• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.7
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• pp.512-520
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• 2007

The design of a ground-source heat pump system includes specifications for a ground loop heat exchanger where the heat transfer rate depends on the effective thermal conductivity of the ground and the effective thermal resistance of the borehole. To evaluate these heat transfer properties, in-situ thermal response tests on four vertical test boreholes with different grouting materials were conducted by adding a monitored amount of heat to circulating water. The line-source method is applied to the temperature rise in an in-situ test and extended to also give an estimate of borehole effective thermal resistance. The effect of increasing thermal conductivity of the grouting materials from 0.818 to $1.104W/m^{\circ}C$ resulted in overall increases in effective thermal conductivity by 15.8 to 56.3% and reductions in effective thermal resistance by 13.0 to 31.1%.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.2
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• pp.95-102
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• 2011

A ground loop heat exchanger in a ground source heat pump system is an important unit that determines the thermal performance of a system and its initial cost. 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 study was performed to investigate the effect of some parameters such as borehole lengths, various grouting materials and U tube configurations on ground effective thermal conductivity and borehole thermal resistance. In this study, thermal response tests were conducted using a testing device to 9 different ground loop heat exchangers. From the experimental results, the length of ground loop heat exchanger affects to the effective thermal conductivity. The results of this experiment shows that higher thermal conductivity of grouting materials leads to the increase effective thermal conductivity from 22 to 32%. Also, mounting spacers have increased by 14%.

• Journal of the Korean Solar Energy Society
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• v.38 no.5
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• pp.37-47
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• 2018

The heating performance of a solar thermal seasonal storage system applied to a glass greenhouse was analyzed numerically. For this study, the gardening 16th zucchini greenhouse of Jeollanam-do agricultural research & extension services was selected. And, the heating load of the glass greenhouse selected was 576 GJ. BTES (Borehole Thermal Energy Storage) was considered as a seasonal storage, which is relatively economical. The TRNSYS was used to predict and analyze the dynamic performance of the solar thermal system. Numerical simulation was performed by modeling the solar thermal seasonal storage system consisting of flat plate solar collector, BTES system, short-term storage tank, boiler, heat exchanger, pump, controller. As a result of the analysis, the energy of 928 GJ from the flat plate solar collector was stored into BTES system and 393 GJ of energy from BTES system was extracted during heating period, so that it was confirmed that the thermal efficiency of BTES system was 42% in 5th year. Also since the heat supplied from the auxiliary boiler was 87 GJ in 5th year, the total annual heating demand was confirmed to be mostly satisfied by the proposed system.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.12
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• pp.1175-1182
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• 2004

Installations of vertical boreholes for the ground source heat pump system are expensive to install. One way to reduce the initial cost is to increase the specific heat extraction rate of borehole system. However, as the specific heat extraction rate increases the temperature of borehole fluid decreases with the resultant lower Coefficient Of Performance in Heating(COPH) of heat pump system. The purpose of this study is to provide the basic informations about the performance of heat pump system with the specific heat extraction rate and soil thermal properties such as thermal conductivity and temperature. It is shown that the specific heat extraction rate is the most important parameter for the ground source heat pump system. To obtain the reasonable COPH value (COPH > 3) the heat extraction rate should be about 25 W/m or less. Accurate measurements of soil thermal properties are also very important to design the system properly. The effects of borehole thermal resistances are also examined in this study.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.836-842
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• 2011

The lateral stability of bridge foundations against train moving load, emergency stopping load, earthquakes, and so on is very important for a railway bridge foundation. A borehole test is much more accurate than laboratory tests since it is possible to minimize the disturbance of ground conditions on the test site. The representative borehole test methods are Dilatometer, Pressuremeter and Lateral Load Tester, which usually provide force-resistance characteristics in elastic range. In order to estimate P-y curves using those methods, the non-linear characteristics of soil which is one of the most important characteristics of the soil cannot be obtained. Therefore, P-y curves are estimated usually using elastic modulus ($E_O$, $E_R$) of lateral pressure-deformation ratio obtained within the range of elastic behavior. Even though the pile foundation is designed using borehole tests in field to increase design accuracy, it is necessary to use a higher safety factor to improve the reliability of the design. A Large Displacement Borehole Testmeter(LDBT) is developed to measure nonlinear characteristics of the soil in this study. P-y curves can be directly achieved from the developed equipment. Comparisons between measured P-y curves the LDBT developed equipment, theoretical methods based on geotechnical investigations, and back-calculated P-y curves from field tests are shown in this paper. The research result shows that the measured P-y curves using LDBT can be properly matched with back-calculated P-y curves from filed tests by applying scale effects for sand and clay, respectively.

