• Title/Summary/Keyword: Ground effective thermal Conductivity

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Measurements of In-situ Thermal Conductivity of Closed Type Ground Heat Exchanger in Korea (국내의 주요 지역에서 밀폐형 열교환기의 열전도도 측정)

  • Jung, Kye-Hoon;Lim, Hyo-Jae;Han, Ji-Won;Park, Kyung-Woo
    • Proceedings of the KSME Conference
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    • 2007.05b
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    • pp.3401-3406
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    • 2007
  • This study was performed to acquire the reliable in-situ thermal conductivity of closed type ground heat exchanger used in ground source heat pump. We selected four sites(Cheonan, Daejeon, Daegu, Gwangju) which are central area of South Korea. Test results show that the effective thermal conductivities are 2.33 W/m$^{\circ}C$, 2.50 W/m$^{\circ}C$, 2.75 W/m$^{\circ}C$ and 2.86 W/m$^{\circ}C$. From this data, we can see that thermal conductivity varies about the range of 23% with the sites. Also, thermal conductivity increases up to 20% by changing grouting material from low salica sand to high one.

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A Study on Regional Distribution of the Ground Effective Thermal Conductivity (지중 유효 열전도도의 지역별 분포)

  • Kong, Hyoung Jin;Kwon, Soon-Ki;Ji, Seung Gyu
    • Transactions of the KSME C: Technology and Education
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    • v.4 no.1
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    • pp.43-47
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    • 2016
  • Ground source heat pump(GSHP) systems is known as environmental friendly and energy saving. Especially a ground heat exchanger is an important unit that determines the thermal performance of a system and initial cost. In design phase of vertical GSHP system, it is recommended that the effective borehole thermal resistance, be determined from in-situ thermal response test. In this study, ground effective thermal conductivity was categorized by a region. As a result of the study, the ground thermal conductivity of national average was analyzed as 2.56 W/mK. The highest regional average of thermal conductivity is 2.68 W/mK in Seoul, and the lowest is 2.28 W/mK in Busan. Also, the thermal conductivity on the coast has been analyzed approximately 30% lower than the average.

Predicting the Effective Thermal Conductivity of Sand-Water Mixtures Used for Grouting Materials (그라우팅 재료로 사용되는 모래-물 혼합물의 열전도도 예측)

  • Sohn, Byong-Hu;Lim, Hyo-Jae
    • Proceedings of the SAREK Conference
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    • 2008.06a
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    • pp.761-768
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    • 2008
  • This paper presents the results of a laboratory study on the thermal conductivity of sand(silica, quartzite, limestone, sandstone, granite and masonry sand)-water mixtures used in ground heat exchanger backfilling materials. Nearly 260 tests were performed in a thermal conductivity measuring system to characterize the relationships between the thermal conductivity of mixtures and the water content. The experimental results show that the thermal conductivity of mixtures increases with increasing dry density and with increasing water content. The most widely used empirical prediction models for thermal conductivity of soils were found inappropriate to estimate the thermal conductivity of unsaturated sand-water mixtures. An improved model using a exponential relationship to compute the thermal conductivity of dry sands and empirical relationship to assess the normalized thermal conductivity of unsaturated sand-water mixtures is presented.

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An Experimental Study on the Thermal Performance Measurement of Standing Column Well type Borehole Heat Exchanger (스탠딩컬럼웰형(SCW) 지중열교환기의 열성능 측정에 관한 실험적 연구)

  • Lee, Sanghoon;Choe, Yongseok;An, Kunmuk
    • 한국신재생에너지학회:학술대회논문집
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    • 2010.11a
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    • pp.122.2-122.2
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    • 2010
  • Knowledge of ground thermal properties is most important for the proper design of BHE(borehole heat exchanger) systems. The configure type, pipe size and thermal performance of the BHE is highly dependent on the ground source heatpump system-efficiency and instruction cost. Thermal response tests with mobile measurement devices were developed primarily for in-situ determination of design data for Standing Column Well apply. The main purpose has been to determine in-situ values of effective ground thermal conductivity and thermal resistance, including the effect of ground-water flow and natural convection in the boreholes. The test rig is set up on a some trailer, and contains a sub-circulation pump, a boiler, temperature sensors, flow meter and a data logger for recording the temperature and circulation fluid flow data. A constant heating power is injected into the SCW through the test rig and the resulting temperature change in the SCW is recorded. The recorded temperature data are analysed with a line-source model, which gives the effective in-situ values of rock thermal conductivity and thermal resistance of SCW.

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An Experimental Study on the Thermal Performance Measurement of Large Diameter Borehole Heat Exchanger(LD-BHE) for Tripe-U Pipes Spacer Apply (3중관용 스페이서를 적용한 대구경 지중열교환기의 성능측정에 관한 연구)

  • Lee, Sang-Hoon;Park, Jong-Woo;Lim, Kyoung-Bin
    • 한국신재생에너지학회:학술대회논문집
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    • 2009.11a
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    • pp.581-586
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    • 2009
  • Knowledge of ground thermal properties is most important for the proper design of large scale BHE(borehole heat exchanger) systems. The type, pipe size and thermal performance of the BHE is highly dependent on the ground source heatpump system-efficiency and instruction cost. Thermal response tests with mobile measurement devices were developed primarily for insitu determination of design data for large diameter BHE for triple-U spacer apply. The main purpose has been to determine insitu values of effective ground thermal conductivity and thermal resistance, including the effect of ground-water flow and natural convection in the boreholes. The test rig is set up on a some trailer, and contains a circulation pump, a inline heater, temperature sensors, flow meter, power analysis meter and a data logger for recording the temperature, fluid flow data. A constant heat power is injected into the borehole through the tripl-U pipes system of test rig and the resulting temperature change in the borehole is recorded. The recorded temperature data are analysed with a line-source model, which gives the effective insitu values of rock thermal conductivity and borehole thermal resistance of large diameter BHE for spacer apply.

