Development of a High Efficiency Ceiling Fan

Abstract

The potential of ceiling fans to improve comfort during the cooling season is well documented (Rohles et al.. 1983; Fairey et al.. 1986). There are at least two cases: In the first where air conditioning is unavailable, adding ceiling fans may significantly improve building comfort and health although actually increasing energy use. However, the more common circumstance is where ceiling fans are used with the objective of providing a higher cooling system thermostat set point with acceptable comfort. Fans can also potentially avoid the use of air conditioning during "swing" seasons. Although studies commonly suggest a 2-6OF increase in the thermostat set point, data from 386 surveyed Central Florida households suggests that although fans are used an average of 13.4 hours per day, no statistically valid difference can be observed in thermostat settings between households using fans and those without them (James et al., 1996). Part of this may be due to the lack of sufficiently wide air distribution coverage within rooms (Rohles et al, 1983; Sonne and Parker, 1998). Studies touting potential cooling savings of up to 40% have usually been sponsored by fan manufacturers (eg. A.D. Little, 1981). These often make unrealistic assumptions such as presuming that occupants are within four feet of a fan with only one fan in use and a 6°F elevation of the thermostat setting. An environmental chamber study by Consumer Reports showed that the long-reported de-stratification benefits when heating are largely unsubstantiated (Consumer Reports. 1993). Thus. benefits from ceiling fans are only to reduce cooling needs and this is completely contingent on sufficient changes in interior comfort to warrant raising of the cooling thermostat. Two other factors must be taken into account in assessing the benefits of fans: their actual energy use and the added internal heat gains produced by the fans during operation. The measured electrical demand of ceiling fans varies between 5 and 115 Watts depending on model and speed selection. A power demand of 40 W at medium speed is probably typical (Chandra, 1985). Thus, a fan used for six months of the year would use 175 kwh. With 4.3 ceiling fans in an average Florida home, this amounts to about 800 kwh of fan energy consumption --about 5% of total electricity use. Also, all of the energy use of fans is eventually converted to heat within the home which must eventually be removed by ventilation air or the cooling system.