Refrigerators and Heat Pumps are RESERVED HEAT ENGINES.

Definition of Refrigerator -

A Refrigerator is a device operating on a cycle which removes heat from a low temperature body and rejects it to a body at high temperature on the expense of external work supplied.

Definition of Heat Pump -

If the objective of the system is to deliver heat energy at higher temperature T1 , then the temperature T2 corresponds to ambient temperature. Such a device is called as Heat Pump.

Coefficient of Performance [ C.O.P.] -

The efficiency of refrigerators and heat pumps is expressed in terms of Coefficient of Performance.

From 1st Law, W = Q1 - Q2………………..(i)

(C.O.P.)Refrigerator = Desired Effect / Energy Input = Q2/W………………..(ii)

(C.O.P.)Heat Pump = Desired Effect / Energy Input = Q1/W……………………(iii)

(C.O.P.)Heat Pump - (C.O.P.)Refrigerator = Q1-Q2/W (From Eqn ii and iii)

= 1 (From Eqn i)

(C.O.P.)Heat Pump- (C.O.P.)Refrigerator = 1