Building Environment and Human Comfort

Thermal Comfort

Comfort

That condition of mind that expresses satisfaction withthe environment – CIBSE

Environmental Factors Considered for Comfort

Thermal Condition

Comfort

Environmental Factors Considered for Comfort

Visual Condition

Comfort

Environmental Factors Considered for Comfort

Acoustic Condition

Comfort

Environmental Factors Considered for Comfort

Indoor Air Quality (IAQ)

Comfort

Environmental Factors Considered for Comfort

Electromagnetic Fields

Static Electricity

Health Aspects

• A state of complete physical, mental and social well-being, not merely the absence ofdisease and infirmity - World Health Organization

Occupants Experience Symptoms• mausea• mucosal dryness or irritation, runny nose, eye problems,• headaches, skin problems, heavy head and flu-like symptoms,

If a significant proportion of occupants experience these symptoms then, bydefinition the occupants are suffering from ‘sick building syndrome’

Thermal comfort

• Factors Affecting Thermal ComfortA person’s sensation of warmth is influenced by the following main physical parameters, which constitute the thermal environment

air temperature

mean radiant temperature

relative air speed

humidity.

• Besides these environmental factors there are personal Factors that affect thermal comfort:

Metabolic heat production

Clothing.

Thermal comfort

It is also required that there be no local discomfort(either warm or cold) at any part of the humanbody due to followings;

Asymmetric thermal radiation

Draughts

Warm or cold floors

Vertical air temperature differences.

Thermal comfort

Body Temperature

37 C 34 C

Hot Cold

•The normal body core temperature is 37 C.• We have separate heat and cold sensors.• Heat sensors are located in the skin.Signals when temperature is higher than 37oC.• Cold sensors are located in the skin. Theysend signals when skin temperature is below34 oC.• There are more cold sensors that warmsensors.• Heating mechanism:– Reduced blood flow.– Shivering.• Cooling mechanism:– Increased blood flow.– Sweating (Evaporation)

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•Heat sensor sends impulses to the hypothalamus when temperature exceeds 37 oC.

•Cold sensors sends impulses to the hypothalamus when skin temperature below 34 oC.

•The bigger temperature difference, the more impulses.

•If impulses are of same magnitude, you feel thermally neutral.

•If not, you feel cold or warm.

Warmimpulses

Coldimpulses Activity

Perception of Thermal Environment

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The Energy Balance

•Thermal Comfort can only be maintained when heat produced by metabolism equals the heat lost from body.

HeatProdu-ced

HeatLost

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The Energy Balance

•Parameters influencing the heat loss from a person

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.

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

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Mapping Physical & Psychological Comfort Territories

temperature

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Mapping Physical & Psychological Comfort Territories

-- dishealth

-- dishealth

conditions the body’s response

Heat Flow to/from Human Body

Conduction (sensible)

Convection (sensible)

Radiation (sensible)

Evaporation/Condensation

(latent)

Conduction

The flow of heat between two adjacent and touching solids (or from one part to another part within an object) by direct interaction between moleculesexample: walking on a beach in your bare feet

for comfort, the key environmental variable is: SURFACE TEMPERATURE

Convection

The flow of heat from the surface of a material to/from a surrounding fluid (usually air); the free motion of molecules of the fluid is very important in promoting heat flow example: fanning yourself with a newspaper

for comfort, the key environmental variables are: AIR TEMPERATURE | AIR SPEED

Radiation

The flow of heat between objects that are not in direct contact—but that can “see” each other via electromagnetic radiation; the objects may be a few inches or a million miles apartexample: warming yourself in front of a fireplace

for comfort, the key environmental variable is: SURFACE TEMPERATURE

Evaporation

The flow of heat that must be provided as a material changes state (from a liquid to a gas); this heat represents the energy required to break molecular bonds (called the latent heat of vaporization)example: feeling cool coming out of a swimming pool on a breezy day

for comfort, the key environmental variables

are: RELATIVE HUMIDITY | AIR SPEED

Physical Basis of Thermal Comfort

Fundamentally, comfort involves a heat balance (a thermal equilibrium) … where:

heat in ≈ heat out

where “heat in” is provided by metabolism, radiation, conduction, convection

where “heat out” is via radiation, conduction, convection, evaporation

Heat Flow to/from Human Body

Sensible Heat

– Flows via conduction, radiation, and convection

– Flow rate is generally related to space temperatures

Latent Heat

– Flows via evaporation

– Flow rate is generally related to space humidity

Total Heat Flow = sensible + latent flows

Heat Flow Mechanisms

three external “to” mechanisms; four “from” mechanisms

The Mechanisms Adapt

the body automatically adapts to surrounding environmental conditions in its quest for thermal equilibrium; under high temperatures, evaporation becomes critically important

