• Title/Summary/Keyword: 지중 유효 열전도도

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The Outlet Temperature Prediction of In-Situ Thermal Response Test using CFD Analysis (CFD 해석을 이용한 현장 열응답 시험의 출구온도 예측)

  • Sim, Yong-Sub;Lee, Hee-Sang
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.17 no.1
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    • pp.28-35
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    • 2016
  • The in-situ thermal response test for the design of a ground heat exchanger of geothermal heat pumps have difficulty in predicting the outlet temperature according to the variation of conditions due to the expense and time. This paper suggests a 3-D CFD analysis method to predict the heat transfer performance of vertical type ground heat exchanger, which is mostly used in national, and the outlet temperature and the slope of two in-situ thermal response tests were compared to test the proposed CFD reliability. The results of CFD analysis showed that the outlet temperature was predicted to within $0.5^{\circ}C$ of the actual value and the slope was predicted to within 1.6%. The reliability of the CFD analysis method was confirmed using this process, and the outlet temperature prediction of the two in-situ thermal response tests was obtained by changing ${\pm}20%$ of the flow rate and the effective thermal conductivity conditions, respectively. The results of CFD analysis showed that the outlet temperature of Case 1 was 28.0 (-20%) and $29.6^{\circ}C$ (+20%) for the flow rate variation and $29.6^{\circ}C$ (-20%) and $28.0^{\circ}C$ (+20%) for the effective thermal conductivity variation, and the outlet temperature of Case 2 was 28.4 (-20%) and $29.8^{\circ}C$ (+20%) for the flow rate variation and $29.7^{\circ}C$(-20%) and $28.4^{\circ}C$(+20%) for the effective thermal conductivity variation.

Effect of Some Parameters on Ground Effective Thermal Conductivity (지중열교환기 설치 조건이 지중 유효 열전도도에 미치는 영향)

  • Choi, Jae-Ho;Lim, Hyo-Jae;Kong, Hyoung-Jin;Sohn, Byong-Hu
    • Proceedings of the SAREK Conference
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    • pp.33-38
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    • 2008
  • A ground-loop heat exchanger in a ground source heat pump system is an important unit that determines the thermal performance of a system and its initial cost. The Size and performance of this heat exchanger is highly dependent on ground thermal properties. A proper design requires certain site-specific parameters, most importantly the ground effective thermal conductivity, the borehole thermal resistance and the undisturbed ground temperature. This study was performed to investigate the effect of some parameters such as borehole lengths, various grouting materials and U-tube configurations on ground effective thermal conductivity. In this study, thermal response tests were conducted using a testing device with 9-different ground-loop heat exchangers. From the experimental results, the length of ground-loop heat exchanger affects to the effective thermal conductivity. Among the various grouting materials, the bentonite-based grout with silica sand shows the largest thermal conductivity value.

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Evaluation of Ground Effective Thermal Conductivity and Borehole Effective Thermal Resistance from Simple Line-Source Model (단순 선형열원 모델을 이용한 지중 유효 열전도도와 보어홀 유효 열저항 산정)

  • Sohn, Byong-Hu
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.19 no.7
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    • pp.512-520
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    • 2007
  • The design of a ground-source heat pump system includes specifications for a ground loop heat exchanger where the heat transfer rate depends on the effective thermal conductivity of the ground and the effective thermal resistance of the borehole. To evaluate these heat transfer properties, in-situ thermal response tests on four vertical test boreholes with different grouting materials were conducted by adding a monitored amount of heat to circulating water. The line-source method is applied to the temperature rise in an in-situ test and extended to also give an estimate of borehole effective thermal resistance. The effect of increasing thermal conductivity of the grouting materials from 0.818 to $1.104W/m^{\circ}C$ resulted in overall increases in effective thermal conductivity by 15.8 to 56.3% and reductions in effective thermal resistance by 13.0 to 31.1%.

The Effects of the Installation Conditions of Ground Loop Heat Exchanger to the Thermal Conductivity and Borehole Resistance (지중열교환기 설치 조건이 지중 유효 열전도도와 보어홀 열저항에 미치는 영향)

  • Lim, Hyo-Jae;Kong, Hyoung-Jin;Kang, Sung-Jae;Choi, Jae-Ho
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.23 no.2
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    • pp.95-102
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    • 2011
  • A ground loop heat exchanger in a ground source heat pump system is an important unit that determines the thermal performance of a system and its initial cost. A proper design requires certain site specific parameters, most importantly the ground effective thermal conductivity, the borehole thermal resistance and the undisturbed ground temperature. This study was performed to investigate the effect of some parameters such as borehole lengths, various grouting materials and U tube configurations on ground effective thermal conductivity and borehole thermal resistance. In this study, thermal response tests were conducted using a testing device to 9 different ground loop heat exchangers. From the experimental results, the length of ground loop heat exchanger affects to the effective thermal conductivity. The results of this experiment shows that higher thermal conductivity of grouting materials leads to the increase effective thermal conductivity from 22 to 32%. Also, mounting spacers have increased by 14%.

