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Energies, Volume 12, Issue 9 (May-1 2019)

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Cover Story (view full-size image) The use of a simple and convenient mobile system for drying biomass near collection sites and the [...] Read more.
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Open AccessArticle
Long-Term Monitoring of Sensible Thermal Storage in an Extremely Cold Region
Energies 2019, 12(9), 1821; https://doi.org/10.3390/en12091821
Received: 20 March 2019 / Revised: 20 April 2019 / Accepted: 7 May 2019 / Published: 13 May 2019
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Abstract
We present more than one-year of monitoring results from a thermal energy storage system located in a very cold place with a long winter season. The studied house is in Palmer city, Alaska (~62° N, ~149° W). The house is equipped with solar [...] Read more.
We present more than one-year of monitoring results from a thermal energy storage system located in a very cold place with a long winter season. The studied house is in Palmer city, Alaska (~62° N, ~149° W). The house is equipped with solar PV for electricity production and solar thermal collectors which were linked to a sensible thermal energy storage system which is underneath the house’s normally unoccupied garage and storage space. Sensors were installed in the thermal storage and solar thermal collector array to monitor system temperatures. In addition, TRNSYS was used for numerical simulation and the results were compared to experimental ones. The maximum observed garage ambient temperature was ~28 °C while the simulated maximum ambient garage temperature was found to be ~22 °C. Results indicate that seasonal solar thermal storages are viable options for reducing the cost of energy in a region with extended freezing periods. This is significant for Alaska where the cost of energy is 3–5 times the national average. Full article
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Open AccessArticle
Turning Filling Material into Proppant for Coalbed Methane in Poland—Crush Test Results
Energies 2019, 12(9), 1820; https://doi.org/10.3390/en12091820
Received: 4 March 2019 / Revised: 30 April 2019 / Accepted: 30 April 2019 / Published: 13 May 2019
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Abstract
The search for unconventional energy resources such as coalbed methane (CBM) is on the rise in Poland due to the demand for energy resources and protection of the environment. CBM production has a lower impact on the environment when compared with coal production. [...] Read more.
The search for unconventional energy resources such as coalbed methane (CBM) is on the rise in Poland due to the demand for energy resources and protection of the environment. CBM production has a lower impact on the environment when compared with coal production. Its development is known to be cost effective due to its use of shallow depths with large gas quantities. Sand is one of the by-products (waste) from open-pit mining operations. Conventional disposal of this material is achieved by storage in heaps and its deployment as landfill as well as filling material for mine pits. This paper investigates the potential use of sand (filler) as a proppant for hydraulic fracturing in coalbed methane formations in Poland through crush test measurements in both single and cyclic loadings. The crush test helps to identify proppant strength under various load applications. Test results show that the sand qualifies for the 4 K (maximum allowable stress is 27.58 MPa) and 3 K (maximum allowable stress 20.68 MPa) crush classifications under single and cyclic conditions, respectively. This finding shows the viability and potential of the investigated sand as a proppant for hydraulic fracturing in shallow coalbed methane formations in Poland. Furthermore, its use could help filler-providing companies to maintain their production level and save jobs. Notably, it would contribute to the reduction of environmental problems associated with the management of waste, such as that from open-pit mining operations. Full article
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Open AccessArticle
Anaerobic Digestion Technology for Methane Production Using Deer Manure Under Different Experimental Conditions
Energies 2019, 12(9), 1819; https://doi.org/10.3390/en12091819
Received: 29 March 2019 / Revised: 7 May 2019 / Accepted: 9 May 2019 / Published: 13 May 2019
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Abstract
Anaerobic digestion (AD) is an important technology for the treatment of livestock and poultry manure. The optimal experimental conditions were studied, with deer manure as a fermentation material and mushroom residue as an inoculum. At the same time, methane production was increased by [...] Read more.
