• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2007년도 동계학술발표대회 논문집
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• pp.423-428
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• 2007

This study was performed to construct a geothermal data base about thermal conductivity of ground heat exchanger and thermal properties of grouting material which used to refill the borehole. We have acquired geothermal data sets from 39 sites over wide area of South Korea except to Jeju island. From data analysis, the range of thermal conductivity is 1.5$\sim$4.0 W/mK. It means that thermal conductivity varies with grouting material as well as regional geology and ground water system.

• Smart Structures and Systems
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• 제24권5호
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• pp.587-595
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• 2019

Deformation measurement of large scale structures, such as the ground beds of high-rise buildings, tunnels, bridge, and railways, are important for insuring service quality and safety. The pose-relay videometrics method and displacement-relay videometrics method have already presented to measure the pose of non-intervisible objects and vertical subsidence of unstable areas, respectively. Both methods combine the cameras and cooperative markers to form the camera series networks. Based on these two networks, we propose two novel videometrics methods with closed-loop camera series network for deformation measurement of large scale structures. The closed-loop camera series network offers "closed-loop constraints" for the camera series network: the deformation of the reference points observed by different measurement stations is identical. The closed-loop constraints improve the measurement accuracy using camera series network. Furthermore, multiple closed-loops and the flexible combination of camera series network are introduced to facilitate more complex deformation measurement tasks. Simulated results show that the closed-loop constraints can enhance the measurement accuracy of camera series network effectively.

• 설비공학논문집
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• 제24권4호
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• pp.306-314
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• 2012

Several numerical or analytical models have been proposed to analyze the thermal response of vertical ground heat exchangers (GHEX). However, most models are valid only after several hours of operation since they neglect the heat capacity of the borehole. Recently, the short time response of the GHEX became important in system simulation to improve efficiency. In this paper, a simple new method to evaluate the short time response of the GHEX by using an analogy model of electric circuit transient analysis was presented. The new transient heat exchanger model adopting the concept of thermal capacitance of the borehole as well as the steady-state thermal resistance showed the transient thermal resistance of the borehole. The model was validated by in-situ thermal response test and then compared with the DST model of the TRNSYS program.

• 한국지열·수열에너지학회논문집
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• 제13권2호
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• pp.9-15
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• 2017

When applying geothermal systems in cities such as seoul where high density development prevails, the selection of geothermal system capable of obtaining a large capacity in the limited grounds is necessary. In this study, an easy-to-use design tool is developed in the form of spreadsheet by applying the calculation theory of existing closed-loop vertical ground heat exchanger that can be used in the early design stage of the open-loop ground heat exchanger. By only using the maximum cooling and heating load, it is possible to calculate optimal design open-loop ground heat exchanger. Further research is needed, we are plan to improve the program considering the heat loss of groundwater flowing in the inner casing, G-Function for Open-Loop, and verification by applying actual projects.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 세계 도시지반공학 심포지엄
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• pp.385-395
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• 2009

In this study, a series of numerical analysis has been accomplished on the thermal performance and sectional efficiency of a closed-loop vertical ground heat exchanger (U-loop) in a geothermal heat pump system (GHP) considering the circulating fluid, pipe, grout and soil formation. A finite element analysis program, ABAQUS, was employed to evaluate the temperature distribution on the cross section of the U-loop system involving HDPE pipe/grout/formation and to compare sectional efficiency between the conventional U-loop and a new latticed HDPE pipe system. Especially, the latticed pipe is equipped with a thermal insulation zone in order to reduce thermal interference between the inflow pipe and the outflow pipe. Also, a thermal stress analysis was performed with the aid of ABAQUS. 3-D finite volume analysis program, FLUENT, was adapted to analyze a coupled system between fluid circulation in the pipe and heat transfer and simulate an operating process of the closed-loop vertical ground heat exchanger. In this analysis, the effect of the thermal properties of grout, rate of circulation pump, distance between the inflow pipe and the outflow pipe, and the effectiveness of the latticed HDPE pipe system are taken into account.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 하계학술발표대회 논문집
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• pp.776-781
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• 2008

A ground heat exchanger in a GSHP 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 the 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 paper is part of a research project aiming at constructing a database of these site-specific properties, especially ground effective thermal conductivity. The objective was to develop and evaluation method, and to provide this knowledge to design engineers. To achieve these goals, thermal response tests were conducted using a testing device at nearly 150 locations in Korea. The in-situ thermal response is the temperature development over time when a known heating load imposed, e.g. by circulating a heat carrier fluid through the test exchangers. The line-source model was then applied to the response test data because of its simplicity. From the data analysis, the range of ground effective thermal conductivity at various sites is $1.5{\sim}4.0\;W$/mK. The results also show that the ground effective thermal conductivity varies with grouting materials as well as regional geological conditions and groundwater flow.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 춘계 학술발표회
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• pp.179-187
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• 2009

Bentonite-based grouting has been popularly used to seal a borehole installed for a closed-loop vertical ground heat exchanger in a geothermal heat pump system (GHP) because of its high swelling potential and low hydraulic conductivity. The bentonite-based grout, however, has relatively lower thermal conductivity than that of ground formation. Accordingly, it is common to add some additives such as silica sand to the bentonite-based grout for enhancing thermal performance. In this study, graphite is adapted to substitute silica sand as an addictive because graphite has very high thermal conductivity. The effect of graphite on the thermal conductivity of bentonite-based grouts has been quantitatively evaluated for seven bentonite grouts from different product sources. In addition, comparisons of viscosity between applications of graphite and silica sand as additives has been carried out. In conclusion, using graphite has thermal conductivity about three times higher than that of silica sand.

