.3. ASHRAE comfort charts
The American Society of Heating, Refrigeration and Air- conditioning Engineers (ASHRAE) introduced the Effective Temperature (ET) index, which combines air temperature, humidity and air speed in a single index using skin wettedness (w) as a predictor of discomfort. Skin wettedness is defined as the ratio of the actual evaporative loss at the skin surface to the maximum loss that can occur in the same environment, i.e. when the skin is completely wet [21]. This chart suggested the neutral comfort zone at 23.5 1C dry-bulb temperature, 50% relative humidity, and 0.06 skin wettedness (i.e., no sweating) for light clothing. This index was further improved in 1967 to include weather influence until 1981 when mean radiant tempera- ture (MRT) factor is considered [19,20].