FORMATION THERMAL CONDUCTIVITY
TEST AND DATA ANALYSIS
Analysis for: Mr. Jerry Linning
School District #70, Port Alberni
4690 Roger St,
Port Alberni, BC V9Y 3Z4
Test location: 4100 Roger St, Port Alberni, BC
Report Date: April 20, 2009
Test performed by: MEG Geothermal Corp.
Phone: (604) 988-3388
Fax: (604) 988-3329
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Purpose of the FTC Test
The performance of a geoexchange ground loop system can be greatly dependent on the
characteristics of the rock/soil formation underlying the site and the final field configuration design. A
Formation Thermal Conductivity (FTC) test for thermal conductivity allows an opportunity to predict
the performance of a singular test well, so that the information can be applied to the design of a full-
scale ground loop system.
The geothermal system designer uses the FTC test information to size the ground loop with respect
to the calculated design heating and cooling loads, typically through the aid of computer based
geothermal design programs. Without the FTC information, over-sizing or under-sizing of the ground
loop may occur. An over-sized ground loop will increase capital costs, while delivering little increased
performance. An under-sized ground loop could diminish system economics by requiring increased
energy use from the system heat pumps and causing the field to fall below or climb above the
acceptable operating temperature range.
MEG Geothermal Corp. was retained to provide a Formation Thermal Conductivity (FTC) test at the
4100 Roger St, Port Alberni, BC location. The results of this analysis provide the thermal conductivity
and thermal diffusivity of the soil/rock formation surrounding the test borehole.
The American Society of Heating, Refrigeration, and Air-Conditioning Engineers (ASHRAE) as well
as the article Field Tests for Ground Thermal Properties – Methods and Impact on Ground Source
Heat Pump Design; Kavanaugh, ASHRAE Transactions 2000, Volume 106, Pt.1 recommend a set of
standards for performing formation thermal conductivity tests for geothermal applications. MEG
Geothermal Corp. is committed to adhering to the published specifications. Some of these standards
are listed below:
1. Required Test Duration – A minimum test duration of 36 hours is recommended, with a
preference towards 48 hours.
2. Power Quality – The standard deviation of the power should be <1.5% of the average power,
with maximum power variation of <10% of the average power. The heat flux rate should be
15W (51 Btu/hr) to 25W (85 Btu/hr) per foot of borehole depth to best simulate the expected
peak loads on the U-bend.
3. Undisturbed Soil Temperature Measurement – The undisturbed soil temperature should be
determined by recording the minimum loop temperature as the water returns from the U-bend
at test startup.
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4. Installation Procedures for Test Loops – The bore diameter is to be no larger than 6 inches,
with 4.5 inches being the target diameter. To ensure against bridging and voids, the bore
annulus is to be uniformly grouted from the bottom to the top using a tremie pipe.
5. Time Between Loop Installation and Testing – A minimum delay of five days between loop
installation and test startup is recommended if the formation is expected to have a low thermal
conductivity or if low conductivity grouts (< 0.75 Btu/hr·ft·ºF) are used. A minimum delay of
three days is recommended for all other conditions.
6. The thermal resistance of the bore (pipe and grout) should be minimized so that the measured
temperature rise is a strong function of the thermal properties of the soil.
7. The depth of the test bore should be near the expected length of the ground loop.
For a complete list of recommended procedures, refer to ASHRAE’s 2003 HVAC applications
handbook, page 32.14.
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MEG Geothermal Corp. uses the "line source" method of data analysis. The line source equation
used is not valid for the results obtained in the first few hours of the test. Also, the line source method
assumes an infinitely thin line source of heat in a continuous medium. If a U-bend grouted in a
borehole is used to inject heat into the ground at a constant rate in order to determine the average
formation thermal conductivity, the test must be run long enough to allow the finite dimensions of the
U-bend pipes and the grout to become insignificant. Experience has shown that the amount of time
required to allow early test time error and finite borehole dimension effects to become insignificant is
approximately four to ten hours.
In order to analyze real data from a formation thermal conductivity test, the average temperature of
the water entering and exiting the U-bend heat exchanger is plotted versus the natural log of time.
Using the Method of Least Squares, the linear equation coefficients are then calculated that produce
a line that fits the data. This procedure is normally repeated for various time intervals to ensure that
variations in the power or other effects are not producing erroneous results.
