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Abstract: The technology of embedding heat exchange tubes in diaphragm walls is a new direction for Ground-coupled Heat Pumps (GCHP). This paper examines the heat transfer model and design method for geothermal heat exchangers in diaphragm walls, which are seldom investigated in the world. Two-dimensional (2D) heat transfer models for diaphragm wall heat exchangers (DWHE) are established. A design method for DWHE is further developed to calculate the hourly heat exchange capacity of DWHE and to get the reasonable design parameter of DWHE. The DWHE model over the excavation line has the same changing trend with numerical solutions, and the relative errors between them are less than 2%. The relative errors of calculated heat exchange rate per meter using DWHE model and measured data are less than 6% after running 10h. The relative errors of temperature between DWHE model under the excavation line and the measured data at different positions are no more than 9%, whereas the relative error between the tradition models in GCHP (line source model and finite-line source model) and the measured data may reach as much as 40%. [Copyright &y& Elsevier]

Abstract: The ground-coupled heat pump (GCHP) systems have been identified as one of the best sustainable energy technologies for space heating and cooling in buildings. While the foundation piles of buildings are used to partly take the place of boreholes in the ground heat exchanger (GHE) in recent years, the classical approaches of the line heat source model and the “hollow” cylindrical heat source model for the borehole GHEs fail for thermal analysis and design of the pile GHEs. Evolved from the classical models, a new “solid” cylindrical source model is presented in this paper to consider both the radial dimension and the heat capacity of the borehole or pile. Expressions of the analytical solution are derived for 1-D and 2-D new models by means of the Green’s function method. Results obtained from the new 1-D model are compared with the classical line source and “hollow” cylindrical source models of the borehole GHE, and also validated by a numerical solution of the same model. While the 1-D and 2-D solid cylindrical source models can provide adequate tools for design and simulation of the pile GHEs, improvement can also be achieved in simulating the temperature response of the borehole GHEs, especially for short time steps. [Copyright &y& Elsevier]