Center for the Built Environment

Air temperature thresholds are investigated and proposed for acceptable comfort in air-conditioned buildings. Using the ASHRAE database of field studies in which acceptability votes were obtained from occupants, it is shown that within the thresholds, the acceptability is indistinguishable. Therefore, there is little gain from conditioning spaces to an “optimum” air temperature and a significant energy savings. However beyond the thresholds, there is a significant drop-off in acceptability. Ideally, air-conditioning would be used only when the environmental conditions are beyond the thresholds. The use of ceiling fans or personal environmental control systems broadens the threshold range. Thresholds are determined for both air-conditioned and ventilation-cooled buildings in the database. The equally-acceptable range between the thresholds is 8 – 10 K wide in both types of buildings. It is possible that a perception of reduced air quality in warm environments could impose an upper temperature threshold. Perceived air quality (PAQ) is examined in two laboratory studies done at air temperatures from 18 - 30 deg C. PAQ is seen to be closely correlated to thermal comfort rather than temperature; as long as thermal comfort is maintained by the air movement, PAQ will be acceptable. Relationships between temperature thresholds and productivity, operating setpoints, and energy use are also discussed.