Human Thermal Comfort .Standard Based on Predicted Mean Vote Model

GREENARCS – GREEN ARCHITECTURE AND ARTS ONLINE MAGAZINE (ENGLISH). YEAR 1 2014

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Moossavi, Seyed Morteza. (2014). Human Thermal Comfort Standard Based on Predicted Mean

Vote Model. GREENARCS – Green Architecture and Arts Online Magazine (English), Year 1,

http://greenarcs.com/?p=1117

Human Thermal Comfort Standard Based on

Predicted Mean Vote Model

Seyed Morteza Moossavi

Ph.D. Scholar of Architecture, M.D. Arch.

Architecture & Ekistics Department

Jamia Millia Islamia, New Delhi

____________________________________________

Keywords: Architecture, Green Architecture, Human Thermal Comfort, PMV Model

Abstract

Energy efficiency in buildings is one of the most important aims for the world.

Residential buildings are very important because of its highest percentage of

energy consumption. Thermal comfort is one of the most important parameters in

human life and architecture especially according to energy consumption.

Standards about human thermal reflections and thermal comfort through ISO

7730 and ASHRAE standard with three sub-systems as operative, adaptive and

PMV thermal comfort standards are basis standards and systems.

There are four environmental variables affecting the thermal comfort of the human

body: Air temperature, Radiation, Humidity, Air speed.

Additionally, two personal variables influence thermal comfort: Clothing, Level of

activity.

In this article, Predicted Mean Vote model of thermal comfort standard based on

Fanger’s model and ASHRAE standard 55 as one of the most important models is

explained and it is tried to present a standard for human thermal comfort in all

conditions and climates.

Introduction

The importance of energy efficient buildings has assumed great urgency today.

Figure 1 shows the residential consumption of energy in most industrial countries



is the most consumption and every change of design and construction methods to

optimum methods will help to improve energy problem in the world.

Figure 1 Primary energy (2003) 1

Though the benefit of solar passive building design is immense, there are also

some limitations for construction of such buildings. The fundamental problems are

two things to use and green architecture or green building design techniques:

- The lack of efficient and low-effect of being Passive systems for thermal

comfort.

- High initial cost and unaesthetic active systems and techniques.

Thus in whole researchers and architects should answer to two problems in green

architecture researches:

- To achieve more efficient and more effective techniques in passive

systems.

- Create active systems cheaper.

Figure 2 Life Cycle Energy Use2

1 World Business Council for Sustainable Development Website



Human thermal comfort relates to heating, cooling and ventilation and as figure 2

shows, these factors include about 84 percent of energy use in a house. So

thermal comfort can be called the most important factor in energy use in a

residential building.

Human Thermal Comfort

Climate Sensitive Architecture – is a response to the climate

• Based on analysis of climate zone and micro-climate needs

• Based on attaining comfort level in bio-climatic chart

• Identification of Passive design elements such as walls, openings, roofs, etc. &

the use of appropriate technology & materials

• Preparing Passive design strategies – heating, cooling, ventilation,

humidification/ dehumidification

Implications

• Reduced energy costs and loads during active life of building

• Thermal comfort of occupants

• Reduced impact (heat island) on the external environment3

Studies show that building occupants are more comfortable and satisfied when

they have some control over their environment, especially regarding temperature,

lighting, and visibility.4

Thermal sensation is subjective, meaning that not all people will experience

comfort in the same thermal environment. For indoor conditions, comfort zones

are typically implemented to satisfy 80% of people.5

There are four environmental variables affecting the thermal comfort of the human

body:

• air temperature

• radiation

• humidity

2 Cat, To, Ing, et al., 2007. P.36

3 Udyavar, R. 2006. P.4

4 Schalcher, H. 2008. P.78

Foundation. 5 Al-Asir, Awadallah, Blomsterberg et al., 2009. P. 115



• air speed

Additionally, two personal variables influence thermal comfort:

• clothing

• level of activity

However, other personal factors related to adaptation and acclimatization have

proven to affect thermal sensation and are discussed below.6

Human Thermal Comfort Standards

Human thermal comfort is defined by ASHRAE (American Society of Heating,

Refrigerating and Air-Conditioning Engineers) as the state of mind that expresses

satisfaction with the surrounding environment ().7 Also it is defined in British

Standard BS EN ISO 7730 as: ‘That condition of mind which expresses

satisfaction with the thermal environment.’ ISO standard 7730 for the thermal

environment (ISO, 2005) relates to human physiology and heat transfer, and is

based on Fanger’s studies and his PMV equation. In this article thermal comfort

standard basis on ASHRAE PMV method is explained.

