer

(c) Rayman 1.2 software (standing or walking person)

Assessment of Mean Radiant Temperature Outdoors

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Thorsso

n, S., et al. (2

007). "D

ifferent m

ethods fo

r estimatin

g the m

ean rad

iant tem

peratu

re in an

 outdoor u

rban

 setting." 

Intern

ational Jo

urnal o

f Clim

atology

27: 1983‐1993. 

Assessment of Mean Radiant Temperature Outdoors

Measurement of the Human Heat Balance Parameters: Urban Canyon

Tmrt

Source: Gerd Jendritzky

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Estimation of the Human Heat Balance Parameters: Metabolism

http://lumasenseinc.com/EN/products/thermal‐comfort/

Insulation in Clothing

http://lumasenseinc.com/EN/products/thermal‐comfort/

0,15 Clo0.5 Clo

1.0 Clo

1.2 Clo

1 clo = thermal insulation value of 0.155 m2 K/W 

ASI2 ‐ Prof. Richard de Dear ‐ Part 1

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How to measure clo values

Current generation sweating manikins

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Estimation of Insulation Value (clo)

http://lumasenseinc.com/EN/products/thermal‐comfort/

Thermal environment

Thermo‐regulation

Thermal comfort

Source:   George Havenith

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Human Thermophysiological Models

Source: Jan Stolwijk 1980 mathematical models of thermoregulation

Gagge’s Two-Node Model of Thermoregulation

• skin’s cold load error CSIGsk = 33.7 ‐ tsk for tsk < 33.7C

= 0               for tsk 33.7C• core’s cold load error 

CSIGcr  = 36.8 ‐ tcr for tcr < 36.8C= 0                for tcr 36.8C

• skin’s warm load errorWSIGsk = tsk ‐ 33.7    for tsk > 33.7C

= 0              for tsk 33.7C• core’s warm load error 

WSIGcr  = tcr ‐ 36.8     for tcr > 36.8C= 0                for tcr 36.8C

• whole body’s warm load error (core + periphery composite) WSIGb  = tb – neutralb for tb > neutralbC

= 0   for tb neutralbC

Load Error is the magnitude of neural drive for effector activity(sweating, shivering, vasoconstriction, vasodilation)

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Multinode Thermophysiological Models

Source: Dusan Fiala

Operational definitions of thermal comfortusually infer it from thermal sensations.

Neutral actually means no thermal sensation at all; neither warm nor cool

Thermal Acceptability is assumed to coincide with the central three sensation votes. Acceptability connotes behaviour.

But where does Thermal Pleasure fit in all of this?

Thermal environment

Thermo‐regulation

Thermal comfort

+2 Warm

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How does thermal comfort relate to behavioural thermoregulation?

thermal environment

body heat‐balance 36.8oC

thermoreception & integration

physiologicalthermoregulation Thermal dis/comfort

behaviouralthermoregulation

Outdoor Comfort Indices

Source: G

erd

Jendritzky

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Steady-State Human Heat Balance IndicesSource: G

erdJen

dritzky

For subjects sitting indoors, sedentary, the assumption of steady‐state are probably reasonable, but many if not most exposures in urban outdoor and semi‐outdoor climates the term “transient exposure” is probably more apt.     

UTCI  universal thermal climate index

Cutaneous Thermorereceptors – the key to perception of transient thermal environments

Located within skin. Cold receptors are closer to surface than warm receptors.Hensel measured two modes of output – static and dynamic discharges

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Cutaneous Thermorereceptors

Skin cold receptors are more sensitive to transientsthan warm receptors

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Conclusions

• Thermal comfort is part of the thermoregulatory loop

• Most of the knowledge and tools for understanding thermal comfort in outdoor and semi-outdoor settings has been borrowed from indoor environment research

• Thermal comfort research outdoors is usually based on notions of steady-state heat balance which may not always be appropriate

• In the next lecture we will explore non-steady-state and anisothermal perception, introducing the concept of alliesthesia

End, Thank you

Richard de DearThe University of SydneyRichard.Dedear@sydney.edu.ausydney.edu.au/architecture/research/ieq/index.shtml