CeilingFans

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.