Efficient refrigerant strategies for large-scale geothermal heat pumps: Triple analysis of energy, exergy, and cost

The escalating global demand for energy, coupled with the challenges posed by climate change, necessitates the transition to sustainable and renewable energy solutions. Geothermal energy, particularly when integrated with advanced heat pump systems, offers a reliable and efficient means for space conditioning, encompassing both heating and cooling applications. This study conducts a comprehensive thermodynamic, exergy, and economic analysis of a large-scale geothermal heat pump system designed for a six-classroom educational facility located in Yazd, Iran. The thermal loads for heating and cooling, determined via the Design-Builder simulation software, were found to be 66.43 kW and 55.05 kW, respectively. Using the Engineering Equation Solver (EES) for detailed thermodynamic modeling, five refrigerants were evaluated in terms of their performance. Among them, R12 was identified as the most thermodynamically efficient, achieving a maximum coefficient of performance (COP) of 4.005 in heating mode and 4.547 in cooling mode. Additionally, R12 exhibited the lowest exergy destruction, with values of 12.7 kW and 15.04 kW for heating and cooling modes, respectively. However, despite R12’s superior thermodynamic efficiency, its environmental implications, notably its high ozone depletion potential (ODP) and global warming potential (GWP), pose significant concerns for its continued use. From an economic standpoint, R22 was found to be the most cost-effective refrigerant, with initial capital costs for the system estimated at $44,829 in heating mode and $41,452 in cooling mode. This study thus highlights the critical trade-offs between system performance, environmental impact, and economic feasibility, providing invaluable insights into the optimization of geothermal heat pump systems for sustainable and cost-efficient building climate control.