Research On Heat Pump Air Conditioning System And Strategies For Climate Control Load Reduction In Electric Vehicles

The electric vehicles(EVs),which has low pollution and fuel consumption,is listed in the 13 th Five-Years Plan.Although good as it is,the range of the EVs is still the main barrier in its adoption.This situation becomes even worse when the air conditioning(AC)system is turned on.The range decrease can up to 50% due to AC energy consumption in low ambient conditions.It is drawing much attention in the industry on reducing the climate control energy consumption of vehicle air conditioning system.To achieve that,two ways are available.Frist one is reducing the climate control load of AC system.The second is improving the efficiency of the AC system.According to the requirements above,the work done in this paper is as follows:1.The characterization of vehicle climate control load.In this paper,a new method is provided to determine the climate control load of vehicles.The steady-state climate control load in both winter and summer conditions are determined for several vehicles.The transient warm up load in winter is also considered.It is found that the cooling load in summer is consist of ventilation load,solar radiation load and ambient load,while the ventilation and solar radiation load is the major parts.The heating load consists of ventilation load and ambient load,while the ventilation load is also the major part.Based on the load characterization,a semi-empirical equation for ambient load is provided,which is capable of calculating the ambient load within ±15% accuracy.The model for transient load is capable of predicting the cabin temperature within 0.5?.2.Heat pump system with two different structures were designed and tested.The first heat pump system was a 4-way valve heat pump air conditioning system with two heat exchangers.The cooling performance and heating performance under different ambient were tested.The on road test of the first system showed that it is capable of meeting the heating requirements when ambient temperature above 6?.Then the second heat pump system,a 3-heat exchanger heat pump system was built and its heating performance under mild low temperature was optimized using compressor with larger displacement.The heat pump using R407 C was also tested.The on vehicle test showed that the heat pump system can meet the warm up requirements of the target vehicle.3.The economized vapor injection system is also studied in this paper.The system performance under low ambient was investigated,and the effects of injection pressure and the capacity of economizer are discussed.Based on these,the reason for the “optimized injection pressure” under which the system heating capacity will reach its maximum value is analyzed.It is found that with vapor injection,the heating capacities of the system are increase by 35% on average.The COPs of the vapor injection system are nearly the same with the original system,with only 0.14% decrease compared to the original system.The discharge temperature of the compressor is also lower,which a 10.75? decrease on average is achieved.The optimized injection pressure is determined by the capacity of economizer and the character of the compressor.The enthalpy difference across the evaporator will first increase and then decrease with the rising of injection pressure,and the injection pressure at the turning point is the optimized injection pressure.The EVI heat pump system was then installed on a vehicle and tested in road test.The test results showed that the range of the tested EV can be extended by 25% in-10? ambient.4.The annual energy consumption model of mobile AC system is established,and the AC energy consumption are evaluated in major cities across China.The model is established based on thermal comfort,daily driving intensity and system bench test data.It is found that the energy consumption of AC system will greatly affect the driving range of EVs.A 30% decrease may occur when PTC is turned on in winter.5.The energy saving method are provide,including heat pump heating and utilizing the recirculated air.It is found that utilizing recirculated air and heat pump heating combined can extent the driving effect by 25%.