Anaerobic digestion (AD) is an important technology for the treatment of livestock and poultry manure. The optimal experimental conditions were studied, with deer manure as a fermentation material and mushroom residue as an inoculum. At the same time, methane production was increased by adding zeolite and changing the magnetic field conditions. The results showed that a 6% solid content was the best condition for producing methane. The optimal conditions for methane production were obtained by adding 35 g of mushroom residue to 80 g of deer manure at 35 °C. The addition of organic wastewater (OW) improved methane production. The result of improving the methane production factor showed that adding zeolite during the reaction process could increase the methane production rate. When the amount of zeolite was over 8% total solids (TSes), methane production could improve, but the rate decreased. Setting a different magnetic field strength in the AD environment showed that when the distance between the magnetic field and the reactor was 50 mm and the magnetic field strength was 10–50 mT, the methane production increment and the content of methane in the mixed gases increased. Full article
(This article belongs to the Special Issue Biomass Pretreatment and Biomass Conversion to Biofuels)
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Open AccessFeature PaperArticle
A Restarting Strategy for Back-EMF-Based Sensorless Permanent Magnet Synchronous Machine Drive
Energies 2019, 12(9), 1818; https://doi.org/10.3390/en12091818
Received: 16 April 2019 / Revised: 9 May 2019 / Accepted: 10 May 2019 / Published: 13 May 2019
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Abstract
Safely starting a spinning position sensorless controlled permanent magnet synchronous machine is difficult because the current controller does not include information regarding the motor position and speed for suppressing the back-electromotive force (EMF)-induced current. This paper presents a restarting strategy for back-EMF-based sensorless [...] Read more.
Safely starting a spinning position sensorless controlled permanent magnet synchronous machine is difficult because the current controller does not include information regarding the motor position and speed for suppressing the back-electromotive force (EMF)-induced current. This paper presents a restarting strategy for back-EMF-based sensorless drives. In the proposed strategy, the existing back-EMF and position estimator are used and no additional algorithm or specific voltage vector injection is required. During the restarting period, the current controller is set to a particular state so that the back-EMF estimator can rapidly estimate motor voltage without using rotor position and speed. Then, this voltage is used to decouple the back-EMF of the motor in the current controller in order to suppress the induced current. After the back-EMF is decoupled from the current controller, sensorless control can be restored with the estimated position and speed. The experimental results indicated that the induced current can be suppressed within four to five sampling periods regardless of the spinning conditions. Because of the considerably short time delay, the motor drive can restart safely from various speeds and positions without causing overcurrent fault. Full article
(This article belongs to the Special Issue Permanent Magnet Synchronous Machines)
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Open AccessArticle
A Methodology for Dependability Evaluation of Smart Grids
Energies 2019, 12(9), 1817; https://doi.org/10.3390/en12091817
Received: 13 March 2019 / Revised: 8 April 2019 / Accepted: 13 April 2019 / Published: 13 May 2019
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Abstract
Smart grids are a new trend in electric power distribution, which has been guiding the digitization of electric ecosystems. These smart networks are continually being introduced in order to improve the dependability (reliability, availability) and efficiency of power grid systems. However, smart grids [...] Read more.
Smart grids are a new trend in electric power distribution, which has been guiding the digitization of electric ecosystems. These smart networks are continually being introduced in order to improve the dependability (reliability, availability) and efficiency of power grid systems. However, smart grids are often complex, composed of heterogeneous components (intelligent automation systems, Information and Communication Technologies (ICT) control systems, power systems, smart metering systems, and others). Additionally, they are organized under a hierarchical topology infrastructure demanded by priority-based services, resulting in a costly modeling and evaluation of their dependability requirements. This work explores smart grid modeling as a graph in order to propose a methodology for dependability evaluation. The methodology is based on Fault Tree formalism, where the top event is generated automatically and encompasses the hierarchical infrastructure, redundant features, load priorities, and failure and repair distribution rates of all components of a smart grid. The methodology is suitable to be applied in early design stages, making possible to evaluate instantaneous and average measurements of reliability and availability, as well as to identify eventual critical regions and components of smart grid. The study of a specific use-case of low-voltage distribution network is used for validation purposes. Full article
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Open AccessArticle
Quantitative Analysis of Consumer Preferences of Windows Set in South Korea: The Role of Energy Efficiency Levels
Energies 2019, 12(9), 1816; https://doi.org/10.3390/en12091816
Received: 28 March 2019 / Revised: 27 April 2019 / Accepted: 5 May 2019 / Published: 13 May 2019
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Abstract
The building sector is considered to be important for Korean energy issues as it accounts for approximately 20% of Korea’s final energy consumption. As one of Korea’s passive strategies in its emission reduction plan is reducing energy consumption through improvements in energy efficiency [...] Read more.
