E3S Web Conf.
Volume 205, 20202nd International Conference on Energy Geotechnics (ICEGT 2020)
|Number of page(s)||6|
|Section||Minisymposium: Geothermal Use of Built Urban Infrastructures and the Shallow Subsurface for Energy Storage and Production (organized by Frank Wuttke, Thomas Nagel, Sebastian Bauer and David Smeulders)|
|Published online||18 November 2020|
Modeling of shallow, horizontal, unsaturated, ground-based heat exchangers with consideration of dry zone formation
University of Wisconsin-Madison, Department of Civil and Environmental Engineering, 53705 Madison, WI, USA
* Corresponding author: firstname.lastname@example.org
High fluid temperatures in ground-based heat exchangers (GHXs) during the cooling season may result in a decrease in thermal conductivity of adjacent backfill (λbackfill), potentially causing degradation in the performance efficiency of the GHX system. In this study, numerical modeling was performed using the SVOffice™ finite-element software to evaluate coupled heat and moisture transfer around two GHXs. Constant-temperature boundary conditions of 35 ºC were applied to the GHX surfaces, and thermal properties of the backfill were controlled for comparisons. For estimate typical hydraulic and thermal properties for the modeling, laboratory tests and literature review were performed. Modeling results indicate that coupled heat and moisture transfer occurs rapidly near the GHX involving a dry zone formation when λbackfill decreases. A boundary between dry and wet zones where soil thermal properties rapidly change was observed around 50% GHX temperature dissipated (T50), and accordingly T50 was used to optimize the pipe configuration. Coupled heat and moisture transfer increased when the GHX configurations were optimized with consideration of dry zone formation. These results imply that thermally enhanced, engineered backfill and optimized configurations can enhance GHX system efficiency.
© The Authors, published by EDP Sciences, 2020
This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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