Window Air Conditioners Reduce Energy Costs
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Window Air Conditioners Reduce Energy Costs

While most people consider high efficiency central air conditioning systems the ultimate in energy efficiency, window-mounted air conditioners or room air conditioners may be more efficient in operation than central AC systems. The best window AC models have an EER (Energy Efficiency Ratio) of about 10 or 11 and central air conditioners have an EER of 14 or 15. This article will discuss the difference in central and window-mounted air conditioners so you can determine which system is best for you.

While most people consider high efficiency central air conditioning systems the ultimate in energy efficiency, window-mounted air conditioners or room air conditioners may be more efficient in operation than central AC systems. The best window AC models have an EER (Energy Efficiency Ratio) of about 10 or 11 and central air conditioners have an EER of 14 or 15.

Air Conditioner Efficiency Ratings

Data indicates that the electricity used for home air conditioning represents almost 5% of all the electricity produced in the United States. There are two ratings used to measure the efficiency of central air conditioners: the Energy Efficiency Ratio (EER) and the Seasonal Energy Efficiency Ratio (SEER). Central air conditioners are rated by both EER and SEER while room air conditioners are rated only by EER.

EER is the cooling capacity of the appliance (in Btu/h) at an outdoor temperature of 95°F divided by the current draw of the appliance in watts. Room air conditioners that use at least 10% less energy than the federal standard are eligible for an Energy Star label. When shopping for a room air conditioner, look for an Energy Star unit with an EER of 10.7 or more.

SEER is the total cooling output (in Btu) over the cooling season divided by the total electrical energy input (in watt-hours) over the cooling season. For typical residential air conditioners, EER equals about 0.875 SEER but it can vary between air conditioner models. If you are looking to replace your central air conditioner, look for an Energy Star unit with a SEER of at least 14.5 and an EER of at least 12.

Some engineers and designers have complained that air conditioner manufacturers design equipment to achieve a high score on the laboratory SEER test, even when some of the solutions used to achieve high test scores result in poor performance or efficiency in the field. According to some experts, problems with the SEER rating system may make EER a more useful measure for comparing the efficiency of central air conditioners.

Window AC versus Central AC

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. A recent study suggests that window AC units use less energy on a per cooling degree day and per square footage basis by a factor of 1.75.

Here are the reasons why window-mounted air conditioners can be more efficient than central air conditioning:

  • Homeowners with central air conditioning cool the entire home, even unoccupied rooms, while people living in homes with window-mounted air conditioners are more likely to cool one or two rooms or just the room they are in.
  • Central air conditioners typically have ducts located in unconditioned spaces such as basements or attics and duct losses can account for up to 20% of the air conditioner’s cooling output.
  • Window air conditioners are often noisy so homeowners notice when they are on and turn them off when they leave a room. Homeowners with central air conditioning often leave their air conditioning system on all day, even when the home is unoccupied.
  • Central air conditioners tend to be oversized meaning that more energy is used to cool the home or the system does not run long enough to provide adequate dehumidification so the thermostat setting is lowered to keep the unit running  longer.
  • While the ratings of the compressor and blower are higher for central air conditioning units, the installed system rating is lowered by poor installation of ductwork, blocked registers, or lack of maintenance.
  • Nighttime cooling loads are small and only needed in bedrooms, around 6,000 Btu/h (1/2-ton of cooling) or less per room; central AC systems must cool the entire home (18,000 to 48,000 Btu/h or 2 ½ to 4-tons of cooling)

Takeaways

Efficient air conditioning equipment does not save money if it encourages waste.

Two or three window air conditioning units cost less to install than central air conditioning.

Bad ductwork is one of the biggest sources of waste in central air conditioning systems. If you have central air conditioning, be sure to seal all of the seams in your ductwork.

Turn off your air conditioner when you are not at home.

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