Through the analysis process, the collected raw data is converted to spreadsheet format (Microsoft
Excel®) for final analysis.
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Formation Thermal Conductivity Test Report
Date: …………………………………………... April 14-16, 2009
Location: ……………………………………….4100 Roger St, Port Alberni, BC
Undisturbed Soil temperature: ……………… Approx. 50.4 F
Borehole Diameter: ………………………….. 6.0 inches
Length Type (ft2/day)
0-20' Brown till 0.7
20'-22' Clay gravel wet 0.6
22'-46' Till 0.7
46'-250' Shale (no water) 0.7
250 Weighted average: 0.70
U-bend Size: …………………………………..1” HDPE
U-bend length: ……………………………….. 251 ft.
Grout type: ……………………………………. 20% Gopher Grout
Grouted portion: ……………………………… 0-251 ft
Test duration: ………………………………… 42.05 hours
Average Voltage: ……………………………. 236.12 V
Average Power: ……………………………… 5,000 W
Logged average circulator flow rate: ……… 5.65 usgpm
Item Value Note
Std. Dev. Of Average 0.11% must be less than 1.5%
Max. Power Variance 0.33% must be less than 10%
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4100 Roger St, Port Alberni, BC
April 14-16, 2009
TEMPERATURE RESPONSES DURING TESTING
SUPPLY TEMP 4400.0
65.0 AVERAGE TEMP
0.02 6.68 13.35 20.02 26.68 33.35 40.02
Figure 1: Temperature vs Time Data
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Line Source Data Analysis
4100 Roger St, Port Alberni, BC
April 14-16, 2009
AVERAGE TEMPERATURE VS NATURAL LOG OF TIME
70.0 y = 4.1495x + 57.579
4.00 4.50 5.00 5.50 6.00 6.50 7.00 7.50 8.00
Figure 2: Temperature vs Natural Log of Time
Time Period Slope Average Heat Input Thermal Conductivity
Btu/hr-ft W/ft Btu/hr-ft-°F W/m-K
18.02 - 42.05 hours 4.1495 67.97 19.9 1.30 2.25
The temperature vs. time data was analyzed using the line source analysis for the time period shown.
An average linear curve fit was applied to the data between 18.02 and 42.05 hours. The slope of the
curve was found to be 4.1495. The resulting thermal conductivity was found to be 1.30 Btu/hr-ft-°F
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Estimated Thermal Diffusivity
A weighted average of the thermal diffusivity values of the various rock/soils encountered in the drill
log provided an approximate formation thermal diffusivity of 0.70 ft2/day.
Thermal Conductivity (Btu/h-ft-°F): …………………………………... 1.30
Estimated Thermal Diffusivity (ft2/day): ……………………………… 0.70
This report and analysis was completed by MEG Geothermal Corp. and it’s agents for the purpose of
determining the Formation Thermal Conductivity of the soil/rock formation underlying the site at 4100
Roger St, Port Alberni, BC. Use of this information, either directly or indirectly, by other parties shall
be at their own risk.
The values presented were obtained utilizing the methods and techniques commonly accepted for the
purpose of FTC testing as of the writing of this report. The values represent the conditions
encountered and registered at the location of the test borehole. We caution that different underlying
soil/rock formation characteristics could be encountered elsewhere on the same site thus affecting
the overall thermal conductivity and diffusivity.
It is strongly recommended that the thermal conductivity and diffusivity values are used by an
experienced geothermal field designer, in conjunction with appropriate geoexchange field sizing
software. It is imperative that the geoexchange field be sized for the anticipated design heating and
cooling load of the future facility, expressed typically in ton-hours per month, in order to adequately
predict the effect of loads on the borehole field. Final bore field configuration can also greatly affect
the final operating success of a geothermal system. To minimize field design errors, FTC information
and field design should be analyzed by a qualified Registered Professional Engineer who regularly
practices in the field of geothermal design and energy modeling.
Note: Owners of buildings designed with geothermal systems are cautioned that building renovations,
additions, or primary element characteristic changes (modifications to insulation levels or glazing
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characteristics), or major occupancy and use changes, may alter the building load/geoexchange field
This report and underlying calculations were reviewed by Mr. Emmanuel Lavoie, P. Eng, APEGBC.
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