Thermal comfort is affected by environmental and personal factors including air temperature, radiant temperature, air velocity, humidity, clothing insulation, and metabolic heat. The Predicted Mean Vote (PMV) model developed by Fanger predicts thermal sensation on a 7-point scale based on these factors, with a score of 0 indicating neutral comfort. The Percentage of People Dissatisfied (PPD) model relates PMV to the percentage expected to feel thermally dissatisfied, with less than 20% considered comfortable conditions.

1. Parameters Controlling Thermal Comfort
Environmental factors-
Personal factors-
o Air Temperature
o Radiant Temperature- due to heat source in
environment
o Air Velocity
o Humidity
o Clothing Insulation
o Metabolic Heat
❖ Thermal comfort means a constant internal body temperature i.e. 37.2 deg.
❖ Human health is the best and human being is most efficient at a mean daily
temperature of 18 deg C when mean relative humidity is 80% (Sharma, 1977)
Note: Thermal Comfort shall be the requirement to be satisfied by the solar passive systems

2. Heat Exchange of Body with Surroundings
Where,
M = metabolic rate
R = net radiation
Cv = convection (sensible & latent heat losses through respiration)
Cd = conduction (heat loss to the ambient including clothing)
E = evaporation heat loss
ΔS = change in heat stored
o Heat lost by the body should be exactly equal to the excess metabolic heat
generated by the body for proper thermal comfort. This is given by:

3. Measurement of Thermal Comfort- empirical indices
Effective temperature-
Corrected Effective Temperature- including air velocity of 0.1 m/s
It is the temperature of a still saturated atmosphere in the
absence of radiation. It combines the effect of dry air
temperature and humidity. It is measured in deg C.
Where GT is Globe Temperature
Wet Bulb Globe Temperature (WBGT)- combines the effects of air temp, low
temperature radiant heat, and air
movement of still saturated air

4. Operative temperature-
Where,
MRT = mean radiant temperature
hr = radiation heat transfer coefficient
hc = convection heat transfer coefficient
DBT= dry bulb temperature
Tropical summer index-
It is defined as the temperature of still air, at 50% relative humidity, which causes
the same thermal sensation as the given environmental condition.

5. Where,
ta = ambient air temperature (dry bulb temperature in deg)
Pa = Partial vapour in mb
v = air velocity in m/s

7. Thermal Comfort Analysis
Predicted Mean Vote (PMV) model
• Developed by Prof. P. O. Fanger.
• Collected data by subjecting a large
no. of people to different
conditions within a climatic
chamber and having them select a
position on a scale describing their
thermal comfort
• A mathematical model of the
relationship between all the
environmental and physiological
factors considered was then
derived from the data
• Predicts the mean value of the
votes of a large group of persons
on the 7-point thermal sensation
scale.
VALUE SENSATION
+3.0 Hot
+2.0 Warm
+1.0 Slightly Warm
0 Neutral
-1.0 Cool
-2.0 Slightly Cool
-3.0 Cold

8. Contd/-
• Range of scale: -3.0 to +3.0
• Thermally Neutral Environment: 0 PMV Value
• Moving towards positive direction: Warmer side
• Moving towards negative direction: Colder side
• Ideal PMV Range: -0.5 to +0.5
• Used as a standard thermal comfort model in ASHRAE Standard 55 [5] as well
as in ISO Standard 7730:2005
PMV model calculated using 6 primary variables only, which are as follows:
o Rate of metabolism (M)
o Clothing insulation (fcl
)
o Air temperature (ta
)
o Mean radiant temperature (tr
)
o Air velocity (var
)
o Humidity (RH)
Expected
Parameters
Measurable
Quantities

9. Percentage People Dissatisfied (PPD) model
• Although PMV is an important parameter to assess the thermal environment of
an area, it is also crucial to examine whether the people occupying the indoor
space would be satisfied with their thermal environment or not
• Developed by Prof. P. O. Fanger
• Relates the satisfaction of the occupants with the predicted mean vote values
obtained
• Establishes a quantitative prediction of the percentage of thermally dissatisfied
people who feel too cool or too warm
• Depends on PMV value
• Range: 0 to 100%
• All Occupants Satisfied: 0%
• All Occupants Dissatisfied: 100%
• For an environment to be called thermally comforting, at least 80% of the
occupants need to be satisfied.

11. Formula for calculating PMV and PPD

12. Terminologie
s
• PMV – Predicted Mean Vote
• L – Thermal Load on the body of an
occupant (W/m2
)
• hc
– Convective Heat Transfer Coefficient
(W/m2
K)
• var
– Relative velocity of air (m/s)
• ADu
– Dubois Area (m2
)
• va
– Velocity of air (m/s)
• te
– Ambient Temperature (o
C)
• pa
– Water Vapour Partial Pressure (kPa)
• ps
– Partial Vapor Pressure of Saturated
Air (kPa)
• tcl
– Surface temperature of clothing (°C)
• tsk
– External skin temperature (°C)
• PPD – Percentage People Dissatisfied
• tr
– Mean Radiant Temperature (°C)
• ta
– Air Temperature (o
C)
• M – Metabolic Rate (W/m2
)
• W – Effective Mechanical Power (W/m2
)
• H – Sensitive Heat Losses (W/m2
)
• Ec
– Heat exchange by evaporation on
skin (W/m2
)
• Cres
– Heat exchange by convection in
breathing (W/m2
)
• Eres
– Evaporative Heat exchange in
breathing (W/m2
)
• fcl
– Clothing surface area factor
2