Exergy analysis of heat pump air conditioning systems for pure electric vehicle use with low-GWP refrigerants

The exergy analysis of low-global warming potential (GWP) alternative refrigerants, R1234yf, R152a and R744 for heat pump air conditioning (HPAC) systems used in pure electric vehicles (EVs) is conducted via simulation. The results reveal that the system exergy efficiencies (SEEs) of R1234yf-HPAC and R152a-HPAC under identical cooling or heating capacity are similar due to their close thermodynamic properties. The largest exergy destruction component in R1234yf- and R152a-HPACs is the compressor. While for R744-HPAC, the compressor and expansion valve cause major exergy destruction. Moreover, the results also indicate that the SEE of R744HPAC is at least 20 % lower than that of R1234yf-HPAC when producing identical cooling capacity, while it is on average twice that of R1234-HPAC when producing identical heating capacity. Furthermore, the measures to improve SEE of HPAC systems with different refrigerants are discussed by examining the effects of varying operating conditions. It is suggested to lower compressor speed under both cooling and heating conditions, increase condenser airflow or reduce evaporator airflow of R1234yf-, R152a- and R744-HPACs under cooling condition; for cabin heating, it is advisable to increase the evaporator airflow or decrease condenser airflow for R1234yf- and R152a- HPACs and enlarge condenser airflow for R744-HPAC to elevate SEE.