Journal of the Korean Society of Mineral and Energy Resources Engineers (한국자원공학회지)

The Korean Society of Mineral and Energy Resources Engineers (한국자원공학회)
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Application of the Horner Plot Method in Thermal Response Test Interpretation

Horner plot을 이용한 열응답 실험 해석

Shim, Byoung-Ohan
심병완

  • Published : 2008.08.28
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Abstract

The selection of TRT and its interpretation method are important to design an economical geothermal heat pump system because heat exchange rate of a borehole heat exchanger system highly depends on effective thermal conductivity of ground.Two thermal response tests (TRTs) are performed in a 200 m long vertical closed-loop borehole heat exchanger, and thermal conductivities are estimated with a conventional method using the line source theory, and the Horner plot method. The Horner plot method is applied to recovered circulation fluid temperatures during fluid circulation after power shut-in, and recovered ground temperatures were measured by a fiber optic temperature sensing method. The estimated thermal conductivity using the conventional method is 2.75W/m/K, and that using the Horner plot method is 2.87 W/m/K. The average effective thermal conductivity using the Horner plot method with fiber optic temperature sensing data is 2.88 W/m/K and the average core sample thermal conductivity measured in a lab is 2.90 W/m/K. By comparison of each results with core thermal conductivity data, three different interpretation methods show reliable results.

2회의 열응답 실험이 200 m 심도의 수직밀폐형 지중열교환기에서 실시되었으며, 일반적인 라인소스 모델과 Horner plot 방법을 이용하여 지반의 열전도도를 계산하였다. 본 연구에서는 일반적인 선형열원 방정식과 순환펌프 가동에 의한 회복되는 순환수 온도 자료를 이용한 Horner plot 방법 적용, 그리고 순환펌프 중지 후 광섬유온도 센서를 이용한 회복되는 지반의 온도를 이용한 Horner plot 방법을 적용하였다. 일반적인 선형열원 방정식에 의한 지중열교환기공의 평균 유효열전도도는 2.75 W/m/K이며, 그리고 히터를 중지 시킨 후 순환펌프만 계속 가동시켜 회복되는 자료의 Horner plot 방법을 적용하여 계산된 유효열전도도가 2.87 W/m/K이다. 광섬유 센서 온도 측정법을 이용한 Horner plot method 적용에서는 2.88 W/m/K의 평균유효열전도도와 심도별 유효열전도도를 나타내었으며 코어의 평균 열전도도는 2.90 W/m/K이다. 3가지 TRT 해석 결과를 코어 열전도도와 비교한 결과 각 해석 방법들이 적절한 신뢰성을 가지는 것으로 판단되었다. 지중열교환기 시스템의 열교환율은 유효열전도도에 따라 크게 달라지므로 지반의 특성 및 목적에 가장 적합한 열응답 실험 및 해석 방법을 선택하여 유효열전도도를 계산하는 것이 경제적인 시스템 설계에 중요하다고 판단된다.

Keywords

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