• 대한토목학회논문집
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• 제35권2호
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• pp.361-375
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• 2015

에너지파일은 기존의 수직밀폐형 지중열교환기를 경제적으로 대체할 수 있는 새로운 형태의 지중열교환기이다. 즉, 에너지파일은 건물의 기초 구조물과 지중열교환기의 역할을 동시에 수행하는 에너지 구조체로서, 말뚝 기초 내부에 열교환 파이프를 삽입하고 파이프를 통해 유체를 순환시켜 지반과의 열교환을 유도한다. 본 연구에서는 병렬 U형(5쌍, 8쌍, 10쌍)의 열교환 파이프를 대구경 현장타설 에너지파일에 삽입하여, 3본의 에너지파일을 실규모로 시공하였다. 또한 현장 열응답 시험(In-situ thermal response tests, TRTs)을 수행하고 시공된 현장타설 에너지파일과의 열교환 효율을 비교하기 위하여 30m 깊이의 수직밀폐형 지중열교환기를 별도로 시공하였다. 병렬 U형 현장타설 에너지파일에 대해서는 냉난방 부하를 인공적으로 주입하는 열교환 성능 평가시험을 수행하여 열교환 성능(heat exchange rate)을 평가하였다. 마지막으로 현장타설 에너지파일의 적용성 평가를 위해 산정된 상대 열교환 효율(relative heat exchange efficiency) 및 열교환 성능을 선행 연구 결과와 비교하였으며, 본 연구에서 시공된 현장타설 에너지파일은 안정적이고 효율적인 열성능을 보이는 것으로 나타났다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 춘계학술대회 초록집
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• pp.167.1-167.1
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• 2010

본 연구에서는 수직 밀폐형 지중열교환기 뒤채움용 그라우트의 종류와 첨가재 종류, 지중열교환기 파이프 단면에 따른 지중열교환기의 성능을 비교 평가하기 위해 현장 시험 시공과 현장 열응답 시험을 수행하였다. 뒤채움용 그라우트재는 벤토나이트와 시멘트를 사용하였으며 첨가제로는 천연규사와 흑연을 적용하였다. 지중열교환기 파이프 단면은 일반적으로 시공되는 U-loop 파이프 단면과 파이프 사이의 열간섭 효과를 최소화 한 3공형 파이프 단면이 적용되었다. 시멘트-천연규사 그라우트재가 벤토나이트-천연규사 그라우트재 보다 큰 지중 유효열전도도를 보이고 흑연을 첨가한 그라우트는 시멘트와 벤토나이트 모두에서 천연규사만 첨가하였을 때 보다 지중 유효열전도도가 높게 나타났다. 3공형 파이프 단면의 경우 단면에 따른 영향을 비교하기 위해 그라우트는 시멘트-천연규사와 벤토나이트-천연규사를 사용하였으며 지중 유효열전도도 측정결과 각각 3.64 W/mK, 3.40 W/mK으로 일반 U-loop 파이프 단면을 사용하였을 때 보다 높게 나타났다.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2010년도 정기 학술발표대회
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• pp.91.1-91.1
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• 2010

본 연구에서는 수직 밀폐형 지중 열교환기를 현장 시험시공하고 현장 열응답 시험을 수행하여 보어홀과 지반의 유효열전도도를 측정하였다. 뒤채움용 그라우트재는 벤토나이트와 시멘트가 고려되었으며 첨가제로는 천연규사와 흑연을 사용하고, 지중 열교환기 파이프 단면은 일반적으로 시공되는 U-loop 파이프 단면과 파이프 사이의 열간섭 효과를 최소화 한 3공형 파이프 단면이 착용되었다. 시멘트-천연규사 그라우트재가 벤토나이트-천연규사 그라우트재 보다 큰 유효열전도도를 보이고 흑연을 첨가한 그라우트는 시멘트와 벤토나이트 모두에서 천연규사만 첨가하였을 때 보다 유효열전도도가 높게 나타났다. 3공형 파이프 단면의 경우 단면에 따른 영향을 비교하기 위해 그라우트는 시멘트-천연규사와 벤토나이트-천연규사를 사용하였으며 유효 열전도도 측정결과 각각 3.65 W/mK, 3.40 W/mK으로 일반 U-loop 파이프 단면을 사용하였을 때 보다 높게 나타났다.