Micro Channel Heat Exchanger, Heat Pump Cycle, Automotive HVAC System, Variable Pass Design, Frost Performance
Micro channel heat exchanger (MC-HEX) is more effective for a performance enhancement than traditional fin and tube heat exchanger (F&T). MC-HEX was applied to the automotive HVAC system at first, and it is applied to a residential air-conditioner recently. Because MC-HEX helps to reduce refrigerant quantities in air-conditioner systems, we apply MC-HEX to not only cooling mode cycle but also heat pump cycle for residential air-conditioner. It means that our MC-HEX could solve the issue of frost in heating mode. On the other hand, heat pump cycle came to be applied to automotive HVAC system for reducing consumption electricity of EV and HEV/PHEV. However, the typical automotive heat pump cycle is different from the heat pump cycle of residential air-conditioner. Usually heat pump cycle of residential air-conditioner is constructed in two heat exchangers with reverse cycle mode, but automotive heat pump cycle is constructed in three heat exchangers without reverse cycle mode. Therefore, MC-HEX of residential air-conditioner cannot be applied to automotive HVAC system especially for outside heat exchanger. In this paper, our MC-HEX for outside unit of residential air-conditioner is modified to apply to automotive heat pump cycle. The pass design of our MC-HEX for outside unit of residential air-conditioner gives priority to the performance in the evaporation condition (heating mode) because of improving annual efficiency. As a result, the condensation performance should decrease, because the most suitable pass design of the condensation is different from evaporation in MC-HEX. But MC-HEX for automotive heat pump system has to give priority to the performance in the condensation condition (cooling mode) with high frost performance. This trade-off is solved by developing a variable circuit which applied the pass arrangement that is different from a condensation condition and an evaporation condition. The distribution control structure of the header inside which can correspond to the down flow of the refrigerant in the evaporation condition is also developed for automotive heat pump system. As a result, our MC-HEX has same condensation performance with automotive HVAC system and same evaporation performance and frost performance with residential air-conditioner.