A/C Energy Savings: Turning It Off While You’re Away IS Efficient

June 25, 2014
Ross and Witmer

As summer arrives, you’ll hear lots of helpful hints to improve A/C energy savings. Some of them are actually true. One that isn’t, however, is the old idea that it’s more energy efficient to leave the air conditioner on all day while you’re gone than to turn it off and let the house heat up. The premise is that an A/C running continuously uses less electricity maintaining a consistent indoor temperature than it does if it has to cool down a hot house after being shut off all day. The actual electricity consumption figures, however, don’t support this notion. Here’s why A/C energy savings are actually improved by turning the unit off for long spans when the house is unoccupied:

  • Air conditioners move heat energy out of the house most efficiently when they are running extended On cycles, such as when the unit is turned on to cool a house down from 85 degrees to 75 degrees. The more numerous, shorter On/Off cycles necessary to maintain small variations in temperature when running all day long use more electricity.
  • A critical part of air conditioning is humidity reduction. Dry air holds less heat energy and enhances A/C cooling performance. Humidity extraction at the air conditioner evaporator coil is more efficient when the unit runs sustained On cycles. Since an A/C must run for several minutes before any humidity extraction begins, short cycles during the day don’t remove humidity as effectively.

Air Conditioner Facts

Here’s how the actual numbers look. Researchers compared electricity consumption of an air conditioner running all day long to maintain an indoor temperature of 78 degrees versus a unit that stays off all day, then is turned on and cools a hot house from 87 degrees down to 77.5 degrees in one hour. Results showed the A/C left on all day consumed over three times more electricity than the unit left off and then run for a single hour to achieve the same indoor temperature.

During very hot weather, however, it probably does make sense to keep your A/C turned on at a higher temperature – perhaps 85 degrees – all day. Some cooling systems have a very difficult time recovering to a comfortable temperature if it gets above 90-95 degrees inside a house during the day. This heat also can damage home fixtures, food and personal belongings.

For more information about improving A/C energy savings in the Charlotte area, contact Ross & Witmer today.

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