• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.4
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• pp.1-7
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• 2018

The gases emitted from internal combustion engines using fossil fuels are causing many social problems, such as environmental pollution, global warming, and adverse health effects on the human body. In recent years, the demand for renewable energy has increased, and government policy support and research and development are also active. In the collecting part of a solar energy system, which is widely used at home, propylene glycol (PG) (anti-freeze), as a heating medium, is mixed with water at a fixed value of 50%, and the heat is transferred to the collecting part at subzero temperatures. On the other hand, when leakage occurs in the heat medium in the heat collecting part, supplemental water is supplied to the solar heat collecting part due to the characteristics of the solar heat system, so that the concentration of antifreeze in the replenishing water becomes low. As a result, the temperature of the solar heat collecting part is lowered resulting in a frost wave, which causes economic damage. The purpose of this study was to develop a device capable of controlling the antifreeze concentration automatically in response to a temperature drop to prevent freezing of the heat collecting part generated in the solar energy system. The electrical conductivity of the H2O component was larger than that of PG, and the resistance increased with decreasing temperature. The PG concentration control values of 40, 50, and 60% should be controlled through calibration with a PG concentration of 39.6, 50.7, and 60.1%.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.29 no.10
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• pp.551-557
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• 2017

Most European economies, Japan, and many governments have made it a major policy to expand the green business by disseminating heat pump technology, which has a large $CO_2$ reduction effect. The heat pump of all heat sources has been recognized as renewable energy and the policy to encourage has been implemented. In the recently revised Renewable Energy Law, the hydrothermal source (surface sea water) heat pump was newly included in renewable energy. In addition, the scope of application of heat pumps has expanded in the mandatory installation of renewable energy for new buildings, remodeling buildings, and reconstructed buildings based on this law. However application to heat pumps using all natural energy as heat source has been put off. In this revision, the ratio of renewable energy to the total energy produced by the heat pump was fixed at 73%, which depends on coefficient of performance of heat pump. The ratio of renewable energy is $1-1.8/COP_H$, and should be calculated including the coefficient of performance of the heat pump. Using a high efficiency heat pump or a high-temperature heat source increases the coefficient of performance and also reduces $CO_2$ emissions. It is necessary to expand the application of heat pumps as renewable energy equipment and to improve the correct calculation of renewable energy production.

• Journal of Energy Engineering
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• v.21 no.4
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• pp.356-361
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• 2012

Recently, even though the researches on renewable energy like geothermal, wind, solar energy have been performed widely, its use-rate in total energy is still low. This study was carried out to investigate the performance of hybrid heating system, which consisted of solar collector of thermosyphon tube type and X-L pipe boiler. Especially, new type of solar collector was tried and compared with double tube type and, futhermore, performance and safety on X-L pipe boiler were investigated. As the results, efficiency of solar collector of thermosyphon tube type was higher 20.7% than that of double tube type, mainly due to its structural characteristics. It was also confirmed that temperature of special heat medium used X-L pipe boiler rose up about 20% rapidly in comparison with that of pure water.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.2C
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• pp.69-77
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• 2012

In general, geothermal energy pile and horizontal ground heat exchangers are installed in shallower depths than conventional vertical ground coupled heat pumps. Consequently their heat exchange performance is strongly governed by thermal conductivity of soil layer. Previous studies have shown that the thermal conductivity of soil above ground water table significantly affects the heat exchange rate because of partially saturated condition in soil and consequent variation of soil thermal conductivity. This paper presents a study result on the prediction of thermal conductivity of weathered granite soils. For weathered granite soils sampled from 5 locations, thermal conductivity tests were conducted with varying porosity and degree of saturation. The existing thermal conductivity models in literatures appeared inappropriate to the weathered granite soils. Hence, an empirical equation was proposed in this paper and its validity was examined by applying it to thermal conductivity test results obtained for weathered granite soils in this study and from literatures.

• Geophysics and Geophysical Exploration
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• v.8 no.2
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• pp.184-190
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• 2005

We have attempted to give some physical into the factors that control the response of subsurface target to plane wave excitation at VLF (very low frequency) frequencies. Although the VLF technique has some serious disadvantages, such as a lack of penetration depth and limited frequencies, its advantages are also extremely important to have made it by far the most popular electromagnetic technique in current use. In the magnetic-field measurement mode these lightweight, relatively low-priced tools allow us to survey large areas rapidly and inexpensively, to locate and roughly define subsurface electrical conductors. When used in the electric-field mode the technique is, in simple environments, capable of quantitative interpretation and once again the speed and relative cheapness of these devices makes them a natural 'first electromagnetic tool ' to use in reconnaissance mapping.

