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

Abstract

Summary 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%.

Effects of injection styles on heating performance of a heat pump with sub-cooler refrigerant injection: Experimental and thermodynamic analysis

“…The injection style, including liquid injection, two-phase injection and super-heated vapour injection, was quantified by the injection super-heated degree (4T inj ), 12 which is defined as the temperature difference between the saturation temperature corresponding to the injection pressure (P inj ) and the injection refrigerant temperature (T inj,out ) in the injection pipe.…”

“…The specifications of the measuring sensors utilized in the test and corresponding uncertainties are shown in Table 1. 12…”

“…Yang 10 and QV 11 combined liquid injection with SCRI and FTRI to achieve two-phase injection, respectively. Tu 12 realized two-phase injection by adjusting the openings of the main electronic expansion valve (MEEV) and sub-cooling electronic expansion valve (SEEV) in the heat pump with a sub-cooler.…”

“…40 Some test results demonstrate that the injection effect of two-phase injection was better than that of vapour injection and liquid injection. [10][11][12]40,41 For example, Yang et al 10 studied that the Q h and COP of twophase injection were 11.8% and 4.8% higher than those of vapour injection, respectively. Kim et al 40 shows that the COP of two-phase injection was 1-3% higher than that of vapour injection, and 2-4.4% after optimization control measures.…”

Thermodynamic performance evaluation of the CO 2 parallel compression supermarket refrigeration system with a subcooler

“…Subcooling is a common strategy in traditional refrigeration cycles used by many researchers to improve refrigeration system capacity and performance.. 16,17 The subcooling is usually provided by the system itself, and part of the liquid refrigerant will be throttled and absorb heat to subcool the rest part of the liquid refrigerant. Adding a subcooler into a refrigeration system can increase the cooling load, resulting in higher COP.…”