• 대한설비공학회:학술대회논문집
• /
• 대한설비공학회 2007년도 동계학술발표대회 논문집
• /
• pp.429-433
• /
• 2007

Cement mortar and concrete can be used as grouts but problems regarding shrinkage and the discord of coefficients of thermal expansion between grouts and HDPE pipes has to be solved. Thermal conductivities of wet condition two times larger than those of dry condition, except for pure cement mortar. The addition of sand into the cement grouts greatly increases the thermal conductivity. The addition of bentonite into the cement grouts reduces thermal conductivity thus reducing the density. Bentonite grouting must be used only below the groundwater table since bentonite grouts possesses high shrinkage property in dry condition. The addition of sand prevents the shrinkage of bentonite grouts. Bentonite manufactured in Korea can be used since they possess similar thermal conductivities with imported products. The addition of sand into the bentonite grouts greatly increases the thermal conductivity.

• 대한설비공학회:학술대회논문집
• /
• 대한설비공학회 2005년도 동계학술발표대회 논문집
• /
• pp.161-166
• /
• 2005

The objectives of this paper are to estimate the ground thermal conductivity by ground heat exchangers in two different places - Chooncheon and Wonjoo, and to analyze the effect of ground thermal conductivity on the ground thermal diffusivity and the size of the ground heat exchanger. In Chooncheon area, a single-U type HDPE pipe (25mm diameter) with borehole diameter of 150mm, length of 150m is installed. In Wonjoo area, a single-U type HDPE pipe (40mm diameter) with borehole diameter 150mm, length of 200m is installed. It is found that the ground thermal conductivities are estimated as 2.69 $W/m^{\circ}C$ and 2.99 $W/m^{\circ}C$ in Chooncheon and Wonjoo, respectively. It is also found that the ground heat exchanger size is reduced by 8.6% with 25% increase of ground thermal conductivity, and increase by 11.8% with 25% decrease of ground thermal conductivity.

• 설비공학논문집
• /
• 제26권10호
• /
• pp.460-466
• /
• 2014

This paper uses in-situ thermal response tests to present the characteristics of the ground thermal conductivities of three different SCW GHX. These SCW GHXs were installed in the same site in Seojong City. The three different cases are distinguished by the flow direction and the presence of a filler. The first type (A) is constructed for water to flow downstream. The second (B) and third (C) types are designed for water to flow upstream, and a filler is additionally inserted into the third type. The results of the in-situ thermal response tests, indicate that the ground thermal conductivity for types (A), (B) and (C) are of $4.84W/m{\cdot}K$, $3.40W/m{\cdot}K$, and $11.62W/m{\cdot}K$, respectively.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2007년도 춘계학술대회B
• /
• pp.3401-3406
• /
• 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.

• 한국신재생에너지학회:학술대회논문집
• /
• 한국신재생에너지학회 2011년도 춘계학술대회 초록집
• /
• pp.195.2-195.2
• /
• 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.

• 지질공학
• /
• 제23권4호
• /
• pp.389-398
• /
• 2013

국내에서 열물성에 관한 연구는 지역별, 암종별 열물성 파악을 위주로 진행되었으나, 지열냉난방시스템 설계 시에 실시하는 TRT (thermal response test)의 열전도도와 차이가 크게 나타남에 따라 본 연구에서는 지하수 부존량이 풍부한 지역에서 시료를 통한 열전도도와 TRT를 통한 열전도도를 비교하였다. 토양 시료의 열전도도는 1.32 W/m-K, 암석 시료의 열전도도는 2.88 W/m-K로 나타났으며, TRT로 측정된 열전도도는 3.13 W/m-K로 나타나 암석 시료보다 약 10% 정도 높게 나타났다. 연구지역은 지하수가 풍부하고 0.01의 수리경사를 가지고 있어 이 차이는 지하수 흐름에 의한 영향이라고 판단된다. 라인소스(line source) 이론에 따르면 TRT는 지반의 순수한 열전도도를 산정하는 것이 목적이므로, 국내 SCW (standing column well)형의 TRT는 라인소스 이론에 적합하지 않으며 지열냉난방시스템 설계 시에는 시료를 통한 열전도도값을 사용하는 것이 타당하다고 판단된다.

• 한국태양에너지학회 논문집
• /
• 제33권1호
• /
• pp.66-72
• /
• 2013

In this study, the thermal conductive characteristics and basic properties of the nine commercial products of bentonite grouts were studied. Six of the nine products for ground heat exchanger systems are imported and others for civil engineering are domestic. The thermal conductivities of all bentonite products are nearly similar among products. The free swell indexes, viscosities and filter losses of the ground heat exchanger grouts are lower than those of the civil engineering ones. These characteristics seem to increase of the fluidity to fill the bentonite slurry to bore-hall perfectly, rather than to prevent underground water penetration. Thus, the mixtures of bentonites and sands are recommended for high thermal conduction grouts.

• 설비공학논문집
• /
• 제23권5호
• /
• pp.356-364
• /
• 2011

Storage and transfer heat in soils is governed by the soil thermal properties and these properties are therefore needed in many engineering applications, including horizontal ground heat exchanger for ground-coupled heat pumps. This paper presents the evaluation results of the thermal diffusivity of soils (silica, quartzite, limestone, sandstone, granite, and two masonry soils used for the trench backfilling materials of the horizontal ground heat exchanger. To assess this thermal property, we (i) measure the soil thermal conductivities using single-probe method and (ii) use the de Vries method of summing the heat capacities of the soil constituents. The results show that the thermal diffusivity tends to increase as dry soil begins to wet, but it approaches a constant value or even decreases as the soil continues to wet. Combined algorithm with and improved model for the thermal conductivity of soils and the constituent equation provides accurate estimates of the soil thermal diffusivity.

• 한국지열·수열에너지학회논문집
• /
• 제7권2호
• /
• pp.51-59
• /
• 2011

Storage and transfer heat in soils are governed by the soil thermal properties and these properties are therefore needed in many engineering applications, including horizontal ground heat exchanger for ground-coupled heat pumps. This paper presents the measured results of the thermal diffusivity of soils(silica, quartzite, limestone, sandstone, and masonry soils) used for the trench backfilling materials of the horizontal ground heat exchanger. To assess this thermal property, we (i) measure the soil thermal conductivities and volumetric heat capacities using dual-probe method and (ii) compare the estimates from the de Vries method of summing the heat capacities of the soil constituents. The results show that the thermal diffusivity tends to increase as dry soil begins to wet, but it approaches a constant value or even decreases as the soil continues to wet. Measurements made by using the dual-probe method agreed well with independent estimates obtained using the single-probe method.

• 한국지열·수열에너지학회논문집
• /
• 제7권1호
• /
• pp.10-16
• /
• 2011

Performance of ground-source heat pumps (GSHPs) is mainly affected by ground heat exchangers which makes up more than 40% of construction cost. Exact construction and grout as backfill are important, because it is difficult to repair after being installed. As grout materials, bentonite grout material and cement material are used In this paper, thermal conductivity according to mix proportion of cement grout has been experimentally studied. Some variables were set to evaluate thermal conductivities according to change in cement content, unit water ratio, mass per volume of fresh mortar, and aggregate types. From the experimental analysis, high performance cement grout has been proposed.