The building sector is considered to be important for Korean energy issues as it accounts for approximately 20% of Korea’s final energy consumption. As one of Korea’s passive strategies in its emission reduction plan is reducing energy consumption through improvements in energy efficiency because the energy loss mostly occurs from window sets, this study aims to examine the preferences and role of the energy efficiency level of window sets in South Korea. Given that the lifespan of a building exceeds 20 years, a building’s energy efficiency significantly impacts accumulated energy savings. However, window sets affect not only energy efficiency, but also the interior appearance of the building; therefore, it is important to understand consumer preferences and to examine their effect on building energy reduction accordingly. Using a mixed logit model, this study analyzes window set preferences and energy savings. As a result, this study determines that consumers consider the energy efficiency level to be the second most important factor in determining window preference, following the cost of the window. In addition, this study found that the marginal willingness to pay for efficiency level 2 window sets compared to level 3 window sets is USD 1256. For level 1 window sets, this figure increases to USD 3140. Further, a scenario analysis is conducted to analyze the government incentive program’s effectiveness in encouraging consumers to purchasing higher energy efficiency more efficient products, and thus in promoting the eco-friendly consumption of in households. Taking into consideration of households’ willingness to pay and cost saving amount for using energy efficient window sets, the optimal value of government incentives of is found to be approximately USD 700 is found to be optimal. Full article
(This article belongs to the Special Issue Energy Policy in South Korea)
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Open AccessArticle
An Alterable Structure Power Router with General AC and DC Port for Microgrid Applications
Energies 2019, 12(9), 1815; https://doi.org/10.3390/en12091815
Received: 2 April 2019 / Revised: 2 May 2019 / Accepted: 10 May 2019 / Published: 13 May 2019
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Abstract
This paper proposes an alterable structure power router (PR) topology which shares the ability of general Alternating Current (AC) and Direct Current (DC) port. This alterable structure PR aims to better implement the interconnections among micro-grids, renewable energy, and traditional grids. The PR’s [...] Read more.
This paper proposes an alterable structure power router (PR) topology which shares the ability of general Alternating Current (AC) and Direct Current (DC) port. This alterable structure PR aims to better implement the interconnections among micro-grids, renewable energy, and traditional grids. The PR’s converter structure is alterable according to the system power. Based on the operation analysis of the PR, the mathematic model of the power router is established and the relationship between switch states and port voltage is analyzed. According to the PR mathematical model, the control method is designed to realize current control in both AC and DC mode. With the proposed power router topology, the PR’s port can be used in both AC and DC situations, which saves the cost of traditional PRs and increases economic efficiency. The simulation and experimental results prove the good steady-state and dynamic performance of the proposed power router topology. Full article
(This article belongs to the Section Smart Grids and Microgrids)
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Open AccessArticle
Effects of the Heat Transfer Fluid Selection on the Efficiency of a Hybrid Concentrated Photovoltaic and Thermal Collector
Energies 2019, 12(9), 1814; https://doi.org/10.3390/en12091814
Received: 1 March 2019 / Revised: 13 April 2019 / Accepted: 21 April 2019 / Published: 13 May 2019
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Abstract
This work focuses on the performance study of the PowerCollector™, a concentrated photovoltaic thermal system with a custom-made geometry and a photovoltaic cell cooling technology. To do so, a model that portrays the behavior of this concentrating solar system was developed. In order [...] Read more.
This work focuses on the performance study of the PowerCollector™, a concentrated photovoltaic thermal system with a custom-made geometry and a photovoltaic cell cooling technology. To do so, a model that portrays the behavior of this concentrating solar system was developed. In order to validate all the information obtained with its simulation, measurements were taken from an experimental setup and were compared to the respective results predicted by this exact same model. It should be noted that all these procedures were based on the fluid for which the PowerCollector™ has been designed (water). Hence, the efficiency enhancement using nanofluids was also considered, as data from some studies addressing this issue were analyzed. Alongside all of this, the corrosion and erosion effects on the pipes incorporated in this system and originated by all the fluids mentioned throughout this investigation were also evaluated. In summary, with this entire study, it could be concluded that nanofluids may represent an appropriate alternative to water, as long as they are chosen according to all particularities of each case. Full article
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Open AccessArticle
Combination Optimization Configuration Method of Capacitance and Resistance Devices for Suppressing DC Bias in Transformers
Energies 2019, 12(9), 1813; https://doi.org/10.3390/en12091813
Received: 2 April 2019 / Revised: 6 May 2019 / Accepted: 9 May 2019 / Published: 13 May 2019
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Abstract
The ground current of a high-voltage direct current (HVDC) transmission system can cause DC bias in transformers near the grounding electrode during monopole operations, which affects the alternating current (AC) power system operation. Owing to multiple bias current flow paths, a capacitance blocking [...] Read more.
