• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.195.2-195.2
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• 2011

The borehole heat exchanger of Geothermal Heat Pump (GHP) system should be sustainable and cost effective for long term operation. To guaranty the performance of the system thermal Response Tests (TRTs) with simple recommended procedures have been applied in many countries. Korea government developed a standard TRT procedure in order to control the quality on GHP projects. In the TRT procedure interpretation method has a rule that data set has to be interpreted by the line source model(LSM). The LSM employes some assumptions that surrounding medium is homogeneous and the line source is infinite and constant heat flux, however real ground condition is unisotropic and heterogeneous, and showing regional or local ground water flows in many cases. We need to develope improved evaluation models to estimate accurate ground thermal conductivity with respect to geological and influence of ground water because current TRT standard test procedure has limitations to be applied for every locations and system. This study surveyed the uncertainty of the thermal parameters from the interpretation method considering different evaluation period. The interpretation of 208 TRT data sets represents limitations of LSM application that some obtained ground thermal conductivities are statistically unstable and convergence time of ground thermal conductivity over test period shows trends responding the length of test period. This evaluation study will be helpful to provide some effective procedure for the thermal parameter estimation and to complement current TRT standard procedure.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.9
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• pp.614-623
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• 2008

This paper presents the results of a laboratory study on the thermal conductivity of and(silica, quartzite, limestone, sandstone, granite and two masonry sands)-water mixtures used for 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 hat 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 an 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.

• 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.

• 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.

• 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.

• 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.

• 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.

• 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.

• Proceedings of the SAREK Conference
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• 2009.06a
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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.

• 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.