• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.193-196
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• 2014

Experimantal evaluation of an energy storage device with high rotational speed to store regenerative energy which might be generated during the braking period of the trains is presented. The proposed ESS is small scale model and has 5kW output power, high rotational speed. In general railway trains generate regenerative energy for 10-20 sec when the train brakes and also high traction energy is needed for very short moment (10 sec) when the train increases the traction force. Considering such characteristics of the railway system energy storage device for the railway should have very fast response property. Among the various energy storage devices flywheel energy storage system has the fastest response property, which means that flywheel ESS is the most suitable for the railway system.

• Journal of the Korean Solar Energy Society
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• v.40 no.2
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• pp.1-10
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• 2020

Korea government published renewable energy obligation policy that public building must be supplied some part of total consumption energy (2019: 27%, 2020: 30%). RETScreen is freely available global energy tool that developed by Canadian National Energy Laboratory to quantify energy saving to compare conventional system. This program can be performed energy modeling, cost analysis, greenhouse gas emission analysis and financial analysis. In this study, GSHP (Ground source heat pump) heating and cooling system were studied for the energy deliverly and ROI (Return On Investment) in an office building. Three cases were studied according to the number of HP (Heat pump) units for the 1,000㎡ office building located in Daejeon. Results indicated that the energy delivery of the case 1 (1 HP unit) covered 57% of the office building heating and cooling energy consumption. The case 2 (2 HP units) covered 87.8% and the case 3 (3 HP units) covered 96.8% of the office building energy consumption. The ROI of the case 1 indicated 7.9 years. While 8.2 years for the case 2 and 9.7 years for the case 3.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2019.05a
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• pp.106-107
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• 2019

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2018.11a
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• pp.125-126
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• 2018

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.10
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• pp.4625-4641
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• 2016

The performances of two commonly used feature detectors for wireless energy-harvesting cognitive radio systems are compared with the energy detector under energy causality and collision constraints. The optimal sensing duration is obtained by analyzing the effect of the detection threshold on the average throughput and collision probability. Numerical examples show that the covariance detector has the optimal sensing duration depending on an appropriate choice of the detection threshold, but no optimal sensing duration exists for the ratio of average energy to minimum eigenvalue detector.

• New & Renewable Energy
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• v.10 no.1
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• pp.6-19
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• 2014

Organic Rankine cycle (ORC) has been widely used to convert renewable energy such as solar energy, geothermal energy, or waste energy etc., to electric power. For a small scale output power less than 10 kW, turbo-expander is not widely used than positive displacement expander. However, the turbo-expander has merits that it can operate well at off-design points. Usually, the available thermal energy for a small scale ORC is not supplied continuously. So, the mass flowrate should be adjusted in the expander to maintain the cycle. In this study, nozzles was adopted as stator to control the mass flowrate, and radial-type turbine was used as expander. The turbine operated at partial admission. R245fa was adopted as working fluid, and supersonic nozzle was designed to get the supersonic flow at the nozzle exit. When the inlet operating condition of the working fluid was varied corresponding to the fluctuation of the available thermal energy, optimal operating condition was investigated at off-design due to the variation of mass flowrate.

• New & Renewable Energy
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• v.19 no.2
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• pp.31-39
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• 2023

Salinity gradient energy can be generated from a mixture of water streams with different salt concentrations by using reverse electrodialysis (RED). In this study, we evaluated the effect of stack size and number of cell pairs on the energy efficiency and specific energy of the RED process. Additionally, we studied the prementioned parameters to maximize the power density of RED. The performance of the RED stack which used a patterned ion exchange membrane, was evaluated as a function of stack size and feed flow rate. Moreover, it was noted that an increase in stack size increased the ion movement through the ion exchange membrane. Furthermore, an increase in feed flow rate led to a reduction in the concentration variation, resulting in an increase in OCV and power density. The energy efficiency and specific energy for 100 cells in the 10 × 10 cm² stack were the highest at 12% and 0.05 kWh/m³, respectively, while the power density from 0.33 cm/s to 5 × 5 cm² stack was the highest at 0.53 W/m². The study showed that the RED performance can be improved by altering the size of the stack and the number of cell pairs, thereby positively affecting energy efficiency and specific energy.

• Land and Housing Review
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• v.11 no.1
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• pp.95-101
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• 2020

In the past few decades, the global population growth and rapid economic development have resulted in significant increases in building energy consumption. To reduce greenhouse-gas emissions and building energy consumption, building materials and energy technologies must be optimized. Building retrofitting is a more efficient method than reconstruction to improve the building energy performance. In order to improve the energy performance of existing buildings, this study proposed energy-efficiency retrofit plans and derived cost-effective retrofit plan. The energy efficient retrofit method is achieved through the packaging of energy technology and the energy and cost reduction effect of the energy efficiency retrofit package are analyzed. As a result of the study, the energy-efficiency retrofit package showed an energy reduction effect of up to 60% or more and a construction cost reduction of about 30%. This study argues that optimal energy and construction cost reduction of existing buildings are possible through the packaging of energy efficiency technology.

• New & Renewable Energy
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• v.20 no.1
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• pp.88-94
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• 2024

This study explored the potential and implementation of renewable energy sources in Sri Lanka, focusing on the theoretical potential of solar and wind energy to develop self-reliant energy models. Using advanced climate data from the European Centre for Medium-Range Weather Forecasts and Global Solar/Wind Atlas provided by the World Bank, we assessed the renewable energy potential across Sri Lanka. This study proposes off-grid and minigrid systems as viable solutions for addressing energy poverty in rural regions. Rural villages were classified based on solar and wind resources, via which we proposed four distinct energy self-reliance models: Renewable-Dominant, Solar-Dominant, Wind-Dominant, and Diesel-Dominant. This study evaluates the economic viability of these models considering Sri Lanka's current energy market and technological environment. The outcomes highlight the necessity for employing diversified energy strategies to enhance the efficiency of the national power supply system and maximize the utilization of renewable resources, contributing to Sri Lanka's sustainable development and energy security.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.782-787
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• 2008

The Kalina cycle simulation study was carried out for a preliminary design of a geothermal power generation system. The Kalina cycle system can be used for the utilization of a low-temperature heat sources such as geothermal and industrial waste heat that are not hot enough to produce steam. The sea/river water can be considered as a cooling media. A steady-state simulation model was developed to analyze and optimize its performance. The model contains a turbine, a pump, an expansion valve and heat exchangers. The turbine and pump were modelled by an isentropic efficiency, while a condenser, an evaporator and a regenerative heat exchanger were modeled by UA-LMTD method with a counter-flow assumption. The simulation results show that the power generation efficiency over 10% is expected when a heat source and sink inlet temperatures are $100^{\circ}C$ and $10^{\circ}C$ respectively.