Journal of the Korean Society for Geothermal and Hydrothermal Energy (한국지열·수열에너지학회논문집)

Korean Society for Geothermal and Hydrothermal Energy (한국지열·수열에너지학회)
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Thermal Property Measurement of Bentonite-Based Grouts and Their Effects on Design Length of Vertical Ground Heat Exchanger

벤토나이트 그라우트의 열물성 측정 및 열물성이 수직 지중열교환기 설계 길이에 미치는 영향

  • 손병후 (한국건설기술연구원 녹색건축연구센터)
  • Received : 2019.05.03
  • Accepted : 2019.05.28
  • Published : 2019.06.01
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Abstract

In a ground-source heat pump (GSHP) system, a vertical ground heat exchanger (GHE) is widely accepted due to a higher thermal performance. In the vertical GHE, grout (also called grouting material) plays an important role in the heat transfer performance and the initial installation cost of the GHE. Bentonite-based grout has been used in practice because of its high swelling potential and low hydraulic conductivity. This study evaluated the thermo-physical properties of the bentonite-based grouts through lab-scale measurements. In addition, we conducted performance simulation to analyze the effect of mixed ratio of grouts on the design length and thermal performance of the vertical GHE. The simulation results show that thermally-enhanced grouts improve the heat transfer performance of the vertical GHE and thus reduce the design length of GHE pipe.

Keywords

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Fig. 1. Thermal conductivity measurement of grout samples using QL-30.

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Fig. 2. Viscosity measurement of grout samples using spindle type viscometer (DV2T).

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Fig. 3. Cross-sectional image of measurement apparatus for measuring the effect of saline water on the thermal properties of bentonite grout (Sample 6).

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Fig. 6. Building 3D modelling for this study.

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Fig. 7. Hourly cooling and heating loads.

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Fig. 9. Effect of thermal conductivity of grout on maximum EST and annual power consumption of heat pump.

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Fig. 10. Effect of thermal conductivity of grout on design length of vertical GHE.

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Fig. 4. Thermal conductivity and viscosity measurement results of grout samples with mixed ratio and resting time.

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Fig. 5. Thermal conductivity and viscosity measurement results of grout samples with different salinity concentration.

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Fig. 8. EST variation with different grout thermal conductivity.

Table 2. Measurement results of grout samples with resting time

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Table 3. Measurement results of grout samples with different saline water content

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Table 4. Vertical GSHP System specifications for simulation analysis

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Table 1. Mixed ratio of grout samples (wt.%)

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