Measuring Environmental Factors

data logging

air temperature,RH, wind speed

air speed

surfacetemperature

wet and dry bulb temperatures

MRT

MRT stands for mean radiant temperature

MRT is the (hypothetical) uniform temperature of surrounding surfaces with

which the human body would exchange the same heat by radiation as occurs in an

actual (non-uniform) environment

MRT

Surface temperatures in a typical room are often not all the same (for example, cold

window glass, warm radiators); the human body will radiate to/from these different surfaces. MRT is the temperature (if all

surfaces were at this one temperature) at which the body would exchange the same heat by radiation as occurs in the messy,

many-temperature real space.

Personal Factors Affecting Comfort

• Physical– Clothing (specifically its insulation value in “clo”)

– Activity level (specifically metabolic heat production in “met”)

• Mental– State of mind (experiences, expectations, influences of

other conditions, …)

These factors are not controlled through design, but must be understood by a designer as they will affect occupant thermal comfort responses

Physical Basis of Thermal Comfort

The potential for thermal equilibrium is:

– Influenced by environmental factors

• Often common to all occupants in a space

• Designer must control these conditions

– Influenced by personal physical factors

• Individual to each occupant in a space

• Designer must be aware of and consider these conditions

The Designer’s Job

• Understand the physical basis of thermal

comfort and related variables

• Appreciate the influence of the psychological aspects of thermal comfort

• Use this understanding and appreciation to design spaces that building users will decide are thermally comfortable

ASHRAE Thermal Comfort Chart

comfortzone(s)

addressing operative temperature, relative humidity, and occupant clothing

For 80% occupant acceptability

Combined Heath Effect: Temperature + Humidity

http://www.nws.noaa.gov/om/heat/index.shtml

Humidity indoors

• Indoor humidity is a function of

– Outdoor humidity

– Indoor sources:

– Unvented cooking,

– Unvented bathrooms

– Showering

– Number of Occupants

– Humidifier use

– Air conditioner use

– Clothes drying--mechanical or air drying

Humidity - Health Effects

(from Arundel et al., 1986)

Optimum

ZoneBacteria

Viruses

Fungi

Mites

Respiratory Infections*

Allergic Rhini tis and Asthma

Chemical Interactions

Ozone Production

10 20 30 40 50 60 70 80 90

Percent Relative Hu midity

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Conditions for Thermal Comfort•Two conditions must be fulfilled to maintain Thermal Comfort:

– Heat produced must equal heat lost.– Signals from Heat and Cold sensors

must neutralise each other.

•Mean Skin Temp. and Sweat Loss are the only physiological parameters which influence the heat balance at a given Metabolic Rate•The sweat production is used instead of body core temperature, as measure of the amount of warm impulses.•Relation between the parameters found empirically in experiments.•No difference between sex, age, race or geographic origin.

Metabolic Rate

Metabolic Rate

80

100

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0 1 2 3 4

0 1 2 3 4

20

40

60

W/m2

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29

30

32

33

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Comfort Equation

Comfort Equation

Comfort Equation

Comfort Equation

H (Dry Heat Loss)

Ec Evaporative heat exchange at the skin

Cres Respiratory convective heat exchange

Eres Respiratory evaporative heat exchange

Thermal comfort predictive model

Most widely used :

•Comfort equation method (heat balance method)

(Links environmental conditions to body thermal load)

•Predicted Mean Vote method (PMV model).

(links body thermal load to a Thermal sensation scale)

•Predicted percentage of dissatisfied (PPD).

(Empirically PMV is related to PPD)

Standards:

•ASHRAE Standard 55-2004: “Thermal Environmental conditions for Human

Occupancy.”

•ISO Standard 7730: “Moderate thermal environments- Determination of the

PMV and PPD Indices and specification of the conditions for thermal comfort”.

Predicted Mean Vote Scale

- +3 Hot

- +2 Warm

- +1 Slightly warm

- +0 Neutral

- - 1 Slightly cool

- -2 Cool

- -3 Cold

The PMV index is used to quantify the degree of discomfort

Predicted Mean Vote (PMV) Index

• The PMV index is mathematically complex to compute, so Fanger (1970) provided look-up tables to help practitioners determine appropriate thermal conditions.

