An air conditioner using refrigerant R-134a as the working fluid and operating on the ideal vapor-compression refrigeration cycle is to maintain a space at 22°C while operating its condenser at 1000 kPa.

a. Determine the COP of the system when a temperature difference of 2°C is allowed for the transfer of heat in the evaporator.

COP=13.37

Explanation:

Considering the allowed temperature difference the temperature in the evaporator will be 20°. The enthalpy and entropy at this temperature are obtained from table for the saturated vapor phase:

h_1=261.64 kJ/kg

s_1=0.92254 kJ/kgK

The enthalpy at state 2 is determined from the given condenser pressure and the condition s_2 = s_1 with data from table using interpolation:

h_2=273.18 kJ/kg

The enthalpy at states 3 and 4 is determined from the saturated liquid value for the condenser pressure from table:

h_3=h_4=107.34 kJ/kg

the COP is then:

COP=qL/w

= h_1 - h_4 / h_2 - h_1

=13.37