Numerical analysis of the effect of different soil types and water content on heat transfer performance of horizontal buried pipes

In order to reveal the heat transfer performance of the horizontal buried pipe heat exchanger in the ground source heat pump system in different soil types, this paper, based on the theoretical knowledge of soil capillary water, combined with the means of numerical simulation, discusses the influence of the difference of three-phase composition in different types of energy storage soil on the heat transfer characteristics of the horizontal buried pipe heat exchanger. The results show that under the cooling condition of 308.15 K, the outlet water temperature of the horizontal pipe in the loam soil decreases to 303.3 K and the temperature difference between the inlet and outlet water is 4.9 K. The heat transfer perlinear meter of the buried pipe is 37.1 W/m. That means the heat transfer efficiency of the horizontal pipe in the loam soil is significant. When different soils(sandy soil, loam soil and clay soil) go through the same refrigeration cycle, the heat transfer process of the horizontal pipe has the least effect on the temperature distribution of loam soil, with the lowest thermal accumulation risk coefficient of the pipe. The research result shows that the soil heat conductivity has greater impact on the heat exchange capability of the horizontal pipe than the soil specific heat capacity. The heat transfer capacity of the horizontal pipe can be enhanced by compacting back fill materials, decreasing the porosity, improving the soil phase conductivity, and increasing the buried depth to utilize the higher specific heat capacity of groundwater.