Performance study and multi-objective optimization of two-stage compression single-screw air-source heat pump system

Single screw compressors have the advantages of simple structure, large capacity, and high efficiency, making them very suitable for application in air source heat pumps. In order to expand the application scope of single screw air source heat pumps, this paper proposes a two-stage compressed single screw air source heat pump, establishes energy analysis models and exergy analysis models, and discusses the influence of variable operating conditions on the performance of this heat pump system; A thermal economic analysis model is established to study the impact of operating conditions and volume ratio (Rv) on the unit heating cost (UCH), and an NSGA-II multi-objective optimization model is established. The results show that at a fixed Rv, within the range of evaporation temperature changes, the maximum coefficient of heating performance (COP_h) of the flash tank cycle (FT cycle) can reach 3.05, and the maximum exergy efficiency of the FT cycle can reach 37.13 %; The maximum COP_h of the subcooler cycle (SC cycle) is 2.84, and the maximum exergy efficiency of the SC cycle is 33.36 %. When the Rv is variable, the optimal COP_h and optimal exergy efficiency of the SC cycle system are 2.61 and 33.19 %, respectively, at an evaporation temperature of -5 ℃, a condensation temperature of 65 ℃, and a Rv of 0.46. After multi-objective optimization, the COP_h of R22 system is the highest, which is 3.09; The R290/R600 system has the highest exergy efficiency of 38.44 %; The R32/RE170 system has the smallest UCH, which is 0.1001 $kWh⁻¹.