Experimental and theoretical assessments on the systematic performance of a single-stage air-source heat pump using ternary mixture in cold regions

Abstract

The performance of air-source heat pump is strongly influenced by ambient temperature variation. Improving its stability and efficiency during wintertime is important for promoting its applications, while existing studies paid few attentions to flexible parameter regulation of heat pump using mixture. In this paper, a single-stage compound air-source heat pump using ternary mixture was theoretically simulated and experimentally tested, in which operating parameters including pressure and concentration could be regulated with the cooperation of multiple valves and reservoirs. Using CO2/R134a/R600, operating pressure and mixture concentration were successfully regulated at ambient temperature from −30 ℃ to 0 ℃, achieving a coefficient of performance from 1.834 to 2.546 when producing hot water at 75 ℃. Whether R134a inclusion was favorable to energy performance depended on its influence on the temperature matching in recuperative process, especially the heat transfer process in recuperator. The addition of R134a significantly alleviated the increase of operating pressure and thus enlarged the operation range of this heat pump. The flammability range of CO2/R134a/R600 was calculated, indicating the insignificant influence of R134a on flammability retardance in the studied range of this paper. The significance of this study is further revealed with the potential advances of heat transfer technique and new-generation refrigerant. The findings in this paper contribute to: 1) the modification of air-source heat pump for operation at low temperature; 2) the regulation method for mixed-refrigerant system; 3) the exploration of new mixed-refrigerant in thermodynamic cycle.