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


4 Environmental Indices


4.1 Operative Temperature


where    to = operative temperature

            ta = ambient air temperature

            tr = mean radiant temperature

            hc = convective heat transfer coefficient

            hr = mean radiative heat transfer coefficient


4.2 Mean Radiant Temperature



where    tr = mean radiant temperature

            ti = temperature of the surrounding surface i, i=1,2,....,n

FoŽ i = shape factor which indicates the fraction of total radiant energy leaving the clothing surface 0 and arriving directly on surface i, i=1,2,...n


4.3 Effective Temperature

Effective temperature (ET*) is the uniform temperature of a radiantly black enclosure at 50% relative humidity, in which an occupant would experience the same comfort, physiological strain and heat exchange as in the actual environment with the same air motion.



Figure 3 Standard Effective Temperature and ASHRAE Comfort Zones