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Environmental Earth Sciences

, 77:152 | Cite as

Determination of ground thermal properties for energy piles by thermal response tests

  • Jin LuoEmail author
  • Haifeng Zhao
  • Wei Huang
  • YongQiang Zhu
  • Wei Xiang
  • Joachim Rohn
Thematic Issue
Part of the following topical collections:
  1. Subsurface Energy Storage II

Abstract

Thermal properties of ground heat exchanger (GHE) such as effective thermal conductivity and borehole thermal resistance are commonly measured in the field by thermal response tests (TRTs). TRT has been proved to be a consolidated method to determine thermal properties of traditional borehole heat exchangers (BHEs). However, there is still lack of data for adopting TRT on energy piles with often a large diameter and deficiency in validation of TRT results with geological materials. In this study, ground thermal properties for typical configured GHEs of energy piles are investigated. Three TRTs are conducted and the obtained results are analyzed. Effective thermal conductivity, λeff, of the ground derived by following the traditional linear source model shows large deviation as compared to the thermal conductivity of the geological materials. In order to determine λeff properly, the linear source model is modified and an equivalent radius, req, of energy piles is considered. The λeff estimated by the modified model shows a good agreement with thermal conductivity of the in situ geological materials. In addition, there has been no obvious correlation between borehole thermal resistances and thermal efficiency due to heat transport of energy piles that depends not only by borehole thermal resistance but also by the pile’s diameter and ground conditions. The findings drawn from this study indicate that the modified model is reasonable and useful in determining thermal properties of energy piles.

Keywords

Ground heat exchanger Energy pile Effective thermal conductivity Borehole thermal resistance 

List of symbols

T

Temperature (°C)

r

Radius (m)

Q

Amount of energy (J)

q

Thermal transfer rate (W)

W

Water pumping rate (m3/h)

c

Volumetric heat capacity (J/m3 K)

H

Length (m)

D

Diameter (m)

t

Time (s)

P

Ply (mm)

R

Thermal resistance (m K/W)

Greek symbols

ρ

Density (g/cm3)

λ

Thermal conductivity (W/m K)

α

Thermal diffusivity (m2/s)

γ

Euler constant

First-order derivativeness

Subscripts

Inlet

Inlet flow

Outlet

Outlet flow

f

Fluid

s

Ground surrounding

eq

Equivalent

b

Borehole

w

Water

p

Pipe

eff

Effective

g

Grouting

e

External diameter

Notes

Acknowledgements

This work was funded by National Natural Science Foundation of China (NSFC) (Authorized No. 41502238) and Fundamental Research Funds for the Central Universities, China University of Geosciences (Wuhan) No. CUGL150818. The financial support provided by China Scholarship Council (CSC) during the visit at University of California, Berkeley, is deeply appreciated.

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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  • Jin Luo
    • 1
    Email author
  • Haifeng Zhao
    • 2
  • Wei Huang
    • 1
  • YongQiang Zhu
    • 1
  • Wei Xiang
    • 1
  • Joachim Rohn
    • 3
  1. 1.Faculty of EngineeringChina University of Geosciences (Wuhan)WuhanPeople’s Republic of China
  2. 2.Survey Research Institute of the Three Gorges Co. Ltd.WuhanPeople’s Republic of China
  3. 3.GeoZentrum Nordbayern, University of Erlangen-NürnbergErlangenGermany

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