EXERGY ANALYSIS OF A VAPOR COMPRESSION HEAT PUMP WORKING WITH R12 ALTERNATIVES

In the present work, exergy analysis method is applied to estimate exergy and exergy loss of each component, total exergy loss, dimensionless exergy loss of each component, and exergetic efficiency of vapor compression heat pump for simultaneous cooling and heating applications over a wide range of operating conditions. Varied parameters include evaporation and condensation temperatures, refrigerant type and compressor speed. Five refrigerants namely; R12, R124, R134a, R152a and R290 are used as working fluids. Evaporation temperature ranging from 0 to 10°C is used to achieve the required water supply temperature for chiller systems. Condensation temperature is varied between 50 and 80°C to cover a wide range of applications such as hot water supply, drying, cleaning ... etc. Compressor speed is changed from 750 to 3000rpm. Results showed that the change in compressor speed yields the highest influence on the refrigerant mass flow rate followed by that of evaporation temperature and then by that of the condensation temperature. This leads to that varying of compressor speed can effectively control exergy output of the heat pump. Effect of the evaporation temperature on exergy loss rate and its dimensionless exergy loss of the compressor and expansion device is essential. The exergy loss rate of the expansion device is more sensitive to the condensation temperature followed by the compressor, liquid-suction: neat exchanger, the condenser and the evaporator in that order. However, at higher condensation temperatures, the expansion device and the compressor yield about 47% and 35% of total exergy loss respectively. R290 demands the highest input exergy while R124 needs the lowest required exergy. From high useful exergy point of view, the preferable refrigerants are R290, R152a, R134a, R12 and R124 in that order. At evaporation temperature of 0°C, the maximum exergetic efficiency can be obtained by R152a followed by R12, R124, R134a and finally by R290. However, at evaporation temperature of 10°C, the maximum efficiency value of the VCHP for simultaneous cooling and heating applications is 0.54, 0.53, 0.49, 0.48 and 0.44 for R12, R152a, R124, R134a and R290 respectively. The condensation temperatures ranging from 55°C to 60°C yield the maximum exergetic efficiency for all refrigerants under investigation.