• The Journal of the Korea Contents Association
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• v.18 no.1
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• pp.422-430
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• 2018

Increase in oil prices and building energy consumption has been a great burden for Korea which has significant energy dependence on foreign energy sources. In this context, reduction of building energy consumption, which comprises 40% of total energy consumption, is a very important issue. This research therefore empirically analyzed a hospital "P" that implemented ICT-based energy consumption and cost reduction initiative. The hospital first replaced existing water absorber for heating/cooling air and boiler for heating water with water heat storage heat pump system. This was accompanied by subscribing to different electricity price plans to maximize cost reduction. Secondly, the hospital additionally applied ICT-based optimized control algorithm that considers surrounding factors (external temperature, changes in energy demand). The analysis of these mechanisms indicate that the ICT-based energy consumption and cost reduction initiative for hospitals can reduce energy consumption by 53.6% with replacement of low-efficiency equipment and additionally by 18.2% with optimized control algorithm. The mechanisms will provide energy consumption reduction opportunities for other hospitals and buildings with high energy consumption.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.10a
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• pp.663-664
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• 2012

• Journal of Power Electronics
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• v.16 no.3
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• pp.1036-1045
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• 2016

This paper presents a novel control strategy for passive output filter reduction using an active output filter. The proposed method achieves the dual-function of regulating the output voltage ripple and output voltage variation during load transients. The novel control strategy allows traditional simple voltage controllers to be used, without requiring the expensive current sensors and complex controllers used in conventional approaches. The proposed method is verified with results from a 125-W forward converter.

• Korean Journal of Microbiology
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• v.34 no.3
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• pp.126-131
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• 1998

Reduction of hexavalent chromium to its trivalent form by leachate microorganisms was studied in batch and bench-scale continuous stirred tank reactor. The inoculum was a culture of microorganisms in leachate and capable of providing up to 90% chromate reduction during 72 h batch assay with $20mg\;Cr(VI)\;L^{-1}$ in minimal media containing different levels of leachate (10 to 60%) and glucose (50 to 200 mM). Addition of glucose increased the efficiency of chromate reduction, but adverse effect was observed with increase of leachate probably due to the competitive inhibition between chromate and sulfate ions. The continuous culture experiment was conducted for 124 days using synthetic feed containing different levels of chromate (5 to $65mg\;L^{-1}$) at room temperature. With a hydraulic retention time of 36 h, chromate reduction efficiency was mostly 100% when Cr(VI) concentrations in the reactor were in the range of 5 to $50mg\;L^{-1}$ Specific rate of Cr(VI) removal was calculated as $3.492mg\;g^{-1}\;protein\;h^{-1}$ during the period of 101~124 days from the start-up which showed 81.2% of average reduction efficiency. The results indicate the potential application of using leachate microorganisms for detoxification of hexavalent chromium in various chromium-contaminated wastewater from landfill or tannery sites.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.6
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• pp.954-959
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• 2015

In this paper, 110kW high output density, high efficiency Permanent Magnet Synchronous Motor which can be applied on tram’s traction system is introduced, along with its output and loss characteristics. The motor model is 2pole 18slot model and its size has been reduced through the high speed for high output density. Especially, structure and retainer sleeve structure is applied to its structure, which is also appropriate for high speed rotation. This kind of structure has eddy current loss problem on the surface of rotor, which must be reduced for high output density design. This study has designed the most optimized additional design parameter in order to improve the output characteristics and efficiency of previous produced 2pole 18 slot 110kW motor model and how the width of airgap affects from the loss perspective is mainly analyzed. Finally, the analysis on the extent of the efficiency improvement effect compared to the previous model has performed through electromagnetic FEM analysis. The influence of airgap flux density distribution has also been thoroughly examined.

• Journal of Mechanical Science and Technology
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• v.18 no.6
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• pp.979-989
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• 2004

Numerical simulations have been performed to investigate tip clearance effect on through-flow and performance of a centrifugal compressor which has the same configuration of impeller with six different tip clearances. Secondary flow and loss distribution have been surveyed to understand the flow mechanism due to the tip clearance. Tip leakage flow strongly interacts with mainstream flow and considerably changes the secondary flow and the loss distribution inside the impeller passage. A method has been described to quantitatively estimate the tip clearance effect on the performance drop and the efficiency drop. The tip clearance has caused specific work reduction and additional entropy generation. The former, which is called inviscid loss, is independent of any internal loss and the latter, which is called viscous loss, is dependent on every loss in the flow passage. Two components equally affected the performance drop as the tip clearances were small, while the efficiency drop was influenced by the viscous component alone. The additional entropy generation was modeled with all the kinetic energy of the tip leakage flow. Therefore, the present paper can provide how to quantitatively estimate the tip clearance effect on the performance and efficiency.

