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%.