Performance Evaluation of Large Borehole Ground-Loop Heat Exchanger (저심도 대구경 지중열교환기의 설치조건에 따른 성능 연구)

  • Yoo, Gyu-Sang;Park, Il-Mun;Choi, Jae-Ho;Shin, Hyun-Joon
    • Proceedings of the SAREK Conference
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    • pp.58-63
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    • 2009
  • A ground-loop heat exchanger for the ground source heat pump system is the core equipment determining the thermal performance and initial cost of the system. The size and performance of the heat exchanger is highly dependent on the ground thermal properties - the ground effective thermal conductivity, the borehole thermal resistance and the undisturbed ground temperature. Nowadays, precast concrete piles using steel reinforced precast concrete piles - energy piles - are used to reduce the installing cost of the ground-loop heat exchanger. We were carried out some tests to investigate the effects of some parameters such as borehole length, grouting materials and U-tube configuration of the energy piles. 4 concrete piles, each measuring $250mm{\sim}400mm$ in diameter and approx. 10m in length, and rigged with single spiral and 3 U-tube loop of $16mm{\times}2.3mm$ PB piping. The thermal response tests were conducted using a testing device for 4-different ground-loop heat exchangers. During the heating period, the energy piles absorb the heat of 0.89kW to 1.37kW.

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An Experimental Study on the Effect of Ground Heat Exchanger to the Overall Thermal Conductivity (지중열교환기 설치 조건이 지중 유효 열전도도에 미치는 영향에 관한 실험적 연구)

  • Kong, Hyoung-Jin;Lim, Hyo-Jae;Choi, Jae-Ho;Sohn, Byong-Hu
    • Proceedings of the SAREK Conference
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    • pp.45-51
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    • 2009
  • A ground-loop heat exchanger in a ground source heat pump system is an important unit that determines the thermal performance of a system and its initial cost. The size and performance of this heat exchanger is highly dependent on ground thermal properties. A proper design requires certain site-specific parameters, most importantly the ground effective thermal conductivity, the borehole thermal resistance and the undisturbed ground temperature. This study was performed to investigate the effect of some parameters such as borehole lengths, various grouting materials and U-tube configurations on ground effective thermal conductivity. In this study, thermal response tests were conducted using a testing device with 9-different ground-loop heat exchangers. From the experimental results, the length of ground-loop heat exchanger affects to the effective thermal conductivity. Among the various grouting materials, the bentonite-based grout with silica sand shows the largest thermal conductivity value.

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Evaluation of Performance of Grouts and Pipe Sections for Closed-loop Vertical Ground Heat Exchanger by In-situ Thermal Response Test (현장 열응답 시험을 통한 수직 밀폐형 지중열교환기용 그라우트와 열교환 파이프 단면의 성능 평가)

  • Lee, Chul-Ho;Park, Moon-Seo;Min, Sun-Hong;Choi, Hang-Seok;Sohn, Byong-Hu
    • Journal of the Korean Geotechnical Society
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    • v.26 no.7
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    • pp.93-106
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    • 2010
  • In performing a series of in-situ thermal response tests, the effective thermal conductivities of six vertical closed-loop ground heat exchangers were experimentally evaluated and compared one another, which were constructed in a test bed in Wonju. To compare thermal efficiency of the ground heat exchangers in field, the six boreholes were constructed with different construction conditions: grouting materials (cement vs. bentonite), different additives (silica sand vs. graphite) and the shape of pipe-sections (general U-loop type vs. 3 pipe-type). From the test results, it can be concluded that cement grouting has a higher effective thermal conductivity than bentonite grouting, and the efficiency of graphite better performs than silica sand as a thermally-enhancing addictive. In addition, a new 3 pipe-type heat exchanger provides less thermal interference between the inlet and outlet pipe than the conventional U-loop type heat exchanger, which results in superior thermal performance. Based on the results from the in-situ thermal response tests, a series of economic analyses have been made to show the applicability of the new addictives and 3 pipe-type heat exchanger.