THE GENERALLY accepted view that an attic fan will reduce your air-conditioning bills has been challenged by new research by the National Bureau of Standards and the Department of Energy.
An attic fan may cost more to operate than you save on the air conditioning, according to the study, just released at a seminar here sponsored by the National Bureau of Standards and the Department of Energy.
But a whole-house fan, used when the outside temperature is below 82 degrees, can bring substantial savings in the summer cooling bills, the study found.
In tests last summer at houses where extra attic ventilation was installed, NBS researchers found a less than 3 per cent drop in the heat that eventually had to be dissipated by air conditioning.
"The reduction in energy consumption of a properly sized air conditioner was . . . offset by the energy consumption of the power vent," they reported.
The researchers concluded "that attic ventilation was not an effective energy conservation procedure for these houses which had moderately insulated attics."
The attic fan was a 14-inch model, with a thermostat to turn it on when attic temperatures reached 100 degrees and off at 85 degrees. The researchers report the thermostat didn't work, so the fan ran more than it should have.
The attic fan was tested on sunny days with light breezes and temperatures above 90 degrees. In one house, the fan cooled the attic about as well as turbine or ridge ventilation, but in another house, neither turbine nor soffit venting were as effective as the fan.
The attic fan helped cool the air conditioning ducts running under the attic floor, thereby making the air conditioner run a little less often. But power attic ventilation was found to have little cooling effect on the houses' living space, and in the long run, consumed more power than it saved.
The report concluded, ". . . Under the test conditions, attic ventilation for these houses was shown to have an insignificant effect on . . . indoor comfort."
For the whole-house ventilation tests, the researchers turned on the air conditioner at 7:45 a.m., and ran it until the outdoor temperature dropped to 82 degrees late in the day. Then they shut off the air conditioner, opened all the whole-house fan on high speed. It ran constantly until 4 a.m., when a clock timer shut it off.
On days the average temperature exceeded 75 degrees, alternating use of the whole-house fan with the air conditioner alone. The hotter the day, the lower the savings were.
The researchers said homeowners in the norther half of the U.S. could reduce summer energy costs by using whole house ventilation with air conditioning. "Since a whole-house fan consumes approximately one tenth the energy of a central air conditioner, the energy savings will be substantial."
But because of regional differences in weather conditions, the researchers hesitate to apply their Houston findings to all parts of the country.
"These results are based on very limited data. Further testing to evaluate the energy savings of whole house ventilation is needed," they cautioned.
Using a whole-house fan to ventilate your house with outside air that may be as warm as 82 degrees may not seem like a cool idea. But, the researchers say, when the air circulates, you feel cooler than you actually are.
"This air movement (from whole-house fans) . . . produces a sensation of comfort even though the indoor temperature is elevated above the normal comfort point for still air."
For the record, the whole-house fan used by in the tests was a two-speed, 42-incher, rated at 1/3 horsepower and 250 watts.
The tests were made in three identical houses in a suburb of Houston, Texas. The house were new, woodframe ramblers with brick veneer outer covering. Each had a gable roof with light brown shingles, and each was cooled by a 2 1/2-ton central air conditioner.