• Journal of the Korean Solar Energy Society
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• v.32 no.5
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• pp.59-67
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• 2012

In this study,the compact type solar thermal and ground coupled heat pump hybrid system for space heating/cooling and hot water supply has been developed. This hybrid system was installed in Zero Energy Solar House(ZeSH) in KIER for the demonstration. The thermal performance and operational characteristics of this hybrid system were analysed especially. The results are as follows. (1) This hybrid system was designed in order to address the existing disadvantages of solar thermal/ground coupled heat pump system. For this design, all parts except solar collector and ground coupled heat pump were integrated into a single product in a factory. The compact type unit includes two buffer tanks, an expansion tank, pumps, valves, a controller, etc. This system has an advantage of easy installation with simple plumbing work even in narrow space. (2) The thermal charging and discharging time of the buffer tanks and its characteristics by ground coupled heat pump, and heat pump COP according to geo-source temperature and buffer storage temperature have been studied. This system was found to meet well to the heat load without any other auxiliary heating equipment. (3) The operating hours of the ground coupled heat pump as a backup device of solar thermal can be reduced significantly by using solar heat. It was also found that the minimum heating water supply setting temperature and maximum cooling water supply setting temperature make an influence on the heat pump COP. The lower heating water and the higher cooling water temperature, the higher COP. In this respect, the hybrid system's performance can be improved in ZeSH than conventional house.

• Membrane Journal
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• v.26 no.4
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• pp.310-317
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• 2016

Lithium ion secondary battery (LISB) is an energy conversion system operated via charging-discharging cycle based on Lithium ion migration. LISB has a lot of advantages such as high energy density, low self-discharge rate, and a relatively high lifetime. Recently, increasing demands of electric vehicles have been encouraging the development of LISB with high capacity. Unfortunately, it causes some critical safety issues. It includes dendrite formation on negative electrode, resulting in electric shortage problems and battery explosion. Also, the elevated temperatures occurred during the LISB operation induces thermal shrinkage of polyolefin (e.g., polyethylene and polypropylene) separators. Consequently, the low thermal stability leads to decay of LISB performances and the reduction of lifetime. In this study, sulfonated poly (arylene ether sulfone) (SPAES) random copolymers were used as key materials to prepare polyolefin pore-filling separator. The resulting separators were evaluated in the term of metal ion chelation capability associated with dendrite formation, $Li^+$ ion conductivity and thermal durability.

• Journal of the Korea Concrete Institute
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• v.28 no.4
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• pp.395-405
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• 2016

The thermal and mechanical properties of fiber-reinforced mortars for thermal energy storage were investigated in this paper. The effect of the combination of different cementitious composite on the thermal and mechanical characteristics of fiber-reinforced mortars was investigated. Experiments were performed to measure mechanical properties including compressive strength before and after thermal cycling and split tensile strength, and to measure thermal properties including thermal conductivity and specific heat. The results showed that the residual compressive strength of mixtures with OPC and graphite was greatest among the mixtures. Thermal conductivity of mixtures with alumina cement was greater than that of mixtures with OPC, indicating favor of alumina cement for charging and discharging in thermal energy storage system. The addition of zirconium into alumina cement increased specific heat of mixtures. Test results of this study could be used to provide information of material properties for thermal energy storage concrete.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.4
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• pp.414-420
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• 2017

The thermal characteristics of concrete fabricated with blast furnace slag were investigated in this paper. Test parameters included water-binder ratio and the content of furnace slag. Experimental program were performed to measure mechanical properties including compressive strength and split tensile strength under high-temperature thermal cycling, and to measure thermal properties including thermal conductivity and specific heat. Test results showed that the residual compressive strength of mixtures with blast furnace slag was greater than that of mixture without blast furnace slag. In addition, thermal conductivity of mixtures with blast furnace slag was greater than that of mixtures without blast furnace slag. It indicates that blast furnace slag was favorable for charging and discharging in thermal energy storage system. Test results of this study would be used to design concrete module system of thermal energy storage.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.46 no.7
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• pp.39-46
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• 2009

A fast-switching current-pulse driver for light emitting diode (LED) backlight is proposed. It uses a regulated drain current mirror (RD-CM) [1] and a high-voltage NMOS transistor (HV-NMOS). It achieves the fast-response current-pulse switching by using a dynamic gain-boosting amplifier (DGB-AMP). The DGB-AMP does not discharge the large HV-NMOS gate capacitance of the RD-CM when the output current switch turns off. Therefore, it does not need to charge the HV-NMOS gate capacitance when the switch turns on. The proposed current-pulse driver achieves the fast current switching by removing the repetitive gate discharging and charging. Simulation results were verified with measurements performed on a fabricated chip using a 5V/40V 0.5um BCD process. It reduces the switching delay to 360ns from 700ns of the conventional current-pulse driver.

