• Journal of Communications and Networks
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• v.12 no.3
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• pp.231-239
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• 2010

In cluster-based wireless sensor networks, the energy could be saved when the nodes that have data to transmit participate in cooperative multiple-input multiple-output (MIMO). In this paper, by making the idle nodes that have no data to transmit participate in the cooperative MIMO, it is found that much more energy could be saved. The number of the idle nodes that participate in the cooperative MIMO is optimized to minimize the total energy consumption. It is also found that the optimal number of all the nodes participating in cooperative communication does not vary with the number of nodes that have data to transmit. The proposition is proved mathematically. The influence of long-haul distance and modulation constellation size on the total energy consumption is investigated. A cooperative MIMO scheme with help-node participation is proposed and the simulation results show that the proposed scheme achieves significant energy saving.

• Journal of Electrical Engineering and Technology
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• v.8 no.5
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• pp.1070-1077
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• 2013

Owing to the consistent increase in energy efficiency issues, studies for improving regenerative energy utilization have been receiving attention in the Urban DC railway systems, where currently, the utilization of regenerative energy is low due to the lack of a specific plan for using this energy. The regenerative energy in railway systems has a low efficiency problem which results in the increase of the catenary voltage and a possibility to create problems to the electrical devices connected to the system. This paper deals with the power integration of large urban railway subsystems to improve regenerative energy utilization where the railway subsystems are integrated with other railway subsystems to improve the energy efficiency. Through the case studies, to find the realistic effect of integrated operation, the Seoul Metro subsystems, namely Line 5 and Line 7, has been applied. Also, evaluation for the electricity cost saving has been performed by using KEPCO electricity cost table.

• Journal of Environmental Policy
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• v.11 no.4
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• pp.85-105
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• 2012

In this paper, the energy efficiency of wastewater utilities was evaluated to explore ways to save energy via operational measures. The correlation of each wastewater characteristic parameter to energy was assessed to find a set of parameters that explained most of the variations in energy use among utilities. The results show that increases in inflow, influent COD concentration, and ratio of advanced treatment generally increased the energy use. On the other hand, increases in load factor (influentaverage flow/design flow) reduced the energy use. In the regression analysis, the energy efficiency was highest in the A2O advanced process. On the other hand, the membrane process (among the advanced processes) and the contacted aeration process (among the secondary processes) require more efforts in saving energy. However, the data base system related to energy use must be supplemented in order for more accurate analysis of energy consumption in wastewater treatment facilities. In particular, i) electricity consumption of relay pumps and, ii) energy usage per unit process, iii) pump power usage to discharge treated wastewater in a long distance, if necessary, and iv) alternative energy production and utilization status must be recorded. By utilizing the results of the analysis conducted in this study, it is possible to quantify a level of energy savings needed and establish customized energy saving measures to achieve a certain target level for benchmarking a successful case of wastewater utilities.

• International Journal of Internet, Broadcasting and Communication
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• v.14 no.1
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• pp.188-193
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• 2022

The energy efficiency of memory systems is an important task in designing future computer systems as memory capacity continues to increase to accommodate the growing big data. In this article, we present an energy-efficient last-level cache management policy for future mobile systems. The proposed policy makes use of low-power PCM (phase-change memory) as the main memory medium, and reduces the amount of data written to PCM, thereby saving memory energy consumptions. To do so, the policy keeps track of the modified cache lines within each cache block, and replaces the last-level cache block that incurs the smallest PCM writing upon cache replacement requests. Also, the policy considers the access bit of cache blocks along with the cache line modifications in order not to degrade the cache hit ratio. Simulation experiments using SPEC benchmarks show that the proposed policy reduces the power consumption of PCM memory by 22.7% on average without degrading performances.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.2
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• pp.628-649
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• 2017

Security and resource-saving are both demands of the fifth generation (5G) wireless networks. In this paper, we study the secrecy spectrum efficiency (SSE) and secrecy energy efficiency (SEE) of a K-tier massive multiple-input multiple-output (MIMO) enabled heterogeneous cellular network (HetNet), in which artificial noise (AN) are employed for secrecy enhancement. Assuming (i) independent Poisson point process model for the locations of base stations (BSs) of each tier as well as that of eavesdroppers, (ii) zero-forcing precoding at the macrocell BSs (MBSs), and (iii) maximum average received power-based cell selection, the tractable lower bound expressions for SSE and SEE of massive MIMO enabled HetNets are derived. Then, the influences on secrecy oriented spectrum and energy efficiency performance caused by the power allocation for AN, transmit antenna number, number of users served by each MBS, and eavesdropper density are analyzed respectively. Moreover, the analysis accuracy is verified by Monte Carlo simulations.

