Experimental Performance Comparison of R134a and R1234yf Automobile Heat Pump Systems

This study investigates comparative experimental performance of an air-source automotive heat pump (AHP) system using a fixed capacity swash plate compressor for the refrigerants R134a and R1234yf, an alternative refrigerant for automotive air conditioning (AAC) systems with a low global warming potential. For this aim, an experimental AHP system was developed from the original components of an AAC system belonging to a compact car. The experimental system was equipped with a reversing valve to operate it in heat pump mode and second thermostatic expansion valve. The temperatures of the refrigerant and air streams at the inlet and outlet of each critical component were measured by type-K thermocouples. The refrigerant pressures were measured by pressure transmitters and refrigerant mass flow rate was measured by a Coriolis mass flow meter. The compressor speed and the torque applied to the compressor shaft were continually monitored. For each refrigerant, the AHP system was tested at six different compressor speeds between 800 and 2800 rpm with intervals of 400 rpm. For each refrigerant and compressor speed, the temperatures of the air streams at the inlets of the condenser and evaporator were both maintained simultaneously equal to four different values, namely 0, 5, 10 and 15°C. Using experimental data, properties of each refrigerant were obtained from REFPROP software. Then, the heating capacity and power absorbed by the refrigerant in the compressor were evaluated from the conservation of energy principle. Furthermore, the total power inlet to the system, coefficients of performance for heating based on compressor power and total power inlet, conditioned air stream temperature and compressor discharge temperature were also determined. It was found that the AHP system using R1234yf provided on average 9.9°C lower conditioned air stream temperatures, 18.2°C lower compressor discharge temperatures and 20.7% less heating capacities compared to the AHP system with R134a. Furthermore, the R1234yf AHP system yielded on average 14.9% less compressor power and 9.0% lower coefficient of performance based on compressor power. These results reveal that the AHP systems using R1234yf require higher compressor capacities as well as condenser and evaporator heat transfer areas to provide the same heating capacity.