The ground current of a high-voltage direct current (HVDC) transmission system can cause DC bias in transformers near the grounding electrode during monopole operations, which affects the alternating current (AC) power system operation. Owing to multiple bias current flow paths, a capacitance blocking device installed at the neutral point of a transformer may increase the DC bias in adjacent transformers, while suppressing the DC current in that transformer. This paper introduces the use of an effective bias current indicator to describe the effect of the grounding current on transformers in a network, considering the wiring characteristics of the autotransformers and the power system topology. Additionally, a combination optimization method for the capacitance and resistance is applied in order to determine the minimum number of installed devices that restrict the maximum effective bias current throughout the network to a permissible range. A genetic algorithm based on an improved roulette selection method is adopted to solve the optimal configuration problem. The method is validated by using a test case based on the Xizhe HVDC transmission receiving-end grid near the Jinsi grounding electrode. The configuration of the capacitance and resistance was optimized by the improved genetic algorithm. This method can achieve the desired level of DC bias management with fewer devices than the conventional method, which verifies the feasibility and superiority of the proposed optimization method. Full article
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Open AccessArticle
Energy Storage Sizing Strategy for Grid-Tied PV Plants under Power Clipping Limitations
Energies 2019, 12(9), 1812; https://doi.org/10.3390/en12091812
Received: 4 April 2019 / Revised: 7 May 2019 / Accepted: 9 May 2019 / Published: 13 May 2019
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Abstract
This paper presents an analyses of an Energy Storage System (ESS) for grid-tied photovoltaic (PV) systems, in order to harness the energy usually lost due to PV array oversizing. A real case of annual PV power generation analysis is presented to illustrate the [...] Read more.
This paper presents an analyses of an Energy Storage System (ESS) for grid-tied photovoltaic (PV) systems, in order to harness the energy usually lost due to PV array oversizing. A real case of annual PV power generation analysis is presented to illustrate the existing problem and future solutions. Three PV modeling techniques have been applied to estimate non-measured non-harnessed PV power to provide an ESS energy and power sizing strategy. Moreover, a control strategy to store or release power from the DC-link, without modifying the Maximum Power Point Tracking (MPPT) strategy, is presented. The results show an estimation of the annual power loss caused by oversizing the PV array. The ESS sizing strategy gives insight into not only the energy requirements, but also the power requirements of the system. Simulation results show that the proposed ESS control strategy is capable of harnessing the extra power without modifying the existing power converter of the PV plant nor its control strategy. Full article
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Open AccessArticle
Energy Management Optimization and Voltage Evaluation for Residential and Commercial Areas
Energies 2019, 12(9), 1811; https://doi.org/10.3390/en12091811
Received: 3 April 2019 / Revised: 5 May 2019 / Accepted: 8 May 2019 / Published: 13 May 2019
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Abstract
In most smart grids, load management techniques are required to handle multiple loads of several types. This paper studies decentralized demand-side management (DSM) in a grid with different types of appliances in two service areas: one with many residential households, and one bus [...] Read more.
In most smart grids, load management techniques are required to handle multiple loads of several types. This paper studies decentralized demand-side management (DSM) in a grid with different types of appliances in two service areas: one with many residential households, and one bus with commercial customers. Each building runs an individual optimal DSM to reschedule the usage time of its flexible appliances to reduce its electric energy cost at a manageable sacrifice of inconvenience according to the forecasted time-varying electricity price. Using the developed model, we examined the effectiveness of decentralized DSM by comparing its performance on the operation status of the grid in terms of electricity cost saving, rooftop photovoltaic (PV) utilization efficiency, voltage fluctuation, power loss, voltage rises, and reverse power flows, which can easily be seen at the commercial load bus. Full article
(This article belongs to the Special Issue Electric Power Systems Research 2019)
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Open AccessArticle
Design and Implementation of a Hybrid Single T-Type Double H-Bridge Multilevel Inverter (STDH-MLI) Topology
Energies 2019, 12(9), 1810; https://doi.org/10.3390/en12091810
Received: 23 March 2019 / Revised: 2 May 2019 / Accepted: 3 May 2019 / Published: 13 May 2019
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Abstract
Multilevel inverters are proficient in achieving a high-quality staircase output voltage waveform with a lower amount of harmonic content. In this paper, a new hybrid multilevel inverter topology based on the T-type and H-bridge module is presented. The proposed topology aims to achieve [...] Read more.
