A vapor compression heat pump is driven by a power cycle having a thermal efficiency of 25%. For the heat pump, refrigerant 12 is compressed from saturated vapor at 2.0 bars to the condenser pressure of 12 bars. The isentropic efficiency of the compressor is 80%. Saturated liquid enters the expansion valve at 12 bars. For the power cycle, 80% of the heat rejected by it is transferred to the heated space which has a total heating requirement of 500 kJ/min. Determine the power input to the heat pump compressor.
The following data for refrigerant 12 may be used.
|
Pressure
Bar
|
Temperature
0C
|
Enthalpy,
kJ/kg
|
Entropy, kJ/kg.K
|
|
|
|
Liquid
|
Vapor
|
Liquid
|
Vapor
|
|
2.0
|
–12.53
|
24.57
|
182.07
|
0.0992
|
0.7035
|
|
12.0
|
49.31
|
84.21
|
206.24
|
0.3015
|
0.6799
|
Vapor specific heat at constant pressure = 0.7 kJ/kg. K