• The Journal of Engineering Geology
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• v.17 no.2 s.52
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• pp.177-185
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• 2007

Most of hot springs don't spring out naturally but are pumped by submersible pumps in Korea. When pumped piezometric head in a well is dropped with proportion to quantity. This research investigates relationships between quantity and drawdown at the Onyang hot spring area. There are 38 wells at this area and the depths of wells range from 124 m to 303 m. Piezometric heads of 4 wells were observed for about 10 months. Fluctuation patterns of piezometric heads seem to be a sine curve with a you period by a high demand and a slack season. Drawdowns of fluctuations were about 98-139 m depth to water table when wells were pumped at $2,300-4,800m^3/day$. A equation was made through analyzing quantity and drawdown.

• The Journal of Engineering Geology
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• v.21 no.1
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• pp.35-43
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• 2011

Time series analysis was applied to groundwater level, water temperature, and electrical conductivity data obtained from monitoring wells around ground-source heat pumps at Sangji University of Wonju (standing column well type) and at Jungwon University of Goesan (closed loop type), from 21 May to 12 October 2010. We found large temporal variations in the characteristics of groundwater at Wonju, but only minor variations at Goesan. These results may improve our understanding of the effects of ground-source heat pumps on the characteristics of surrounding groundwater, according to the installation method for the pumps.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2000.09a
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• pp.105-115
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• 2000

As large underground projects such as radioactive waste disposal, hot water and heat storage, and geothermal energy become influential, the study, which consider all aspects of thermics, hydraulics and mechanics would be needed. Thermo Hydro-Mechanical coupling analysis is one of the most complex numerical technique because it should be implemented with the combined three governing equations to analyze the behavior of rock mass. In this study, finite element code, which is based on Biot's consolidation theory, was developed to analyze the thermo-hydro-mechanical coupling in continuum rock mass. To verify the implemented program, one-dimensional consolidation model under the isothermal and non-isothermal conditions was analyzed and was compared with the analytic solution. The parametric study on two-dimensional consolidation was also performed and the effects of several factors such as poisson's ratio and hydraulic anisotropy on rock mass behavior were investigated. In the future, this program would be revised to be used for analysis of general discontinuous media with incorporating discrete joint model.

• Tunnel and Underground Space
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• v.10 no.3
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• pp.355-365
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• 2000

As large underground projects such as radioactive waste disposal, hot water and heat storage, and geothermal energy become influential, the study, which consider all aspects of thermics, hydraulics and mechanics would be needed. Thermo-Hydro-Mechanical coupling analysis is one of the most complex numerical technique because it should be implemented with the combined three governing equations to analyze the behavior of rock mass. In this study, finite element code, which is based on Biot's consolidation theory, was developed to analyze the thermo-hydro-mechanical coupling in continuum rock mass. To verify the implemented program, one-dimensional consolidation model under the isothermal and non-isothermal conditions was analyzed and was compared with the analytic solution. The parametric study on two-dimensional consolidation was also performed and the effects of several factors such as poisson's ratio and hydraulic anisotropy on rock mass behavior were investigated. In the future, this program would be revised to be used for analysis of general discontinuous media with incorporating discrete joint model.

• Journal of Soil and Groundwater Environment
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• v.21 no.3
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• pp.64-81
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• 2016

To analyze the influence of various groundwater flow rates (specific discharge) on BHE system with balanced and unbalanced energy loads under assuming same initial temperature (15℃) of ground and groundwater, numerical modeling using FEFLOW was used for this study. When groundwater flow is increased from 1 × 10⁻⁷ to 4 × 10⁻⁷m/s under balanced energy load, the performance of BHE system is improved about 26.7% in summer and 22.7% at winter time in a single BHE case as well as about 12.0~18.6% in summer and 7.6~8.7% in winter time depending on the number of boreholes in the grid, their array type, and bore hole separation in multiple BHE system case. In other words, the performance of BHE system is improved due to lower avT in summer and higher avT in winter time when groundwater flow becomes larger. On the contrary it is decreased owing to higher avT in summer and lower avT in winter time when the numbers of BHEs in an array are increased, Geothermal plume created at down-gradient area by groundwater flow is relatively small in balanced load condition while quite large in unbalanced load condition. Groundwater flow enhances in general the thermal efficiency by transferring heat away from the BHEs. Therefore it is highly required to obtain and to use adequate informations on hydrogeologic characterristics (K, S, hydraulic gradient, seasonal variation of groundwater temperature and water level) along with integrating groundwater flow and also hydrogeothermal properties (thermal conductivity, seasonal variation of ground temperatures etc.) of the relevant area for achieving the optimal design of BHE system.