Variable-circuitry heat exchanger for performance improvement of R290 air source heat pump system

Abstract

Due to the significant differences in phase-change heat transfer and flow characteristics of refrigerants during the evaporation and condensation processes in fin-and-tube heat exchangers (FTHXs), the optimal refrigerant circuits for these two conditions are different. However, in conventional air source heat pumps (ASHPs), the refrigerant circuitry of the FTHX remains fixed under varying operational conditions. Variable-circuitry has garnered attention for the ability to match the characteristics between different conditions and circuits. However, current research on variable-circuitry mainly focuses on R410A and R32, which is not entirely applicable to R290 because of differences in refrigerant properties. Therefore, this paper proposes the variable-circuitry heat exchanger (VCHX) for an ASHP using R290, which can satisfy the optimal refrigerant circuits for both the evaporator and condenser. Firstly, a numerical analysis study was implemented to reveal the effect of various refrigerant circuits on FTHX performance. According to the calculated results, the optimal circuits for different modes, i.e. 3-1-VCHX and 2-1-VCHX, were constructed. Comparative tests were then conducted between the VCHX systems and the prototype system adopting the China annual performance factor (APF) standard. The experimental results indicated that the APF of the 3-1-VCHX and 2-1-VCHX systems increased by 5.58 % and 5.64 %, and the annual energy consumption (AEC) of the two VCHX systems decreased by 5.24 % and 5.30 %. Additionally, the evaluation of Life Cycle Climate Performance (LCCP) showed that the VCHX technique could reduce carbon emissions by more than 5 % over the life-cycle of the ASHP. Compared to R32 and R410A systems, R290 systems reduced total carbon emissions by 5.85 % and 19.95 %, respectively. Overall, the VCHX technique offers considerable economic and environmental benefits. The contribution of this paper can provide new thoughts for optimizing refrigerant circuitry in ASHPs under various conditions.