Insights from field experiments to conduct thermal response tests with heating cablesJr etal2014 heating_sections_trt
0 likes1,446 views
This document summarizes research on using heating cable sections to conduct thermal response tests (TRTs) at lower costs than conventional methods. Key points: - Heating cable sections allow measuring thermal conductivity profiles in boreholes, providing data to design efficient ground source heat pump systems. - Tests conducted in Canada found heating section tests produced consistent thermal conductivity values compared to conventional TRTs, while reducing equipment needs, costs, and consumed energy by around 90%. - Further research aims to use heating section profiles to identify favorable geological layers, explore deep geothermal resources, and correct temperature profiles for paleoclimate effects.
![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
tt
Fo
−
=
α
[ ])'()(
2 s
, FogFog
q
T rz −=∆
πλ
=∆
H
r
Fog
q
Tz ,
2 sπλ
2
s
H
t
Fo
α
=](https://image.slidesharecdn.com/jretal2014heatingsectionstrt-140518104720-phpapp02/85/Insights-from-field-experiments-to-conduct-thermal-response-tests-with-heating-cablesJr-etal2014-heating_sections_trt-9-320.jpg)
Insights from field experiments to conduct thermal response tests with heating cablesJr etal2014 heating_sections_trt
- 1. 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 forum Montréal – May 16, 2014
- 2. Ground source heat pump systems • Use to heat and cool buildings with geothermal resources of very-low temperature (< 30 °C) • Provide energy savings • 60-70 % heating • 30-40 % cooling • Contribute to greenhouse gasses reductions • Expensive installation cost
- 3. Ground source heat pump systems • Appropriate design can help to constrain ground heat exchanger length • In situ assessment of the subsurface temperature and thermal conductivity (TC) is needed • Test performed in a exploration borehole with a ground heat exchanger
- 4. 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 a TC profile Raymondetal.2011 Acunaetal.2009
- 5. 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
- 6. 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
- 8. Heating sections test analysis Recovery temperatures are reproduced with a finite heat source equation RaymondandLamarche2014 2 2 /2 s 2 2 s /2 ( ') 2 ( , , ) 4 ( ') H H r z z erfc tq T r z t dz r z z α πλ + − + − ∆ = + − ∫
- 9. 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 tt Fo − = α [ ])'()( 2 s , FogFog q T rz −=∆ πλ =∆ H r Fog q Tz , 2 sπλ 2 s H t Fo α =
- 10. Heating sections test analysis Comparison of the finite and infinite linear heat source solution RaymondandLamarche2014
- 11. A solver is used to minimize the difference between computed and observed temperatures Heating sections test analysis
- 13. Time for temperature to become uniform ΔT < 0.1 °C within r ≤ 0.042 m Raymondetal.2014
- 14. Numerical validation with analysis of simulated tests Raymond et al. 2014
- 15. Perforated disks to block water convection Field experiments and numerical simulations conducted to evaluate the disk impacts Raymond et al. 2014
- 16. Perforated disks to block water convection Raymond et al. 2014
- 17. Raymondetal.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
- 18. • Bulk TC from conventional test 3.00 W/mK • Average TC from heating sections test 3.35 W/mK Test with 10 heating sections at Versaprofile factory
- 19. 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
- 20. 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 %
- 21. Comparison of various TRT technologies Conventional TRT Flowing Sensor Fiber 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 method Infinite heat source Infinite heat source (assumed) Infinite heat source Finite heat source Earth’s heat flow modeling
- 22. 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 the exploration of deep geothermal resources BlackwellandRichards2004 z T q ∂ ∂ −= sλ
- 23. 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 alternative Zehner et al. 2012
- 24. 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