building env. & human comf
TRANSCRIPT
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Building Environment
and Human ComfortCT10404
Thermal Comfort
By: Pubudu Kudahetti
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Comfort
That condition of mind that expresses satisfaction with
the environment – CIBSE
Environmental Factors Considered for Comfort
Thermal Condition
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Comfort
Environmental Factors Considered for Comfort
Visual Condition
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Comfort
Environmental Factors Considered for Comfort
Acoustic Condition
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Comfort
Environmental Factors Considered for Comfort
Indoor Air Quality (IAQ)
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Comfort
Environmental Factors Considered for Comfort
Electromagnetic Fields
Static Electricity
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Health Aspects
• A state of complete physical, mental and social well-being, not merely the absence of disease 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, by definition the occupants are suffering from ‘sick building syndrome’
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Thermal comfort
• Factors Affecting Thermal Comfort A person’s sensation of warmth is influenced by the following mainphysical 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.
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Thermal comfort
It is also required that there be no local discomfort
(either warm or cold) at any part of the human
body due to followings;
Asymmetric thermal radiation
Draughts
Warm or cold floors
Vertical air temperature differences.
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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 37
oC.
• Cold sensors are located in the skin. They
send signals when skin temperature is below34 oC.
• There are more cold sensors that warm
sensors.
• Heating mechanism:
– Reduced blood flow. – Shivering.
• Cooling mechanism:
– Increased blood flow.
– Sweating (Evaporation)
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•Heat sensor sends impulses to
the hypothalamus whentemperature exceeds 37 oC.
•Cold sensors sends impulses tothe hypothalamus when skintemperature below 34 oC.
•The bigger temperaturedifference, the more impulses.
•If impulses are of samemagnitude, you feel thermallyneutral.
•If not, you feel cold or warm.
Warm
impulsesCold
impulses 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.
Heat
Produ-
ced
Heat
Lost
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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 thecomfort equation.
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Mapping Physical & Psychological Comfort
Territories
temperature
h u m i d i t y
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Mapping Physical & Psychological Comfort
Territories
-- dishealth
-- dishealth
conditions the body’s response
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Heat Flow to/from Human Body
Conduction (sensible)
Convection (sensible)
Radiation (sensible)
Evaporation/Condensation
(latent)
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Conduction
The flow of heat between two adjacentand touching solids (or from one part toanother part within an object) by direct
interaction between moleculesexample: walking on a beach in your barefeet
for comfort, the key environmental variableis: SURFACE TEMPERATURE
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Radiation
The flow of heat between objects that are notin direct contact—but that can “see” eachother via electromagnetic radiation; theobjects may be a few inches or a million miles
apartexample: warming yourself in front of afireplace
for comfort, the key environmental variable is:SURFACE TEMPERATURE
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Evaporation
The flow of heat that must be provided as amaterial changes state (from a liquid to a gas);this heat represents the energy required tobreak molecular bonds (called the latent heat
of vaporization)example: feeling cool coming out of aswimming pool on a breezy day
for comfort, the key environmental variables
are: RELATIVE HUMIDITY | AIR SPEED
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Physical Basis of Thermal Comfort
Fundamentally, comfort involves a heat balance (athermal 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
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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
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Heat Flow Mechanisms
three external “to” mechanisms; four “from”
mechanisms
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The Mechanisms Adapt
the body automatically adapts to surrounding environmental conditions in its quest for thermalequilibrium; under high temperatures, evaporation becomes critically important
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Measuring Environmental Factors
data logging
air temperature,
RH, wind speed
air speed
surface
temperature
wet and dry bulbtemperatures
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MRT
MRT stands for mean radiant temperature
MRT is the (hypothetical) uniformtemperature of surrounding surfaces with
which the human body would exchange the
same heat by radiation as occurs in an
actual (non-uniform) environment
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MRT
Surface temperatures in a typical room areoften not all the same (for example, cold
window glass, warm radiators); the human
body will radiate to/from these differentsurfaces. MRT is the temperature (if all
surfaces were at this one temperature) at
which the body would exchange the sameheat by radiation as occurs in the messy,
many-temperature real space.
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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 ofother conditions, …)
These factors are not controlled through design, butmust be understood by a designer as they will affectoccupant thermal comfort responses
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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 theseconditions
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The Designer’s Job
• Understand the physical basis of thermal
comfort and related variables
• Appreciate the influence of the psychologicalaspects of thermal comfort
• Use this understanding and appreciation to designspaces that building users will decide are thermallycomfortable
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ASHRAE Thermal Comfort Chart
comfort
zone(s)
addressing operative temperature, relative humidity, and occupant clothing
For 80% occupant acceptability
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Combined Heath Effect: Temperature + Humidity
http://www.nws.noaa.gov/om/heat/index.shtml
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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
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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 arethe only physiological parameterswhich influence the heat balance at a
given Metabolic Rate•The sweat production is used insteadof body core temperature, as measureof the amount of warm impulses.
•Relation between the parametersfound 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
S w
e a t p r o d .
29
30
32
3334
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Comfort Equation
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Comfort Equation
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Comfort Equation
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Comfort Equation
H (Dry Heat Loss)
Ec Evaporative heat exchange at the skin
Cres Respiratory convective heat exchange
Eres Respiratory evaporative heat exchange
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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 thePMV and PPD Indices and specification of the conditions for thermal comfort”.
