As vehicle emission regulations become increasingly rigorous, the automotive industry is accelerating the development of electrified vehicle platforms such as Battery Electric Vehicles (BEV) and Plug-in Hybrid Electric Vehicles (PHEV). Since the available waste heat from these vehicles is limited, additional heat sources such as electric heaters are needed for cabin heating operation. The use of a heat pump system is one of the solutions to improve EV driving range at cold ambient conditions. In this study, an efficient gas-injection heat pump system has been developed, which achieves high cabin heating performance at low ambient temperature and dehumidification operation without the assistance of electric heaters.
2.Outline of Developed System
(1) High Cabin Heating Performance under Low Ambient Temperature
Gas-injection cycle expands refrigerant from high pressure into intermediate pressure first. The 2-phase refrigerant at intermediate pressure is then separated into gas and liquid. The gas is injected back to the compressor, and the liquid is further expanded to low pressure and fed into outer heat exchanger for evaporation. Enthalpy increases by bypassing the gaseous refrigerant back to the compressor at intermediate pressure while the ratio of liquid refrigerant for evaporation is increased which improves absorbing of heat from the ambient. Refrigerant flow rate also increases and so does heating performance by injecting gas refrigerant with high density to the intermediate port of the compressor. This system allows the gas-injection cycle to have a simple structure with a gas-liquid separator, a second throttle, and an integrated valve for changing the flow. (Fig.1)
Fig.1 Compact gas-liquid separator
(2) Dehumidification and Heating
For a mobile heat pump system with no waste heat available, cooling cycle is still controlled for air dehumidification but capacity control of outer heat exchanger (heat release or absorption) is key for reheating control, since reheating depends on dehumidification and required performance for cooling cycle. If an outer heat exchanger is used for heat rejection to ambient,
the system can use just a portion of the heat from
dehumidification for reheating to meet low reheating needs. On the other hand if the outside heat exchanger is used as heat absorber, the heat from the ambient can be used for reheating in addition to the dehumidification heat to meet high reheating needs. Operating an outer heat exchanger unit as a heat releaser or absorber can be controlled based on refrigerant cycle balance.(Fig.2)
Fig.3 shows developed heat pump system, which can efficiently provide comfort and defogging of the windshield under low temperature conditions.
Fig.2 Capacity control of dehumidifying heating
Fig.3 System congfigration
*1 Member，DENSO CORPORATION（1-1 Showa-cho, Kariya, Aichi）
*2 DENSO CORPORATION（1-1 Showa-cho, Kariya, Aichi）