Coefficient of Performance

coefficient of performance [¦kō·ə′fish·ənt əv pər′fȯr·məns]

(thermodynamics)

In a refrigeration cycle, the ratio of the heat energy extracted by the heat engine at the low temperature to the work supplied to operate the cycle; when used as a heating device, it is the ratio of the heat delivered in the high-temperature coils to the work supplied.

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coefficient of performance

1.In a heat pump, the dimensionless ratio of heat produced to the energy supplied.

2. In a refrigerating unit, the dimensionless ratio of the heat removed to the energy expended in removing it.

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Coefficient of Performance 

of a refrigerating machine, a dimensionless quantity—usually greater than unity—that characterizes the efficiency of the operation of a refrigerating machine. The coefficient of performance (COP) of a refrigerating machine is the ratio of the machine’s refrigerating capacity to the amount of energy expended or work performed per unit time in carrying out the machine’s refrigeration cycle. The COP is determined by the type of refrigeration cycle on which a machine operates and by the efficiency of the machine’s main components; for a given machine, it depends on the temperature conditions under which the machine operates.

A distinction is made between the theoretical COP and the actual COP of a refrigerating machine. In particular, the theoretical COP of an ideal vapor-compression machine operating on the reverse Carnot cycle is independent of the type of refrigerant used and is given by the expression ε_c = T₀/(T – T₀), where T₀ is the absolute temperature of the object to be cooled (that is, the boiling point of the refrigerant) and T is the absolute temperature of the environment (that is, the condensation temperature of the refrigerant). At a given environmental temperature T, the more energy expended per unit of refrigeration obtained, the lower the temperature T₀ of the object to be cooled. The temperature T₀ characterizes the thermodynamic efficiency of the refrigeration.

The theoretical COP for all other refrigeration cycles does not exceed ε_c for machines operating under the same temperature conditions. The COP of a real refrigerating machine is always less than the theoretical COP.