Thermodynamic analysis and LCCP evaluation of kangaroo heat pump cycle for electric vehicles

The performance of heat pumps in electric vehicles drops significantly at low ambient temperatures due to low suction density and high-pressure ratios. To resolve this issue, we proposed the kangaroo heat pump cycle (KC). It is an enhanced flash tank-based vapor injection heat pump cycle (FT-VIC) that adds a sub-cycle before the refrigerant enters the flash tank, which increases the injection mass flow rate and leads to a higher heating capacity. Thermodynamic cycle models were developed for the basic heat pump cycle, FT-VIC, and KC. Furthermore, their heating performances, the annual energy consumption, and life cycle climate performance (LCCP) were evaluated and compared while using R-1234yf as the refrigerant. Results show that as compared to the FT-VIC, the KC increases the heating capacity by 25.7% and 20.1% and reduces the coefficient of performance by 25.8% and 18.9% when the ambient temperature is-5 degrees C and-15 degrees C, respectively. Due to the additional weight of the sub-cycle, the LCCP of KC is on average 4.6% higher than that of FT-VIC. In conclusion, the KC can provide more heating capacity in extremely cold conditions with additional energy consumption but is still more efficient than relying on the low-efficient PTC heater to meet the target heating capacity.

Automated summary

The study proposes an enhanced heat pump cycle, the kangaroo heat pump cycle (KC), to improve the heating capacity of heat pumps in electric vehicles at low ambient temperatures. Compared to the flash tank-based vapor injection heat pump cycle (FT-VIC), the KC increases the heating capacity by 25.7% and 20.1% at -5 degrees C and -15 degrees C, respectively.