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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
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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 comfortstandards (e.g. ASHRAE, 2004: ISO, 1994).
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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
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Predicted Percentage Dissatisfied (PPD) Index
-0.5 < PMV <0.5 when PPD < 10%
PPD = 100-95 exp[-(0.03353PMV4+0.2179PMV2]
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Predicted Percentage Dissatisfied (PPD) Index
PPD = 100-95 exp[-(0.03353PMV4+0.2179PMV2]
-< PMV <0.5 when PPD < 100.5 %
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PMV/PPD Method
PMV = [0.303 exp ( -0.036 M ) + 0.028 ] L
L - Thermal load on the body
L = Internal heat production - heat loss to the actual
environmentL = M - W - [( Csk + Rsk + Esk ) + ( Cres + Eres )]
Predicted Percentage Dissatisfied (PPD)
PPD = 100 - 95 exp [ - (0.03353 PMV4 + 0.2179
PMV2)]
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PMV PPD
0 5%
+- 0.5 20%
+-1.0 50%
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Graphical representation Thermal comfort zones?
• ASHRAE 55-2004
– Based on
satisfaction (20%PPD)
– Season dependent
– For Officebuildings- nothomes
• Environmental
Factors:
– Metabolic rate-activity
– Clothing- insulation
– Air temperature
– Radiant temperature
– Air- speed
– HumidityOperative temperature
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Operative Temperature
Operative temperature (To):
To = 0.45 Tair + 0.55 Tmrt
Tmrt - Mean radiant temperature
Tmrt = S AiTi / S Ai
Ti - Surface temperature of enclosure i
Ai - Area of surface i
NOTE: Operative temperature is the same as
dry bulb temperature if there is no radiant
heat!!! ( cos Tair =Tmrt)
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Graphical representation Thermal comfort zones?
• ASHRAE 55-2004 – Based on
satisfaction (20%PPD)
– Season dependent
– For Officebuildings- not
homes (specificactivity level,clothing level)
– Adjusted comfort
zones for other
Summer
Winter
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PMV and PPD
•PMV-index (Predicted Mean Vote) predicts the subjective ratings of the environment in agroup of people.
•PPD-index predicts the number of dissatisfied people.
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What should be Estimated?
Parameters to estimate and calculate are:
Met - Estimation of Metabolic Rate
Clo - Calculation of Clo value
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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 MetStanding, 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
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Met Value Examples
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Calculation of Insulation in Clothing
• 1 Clo = Insulation value of 0,155 m2 oC/W
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Cl l bl
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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, cushioned
Armchair
0.000.100.20
0.0000.0160.032
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Adj f Cl V l
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Adjustment of Clo Value
1.0 Clo 0.5 Clo
1.2 met
Operative Temperature
P
P D ( P
r e d i c t e d P
e r c e n t a g e D i s s a t i s f i e
d )
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M R di t T t
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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 theactual enclosure.
•Measuring all surface temperatures and calculation of angle factors is timeconsuming. Therefore use of Mean Radiant Temperature is avoided whenpossible.
O ti d E i l t T t
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Operative and Equivalent Temperature
Operative temperature
Equivalent temperature
For given values of humidity, air speed,
metabolic rate, and clothing insulation, a
comfort zone may be determined. The comfort
zone is defined in terms of a range of operative
temperatures that provide acceptable thermal
environmental conditions or in terms of thecombinations of air temperature and mean
radiant temperature that people find thermally
acceptable
O ti d E i l t T t
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Operative and Equivalent Temperature
Operative temperature Equivalent temperature
P j t d A F t
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Projected Area Factor
tr = 20 C tr = 20 C tr = 20 C
O ti T t
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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.
D H t L
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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 temperature
as the surface temperature of a person’s clothing.
C f t T t
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Comfort Temperature
1,7 CLO
2,5 METRH=50%
tco=6oC.
0,8 CLO
2,2 METRH=50%
tco=18oC.
0,5 CLO
1,2 METRH=50%
tco=24,5oC.
General Thermal Comfort
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General Thermal Comfort
General Thermal Comfort
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General Thermal Comfort
Local Thermal Discomfort
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Local Thermal Discomfort
•Draught Radiation
Asymmetry
Vertical Air
Temperature
Differences
Floor
Temperature
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Draught
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Draught
•The sensation of
Draught dependson the airtemperature.
•At lower airtemperatures ahigher number
will bedissatisfied.
Mean Air Velocity
Evaluating Draught Rate
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Evaluating Draught Rate
•Fluctuations in Air Velocity is describedby Turbulence Intensity (Tu).
•Draught Rate equation is based onstudies of 150 people, and stated in• ISO 7730.
Tu = 100*( SD / va)
SD:Standard Deviation of Air Velocity
va: Local Mean Air Velocity
Radiation Asymmetry
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Radiation Asymmetry
•Radiant Temperature Asymmetry is perceived uncomfortable.•Warm ceilings and cold walls causes greatest discomfort.
Vertical Air Temperature Difference
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Vertical Air Temperature Difference
•Vertical Air Temperature Difference is
the difference between AirTemperature 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.
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Workplace Measurements
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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.
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Questions