Performance comparison of a direct heat pump using R1234yf and indirect heat pumps using R1234yf and R290 designed for cabin heating of electric vehicles

When using R290 as an alternative to R1234yf for heat pump (HP) cabin heating systems, indirect system (IDS) should be employed to address safety issues owing to its high flammability. However, studies comparing the performance of a direct system (DS) using R1234yf and an IDS using R290 are limited. In this study, the performance characteristics of DS-HPR1234yf, IDS-HPR1234yf, and IDS-HPR290 were compared to verify the feasibility of applying R290 to cabin heating systems in electric vehicles. Compared with DS-HPR1234yf, the heating capacity (QHP) and compressor work (WHP) of IDS-HPR1234yf decreased by 2.8% and increased by 4.5% on average, respectively, owing to the system configuration effects. QHP and WHP of IDS-HPR290 increased by 42.1% and 51.0%, respectively, over those of DS-HPR1234yf owing to the refrigerant and system configuration effects. Thus, at −20 °C, COPHP (HP’s coefficient of performance) of IDS-HPR290 was 1.8, which was 4.9% higher than that of DS-HPR1234yf, owing to the high decrease rate of WHP. Additionally, considering the use of HP and positive temperature coefficient (PTC) heaters, COPHP+PTC of IDS-HPR290 was 6.7–22.1% higher than that of DS-HPR1234yf owing to its superior QHP, and the driving range (DR) of IDS-HPR290 was 7.2–20% higher than that of DRPTC.