• Journal of the Korean Society of Marine Environment & Safety
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• v.18 no.3
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• pp.267-272
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• 2012

Carbon emission generated by energy issues is one of the major problems which all countries concern. The International Energy Agency recommends to improve 15-30[%] of energy efficiency than now. Government has pushed the domestic energy saving policies and incentives and penalties were also given in that direction. Pumps are widely used to transfer fluids and they consume at least 20[%] power of each nation. Their loss of energy is huge if they have been operated at low efficiency for long time. Low efficiency of these pumps is often due to incorrect design or degradation. Pump efficiency can be measured to estimate energy loss. If it is low, the pump may be repaired or replaced with new one. This paper introduces thermodynamic method to measure pump efficiency using only two kinds of sensors for temperature and pressure. It can calculate best efficiency point(BEP) of actual systems easily and fast. Its values were compared with the real performance curve provided by pump maker and we got almost similar performance curves from the repeated experiment.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.751-756
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• 2009

In the perspective of saving energy in buildings, the high performance of insulation and air tightness for improving the heating and the cooling efficiency, has brought economically positive effects. However, these building energy saving technologies cause the lack of ventilation, which is the direct cause of increasing the indoor contaminants, and is also very harmful to the residents, because they spend over 90% of their time indoors. Therefore, the ventilation is important to keep the indoor environment clean and it can also save the energy consumption. In this study, a HEPA type nano ceramic filter is designed as a passive ventilation system to collect airborne particles and to supply fresh outdoor air. The double layer filter, which has $30{\mu}m$ in diameter at the conditions of 10wt% of concentration and 3kV/cm of the electric intensity, is produced by electrospinning. The filtration coating technology is confirmed in the solution with $SiO_2$ nano particles using polymer nano fibers. Also double layer filters are coated with $SiO_2$ nano particles and finally the porous construction materials are made by sintering in the electric furnace at $200{\sim}1400^{\circ}C$. The efficiency is measured 96.67% at the particle size of $0.31{\mu}m$, which is slightly lower than HEPA filter. However the efficiency is turned out to be sufficient.

• Journal of Ocean Engineering and Technology
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• v.32 no.6
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• pp.419-426
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• 2018

Recently, in an effort to reduce the energy efficiency design index (EEDI), studies on energy saving devices (ESDs) have been conducted. In this study, we designed a post-device suitable for a KRISO container ship (KCS) using computational fluid dynamics (CFD). In order to increase the efficiency of the post-device, a twisted rudder was used, which has a proven performance (showing a 1.34% reduction in DHP compared to the bare hull at 24 knots) in previous research at Pusan National University. In addition, an increase in efficiency was expected by the use of a rudder bulb, including the discontinuous section of the twisted rudder and a divergent propeller cap to prevent the contraction of the wake. The optimization criterion was the case where the delivery power was the least compared with the bare hull. We analyzed the cause of the efficiency increase through an analysis of the self-propulsion factor. The case study for optimization was divided into 4 types (1. clearance of the bulb and cap, 2. shape of the bulb, 3. size of the bulb and cap, and 4. asymmetric bulb). Finally, with a clearance of 50 mm from the ship, a spherical bulb with the cap having an angle of $5^{\circ}$, and an asymmetric rudder bulb with a bulb diameter of 1.2HH/1.4H (horizontal/vertical) showed a 2.05% reduction in DHP compared to the bare hull at 24 knots. We will fabricate a post-device that will be optimized in the future and verify the performance of the post-device through model tests.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.05a
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• pp.24-25
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• 2014

Up to now, most the fenestration industry is consisted of glazing and window frame in Korea. According to the Fenestration Energy Consumption Efficiency Rating System and Energy Saving Design Standards of Buildings, u-value of fenestration is defined as the value of calculation with glazing and frame. For this reason, when applying for a building permit, in most cases, the official approval test report of the set of windows and doors is used. Nevertheless, in windows construction progresses, most construction manager take delivery of the glazing and frame separately. For those reason, windows and doors are constructed regardless of the report of the Fenestration Energy Consumption Efficiency Rating System in most construction fields. From now on, the research of the connection method between reality of policy and reality of construction fields should be carried out.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.8
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• pp.4012-4018
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• 2013

This paper proposes an energy conservation scheme when apartment remodeling is provided, which analyzes the energy conservation techniques that are suitable for overseas passive houses. Subsequently, a passive solution that is more suitable for our country is derived. In order to examine the energy saving rate applying to passive solution, it evaluates the energy saving rate of 5 specific cases by taking advantage of internal building energy efficiency rating certification system, classifies them and analyzes them. Finally, a rational alternative is devised, and then which is implemented in the internal apartment housing remodeling project. This scheme can save 40% of the energy in comparison with typical apartment building.