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Energies 2017, 10(5), 703; doi:10.3390/en10050703

A Numerical Study on the Impact of Grouting Material on Borehole Heat Exchangers Performance in Aquifers

1
Civil and Environmental Engineering Department, Politecnico di Milano, P.zza L. da Vinci 32, Milano 20133, Italy
2
Energy Department, Politecnico di Milano, via Lambruschini 4, Milano 20156, Italy
*
Author to whom correspondence should be addressed.
Academic Editors: Rajandrea Sethi and Alessandro Casasso
Received: 24 March 2017 / Revised: 11 May 2017 / Accepted: 12 May 2017 / Published: 17 May 2017
(This article belongs to the Special Issue Low Enthalpy Geothermal Energy)
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Abstract

U-pipes for ground source heat pump (GSHP) installations are generally inserted in vertical boreholes back-filled with pumpable grouts. Grout thermal conductivity is a crucial parameter, dominating the borehole thermal resistance and impacting the heat exchanger efficiency. In order to seal the borehole and prevent leakages of the heat carrier fluid, grouting materials are also hydraulically impermeable, so that groundwater flow inside the borehole is inhibited. The influence of groundwater flow on the borehole heat exchangers (BHE) performance has recently been highlighted by several authors. However groundwater impact and grouting materials influence are usually evaluated separately, disregarding any combined effect. Therefore simulation is used to investigate the role of the thermal and hydraulic conductivities of the grout when the BHE operates in an aquifer with a relevant groundwater flow. Here 3 main cases for a single U-pipe in a sandy aquifer are compared. In Case 1 the borehole is back-filled with the surrounding soil formation, while a thermally enhanced grout and a low thermal conductivity grout are considered in Case 2 and Case 3 respectively. Simulations are carried out maintaining the inlet temperature constant in order to reproduce the yearly operation of the GSHP system. For each of the 3 cases three different groundwater flow velocities are considered. The results show that a high thermal conductivity grout further enhances the effects of a significant groundwater flow. The conditions when neglecting the grout material in the numerical model does not lead to relevant errors are also identified. View Full-Text
Keywords: geothermal energy; borehole heat exchanger; grouting material; numerical modeling; MT3DMS; groundwater geothermal energy; borehole heat exchanger; grouting material; numerical modeling; MT3DMS; groundwater
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Alberti, L.; Angelotti, A.; Antelmi, M.; La Licata, I. A Numerical Study on the Impact of Grouting Material on Borehole Heat Exchangers Performance in Aquifers. Energies 2017, 10, 703.

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