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Recent advances in thermal conductivity testing

2013 Canadian GeoExchange Conference and Trade Show
by

Jasmin Raymond

on 4 May 2013

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Transcript of Recent advances in thermal conductivity testing

thermal c nductivity testing Jasmin Raymond, HydroGeoPro 2013 Canadian GeoExchange Conference and Trade Show http://www.hydro-geo.net Thermal Conductivity (TC) Tests Carried out at the pre-feasibility stage of commercial size projects
Used to determine thermal properties to design systems
Roughly 750 tests/year in Canada
Generally considered expensive Measured properties
Undisturbed subsurface temperature To
Subsurface thermal conductivity Ks
Borehole thermal resistance Rb Canadian market
7039 HP units for the commercial sector in 2009 (CGC, 2010)
4 units/project
50 % vertical systems
85 % new projects Circulation of heated water through a ground heat exchanger (GHE)
Measurement of inlet and outlet water temperature as well as flow rate
Assessment of bulk properties over the length of the borehole
Steps:
1 –Install an insulate the unit
2- Circulate water to measure the undisturbed temperature
3- Purge air trapped in the pipe
4- Start heat injection and measure temperature increments
Heat injection rate 15 to 24 W/ft (50 to 80 W/m)
Temperature difference at inlet and outlet 5 to 13 °F (3 to 7 °C)
Current of high voltage 240V/30-60A
5- Stop field test, retrieve data and analyze measurements Recent advances in Conventional TC test methodology Stop heat injection

Keep water circulation

Measure inlet and outlet temperature

Analyze data with curve fitting methods Measurement of
thermal recovery Advantages: 2 temperature curves

2 steps analysis of 2 parameters

Quality c ntrol assessment of borehole installations ks = 1.7 Btu/hrft°F
(3.0 W/mK) Rb = 0.112 hrft°F/Btu
(0.065 mK/W) Example of quality
control assessment 4 TC tests on ground heat exchangers - 500 ft (152 m) length
6 in (0.15 m) borehole diameter
1.25 in (0.032 m) U-pipe HDPE
Space clips every 10 ft (3 m)
K grout 1 Btu/hrft°F (1.7 W/mK) Measured
Rb %
hrft°F/Btu (W/mK) Difference
0.192 (0.111) 12-18
0.173 (0.100) 1-6
0.157 (0.091) 4-9
0.159 (0.092) 2-8 Theoretical
Multipole model

Rb = 0.163-0.172 hrft°F/Btu
(0.094-0.099 W/mK) Measurement of temperature inside the borehole during TC test Assess a full Ks profile of the subsurface

Identify formations of higher Ks

Reduce GHE length Fujii et al., 2009 Raymond et al., 2011 Fiber optic cables Flowing sensor Thermostratigraphy Heating cables Developed in Japan and Sweden
Fiber optic cables are installed inside the pipe of the GHE
A device at surface sends optical pulses and calculates temperature along the cable
Temperature is measured at different depths during the heat injection and the recovery periods
Flow of water is stopped during recovery
Measured temperatures are reproduced to infer the thermal conductivity at different depths © Acuña Fujii et al., 2009 Acuña et al., 2009 Developed in Spain
A submersible spherical sensor is introduced in the pipe of the GHE while water is flowing
The capsule encloses a data logger
Data is retrieved when the sensor complete the loop © Martos © Martos Martos et al., 2011 Initially applied to geoexchange technologies in Switzerland
A submersible temperature probe is lowered into the pipe of a GHE to make a temperature profile
The probe as a high resolution (0.001 °C) to log small variations of the geothermal gradient
The thermal conductivity of the rock units is calculated according to the variations of the geothermal gradient and the Earth heat flow at the studied site
The method is restricted to regions where decent heat flow measurements have been carried out
Properties in the upper portion of the borehole can’t be assessed Rohner et al., 2005 Upper section of the profile is affected by atmospheric temperature changes and topography http://www.heatflow.und.edu Global Heat Flow Database The density of heat flow data in many regions of N-A and Eu is not sufficient to use thermostratigraphy for an accurate estimation of Ks Developed in Canada
Heating cables are lowered into the pipe of the GHE
Electric current flows through the cable to inject heat
Required heat injection rate is smaller than that of the conventional TC test method
Temperature is measured at different depths during the recovery period
Test can be performed in various types of GHE including those of direct exchange (DX) systems
Results are not affected by surface variations of atmospheric temperature Raymond et al., 2010 TC test with heating cables on a DX system at in Montreal Temperature sensors Analysis of recovery temperatures Thermal conductivity profile © Raymond © Raymond Raymond et al., 2011 Demonstration project by HydroGeoPro in collaboration with funded by
Ground heat exchanger made with a single U-pipe (HDPE) at Versaprofiles facilities
460 ft (140 m) length
14 temperature sensors Portable unit for TC tests with heating cables Conventional Fiber optic Flowing Thermo- Heating
TC Test cables sensor stratigraphy cables

Test time hh hhh hh h hhh
Time spent in the field hh hh hh h h
Equipment weight +++ +++ +++ - +
Power requirement high high high none low
Spatial restrictions no no no yes no
Measured parameters To,Ks,(Rb) To,Ks,Rb To,Ks,(Rb) To,Ks To,Ks
Profile no yes yes yes yes
Cost $$$ $$$$$ $$$$ $ $$ Comparison of methods Presentation available on http://prezi.com/user/jasminraymond/ Get in touch with me through http://www.linkedin.com/in/jasminraymond Analysis of a vertical T profile Analysis of recovery temperatures at depths Borehole sections Ks profile Temperature profile during heat injection Shorter borehole in a zone of higher Ks Tech4ksPROFILE
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