Performance Analysis of a Deep Vertical Closed-Loop Heat Exchanger through Thermal Response Test and Thermal Resistance Analysis

열응답 실험 및 열저항 해석을 통한 장심도 수직밀폐형 지중열교환기의 성능 분석

  • Received : 2016.11.18
  • Accepted : 2016.12.20
  • Published : 2016.12.28


Due to the limited areal space for installation, borehole heat exchangers (BHEs) at depths deeper than 300 m are considered for geothermal heating and cooling in the urban area. The deep vertical closed-loop BHEs are unconventional due to the depth and the range of the typical installation depth is between 100 and 200 m in Korea. The BHE in the study consists of 50A (outer diameter 50 mm, SDR 11) PE U-tube pipe in a 150 mm diameter borehole with the depth of 300 m. In order to compensate the buoyancy caused by the low density of PE pipe ($0.94{\sim}0.96g/cm^3$) in the borehole filled with ground water, 10 weight band sets (4.6 kg/set) were attached to the bottom of U-tube. A thermal response test (TRT) and fundamental basic surveys on the thermophysical characteristics of the ground were conducted. Ground temperature measures around $15^{\circ}C$ from the surface to 100 m, and the geothermal gradient represents $1.9^{\circ}C/100m$ below 100 m. The TRT was conducted for 48 hours with 17.5 kW heat injection, 28.65 l/min at a circulation fluid flow rate indicates an average temperature difference $8.9^{\circ}C$ between inlet and outlet circulation fluid. The estimated thermophysical parameters are 3.0 W/mk of ground thermal conductivity and 0.104 mk/W of borehole thermal resistance. In the stepwise evaluation of TRT, the ground thermal conductivity was calculated at the standard deviation of 0.16 after the initial 13 hours. The sensitivity analysis on the borehole thermal resistance was also conducted with respect to the PE pipe diameter and the thermal conductivity of backfill material. The borehole thermal resistivity slightly decreased with the increase of the two parameters.


Supported by : 에너지기술평가원


  1. MOTIE (Ministry of Trade, Industry and Energy), The second national energy master plan, 2014.
  2. Lee, Dae-sung, Korea Institute of Geoscience and Mineral Resources, Geological map of Korea, 1:50,000, 1974.
  3. Cho, Heuy-Nam, Lee, Dal-Heui and Jeong, Gyo-Cheol, Efficiency of geothermal energy generation assessed from measurements of deep depth geothermal conductivity, The Journal of Engineering Geology, Vol.22, No.2, pp. 233-241, 2012.
  4. Austin WA. Development of an in-situ system for measuring ground thermal properties. Master's thesis. Oklahoma State University. USA, 1998.
  5. Focaccia S., Thermal response test numerical modeling using a dynamic simulator, Geothermal Energy, 1:3, 2013.
  6. Gehlin S. Thermal response test: method development and evaluation. Ph.D. thesis. Lulea University of Technology; 2002.
  7. Kavanaugh S, Xie L, and Martin C. Investigation of methods for determining soil and rock formation thermal properties from short term field tests. Final Report for ASHRAE TRP-1118, 2000.
  8. Koenig A., Thermal resistance of borehole heat exchangers composed of multiple loops and custom shapes. Geothermal Energy, 3:10, 2015.
  9. Koenig, A., and M. Helmke. ''Development of a thermal resistance model to evaluate wellbore heat exchange efficiency.'' Int J Energy Environ 5.3, 297-304, 2014.
  10. Raymond J, Therrien R, Gosselin L, and Lefebvre R. A review of thermal response test analysis using pumping test concepts. Ground Water, 49:932-45, 2011.
  11. Sanner B, Mands E, Sauer M, and Grundmann E. Technology, development status, and routine application of thermal response test. In: Proceedings of EGC; 2007.
  12. Shim B.O., and Park C.-H., Ground thermal conductivity for (ground source heat pumps) GSHPs in Korea, Energy, 56, 167-174, 2013.
  13. Signorelli S., Simone Bassetti, Daniel Pahud, and Thomas Kohl, Numerical evaluation of thermal response tests, Geothermics, Volume 36, Issue 2, Pages 141-166, 2007.
  14. Wagner R, and Clauser C. Evaluating thermal response tests using parameter estimation for thermal conductivity and thermal capacity. Journal of Geophysics and Engineering, 2:349, 2005.