The ‘rational’ approach to thermal comfort seeks to explain the response of people

to the thermal environment in terms of the physics and physiology of heat transfer.

An ‘index’ of thermal comfort is developed which expresses the thermal state of

the human body and in terms of the thermal environment.8

Thermal comfort is affected by heat conduction, convection, radiation, and

evaporative heat loss. Thermal comfort is maintained when the heat generated by

human metabolism is allowed to dissipate, thus maintaining thermal equilibrium

with the surroundings. Any heat gain or loss beyond this generates a sensation of

discomfort. It has been long recognized that the sensation of feeling hot or cold is

not just dependent on air temperature alone.

6 The same Source.

7 ANSI/ASHRAE Standard 55, 2004.

8 J. Fergus Nicol and Michael A Humphreys , 2002.



Predicted Mean Vote (PMV) Thermal Comfort Model

Fanger has developed a model for thermal comfort that is presented by ASHRAE.

This model is Predicted Mean Vote model (PMV). The PMV equation only applies

to humans exposed for a long period to constant conditions at a constant

metabolic rate. Conservation of energy leads to the heat balance equation:

H – Ed – Esw – Ere – L = R + C

Equation 1

Where,

H = internal heat production

Ed = heat loss due to water vapour diffusion through the skin

Esw = heat loss due to sweating

Ere = latent heat loss due to respiration

L = dry respiration heat loss

R = heat loss by radiation from the surface of the clothed body

C = heat loss by convection from the surface of the clothed body

The equation is expanded by substituting each component with a function

derivable from basic physics. All of the functions have measurable values with

exception of clothing surface temperature and the convective heat transfer

coefficient which are functions of each other. To solve the equation, an initial

value of clothing temperature is estimated, the convective heat transfer coefficient

computed, a new clothing temperature calculated etc., by iteration until both are

known to a satisfactory degree.

Now let us assume the body is not in balance and write the heat equation as:

L = H – Ed – Esw – Ere – L – R - C,

Equation 2

where L is the thermal load on the body.



Define thermal strain or sensation, Y, as some unknown function of L and

metabolic rate. Holding all variables constant except air temperature and

metabolic rate, we use mean votes from climate chamber experiments to write Y

as function of air temperature for several activity levels. Then substituting L for air

temperature, determined from the heat balance equation above, evaluate the

partial derivative of Y with respect to L at Y=0 and plot the points versus metabolic

rate. An exponential curve is fit to the points and integrated with respect to L. L is

simply renamed "PMV" and we have (in simplified form).9

Then a Predicted Mean Vote (PMV) that predicts the mean response of a large

number of occupants is defined based on the thermal sensation scale.

The PMV is defined by Fanger as:

[ ( ) ]

Equation 3

Where,

PMV = Predicted Mean Vote Index

M = metabolic rate

L = thermal load - defined as the difference between the internal heat production

and the heat loss to the actual environment - for a person at comfort skin

temperature and evaporative heat loss by sweating at the actual activity level. The

thermal load has to be obtained by solving the heat balance equation for the

human body.10

The table below indicates the sensible and latent (steam) heat loss from people.

The values can be used to estimate heat loads handled by air conditioning

systems. So it is possible to calculate thermal load (L) through this table.

Note that the values are based on older ISO and ASHRAE standards. Later ISO

and ASHRAE standards should be checked for updated values.

9University of Strathclyde Engineering Website

10 IIT Kharagpur, (2008), Part 29, Page 14



Table 1 Sensible and Latent Heat Loss According to Metabolic rates and Room dry Bulb

Temperature11

Degree

of

Activity

Typical

Application

Average

Metabolic

rate -

male

adult

(W)

Room Dry Bulb Temperature (oC)

28 27 26 24 22 20

Sens. Lat. Sens. Lat. Sens. Lat. Sens. Lat. Sens. Lat. Sens. Lat.

