Subsection 10.6.10 Heat Pump and Refrigerator
Heat flows from hot body to cold body naturally. The reverse process, however, cannot occur by itself. To transfer heat from a low temperature region to a high temperature requires special devices called refrigerators or heat pump. Heat pumps transfer heat from a low temperature medium to a high temperature one. Refrigerators and heat pumps are essentially the same devices; they differ in their objectives only. Refrigerator is to maintain the refrigerated space at a low temperature. On the other hand, a heat pump absorbs heat from a low temperature source and supplies the heat to a warmer medium. Heat pumps and refrigerators are heat engine working in backward direction. They transfer heat from cold to hot.
Subsubsection 10.6.10.1 Coefficient of Performance, COP:
The performance of refrigerators and heat pumps is expressed in terms of the coefficient of performance (COP) which is defined as
\begin{equation*}
COP = \frac{benefit}{cost}
\end{equation*}
\begin{equation*}
COP_{R} = \frac{Q_{c}}{W}, \quad \text{ for Refrigerator}
\end{equation*}
\begin{equation*}
COP_{HP} = \frac{Q_{h}}{W}, \quad \text{for Heat Pump}
\end{equation*}
Since \(Q_{h} =Q_{c}+W,\) it can be seen that
\begin{equation*}
COP_{HP}= COP_{R}+1
\end{equation*}
