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-HP_R1234yf, IDS-HP_R1234yf, and IDS-HP_R290 were compared to verify the feasibility of applying R290 to cabin heating systems in electric vehicles. Compared with DS-HP_R1234yf, the heating capacity (Q_HP) and compressor work (W_HP) of IDS-HP_R1234yf decreased by 2.8% and increased by 4.5% on average, respectively, owing to the system configuration effects. Q_HP and W_HP of IDS-HP_R290 increased by 42.1% and 51.0%, respectively, over those of DS-HP_R1234yf owing to the refrigerant and system configuration effects. Thus, at −20 °C, COP_HP (HP's coefficient of performance) of IDS-HP_R290 was 1.8, which was 4.9% higher than that of DS-HP_R1234yf, owing to the high decrease rate of W_HP. Additionally, considering the use of HP and positive temperature coefficient (PTC) heaters, COP_{HP + PTC} of IDS-HP_R290 was 6.7–22.1% higher than that of DS-HP_R1234yf owing to its superior Q_HP, and the driving range (DR) of IDS-HP_R290 was 7.2–20% higher than that of DR_PTC.