The hot stack performance of the shallow geothermal heat pump system with/without intensification state of groundwater seepage in Nanjing (China)

As a renewable and clean energy, the shallow geothermal energy and its corresponding buried pipe heat pump technology applications have become a hot topic of domestic and foreign scholars as well as industry researches. While the hot stack problem around rock and soil is a serious problem, which is harmful for the thermal performance and actual operation of the buried pipe heat pump system. In this paper, the numerical analysis and thermal response test on the hot stack problems of surrounding rock soil after continuous operation with or without intensification state groundwater seepage have been studied. Besides, the static reserves and exploitation amount for the Nanjing Hexi area test site on shallow geothermal energy development and utilization have been conducted. Results show that under the non-flow conditions, the increase of buried pipe inlet velocity, inlet temperature and buried depth of pipe are as effective way to increase the thermal performance of the heat exchanger. In the case of groundwater seepage, the distribution of the temperature of rock and soil mass is influenced by the groundwater seepage, and the hot stack problem can be not considered when the groundwater flow rate is greater than 5 × 10−6 m/s. The static reservation is 1.60E + 13 kJ in summer and 8.01E + 12 kJ in winter, which is accounts for the proportion of up to 72% of shallow ground thermal resources, meaning the buried pipe of GSHP application potential is very considerable.