• Title/Summary/Keyword: thermal response test

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Thermal Response Test (TRT) interpretation and the status in Korea (열응답 실험 해석 및 국내 현황)

  • Shim, Byoung Ohan;Choi, Choonghyun
    • 한국신재생에너지학회:학술대회논문집
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    • pp.168.2-168.2
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    • 2010
  • The growing market for geothermal heat pump system requires great consideration of quality control and assurance in design and construction. The borehole heat exchanger of GHP system should be sustainable, economical and ecological. Thermal Response Test (TRT) is a useful method for site investigation to obtain reliable data for a optimal system design from the technical and economical aspect. Intensive researches combined with exchange of experiences on an international level within the IEA ECES Annex 21 improved the technology. Major subjects on the interpretation of TRT are development of improved evaluation models, evaluation of the TRT with respect to geological layers and investigation of the influence of ground water. Current status of TRT in South Korea, as well as a new version of the Korean TRT standard test procedure was presented. TRT is mostly used for governmental supported projects with corresponds to more than 100 GCHP systems per year. More than 200 tests are applied, mostly on single U-tube heat exchangers (about 95%). Bentonite is the most common grouting to be used. KIGAM (Korea Institute of Geoscience & Mineral Resources) is also keeping a GIS geological and geothermal database. In the institute also laboratory measurements of rock properties are carried out. About 90% of the laboratory measurements of the rock heat conductivity shows higher values than the in-situ TRT.

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A study on thermal behavior of energy textile by performing in-situ thermal response test and numerical simulation (현장 열응답 시험과 수치해석을 통한 터널에 적용된 에너지 텍스타일의 열적 거동 연구)

  • Lee, Chul-Ho;Park, Moon-Seo;Min, Sun-Hong;Jeoung, Jae-Hyeung;Choi, Hang-Seok
    • Proceedings of the Korean Geotechical Society Conference
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    • pp.325-335
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    • 2010
  • A new geothermal energy source obtained from a tunnel structure has been studied in this paper. The geothermal energy is extracted through a textile-type ground heat exchanger named "Energy Textile" that is installed between a shotcrete layer and a guided drainage geotexitle. A test bed was constructed in an abandoned railway tunnel to verify the geothermal heat exchanger system performed by the energy textile. To evaluate the applicability of the energy textile, we measured the thermal conductivity of shotcrete and lining samples which were prepared in accordance with a common mixture design. An overall performance of the energy textile installed in the test bed was evaluated by carrying out a series of in-situ thermal response test. In addition, a 3-D finite volume analysis (FLUENT) was adopted to simulate the operation of the ground heat exchanger being encased in the energy textile with the consideration of the effect of the shotcrete and lining thermal conductivity.

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Evaluation of Thermal Conductivity for Grout/Soil Formation Using Thermal Response Test and Parameter Estimation Models (열응답 시험과 변수 평가 모델을 이용한 그라우트/토양 혼합층의 열전도도 산정)

  • Sohn Byong Hu;Shin Hyun Jun;An Hyung Jun
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.17 no.2
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    • pp.173-182
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    • 2005
  • The Performance of U-tube ground heat exchanger for geothermal heat Pump systems depends on the thermal properties of the soil, as well as grout or backfill materials in the borehole. In-situ tests provide a means of estimating some of these properties. In this study, in-situ thermal response tests were completed on two vertical boreholes, 130 m deep with 62 mm diameter high density polyethylene U-tubes. The tests were conducted by adding a monitored amount of heat to water over a $17\~18$ hour period for each vertical boreholes. By monitoring the water temperatures entering and exiting the loop and heat load, overall thermal conductivity values of grout/soil formation were determined. Two parameter estimation models for evaluation of thermal response test data were compared when applied on the same temperature response data. One model is based on line-source theory and the other is a numerical one-dimensional finite difference model. The average thermal conductivity deviation between measured data and these models is of the magnitude $1\%$ to $5\%$.

