| The development of improved thermal comfort inside the vehicle and its battery thermalmanagement technology would contribute to the popularization of pure electric vehicle. Itexists the same or complementary needs between the cooling and heating demand of the cabinand that of battery, thus making it possible for the comprehensive utilization of the batterypack’s heat production and vehicle air-conditioner’s cooling and heating capacity.Firstly, the heat production rate and heat transfer characteristics of the LiFePO4batteriesare studied. The heat production models under constant current discharge and dynamic currentdischarge conditions are founded through the combination of computational and experimentalmethods. Secondly, the dynamic cooling load and heating load curves of the cabin areobtained through experiments using the multi-channel heat flux meter HFM-215andHFM-215N. Thirdly, a cross-matching analysis is performed to understand the coolingdemand and heating demand of the cabin and battery pack in hot summer and cold winter,respectively. Thus the cooling and heating demand characteristics of cabin and battery pack,and waste heat utilization produced by the battery pack under different outdoor environmenttemperature and vehicle speed are obtained. Based on the study above, the integrated thermalmanagement system combined heat pump air conditioner with electric vehicle’s battery packis designed. Finally, the battery thermal management effect under natural wind forcedconvection and refrigerant of vehicle heat pump air conditioning are compared using Fluent.The heat production models of constant current discharge and dynamic current dischargecan be used for battery heat behavior prediction. It is found that the peak heat production rateand corresponding peak cooling demand of the E6EV’s battery pack reach to3100W and2500W, respectively when the vehicle speed is120km/h and the outdoor environment is40℃.The dynamic cooling load and heating load curves of the cabin are obtained throughexperiments. It shows that in the cooling model, about2092W heat load, accounted for44.2%of the total heat load inside the cabin, flows into the cabin through the vehicle windows and inthe heating model, the heat loss is evenly distributed between car’s envelopes. Additionally,the solar radiation bears greater influence to the cooling load in summer and minor influenceto the heating load in winter.A cross-matching analysis is performed to understand the cooling demand and heatingdemand of the cabin and battery pack respectively in hot summer and cold winter. There arethree kinds of thermal condition of the cabin and battery pack, namely cooling demand, heating demand and thermal comfortable. The peak heat dissipation of the battery pack is1066W when the ambient temperature is28℃, while it would increase to2500W when theambient temperature reaches to40℃. The peak cooling demand inside the cabin is4800W.Therefore, the maximum total cooling demand of the cabin and the battery pack is about7300W. The peak heating capacity of the vehicle air conditioner could be used for heating thebattery pack is2500W which is limited to the peak heat dissipation of the battery pack.Furthermore, the possibility of the utilization of the waste heat produced by the batterypack is analyzed. The results showed that the ideal waste heat can be used is about2020Wand the ideal maximum available utilization time is39.7minutes when the ambienttemperature is16℃and the drive speed is up to120km/h. However, the waste heat utilizationis still uneconomic and inefficient because normally the speed of EVs is no more than80km/hand no waste heat can be utilized when the vehicle speed below80km/h.Based on these analyses, the integrated thermal management system combined heatpump air conditioner with electric vehicle’s battery pack is designed. The battery thermalmanagement effect under natural wind forced convection and refrigerant of vehicle heat pumpair conditioning are further compared using Fluent. The simulation results show that thehighest temperature of the battery would exceed45℃using wind forced convection coolingwhen the ambient temperature reaches to35℃and the drive speed is80km/h, while thebattery temperature can be maintained within the preferred temperature range and thetemperature difference of the battery pack can be controlled in the range of5℃usingrefrigerant for thermal management. |
