Research on renewable energy coupling system based on medium-deep ground temperature attenuation

Medium-deep geothermal has large reserves, a high temperature, a high heat flow density, and other characteristics, but the traditional medium-deep ground heat pump system have long relied on heating from the ground, and soil temperature decreases annually. Using a community building heating system as an example, from a point of view of heat accumulation or not, this article examines the design of a photovoltaic photothermal coupled medium-deep ground source heat pump system (PV/T-GSHP) and a photovoltaic-assisted medium-deep ground source heat pump coupled air source heat pump system (PVGSHP-ASHP). First, the operational performance of a typical GSHP system was compared to that of the PV/T-GSHP and PVGSHP-ASHP systems, both of which were built using TRNSYS. Second, the energy balance and electrical consumption of each system were compared. Finally, the effect of the PV/T-GSHP system’s key parameters and the different ASHP load ratios in the PVGSHP-ASHP system on soil temperature were analyzed. The results showed that after 20 years of operation, the average soil temperature decreased from 38.29 °C to 36.89 °C for the GSHP system, resulting in a decrease in the performance coefficient of the ground source heat pump and the system performance coefficient. The PV/T-GSHP system can address the issue of declining soil temperature with an increase in soil temperature of 0.09 °C. The PVGSHP-ASHP system can mitigate the issue of decreasing soil temperature. The PVGSHP-ASHP system is better than the PV/T-GSHP system in terms of electricity economy. In the PV/T-GSHP system, the larger PV/T component area of similar structures, the smaller flow rate of the heat collector pump, and the volume, inclination, and set temperature of the heat storage tank that are more suitable for the system can achieve higher soil temperatures. As the air-source load ratio increases, the rate at which the soil temperature in the PVGSHP-ASHP system decreases progressively decelerates.