Theoretical analysis on optimal configurations of heat exchanger and compressor in a two-stage compression air source heat pump system

• Optimization of a flash tank cycle based heat pump system is conducted.
• The optimal thermal conductance allocations are obtained under given conditions.
• The system heating capacities are affected by thermal conductance allocation.
• There exists an optimal compressor displacement ratio for optimum system COP.

This paper presents an optimum system configuration analysis for a flash tank cycle (FTC) based two-stage compression air source heat pump system using a developed theoretical model with lumped parameter method. The analysis is carried out with respect to the thermal conductance allocation of total heat-exchanger inventory (condenser and evaporator) as well as the volume ratio of low-pressure compressor to high-pressure compressor in the system. The analysis results indicate that the heating coefficient of performance (COP) of the heat pump system can be maximized by optimally allocating the thermal conductance inventory of the two heat exchangers. Moreover, there also exists an optimal compressor volumetric displacement ratio, corresponding to the optimum system COP, when the cooling capacity of system is specified. The effects of main operation parameters on the configuration parameters and optimal performances have been discussed. The obtained results may provide some guide for the FTC based air source heat pump system optimization.