PMV & PPD

The PMV index predicts the mean response of a larger group of people according to the ASHRAE thermal sensation scale where

+3 hot

+2 warm

+1 slightly warm

0 neutral

-1 slightly cool

-2 cool

-3 cold

The PMV index is expressed by P.O. Fanger as

PMV = (0.303 e^-0.036M + 0.028) L   (1)

where

PMV = Predicted Mean Vote Index

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 at comfort skin temperature and evaporative heat loss by sweating at the actual activity level

PPD - Predicted Percentage Dissatisfied Index

Predicted Percentage Dissatisfied - PPD - index is a quantitative measure of the thermal comfort of a group of people at a particular thermal environment.

http://www.engineeringtoolbox.com/predicted-mean-vote-index-PMV-d_1631.html