thermal comfort building physics, lo-lo cdt thursday 6 th october 2011
TRANSCRIPT
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Thermal Comfort
Building Physics, Lo-Lo CDT
Thursday 6th October 2011
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Thermal Comfort
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What is Thermal Comfort?
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Definition of Thermal Comfort
“That condition of mind which expresses satisfaction with the thermal environment”
(ISO 7730)
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Thermal Comfort Variables
(7-Point ASHRAE Scale)
hot
warm
slightly warm
neutral (comfortable)
slightly cool
cool
cold
3
2
1
0
-1
-2
-3-3 -2 -1 0 1 2 3
Thermal Sensation
0
20
40
60
80
100
Per
cen
tag
e D
issa
tisf
ied
[%
]
Thermal Sensation Percentage of Dissatisfied
Thermal Comfort
TS may also be the mean vote for a group of individuals
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Necessary Conditions for Thermal Comfort
1. Heat balance of the human body
2. Comfortable psychological conditions
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Heat Balance of the Human Body
Metabolic heatproduction
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Components of the Environmental Heat Loss and the Human Heat Balance
Ta , rh
rh
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Factors Affecting Human Heat Balance
• Environmental parameters– Air temperature (Ta)– Mean radiant temperature of surfaces (Tr)– Air velocity (va)– Air relative humidity (rh)
• Personal factors– Physical activity (M)– Clothing insulation (Icl)
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Personal Factors: Clothing
Clo: a unit used to express the thermal insulation provided by garments and clothing ensembles: 1 clo = 0.155 m2 °C/W
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Personal Factors: ClothingEnsemble
Icl (clo)
Briefs; knit, short-sleeve sport shirt; walking shorts and belt; calf-length socks; hard-soled shoes
0.4
Briefs; broadcloth, long-sleeve shirt; long fitted trousers and belt; calf-length socks; hard-soled shoes
0.6
Panties; half-slip; broadcloth, long-sleeve blouse; single-breasted suit jacket; A-line, knee-length skirt; pantyhose; thongs/sandals
1.0
Briefs; t-shirt; broadcloth, long-sleeve shirt; long-sleeved, round-neck sweater; thick, straight, long, loose trousers and belt; calf-length socks; hard-soled shoes
1.0
Flannel, long-sleeve, long nightgown; thick, long-sleeve, wrap, long robe; slippers
1.7
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Personal Factors: Metabolic RateMet: a unit used to describe the energy generated inside the body due to metabolic activity. It is defined as 58.2W/m2 which is the energy produced per unit surface area of an average person, seated at rest: 1 met = 58.2 W/m2
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Metabolic Rates for Typical TasksActivity
Metabolic rate (Met)
Reclining 0.8
Seated, quietly 1.0
Sedentary activity (office, dwelling, lab, school) 1.2
Standing, relaxed 1.2
Light activity, standing (shopping, lab, light industry) 1.6
Medium activity, standing (shop assistant, domestic work, machine work)
2.0
High activity (heavy machine work, garage work) 3.0
© ASHRAE
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Effect of Activity Level
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Physiological Conditions for Thermal Comfort
Esk = 0.00305 [5733-6.99(M-W)-Pa] + 0.42 [(M-W) - 58.2]
Sweat rate
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Predicted Mean Vote• The mean vote of a group of individuals can
be predicted.• The Fanger model of human thermal comfort
enables this. • The model is really only applicable for a body
in thermal equilibrium with it’s surroundings.• PMV is calculated on a 7-point scale from -3
to +3 – so it is directly comparable with TS.
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Comfort Equation (Fanger)
Metabolic heat generation [W/m2]
External work [W/m2]
Dry heat losses [W/m2]:- Convection: C = hc (Ts-Ta)- Radiation: R = hr (Ts-Tr)
Skin evaporation [W/m2]:- Moisture diffusion- Evaporation of sweating
Respiration [W/m2]:- Latent heat loss: Lr- Convective heat loss:
CrLr+Cr=1.72.10-5M(5876-Pa) + 0.0014M(34-Ta)Ts = Body’s mean surface temperature
Tr = Mean (radiant) temperature of surrounding surfaces
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Resultant Temperature - Tres
h = hc + hr
Dry heat loss = Surface convection + Thermal radiation
hc Ta + hr Tr
hc + hr Tres =
In indoor spaces: hc ~ hr :
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Calculating PMV
• When a body is out of equilibrium then thermal strain is experienced, as measured by L:
• The value of L can be used to calculate PMV as follows:
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The complete equation set
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Comfort Zone / Envelope
(7-Point ASHRAE Scale)
hot
warm
slightly warm
neutral (comfortable)
slightly cool
cool
cold
3
2
1
0
-1
-2
-3-3 -2 -1 0 1 2 3
Thermal Sensation
0
20
40
60
80
100
Per
cen
tag
e D
issa
tisf
ied
[%
]
Thermal Sensation Percentage of Dissatisfied
Comfort ‘zone’or ‘envelope’
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Comfort Envelope (ASHRAE Std 55R)
o o
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CIBSE: Recommended Design values for Tres (now Top is used)
Building Space Tres / °C
Hotel Bedrooms (luxury) Public rooms Entrance halls and foyers
24°C 21°C 18°C
Libraries Reading rooms (height >4m) Store rooms
20°C 15°C
Offices General
20°C
Schools and Colleges Classrooms
18°C
Swimming Baths Changing rooms Pool hall
22°C 26°C
Warehouses Working and packing spaces Storage space
16°C 13°C
Tres has been replaced in UK thermal comfort work by the operative temperature (Top).
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ASHRAE (USA): acceptance of adaptation
• Applicable to buildings that are: naturally ventilated buildings, not mechanically cooled, have operative windows.
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BS EN15251: UK and Europe
• Applicable to free-floating buildings PPD=20%
Operative temperature
Weighted running mean ambient temperature
Cat IIICat II
Cat I
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BS EN15251: UK and Europe
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Thermal comfort: an
important factor in satisfaction
and productivity assessment.
ISO 10551 measurement questionnaire
Q.1: How are you feeling at this precise moment?
Q.2: Do you find this . . . ?
Q.3: Please state how you would prefer to be now?
Q4. How do you judge this environment (local climate) on a personal level?
Clearly acceptable
Just acceptable
Just unacceptable
Clearly unacceptable
Q5. Please state your personal tolerance of this environment. In your opinion. Is it . . .?
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POE: Comfort and productivity
• Thermal comfort ranked most important for productivity in all building types.
• Perceived productivity increases with better thermal comfort in all building types.
Source: Leaman and Bordass (2007) Are users more tolerant of green buildings, BR&I, Vol. 35, no. 6, pp 662-673.
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Summary• Thermal comfort is important for well-being
and productivity• Comfort depends on environmental factors
(Ta, Tr, Va, Rh)• Comfort depends on personal factors (Met,
Clo)• Guidelines for indoor comfort are now based
on Top (which replaces Tres) or comfort envelopes