The Effect of Air Velocity on Comfort at Moderate Activity Thermal Levels

The primary purpose of this study was to determine if the thermal comfort of subjects working at a moderate level of activity (2.3 MET) was improved or adversely affected by air motion. second purpose of the study was to compare experimental results with the predicted responses given by the Fanger thermal comfort model and the Azer thermal response model. Tests were conducted with subjects wearing 0.65 clo and 1.09 clo of clothing insulation and with relative air velocities of approximately 40 fpm (0.20 m/s) and 240 fpm (1.2 m/s). The air temperature was varied over a range selected to include the optimum comfort level. The results indicate that comfort is as good, if not better, with the higher air velocity. The experimental results showed a higher sensitivity to temperature than predicted by either model. INTRODUCTION Previous studies (Konz et alo 1983; Mclntyre 1978; Rohles et al. 1974, 1982, 1983; Rosen and Konz 1982) have shown that the use of fans has no adverse effect on the level of comfort that can be attained, and they may actually enhance comfort in some situations. These studies were all conducted with sedentary subjects. However, many people spend a good deal of time at moderate activity (1.5 MET to 2.5 MET), which is certainly more typical of industrial workplaces and probably many office and home environments also. It was felt that moderate activity levels actually represent a better application for fans than sedentary activity levels for at least two reasons. First, these higher activity levels require fairly low dry-bulb temperatures to maintain thermal neutrality with no air motion, particularly if much clothing must be worn, It may not be practical, or economical, to provide these conditions in many circumstances. Second, moderate activity implies an active person. The adverse sensations produced by air motion are probably less noticed by the active person. Moderate activity levels, therefore, should allow tolerance of higher air velocities than will be accepted by sedentary subjects. The primary purpose of this study was to determine if air motion affected comfort when subjects were working at a moderate activity level. A second objective was to compare the experimental data collected to the thermal models of Fanger (1970) and Azer (1977). EXPERIMENTAL DESIGN AND PROCEDURES This project had only a limited budget and thus was commensurately limited in scope. It was exploratory in nature and was not intended to yield definitive mathematical relationships for comfort. A considerable amount of additional data will be required to develop such relationships. One activity level (2.3 MET) was used for all tests. Two clothing insulation values (0.65 clo and 1.09 clo) and two air motion conditions for each value of clothing insulation were used. Dry-bulb temperature was varied for each clothing-air motion combination to provide conditions that ranged from cooler than to hotter than conditions required for thermal neutrality. B. W. Jones is Associate Professor and Director, Institute for Environmental Research, K. Hsieh is graduate research assistant, Department of Mechanical Engineering, Kansas State University; H. Hashinaga is associate manager, Gas Equipment R & D Department, Osaka Gas Company. 761 ©ASHRAE. All rights reserved. Courtesy copy for SSPC 55 Committee to exclusively use for standards development. May not be distributed, reproduced nor placed on the internet.