Methods For Determining The Thermal Conductivity Of Underground Soil And Results Analysis

The thermal property of underground soil plays an important role in the proper design of closed-loop, Ground Source Heat Pump (GSHP) systems .The numbers of boreholes and the depth of each borehole are highly dependent on the soil thermal property. Consequently, depending on the geographic location and the drilling cost, the soil thermal properties mainly influence the initial cost to install a GSHP system. But the designers of the ground loop heat exchangers have a very difficult job to find the "true " thermal property.This thesis presented several test methods and analysis models for determining the thermal conductivity of underground soil that might be applied to borehole heat exchangers. By simplifying the G-function, a simplified cylindrical source model was derived. A numerical program was compiled for the simplified cylindrical source model incorporating the parameter estimation technique.A two-dimensional numerical heat transfer model for the vertical ground loop heat exchanger was developed on the basis of finite element thermal analysis software, and incorporated the parameter estimation technique to estimate the thermal conductivity of the soil around the borehole. The numerical finite element model was verified by comparing results with the simplified cylindrical source model.The line source model, the simplified cylindrical source model and the two-dimensional numerical model were used to determine the thermal conductivity of underground soil. And the sensitivity of the results to some different parameters was analyzed, such as, the length of the test, the soil initial temperature, the soil volumetric specific heat, the grout thermal properties and the shank space.