ASHRAE Standard 55

As mentioned earlier, occupant complaints of discomfort in build­ings may be caused by uncomfortable temperatures or extreme humidity levels. In 1966, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) created a standard to quantify thermal comfort. Entitled ASHRAE Standard 55-1966, “Thermal Environmental Conditions for Human Occupancy,” this document introduced a definition for thermal comfort that states: “Thermal comfort is that condition of mind that expresses satisfaction with the thermal environment.” Standard 55 specified the appropriate environment that would lead to thermal comfort for indoor inhabitants of building spaces. Based on summer and winter temperatures with indoor relative humidity as the variable, the 1992 edition of ASHRAE Standard 55 specifies that the optimal comfort range for indoor relative humidity is between 30 and 60 percent. The standard also speci­fies that to decrease the possibility of discomfort due to low humid­ity, dew-point temperature in occupied spaces should not be less than 37°F (З^).1

The upper range of the comfort zone for summer use will be tol­erable for most lightly clothed adults until the relative humidity rises above 60 to 65 percent. At that condition, discomfort will be experienced by many building occupants because of their inability to dissipate metabolic moisture. Increases in air velocity are bene­ficial under these conditions, but velocities above about 70 ft/min generally will result in unpleasant working conditions because of drafts, blowing papers, and so on.2