• Title/Summary/Keyword: Ground-loop heat exchanger

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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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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%.

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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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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Effect of Grouting Materials on Ground Effective Thermal Conductivity (그라우팅 재료가 지중 유효열전도도에 미치는 영향)

  • Sohn, Byong-Hu
    • Proceedings of the KSME Conference
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    • pp.3371-3376
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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 thermal conductivity of the ground. To evaluate this heat transfer property, in-situ thermal response tests on four vertical test boreholes with different grouting materials were conducted by adding a monitored amount of heat to water over various test lengths. By measuring the water temperatures entering and exiting the loop, water flow rate, and heat load, effective thermal conductivity values of the ground were determined. The effect of increasing thermal conductivity of grouting materials from 0.82 to 1.05 W/m$^{\circ}C$ resulted in overall increases in effective ground thermal conductivity by 25.8% to 69.5%.

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Numerical Analysis on the Heat Transfer Characteristics of HDPE Pipe with the Variation of Geometries for Ground Loop Heat Exchangers (지중열교환기의 고밀도폴리에틸렌 배관 형상에 따른 열전달 성능 특성에 대한 수치해석적 연구)

  • Mensah, Kwesi;Choi, Jong Min
    • Journal of the Korean Society for Geothermal and Hydrothermal Energy
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    • v.12 no.4
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    • pp.33-39
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    • 2016
  • A ground source heat pump (GSHP) system is recommended as a heating and cooling system to solve the pending energy problem in the field of air conditioning, because it has the highest efficiency. However, higher initial construction cost works as a barrier to the promotion and dissemination of GSHP system. In this study, numerical analysis on the characteristics of high density polyethylene (HDPE) pipe with spiral inside was executed. The heat transfer and flow characteristics of it were compared with those of a conventional smooth HDPE pipe. The heat transfer coefficient and pressure drop of the spiral HDPE pipe were higher than those of the smooth HDPE pipes at the same fluid flow rate. By decreasing the flow rate, the spiral HDPE pipe represented similar values of heat transfer coefficient and pressure drop to the smooth HDPE pipe. The lower flow rate of the spiral HDPE pipe comparing with it of the smooth HDPE pipe is estimated to reduce the length of the ground loop heat exchanger.

Analysis of Effective Soil Thermal Conductivities and Borehole Thermal Resistances with a Line Source Method (선형열원법에 의한 지중유효열전도도와 보어홀 전열저항 해석)

  • Lee, Se-Kyoun;Woo, Joung-Son;Ro, Jeong-Geun
    • Journal of the Korean Solar Energy Society
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    • v.30 no.4
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    • pp.71-78
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    • 2010
  • Investigation of the effective soil thermal conductivity(k) is the first step in designing the ground loop heat exchanger(borehole) of a geothermal heat pump system. The line source method is required by New and Renewable Energy Center of Korea Energy Management Corporation in analyzing data obtained from thermal response tests. Another important factor in designing the ground loop heat exchanger is the borehole thermal resistance($R_b$). There are two methods to evaluate $R_b$ : one is to use a line source method, and the other is to use a shape factor of the borehole. In this study, we demonstrated that the line source method produces better results than the shape factor method in evaluating $R_b$. This is because the borehole thermal resistance evaluated with the line source method characteristically reduces the temperature differences between an actual and a theoretical thermal behaviors of the borehole. Evaluation of $R_b$ requires soil volumetric heat capacity. However, the effect of the soil volumetric heat capacity on the borehole thermal resistance is very small. Therefore, it is possible to use a generally accepted average value of soil volumetric heat capacity($=2MJ/m^3{\cdot}K$) in the analysis. In this work, it is also shown that an acceptable range of the initial ignoring time should be in the range of 8~16hrs. Thus, a mean value of 12 hrs is recommended.

Study on Capacity Alteration of Geothermal Heat Exchanger by Changing Design Condition (설계조건 변화에 따른 지중열교환기 길이 변화 연구)

  • Park, Jong Il;Park, Kyung Soon
    • Journal of the Korean Society for Geothermal and Hydrothermal Energy
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    • v.9 no.4
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    • pp.9-14
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    • 2013
  • A ground loop heat exchanger for the ground source heat pump system is the important equipment determining the thermal performance and initial cost of the system. The length and performance of the underground heat exchanger is dependent on ground thermal conductivity, operation hours, ground loop diameter, grout, ground loop arrangement, pipe placement and design temperature. In this study we find out heat exchanger length with various design factor.

Effect of the Design Parameters of Geothermal Heat Exchanger Design Length (설계변수가 수직밀폐형 지중열교환기 설계길이에 미치는 영향)

  • Min, Kyong-Chon;Choi, Jae-Ho
    • Journal of the Korean Society for Geothermal and Hydrothermal Energy
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    • v.7 no.2
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    • pp.10-15
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    • 2011
  • 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 length and performance of the heat exchanger is dependent on the ground thermal conductivity, the operation hours, the ground loop diameter, the grout, the ground loop arrangement, the pipe placement and the design temperature. The result of this simulation shows that higher thermal conductivity of grouting materials leads to the decrease length of geothermal heat exchanger from 100.0 to 84.4%.

Thermal Conductivity Measurement of Grouting Materials for Ground Heat Exchanger Borehole (지중 열교환기 보어홀 그라우팅 재료의 열전도도 측정)

  • Sohn, Byong-Hu;Shin, Hyun-Joon
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.18 no.6
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    • pp.493-500
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    • 2006
  • This paper concerns the measurement of thermal conductivity of grouting materials for ground loop heat exchanger. A thermal conductivity meter, QTM-500 based on modified transient hot wire method was used to measure the thermal conductivity of neat bentonite and mixtures of bentonite and various additives. Relative to the total mixture mass, as the percent additive was increased the mixture thermal conductivity increased. For the bentonite-silica sand mixtures, the higher density of the sand particles resulted in much higher mixture thermal conductivity. The quartzite and silica sands produced the largest increases in mixture thermal conductivity, while common masonry and limestone sands produced lower thermal conductivity increases.