A Study on the Effects of Design Parameters of Vertical Ground Heat Exchanger on the Borehole Thermal Resistance

수직밀패형 지중열교환기의 설계인자가 보어홀 전열저항에 미치는 영향에 관한 연구

  • Chang, Keun Sun (Department of Mechanical Engineering, Sunmoon University) ;
  • Kim, Min-Jun (Korea Refrigeration and Air-conditioning Assessment Center)
  • 장근선 (선문대학교 기계공학과) ;
  • 김민준 (한국냉동공조인증센터)
  • Received : 2018.07.18
  • Accepted : 2018.10.05
  • Published : 2018.10.31


Currently, vertical closed ground heat exchangers are the most widely utilized geothermal heat pump systems and the major influencing parameters on the performance of ground heat exchangers are the ground thermal conductivity(k) and borehole thermal resistance($R_b$). In this study, the borehole thermal resistance was calculated from the in-situ thermal response test data and the individual effects of design parameters (flow rate, number of pipe, grout composition) on the borehole thermal resistance were analyzed. The grout thermal resistance was also compared with the correlations in the literatures. The borehole thermal resistance of the investigated ground heat exchanger results in 0.1303 W/m.K and the grout thermal resistance (66.6% of borehole thermal resistance) is the most influencing parameter on borehole heat transfer compared to the other design parameters (pipe thermal resistance, 31.5% and convective thermal resistance, 1.9%). In addition, increasing the thermal conductivity of grout by adding silica sand to Bentonite is more effective than the other design improvements, such as an increase in circulating flowrate or number of tubes on enhancing borehole heat transfer.


Geothermal Heat Pump System;GHE : Ground Heat Exchanger;Ground Thermal Conductivity;Borehole Thermal Resistance;TRT: Thermal Response Test


Supported by : 선문대학교


  1. Kim, M. J., A study on the thermal performance evaluation of a borehole ground heat exchanger using in-situ thermal response test, Ph.D thesis, Sunmoon University, KOREA, 2017.
  2. Ministry of Trade, Industry and Energy Announcement 2015-263, Standards of Support, Installation and Management for New and Renewable Energy System, (2015).
  3. K. S. Chang, M. J. Kim, "Thermal performance evaluation of vertical U-loop ground heat exchanger using in-situ thermal response test", Renewable Energy, Vol.87, Part 1, pp.585-591, 2016. DOI:
  4. Incropera, F. P. and Dewitt, Fundamentals of Heat and Mass Transfer, 4th Edition, 1996, John Wiley and Sons, Inc.
  5. Remund, C.P., Borehole thermal resistance: laboratory and field studies, 1999, ASHRAE Transactions, 105(1): pp. 439-445.
  6. L. Lamarche, S. Kajl, B. Beauchamp, "A review of methods to evaluate borehole thermal resistances in geothermal heat pump systems", Geothermics, Vol.39, No.2, pp.187-200, 2010. DOI:
  7. M. H. Sharqawy, E. M. Mokheimer, H. M. Badr, "Effective pipe-to-borehole thermal resistance for vertical ground heat exchanger", Geothermics, Vol.38, No.2, pp.271-277, 2009. DOI:
  8. Shonder, J.A. and Beck, J.V., Determining effective soil formation thermal properties from field data using a parameter estimation technique, 1999, ASHRAE Transactions Vol. 105, part 1, pp 458-466.
  9. Gu, Y., O'Neal, D., Development of an equivalent diameter expression for vertical U-tubes used in ground-coupled heat pumps. ASHRAE Transactions, (1998) 104(2): pp. 1-9.
  10. Ground Loop Design User's Manual, Gaia Geothermal, USA, 2007, pp. 1-136.
  11. K. S. Chang, M. J. Kim, "Analysis and thermal response test for vertical ground heat exchanger with two U-loop configuration", International Journal of Energy Research, Vol.40, No.2, pp.189-197, 2016. DOI: