| Lack of engine waste heat for the electric vehicle, electric heater is often used for heating cabin air in winter. However, its low heating efficiency shorts the driving mileage. Compared to the electric heater, heat pump with better heating and cooling efficiency is the best. However, to apply heat pump to electric vehicles is not easy. First, under cold conditions, the low heating coefficient of performance(COP) needs to be improved. Second, a finned tube heat exchanger is the main type for heat pump. For heavy-weight and low aseismic capacity of a finned tube heat exchanger, it cannot meet the demand of aseismic and lightweight design for electric vehicles. Considering thermal comfort of cabin environment, an air conditioner should be wisely controlled according to the thermal load. Automobile heat pump from design to application is a frontline research.Micro channel heat exchanger with advantages of lightweight and better aseismic ability is applied in the designed DC inverter automobile heat pump. Because of the special design for the micro channel heat exchanger in the paper, a series of problems for applying micro channel heat exchanger in the heat pump. For instance, a heat exchanger is not only used as evaporator but also condenser well, better drainage, refrigerant distribution and anti-frosting characteristics are obtained and the heating performance is improved substantially. In the paper, the effect of scroll compressor speed and starting characteristics, outdoor temperature and the surface temperature distribution of outdoor exchanger on the performance is studied, and the control strategy is also developed. Main research conclusions are as follows:(1) As the compressor speed increased, cooling and heating capacity showed a tendency to rise, while the cooling and heating COP decreased and longer time was needed to stabilize. While starting the heat pump, thermal load was the largest and compressor started with 4000 rpm. When the automobile interior temperature reached the comfort value, the compressor should work with suitable speed, which matched the thermal load. At the same time, by increasing vehicle speed, surface convective heat transfer coefficient of vehicle enclosure increased and the thermal load decreased, while the performance was improved.(2) Under cooling conditions, the cooling COP decreased with the increase of the outdoor temperature. Under heating conditions, when the outdoor temperature ranged from 0 to 9℃, the outdoor heat exchanger would frost and the heating performance associated with defrosting control strategy. When the outdoor temperature was below 0℃, the lower outdoor temperature led to the lower heating COP.(3) BP neural network was used to study the relation of the surface temperature distribution characteristics on external heat exchanger and heat pump performance. The experiment results showed the weighting coefficient of surface temperature distribution characteristics on the cooling and heating COP were 34.97% and 43.90%, respectively, and the surface temperature distribution characteristics was mostly affected by the heat exchanger pressure drop. By arranging the external exchanger in a vertical position from the odd horizontal position, heat exchanger pressure drop decreased by an average of 27.32% under cooling conditions, and better drainage and refrigerant distribution characteristics were obtained and the cooling and heating COP were 1.1 and 1.8 times of odd system, respectively. |
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