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Development of a High Efficiency Ceiling Fan
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Date
2000
Journal Title
Journal ISSN
Volume Title
Publisher
Energy Systems Laboratory (http://esl.tamu.edu)
Texas A&M University (http://www.tamu.edu)
Texas A&M University (http://www.tamu.edu)
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.