Comparative performance and injection characteristic of air source heat pump with conventional and active refrigerant injection

Abstract

An active sub-cooler refrigerant injection (ASCRI) based on low-grade heat source was proposed. This injection method can convert the external heat source into heating capacity (Qh) in the form of refrigerant injection enthalpy difference, thus greatly increasing the Qh and solving the problem that the heat pump with conventional refrigerant injection (CSCRI) cannot be applied in extremely cold areas. The thermodynamic model has been built to calculate the heat pump performance (HPP) parameters and determine the influence factors. The HPP and injection characteristic of CSCRI and ASCRI were comparatively tested. Experimental results show that effects of ASCRI on improving the performance were better than those of the CSCRI. At low ambient temperature, the maximum Qh/coefficient of performance (COP) of the heat pump with CSCRI and ASCRI were 6611 W/2.33 and 7730 W/2.49, 17.8 %/11.5 % and 37.7 %/19.1 % higher than those of the none-injection heat pump, respectively. The bandwidth characteristic of the ASCRI was superior to that of the CSCRI. For the Qh/COP, the effective bandwidth scopes of the sub-cooling electronic expansion valve with CSCRI and ASCRI account for 8 %/2 % and 75 %/60 % of total opening range, respectively.

Keywords

• Heat pump
• Refrigerant injection
• Active refrigerant injection
• Low-grade heat source
• Coefficient of performance