• Environmental and Resource Economics Review
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• v.10 no.2
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• pp.135-159
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• 2001

This study analyses the energy consumption increase by using a physical production index (PPI) based decomposition method. The energy efficiency of the Korean industry deteriorated to a large extent in the 1992 to 1997 period. This outcome, however, does not contradict the result of a previous study that the physical energy intensities (measured by energy use per production unit) decreased in four Korean energy intensive industries such as steel, cement, petrochemical and pulp and paper in the same period. Although the physical energy intensities in four industries considered decreased significantly, the energy efficiency of the Korean industry deteriorated because the increase in the value-added production was smaller than that in the physical production except for the steel industry. This outcome suggests that the reduction in the physical energy intensity alone will not result in reducing the economic energy intensity, thereby reducing the increase in the energy consumption of the Korean industry. Therefore, it necessitates to restructure the Korean industry towards a higher value-added production and to strengthen energy efficiency improvement efforts in the Korean industry. As the overinvestment in the energy intensive industries caused a deep price fall of Korean products and a reduction of the value added of the Korean industry and with it an increase in the economic energy intensity, a decrease in this intensity will highly depend on reducing the overcapacity in the energy intensive industries which was partly responsible for the currency and economic crisis of 1997.

• ETRI Journal
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• v.38 no.1
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• pp.133-140
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• 2016

This paper presents a method of parasitic inductance reduction for high-speed switching and high-efficiency operation of a cascode structure with a low-voltage enhancement-mode silicon (Si) metal-oxide-semiconductor field-effect transistor (MOSFET) and a high-voltage depletion-mode gallium nitride (GaN) fielde-ffect transistor (FET). The method is proposed to add a bonding wire interconnected between the source electrode of the Si MOSFET and the gate electrode of the GaN FET in a conventional cascode structure package to reduce the most critical inductance, which provides the major switching loss for a high switching speed and high efficiency. From the measured results of the proposed and conventional GaN cascode FETs, the rising and falling times of the proposed GaN cascode FET were up to 3.4% and 8.0% faster than those of the conventional GaN cascode FET, respectively, under measurement conditions of 30 V and 5 A. During the rising and falling times, the energy losses of the proposed GaN cascode FET were up to 0.3% and 6.7% lower than those of the conventional GaN cascode FET, respectively.

• Advances in Energy Research
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• v.3 no.3
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• pp.157-165
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• 2015

This research investigates the effect of natural dust accumulation on the glass cover of solar thermal energy conversion systems. Four similar, locally manufactured, flat plate solar collectors are used. All collectors are South oriented with tilt angle of $40^{\circ}$. The glass cover of one collector is kept clean of dust during the experimental period while the second collector is cleaned at the beginning of each month. The third collector is cleaned every two months while the fourth collector is kept un-cleaned throughout the experimental period of four months. The calculated parameters are the solar heat gain rates and the corresponding values of the thermal efficiency. The result of the present work indicates that the percentage of fractional reduction of the useful heat gain rate due to dust accumulation during a period of one and two months is 11.4% and 17.0%, respectively. The percentage decrease of thermal efficiency during the same duration periods is 4.0% and 6.1%, respectively. The percentage of fractional reduction of the useful heat gain rate due to dust accumulation during a period of three and four months is 27.8% and 31.9%, respectively. The percentage decrease of monthly thermal efficiency during the same duration period is 10.2% and 11.3%, respectively.

• Nuclear Engineering and Technology
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• v.50 no.3
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• pp.462-469
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• 2018

The background spectrum of a $3^{{\prime}{\prime}}{\times}3^{{\prime}{\prime}}$ NaI(Tl) well-type scintillation SILENA detector was measured without shielding, in 6 cm thick lead shielding, and with 2 mm thick electrolytic copper covering the detector inside the lead shielding. The relative remaining background of the lead shield lined with copper was found to be ideal for low-level environmental radioactive spectroscopy. The background total count rate in the (20-2160 KeV) was reduced 28.7 times by the lead and 29 times by the Cu + Pb shielding. The effective reduction of background (1.04) by the copper mainly appeared in the energy range from X-ray up to 500 KeV, while for the total energy range the ratio is 1.01 relative to the lead only. In addition, a strong relation between the full-energy peak absolute efficiency and the detector well height was found using gamma-ray isotropic radiation point sources placed inside the detector well. The full-energy peak efficiency at a midpoint of the well (at 2.5 cm) is three times greater than that on the detector surface. The energy calibrations and the resolution of any single energy line are independent of the locations of the gamma source inside or outside of the well.