Intermediate Vapor Bypass, Mobile Heat Pump, Low ambient temperature
With market share of electric vehicles continue to grow, there is an increasing demand of mobile heat pump for cabin climate control, as it has much higher energy efficiency than electric resistive heating and hence much less impact on electric drive range. However, current mobile heat pump systems using low pressure refrigerant like R134a and R1234yf suffer from significant heating capacity loss at low ambient temperature. As a result, a large electric heater needs to be installed to supplement the capacity shortage at low ambient temperature, and electric drive range can be greatly reduced due to large power consumption for cabin heating. In this paper, the drop of heating capacity at low ambient temperature was experimentally and numerically studied. Pressure drop and refrigerant maldistribution in the outdoor heat exchanger in HP mode were found to be the most important factors. A novel design of the outdoor heat exchanger using intermediate vapor bypass in HP mode and the corresponding system architecture were proposed. The proposed outdoor heat exchanger turns into a condenser with integrated receiver and subcooler in A/C mode. A proof-of-concept heat exchanger prototype was made by modifying the baseline heat exchanger and tested in the lab. The result has shown 35% improvement of heating capacity at -20 ̊C ambient condition. Optimization of the outdoor heat exchanger design was investigated with a system model.