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The maximum coefficient of performance of a two-stage combined heat pump system affected by multi-irreversibilities

SYNOPSIS A general cycle model which includes the multi- irreversibilities often existing in real heat pump systems is established and used to analyse the influence of the irreversibility of finite-rate heat transfer across finite temperature differences, the heat leak between the external heat reservoirs, and the internal dissipation of the working fluid on the performance of a two-stage combined heat pump system. The coefficient of performance is taken as an objective function for optimisation. The maximum coefficient of performance with non-zero specific heating load is determined and other corresponding performance parameters, such as the specific heating load, temperatures of the working fluid in the isothermal processes, the optimal distribution of the heat transfer areas of heat exchangers, and the power input of the heat pump system, are calculated. The results obtained here are more general than those obtained from a two-stage endoreversible combined heat pump system and can guide the optimal design and operation of real combined heat pump systems.