Effective pipe-to-borehole thermal resistance for vertical ground heat exchangers

Sharqawy, Mostafa H.; Mokheimer, Esmail M. A.; Badr, H. M.

doi:10.1016/j.geothermics.2009.02.001

Cited by 118 publications

(74 citation statements)

References 6 publications

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“…Previous studies employed finite element numerical techniques (Sharqawy 2009;Sagia 2012;Liao 2012). While these are rigorous, they have also proven to be cumbersome to construct.…”

mentioning

confidence: 99%

Thermal resistance of borehole heat exchangers composed of multiple loops and custom shapes

Koenig

2015

Geotherm Energy

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Background: The thermal resistance of a borehole can be reduced by employing thermally enhanced grout, increasing the surface area of the loop and locating the legs proximal to the bore wall. Thermal models that are used to predict borehole heat exchange are characterized by either simplified formulations that are restrictive in their application, but utilitarian, or complex multi-dimensional analyses that are cumbersome to implement. Methods: The borehole resistance methodology presented here offers a straightforward solution that is built on single loop conduction shape factor analysis with thermal shunt accounting and pipe-pipe configuration analysis, to extend to multi-loop borehole configurations and custom kidney extrusions. Results: The borehole resistance predictions are compared to published data and information listed by manufacturers of multi-loop products in third party thermal tests against standard loops. The results are found to agree within the constraints posed by the model assumptions. The methodology offers a straightforward solution that can be incorporated into popular geothermal loop sizing software such as GLD, GLHEPRO and other system software. Conclusions: The advantages and challenges of these advanced loop designs are discussed and conclusions drawn. By reducing the bore resistance, one can take advantage of less drilling and proportionally less capital cost for the bore field, while achieving the same loop temperatures.

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“…Previous studies employed finite element numerical techniques (Sharqawy 2009;Sagia 2012;Liao 2012). While these are rigorous, they have also proven to be cumbersome to construct.…”

mentioning

confidence: 99%

Thermal resistance of borehole heat exchangers composed of multiple loops and custom shapes

Koenig

2015

Geotherm Energy

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“…6, the R eff may increase to a greater extent. By co mparing the results of case B with models, the numerical results are approximately 6~22% higher than Remund (1999) and 15~26% lower than Sharqawy et al (2009).…”

Section: Model Validationmentioning

confidence: 85%

“…The effective thermal resistances R eff in case B, C and D can be modified by co mbining the equations of R b as presented by Shonder and Beck (1999), Gu and O'Neal (1998), Remund (1999) and Sharqawy et al (2009). The R eff is plotted in Fig.…”

Section: Model Validationmentioning

confidence: 99%

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Quantitative evaluation of improper backfilling in vertical borehole

Chen

Mao

2016

JTST

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Vertical ground heat exchanger (GHE) is widely being used to exchange heat into the ground by using the system of ground source heat pump (GSHP). The stability and thermal performance of GHE mainly relate to the grout, the advantages of GHE can be negated if the grout is not backfilled properly. In order to study the influence of grout backfilling in a vertical GHE, this study established a 2D steady-state heat conduction model, which simulated 4 cases as follows: (1) fine backfilling, (2) porous backfilling, (3) hole-wall delaminating and (4) pipe-wall delaminating. The thermal resistances inside borehole in 4 cases were estimated by using numerical and analytical methods. It has been observed that improper backfilling generates heat barriers, prolongs the time required for heat transfer and reduces heat exchange capacity. The pipe-wall delaminating greatly increases the thermal resistance and brings the worst impact to a GHE.

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“…It represents the resistance in exchanging heat between ground and thermo-vector fluid and can be higher or lower depending on material properties and geometry, as well as on quality of installation. In this paper, we assume that installation quality is optimum, so that grouting is homogeneous along the hole and the borehole section is regular (Sharqawy et al 2009). …”

Section: Introductionmentioning

confidence: 99%

Thermal response test for shallow geothermal applications: a probabilistic analysis approach

2015

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Background: Thermal Response Test (TRT) is an onsite test used to characterize the thermal properties of shallow underground, when used as heat storage volume for shallow geothermal application. It is applied by injecting/extracting heat into geothermal closed-loop circuits inserted into the ground. The most common types of closed loop are the borehole heat exchangers (BHE), horizontal ground collectors (HGC), and energy piles (EP). The interpretation method of TRT data is generally based on a regression technique and on the calculation of thermal properties through different models, specific for each closed loop and test conditions.

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Effective pipe-to-borehole thermal resistance for vertical ground heat exchangers

Cited by 118 publications

References 6 publications

Thermal resistance of borehole heat exchangers composed of multiple loops and custom shapes

Thermal resistance of borehole heat exchangers composed of multiple loops and custom shapes

Quantitative evaluation of improper backfilling in vertical borehole

Thermal response test for shallow geothermal applications: a probabilistic analysis approach

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