Multilevel inverters are proficient in achieving a high-quality staircase output voltage waveform with a lower amount of harmonic content. In this paper, a new hybrid multilevel inverter topology based on the T-type and H-bridge module is presented. The proposed topology aims to achieve a higher number of levels utilizing a lower number of switches, direct current (dc) voltage sources, and voltage stresses across different switches. The basic unit of the proposed single T-type and double H-bridge multilevel inverter (STDH-MLI) produces 15 levels at the output using three dc voltage sources. The proposed topology can be extended by connecting a larger number of dc voltage sources in the T-type section. The nearest level control (NLC) switching technique is used to generate gate pulses for switches to achieve a high-quality output voltage waveform. In addition, a simplified way to achieve NLC is also described in the paper. A detailed comparison with other similar topologies is provided to set the benchmark of the proposed topology. Finally, experimental work is carried out to validate the performance of the proposed topology. Full article
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Open AccessArticle
Proposal of a Novel Semi-Submersible Floating Wind Turbine Platform Composed of Inclined Columns and Multi-Segmented Mooring Lines
Energies 2019, 12(9), 1809; https://doi.org/10.3390/en12091809
Received: 12 April 2019 / Revised: 7 May 2019 / Accepted: 8 May 2019 / Published: 12 May 2019
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Abstract
The semi-submersible floating offshore wind turbine has been studied in detail due to its good stability. However, the occurrence of typhoons are very frequent in China’s offshore area, putting forward a higher requirement for the stability of the floating wind turbine system. By [...] Read more.
The semi-submersible floating offshore wind turbine has been studied in detail due to its good stability. However, the occurrence of typhoons are very frequent in China’s offshore area, putting forward a higher requirement for the stability of the floating wind turbine system. By changing the connection mode of the mooring line as well as the structural form of the platform based on the original OC4 model, two groups of models were examined by an in-house developed code named as the Analysis Tool of Floating Wind Turbine (AFWT). The influence of the arrangement of the mooring lines and the inclination angle of the upper columns on the motion response were clarified. It was found that the surge motion of the platform would be obviously decreased by decreasing the length of the upper segments of the mooring lines, while the heave motion of the platform would be significantly decreased as increasing the inclined angle of the columns. Therefore, a new model integrating the optimized multi-segmented mooring lines and the optimized inclined columns was proposed. The examinations showed that compared with the response motions of the original OC4 semi-submersible model, the proposed model could reduce both the surge and heave motions of the platform effectively. Full article
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Open AccessArticle
The Economic Effects of the Development of the Renewable Energy Industry in China
Energies 2019, 12(9), 1808; https://doi.org/10.3390/en12091808
Received: 23 April 2019 / Revised: 7 May 2019 / Accepted: 9 May 2019 / Published: 12 May 2019
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Abstract
It is believed that renewable energy may become a dominant energy in the future. However, whether renewable energy can promote industry development like the use of fossil energy is still unknown. This paper uses social accounting matrix (SAM) multiplier model to analyze the [...] Read more.
It is believed that renewable energy may become a dominant energy in the future. However, whether renewable energy can promote industry development like the use of fossil energy is still unknown. This paper uses social accounting matrix (SAM) multiplier model to analyze the economic effects of renewable and coal energy in China. The transmission mechanisms of renewable and coal energy on production factors are also compared from the perspective of sector industry chain based on the structural path analysis (SPA) analysis method. We found that; renewable energy plays a stronger role in promoting the national economy than coal energy. Meanwhile, renewable energy can better promote the upgrading of the industrial structure compared with coal energy. Additionally, renewable energy affects economic development, mainly through the intermediate industries such as electrical machinery manufacturing and transportation, warehousing and service industries. These findings provide further insights into the influence path of renewable energy, which yields important implications for reasonably designing and choosing new energy development planning. Full article
(This article belongs to the Special Issue Economics of Sustainable and Renewable Energy Systems)
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Open AccessReview
Current Policy and Technology for Tidal Current Energy in Korea
Energies 2019, 12(9), 1807; https://doi.org/10.3390/en12091807
Received: 28 March 2019 / Revised: 6 May 2019 / Accepted: 8 May 2019 / Published: 12 May 2019
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Abstract
As global energy consumption continues to increase, the negative impact of global warming also grows. Therefore, eco-friendly energy policy is being established all over the world. Korea’s energy consumption problems are further complicated by the country’s high dependence on energy sourced overseas. Korean [...] Read more.
As global energy consumption continues to increase, the negative impact of global warming also grows. Therefore, eco-friendly energy policy is being established all over the world. Korea’s energy consumption problems are further complicated by the country’s high dependence on energy sourced overseas. Korean energy policy is evolving rapidly to address these problems. Korea has begun to phase out nuclear power and is focusing on developing new sources of renewable energy. So there has been substantial interest in the development of ocean energy. Of all ocean energy technologies, tidal current energy is the closest to the commercialization. Especially, the southwestern coast of Korea is the most promising candidate site for the development of tidal current energy owing to the abundant tidal current energy resource. Meanwhile, ocean energy policy is an important factor in determining the development of ocean energy. Thus, this paper presents the overview of the current status of policy and technology for the tidal current energy system in Korea. These policies explained in this paper can provide significant interest and motivation for the use of tidal current energy resources. Full article
(This article belongs to the Special Issue Energy Policy in South Korea)
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Open AccessArticle
Design and Simulation of an Energy Homeostaticity System for Electric and Thermal Power Management in a Building with Smart Microgrid
Energies 2019, 12(9), 1806; https://doi.org/10.3390/en12091806
Received: 22 April 2019 / Revised: 9 May 2019 / Accepted: 10 May 2019 / Published: 12 May 2019
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Abstract
Nowadays, microgrids are gaining importance in electric power generation and distribution environments due to their flexibility, versatility, scalability and the possibility of supplying ancillary services when connected to the grid. They allow for the customization of electric supply for very different types of [...] Read more.
