Operational Response of a Soil-Borehole Thermal Energy Storage System
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 142, Issue 4
Abstract
This study focuses on an evaluation of the subsurface ground temperature distribution during operation of a soil-borehole thermal energy storage (SBTES) system. The system consists of an array of five 9 m-deep geothermal heat exchangers, configured as a central heat exchanger surrounded by four other heat exchangers at a radial spacing of 2.5 m. In addition to monitoring the temperature of the fluid entering and exiting each heat exchanger, 5 thermistor strings were embedded in boreholes inside and outside of the array to monitor changes in ground temperature with depth. After 75 days of heat injection at a constant rate of , corresponding to 11.5 GJ of thermal energy, the average ground temperature in the array increased by 7°C. However, depending on the storage volume definition, only 2.43–4.86 GJ of thermal energy was stored attributable to heat losses. After a 4-month rest period the heat storage was observed to decrease by 60% owing to further heat losses. The trends in subsurface temperatures during heat injection were consistent with results from a simplified heat injection simulation using the system thermal conductivity estimated from a line source analysis. Although the heat injection rate of is smaller than that expected in actual SBTES systems (), an energy balance analysis indicates the number of boreholes in the array was too few to effectively concentrate the heat injected within the subsurface. Nonetheless, the results provide an experimental reference point between a single borehole and a larger SBTES system.
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Acknowledgments
Funding from National Science Foundation (NSF 1230237) is much appreciated. The opinions are those of the authors alone and do not reflect the viewpoint of the sponsor.
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Published In
Journal of Geotechnical and Geoenvironmental Engineering
Volume 142 • Issue 4 • April 2016
Copyright
© 2015 American Society of Civil Engineers.
History
Received: Feb 19, 2015
Accepted: Sep 14, 2015
Published online: Dec 22, 2015
Published in print: Apr 1, 2016
Discussion open until: May 22, 2016
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