Refrigerator Efficiency

Refrigerators are cyclic vapour-compression devices used to remove heat from a closed space such as the inside of a fridge or room. The second law of thermodynamics led to the expression of the Clasius Statement, which says "It is impossible to construct a device which operates on a cycle and whose sole effect is the transfer of heat from a cooler body to a hotter body [1]". This means a refrigerator cannot be run unless it is driven by an external power source. The efficiency with which they do this is expressed by the coefficient of performance (COPR), a ratio of heat removed to work put in, which can be calculated by:

COPR=Desired output/Required Input = QL/Wnet,inWhere QL is the energy being removed from the refrigerated space, and Wnet,in is the net work done by the refrigeration unit. The coefficient of performance can be greater than 1 (hence why it isn't called an efficiency)The maximum coefficient of performance is given when the temperature of the system to which heat is dispelled is equal to the temperature of the system to be cooled.

[1] Nuclear Power, "Clasius statement of the second law," in Nuclear Power, . [Online]. Available:  https://www.nuclear-power.net/nuclear-engineering/thermodynamics/laws-of-thermodynamics/second-law-of-thermodynamics/clausius-statement-of-the-second-law/. Accessed on: Mar. 14, 2019.

[Image] B. Afework, J. Hanania, K. Stenhouse, J. Donev, "Coefficient of performance," in Energy Education, May. 18, 2018. [Online]. Available: https://energyeducation.ca/encyclopedia/Coefficient_of_performance. Accessed on Mar. 14, 2019.