Performance optimization of geothermal-driven ORC with coupling modulation of evaporation/condensation temperatures

This study presents a coupling optimization model for a geothermal fluid-driven Organic Rankine Cycle power generation system that integrates thermal and economic performance. The investigation begins with optimizing the evaporation temperatures of six working fluids, followed by adjusting the condensation temperature to enhance the system's thermal efficiency. Additionally, a comprehensive economic analysis of the total investment and component-level cost was conducted. The results demonstrate that both increasing the evaporation temperature and decreasing the condensation temperature can improve the system’s thermal performance. and reduce operational expenses. By comprehensively considering the system net output power (W net) and unit cost (C i), and adopting the multi-objective optimization strategy coupling the NSGA-II algorithm and entropy weight TOPSIS method, it is determined that R245fa is selected as the optimal working fluid under the geothermal fluid temperature of 140 °C, with an optimal evaporation temperature of 118 °C and a condensation temperature of 8 °C. Compared to the current system, adopting R245fa increases the net output power by 46.6% while reducing the unit cost (C i) by 50.2%. The total investment cost of the system rises by 15.23%, with 79% of the additional cost concentrated on the evaporator and condenser, providing valuable guidance for practical retrofit projects.