Abstract:

Rock and soil mass not only influences the distribution features of ground temperature field, but also is the key factor of evaluation of shallow geothermal energy resources and engineering design. To obtain the thermal properties and heat transfer performance of local rock and soil is the lynchpin to guarantee the efficient and stable operation of the heat pump. According to the field test results of heat exchange performance of ground-source heat pump projects under construction in Beijing, we study the effects of integrated thermal conductivity by stratum structure, lithology, hydro-geological conditions and backfill material. The results showed that it’s beneficial to improve the heat transfer performance of the system by means of selecting appropriate backfill materials under the same conditions. The heat exchange performance of bentonite and cement as backfill material is improved by 17.6% and 19.7% respectively compared with fine sand. It can be concluded that the rock-soil mass and groundwater are the substance bases of accumulation and spread of thermal energy. The groundwater and strata texture determine the distribution pattern of geotemperature field and heat transfer efficiency. There is a direct relationship between heat transfer efficiency of ground heat exchanger with soil particles, groundwater table and groundwater seepage. The larger soil particles become, the less groundwater depth gets. The seepage velocity has obvious invigoration effect on the heat transfer efficiency of ground heat exchanger.

Key words: shallow geothermal energy, integrated thermal conductivity, thermal response, ground source heat pump, Beijing plain