Nowadays, microgrids are gaining importance in electric power generation and distribution environments due to their flexibility, versatility, scalability and the possibility of supplying ancillary services when connected to the grid. They allow for the customization of electric supply for very different types of consumers. Therefore, a new control model for power and energy management based on homeostaticity of electric power systems (EPS) is presented, which has been already analyzed and approved by ENEL Chile in its developmental stage. ENEL, the largest electric utility in the country, is interested in incorporating smart microgrids in the electricity distribution market, as part of a worldwide policy. Such microgrids are to be installed in buildings serviced by ENEL. To demonstrate the model’s utility, a Simulink model of a real microgrid is used, which is comprised of PV generation, energy storage, an air conditioning (AC) equipment and thermal storage of the building upon which the microgrid is installed. The behavior of every element is simulated, including the dynamic thermal model of the building in order to optimize energy management and power supply versus consumption. The behavior of the whole system is analyzed under different environmental profiles and energy consumption patterns using the proposed homeostaticity system. Full article
(This article belongs to the Section Smart Grids and Microgrids)
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Open AccessArticle
Modified Power Curves for Prediction of Power Output of Wind Farms
Energies 2019, 12(9), 1805; https://doi.org/10.3390/en12091805
Received: 31 March 2019 / Revised: 6 May 2019 / Accepted: 6 May 2019 / Published: 12 May 2019
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Abstract
Power curves are used to model power generation of wind turbines, which in turn is used for wind energy assessment and forecasting total wind farm power output of operating wind farms. Power curves are based on ideal uniform inflow conditions, however, as wind [...] Read more.
Power curves are used to model power generation of wind turbines, which in turn is used for wind energy assessment and forecasting total wind farm power output of operating wind farms. Power curves are based on ideal uniform inflow conditions, however, as wind turbines are installed in regions of heterogeneous and complex terrain, the effect of non-ideal operating conditions resulting in variability of the inflow must be considered. We propose an approach to include turbulence, yaw error, air density, wind veer and shear in the prediction of turbine power by using high resolution wind measurements. In this study, two modified power curves using standard ten-minute wind speed and high resolution one-second data along with a derived power surface were tested and compared to the standard operating curve for a 2.5 MW horizontal axis wind turbine. Data from supervisory control and data acquisition (SCADA) system along with wind speed measurements from a nacelle-mounted sonic anemometer and wind speed measurements from a nearby meteorological tower are used in the models. The results show that all of the proposed models perform better than the standard power curve while the power surface results in the most accurate power prediction. Full article
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Open AccessFeature PaperArticle
The Impact of Biodiesel Fuel on Ethanol/Diesel Blends
Energies 2019, 12(9), 1804; https://doi.org/10.3390/en12091804
Received: 15 March 2019 / Revised: 29 April 2019 / Accepted: 7 May 2019 / Published: 12 May 2019
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Abstract
The interest in biofuels was stimulated by the fossil fuel depletion and global warming. This work focuses on the impact of biodiesel fuel on ethanol/diesel (ED) fuel blends. The soybean methyl ester was used as a representative composition of typical biodiesel fuels. The [...] Read more.
