KSCE Journal of Civil and Environmental Engineering Research (대한토목학회논문집)

Korean Society of Civil Engeneers (대한토목학회)
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Thermal Behavior of Energy Pile Considering Ground Thermal Conductivity and Thermal Interference Between Piles

주변 지반의 열전도도를 고려한 PHC 에너지파일의 열 거동 및 파일 간 열 간섭 현상에 대한 수치해석 연구

  • 고규현 (카이스트 건설 및 환경공학과) ;
  • 윤석 (카이스트 건설 및 환경공학과) ;
  • 박도원 (카이스트 건설 및 환경공학과) ;
  • 이승래 (카이스트 건설 및 환경공학과)
  • Received : 2013.03.05
  • Accepted : 2013.09.04
  • Published : 2013.11.30
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Abstract

In general, ground's thermal properties, types of heat exchanger, operational method, thermal interference between piles can be considered as key factors which affect the thermal performance of energy pile. This study focused on the effect of these factors on the performance by a numerical model reflecting a real ground condition. Depending on the degree of saturation of ground, pile's heat transfer rate showed a maximum difference of three times, and the thermal resistance of pile made a maximum difference of 8.7%. As for the type of heat exchanger effects on thermal performance, thermal efficiency of 3U type energy pile had a higher value than those of W and U types. The periodic operation (8 hours operation, 16 hours pause) can preserve about 20% of heat efficiency compared to continuous operation, and hence it has an advantage of preventing the thermal accumulation phenomenon. Thermal interference effect in group piles may vary depending on the ground condition because the extent decreases as the ground condition varies from saturated to dry. The optimal separation distance that maintains the decreasing rate of heat efficiency less than 1% was suggested as 3.2D in U type, 3.6D in W type, and 3.7D in 3U type in a general ground condition.

일반적으로 에너지파일의 열적 성능에 영향을 주는 중요한 인자로 지반의 열 물성, 열 교환기 형태, 운용방법, 파일 간 열 간섭 등이 고려될 수 있다. 본 연구에서는 지반의 실제 조건을 반영한 수치모델을 통해 이들 인자들이 미치는 영향을 살펴보았다. 지반의 포화 정도에 따라서 파일의 열 교환율은 최대 3배까지 차이를 보였으며, 열 저항은 최대 8.7%의 차이가 발생하였다. 또한 열 교환기 유형이 파일의 열 성능에 영향을 주며, 3U-Type이 W나 U-Type에 비해 상대적으로 높은 열 효율을 보였다. 운용방법에 있어서, 부분가동 시(8시간 가동, 16시간 휴지) 연속가동에 비해서 약 20%의 열효율을 보전할 수 있으며, 장기적인 열 축적현상을 방지하는데 유리하다. 지반의 조건에 따라 군 말뚝에 의한 열 간섭 정도가 달라지는데, 지반이 포화상태에서 건조 상태로 갈수록 군 말뚝에 의한 열 간섭효과는 감소한다. 일반적인 지반조건에서 열 교환 감소율 1%미만을 유지하는 적정 이격 거리는 U-Type에서 최대 3.2D, W-Type에서 최대 3.6D, 3U-Type에서 최대 3.7D로 산정되었다.

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References

  1. Bourne-Webb, P. J., Amatya, B., Soga, K., Amis, T., Davidson, C. and Payne, P. (2009). "Energy pile test at lambeth college, London: Geotechnical and thermodynamic aspects of pile response to heat cycles." Geotechnique, Vol. 59, No. 3, pp. 237-248. https://doi.org/10.1680/geot.2009.59.3.237
  2. Comsol multiphysics product booklet. (2012). Comsol multiphysics 4.3a, USA.
  3. Du, C. and Chen, Y. (2011). "An average fluid temperature to estimate borehole thermal resistance of ground heat exchanger." Renewable Energy, Vol. 36, pp. 1880-1885. https://doi.org/10.1016/j.renene.2010.10.033
  4. Geothermal Design Studio User's Manual. (2012). Ground loop design premier, USA.
  5. Incropera, F. P. and Dewitt, D. P. (2002). Fundamentals of heat and mass transfer, 5th ed. John Wiley & Sons Inc., NY, USA, p. 981.
  6. Jeong, S. S., Song, J. Y., Min, H. S. and Lee, S. J. (2010). "Thermal influential factors of energy pile." Journal of the Korean Society of Civil Engineers, Vol. 6, No. 6C, pp. 231-239 (in Korean).
  7. Lurie, M. V. (2008). Modeling of oil product and gas pipeline transportation, WILEY-VCH Verlag GmbH & Co., KGaA, Weinheim.
  8. Ministry of Science and Technology. (2006). Development of deep, low-enthalpy geothermal energy, KIGAM.
  9. Ozudogru, T., Brettmann, T., Olgun, C. G., Martin, J. R. and Senol, A. (2012). "Thermal conductivity testing of energy piles: Field testing and numerical modeling." GeoCongress 2012, pp. 4436-4445.
  10. Park, H. K., Lee, S. R., Yoon, S. and Choi, J. C. (2013). "Evaluation of thermal response and performance of PHC energy pile: Field experiments and numerical simulation." Applied Energy, Vol. 103, pp. 12-24. https://doi.org/10.1016/j.apenergy.2012.10.012
  11. Rees, S. W., Adjail, M. H., Zhou, Z., Davies, M. and Thomas, H. R. (2000). "Ground heat transfer effects on the thermal performance of earth-contact structures." Renew Sustain Energy Rev, Vol. 4, No. 3, pp. 213-65. https://doi.org/10.1016/S1364-0321(99)00018-0
  12. Rees, S. W., Adjail, M. H., Zhou, Z., Davies, M. and Thomas, H. R. (2000). "Ground heat transfer effects on the thermal performance of earth-contact structures." Renewable & Sustainable Energy Reviews, Vol. 4, Issue. 3, pp. 213-265. https://doi.org/10.1016/S1364-0321(99)00018-0
  13. Sagia, Z., Stegou, A. and Rakopoulos, C. (2012). "Borehole resistance and heat conduction around vertical ground heat exchangers." The Open Chemical Engineering Journal, Vol. 6, pp. 32-40. https://doi.org/10.2174/1874123101206010032
  14. Sohn, B. H. and Choi, J. M. (2012). "Performance prediction of geothermal heat pump (GHP) system with energy piles using simulation approach." SAREK, Vol. 24, Issue. 2, pp. 155-163 (in Korean).
  15. Song J. Y. (2011). A study on the influence factors of PHC energy piles based on thermal and structural characteristics, Master Thesis, Yonsei University.
  16. Yoon, S., Park, S., Park, H. K., Go G. H. and Lee S. R. (2011). "Evaluation of heat transfer characteristics in double-layered and single-layered soils." KSGEE, Vol. 7, No. 2, pp. 43-50 (in Korean).

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