air-source heat pump; economizer; internal heat exchanger; COP; heating capacity.
Air-source heat pump (ASHP) has been widely used for residential heating and domestic hot water due to its energy saving and environmental protection as well as its high efficiency. However, with ambient temperature decreasing, the heating performance of conventional ASHP degrades rapidly which restricts its application in cold regions. In order to improve the heating performance of ASHP, this paper not only analyzes two ASHP cycles using economizer vapor injection (EVI) and internal heat exchanger (IHX) theoretically and experimentally, but also compares the heating performance of both cycles with a conventional cycle. The results showed that both EVI cycle and IHX cycle have better potential for application in low ambient temperature environments. The further study indicated that the heating capacity and power consumption of EVI cycle were higher than those of IHX cycle at the same ambient temperature while the COP of EVI cycle was lower than that of ASHP with IHX due to the different refrigerant mass flow. In addition, using EVI could reduce the discharge temperature significantly while using IHX increased the discharge temperature in comparison to the conventional ASHP. Furthermore, ambient temperature range from -15Â°C to -10Â°C can be chosen as the switch range of the two cycles to satisfy the heating performance and economy simultaneously.Â