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A study on cement-based grout for ground heat exchangers (지중 열교환기용 시멘트 그라우트에 관한 연구)

  • Lee, Dong-Ju;Baek, Hwan-Jo;Kim, Gyoung-Man
    • Journal of Industrial Technology
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    • v.31 no.B
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    • pp.27-36
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    • 2011
  • In this paper, the applicability of cement grout has been studied as an alternative to bentonite grout for backfill ground heat exchangers. To provide an optimal mixture design, the thermal conductivity of cement grout and bentonite grout with various mixture ratios were experimentally evaluated and compared. Numerical analyses using Fluent(FVM program) were applied to compare the thermal transfer efficiency of the cement grout with that of the bentonite grout used in the construction. Also the effective ground thermal conductivity was measured by In-situ thermal response test. The results showed that the thermal efficiency of the cement grout was better than the bentonite grout. Consequently, the cement grout could be an alternative with more thermal efficiency to bentonite grout for ground heat exchangers.

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An Experimental Study on the Thermal Performance Measurement of Vertical Borehole Heat Exchanger(BHE) (수직형 지열 열교환기(BHE)의 열성능 측정에 관한 실험적 연구)

  • Lim Kyoung-Bin;Lee Sang-Hoon;Soung Nak-Won;Lee Chang-Hee
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.30 no.8 s.251
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    • pp.764-771
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    • 2006
  • Knowledge of ground thermal properties is most important for the proper design of large BHE(borehole heat exchanger) systems. Thermal response tests with mobile measurement devices were first introduced in Sweden and USA in 1995. Thermal response tests have so far been used primarily for in insitu determination of design data for BHE systems, but also for evaluation of grout material, heat exchanger types and ground water effects. The main purpose has been to determine insitu values of effective ground thermal conductivity, including the effect of ground-water flow and natural convection in the boreholes. Test rig is set up on a small trailer, and contains a circulation pump, a heater, temperature sensors and a data logger for recording the temperature data. A constant heat power is injected into the borehole through the pipe system of test rig and the resulting temperature change in the borehole is recorded. The recorded temperature data are analysed with a line-source model, which gives the effective insitu values of rock thermal conductivity and borehole thermal resistance.

Evaluation of performance of closed-loop vertical ground heat exchanger by In-situ thermal response test (현장 열응답 시험을 통한 수직 밀폐형 지중열교환기의 성능 평가)

  • Lee, Chul-Ho;Park, Moon-Seo;Kwak, Tae-Hoon;Choi, Hang-Seok
    • Proceedings of the Korean Geotechical Society Conference
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    • 2010.03a
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    • pp.229-239
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    • 2010
  • Performing a series of in-situ thermal response tests, the effective thermal conductivity of six vertical closed-loop ground heat exchangers was experimentally evaluated and compared each other, 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 that of bentonite grouting, and the efficiency of graphite better performs over 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.

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Evaluation of Effective Thermal Conductivity and Thermal Resistance in Ground Heat Exchanger Boreholes (지중 열교환기 보어홀에서의 유효 열전도도 및 열저항 산정)

  • Sohn Byong Hu;Shin Hyun-Joon;Park Seong-Koo
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.17 no.8
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    • pp.695-703
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    • 2005
  • The objective of this study is to determine the effective thermal conductivity and thermal resistance values in test boreholes with three different fill materials. To evaluate these heat transfer properties, in-situ tests on four vertical boreholes were conducted by adding a monitored amount of heat to water over various test lengths. Two parameter estimation models, line-source and numerical one-dimensional models, for evaluation of thermal response test data were compared when applied on the same four data sets. Results show that the average thermal conductivity deviation between measured data and these two models is in the range of $3.03\%$ to $4.45\%$. The effect of increasing grout thermal conductivity from 1.34 to 1.82 $W/m^{\circ}C$ resulted in overall increases in effective formation thermal conductivity by $11.1\%$ to $51.9\%$ and reductions in borehole thermal resistance by $11.6\%$ to $26.1\%$.

Study on the Thermal Conductivity of Frozen Soil Considering Various Experimental Conditions (다양한 실험조건을 고려한 동결 사질토의 열전도도 산정에 대한 연구)

  • Kim, Hee-Won;Go, Gyu-Hyun
    • Journal of the Korean Geotechnical Society
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    • v.39 no.9
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    • pp.5-11
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    • 2023
  • In analyzing geotechnical structures, the analysis fields are becoming increasingly diversified. In particular, the need for predicting the thermal behavior of ground materials has become important in fields related to soil freezing. To ensure a reliable assessment of the freezing behavior of the ground, considering the variation in the effective thermal conductivity of soil specimens under various conditions is crucial. In this study, probe experiments were conducted by varying the porosity, initial degree of saturation, and read time settings of the meter. Next, the factors influencing the effective thermal conductivity of the frozen sandy soil were evaluated. The experimental results conducted under different porosity conditions showed a tendency for the effective thermal conductivity of frozen soil to increase as the specimen's porosity decreased. However, as the degree of saturation of the specimen increased, the effective thermal conductivity also increased. The sensitivity of the meter's read time setting to the measurement of effective thermal conductivity was observed. When the read time was set to 1 min, the measured values were in a range similar to that obtained in previous studies conducted in Korea with the same soil specimen.