Insights from field experiments to conduct thermal response tests with

heating cables

Jasmin Raymond, Louis Lamarche

and Michel Malo

7th Geothermal heat pump business and policy forumMontréal – May 16, 2014

Ground source heat pump systems

• Use to heat and cool buildings withgeothermal resources of very-lowtemperature (< 30 °C)

• Provide energy savings• 60-70 % heating• 30-40 % cooling

• Contribute to greenhouse gassesreductions

• Expensive installation cost

Ground source heat pump systems

• Appropriate design can help toconstrain ground heat exchangerlength

• In situ assessment of the subsurfacetemperature and thermal conductivity(TC) is needed

• Test performed in a explorationborehole with a ground heatexchanger

Conventional thermal response tests (TRTs)

• 50 to 80 W/m• 240 V / 30-50 A• A fuel-fired generator

supplies power• Expensive • Provide a bulk TC value• A fiber optic cable can be

used to obtain aTC profile

Raymond et al. 2011

Acuna

et al. 2009

Thermal response tests with a low power source

• 20 to 40 W/m trough 10-15 sections

• 120 V / 10 A• No need for

a generator• Potential to

save cost (50%)

• Provide a TC profile

Raymond and Lamarche 2014 US Patent: 61859909

Heating sections test methodology

Field operations

• Cable assembly is lowered in the borehole

• Initial temperature is measured at the middle of the heating sections

• Heat is injected during 50-75 h• Recovery temperature is

measured

Heating sections test analysis

Recovery temperatures are reproduced with a finite heat source equation

Raymond and Lam

arche 2014

2 2

/2s

2 2s /2

( ')

2( , , )

4 ( ')

H

H

r z zerfc

tqT r z t dz

r z z

α

πλ

+

−

+ − ∆ =

+ −

∫

Heating sections test analysis

• Temperature response approximated with a g-function• r = 0,01 m and H = 1.36 m• Recovery taken into account with the superposition principle

2

offs )(

H

ttFo

−=

α

[ ])'()(2 s

, FogFogq

T rz −=∆πλ

=∆

H

rFog

qTz ,

2 sπλ

2

s

H

tFo

α=

Heating sections test analysis

Comparison of the finite and infinite linear heat source solution

Raymond and Lamarche 2014

A solver is used to minimize the difference between computed and observed temperatures

Heating sections test analysis

Raymond and Lamarche 2014

Time for

temperature

to become

uniform

ΔT < 0.1 °C within r ≤ 0.042 m

Raymond et al. 2014

Numerical

validation

with analysis

of simulated

tests

Raymond et al. 2014

Perforated disks to block water convection

Field experiments and numerical simulations conducted to evaluate the disk impacts

Raymond et al. 2014

Perforated disks to block water convection

Raymond et al. 2014

Raymond et al. 2014 No disk

TC = 4.10 W/mK

Disks

3 above / 3 below

TC = 3.29 W/mK

Disks

4 above / 3 below

TC = 3.20 W/mK

• Bulk TC from conventional test3.00 W/mK

• Average TC from heating sections test 3.35 W/mK

Test with 10

heating sections

at Versaprofile

factory

Possible explanations for differences

in bulk and average TC

• Change of the groundwater flow regime• Bedrock is fractured, bottom of hole collapsed• Site topography – 3.3 % slope• Conventional test – Jan 2009• Heating section test – Nov 2013

• Thermal conductivity measurement in the sandy overburden (low TC) was not performed with the heating sections test

• TC values are local estimates

www.geosurvey.state.co.us

Energy consumed during the conventional

and heating sections tests (72 h)

• Conventional • 66.5 W m-1

• 9308 W• 670 kWh

• Heating sections • 32 W m-1

• 105.6 V• 8.0 A• 61 kWh

~9 %~9 %~9 %~9 %

Comparison of various TRT technologies

Conventional

TRT

Flowing

SensorFiber optic

Heating

sections

Thermo-

stratigraphy

Data profiling No Yes Yes Yes Yes

Test time hh hh hhh hhh h

Time spent in the field hh hh hh h h

Equipment weight +++ +++ +++ + -

Equipment complexity ++ +++ ++++ + -

Power requirement High High High Low None

Cost $$$ $$$$ $$$$$ $$ $

Spatial restriction No No No No Yes

Measured parameters T0, λs, R’bh T0, λs T0, λs, R’bh T0, λs T0, λs

Analysis methodInfinite heat

source

Infinite heat source

(assumed)

Infinite heat source

Finite heat source

Earth’s heat flow modeling

Possible market outlets for the heating sections test

• Alternative TRT to design ground source heat pump systems• Low cost• Light equipment• Provides TC profile to identify favorable layers

to reduce bore length

• Assessment of the Earth’s heat flow for theexploration of deep geothermal resources

Bla

ckw

ell

and R

ichard

s 2

004

z

Tq

∂

∂−=

sλ

Exploration for high temperature reservoirs

of hydrothermal systems

• Shallow (2-20 m depth) temperature surveys are carried out to identify thermal anomalies

• A screening method before spending M$ in deep boreholes• Difficultly applicable to subtle thermal anomalies of low-temperature

sedimentary basins – heating sections tests could be an alternativeZehner et al. 2012

Further research – thermostratigraphy

• Correct temperature profile for paleoclimatic effects to:• Scale-up local TC measurements• Determine heat flow• Infer thermal anomalies

Chouinard and Mareschal 2007