• Information from these tables, and graphical representations of comfort conditions, is also provided in modern thermal comfort standards (e.g. ASHRAE, 2004: ISO, 1994).

Predicted Mean Vote (PMV) Index

The PMV index predicts the mean response

of a large group of people according to the

ASHRAE thermal sensation scale

Predicted Percentage Dissatisfied (PPD) Index

-0.5 < PMV <0.5 when PPD < 10%PPD = 100-95 exp[-(0.03353PMV4+0.2179PMV2]

Predicted Percentage Dissatisfied (PPD) Index

PPD = 100-95 exp[-(0.03353PMV4+0.2179PMV2]

-< PMV <0.5 when PPD < 100.5 %

PMV/PPD Method

PMV = [0.303 exp ( -0.036 M ) + 0.028 ] LL - Thermal load on the body

L = Internal heat production - heat loss to the actual environment

L = M - W - [( Csk + Rsk + Esk ) + ( Cres + Eres )]

Predicted Percentage Dissatisfied (PPD)PPD = 100 - 95 exp [ - (0.03353 PMV4 + 0.2179

PMV2)]

PMV PPD

0 5%

+- 0.5 20%

+-1.0 50%

Graphical representation Thermal comfort zones?

• ASHRAE 55-2004– Based on

satisfaction (20% PPD)

– Season dependent

– For Office buildings- not homes

• Environmental Factors:

– Metabolic rate-activity

– Clothing- insulation

– Air temperature

– Radiant temperature

– Air- speed

– HumidityOperative temperature

Operative Temperature

Operative temperature (To):To = 0.45 Tair + 0.55 Tmrt

Tmrt - Mean radiant temperatureTmrt = S AiTi / S Ai

Ti - Surface temperature of enclosure iAi - Area of surface i

NOTE: Operative temperature is the same as dry bulb temperature if there is no radiant heat!!! ( cos Tair =Tmrt)

Graphical representation Thermal comfort zones?

• ASHRAE 55-2004– Based on

satisfaction (20% PPD)

– Season dependent

– For Office buildings- not homes (specific activity level, clothing level)

– Adjusted comfort zones for other conditions (ie. air speed, clothing

Summer

Winter

PMV and PPD

•PMV-index (Predicted Mean Vote) predicts the subjective ratings of the environment in a group of people.

•PPD-index predicts the number of dissatisfied people.

What should be Estimated?

Parameters to estimate and calculate are:

Met - Estimation of Metabolic Rate

Clo - Calculation of Clo value

Metabolic Rate•Energy released by metabolism depends on muscular activity.

•Metabolism is measured in Met • (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.

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

0.8 Met

1 Met

8 Met

4 Met

Met Value Table

Activity Metabolic Rates [M]

