Borehole thermal energy storage (BTES) in soils combined with solar thermal energy harvesting is a renewable energy system for the heating of buildings. The first community-scale BTES system in North America was installed in 2007 at the Drake Landing Solar Community (DLSC) in Okotoks, AB, Canada, and has since supplied >90% of the thermal energy for heating 52 homes. A challenge facing BTES system technology is the relatively low efficiency of heat extraction. To better understand the fluid flow and heat transport processes in soils and to improve BTES efficiency of heat extraction for future applications, a three-dimensional transient coupled fluid flow and heat transfer model was established using TOUGH2. Measured timedependent injection temperatures and fluid circulation rates at DLSC were used as model inputs. The simulations were calibrated using measured soil temperature time series. The simulated and measured temperatures agreed well with a subsurface having an intrinsic permeability of 1.5 ´ 10 −14 m 2 , thermal conductivity of 2.0 W m −1 °C −1 , and a volumetric heat capacity of 2.3 MJ m −3 °C −1 . The calibrated model served as the basis for a sensitivity analysis of soil thermal and hydrological parameters on BTES system heat extraction efficiency. Sensitivity analysis results suggest that: (i) BTES heat extraction efficiency increases with decreasing soil thermal conductivity; (ii) BTES efficiency decreases with background groundwater flow; (iii) BTES heat extraction efficiency decreases with convective heat losses associated with high soil permeability values; and (iv) unsaturated soils show higher overall heat extraction efficiency due to convection onset at higher intrinsic permeability values.Abbreviations: BTES, borehole thermal energy storage; DLSC, Drake Landing Solar Community.Growing concerns about greenhouse gas emissions and fossil fuel consumption have motivated the increased development of renewable energy systems including solar thermal energy harvesting technologies for the heating and cooling of buildings. In recent decades, borehole thermal energy storage (BTES) systems with heat derived from solar technology are rapidly gaining attention and use worldwide (Claesson and Hellstrom 1981;Dalenbäck and Jilar, 1985;Nordell and Hellström, 2000;Sanner and Knoblich, 1999;Sanner et al., 2003;Morofsky, 2007;Sibbitt et al., 2007Sibbitt et al., , 2011Sibbitt et al., , 2012Wang et al., 2010;Dehkordi and Schincariol, 2014a;Acuna and Palm, 2013;Başer and McCartney, 2015). In BTES systems, a series of U-tube pipes placed in closely spaced (1.5-2.5 m) vertical boreholes are connected to form a closed-loop heat exchanger (Fig. 1). Heat exchange is achieved by circulation of a heat carrier fluid through the closed-loop U-tube pipes. Many BTES systems store heat collected from solar thermal panels in the summer months until it can be extracted for use during the winter months. These thermal energy storage systems present a potentially economical and environmentally sustainable alternative to traditional...
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