• Title/Summary/Keyword: Cast-in-place Energy Pile

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Performance Prediction of Geothermal Heat Pump(GHP) System Using Cast-in-Place Energy Piles (현장 타설 에너지파일을 적용한 지열 히트펌프 시스템의 성능 예측)

  • Sohn, Byonghu;Jung, Kyung-Sik;Choi, Hangseok
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.25 no.1
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    • pp.28-36
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    • 2013
  • The aim of this study is to evaluate the performance of the GHP system with 45 cast-in-place energy piles(CEP) for a commercial building. In order to demonstrate the feasibility of a sustainable performance of the system, transient simulations were conducted over 1-year and 20-year periods, respectively. The 1-year simulation results showed that the maximum and minimum temperatures of brine returning from the CEPs were $23.91^{\circ}C$ and $6.66^{\circ}C$, which were in a range of design target temperatures. In addition, after 20 years' operation, these returning temperatures decreased to $21.24^{\circ}C$ and $3.68^{\circ}C$, and finally reached to stable state. Annual average extraction heat of cast-in-place energy piles was 94.3 MWh and injection heat was 65.7 MWh from the 20 years of simulation results. Finally, it is expected this GHP system can operate with average heating SPF of more than 3.45 for long-term.

Study on Thermal Stress Occurred in Concrete Energy Pile During Heating and Cooling Buildings (냉난방 가동 모사에 따른 콘크리트 에너지파일의 열응력 해석에 대한 연구)

  • Sung, Chihun;Park, Sangwoo;Kim, Byungyeon;Jung, Kyoungsik;Choi, Hangseok
    • Journal of the Korean Society for Geothermal and Hydrothermal Energy
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    • v.11 no.2
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    • pp.12-18
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    • 2015
  • The energy pile, used for both structural foundations and heat exchangers, brings about heat exchange with the ground formation by circulating a working fluid for heating and cooling buildings. As heat exchange occurs in the energy pile, thermal stress and strain is generated in the pile body and surrounding ground formation. In order to investigate the thermo-mechanical behavior of an energy pile, a comprehensive experimental program was conducted, monitoring the thermal stress of a cast-in place energy pile equipped with five pairs of U-type heat exchanger pipes. The heating and cooling simulation both continued for 30 days. The thermal strain in the longitudinal direction of the energy pile was monitored for a 15 operation days and another 15 days monitoring followed, without the application of heat exchange. In addition, a finite element model was developed to simulate the thermo-mechanical behavior of the energy pile. A non-linear contact model was adopted to interpret the interaction at the pile-soil interface, and thermal-induced structure mechanics was considered to handle the thermo-mechanical coupled multi-field problem.

The Effect of Construction Methods on Geothermal Exchange Rates of Cast-in-place Energy Piles (현장타설말뚝형 에너지 파일의 시공형태별 지중 열교환량에 관한 연구)

  • Park, Yong-Boo;Nam, Yu-Jin;Sim, Young-Jong;Sohn, Jeong-Rak
    • LHI Journal of Land, Housing, and Urban Affairs
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    • v.3 no.2
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    • pp.169-175
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    • 2012
  • In recent, there are many studies associated with energy piles to save initial construction cost for ground source heat pump system. In this study, to evaluate geothermal exchange rates two types (a connection type and a slinky type) of cast-in-place energy piles (PRD, 4.5m in depth, 1,200 mm in diameter) were constructed for the tests and their efficiencies were compared with numerical analysis results. As a result, starting with operation, geothermal exchange rate gradually decreases due to exchange of lower ground temperature. In the case of connection type, temperature difference is $0.37^{\circ}C$ in heating mode and $0.34^{\circ}C$, in cooling mode, respectively. In addition, in case of a connection type, geothermal exchange rate in heating mode is 2,314W/m and in cooling mode, 252.2W/m whose value is 9% higher than in heating mode. In the case of slinky type, the average geothermal exchange rate in heating mode is 168.0W/m, which is about 27% lower than that of connection type.

Evaluation of Heat Exchange Efficiency and Applicability for Parallel U-type Cast-in-place Energy Pile (병렬 U형 현장타설 에너지파일의 열교환 효율 및 적용성 평가)

  • Park, Sangwoo;Kim, Byeongyeon;Sung, Chihun;Choi, Hangseok
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.35 no.2
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    • pp.361-375
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    • 2015
  • An energy pile is one of the novel ground heat exchangers (GHEX's) that is a economical alternative to the conventional closed-loop vertical GHEX. The combined system of both a structural foundation and a GHEX contains a heat exchange pipe inside the pile foundation and allows a working fluid circulating through the pipe, inducing heat exchange with the ground formation. In this paper, a group of energy piles equipped with parallel U-type (5, 8 and 10 pairs) heat exchange pipes was constructed in a test-bed by fabricating in large-diameter cast-in-place concrete piles. In addition, a closed-loop vertical GHEX with 30m depth was constructed nearby to conduct in-situ thermal response tests (TRTs) and to compare with the thermal performance of the cast-in-place energy piles. A series of thermal performance tests was carried out with application of an artificial cooling and heating load to evaluate the heat exchange rate of energy piles. The applicability of cast-in-place energy piles was evaluated by comparing the relative heat exchange efficiency and heat exchange rate with preceding studies. Finally, it is concluded that the cast-in-place energy piles constructed in the test-bed demonstrate effective and stable thermal performance compared with the other types of GHEX.

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

  • Min, Sunhong;Park, Sangwoo;Jung, Kyoungsik;Choi, Hangseok
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.33 no.3
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    • pp.1049-1061
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    • 2013
  • 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.

Evaluation on Thermal Performance Along with Constructability and Economic Feasibility of Large-diameter Cast-in-place Energy Pile (대구경 현장타설 에너지파일의 열교환 성능과 시공성 및 경제성 분석)

  • Park, Sangwoo;Sung, Chihun;Lee, Dongseop;Jung, Kyoungsik;Choi, Hangseok
    • Journal of the Korean Geotechnical Society
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    • v.31 no.5
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    • pp.5-21
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    • 2015
  • An energy pile is a novel type of ground heat exchangers (GHEX's) which sets up heat exchange pipes inside a pile foundation, and allows to circulate a working fluid through the pipe for exchanging thermal energy with the surrounding ground stratum. Using existing foundation structure, the energy pile can function not only as a structural foundation but also as a GHEX. In this paper, six full-scale energy piles were constructed in a test bed with various configurations of the heat exchange pipe inside large-diameter cast-in-place piles, that is, three parallel U-type heat exchangers (5, 8 and 10 pairs), two coil type heat exchangers (with a 500 mm and 200 mm pitch), and one S-type heat exchanger. During constructing the energy piles, the constructability of each energy pile was evaluated with consideration of the installation time, the number of workers and any difficulty for installing. In order to evaluate the thermal performance of energy piles, the thermal performance tests were carried out by applying intermittent (8 hours operating-16 hours pause) artificial cooling operation to simulate a cooling load for commercial buildings. Through the thermal performance tests, the heat exchange rates of the six energy piles were evaluated in terms of the heat exchange amount normalized with the length of energy pile and/or the length of heat exchange pipe. Finally, the economic feasibility of energy pile was evaluated according to the various types of heat exchange pipe by calculating demanded expenses per 1 W/m based on the thermal performance test results along with the market value of heat exchange pipes and labor cost.