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Ask Dr. Knowledge

Are refrigerators like air conditioners?

August 1, 2011

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How similar is the operation of a refrigerator to that of an air conditioner? Could a refrigerator be used as an air conditioner?

The basic principles by which air conditioners and refrigerators work are much the same.

First, a refrigerant gas is compressed, which makes it hot. The hot gas then leaves the compressor and travels through pipes, where heat radiates away, and the gas cools off.

As the gas cools, it turns into a liquid, passes through an expansion valve, and evaporates into a region of lower pressure. With the evaporation, the substance cools - just as your body cools as it sweats. The now-cool gas then passes through other pipes making them cold but warming itself up in the process.

Now the gas is back where it started, and the cycle can begin again.

The process for both air conditioners and refrigerators involves making some pipes cold and some hot. The difference between the two lies in the arrangement of the cold and hot pipes.

In an air conditioner, fans blow air over the cold pipes to emit cool air, and the hot pipes are outdoors, where they discharge heat.

In a refrigerator, the cold pipes are inside the walls and they cool off the interior, while the hot pipes are at the back of the structure. If you touch them, you will feel the heat.

While you can get some momentary relief by standing in front of an open refrigerator door, the cooling it provides to a room is more than offset by the heat it radiates from the back.

So unless you have the back of the refrigerator outdoors, in the long run, a refrigerator with an open door will heat up a room.

Ask Dr. Knowledge is written by Northeastern University physicist John Swain. E-mail questions to drknowledge@globe.com or write to Dr. Knowledge, c/o The Boston Globe, PO Box 55819, Boston, MA 02205-5819.