Research Of Soil Heat Transfer And Groundwater Seepage Based On Elliptic Type Three-dimensional Computation Of Convection And Conduction

The ground-source heat pump system stores heat in the soil in summer, and gets heatfrom the soil in winter. The heat transfer problem of GSHPS is a problem of heat seepagemechanical coupling of porous media. Nowadays, there are two main method to solve thisproblem.One is analytic method, the other is numerical computation method. The range ofapplication of the analytic method is limited. To solve this problem by numerical computationmethod, we can make use of business software, or write program by ourselves. Apparently,we can compute with FLUENT conveniently, but we couldn’t modify the internal calculationdetails. Because the software itself hides many computing details.In the future, our task team will make an effort to do more research on heat exchangemechanism of the soil. A model consist of solid phase, liquid phase, gaseous phase inaeration zone and saturated water zone, will be proposed. It will be difficult to solve thisproblem with FLUENT software. Therefore, to write programs by ourselves will be necessary.Given these factors, this paper finished a series of programs in regard to elliptic typethree-dimensional convection and heat transfer, and analyzed some problems of a singleU-vertical ground heat exchanger and five tubes heat exchangers of GSHPS.Proprietary programming method is adopted to write programs of Elliptic typethree-dimensional convection and heat transfer with FORTRAN by this paper. The programsrun with Fortran PowerStation4.0, and were tested with two examples.This paper built the thermal seepage coupling model of a single U-vertical ground heatexchanger of GSHPS，based on the theory of porous medium. Concerning the thermalperformance, the author analyzed the influence of groundwater seepage velocity, porosity,layering of soil in the article. The study found that the greater the speed of seepage, the betterthe thermal performance, and the smaller the porosity, the better the thermal performance. Theresearches also show that the thermal performance would be worse with layers of the thermalconductivity of soil, compared with homogeneous soil, and the thermal performance is almostthe same with layers of the volumetric heat capacity of soil, compared with homogeneoussoil.In addition to that, This paper also built the thermal seepage coupling model of five tubes heat exchangers of GSHPS. The author discussed long-term performance of heatexchangers of GSHPS, under the circumstance of cold and hot dynamic load balancing orimbalance respectively, with a real project. The study finds that with balancing load, theperformance of heat exchangers remain stable in the10years running. However, theperformance of heat exchangers becomes worse, or even couldn’t working with dynamic loadimbalance in the long-term running. This paper also discussed the influence of seepage to fivetubes heat exchangers. It also finds that the seepage could weaken the influence of dynamicload imbalance in the long-term running.