Prediction of ground thermal diffusivity from thermal response tests

Abstract

Ground-coupled heat pump (GCHP) systems are being increasingly utilized in recent years. There are several important parameters in the design of GCHP systems. As ground thermal conductivity is one of the most crucial parameters, it should be measured by conducting in-situ thermal response tests (TRTs). This paper presents the experimental results and analysis of thermal response tests to estimate the ground thermal conductivity and ground thermal diffusivity for three types of ground heat exchangers (GHEs), including U, 2U, and W-type ground heat exchangers (GHEs). Three different types of GHEs were installed in a dredged soil deposit, and continuous TRTs were conducted for 48 h. This study suggests a method to predict ground thermal diffusivity using the infinite line source model from the TRTs. Furthermore, soil samples were collected from different ground layers, and ground thermal properties were measured using laboratory tests. The equivalent ground thermal conductivity and ground thermal diffusivity measured through laboratory tests were compared with the in-situ TRT results that were newly derived in this paper. In addition, ground thermal diffusivity and ground thermal conductivity values that were obtained through research were used as input parameters in numerical analysis. The in-situ TRT results were numerically modeled using the finite element method.