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Impact of operational temperature changes and freeze–thaw cycles on the hydraulic conductivity of borehole heat exchangers

Kupfernagel, Jan-Henrik ; Hesse, Jan Christopher ; Schedel, Markus ; Welsch, Bastian ; Anbergen, Hauke ; Müller, Lutz ; Sass, Ingo (2024)
Impact of operational temperature changes and freeze–thaw cycles on the hydraulic conductivity of borehole heat exchangers.
In: Geothermal Energy : Science – Society – Technology, 2021, 9 (1)
doi: 10.26083/tuprints-00023617
Article, Secondary publication, Publisher's Version

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Item Type: Article
Type of entry: Secondary publication
Title: Impact of operational temperature changes and freeze–thaw cycles on the hydraulic conductivity of borehole heat exchangers
Language: English
Date: 8 April 2024
Place of Publication: Darmstadt
Year of primary publication: 28 October 2021
Place of primary publication: Berlin ; Heidelberg
Publisher: SpringerOpen
Journal or Publication Title: Geothermal Energy : Science – Society – Technology
Volume of the journal: 9
Issue Number: 1
Collation: 25 Seiten
DOI: 10.26083/tuprints-00023617
Corresponding Links:
Origin: Secondary publication DeepGreen

A large share of the primary energy is consumed to provide space heating. Geothermal energy offers a regenerative alternative. For reasons of efficiency and environmental protection, it is important to ensure the system integrity of a borehole heat exchanger (BHE). Previous investigations have focused on the individual components of the BHE or on the grout and pipe systems’ integrity. This study focused on the analysis of the hydraulic system integrity of the complete subsoil–grout–pipe system as well as possible thermally induced changes. For this purpose, a pilot-scale experiment was built to test a 1-m section of a typical BHE under in situ pressure, hydraulic and temperature conditions. During the tests the hydraulic system permeability of the soil and the BHE was measured continuously and separately from each other. In addition, the temperature monitoring array was installed in a 50-cm cross-sectional area. Significant temperature-related fluctuations in the sealing performance could be observed. Hydraulic conductivity limits required by VDI 4640-2 (Thermal use of the underground—ground source heat pump systems, 2019) were exceeded without frost action. The succeeding application of freeze–thaw cycles further enhances the system permeability. The study shows that the thermally induced effects on the system integrity of the BHE are larger and more significant than the subsequent frost-induced effects. The hydrophobic character of the high-density polyethylene (PE-HD) pipes as well as its high coefficient of thermal expansion seem to be the main points of weakness in the system. Optimization research should focus on the interface connection between grout and pipe, whereby hydrophilic pipe materials such as stainless steel or aluminum should also be considered as well as manipulation of the pipe surface properties of PE-HD.

Uncontrolled Keywords: Borehole heat exchanger, Freeze–thaw cycles, Grouting material, Pilot-scale experiment, Hydraulic system conductivity, System integrity
Identification Number: Artikel-ID: 24
Status: Publisher's Version
URN: urn:nbn:de:tuda-tuprints-236178
Classification DDC: 300 Social sciences > 333.7 Natural resources, energy and environment
500 Science and mathematics > 550 Earth sciences and geology
Divisions: 11 Department of Materials and Earth Sciences > Earth Science > Geothermal Science and Technology
Exzellenzinitiative > Graduate Schools > Graduate School of Energy Science and Engineering (ESE)
Date Deposited: 08 Apr 2024 12:26
Last Modified: 10 Apr 2024 06:08
SWORD Depositor: Deep Green
URI: https://tuprints.ulb.tu-darmstadt.de/id/eprint/23617
PPN: 517008610
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