The Coefficient of Performance (COP) is a performance rating that describes the effectiveness of heat pumps, refrigerators, or air conditioners. It is defined as the ratio of useful heating or cooling provided to work (energy) required. The COP is highly dependent on operating conditions, especially absolute temperature and relative temperature between sink and system, and is often graphed or averaged against expected conditions. The COP is typically used to describe a heat pumps heating performance while its operating in heating mode, but it can also be used to describe cooling performance for air conditioners.
For a refrigerator, the COP is defined as the heat removed from the cold reservoir divided by the work done to remove the heat (i.e., the work done by the compressor) . The relevant ratio is the larger this ratio, the better the refrigerator. The COP for heating and cooling are different because the heat reservoir of interest is different. When one is interested in how well a machine cools, the COP is the ratio of the heat taken up from the cold reservoir to input work. However, for heating, the COP is the ratio of the magnitude of the net heat added to the hot reservoir.