Effect of initial ground temperature measurement on the design of borehole heat exchanger (초기 지중온도 측정이 지중 열교환기 설계에 미치는 영향)

  • Song, Yoon-ho;Kim, Seong-Kyun;Lee, Kang-Kun;Lee, Tae-Jong
    • 한국신재생에너지학회:학술대회논문집
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    • pp.600-603
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    • 2009
  • We compared relative importance of thermal conductivity and initial ground temperature in designing borehole heat exchanger network and also we test accuracy of ground temperature estimation in thermal response test using a proven 3-D T-H modeler. The effect of error in estimating ground temperature on calculated total length of borehole heat exchanger was more than 3 times larger than the case of thermal conductivity in maximum 20% error range. Considering 10% of error in estimating thermal conductivity is generally acceptable, we have to define the initial ground temperature within 5% confidence level. Utilizing the mean annual ground surface temperature and the geothermal gradient map compiled so far can be a economic way of estimating ground temperature with some caution. When performing thermal response test for estimating ground temperature as well as measuring thermal conductivity, minimum 100 minutes of ambient circulation is required, which should be even more in case of very cold and hot seasons.

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A Case Study on the Effective Thermal Conductivity Measurement in In-situ Thermal Response Test (현장열응답시험을 이용한 지중열전도도 측정 사례연구)

  • Kim, Min-Jun;Choi, Choong-Hyun;Woo, Jeong-Tae;Chang, Keun-Sun;Kang, Hee-Jeong;Seo, Jeong-Sik
    • 한국신재생에너지학회:학술대회논문집
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    • pp.123.2-123.2
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    • 2010
  • 본 논문에서는 2008년 4월 이후 지열원 열펌프가 설치되어지는 현장에 시험공의 지중열전도도를 현장열응답법을 이용하여 측정하였으며, 그간에 측정된 지중열전도도를 이용하여 전국의 지중온도 및 지중열전도도의 산포도를 정리하였다. 지중열교환기의 심도가 150m일 때 지중온도 분포는 약 $12.0{\sim}19^{\circ}C$의 넓은 분포를 보였으나 대부분의 지중온도가 $15.0{\sim}17.0^{\circ}C$의 범위에 분포하였으며, 지중열전도도의 경우도 마찬가지로 1.50 ~ 9.00 W/mk 값으로 아주 넓은 분포를 보였으나 2.30 ~ 2.90W/mk 값이 가장 많이 나타냈다.

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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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Development of Thermal-Hydro Pipe Element for Ground Heat Exchange System (지중 열교환 시스템을 위한 열-수리 파이프 요소의 개발)

  • Shin, Ho-Sung;Lee, Seung-Rae
    • Journal of the Korean Geotechnical Society
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    • v.29 no.8
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    • pp.65-73
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    • 2013
  • Ground-coupled heat pump system has attracted attention as a promising renewable energy technology due to its improving energy efficiency and eco-friendly mechanism for space cooling and heating. Pipes buried in the ground play a role of direct thermal interaction between circulating fluid inside the pipe and surrounding soils in the geothermal exchange system. However, both complexities of turbulent flow coupling thermal-hydraulic phenomena and very long aspect ratio of the pipe make it difficult to model the heat exchange system directly. Energy balance for fluid flow inside the pipe was derived to model thermal-hydraulic phenomena, and one-dimensional pipe element was proposed through Galerkin formation and time integration of the equation. Developed element is combined to pre-developed FEM code for THM phenomena in porous media. Numerical results of Thermal Response Test showed that line-source model overestimates equivalent thermal conductivity of surrounding soils due to thermal interaction between adjacent pipes and finite length of the pipe. Thus, inverse analysis for the TRT simulation was conducted to present optimal transformation matrix with utmost convergence.