Seated at

rest

Cinema,

theatre,

school

100 50 50 55 45 60 40 67 33 72 28 79 21

Seated,

very light

work

Computer

working 120 50 70 55 65 60 60 70 50 78 42 84 36

Office

work

Hotel

reception,

cashier

130 50 80 56 74 60 70 70 60 78 52 86 44

Standing,

walking

slowly

Laboratory

work 130 50 80 56 74 60 70 70 60 78 52 86 44

Walking,

seated

150 53 97 58 92 64 86 76 74 84 66 90 60

Moderate

work

Servant,

hair dresser 160 55 105 60 100 68 92 80 80 90 70 98 62

Light Mechanical 220 55 165 52 158 70 150 85 135 100 120 115 105

11

The Engineering Toolbox Website. Persons and Metabolic Heat Gain.



Degree

of

Activity

Typical

Application

Average

Metabolic

rate -

male

adult

(W)

Room Dry Bulb Temperature (oC)

28 27 26 24 22 20

Sens. Lat. Sens. Lat. Sens. Lat. Sens. Lat. Sens. Lat. Sens. Lat.

bench

work

production

Moderate

Dancing Party 250 62 188 70 180 78 172 94 156 110 140 125 125

Fast

walking

Mountain

walking 300 80 220 88 212 96 204 110 190 130 170 145 155

Heavy

work Athletics 430 132 298 138 292 144 286 154 276 170 260 188 242

1 W = 3.41

Btu/hr

Figure 3 Heat loss Vs

ConvectionRadiation,

Evaporation, Total Body

Heat12

12

The Same Source.



Figure 4 shows the heat exchange between clothed and nude occupant and the

environment at various operative temperatures. Figure 4 is interpreted as follows:

(a) When the metabolic rate is about 1 met (58.2 W/m2) , there is no body cooling

nor body heating at an operative temperature of about 25.5oC for light clothed

person and 31oC for nude person.

(b) When the operative temperature drops to lower values, the dry heat exchange

is increased and the evaporative heat loss is mainly respired vapour loss. The

skin temperature and the temperature of superficial and deep tissues drop,

resulting in a negative

heat storage.

(c) When the operative

temperature exceeds

29oC, the rate of

evaporative heat loss is

significantly increased

in order to

counterbalance the

reduction of dry heat

exchange to maintain

the thermal equilibrium.

Figure 4 Heat Exchange of Persons with the Environment13

(d) The body temperature tends to rise only when the body is entirely wet, and the

evaporative heat loss is inadequate. There exists a positive rate of heat storage.

(e) Body temperature above 43oC may cause death.

13

City University of Hongkong Website. Heat exchange Between the Human Body and the

