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%.
