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Geotechnical and Geological Engineering

, Volume 33, Issue 2, pp 273–289 | Cite as

The Thermal Behaviour of Three Different Auger Pressure Grouted Piles Used as Heat Exchangers

  • Fleur LoveridgeEmail author
  • C. Guney Olgun
  • Tracy Brettmann
  • William Powrie
Original paper

Abstract

Three auger pressure grouted (APG) test piles were constructed at a site in Richmond, Texas. The piles were each equipped with two U-loops of heat transfer pipes so that they could function as pile heat exchangers. The piles were of two different diameters and used two different grouts, a standard APG grout and a thermally enhanced grout. Thermal response tests, where fluid heated at a constant rate is circulated through the pipe loops, were carried out on the three piles, utilising either single or double loops. The resulting test data can be used to determine the surrounding soil thermal conductivity and the pile thermal resistance, both essential design parameters for ground source heat pump systems using pile heat exchangers. This paper uses parameter estimation techniques to fit empirical temperature response curves to the thermal response test data and compares the results with standard line source interpretation techniques. As expected, the thermal response tests with double loops result in smaller thermal resistances than the same pile when the test was run with a single loop. Back analysis of the pile thermal resistance also allows calculation of the grout thermal properties. The thermally enhanced grout is shown to have inferior thermal properties than the standard APG grout. Together these analyses demonstrate the importance of pile size, grout thermal properties and pipe positions in controlling the thermal behaviour of heat exchanger piles.

Keywords

Ground source heat pumps Piling Pile heat exchangers Thermal properties Thermal response tests 

Abbreviations

APG

Auger pressure grouted pile

APGE

Auger pressure grouted energy pile

AR

Aspect ratio

RMSE

Root mean square error

TG

Thermal grout

List of symbols

Fo

Fourier number (non-dimensional time)

G

G-function

Gc

Concrete G-function

Gg

Pile G-function

H

Pile length

hi

Heat transfer coefficient

\(\dot{m}\)

Mass flow rate

n

Number of pipes

q

Applied power per metre depth

Rb

Pile or borehole resistance

Rc

Concrete resistance

Rp

Pipe resistance

Rpcond

Pipe conductive resistance

Rpconv

Pipe convective resistance

rb

Pile or borehole radius

ri

Pipe inner radius

ro

Pipe outer radius

Sc

Specific heat capacity OR shape factor

s

Shank spacing

T

Temperature

∆T

Change in temperature

Tin

Pile entering temperature

Tout

Pile leaving temperature

t

Time

αg

Thermal diffusivity of ground

Φf

Dimensionless fluid temperature change

Φg

Dimensionless temperature change in the ground

γ

Euler’s constant

λc

Thermal conductivity of concrete/grout

λg

Thermal conductivity of ground

λp

Thermal conductivity of pipe material

Notes

Acknowledgments

This work has been carried out with support from the UK Engineering and Physical Science Research Council (research grant number EP/H049010/1). The second author was supported by the U.S. National Science Foundation under grants No. CMMI-0928807 and CMMI-1100752. The authors would also like to acknowledge Berkel & Company who funded the field testing and Jim Shaver who collected the test data.

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Copyright information

© Springer International Publishing Switzerland 2014

Authors and Affiliations

  • Fleur Loveridge
    • 1
    Email author
  • C. Guney Olgun
    • 2
  • Tracy Brettmann
    • 3
  • William Powrie
    • 1
  1. 1.University of SouthamptonHighfield, SouthamptonUK
  2. 2.Virginia TechBlacksburgUSA
  3. 3.A. H. Beck Foundation Co., Inc.HoustonUSA

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