• Journal of the Korean Geotechnical Society
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• v.29 no.10
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• pp.49-56
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• 2013

The use of geothermal energy has been increased for economic and environmental friendly utilization. Ground thermal conductivity and borehole thermal resistance are very important parameters in the design of geothermal heat pump system. This paper presents an experimental study of heat exchange rate of U and W type ground heat exchangers (GHEs) measured by thermal performance tests (TPTs). U and W type GHEs were installed in a partially saturated dredged soil deposit, and TPTs were conducted to evaluate heat exchange rates under 100-hr continuous operation condition. The heat exchange rates were also calculated by analytical models to estimate borehole thermal resistances and were compared with experimental results. It comes out that multi-pole and equivalent diameter (EQD) models resulted in more accurate agreement than shape factor (SF) model which is currently more often used.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.687-698
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• 2010

Borehole drilled depend on the point is bound to be limited to obtain the 2-D or 3-D layer information for entire targer area. On the other hand, SASW and MASW provide the sectional form of layer information through the shear wave velocity($V_s$). Therefore the useful information of the target area can be derived from SASW, MASW and borehole data. In this research, the correlation reflected locality and nationwide between sectional geo-layer and $V_s$ was investigated and analyzed. The target areas are westside of Pyeongtaek and Incheon. The shear wave velocity($V_s$) obtained from SASW, MASW and borehole data conducted within the scope of crossline for survey was utilized in each region. In the 2D distribution of $V_s$ from SASW, MASW, $V_s$ tend to continually increase deeper and deeper. By the target area, the depth of each representative geo-layer was nested on the sectional distribution map of $V_s$ to suggest the range of $V_s$ in accordance of strata by using borehole data. The 2D sectional geo-layer distribution map is presented based on the range of $V_s$. In addition the correlation between measured and calculated $V_s$ according to the empirical equation was analyzed.

• Geophysics and Geophysical Exploration
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• v.7 no.2
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• pp.121-129
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• 2004

The geostatistical approach was applied to integrate MT (Magneto-telluric) resistivity data and borehole information for the spatial RMR (Rock Mass Rating) evaluation. Generally, resistivity of the subsurface is believed to be positively related to the RMR, thus the resistivity and borehole RMR information was combined in a geostatistical approach. To relate the two different sets of data, we take the MT resistivity data as secondary information and estimate the RMR mean values at unsampled points by identification of the resistivity to the borehole data. Two types of approach are performed for the estimation of RMR mean values. Then the residuals of the RMR values around the borehole sites are geostatistically modeled to infer the spatial structure of difference between real RMR values and estimated mean values. Finally, this geostatistical estimation is added to the previous means. The result applied to a real situation shows prominent improvements to reflect the subsurface structure and spatial resolution of RMR information.

• The Journal of Engineering Geology
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• v.16 no.3 s.49
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• pp.255-263
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• 2006

In an electrical tomographic survey using an inclined borehole with a pole-dipole array, we must consider several factors: a singular point associated with zero potential difference, a spatial discrepancy between electrode and nodal point in a model due to a inclined borehole, and a variation of geometric factors in connection with a irregular topography. Singular points which are represented by the normal distance from current source to the ground surface can be represented by serveral regions due to a irregular topography of ground surface. The method of element division can be applied to the region in which the borehole is curved, inclined or the distance between the electrodes is shorter than that of nodal points, because the coordinate of each electrode cannot be assigned directly to the nodal point if several electrodes are in an element. Test on a three-dimensional (3-D) synthetic model produces good images of conductive target and shoves stable convergence.

• Journal of the Korean Geotechnical Society
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• v.25 no.4
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• pp.55-68
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• 2009

A new borehole roughness and verticality measurement system (BKS-LRPS) for rock socketed drilled shafts were developed and verified its field application. The stability of BKS-LRPS was verified for several field conditions, which included the effect of measuring unit shaking, the application of water/air calibration factors, and the resistance of high water pressure inside piles. Also, effective measurement distances for various conditions of turbidity were defined in the field by measuring borehole roughness and vertical alignment for 6 drilled shafts. Vertical alignments for all drilled shafts could be measured by BKS-LRPS. However, borehole roughness was not able to be measured due to high turbidity caused by RCD drilling processing. Based on the BKS-LRPS field verification, BKS-LRPS is the first borehole roughness and verticality measurement system applying both in the water and air.