Numerical Study Of Heat Transfer Of Vertical U-tube Ground Heat Exchangers In Multiple Ground Layers

As the energy situation and environment pollution become serious, the development ofrenewable energy is the main way to solve the current energy problem, and also thecommon research topic people facing. Ground source heat pump (GSHP) is an importantmeans to use geothermal energy, it is widely applied in HVAC and building heating.However, in practice the effect of energy saving of current GSHP is not significant, and alsoits initial investment is very high, which has become the main bottleneck in thedevelopment of GSHP.As the research of heat exchange of U-tube is a difficult task in GSHP, and directlyaffects the performance and investment of GSHP, the analysis of heat exchange of U-tube isvery important for the application of GSHP. In this paper, the heat transfer and soiltemperature field under multiple ground layers in winter is studied by numerical simulationmethod. Firstly, the three-dimensional mathematical model of coupled heat transferbetween U-tube and soil are established, and the simulation results are validated byexperimental data from the literature. Secondly, based on multiple ground layers, thesimulation of coupled heat transfer between U-tube and soil in winter under one monthoperation is carried out to fide, the soil temperature field and heat transfer of the U-tube,which provides the theory basis for engineering resign. At last, the effect of different factorson the heat transfer between the U-tube and soil by is discussed, including the properties ofback soil, the inlet velocity and temperature, the depth of well and the central space. Theresults provide a guidance for the optimization of GSHP.The results show: the increase of the thermal conductivity of soil can obviouslyenhance heat transfer, but the difference between single model and multiple model is small;the increase of inlet fluid temperature could enhance heat transfer, but it is not suitable forlong run; the increase of inlet velocity is advantageous for heat transfer; the higher thethermal conduction of back soil, the better the underground heat exchanger operates; withthe increase of the center space, the heat transfer of U-tube increases; when the velocity islow, heat transfer decreases with the increase of the depth of well, but with increase of thevelocity, the depth of well almost doesn’t affect the heat transfer; the increase of the depthof well will provide a high total heat transfer and decreases the soil area used. The result of the simulation is valuable for the design of ground-source heat pump system and can beapplied for practical projects, which is propitious to the development and application ofground-source heat pump.