Prediction of Ground Thermal Properties from Thermal Response Test (현장 열응답 시험을 통한 지중 열물성 추정)

  • Yoon, Seok;Lee, Seung-Rae;Kim, Young-Sang;Kim, Geon-Young;Kim, Kyungsu
    • Journal of the Korean Geotechnical Society
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    • v.32 no.7
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    • pp.5-14
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    • 2016
  • The use of geothermal energy has increased for economically and environmentally friendly utilization, and a geothermal heat pump (GSHP) system for space heating and cooling is being used widely. As ground thermal properties such as ground thermal conductivity and ground thermal diffusivity are substantial parameters in the design of geothermal heat pump system, ground thermal conductivity should be obtained from in-situ thermal response test (TRT). This paper presents an experimental study of ground thermal properties of U and 2U type ground heat exchangers (GHEs) measured by TRTs. The U and 2U type GHEs were installed in a partially saturated dredged soil deposit, and TRTs were conducted for 48 hours. A method to derive the thermal diffusivity as well as thermal conductivity was proposed from a non-linear regression analysis. In addition, remolded soil samples from different layers were collected from the field, and soil specimens were reconstructed according to the field ground condition. Then equivalent ground thermal conductivity and ground thermal diffusivity were calculated from the lab test results and they were compared with the in-situ TRT results.

Thermal Conductivity from an in-situ Thermal Response Test Compared with Soil and Rock Specimens under Groundwater-bearing Conditions (지하수 부존지역에서의 토질 및 암석 시료와 현장 열응답시험의 열전도도 비교)

  • Kim, Jin-Sung;Song, Sung-Ho;Jeong, Gyo-Cheol
    • The Journal of Engineering Geology
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    • v.23 no.4
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    • pp.389-398
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    • 2013
  • Studies of the thermal properties of various rock types obtained from several locations in Korea have revealed significant differences in thermal conductivities in the thermal response test (TRT), which has been applied to the design of a ground-source heat pump system. In the present study, we aimed to compare the thermal conductivities of the samples with those obtained by TRT. The thermal conductivities of soil and rock samples were 1.32W/m-K and 2.88 W/m-K, respectively. In comparison, the measured TRT value for thermal conductivity was 3.13W/m-K, which is 10% higher than that of the rock samples. We consider that this difference may be due to groundwater flow because abundant groundwater is present in the study area and has a hydraulic conductivity of 0.01. It is natural to consider that the object of TRT is to calculate the original thermal conductivity of the ground, following the line source theory. Therefore, we conclude that the TRT applied to a domestic standing column type well is not suitable for a line source theory. To solve these problems, values of thermal conductivity measured directly from samples should be used in the design of ground-source heat pump systems.

Evaluation of Thermal Response Test of Energy Pile (에너지 파일의 현장 열응답 시험에 관한 연구)

  • Yoon, Seok;Lee, Seung-Rae;Kim, Min-Jun;Go, Gyu-Hyun
    • Journal of the Korean Geotechnical Society
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    • v.30 no.4
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    • pp.93-99
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    • 2014
  • Use of geothermal energy has been increased for its economical application and environmentally friendly utilization. Particularly, for energy piles, a spiral coil type ground heat exchanger (GHE) is more preferred than line type GHEs such as U and W shaped GHEs. A PHC energy pile with spiral coil type GHE was installed in an area of partially saturated dredged soil deposit, and a thermal response test (TRT) was conducted for 240 hours under a continuous operation condition. Besides, remolded soil samples from different layers were collected in the field, and soil specimens were reconstructed according to the field ground condition. Non-steady state probe methods were conducted in the lab, and ground thermal conductivity and thermal diffusivity were measured for the different soil layers. An equivalent ground thermal conductivity was calculated from the lab test results and it was compared with the field TRT result. The difference was less than 5%, which advocates the use of an equivalent ground thermal conductivity for the multi-layered ground. Furthermore, this paper also represents an equivalent ground thermal diffusivity evaluation method which is another very important design parameter.