Reclining 46 W/m2 0.8 Met

Seated relaxed 58 W/m2 1.0 Met

Clock and watch repairer 65 W/m2 1.1 Met

Standing relaxed 70 W/m2 1.2 Met

Car driving 80 W/m2 1.4 Met

Standing, light activity (shopping) 93 W/m2 1.6 Met

Walking on the level, 2 km/h 110 W/m2 1.9 Met

Standing, medium activity (domestic work) 116 W/m2 2.0 Met

Washing dishes standing 145 W/m2 2.5 Met

Walking on the level, 5 km/h 200 W/m2 3.4 Met

Building industry 275 W/m2 4.7 Met

Sports - running at 15 km/h 550 W/m2 9.5 Met

Met Value Examples

Calculation of Insulation in Clothing

• 1 Clo = Insulation value of 0,155 m2 oC/W

Clo Values Table

Garment description Iclu Clo Iclu m2 C/W

Underwear PantyhoseBriefsPants long legs

0.020.040.10

0.0030.0060.016

Underwear,shirts

BraT-shirtHalf-slip, nylon

0.010.090.14

0.0020.0140.022

Shirts Tube topShort sleevesNormal, long sleeves

0.060.090.25

0.0090.0290.039

Trousers ShortsNormal trousersOveralls

0.060.250.28

0.0090.0390.043

Insulatedcoveralls

Multi-component fillingFibre-pelt

1.031.13

0.1600.175

Sweaters Thin sweaterNormal sweaterThick sweater

0.200.280.35

0.0310.0430.054

Clo Values Table

Garment description Iclu Clo Iclu m2 C/W

Jackets VestJacket

0.130.35

0.0200.054

Coats over-trousers

CoatParkaOveralls

0.600.700.52

0.0930.1090.081

Sundries SocksShoes (thin soled)BootsGloves

0.020.020.100.05

0.0030.0030.0160.008

Skirt,dresses

Light skirt, 15cm above kneeHeavy skirt, knee-lengthWinter dress, long sleeves

0.100.250.40

0.0160.0390.062

Sleepwear ShortsLong pyjamasBody sleep with feet

0.100.500.72

0.0160.0780.112

Chairs Wooden or metalFabric-covered, cushionedArmchair

0.000.100.20

0.0000.0160.032

Calculation of Clo-Value (Clo)

Adjustment of Clo Value

1.0 Clo 0.5 Clo

1.2 met

Operative Temperature

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What should be Measured?

Parameters to measure are:

- ta Air Temperature

- tr Mean Radiant Temperature

- va Air Velocity

- pa Humidity

Mean Radiant Temperature

•The Mean Radiant Temperature is that uniform temperature of an imaginary black enclosure resulting in same heat loss by radiation from the person, as the actual enclosure.•Measuring all surface temperatures and calculation of angle factors is time consuming. Therefore use of Mean Radiant Temperature is avoided when possible.

Operative and Equivalent Temperature

Operative temperature

Equivalent temperature

For given values of humidity, air speed,metabolic rate, and clothing insulation, acomfort zone may be determined. The comfortzone is defined in terms of a range of operativetemperatures that provide acceptable thermalenvironmental conditions or in terms of thecombinations of air temperature and meanradiant temperature that people find thermallyacceptable

Operative and Equivalent Temperature

Operative temperature Equivalent temperature

Projected Area Factor

tr = 20 C tr = 20 C tr = 20 C

Operative Temperature

• The Operative temperature to integrates the effect of ta and tr.

• An Operative Temperature transducer must have same heat exchange properties as an unheated mannequin dummy.

Dry Heat Loss

• Dry Heat Loss or equivalent temperature can be measured directly, using a heated Operative Temperature shaped transducer.

• The Equivalent temperature teq integrates the effect of ta, tr and va .

• The Dry Heat Loss transducer is heated to the same temperatureas the surface temperature of a person’s clothing.

Comfort Temperature

1,7 CLO2,5 METRH=50%tco=6oC.

0,8 CLO2,2 METRH=50%tco=18oC.

0,5 CLO1,2 METRH=50%

tco=24,5oC.

General Thermal Comfort

General Thermal Comfort

Local Thermal Discomfort

•Draught Radiation Asymmetry

Vertical Air Temperature Differences

Floor Temperature

Draught

•Draught is the most common complaint indoors.

•What is felt is Heat Loss.

•Heat Loss is depending on average Air Velocity, Temperature and Turbulence.

•High Turbulence is more uncomfortable, even with the same Heat Loss.

Velocity

m/s

Velocity

m/s

Time

Time

Draught•The sensation of Draught depends on the air temperature.

•At lower air temperatures a higher number will be dissatisfied.

Mean Air Velocity

Evaluating Draught Rate

•Fluctuations in Air Velocity is described by Turbulence Intensity (Tu).•Draught Rate equation is based on studies of 150 people, and stated in • ISO 7730.

Tu = 100*( SD / va)

SD:Standard Deviation of Air Velocityva: Local Mean Air Velocity

Radiation Asymmetry

•Radiant Temperature Asymmetry is perceived uncomfortable.

•Warm ceilings and cold walls causes greatest discomfort.

Vertical Air Temperature Difference

•Vertical Air Temperature Difference is the difference between Air Temperature at ankle and neck level.

Vertical Air Temperature Difference

25 oC

19 oC

Radiant asymmetry in the vertical direction shall be less than 5oC (9oF) under a warm ceiling and less than 10oC (18oF) in the horizontal direction from a cool wall.

Floor Temperature

•Acceptable floor temperatures ranging from 19 to 29 oC.

•The graph is made on the assumption that people wear “normal indoor footwear”.

Workplace Measurements

- 1.1 m

- 0.1 m

- 0.6 m

- 0.1 m

- 1.1 m

- 1.7 m

• Measurements of Vertical Temp. difference and Draught at ankle and neck.• Other measurements should be performed at persons centre of gravity.

Questions