Estimation of soil and grout thermal properties for ground-coupled heat pump systems: Development and application

Ground thermal properties, including the thermal conductivity and diffusivity of both soil and grout, are significant considerations for the design of a ground-coupled heat pump (GCHP) system. However, as a result of the limitations inherent in available response models, few in-situ thermal response tests (TRTs) can identify grout thermal conductivity and diffusivity. This paper proposes a new method to estimate the thermal conductivity and diffusivity of both soil and grout simultaneously using the recently developed infinite composite-medium line source (ICMLS) model. Firstly, a linear dependence analysis is performed on the aforementioned four parameters to ensure the feasibility of the proposed method, leading to an estimation of the minimum TRT duration. Secondly, uncertainty analysis is carried out to analyze the influence of U-pipe shank spacing, as it is considered a sensitive parameter in modeling the heat transfer of ground heat exchangers (GHEs). Thirdly, a genetic algorithm is used to identify these four parameters using the data collected from a TRT. The proposed method is verified using a well-designed sandbox experiment. Finally, its application is demonstrated and evaluated by applying it to the design of a GCHP system for an office building at Hunan University.