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Natural convection in groundwater-filled boreholes used as ground heat exchangers

Spitler, Jeffrey D ; Javed, Saqib LU and Ramstad, Randi Kalskin (2016) In Applied Energy 164. p.352-365
Abstract
In most of the world, borehole heat exchangers used with closed-loop ground source heat pump systems are backfilled with a low permeability grout to prevent water contamination. However, in Scandinavian countries, a different approach is taken – the borehole is sealed at the top and cased down to solid bedrock. The borehole then naturally fills with groundwater in the annular space between the U-tube and the borehole wall. Compared to grouted boreholes, the groundwater filling is advantageous in that it generally results in low borehole thermal resistance due to buoyancy-driven natural convection enhancing the heat transfer. Although this phenomena has been reported in several papers since the late 1980s, no calculation models have been... (More)
In most of the world, borehole heat exchangers used with closed-loop ground source heat pump systems are backfilled with a low permeability grout to prevent water contamination. However, in Scandinavian countries, a different approach is taken – the borehole is sealed at the top and cased down to solid bedrock. The borehole then naturally fills with groundwater in the annular space between the U-tube and the borehole wall. Compared to grouted boreholes, the groundwater filling is advantageous in that it generally results in low borehole thermal resistance due to buoyancy-driven natural convection enhancing the heat transfer. Although this phenomena has been reported in several papers since the late 1980s, no calculation models have been available for use in either design tools or simulation programs. This paper presents experimental measurements from a single well-instrumented borehole under a range of heat transfer rates and annulus temperatures. Nusselt numbers for natural convection in the annulus are correlated against modified Rayleigh number. The results are verified by comparing to borehole thermal resistances predicted with the correlations to actual measurements from a range of boreholes in Sweden and Norway. (Less)
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type
Contribution to journal
publication status
published
subject
in
Applied Energy
volume
164
pages
14 pages
publisher
Elsevier
external identifiers
  • scopus:84951114014
ISSN
1872-9118
DOI
10.1016/j.apenergy.2015.11.041
language
English
LU publication?
no
id
812df971-3669-4933-b85d-5571f1c833e5
date added to LUP
2016-05-26 00:05:38
date last changed
2022-11-11 11:32:32
@article{812df971-3669-4933-b85d-5571f1c833e5,
  abstract     = {{In most of the world, borehole heat exchangers used with closed-loop ground source heat pump systems are backfilled with a low permeability grout to prevent water contamination. However, in Scandinavian countries, a different approach is taken – the borehole is sealed at the top and cased down to solid bedrock. The borehole then naturally fills with groundwater in the annular space between the U-tube and the borehole wall. Compared to grouted boreholes, the groundwater filling is advantageous in that it generally results in low borehole thermal resistance due to buoyancy-driven natural convection enhancing the heat transfer. Although this phenomena has been reported in several papers since the late 1980s, no calculation models have been available for use in either design tools or simulation programs. This paper presents experimental measurements from a single well-instrumented borehole under a range of heat transfer rates and annulus temperatures. Nusselt numbers for natural convection in the annulus are correlated against modified Rayleigh number. The results are verified by comparing to borehole thermal resistances predicted with the correlations to actual measurements from a range of boreholes in Sweden and Norway.}},
  author       = {{Spitler, Jeffrey D and Javed, Saqib and Ramstad, Randi Kalskin}},
  issn         = {{1872-9118}},
  language     = {{eng}},
  pages        = {{352--365}},
  publisher    = {{Elsevier}},
  series       = {{Applied Energy}},
  title        = {{Natural convection in groundwater-filled boreholes used as ground heat exchangers}},
  url          = {{http://dx.doi.org/10.1016/j.apenergy.2015.11.041}},
  doi          = {{10.1016/j.apenergy.2015.11.041}},
  volume       = {{164}},
  year         = {{2016}},
}