• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 추계 학술발표회
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• pp.1638-1646
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• 2008

This paper presents a series of numerical simulations on the thermal performance and sectional efficiency of a closed-loop vertical ground heat exchanger (U-loop) equipped in a geothermal heat pump system (GHP). A 2-D finite element analysis, ANSYS, was employed to evaluate the temperature distribution on the borehole cross section involving HDPE pipe/grout/soil formation to compare the sectional efficiency between the conventional U-loop and a new latticed HDPE pipe system which is equipped with a thermally insulating latice in order to reduce thermal interference between the inflow and outflow pipes. In addition, a 3-D finite volume analysis (Fluent) was used to simulate the operating process of the closed-loop vertical ground heat exchanger by considering the effect of grout's thermal properties, rate of circulation pump, distance between the inflow and outflow pipes, and the effectiveness of the latticed HDPE pipe system. It was observed that the thermal interference between the two strands of U-loop is of importance in determining the efficiency of the ground heat exchanger, and thus it is highly recommendable to modify the cross section configuration of the conventional U-loop system by including a thermally insulating latice between the two strands.

• 한국지열·수열에너지학회논문집
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• 제5권1호
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• pp.19-24
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• 2009

Bentonite-based grouting has been usually used for sealing 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 into the bentonite-based grout for enhancing heat transfer. 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, the viscosity of graphite-added bentonite grout was measured to evaluate the field pumpability of the grout.

• Journal of Biosystems Engineering
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• 제39권2호
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• pp.69-75
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• 2014

Purpose: This paper is aimed at analyzing the heating performance of the vertical closed loop type Geothermal Heat Pump System (GHPS) distributing the farm site and providing basic data of the GHPS. Method: Seedling greenhouse heating was made from October 2012 to May 2013. The seedling greenhouse was divided into 4 sectors (A, B, C and D zone, total $3,300m^2$) with different temperatures. It was heated from 5PM to 8AM, and during the night the greenhouse was covered by non-woven fabric thermal curtains along the upper 2m of the greenhouse for temperature maintenance. In order to analyze the heating performance of the GHPS, power consumption and operating time of the GHPS, inlet and outlet water temperature of the condenser, temperatures of each zone of the greenhouse, and ambient temperature were measured. Results: When operating only one heat pump unit, heat generated in the condenser decreased as the experiment progressed and power consumption increased correspondingly. However, the heating coefficient of performance decreased from 3.3 to 2.0 rapidly. Also, when operating two heat pump units, heat generated in the condenser decreased and power consumption increased. Heating coefficient of performance decreased from 4.5 to 3.7 rapidly. When the set temperature of the greenhouse was $13.7{\sim}20.1^{\circ}C$ and minimum ambient temperature was $-20.8{\sim}4.8^{\circ}C$, the annually accumulated heat and power consumption were 520,623 kW, 142,304 kW, respectively. Conclusion: When the set temperature of the greenhouse was $13.7{\sim}20.1^{\circ}C$ and the minimum ambient temperature was $20.8{\sim}4.8^{\circ}C$, the annually accumulated heat and power consumption were 520,623 kW, 142,304 kW, respectively. When operating only one heat pump unit, the heating COP was 2.0~3.3, and when operating 2 heat pump units, it was 3.7~4.5. If several heat pumps are installed in one GHPS, it is suggested that all heat pumps be operated except in special cases. Because the scale of the water pumps are set to the scale of when all heat pump units are operating, if even one unit is not operating, the power consumption will increase. That becomes the cause of COP decrease.

• KIEAE Journal
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• 제17권3호
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• pp.119-124
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• 2017

Purpose: Groundwater heat pump (GWHP) system has high coefficient of performance than conventional air-source heat pump system and closed-loop type geothermal system. However, there is problem in long-term operation that groundwater raise at the diffusion well and reduced at the supply well. Therefore, it is necessary to accurately predict the groundwater flow, groundwater movement and control the groundwater level in the wells. In this research, in consideration of hydrogeological characteristic, groundwater level and groundwater movement were conducted analysis in order to develop the optimal design method of the two-well system using the pairing pipe. Method: For the optimum design of the two-well system, this research focused on the design method of the pairing pipe in the simulation model. Especially, in order to control the groundwater level in wells, pairing pipe between the supply well and diffusion well was developed and the groundwater level during the system operation was analyzed by the numerical simulation. Result: As the result of simulation, the groundwater level increased to -2.65m even in the condition of low hydraulic conductivity and high pumping flow rate. Consequently, it was found that the developed system can be operated stably.

