///////////////////////////////// EcoSpection Serving the greater Houston area and surrounding coastal counties
	Are ceiling fans really energy efficient?
	CEILING FANS Technology Description Use of natural ventilation and fans for cooling is a time-honored means of reducing air conditioning energy needs in southern climates (Givoni 1976). Optimally, the building is designed for natural ventilation and ceiling and/or portable fans provide increased localized air movement to promote thermal comfort. Since alteration of window location is beyond the realm of weatherization improvements, addition of ceiling or portable fans are appropriate measures to decrease energy use. Also, addition of a screen front door may greatly enhance ventilation and provide additional occupant comfort. There are at least two modes in which ceiling fans can be used. 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 commonly considered case 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. Two other important 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 about average (Char&a 1985). Thus, a fan used for six months of the year would use 175 kWh. Also, all of the energy use of the fan is eventually converted to heat within the home which must eventually be removed by ventilation and or the cooling system. Both of these energy losses must be properly accounted for in order to properly determine the net energy savings from fans. Ceiling and portable fans are readily available and their characteristics are well understood. Although the technology is mature, improvement of fan motor efficiency may be a possible goal. Currently, manufacturers do not provide information on energy consumption of fans at various speeds, nor their efficiencies in air circulation. This could be made readily available by simple tests which would determine fan power consumption and achieved air velocities under reference conditions. Performance /Field Studies The ability of ceiling fans to improve comfort during the cooling season is well documented (Rohles et al. 1983; Fairey et al. 1986). Although studies commonly suggest a 2 - 6 deg. F increase in the thermostat set point, data from 384 surveyed Central Florida households suggests that only the low end of this range can be justified (Vieira and Parker 1991).’ Studies touting potential cooling savings of up to 40% have usually been sponsored by fan manufacturers ( e.g.A .D. Little 198 1). These often make unrealistic assumptions such as presuming that occupants are within four feet of a fan at all times with only one fan in use, and a 6 deg. F elevation of the thermostat setting. A recent environmental chamber study by Consumer Reports showed that the long reported destratification benefits when heating are largely apocryphal (Consumer Reports 1993). Thus, benefits from ceiling fans can only reduce cooling needs. Florida Solar Energy Center A simulation estimating the savings of ceiling and whole house fans was performed by the Florida Solar Energy Center (FSEC). The study assumed that installation of ceiling fans allowed the building cooling thermostat setting to be elevated by 2 deg. F when the occupants were home. Such an analysis, performed for Miami, showed the measure to produce net cooling energy savings (less that of the fans themselves) of 12% or 735 kWh (Parkere t al. 1992). At $O.O5/kWh the payback from the savings from ceiling fans would approach the useful life of the fans (10 years). Utility peak savings may be low or even negative. Of course, results will likely vary significantly by climate. Also, realized savings may be significantly lower since recent interview data collected from low income homes in South Florida suggests that many ceiling fans are used 24-hours a day all year whether cooling is needed or not. Other Considerations Although fans have been used in homes for generations and simulations exist to estimate their benefit, actual savings from their use as an energy efficiency measure is undemonstrated. Adding ceiling or portable fans will likely do more to improve cooling comfort than it will to produce energy savings. This is due to use habits and the potential “take back” effect (homeowners often opt for greater comfort rather than a higher cooling set point). Addition of ceiling or portable fans to homes is a readily available weatherization measure. However the applicability may be effected by the pre- existing saturation of fans. FSEC’s survey of 384 existing households found only 5% of homes did not have ceiling or portable fans with the average home possessing 4.5 fans. Data from the EIA for two states in the southeast shows that ceiling fan saturation is greater than 60% for much of weatherization measure. However the applicability may be effected by the pre- existing saturation of fans. FSEC’s survey of 384 existing households found only 5% of homes did not have ceiling or portable fans with the average home possessing 4.5 fans. Data from the EIA for two states in the southeast shows that ceiling fan saturation is greater than 60% for much of Texas and greater than 40% for most of North Carolina. ’ Estimates of Savings Potential The sources reviewed indicate potential savings from installation of ceiling fans of from between 10 to 20 percent of the cooling energy use. The cost of fan installation assumes use of 4 fans per home at an installed cost  of $100 per fan. This may vary considerable from house to house and geographical location, Also assumed are an electric rate of $.08/kWh and useful life of 10 years. Reference Oak Ridge National Laboratory http://weatherization.ornl.gov/pdf/ORNL_CON_437.pdf Fan Sizing A common rule of thumb is to use a 36" fan for rooms up to 150 square feet, a 42" fan for rooms up to 300 square feet, and a 52" fan for rooms up to 450 square feet. For larger rooms, use two fans.