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# Quality control assessment of vertical ground heat exchanger

ASHRAE Summer Conference, Seattle 2014
by

## Jasmin Raymond

on 1 July 2014

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#### Transcript of Quality control assessment of vertical ground heat exchanger

Quality control assessment of vertical ground heat exchangers
?
Jasmin Raymond
Louis Lamarche
Marc-André Blais
WHY
HOW
EXAMPLE
Success of geothermal projects relies on the heat exchange performances of the bore field
Very little is done to verify such performances and evaluate the quality of ground heat exchangers (GHEs)

Visual inspection is impossible

Doubt may persist about the quality
of the GHEs:
Are space clips correctly holding
the pipe?
Are there air or water pockets in
the grout?
Objective: develop a method to verify the quality of a GHE
Comparison of the borehole thermal resistance (Rb) calculated from design requirements to that measured with a thermal response test (TRT)

Challenges:
Many methods exist to calculate Rb
Uncertainty in pipe spacing and grout thermal conductivity can affect results
Solution to a TRT data set is non-unique

λ
Rb
Ks
Field evaluation of GHE performances
Heat injection during ≥ 40 h
Monitoring of recovery for equivalent duration
Water is kept flowing in the
loop and heat injection stopped
Analysis is performed by curve
matching using infinite
line-source equation
Superposition principle is
used for the recovery
Inlet and outlet temperatures
are averaged (arithmetic, p --> -1)
During the recovery period, temperature becomes uniform in the GHE and is independent of Rb
Raymond et al. (2011)
2- Multipole (Claesson and Hellström, 2011) + Hellström (1981) method
Analytical method relying on exact steady state heat transfer solution
Kgrout and pipe spacing uncertainties are considered
3D, internal heat transfer

Compared with Rb determined with arithmetic average of inlet and outlet temperatures observed during TRT

Calculation of Rb from design requirements and comparison with TRT
1- Remund (1999) method
Analytical method relying
on empirical shape factors
Kgrout uncertainty is considered
2D, no internal heat transfer

Compared with Rb determined with p --> -1 average (Marcotte and Pasquier, 2008) of inlet and outlet temperatures observed during TRT

Ks
Rb
Calculation of Rb from design requirements and comparison with TRT
(Claesson and Hellström, 2011)
Raymond et al. (2011)
Three TRTs performed on different GHE in the St. Lawrence Lowlands (Montreal-Quebec City area, Canada)
All GHE have a similar configuration, except for the depth:
TRT-1) 123 m
TRT-2) 150 m
TRT-3) 151 m
Test duration: 96 to 121 h including recovery
Heat injection rate: 54 to 72 W/m

Analysis and calculation results for Rb
TRT-1 TRT-2 TRT-3
Ks (W/mK) 2.60 2.00 1.68

Rb (mK/W)
TRT (p --> -1) 0.098 0.092 0.092
Remund – 2D 0.087 0.087 0.087

TRT (arithmetic) 0.102 0.094 0.097
Multipole + Hell. – 3D 0.093 0.094 0.096
Comparison considering ±10 % uncertainty in Kgrout with approach 1
Rb determined with TRT (p --> -1) vs Rb calculated with Remund method – 2D
Comparison considering ±10 % uncertainty in Kgrout and pipe spacing using approach 2
Rb determined with TRT (arithmetic) vs Rb calculated with multipole + Hellström method – 3D
Differences 9-11 % ≤ 5 %
Conclusions
Method 1 – Remund – 2D
TRT-1 and TRT-3 outside Rb range for ±10 % Kgrout
Method 2 - Multipole + Hellström – 3D
All TRT are inside Rb range for ±10 % Kgrout and pipe spacing
Method 1 is limited while method 2 is more flexible
Assessments are contradictory but ±10 % uncertainty criteria is arbitrary

Questions ?
jasmin.raymond@inrs.ca
Solution for 1 multipole
Infinite line-source with superposition
Rb with Remund
Hellström extension
Learning objectives
1) Define the steps of a quality control assessment for ground heat exchangers
2) Learn how to read box plots and surface charts to assess the ground heat exchanger performances
Seattle Conference
AIA disclaimer.
ASHRAE is a Registered Provider with The American Institute of Architects Continuing Education Systems. Credit earned on completion of this program will be reported to ASHRAE Records for AIA members. Certificates of Completion for non-AIA members are available on request.This program is registered with the AIA/ASHRAE for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.
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