Techno-Economic Evaluation and Optimization of Medium-Deep Geothermal Heat Pump Systems Integrated with Phase Change Heat Storage

As an effective approach for deep geothermal energy utilization, medium-deep ground source heat pump (MDGSHP) systems have attracted increasing attention in northern China as a low-carbon solution for district heating. However, traditional MD-GSHP systems exhibit insufficient demand-side flexibility, limiting their capacity for real-time coordination with power grid operations. The incorporation of thermal energy storage (TES) into MD-GSHP systems presents a promising pathway to enhance energy flexibility and support demand response. In this study, an MD-GSHP system integrated with latent heat TES was proposed. Firstly, a dynamic simulation model of the integrated system was established based on TRNSYS platform and validated against field data. Sensitivity analysis was then conducted to analyze the influence of PCM storage tank parameters on system performance. Finally, techno-economic optimization was performed to identify the optimal design parameters and the system's potential for performance improvement. The results show that the optimal PCM charging temperature of the heat pump is strongly dependent on the storage tank volume and PCM melting temperature. As the melting temperature and charging temperature increase, both lifecycle economic performance and energy efficiency exhibit a nonmonotonic trend-rising initially and then declining. Under the joint optimization of economic performance and energy efficiency, the system achieves a levelized cost of energy of 0.481 CNY kWh and an SPF of 6.02 after 20-year operation. The research results provide a theoretical basis for guiding the design and operation of deep borehole geothermal systems with integrated TES.