HGS RESEARCH HIGHLIGHT – Numerical analysis of thermal response tests with groundwater flow and heat transfer model
Raymond, J., Therrien, R., Gosselin, L., & Lefebvre, R. (2011). Numerical analysis of thermal response tests with a groundwater flow and heat transfer model. Renewable Energy, 36 (1), 315–324. https://doi.org/10.1016/j.renene.2010.06.044
“We therefore developed a strategy to represent the pipes of a ground heat exchanger by assuming that their behavior could be mimicked with the discrete fracture option of HydroGeoSphere originally developed to simulate solute transport in porous and fractured medium.”
Fig. 5. (a) Model mesh and temperature distribution at (b) the beginning and (c) the end of the heating period (50.5 h) for the TRT simulation, South Dump, BH-4, 07/28/2007. The mesh surface area covers 3.31 x 3.31 m.
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This research, co-authored by J. Raymond, L. Gosselin, R. Lefebvre, and one of Aquanty’s key founding members René Therrien, explores how thermal response tests (TRTs) can be enhanced by employing HydroGeoSphere (HGS) to simulate coupled groundwater flow and heat transfer processes under complex geological settings. The study investigates the limitations of traditional line-source models, particularly in heterogeneous subsurface conditions, and introduces a numerical modelling approach to improve the accuracy of TRT analyses.
Thermal response tests are widely used to assess the thermal conductivity of subsurface materials for designing ground-coupled heat pump systems. Traditional line-source models, while effective under ideal conditions, are often constrained by assumptions such as uniform thermal properties, negligible groundwater flow, and purely conductive heat transfer. This research addresses these challenges by using HGS to model heat transfer processes that account for subsurface heterogeneities, advective heat transfer through groundwater flow, and other site-specific factors.
The study applied the HGS model to two test cases. The first involved validating the numerical approach under ideal conditions at Stillwater, Oklahoma, where line-source assumptions were largely met. Results showed that HGS could replicate the thermal conductivity values obtained using traditional models while offering additional flexibility in accounting for varying test conditions. The second case focused on a test conducted at the South Dump of the Doyon Mine in Québec, Canada—a setting where the line-source model assumptions were not valid due to subsurface heterogeneities, geothermal gradients, and atmospheric temperature fluctuations. In this case, HGS provided a more reliable estimation of thermal properties, revealing significant differences in thermal conductivity compared to the line-source model.
By leveraging HGS's ability to simulate complex heat transfer dynamics, the research demonstrates how numerical modelling can reduce errors and improve the reliability of TRT analyses in challenging geological settings. The study highlights the importance of incorporating site-specific data, such as stratigraphy and groundwater flow conditions, to enhance the accuracy of thermal property estimations.
This work provides critical insights for the geothermal energy sector, emphasizing the need for advanced modelling approaches like HGS to optimize the design of ground-coupled heat pump systems. By overcoming the limitations of traditional analytical models, this research contributes to a deeper understanding of subsurface heat transfer processes, paving the way for more efficient and sustainable geothermal energy solutions.
Abstract:
The Kelvin line-source equation, used to analyze thermal response tests, describes conductive heat transfer in a homogeneous medium with a constant temperature at infinite boundaries. The equation is based on assumptions that are valid for most ground-coupled heat pump environments with the exception of geological settings where there is significant groundwater flow, heterogeneous distribution of subsurface properties, a high geothermal gradient or significant atmospheric temperature variations. To address these specific cases, an alternative method to analyze thermal response tests was developed. The method consists in estimating parameters by reproducing the output temperature signal recorded during a test with a numerical groundwater flow and heat transfer model. The input temperature signal is specified at the entrance of the ground heat exchanger, where flow and heat transfer are computed in 2D planes representing piping and whose contributions are added to the 3D porous medium. Results obtained with this method are compared to those of the line-source model for a test performed under standard conditions. A second test conducted in waste rock at the South Dump of the Doyon Mine, where conditions deviate from the line-source assumptions, is analyzed with the numerical model. The numerical model improves the representation of the physical processes involved during a thermal response test compared to the line-source equation, without a significant increase in computational time.