heat pump, internal heat exchanger, vapor injection, COP, performance comparison
The heating capacity and coefficient of performance (COP) will significantly decrease when the conventional air source heat pump (ASHP) system is operated under low ambient temperature conditions, with the high discharge temperature. The vapor injection technique with an internal heat exchanger (IHX) has been proposed as an effective way to acquire better performance. In this paper, the performance of a R410A two-stage air source heat pump system with the scroll compressor was studied experimentally. According to the experimental results, the heating capacity increased with the vapor injection at the fixed ambient temperature and water temperature, however the discharge temperature decreased. One interesting founding was that the discharge temperature at the ambient temperature of -6°C and -12°C increased slightly when a little refrigerant was injected into the compressor. The optimal point always occurred when the system COP was maximized with the other constant parameters. Furthermore, the peak points of each COP curve were shifted to the right if the ambient temperature was elevated. With variation of the ambient temperature, the peak points of the heat pump with vapor injection technique were compared with those of the conventional system. The results showed that the vapor injection technique could improve the heating performance and enhance the stability and reliability of the compressor. At the ambient temperature of -20°C, the system could have up to 17.01% improved COP and 13.73% decreased discharge temperature, respectively. In addition, the variation of injection ratio with intermediate pressure and expansion valve operating reliability were also investigated.