• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.26 no.9
• /
• pp.409-415
• /
• 2014

Ground-source heat pump (GSHP) systems have become an efficient alternative to conventional cooling and heating methods due to their higher energy efficiency. These systems use the ground as a heat source and the heat sink for cooling mode operation. The purpose of this simulation study is to evaluate the performance of a hypothetical GSHP system in an office building and to assess the energy saving effect against the existing HVAC systems (boiler and turbo chiller). We collected monthly energy consumption data from an actual office building ($32,488m^2$) in Seoul, and created a model to calculate the hourly building loads with EnergyPlus. In addition, we used GLD (Ground Loop Design) V8.0, a GSHP system design and simulation software tool, to evaluate hourly and monthly performance of the GSHP system. The energy consumption for the GSHP system based on the hourly simulation results were estimated to be 582.6 MWh/year for cooling and 593.2 MWh/year for heating, while those for the existing HVAC systems were found to be 674.5 MWh/year and 2,496.4 MWh/year, respectively. The seasonal performance factor (SPF) of the GSHP system was also calculated to be in the range of 3.37~4.28.

• Journal of the Society of Naval Architects of Korea
• /
• v.54 no.6
• /
• pp.515-521
• /
• 2017

Large Cavitation Tunnel (LCT) of KRISO enables us to conduct cavitation tests of the propeller attached to a ship model. As the ship model tests are done at rather high Reynolds number of 107~108, flow measurement system such as pitot tube cannot be employed because of structural safety problems in its system and difficulties in installing it within the test section. Thus, KRISO has developed new 3-D LDV system used in large test section of LCT. There are several difficulties in using 3-D LDV, which did not allow efficient operation of it. The first trouble was the calibration using the conventional pin hole. To make the focus with same laser-beam waists at the wanted position, the high spatial resolution CCD is utilized in the calibration procedure for 3-D LDV. The off-axis configuration provides two velocity components in the horizontal plane and on-axis configuration gives third velocity component in the vertical plane. The horizontal velocity components are also obtained in the coincidence mode, which prevents any misleading results in the off-axis configuration. The nominal wake of Aframax tanker model is measured by the developed 3-D LDV system. The measured hull wake showed good agreement with that obtained by CFD calculation.

• Journal of the Semiconductor & Display Technology
• /
• v.4 no.1 s.10
• /
• pp.9-16
• /
• 2005

In this paper, with loosely coupled transformer Relies-parallel resonant type DC/DC converter is analyzed and adopted to the power source of a TFLM(Transverse Flux Linear Motor). To get more efficient operating mode of the series-parallel resonant type DC/DC converter, theoretical analysis using normalized parameters are accepted. The analysis includes a specially made ferrite transformer with two separately wound half cores in order to evaluate analytically and experimentally the changes in magnetizing the leakage fluxes and inductances caused by the distance between the halves. The proposed converter must be operated in switching Pattern III among the three switching patterns for the Zero Voltage Switching operation. According to Pulse Frequency Modulation(PFM) control method, the output voltage of the proposed circuit can be controlled. The results of the theoretical development are compared with practical measurements from a prototype system.

• Journal of the Institute of Electronics Engineers of Korea SC
• /
• v.37 no.2
• /
• pp.29-36
• /
• 2000

The principle and design of two-stage CMOS operational amplifier with rail-to-rail input and class-AB output stage is presented. The rail-to-rail input stage shows almost constant transconductance independent of the common mode input voltage range in global transistor operation region. This new technique does not make use of accurate current-voltage relationship of MOS transistors. Hence it was achieved by using simple linear relationship of currents. The simulated transconductance variation using SPICE is less the 4.3%. The proposed global two-stage opamp can operate both in strong inversion and in weak inversion. Class AB output stage proposed also has a full output voltage swing and a well-defined quiescent current that does not depend on power supply voltage. Since feedback class- AB control is used, it is expected that this output stage can be operating in extremely low voltage. The variation of DC-gain and unity-gain frequency is each 4.2% and 12%, respectively.

• The Journal of the Acoustical Society of Korea
• /
• v.34 no.6
• /
• pp.432-443
• /
• 2015

Coherence describing the similarity between physical quantities of two signals is a very useful tool to investigate the temporal and spatial characteristics of signals propagating in underwater acoustic waveguide. Ambient noise measurements were made by the vertical received array consisting of three hydrophones as part of the KIOST-HYU joint acoustics experiment, and the coherence for the underwater ambient noise was analyzed. In this paper, the coherence results in cases that the generator in the research vessel was off and turned on are presented. The coherence estimated in the case of the generator operation mode are compared to the predictions obtained using the theoretical model with the directional density function dominated by vertical components propagating downward from the ship. In the case of the generator switch-off, the results are compared to the model predictions with directional density function including the effects of sea surface noise and long-distance shipping noise.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.47 no.4
• /
• pp.31-37
• /
• 2010

