등가열교환율을 적용한 현장타설 에너지파일 설계법 = Design Method for Cast-in-place Energy Pile Considering Equivalent Heat Exchange Rate

국문 초록 (Abstract)

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.

다국어 초록 (Multilingual 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.

참고문헌 (Reference)

1 정상섬, "에너지 파일의 열적거동 인자분석" 대한토목학회 30 (30): 231-240, 2010

2 Wood, C. J, "Use of energy piles in a residential building, and effects on ground temperature and heat pump efficiency" 59 (59): 287-290, 2009

3 Li, X., "Thermal performances of different types of underground heat exchangers" 38 : 543-547, 2006

4 Lee, C., "Thermal performance of cast-in-place concrete energy pile" 3747-3758, 2011

5 Gao, J, "Thermal performance and ground temperature of vertical pile-foundation heat exchangers: A case study" 28 : 2295-2304, 2008

6 Lim, H, "The comparison of the temperature output on energy piles between field measurement and numerical analysis" 966-972, 2012

7 Ryu, H-K, "Study on the design and construction optimize of coil-type PHC enery pile" The Society of Air-conditioning and Refrigerating Engineers of Korea 402-406, 2012

8 Morino, K, "Study on heat exchanged in soil by circulating water in a steel pile" 21 : 65-78, 1994

9 Park, S, "Study on heat exchange characteristics for PHC Energy piles" 2493-2507, 2012

10 Baek, S. K., "Study on ground-coupled heat pump system using hollow piles" Busan University 2004

11 Ministry of knowledge Economy, "Standard and guide supporting for new and renewable energy systems" Korea Energy Management Corporation 2012

12 Park, S, "Research on heat exchange characteristics of coil-type PHC energy pile" Korean Geotechnical Society (KGS) 201-212, 2012

13 Lee, S., "Numerical simulation of seasonal performance of energy pile" 2459-2465, 2012

14 Choi, J. C, "Numerical simulation of ground heat exchanger embedded pile considering unsaturated soil condition" Korean Geotechnical Society (KGS) 213-220, 2010

15 Gao, J, "Numerical and experimental assessment of thermal performance of vertical energy piles" 85 : 901-910, 2008

16 Pahud, D, "Measured thermal performances of the energy pile system of the dock midfield at Zürich Airport" 1-7, 2007

17 Cui, P, "Heat transfer analysis of pile geothermal heat exchangers with spiral coils" 88 : 4113-4119, 2011

18 Knellwolf, C, "Geotechnical analysis of heat exchanger piles" ASCE 137 (137): 890-902, 2011

19 Hamada, Y., "Field performance of an energy pile system for space heating" 39 : 517-524, 2007

20 Laloui, L, "Experimental and numerical investigations of the behavior of a heat exchanger pile" 30 : 763-781, 2006

21 Jun, L., "Evaluation of heat exchange rate of GHE in geothermal heat pump system" 34 : 2898-2904, 2009

22 "Engineeringtoolbox.com"

23 Bourne-Webb, P. J, "Energy pile test at Lambeth College, London: Geotechnical and Thermodynamic Aspects of Pile Response to Heat Cycles" 59 (59): 237-248, 2009

24 Nam, Y, "Development of potential map for ground and groundwater heat pump systems and the application to tokyo" 43 : 677-685, 2011

25 Nam, Y, "Development of a numerical model to predict heat exchang rates for a ground source heat pump system" 40 : 2113-2140, 2008

26 Ryu, H-K., "Development and performance evaluation of ground heat exchanger utilizing PHC pile foundation of building" 28 (28): 56-64, 2008

27 Laloui, L, "Behavior of a dualpurpose pile as foundation and heat exchanger" 40 (40): 388-402, 2003

28 Min, H, "Analysis of thermal efficiency on energy piles considering thermal influence factors" Korean Geotechnical Society 1505-1512, 2012

29 Man, L., "A new model and analytical solutions for borehole and pile ground heat exchangers" 53 : 2593-2061, 2010