Full-scale temperature response function (G-function) for heat transfer by borehole ground heat exchangers (GHEs) from sub-hour to decades

Min Li, Ping Li, Vincent Chan and Alvin C.K. Lai

Applied Energy, 2014, vol. 136, issue C, 197-205

Abstract: Heat transfer by borehole ground heat exchangers involves diverse time–space scales and thus imposes a significant challenge to geothermal engineers. In order to overcome this challenge, this paper develops an analytical full-scale model from the idea of matched asymptotic expansion. The full-scale model is a composite expression consisting of a composite-medium line-source solution (inner solution), a finite line-source solution (outer solution), and an infinite line-source solution. The full-scale model is first verified by a frequency-decomposition method. Furthermore, the full-scale model is reformulated as a multi-stage model based on Duhamel’s theorem to reduce the computational cost. The multi-stage model combines the three separate solutions in a sequential way, i.e., the inner solution for the short-time scale, the conventional infinite line-source solution for the intermediate time scale, and the outer solution for the long-time scale. Finally, we perform a parametric study on a ground heat exchanger with single U-shaped tube, by which the spacing between U-tube legs, the length-to-radius ratio of borehole, the ratios of thermal diffusivities and conductivities of the ground and backfilling material are analyzed.

Keywords: Borehole ground heat exchanger; Temperature response function; Full-scale model; Composite-medium line-source model (search for similar items in EconPapers)
Date: 2014
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (28)

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DOI: 10.1016/j.apenergy.2014.09.013

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