Development of a High Efficiency Ceiling Fan

Abstract

The potential of ceiling fans to improve comfort\nduring the cooling season is well documented (Rohles\net al.. 1983; Fairey et al.. 1986). There are at least\ntwo cases: In the first where air conditioning is unavailable,\nadding ceiling fans may significantly improve\nbuilding comfort and health although actually\nincreasing energy use. However, the more common\ncircumstance is where ceiling fans are used with the\nobjective of providing a higher cooling system\nthermostat set point with acceptable comfort. Fans\ncan also potentially avoid the use of air conditioning\nduring "swing" seasons. Although studies commonly\nsuggest a 2-6OF increase in the thermostat set point,\ndata from 386 surveyed Central Florida households\nsuggests that although fans are used an average of\n13.4 hours per day, no statistically valid difference\ncan be observed in thermostat settings between\nhouseholds using fans and those without them (James\net al., 1996). Part of this may be due to the lack of\nsufficiently wide air distribution coverage within\nrooms (Rohles et al, 1983; Sonne and Parker, 1998).\nStudies touting potential cooling savings of up to\n40% have usually been sponsored by fan manufacturers\n(eg. A.D. Little, 1981). These often make unrealistic\nassumptions such as presuming that occupants\nare within four feet of a fan with only one fan in\nuse and a 6°F elevation of the thermostat setting. An\nenvironmental chamber study by Consumer Reports\nshowed that the long-reported de-stratification\nbenefits when heating are largely unsubstantiated\n(Consumer Reports. 1993). Thus. benefits from\nceiling fans are only to reduce cooling needs and this\nis completely contingent on sufficient changes in\ninterior comfort to warrant raising of the cooling\nthermostat.\nTwo other factors must be taken into account in\nassessing the benefits of fans: their actual energy use\nand the added internal heat gains produced by the\nfans during operation. The measured electrical demand\nof ceiling fans varies between 5 and 115 Watts\ndepending on model and speed selection. A power\ndemand of 40 W at medium speed is probably typical\n(Chandra, 1985). Thus, a fan used for six months of the year would use 175 kwh. With 4.3 ceiling fans in\nan average Florida home, this amounts to about 800\nkwh of fan energy consumption --about 5% of total\nelectricity use. Also, all of the energy use of fans is\neventually converted to heat within the home which\nmust eventually be removed by ventilation air or the\ncooling system.