• Transactions of the Korean hydrogen and new energy society
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• v.26 no.4
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• pp.324-330
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• 2015

The electrolyte flow rates of vanadium redox flow battery play very important role in terms of ion transfer to electrolyte, kinetics and pump efficiency in system. In this paper a vanadium redox flow battery single cell was tested to suggest the optimization criteria of electrolyte flow rates on the efficiencies. The compared electrolyte circulation flow rates in this experimental work were 15, 30 and 45 mL/min. The charge/discharge characteristics of the flow rate of 30 mL/min was the best out of all flow rates in terms of charging and discharging time. The current efficiencies, voltage efficiencies and energy efficiencies at the flow rate of 30 mL/min were the best. The IR losses obtained at thd current density of $40mA/cm^2$, at the flow rates of 15, 30 and 45 mL/min were 0.085 V, 0.042 V and 0.115 V, respectively. The charge efficiencies at the current density of $40mA/cm^2$ were 96.42%, 96.45% and 96.29% for the electrolyte flow rates of 15, 30 and 45 mL/min, respectively. The voltge efficiencies at the current density of $40mA/cm^2$ were 77.34%, 80.62% and 76.10% for the electrolyte flow rates of 15, 30 and 45 mL/min, respectively. Finally, the energy efficiencies at the current density of $40mA/cm^2$ were 74.57%, 77.76% and 73.27% for the electrolyte flow rates of 15, 30 and 45 mL/min, respectively. The optimum flow rates of electrolytes were 20 mL/min in most of operating variables of vanadium redox flow battery.

• Journal of the Korean Institute of Intelligent Systems
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• v.24 no.2
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• pp.141-146
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• 2014

This paper suggests a way of generating one-day load curves for performance improvement of peak shaving in a power system. This Peak Shaving algorithm is a long-term scheduling algorithm of PMS (Power Management System) for BESS (Battery Energy Storage System). The main purpose of a PMS is to manage the input and output power from battery modules placed in a power system. Generally, when a Peak Shaving algorithm is used, a difference occurs between predict load curves and real load curves. This paper suggests a way of minimizing the difference by making predict load curves that consider weekly normalization and seasonal load characteristics for smooth energy charging and discharging.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.11
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• pp.1615-1621
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• 2014

A wireless tram which runs without catenary and instead uses batteries installed in the tram has been recently researched actively. This paper presents a new method maximizing absorption of regenerative energy of a wireless tram and extending life cycle of the energy storage device in the wireless tram by applying line-optimized charging and discharging scenario. Energy efficiency and life cycle of energy storage system (ESS) are highly dependent on the characteristic of operating conditions. For example, frequent charge and discharge with high power cause the problems that decrease the battery life cycles. Hybrid energy storage system (HESS) is combination of two ESSs which have complementary characteristics to each other. HESS can provide even better functionality and performance than the battery only ESS due to the synergy effect of two ESSs. This paper also provides a power distribution strategy and driving scenarios which increase the life cycle and energy efficiency of the HESS consisting of a battery and an ultra-capacitor. The developed strategy was tested and verified by a hardware-in-the-loop-simulation (HILS) system which emulates the a wireless tram.

• Tunnel and Underground Space
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• v.23 no.1
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• pp.78-85
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• 2013

A primary objective in creating a stratified thermal storage is to maintain the thermodynamic quality of energy, so thermally stratified energy can be extracted at temperatures required for target activities. The separation of the thermal energy in heat stores to layers with different temperatures, i.e., the thermal stratification is a key factor in achieving this objective. This paper introduces different methods that have been proposed to characterize the thermal stratification in heat stores. Specifically, this paper focuses on the methods that can be used to determine the ability of heat stores to promote and maintain stratification during the process of charging, storing and discharging. In addition, based on methods using thermal stratification indices, the degrees of stratification of stored energy in Lyckebo rock cavern in Sweden were compared and the applicability of the methods was investigated.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.110-110
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• 2011

The nanomechanical properties of fully lithiated and unlithiated silicon nanowire deposited on silicon substrate have been studied with atomic force microscopy. Silicon nanowires were synthesized using the vapor-liquid-solid process on stainless steel substrates using Au catalyst. Fully lithiated silicon nanowires were obtained by using the electrochemical method, followed by drop-casting on the silicon substrate. The roughness, derived from a line profile of the surface measured in contact mode atomic force microscopy, has a smaller value for lithiated silicon nanowire and a higher value for unlithiated silicon nanowire. Force spectroscopy was utilitzed to study the influence of lithiation on the tip-surface adhesion force. Lithiated silicon nanowire revealed a smaller value than that of the Si nanowire substrate by a factor of two, while the adhesion force of the silicon nanowire is similar to that of the silicon substrate. The Young's modulus obtained from the force-distance curve, also shows that the unlithiated silicon nanowire has a relatively higher value than lithiated silicon nanowire due to the elastically soft amorphous structures. The frictional forces acting on the tip sliding on the surface of lithiated and unlithiated silicon nanowire were obtained within the range of 0.5-4.0 Hz and 0.01-200 nN for velocity and load dependency, respectively. We explain the trend of adhesion and modulus in light of the materials properties of silicon and lithiated silicon. The results suggest a useful method for chemical identification of the lithiated region during the charging and discharging process.