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Window AC getting more efficient  

Window AC getting more efficient

A room or window air conditioning unit can be an energy-efficient option.

Energy Efficiency: Heating, Cooling, Ventilation

Martin Holladay, senior editor with Green Building Advisor and Taunton Press, writes a blog called “Musings of an Energy Nerd.” One of his recent posts relates to the efficiency of window air conditioning units. Here is a sampling of his musings on window air conditioners vs. central air:

Window-mounted air conditioners (also called room air conditioners) aren’t particularly efficient; the best available models have an EER of about 10 or 11. Central air conditioners (also called whole-house air conditioners or split-system air conditioners) are significantly more efficient; it’s possible to buy one with an EER of 14 or even 15.

So if you care about energy efficiency, you should use a central air conditioner, not a window air conditioner — right? Well, not necessarily.

According to the American Council for an Energy-Efficient Economy (ACEEE), the electricity used for home air conditioning represents almost 5 percent of all the electricity produced in the United States. So if you are going to air condition your house, it would appear to make sense to buy the most efficient unit you can find. Find information and tips on air conditioners at ACEEE.

Window units vs. central air conditioning
Even though central air conditioners are more efficient than window-mounted air conditioners, homes equipped with window-mounted air conditioners use less energy for cooling than homes with central air conditioning.

This may seem surprising, but consider this: Homes with central air conditioning usually maintain lower temperatures in more rooms than homes with window-mounted air conditioners. Holladay says that homes with window-mounted air conditioners are energy misers. He says there are several reasons:

  • People living in homes with central air conditioning tend to keep every room in the house cool — even unoccupied rooms — while people living in homes with window-mounted air conditioners are more likely to just cool one or two rooms.
  • Central air conditioners often have ducts located in unconditioned attics. Research has shown that air conditioning systems with ducts in unconditioned attics have duct losses amounting to about 20 percent of the air conditioner’s cooling output.
  • Window air conditioners are often noisy, so homeowners remember to turn them off when they leave a room. By contrast, some homeowners with central air conditioning often leave their air conditioning system on all day, even when the home is unoccupied. As explained in an article by Brian Palmer, “The quiet and unobtrusive functioning of central air conditioners ... can lead to accidental overuse.”

In addition, Holladay suggests:

  • Efficient equipment is no bargain if it encourages waste.
  • Two or three window-mounted air conditioners cost less to install than central air conditioning.
  • Bad ductwork is the Achilles’ heel of central air conditioning systems. If you have central air conditioning, be sure to seal all of the seams in your ductwork and insulate ducts well.
  • If you are designing a new home, be sure to locate all ductwork inside of the home's conditioned envelope.
  • If you aren’t home, turn off your air conditioner.
  • When you’re sleeping, you may only need a 6,000 Btu/h air conditioner to cool your bedroom. It’s wasteful to use a 2-ton central air conditioner for such a small load.
  • If you use one or two window-mounted air conditioners instead of central air conditioning, pat yourself on the back. You probably have a lower carbon footprint than your neighbors who have high-SEER central air conditioners.
  • The most efficient way to air condition your house is probably with ductless minisplit units. The only problem with this approach is the high cost of the equipment. However, if you have a new superinsulated house, and if ductless minisplit units can provide both heating and cooling, then these units may be a good, low-cost solution.

Read his entire post.

For more information, check out ENERGY STAR-qualified room air conditioners  (buying, general information).

P.S. Your electric cooperative reminds you that a geothermal heating and cooling system is an extremely efficient way to both heat and cool your home. Contact your cooperative for more details.


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