The interest in biofuels was stimulated by the fossil fuel depletion and global warming. This work focuses on the impact of biodiesel fuel on ethanol/diesel (ED) fuel blends. The soybean methyl ester was used as a representative composition of typical biodiesel fuels. The heating and evaporation of ethanol–biodiesel–diesel (EBD) blends were investigated using the Discrete–Component (DC) model. The Cetane Number (CN) of the EBD blends was predicted based on the individual hydrocarbon contributions in the mixture. The mixture viscosity was predicted using the Universal Quasi-Chemical Functional group Activity Coefficients and Viscosity (UNIFAC–VISCO) method, and the lower heating value of the mixture was predicted based on the volume fractions and density of species and blends. Results revealed that a mixture of up to 15% biodiesel, 5% ethanol, and 80% diesel fuels had led to small variations in droplet lifetime, CN, viscosity, and heating value of pure diesel, with less than 1.2%, 0.2%, 2%, and 2.2% reduction in those values, respectively. Full article
(This article belongs to the Special Issue Biodiesel Production)
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Open AccessArticle
A Time-Efficient and Accurate Open Circuit Voltage Estimation Method for Lithium-Ion Batteries
Energies 2019, 12(9), 1803; https://doi.org/10.3390/en12091803
Received: 9 March 2019 / Revised: 7 May 2019 / Accepted: 8 May 2019 / Published: 12 May 2019
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Abstract
The open circuit voltage (OCV) of lithium-ion batteries is widely used in battery modeling, state estimation, and management. However, OCV is a function of state of charge (SOC) and battery temperature (Tbat) and is very hard to estimate in terms [...] Read more.
The open circuit voltage (OCV) of lithium-ion batteries is widely used in battery modeling, state estimation, and management. However, OCV is a function of state of charge (SOC) and battery temperature (Tbat) and is very hard to estimate in terms of time efficiency and accuracy. This is because two problems arise in normal operations: (1) Tbat changes with the current (I), which makes it very hard to obtain the data required to estimate OCV—terminal voltage (U) data of different I under the same Tbat; (2) the difference between U and OCV is a complex nonlinear function of I and is very difficult to accurately calculate. Therefore, existing methods have to design special experiments to avoid these problems, which are very time consuming. The proposed method consists of a designed test and a data processing algorithm. The test is mainly constant current tests (CCTs) of large I, which is time-efficient in obtaining data. The algorithm solves the two problems and estimates OCV accurately using the test data. Experimental results and analyses showed that experimental time was reduced and estimation accuracy was adequate. Full article
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Open AccessArticle
A Fast Method to Compute the Dynamic Response of Induction Motor Loads Considering the Negative-Sequence Components in Stability Studies
Energies 2019, 12(9), 1802; https://doi.org/10.3390/en12091802
Received: 25 April 2019 / Revised: 6 May 2019 / Accepted: 8 May 2019 / Published: 12 May 2019
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Abstract
This paper deals with the modeling and simulation of induction motor loads in power system stability studies considering the influence of the negative-sequence components. A practical method for computing the dynamic behavior of an induction motor under asymmetric faults is proposed and implemented [...] Read more.
This paper deals with the modeling and simulation of induction motor loads in power system stability studies considering the influence of the negative-sequence components. A practical method for computing the dynamic behavior of an induction motor under asymmetric faults is proposed and implemented in MATLAB. The accuracy of the proposed method is verified through classical electromagnetic transient simulations using the PSCAD/EMTDC software package. Compared with the existing traditional transient stability simulations, the method increases a little computational burden yet achieves much better simulation accuracy under asymmetric faults. Full article
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Open AccessArticle
A Mixing Behavior Study of Biomass Particles and Sands in Fluidized Bed Based on CFD-DEM Simulation
Energies 2019, 12(9), 1801; https://doi.org/10.3390/en12091801
Received: 19 March 2019 / Revised: 6 May 2019 / Accepted: 6 May 2019 / Published: 12 May 2019
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Abstract
The present paper studied the mixing characteristics of biomass and sands in a fluidized bed. A three dimensional model is calculated on the basis of computational fluid dynamics (CFD) and the discrete element method (DEM), while the lab-scale experiments under similar conditions are [...] Read more.
The present paper studied the mixing characteristics of biomass and sands in a fluidized bed. A three dimensional model is calculated on the basis of computational fluid dynamics (CFD) and the discrete element method (DEM), while the lab-scale experiments under similar conditions are conducted. To investigate the mixing behavior of biomass and sands, particle distribution, particles time averaged kinetic motion and the Lacey index are analyzed and the effects of gas velocity and biomass size are discussed. Gas velocity provides the basic motion for particle movement and biomass particles gain a lot more kinetic motion than sands due to their large size. The biomass mixing process in a horizontal direction is more sensitive to gas velocity than in a vertical direction. Biomass size could slightly affect the mixing quality and a well mixing in fluidized bed could be reached if the size of biomass to sands is smaller than 4 times. Full article
(This article belongs to the Section Bio-Energy)
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Open AccessFeature PaperArticle
Improvement of Organosolv Fractionation Performance for Rice Husk through a Low Acid-Catalyzation
Energies 2019, 12(9), 1800; https://doi.org/10.3390/en12091800
Received: 18 April 2019 / Revised: 8 May 2019 / Accepted: 9 May 2019 / Published: 11 May 2019
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Abstract
For the effective utilization of rice husk, organosolv fractionation was investigated to separate three main components (glucan, xylose, and lignin) with low acid concentration. Reaction temperatures of 170–190 °C, ethanol concentrations of 50%–70% (v/v), and sulfuric acid concentrations of [...] Read more.
