Thermal—economic modelling and optimization of gas engine-driven heat pump systems

Abstract

Gas engine-driven heat pump (GEHP) modelling and optimization are presented in this article. Heat pump cycle modelling included a compressor, condenser, evaporator, expansion valve, and gas engine to drive the compressor. To validate the modelling output results, they were compared with experimental results, and acceptable difference per cent points were obtained and reported. For the optimal design of GEHPs, the total annual cost (sum of operating and investment costs) was defined as the objective function in terms of technical and economic parameters of the system. The genetic algorithm optimization technique was used to obtain the design parameters at the minimum total cost of the system. Eight design parameters of the system (condenser and evaporator pressures in cooling and heating modes, inlet air mass flowrate to indoor and outdoor heat exchangers, and gas engine rotational speed in cooling and heating modes) were selected. The values of the design parameters for a case study were obtained and reported when the total annual cost of the system was minimum. Furthermore, at that system optimal design point, the investment and operating costs were found to be 64.23 per cent and 35.67 per cent of the total cost, the fuel consumptions of the gas engine were 0.956 and 0.658 kg/h, respectively, and the coefficients of performance (COPs) of the GEHP were 1.61 and 1.64 in the cooling and heating modes, respectively. The variation of optimum design parameters in various cooling and heating loads was studied. Finally, sensitivity analysis and the change in design parameters with the change in fuel price and investment cost were studied.