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Thermodynamics: Heat Pump

Heat Pump

A heat pump is very similar to a refrigerator except instead of removing heat from an inside environment and transferring it to an outside environment, it removes heat from an outside environment and transfers it to an inside environment, such as the inside of you a house. The same cycle that is used for a refrigerator is used for a heat pump except it operates in reverse. Refer to the diagram below.

Heat Pump Schematic

Like refrigerators, a heat pump also has a coefficient of performance to show how well it is performing. The coefficient of performance for a heat pump can be calculated using equation 1.

Coefficient of Performance Heat Pump (1)

For a heat pump the coefficient of performance will always be greater than one. In cases that the outside environment very cold than the COP can drop below one. If that happens the heat pump would switch to resistance heating to heat the inside environment. Finally, the coefficient of performance for a heat pump can also be related to the coefficient of performance of a refrigerator by using equation 2.

Coefficient of Performance Heat Pump relation to Coefficient of Performance of a Refrigerator (2)

The coefficient of performance can also be related to U.S. energy efficiency rating (EER) through equation 3.

EER relation coefficeint of Performance Refrigerator (3)

Finally, since a heat pump is a reversed refrigerator it can also be used as an air-conditioner by reversing its cycle. For air-conditioners the coefficient of performance can also be related to U.S. energy efficiency rating (EER) through equation 3.

Typically, the EER would between 8 and 12, and the COP would be between 2.3 and 3.5 for most air conditioners.

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