Effects of subcooling degree and injection super‐heating degree on performance of an air source heat pump with subcooler

Abstract

For a heat pump, three injection styles including liquid, two-phase, and vapor injection are used to improve its performance. But there is no quantitative index to define the injection styles. They are distinguished from the injection configurations. The subcooler refrigerant injection (SCRI) is generally considered as the vapor injection. In this study, the injection super-heating degree (ΔTinj) is introduced as a technical parameter to define the injection style. The ΔTinj is affected by the subcooling degree (ΔTsc). These two parameters are used to study their effects on the heat pump performance. Experimental and theoretical analysis reveals that three injection styles can be selectively achieved in the SCRI configuration by the suitable control of the main and subcooling electronic expansion valves. Additionally, for liquid and two-phase injection, it can improve heating capacity (Qh) by heightening the ΔTsc to increase the heat exchange amount in the evaporator. For vapor injection, in addition to increase of the ΔTsc, the Qh can be enhanced by raising the ΔTinj to lift the compression power of the compressor. The two-phase injection is more beneficial to enhance the heat pump performance than the liquid injection and two-phase injection. The largest Qh and corresponding increase amplitude (δQh) were, respectively, obtained with two-phase injection to be 13 577 W and 13.5%, and the corresponding COP and increase amplitude (δCOP) were, respectively, 2.36 and 16.8%.