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• Air conditioning load reduction strategy in vehicles using recirculated air is provided. • Utilizing the recirculated air can extent the annual driving range by 11−30%. • Energy saving of heat pump heating in electric vehicle air conditioning is provided. The stock of electric vehicle is booming recently. However, the range of the electric vehicle is still a main barrier in its adoption. Air conditioning system is the second largest energy consumption device on vehicle, which will cause significant range reduction during operation. In this paper, the energy-saving effect of utilizing the recirculated air in air conditioning system is evaluated. The outside air ventilation rate based on CO 2 limits and windshield anti-fog requirements are calculated, and the energy-saving effect of this strategy in 30 cities across China is evaluated using an annual energy consumption model. It is found that utilizing the recirculated air can save 14–46% heating energy when using PTC heater, and 33–57% heating energy in heat pump AC system. Throughout a year, utilizing the recirculated air can extend the driving range by 11–30%. Image, graphical abstract [ABSTRACT FROM AUTHOR]

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]