The utilization of geothermal energy through ground buried heat exchanger to provide heat source for buildings has become extremely attractive recent years in China and all over the world. As a key parameter that governs the prediction of the system performance, the effective thermal conductivity of the ground significantly affects the heat transfer process between buried pipes and surrounding rock-soil. This paper conducts a review on the methods of determining the effective thermal conductivities of different rock-soil types composed by various substances proposed in recent years. Based on the analysis of theoretical methods and experimental approaches applied to different rock-soil conditions and other relevant parameters such as the porosity, water content and material construction, etc., the applicabilities of various methods have been justified. According to the deficiencies of basic models, the improved models take into account the effects of the temperature, saturation degree, detailed structure of rock-soil and other parameters to improve the accuracy of prediction value. For certain types of rock-soil, the experimental approaches can provide more accurate results but are expensive and time consuming, which have sometimes been used to improve the accuracy or verify the results of improved model in the appropriate range of porosity and saturation degree for certain types of rocks. The concluding remarks would contribute to the estimation of the heat transfer performance of the buried heat exchanger during the prediction process.

As a kind of clean energy resource, geothermal energy is widely utilized in many fields, especially for heating and ventilation through heat exchangers buried underground. The use of geothermal heat exchange system will contribute to energy saving as well as building sustainable, therefore it has become more and more popular in recent years. Rock-soil thermal conductivity plays a noticeable role in the performance of ground buried heat exchanger. In the present study, a new analytical model was proposed to describe the spatial structure of the multiphase rock-soil and relative position of solid, liquid and gas phase. Through analyzing the relationship among different phases and coding FORTRAN program, the model structure parameters can be obtained for the calculation of parallel thermal resistances. The expression of the thermal conductivity derived from the model was then applied to obtain the thermal conductivity of the Tripoli sand from North Africa, before the results were compared with previous tests. After comparative analysis, the newly proposed model in this study was proved accurate in predicting the thermal conductivity of the chosen soil with around 20% averaged relative error, which will contribute to the prediction of rock-soil thermal properties as well as the design of ground buried heat exchanger.