In this paper, highly efficient dual-band class-F power amplifiers(PAs) for cellular and WLAN bands are suggested and implemented. For the first step, single-band class-F amplifiers at 840MHz, 2.4GHz are designed using commercial E-pHEMT FETs. The performance of two single band PAs are as much as 81.2% of efficiency with the output power of 24.4dBm with 840MHz PA and 93.5% of efficiency with 22.4dBm from the 2.4GHz. For the dual-band class-F PA, the harmonic controlling circuit with ideal SPDT switch was suggested. The length of transmission line is variable by a SPDT switch. As a results, the operation in 840MHz showed the peak efficiency of 60.5% with 23.5dBm, while in 2.4GHz mode the efficiency was 50.9% with the output power of 19.62dBm. Besides, it is shown that the harmonic controller of class-F above 2Ghz could be implemented on the low cost FR-4 substrate.

• Journal of IKEEE
• /
• v.21 no.2
• /
• pp.123-129
• /
• 2017

Proton Exchange Membrane Fuel Cell (FEMFC) is a strong candidate for future automobile and power generation because of its high power density, low emission and low operation temperature. The major concerns of the gas diffusion layer (GDL) inside a FEMFC is water management. The GDL is typically comprised of carbon for electrical conductivity and PTFE for Hydrophobicity. In this simulation, GDL flooding was investigated using a simplified approach method of an established equation models(Fick' Law, Darcy, Law, Stefan-Maxwell diffusion). The performance of GDL was shown using result of the inner heat, water density and oxygen density of the cell using model equations. The catalyst layer mode in FEMFC showed results of effectiveness factor, Butler-volmer and hydrogen flux density. These results are interesting because the influence of several factors has been shown and the information will be helpful for fuel cell design.

• Particle and aerosol research
• /
• v.9 no.3
• /
• pp.139-147
• /
• 2013

The performances of indoor air cleaners including particle cleaning capacity and collection efficiency are usually tested at the condition of the maximum air flow rate of the air cleaners. However, the power consumption of the air cleaners is highly dependent on the air flow rate of the individual air cleaners. Therefore, there seems to be an optimized air flow rate for the air cleaning capacity considering power consumption. In this study, clean air delivery rate(or standard useful area as suggested room size) and power consumption have been investigated for different maximum air flow rates of 15 air cleaners and then compared those for different air flow rate modes of the individual 5 air cleaners selected from the 15 cleaners. For the maximum air flow rate conditions of 15 air cleansers, the power consumption per unit area was less related to the maximum air flow rate. However, for the different air flow rate modes of the selected 5 air cleaners, the lower power consumption per unit area was corresponding to the lower air flow rate mode of the individual air cleaners. When considering the operation time to the desired particle concentrations, there was an optimized one in the medium air flow rate modes for the individual air cleaners. Therefore, not only the maximum air flow rate but also lower air flow rates of individual air cleaners should be considered for estimating air cleaning capacity based on energy consumption per unit area.

• Journal of the Korea Convergence Society
• /
• v.6 no.6
• /
• pp.75-80
• /
• 2015

To train convergence experts ICT infrastructure must be learned IoT use capabilities of things. In this paper, targeted to students that are majoring in computer science, and for the design of the curriculum and the educational model that handles education of operation in general for training IoT-related education for five months to experts of convergence training describe the contents. Course is the basic ability of the process, core competence course, is divided into real-life capability process and on-site training course, was constructed in a total of 10 stages of the process details. Curriculum, it was designed to learn sensing technology, network technology, security, and content production technology. This educational model is utilized for job creation human resource training project of 2015 Ministry of Employment and Labor, it demonstrated the utility to contribute in order to achieve a high completion and the employment rate. Applicable to future university education plans to expand the curriculum, including courses that complement the Java.

• Korean Chemical Engineering Research
• /
• v.46 no.3
• /
• pp.521-528
• /
• 2008

The micro-porous asymmetric PVDF hollow fiber membranes for gas-liquid contactor were prepared by the dry-jet wet phase inversion process and the characteristics of hollow fiber membranes were evaluated by the gas permeation method and scanning electron microscope. The chemical absorbent for removal of $SO_2$ gas was sodium hydroxide at bench scale hollow fiber membrane contactor. The experiments were performed in a counter-current mode of operation with gas in the shell side and liquid in the fiber lumen of the module to examine the effect of various operating variables such as concentration of absorbent, gas flow rate, L/G ratio and concentration of inlet $SO_2$ gas on the $SO_2$ removal efficiency using PVDF hollow fiber membrane contactor. Membrane mass transfer coefficient($k_m$) was calculated by mathematical modeling. The volumetric overall mass transfer coefficient increased with increasing the concentration of absorbent and L/G ratio. The increase of the absorbent concentration and L/G ratio not only provides more sufficient alkalinity but also decreases liquid phase resistance. The volumetric overall mass transfer coefficient increased with increasing gas flow rate due to decreasing the gas phase resistance.