Keywords :
Borehole heat exchanger; Graphite; Ground source heat pump; Grouting material; Thermal transfer; Analytical predictions; Borehole heat exchangers; Borehole resistances; Grouting materials; High thermal conductivity; Thermo-physical property; Water-saturated sand; Energy Engineering and Power Technology; Industrial and Manufacturing Engineering
Abstract :
[en] In borehole heat exchangers (BHE), grouting material plays a significant role in the heat transfer between the ground and the heat carrier fluid in the pipes. To guarantee proper sealing capacity of the grouting materials, the grout must also fulfill suitable hydraulic and mechanical properties. This paper evaluates the performance of various grouting materials, through thermal, hydraulic and mechanical laboratory characterizations. In particular, the addition of graphite powder to improve the thermal properties of grouting material is tested. In parallel, the characteristics of two different widely used commercial grouting materials (i.e. bentonite-based and silica sand-based materials) are also investigated. Afterwards, the specific heat exchange rate and the borehole resistance of borehole heat exchangers are assessed experimentally in a 1 × 1 × 1 m3 sandbox under, successively, dry sand and fully water-saturated sand conditions. During the operations, the monitored temperatures in the sandbox are in good agreement with analytical predictions. This study demonstrates that the homemade admixture prepared with 5% natural flake graphite can be considered as an appropriate grout for BHEs regarding to its rheological and thermo-physical properties. Thermally-enhanced grouting can be of significant interest in a high thermal conductivity ground (such as saturated sand) because it minimizes the thermal resistance of the BHE. © 2014 Elsevier Ltd. All rights reserved.
Funding text :
The financial support from Walloon Region in Belgium is profoundly acknowledged (Grant: 1117492 - GeoTherWal - Programme mobilisateur ERable (E24+)). Furthermore, the authors would like to thank the company Schwenk GmbH Germany, Timcal Company Switzerland and Sika group Belgium for raw materials. The assistance of Mrs Georgia Ratioti (Université de Liège, Belgium) for the measurement of thermal conductivity of grout is also deeply acknowledged.
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