Environment



The metabolic rate, or human body heat or power production, is often measured in

the unit "Met". The metabolic rate of a relaxed seated person is one (1) Met,

where

1 Met = 58 W/m2 (356 Btu/hr)

Equation 4

The mean surface area, the Du-Bois area, of the human body is approximately 1.8

m2 (19.4 ft2). The total metabolic heat for a mean body can be calculated by

multiplying with the area. The total heat from a relaxed seated person with mean

surface area would be

58 W/m2 x 1.8 m2 = 104 W (356 Btu/hr)

Equation 514

Table 2 Typical metabolic rates for some common activities15

Activity W/m2 W

1) Btu/hr

1) Met

Reclining

Sleepimng

46 83 282 0.8

Seated relaxed 58 104 356 1.0

Standing at rest 70 126 430 1.2

Sedentary activity (office, dwelling,

school, laboratory) 70 126 430 1.2

Car driving 80 144 491 1.4

Graphic profession - Book Binder 85 153 522 1.5

14

The Engineering Toolbox. Predict Mean Vote Index (PMV) 15

The same source



Activity W/m2 W

1) Btu/hr

1) Met

Standing, light activity (shopping, laboratory, light industry) 93 167 571 1.6

Teacher 95 171 583 1.6

Domestic work -shaving, washing and dressing 100 180 614 1.7

Walking on the level, 2 km/h 110 198 675 1.9

Standing, medium activity (shop assistant,

domestic work) 116 209 712 2.0

Building industry - Brick laying (Block of 15.3 kg) 125 225 768 2.2

Washing dishes standing 145 261 890 2.5

Domestic work - raking leaves on the lawn 170 306 1043 2.9

Domestic work - washing by hand and ironing (120-220 W) 170 306 1043 2.9

Iron and steel - ramming the mould with a

pneumatic hammer 175 315 1075 3.0

Building industry -forming the mould 180 324 1105 3.1

Walking on the level, 5 km/h 200 360 1228 3.4

Forestry -cutting across the grain with a

one-man power saw 205 369 1259 3.5

Volleyball

Bicycling (15 km/h)

232 418 1424 4.0

Calisthenics 261 470 1602 4.5

Building industry - loading a wheelbarrow with stones and

mortar 275 495 1688 4.7

Golf

Softball

290 522 1780 5.0

Gymnastics 319 574 1959 5.5



Activity W/m2 W

1) Btu/hr

1) Met

Aerobic Dancing

Swimming

348 624 2137 6.0

Sports - Ice skating, 18 km/h

Bicycling (20 km/h)

360 648 2210 6.2

Agriculture - digging with a spade (24 lifts/min.) 380 674 2333 6.5

Skiing on level, good snow, 9 km/h

Backpacking

Skating ice or roller

Basketball

Tennis

405 729 2487 7.0

Handball

Hockey

Racquetball

Cross County Skiing

Soccer

464 835 2848 8.0

Running 12 min/mile

Forestry - working with an axe (weight 2 kg. 33 blows/min.)

500 900 3070 8.5

Sports - Running in 15 km/h 550 990 3377 9.5

1) 1.8 m2 (19.4 ft2) -

The metabolic rates varies from person to person and the intensity of the activity.

The insulation of clothes are often measured in the unit "Clo", where



1 Clo = 0.155 m2K/W

Clo = 0 - corresponds to a naked person

Clo = 1 - corresponds to the insulating value of clothing needed to maintain

a person in comfort sitting at rest in a room at 21 ℃ (70 ℉) with air

movement of 0.1 m/s and humidity less than 50% - typically a person

wearing a business suit

Table Examples of estimates of clothing insulation values (Icl) for use in the PMV thermal

equation of Fanger (1970)

An extension of the index to include a range of activity and clothing values

provides the Standard Effective Temperature (SET) thermal index. (Gagge et al.,

1972) The SET is defined as the temperature of an isothermal environment with

air temperature equal to mean radiant temperature, 50 percent relative humidity,

and still air (v < 0.15 m s -1) in which a person with a standard level of clothing



insulation would have the same heat loss at the same mean skin temperature and

the same skin wettedness as he does in the actual environment and clothing

insulation under consideration.

Table Predicted mean vote (PMV) values from Fanger (1970). Assume rh = 50%; still air,

and ta = ttPMV; +3, hot; +2, slightly warm, +1, warm; +1, warm; 0, neutral; -1, slightly cool;

-2, cool; -3, cold16

16

The Same Source.



Table Clothing insulation for the standard environment used in the definition of standard

effective temperature (SET)17

17

Parsons, Ken. 2002. P. 213



So according to the last equations, tables and figures it is possible to present a

table basis on sensation and physiological state of sedentary person. In the

following table relation between Standard Effective Temperature Index Level and

thermal sensation is observed.

Table Relationship between standard effective temperature (SET) index levels and

thermal sensation18

PPD - Predicted Percentage Dissatisfied Index

Predicted Percentage Dissatisfied - PPD - index is a quantitative measure of the

thermal comfort of a group of people at a particular thermal environment.

Fanger related the PMV to Percent of People Dissatisfied (PPD) by the following

equation:

[ ( )]

18

Parsons, Ken. 2002. P. 214



Equation 6

where dissatisfied refers to anybody not voting for –1, 0 or +1. It can be seen from

the above equation that even when the PMV is zero (i.e., no thermal load on

body) 5 % of the people are dissatisfied! When PMV is within ± 0.5, then PPD is

less than 10 %.19

Figure 3 PPD – Predicted Percentage Dissatisfied

PPD Index20

Based on the studies of Fanger and subsequent sampling studies, ASHRAE has

defined a thermal sensation scale, which considers the air temperature, humidity,

sex of the occupants and length of exposure. The scale is based on empirical

equations relating the above comfort factors. The scale varies from +4 (hot) to –4

(cold) with 0 being the neutral condition.

