Center for the Built Environment

Air movement is one of the six main variables determirzing human thermal comfort; air temperature, relative humidity, mean radiant temperature, metabolic rate, and clothing insulation are the others. Recently, HVACde sign in;zovations, energy conservation concerns, and new laboratory data on fan cooling and drafts have brought substantial ~tttention to the issue of acceptable levels of air movement in qO’ice environments. Thermal comjort standards for indoor occupancy include air movement limits that are constructed from often conflicting evidence and are frequently difficult to apply. A primary reason is that, while air movement can provide desirable cooling in "warm" conditions, it can also increase the risk of unacceptably cool drafts. The transition zone from desirable cooling to uncomfortable draft is a complicated function of physics, physiology, and human expectation. This work focuses on air movement for cooling in the expected temperature range, 25.5°C to 28..5°C, of this transition zone. Fifty-four human subjects were given control of the air supply velocity from a desk fan (FAN), a floor-mounted diffuser (FMD). and a desk-mounted diffuser (DMD) single ambient air temperature. The subjects were asked to adjust the air movement as they pleased to make themselves comfortable. These tests encompassed the full temperature range of the "transition zone," 25.5°C to 28.5°C. Physical measurements of the environment were made and subjective votes collected, including thermal sensation, thermal preference, wor.’~ area preferences, personal control preferences, and health characteristics. A model that predicts the percentage of satisfied people (the PS model) as a function air temperature and air movement in warm conditions is proposed.