Study On The Characteristics Of Horizontal Ground Heat Exchanger With Consideration Of Heat And Moisture Transfer In The Soil

For recent years, the energy and environmental problems are getting severe all aroundthe world, the intense ones of which are the increasement of energy costs and the short supplyof water sources during the everyday production and life. Ground source heat pump (GSHP)system as one of the most energy saving and environmentally friendly technology hasreceived more attention. Horizontal heat exchanger for the GSHP system is popular in USAand Europe, but it is used as a supplement of vertical heat exchanger in China. For achievingthe goal of sustainable use of water and energy resources, the technology combined with theGSHP technology and Low Impact Development technology (LID) is proposed. It is meansthat use the LID technology to increase the water content, so that the performance ofhorizontal heat exchanger in GSHP system could be improved.In this paper, a one-dimensional infiltration physics and mathematical model for waterinfiltration is proposed to study the variation of soil moisture field. Moreover a coupled heatand moisture transfer model for the unsaturated soil was developed to study the characteristicsof horizontal ground heat exchanger. In this model, different soil initial moisture, differentsoil-water characteristics and dry density of the soil were taken in account, which couldimpact the performance of the heat exchanger and the soil.Firstly, based on saturated-unsaturated infiltration theory, a one-dimensional transientmodel along depth direction was established. The model was validated by the existingconstant infiltration experiment. Meanwhile it simulated the humidity field distribution alongdepth direction by a typical Beijing rainfall model. In the simulation, catchment area andrainfall or irrigation were taken in account, which played an important role on soil moisturefield.Secondly, the sandbox experiment for horizontal heat exchanger and the measure methodfor required parameter for describing soil-water characteristics are introduced. Then, theparameter such as soil porosity, soil particle size distribution parameter are determined. By thesandbox experiment, the migration of the temperature field and soil moisture field isobserved.Finally, a coupled heat and moisture quasi-three-dimensional for horizontal heatexchanger and soil was proposed. After sand box test bench was set up, which was conducteda series of experiment, to validate the model. Because the rainfall could improve the moistureof the soil, this model studied the heat transfer rate and temperature or moisture field underdifferent moisture initial content. What’s more, the soil-water characteristics and soil porositywere also taken in account, which could impact the performance of the heat exchanger andthe soil.