3231 -- Extending the Summer Comfort Envelope with Ceiling Fans in Hot, Arid Climates PDF

The purpose of this study was to determine if the summer comfort zone, as given in ASHRAE Standard 55-1981, Thermal Environmental Conditions for Human Occupancy, could be expanded to include conditions obtained in hot, dry climates with a combination of evaporative cooling and the air motion obtained with ceiling fans. The evaporative cooler can provide acceptable cooling for portions of the year in hot, dry climates but is not satisfactory for periods of higher wet-bulb condition& The ceiling fan might extend the period of time that an evaporative cooler could be used.

A study conducted by Rohles, Konz, and Jones (1983) showed that ceiling fans could effectively extend the comfort range to as high as 85°F(29.4°C) and 50% RH. However, the Kansas State University study only investigated conditions at 50% RH, and it did not test conditions higher than 85°F.

This study was conducted on 96 human subjects in the spring of 1986 and attempted to determine the upper limits of the comfort envelope (not just along the 50% RH line) with the higher velocities attained with ceiling fans.

The study shows that velocities between 90 fpm (.46 m/s) and 200 fpm (1.02 m/s) that are provided by a ceiling fan can extend the time that a direct evaporative cooler can be used for thermal comfort in Phoenix. This amounts to extending the comfort period for 995 hours, or 34% of the time in which some form of cooling is required. With the indirect evaporative cooler, it is theoretically possible to provide cooling for the entire season by using the highest air velocities. However, these higher air velocities will not be acceptable to all people.

This study also suggests that the upper comfort limit proposed by Rohles et al. (1983) may be extended for humidities lower than 50% RH, but reduced for higher humidities.