Table 1 The Thermal Sensation Scale of the PMV Index21

Sensation Value

19

IIT Kharagpur, (2008), Part 29, Page 14. 20

The Engineering Toolbox. Predict Mean Vote Index (PMV). 21

Design Builder Website. Energy Plus Thermal Comfort.



Very Cold -4

Cold -3

Cool -2

Slightly Cool -1

Nutral 0

Slightly Warm +1

Warm +2

Hot +3

Very Hot +4

Lowest Possible Percentage Dissatisfied (LPPD) Index

The LPPD is a quantitative measure of the thermal comfort of a room as a whole

for a group of people in a thermally non-uniform environment. It is more useful for

large rooms than for small one. As a recommended design target, LPPD is not to

exceed 6%.22

PMVe – Predicted Mean Vote with Expectancy Factor

PMV was recently extended to better predict indoor comfort in naturally ventilated

buildings in warm climates by including an expectancy factor (Fanger and Toftum,

2002). The new index is called PMVe and is calculated as:

Equation 7

where

e = expectancy factor

Table 3 Expectancy factors for the PMV index (Fanger and Toftum, 2002)23

No. of air-conditioned buildings Expectancy factor e

Many 0.9-1.0

Some 0.7-0.9

Few 0.5-0.7

22

City University of hong Kong. Prediction of thermal Comfort. 23

Fanger, P. Ole, Toftum, Jurn. 2002. 533±536.



The expectancy factor e, depends on how common air-conditioned buildings are;

the more common air-conditioned buildings are, the higher the expectancy factor,

as can be seen in Table 24.

Conclusion

Human thermal comfort is a main parameter in green building design and

construction. There are some models to calculate this parameter. One of the most

important is PMV. Fanger as developer of PMV model has presented a model

basis on thermal sensation and human psychology in different environments.

The main result and formulate of this analyses is the following equation:

[ ( ) ]

M in this equation is Metabolic rates in different actions and L is Thermal Load of

human body in different activities and climates.

Analysis shows that a simplified rate for Standard Effective Temperature basis on

sensation and Psychological State of Sedentary Person as the following:

- Human thermal comfort rate: 22.2℃ - 25.6℃

Warm and hot unaccebtable climates as:

- slightly warm and slightly unaccebtable: 25.6 ℃ - 30.0℃

- warm, uncomfortable: 30.0 ℃ - 34.5℃

- Hot, very unaccebtable: 34.5℃ - 37.7℃

- Very hot, Very Uncomfortable >37.5℃

Cool and cold unaccebtable climates:

- Slightly cool, slightly unaccebtable: 17.5℃ - 22.2℃

- Cool and unaccebtable: 14.5℃ - 17.5℃

- Cold, very unaccebtable 10.0℃ - 14.5℃

- Very cold and very uncomfortable: <10.0℃

Fanger related the PMV to Percent of People Dissatisfied (PPD) by the following

equation:

[ ( )]

Thermal sensation scale, which considers the air temperature, humidity, sex of the

occupants and length of exposure is from +4 (hot) to –4 (cold) with 0 being the

neutral condition.



To better predict indoor comfort in naturally ventilated buildings in warm climates

The new index is called PMVe and is calculated as:

Expectancy factor for many of buildings is 0.9-1.0 basis on Fanger and Toftum

research.

References

- Al-Asir, H. S., Awadallah, T., Blomsterberg, Hakansson, H., Hellstrom, B.,

& Kvist, H. (2009). Climate Conscious Architecture and Urban Design in

Jordan (p. 115). Lund, Sweden: Lund University, Royal Scientific Society.

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Heating, Refrigerating and Air-Conditioning Engineers, Inc.

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Trends Energy Efficiency in Buildings Contents (p. 36). ConchesGeneva:

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pass=, (Accessed 5/8/2010)

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Human Thermal Comfort .Standard Based on Predicted Mean Vote Model

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