Exergy-based ecological optimisation for an endoreversible air heat pump cycle

Abstract

SYNOPSIS On the basis of exergetic analysis, ecological performance analysis and optimisation of an endoreversible simple air heat pump cycle with constant-temperature heat reservoirs is carried out in this paper. An exergy-based ecological optimisation criterion, which consists of maximising a function representing the best compromise between the exergy output rate and exergy loss rate (entropy generation rate and environment temperature product) of the heat pump cycle, is taken as the objective function. The analytical formulae concerning the relationship between the exergy-based ecological function and pressure ratio is derived with heat resistance losses in the hot- and cold-side heat exchangers. The effects of the effectivenesses of the heat exchangers, the ratio of hot-side heat reservoir temperature to ambient temperature and the heat reservoir temperature ratio on the exergy-based ecological function are analysed. The cycle performance optimisations are performed by identifying the optimum pressure ratio and the optimum distribution of heat conductance of the hot- and cold-side heat exchangers for a fixed total heat exchanger inventory, respectively. The expressions of the maximum ecological function are derived. The influences of some design parameters, including heat capacity rate of the working fluid and heat exchanger inventory on the optimal performance of the endoreversible air heat pump are provided by numerical examples. The results show that exergy-based ecological optimisation is an important and effective criterion for the evaluation of air heat pumps.