Building Environment and Human Comfort Thermal Comfort
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
hu
mid
ity
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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
35
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
31
0 1 2 3 4
0 1 2 3 4
20
40
60
W/m2
Sw
eat pro
d.
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