### Abstract

Groundwater flow is one of the most important factors for the design of a ground heat exchanger (GHEX) since the thermal environment of the ground around the buried GHEX is significantly affected by heat convection due to the groundwater flow. Several preceding studies have been conducted to develop analytical solutions to the heat transfer model of GHEX with consideration of groundwater flow. One of these solutions is the combined heat transfer model of conduction and convection. However, the developed combined analytical models are inapplicable to all of the configurations of ordinary GHEXs because these solutions assume that the inner part of the borehole is thermally inert or consists of the same material as that of the surrounding ground. In this paper, the applicability of the combined solid cylindrical heat source model, which is the most suitable to energy piles until now, was evaluated by performing a series of numerical analyses. In the numerical analysis, the inner part of the borehole was modeled as two different materials (i.e., permeable ground formation and impermeable fill such as concrete) to evaluate applicability of the analytical solution along with different diameter-length (D/L) ratios of borehole. In a small value of the D/L ratio, the analytical solution to the combined heat transfer model is in good agreement with the result of numerical analysis. On the other hand, when increasing the D/L ratio, the analytical solution significantly overestimates the effect of groundwater flow on the heat transfer of GHEXs because the analytical solution disregards the existence of the impermeable region in the borehole. Consequently, such tendency is more critical in the GHEX with a large D/L ratio such as large-diameter energy piles.

Original language | English |
---|---|

Article number | 318 |

Journal | Energies |

Volume | 9 |

Issue number | 5 |

DOIs | |

Publication status | Published - 2016 Apr 25 |

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### Keywords

- Analytical solution
- Combined heat transfer model
- Energy pile
- Ground heat exchanger (GHEX)
- Groundwater flow
- Numerical analysis

### ASJC Scopus subject areas

- Computer Science(all)

### Cite this

*Energies*,

*9*(5), [318]. https://doi.org/10.3390/en9050318

**Effect of borehole material on analytical solutions of the heat transfer model of ground heat exchangers considering groundwater flow.** / Park, Sangwoo; Lee, Seokjae; Lee, Hyobum; Pham, Khanh; Choi, Hangseok.

Research output: Contribution to journal › Article

*Energies*, vol. 9, no. 5, 318. https://doi.org/10.3390/en9050318

}

TY - JOUR

T1 - Effect of borehole material on analytical solutions of the heat transfer model of ground heat exchangers considering groundwater flow

AU - Park, Sangwoo

AU - Lee, Seokjae

AU - Lee, Hyobum

AU - Pham, Khanh

AU - Choi, Hangseok

PY - 2016/4/25

Y1 - 2016/4/25

N2 - Groundwater flow is one of the most important factors for the design of a ground heat exchanger (GHEX) since the thermal environment of the ground around the buried GHEX is significantly affected by heat convection due to the groundwater flow. Several preceding studies have been conducted to develop analytical solutions to the heat transfer model of GHEX with consideration of groundwater flow. One of these solutions is the combined heat transfer model of conduction and convection. However, the developed combined analytical models are inapplicable to all of the configurations of ordinary GHEXs because these solutions assume that the inner part of the borehole is thermally inert or consists of the same material as that of the surrounding ground. In this paper, the applicability of the combined solid cylindrical heat source model, which is the most suitable to energy piles until now, was evaluated by performing a series of numerical analyses. In the numerical analysis, the inner part of the borehole was modeled as two different materials (i.e., permeable ground formation and impermeable fill such as concrete) to evaluate applicability of the analytical solution along with different diameter-length (D/L) ratios of borehole. In a small value of the D/L ratio, the analytical solution to the combined heat transfer model is in good agreement with the result of numerical analysis. On the other hand, when increasing the D/L ratio, the analytical solution significantly overestimates the effect of groundwater flow on the heat transfer of GHEXs because the analytical solution disregards the existence of the impermeable region in the borehole. Consequently, such tendency is more critical in the GHEX with a large D/L ratio such as large-diameter energy piles.

AB - Groundwater flow is one of the most important factors for the design of a ground heat exchanger (GHEX) since the thermal environment of the ground around the buried GHEX is significantly affected by heat convection due to the groundwater flow. Several preceding studies have been conducted to develop analytical solutions to the heat transfer model of GHEX with consideration of groundwater flow. One of these solutions is the combined heat transfer model of conduction and convection. However, the developed combined analytical models are inapplicable to all of the configurations of ordinary GHEXs because these solutions assume that the inner part of the borehole is thermally inert or consists of the same material as that of the surrounding ground. In this paper, the applicability of the combined solid cylindrical heat source model, which is the most suitable to energy piles until now, was evaluated by performing a series of numerical analyses. In the numerical analysis, the inner part of the borehole was modeled as two different materials (i.e., permeable ground formation and impermeable fill such as concrete) to evaluate applicability of the analytical solution along with different diameter-length (D/L) ratios of borehole. In a small value of the D/L ratio, the analytical solution to the combined heat transfer model is in good agreement with the result of numerical analysis. On the other hand, when increasing the D/L ratio, the analytical solution significantly overestimates the effect of groundwater flow on the heat transfer of GHEXs because the analytical solution disregards the existence of the impermeable region in the borehole. Consequently, such tendency is more critical in the GHEX with a large D/L ratio such as large-diameter energy piles.

KW - Analytical solution

KW - Combined heat transfer model

KW - Energy pile

KW - Ground heat exchanger (GHEX)

KW - Groundwater flow

KW - Numerical analysis

UR - http://www.scopus.com/inward/record.url?scp=84992524284&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84992524284&partnerID=8YFLogxK

U2 - 10.3390/en9050318

DO - 10.3390/en9050318

M3 - Article

AN - SCOPUS:84992524284

VL - 9

JO - Energies

JF - Energies

SN - 1996-1073

IS - 5

M1 - 318

ER -