Characteristics Of Active Refrigerant Injection Based On External Heat Source And Its Effects On Performance Of An Air Source Heat Pump

Traditional refrigerant injection can slightly improve heat pump performance because the injection enthalpy difference is not included in the heating capacity (Q(h)). This work proposes a novel method of active injection based on an external heat source. The external heat source and the injection refrigerant exchange heat in the sub-cooler and the heat absorbed by the injection refrigerant is converted into the Q(h). The injection characteristics and the heat pump performance at different ambient temperatures, different external heat source temperatures and different sub-cooling electronic expansive valve (SEEV) openings are investigated. The injection characteristic shows that the active injection cycle can greatly improve the heat pump performance and expand the bandwidth of SEEV openings. At low ambient temperature of -12 degrees C and outlet water temperature of 50 degrees C, amplitudes of the Q(h) and COP increased from 8.6% to 48.9%, and 6.6% to 38.3%, respectively, under different SEEV openings. The injection technology widens the effective working scope (EWS) of the SEEV opening. At low temperature of -12 degrees C, the EWS of Q(h) is 75-450 PLS, which accounts for 83.3% of the SEEV working range. This wide bandwidth characteristic provides convenience for application of the injection technology.