Saving Energy? No Sweat
Greentips: July 2009
When temperatures rise, people instinctively resort to air conditioning. But that comfort comes at a price: in 2005, for example, 91.4 million U.S. households consumed 258 billion kilowatt-hours of electricity running air conditioners, according to the Energy Information Administration. That translates to about $24 billion in energy costs and 171 million tons of global warming emissions.
To keep both you and the planet cooler, consider these energy-efficient alternatives:
Evaporative coolers, also known as “swamp” coolers, use a fan to draw outside air through water-saturated pads, making the incoming air 15ºF to 40ºF cooler. They work best in dry or desert climates with little humidity. Two-stage coolers, which first pass the air through a heat exchanger, are effective in areas where temperatures reach or exceed 100ºF. According to the U.S. Department of Energy (DOE), evaporative coolers use about 75 percent less energy than a central air conditioner and cost half as much to install, but because they can consume up to 15 gallons of water per day, their use might be restricted during water shortages.
Whole-house fans installed in the ceiling pull cool evening and morning air into the house, while forcing hot air out through the attic. They use just one-tenth the electricity of a comparably sized air conditioner. Because of the heavy volume of air flow, you may need to install additional attic vents.
Ceiling fans help circulate the air, making it feel cooler. You can even run a ceiling fan in conjunction with an air conditioner set 4ºF higher than you otherwise would, with no change in comfort and less energy use overall (especially when using an Energy Star-rated fan, which is up to 20 percent more efficient than a standard model). To move air effectively, fan blades should be 10 to 12 inches from the ceiling.
Passive cooling strategies are electricity-free ways to reduce the amount of heat entering your home. For example:
- Trees—Planting deciduous trees on the south side of your home can help block sunlight in the summer but allow it through in the winter. According to the DOE, trees can reduce the surrounding air temperature as much as 9ºF, and the air within their shade as much as 25ºF. Keeping an air conditioner in full shade can increase its efficiency up to 10 percent.
- Solar screens—This window-covering fabric blocks up to 90 percent of incoming solar heat without obscuring your view.
- Awnings—These can reduce solar heat gain by 77 percent on west-facing windows, according to the DOE.
If you do decide an air conditioner is necessary, buy an Energy Star-rated model sized for your needs. Switching every room air conditioner sold in the United States to Energy Star models would avoid 650,000 tons of global warming emissions—the equivalent of taking 115,000 cars off the road.
