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Charging and discharging of soil-borehole thermal energy storage systems in the vadose zone

7th International Congress on Environmental Geotechnics : iceg2014

Abstract: This paper is focused on characterization of the heat transfer and water flow processes in a physical model of an array of borehole heat exchangers in an unsaturated soil layer. Soil-borehole thermal energy storage systems are an important new technology to store heat from solar thermal panels in the subsurface during the summer so that it may be extracted later in the winter. The physical model consists of a layer of unsaturated silt compacted atop a layer of saturated sand constructed within an insulated cylindrical tank. Three steel "U"-tube pipes were inserted through the silt layer to form a triangular array of geothermal borehole heat exchangers. Fluid was circulated through the heat exchangers to charge and discharge the borehole array with heat. During this process, the distributions of volumetric water content and temperature in the horizontal and vertical directions were measured using dielectric sensors. Further, the thermal conductivity and specific heat of the silt were also monitored using a thermal probe at the center of the soil layer at mid-height. The results confirm that coupled processes occurring in the unsaturated silt layer lead to an enhanced heat transfer during heat injection and extraction processes beyond that expected for heat transfer due to conduction. Specifically, a stable increase in apparent thermal conductivity of the soil was observed within the array during heat injection, and the distribution of water content through the soil layer indicates that a convective cycle formed in the soil layer.

To cite this article: Baser, T; Linkowski, D and McCartney, JS. Charging and discharging of soil-borehole thermal energy storage systems in the vadose zone [online]. In: Bouazza, Abdulmalek (Editor); Yuen, Samuel T S (Editor); Brown, Bruce (Editor). 7th International Congress on Environmental Geotechnics : iceg2014. [Barton, ACT]: Engineers Australia, 2014: 362-369. Availability: <http://search.informit.com.au/documentSummary;dn=984426953653426;res=IELENG> ISBN: 9781922107237. [cited 28 Jun 17].

Personal Author: Baser, T; Linkowski, D; McCartney, JS; Source: In: Bouazza, Abdulmalek (Editor); Yuen, Samuel T S (Editor); Brown, Bruce (Editor). 7th International Congress on Environmental Geotechnics : iceg2014. [Barton, ACT]: Engineers Australia, 2014: 362-369. DOI: Document Type: Conference Paper ISBN: 9781922107237 Subject: Heat--Transmission; Heat storage; Buildings--Thermal properties; Heat exchangers; Peer Reviewed: Yes Affiliation: (1) Undergraduate Researcher, Department of Civil, Environmental, and Architectural Engineering, University of Colorado, Boulder, CO, USA, email: david.linkowski@colorado.edu
(2) Associate Professor and Lyall Faculty Fellow, Department of Civil, Environmental, and Architectural Engineering, University of Colorado, Boulder, CO, USA, email:john.mccartney@colorado.edu, tel: +001-303-492-0470

Database: Engineering Collection