Within a refrigeration system, the inside of the refrigerator is known as the cold-air reservoir, while the area surrounding the outside of the refrigerator is the hot-air reservoir. A refrigerator works by sucking the heat out of the cold-air reservoir and dumping it in the hot reservoir. The work to do this process is supplied by an electricity-powered compressor that is connected to a wall outlet.
The efficiency of a refrigeration system can be estimated with a ratio known as the coefficient of performance, or COP. The COP is given by the benefit divided by the cost, or
Where Qc is the heat that flows outward from the cold reservoir and W is the work supplied from a wall outlet. This equation can also be expressed in terms of the temperatures Th and Tc, the temperatures of the hot and cold reservoirs respectively. In terms of Th and Tc, the COP is given by
COP≤1ThTc-1=TcTh-Tc
This equation shows that the closer Th and Tc are to each other, the higher the COP of the refrigerator. This makes sense: the smaller the difference in temperature between the hot and cold reservoirs, the less energy is required to transport heat between them. A refrigerator’s COP is dependent on its operating conditions, which can be influenced in the following ways:
COP=TcTh-Tc=255298-255=5.93
Compare this value to the COP of a refrigerator stored in a location that is ten degrees warmer than room temperature, or 308 K:
COP=TcTh-Tc=255308-255=4.81
