Prediction of Thermal Comfort
Home Up Heat Exchange Thermal Comfort Factors Influencing Thermal Comfort Environmental Indices Comfort Zones Prediction of Thermal Comfort Local Thermal Discomfort

 

Prediction of Thermal Comfort

 

6.1 Fanger's Comfort Equation

(5)

where    M = metabolic rate, met

            Icl = cloth index, clo

            v = air velocity, m/s

            tr = mean radiant temperature, oC

            ta = ambient air temperature, oC

            Pw = vapour pressure of water in ambient air, Pa

 

6.2 Fanger's Comfort Chart

Fanger's comfort equation is transformed to produce comfort charts, examples of which are shown in Figures 4 and 5.

 

 

 

 

 

 

6.3 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:

+3 hot

+2 warm

+1 slightly warm

0 neutral

-1 slightly cool

-2 cool

-3 cold

Mathematically, P.O. Fanger expressed PMV as:

(6)

        where                 M = metabolic rate

L = thermal load defined as the difference between the internal heat production and the heat loss to the actual environment for a person hypothetically kept at comfort values of skin temperature and evaporative heat loss by sweating at the actual activity level.

 

6.4 Predicted Percentage Dissatisfied (PPD) Index

 

PPD is a quantitative measure of the thermal comfort of a group of people at a particular thermal environment. Fanger related the PPD to the PMV as follows:

(7)

 

 

6.5 Lowest Possible Percentage Dissatisfied (LPPD) Index

The LPPD is a quantitative measure of the thermal comfort of a room as a whole for a group of people in a thermally non-uniform environment. It is more useful for large rooms than for small one. As a recommended design target, LPPD is not to exceed 6%.