Thermodynamic performance analysis and multi-criteria optimization of a hybrid combined heat and power system coupled with geothermal energy

Hybrid fossil/renewable energy combined heat and power (CHP) systems harness local energy sources, save fossil fuels, and reduce greenhouse gas emissions. Here geothermal energy is integrated into a natural gas driven CHP system by employing both vapor-compressor and absorption cycles through a geothermal heat pump (GSHP). To increase the performance of the heat pumps, the mixed hot water from the internal combustion engine (ICE) is used to preheat the evaporator. Using a multi-criteria optimization method based on energy, economic, environmental and adjustable factors, the optimal allocation ratio of hot water from the ICE is analyzed to maximize the performance of the hybrid CHP system for a specific case building. The necessary thermodynamic models of the system components needed for the optimization are presented. The results demonstrate that the increasing allocation ratio of mixed water for the heat pumps raised the output and coefficient of performance (COP). At optimal allocation ratio maximizing the performance of the CHP system against a set of criteria, the optimum energy saving ratio (ESR), carbon dioxide emission reduction ratio (CDERR), annual cost saving reduction (ACSR), and adjustable ratio are 30.26%, 53.20%, 40.80% and 6.40%, respectively. The hybrid CHP system also shows much higher flexibility than other relevant systems.