A coefficient used in air conditioning, refrigeration, and heat pump cycles as a measure of the performance of the thermodynamic cycles. In refrigeration, the COP is the ratio of the duty of the condenser to the work input to the compressor, whereas in a heat pump the COP is the total heat output as a ratio of the heat equivalent of work required to produce the heating effect. The difference in COP between a heating and cooling system is due to the heat reservoir of interest being different. For a system where cooling is of interest, the COP is the ratio of the heat removed from the cold reservoir to the input work, whereas for a heating system, the COP is the ratio to input work of the heat removed from the cold reservoir together with the heat added to the hot reservoir by the input work. The COP of a refrigeration system usually varies between 3.0 and 9.0 depending on the refrigerant, head and suction pressure of the compressor, and the superheated conditions.