KSCE Journal of Civil and Environmental Engineering Research (대한토목학회논문집)

Korean Society of Civil Engeneers (대한토목학회)
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Design Method for Cast-in-place Energy Pile Considering Equivalent Heat Exchange Rate

등가열교환율을 적용한 현장타설 에너지파일 설계법

  • 민선홍 ((주)에스텍컨설팅그룹 지반사업부) ;
  • 박상우 (고려대학교 건축사회환경공학부) ;
  • 정경식 ((주)에스텍컨설팅그룹 지반사업부) ;
  • 최항석 (고려대학교 건축사회환경공학부)
  • Received : 2012.12.06
  • Accepted : 2013.03.30
  • Published : 2013.05.30
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Abstract

In this paper, a relative heat exchange rate is numerically compared for cast-in-place concrete energy piles with different heat exchange pipe configurations, and a new design method for energy piles is proposed. An equivalent heat exchange rate was estimated for the W-type (one series loop), multiple U-type (four parallel loops), and coil-type heat exchanger installed in the same large-diameter drilled shaft. In order to simulate a cooling operation in summer by a CFD analysis, the LWT (leaving water temperature) into a energy pile was fixed at $35^{\circ}C$ and then the EWT (entering water temperature) into a heat pump was monitored. In case of continuously applying the artificial maximum cooling load for 100 hours, all of the three types of heat exchangers show the marginally similar heat exchange rate. However, in case of intermittently applying the cooling load with a cycle of 8 hours operation-16 hours off for 7 consecutive days, the coil type heat exchanger exhibits a heat exchange rate only 86 % of the multiple U-type due to measurable thermal interference between pipe loops in the energy pile. On the other hand, the W-type possesses the similar heat exchange rate to the multiple U-type. The equivalent heat exchange rates for each configuration of heat exchangers obtained from the CFD analysis were adopted for implementing the commercial design program (PILESIM2). Finally, a design method for cast-in-place concrete energy piles is proposed along with a design chart in consideration of typical design factors.

본 연구에서는 현장타설 에너지파일의 열교환 파이프 배치 형태별 열교환율을 전산유체해석 프로그램(FLUENT)을 이용하여 평가하고, 이를 이용하여 에너지파일의 설계법을 제시하였다. 등가열교환율을 산정하기 위해 동일한 현장타설말뚝 제원에 대해 열교환파이프 배치 형태를 W-형(직렬), 복합 U-형(병렬 4쌍), 나선형의 3가지로 고려하였다. 건물측 부하조건은 여름철 냉방운용를 모사하기 위해 순환수의 에너지파일 유입온도, 즉 히트펌프 유출온도(Leaving water temperature, LWT)를 $35^{\circ}C$로 일정하게 유지하여 에너지파일 유출온도, 즉 히트펌프 유입온도(Entering water temperature, EWT) 변화를 관찰하였다. 지반에 최대 가상부하를 적용한 경우(100시간 연속 냉방부하 조건)에는 3가지 열교환기 형태가 유사한 열교환율을 보인 반면, 실제 히트펌프 가동에 의한 건물 냉방운용을 모사하기 위해 간헐적으로 일일 8시간 운용-16시간 정지를 7일간 반복 해석한 경우에는 W-형(직렬연결)과 복합 U-형(병렬 4쌍) 열교환기는 유사한 열교환율을 보이나, 나선형 열교환기는 파이프 루프 상호 간 열간섭으로 인해 복합 U-형 열교환기에 비해 약 86%의 열교환율을 갖는 것으로 평가되었다. 전산유체해석에 의해 계산된 열교환파이프 배치 형태별 에너지파일의 등가열교환율을 에너지파일 설계프로그램(PILESIM2)에 적용하여 다양한 형상의 현장타설 에너지파일에 대한 설계법과 대표적인 설계변수에 대한 설계도표를 제시하였다.

Keywords

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