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Highlights • A propane heat pump system is proposed as a solution for electric vehicle. • The heating performance of the propane heat pump system was studied. • Different technical solutions have been compared. • Propane heat pump system will be the most competitive solution for electric vehicle. Abstract To solve the problem of driving mileage reduction for electric vehicles during winter resulting from high power consumption for heating and to deal with the global warming issues, propane heat pump is proposed as a novel solution in this paper for the first time. The heating performance characteristics of a mobile propane heat pump system for electric vehicles in cold climate under various operation conditions have been experimentally studied. Different technical solutions for heat pump are also compared in the research. According to the results, propane (R290) system is the strongest competitor at an outdoor ambient temperature above −10°C among all the strategies while CO 2 system may have small advantages when the ambient temperature is −20°C. However, due to CO 2 's poor cooling COP (Coefficient of performance) at high ambient temperature and its high operating pressure, propane heat pump system will be the most competitive solution for electric vehicles. [ABSTRACT FROM AUTHOR]

• Vacant heating core in cooling mode was first utilized for evaporation. • A series cross-parallel dual-evaporator configuration was recommended. • An automotive CO 2 air conditioner with the recommended configuration was tested. • COP was improved by 6∼12% without additional cost. Inefficient performance of CO 2 refrigerant in hot climates has become a major obstacle to its wide application in electric vehicles. In this paper, the vacant heating core in cooling mode was exploited to increase the heat transfer area of evaporator and improve system performance. With the aid of a validated evaporator model and an experimental test rig, performance improvements brought by this added area were evaluated. Results indicated that this area is not suggested to be directly added to cooling core. This necessitates a dual-evaporator (D-E) configuration. For case I (small CO 2 pressure drop), the growth rate in heat transfer rate brought by D -E configuration is 19∼20% and less sensitive to parallel or series operation. Nevertheless, this growth rate for case II (large CO 2 pressure drop) is greatly affected, 30.6∼32.6% for parallel operation and 7.5∼17.6% for series operation. Specifically, it is around 17.5% and 7.5∼13.6% for series cross-parallel and cross-counter arrangements, respectively. By comprehensive consideration, the cross-parallel arrangement is recommended to be adopted. Experimental results indicated that the cross-parallel D -E configuration greatly increases the evaporation temperature and exhibits a slight impact on optimum high pressure within the transcritical cycle. The enhancement in COP brought by this configuration is around 6∼12% without additional cost, and it rises with the decreased air flowrate through evaporator and air velocity through gas cooler and the increased ambient temperature. This indicates that this configuration is an effective and economical technology to alleviate the efficiency degradation issue of transcritical CO 2 automotive air-conditioners. [ABSTRACT FROM AUTHOR]

The main purpose of this work is to enhance the energy efficiency of CO 2 automobile air conditioning system. Theoretical analysis demonstrated that the mixture of CO 2 and propane can improve its performance, thus, experiments have been carried out to see effects of various CO 2 -propane mass fractions of 100/0, 90/10, 80/20, 70/30, 60/40, 50/50 on the system performance at different ambient temperatures and gas cooler frontal air velocities. Experimental results show similar trends with those from the theoretical results. It has been shown that under the same compressor speed, system COP reaches highest at 60% of CO 2 mass fraction, which is 29.4% higher than pure CO 2 system and even achieves equal level of the R134a system, the optimum pressure and discharge temperature are reduced up to a maximum of 40% and 47   °C during the research range. Furthermore, comparison was carried out under the same cooling capacity by adjusting compressor speed for different mass fraction of CO 2 , results demonstrate that the use of CO 2 -propane mixtures yields a maximum COP rise of 22%even when cooling capacity is kept constant. A new optimum high pressure control algorithm for the transcritical CO 2 -propane mixture cycle has been developed based on the experimental data within a deviation of 5%. [ABSTRACT FROM AUTHOR]