• 설비공학논문집
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• 제28권3호
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• pp.103-109
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• 2016

The purpose of this study is to perform comparative economic evaluation for the systems of ground source heat pump (GSHP) and district heating and cooling (DHC) by focusing on the analysis of operation case of GSHP. The adapted research object is a public office building located in Seoul. The capacity of ground source pump is about 3,900 kW. Ground heat exchanger is closed loop type. The analysis period for life cycle cost is 30 years. Economic evaluation is assessed from the viewpoints of the following four parts: initial cost, energy cost, maintenance and replacement cost, and environment cost. The total life cycle cost of GSHP is approximately 8,447 million won. The cost of the DHC System is approximately 3,793 million won. The cost of the DHC is approximately 46% lower than GSHP system under the condition of current rate for GSHP and DHC.

• 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.

• 한국태양에너지학회 논문집
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• 제33권1호
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• pp.57-65
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• 2013

The temperatures with the ground depth, the positions of circulation water in ground heat exchanger were measured and thermal diffusion characteristics with the distances of the direction normal to the borehole was analysed. The deeper the depth of ground, the less the influences of outdoor temperature, but below 10m of ground, there was no influences of ground temperature. When the depth of trench pipe was below the depth of 2m, there was no influence. In the ground of 10m when the distances between the pipe and the other places were above 0.5m, the variations of temperature were less than $1.6^{\circ}C$ and above 2.5m they were less than $0.1^{\circ}C$. When the distances of bore hole were above 5m, there were no. influences of the nearest ground heat exchanger.

• 자원환경지질
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• 제39권5호
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• pp.607-613
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• 2006

내 수문지열계 가운데 수주지열정(SCW)시스템을 합리적으로 설치이용할 수 있는 조건들은 심도별 지온증가율이 명확하고($2^{\circ}C/100m$심도), 기존의 지하수 열펌프가 필요로 하는 순환수의 유량에 비해 최소 $10{\sim}30%$의 중온의 심부지하수가 산출될 수 있어야 하며, 순환수를 공내로 재주입시 공내붕괴가 일어나지 않는 견고한 암석들이 존재 하여야 한다. 수주지열정의 1개공당 굴착심도는 평균 $400{\sim}500m$이며, 이로 부터 개발가능한 지열에너지는 공당 약 $30{\sim}40RT$ 규모인데 비해 1개 수직지중열교환기가 공급가능한 지열에너지는 $2{\sim}3RT$ 정도이다. 즉 수주지열정 1개공은 $10{\sim}15$개의 수직지중열교환기 역할을 한다. 따라서 이 방식은 수직루프 설치장소의 공간 문제를 해소할 수 있는 유일한 대안으로 인식되어, 현재 전국 각지에서 많은 수의 SCW들이 무분별 하게 비과학적으로 설치되고 있다. 이와 같이 해당지역 수문지열계의 수리 지질학적인 특성과 열적인 특성을 명확히 파악하지 않은 상태에서 수주지열정을 설계 시공하는 경우에 나타날 문제점들은 추후 합리적인 천부지열 개발 이용에 지대한 장애요인이 될 것이다. 따라서 본고는 국내 수문지열계에 적합한 수주지열정을 설계 하는데 있어 필요한 일종의 지침서를 제시하기 위해 작성되었다.

• 지질공학
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• 제21권1호
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• pp.35-43
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• 2011

본 연구에서는 원주에 위치한 상지대와 괴산에 위치한 중원대의 여름철 지열히트펌프 가동에 따른 지하수 특성 변화를 이해하기 위해 각 관측정의 2010년 5월 21일에서 10월 12일까지의 수위, 수온, 전기전도도에 대하여 시계열분석을 실시하였다. 지하수를 직접 이용하는 수주지열정 방식의 지열히트펌프가 설치된 상지대의 경우 지열히트펌프 가동에 따른 영향을 많이 받아 지하수 특성이 많이 변화하였다. 반면에 유체를 통해 열교환을 하는 수직밀폐형 방식의 지열히트펌프가 설치된 중원대의 경우 지열히트펌프 가동에 영향을 많이 받지 않아 지하수의 특성 변화가 일어나지 않았다. 이와 같은 결과는 지열 히트펌프시스템의 설치 종류에 따른 지하수 특성 변화를 이해하기 위한 자료로 활용될 수 있을 것으로 기대된다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 추계 학술발표회
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• pp.1475-1486
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• 2008

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 its high swelling potential. However, if the bentonite-based grouting is conducted in coastal areas, the salinity of groundwater changes in the mineral fabric of bentontie. In order words, an increase of cation concentration in groundwater leads to a reduction in the diffuse double-layer thickness in the bentonite mineral structure, and thus the volume of bentointe-based grouts will decrease proportional to the salinity of groundwater. In this paper, the effect of salinity (i.e., NaCl 0.5M, 0.25M, and 0.1M) on the change of swelling potential for bentonite-based grouts has been quantitatively evaluated for seven bentonite grouts from different product sources. In addition, in case of using addictives such as a silica sand to increase the thermal conductivity of bentonite-based grouts, the possibility of particle segregation has been studied considering the viscosity of grouts and salinity of groundwater.