For the effective utilization of rice husk, organosolv fractionation was investigated to separate three main components (glucan, xylose, and lignin) with low acid concentration. Reaction temperatures of 170–190 °C, ethanol concentrations of 50%–70% (v/v), and sulfuric acid concentrations of 0%–0.7% (w/v) were investigated, with the reaction time and liquid-to-solid ratio kept constant at 60 min and 10, respectively. The fractionation conditions for the efficient separation into the three components of rice husk were determined to be 180 °C, 60% (v/v) of ethanol, and 0.25% (w/v) of sulfuric acid. Under these fractionation conditions, 86.8% of the xylan and 77.5% of the lignin were removed from the rice husk, and xylose and lignin were obtained from the liquid in 67.6% and 49.8% yields, respectively. The glucan digestibility of the fractionated rice husk was 85.2% with an enzyme loading of 15 FPU (filter paper unit) of cellulase per g-glucan. Full article
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Open AccessArticle
Deep Learning Approach of Energy Estimation Model of Remote Laser Welding
Energies 2019, 12(9), 1799; https://doi.org/10.3390/en12091799
Received: 22 March 2019 / Revised: 28 April 2019 / Accepted: 1 May 2019 / Published: 11 May 2019
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Abstract
Due to concerns about energy use in production systems, energy-efficient processes have received much interest from the automotive industry recently. Remote laser welding is an innovative assembly process, but has a critical issue with the energy consumption. Robot companies provide only the average [...] Read more.
Due to concerns about energy use in production systems, energy-efficient processes have received much interest from the automotive industry recently. Remote laser welding is an innovative assembly process, but has a critical issue with the energy consumption. Robot companies provide only the average energy use in the technical specification, but process parameters such as robot movement, laser use, and welding path also affect the energy use. Existing literature focuses on measuring energy in standardized conditions in which the welding process is most frequently operated or on modularizing unified blocks in which energy can be estimated using simple calculations. In this paper, the authors propose an integrated approach considering both process variation and machine specification and multiple methods’ comparison. A deep learning approach is used for building the neural network integrated with the effects of process parameters and machine specification. The training dataset used is experimental data measured from a remote laser welding robot producing a car back door assembly. The proposed estimation model is compared with a linear regression approach and shows higher accuracy than other methods. Full article
(This article belongs to the Special Issue Energy Efficiency of Manufacturing Processes and Systems)
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Open AccessArticle
Energy Performance Comparison between Liquid-Desiccant-Assisted Air Conditioning System and Dedicated Outdoor Air System in Different Climatic Regions
Energies 2019, 12(9), 1798; https://doi.org/10.3390/en12091798
Received: 25 April 2019 / Revised: 8 May 2019 / Accepted: 9 May 2019 / Published: 11 May 2019
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Abstract
The main purpose of this research is to analyze and compare the energy performance of two different novel air conditioning systems; one is a dedicated outdoor air system (DOAS) with a parallel system and the other is a heat-pump-integrated liquid-desiccant and evaporative-cooling-assisted 100% [...] Read more.
The main purpose of this research is to analyze and compare the energy performance of two different novel air conditioning systems; one is a dedicated outdoor air system (DOAS) with a parallel system and the other is a heat-pump-integrated liquid-desiccant and evaporative-cooling-assisted 100% outdoor air system (HPLD-IDECOAS). It was assumed that office buildings served by each system were located in six cities representing four different climatic regions in China. The hourly thermal loads of the office buildings meeting the local building design codes of each selected city were predicted by the TRNSYS 18 software package. The hourly thermal load data were imported into the commercial engineering equation solver (EES) program to estimate the operating energy consumption of each system via detailed energy simulations performed using valid system simulation models. The results show that the HPLD-IDECOAS has higher energy-saving potential than the DOAS with a parallel system in climate regions with high humidity, whereas, in dry regions, the difference in energy consumption between the two systems was not significant. Full article
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Open AccessArticle
A Novel Nonintrusive Load Monitoring Approach based on Linear-Chain Conditional Random Fields
Energies 2019, 12(9), 1797; https://doi.org/10.3390/en12091797
Received: 28 March 2019 / Revised: 7 May 2019 / Accepted: 7 May 2019 / Published: 11 May 2019
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Abstract
In a real interactive service system, a smart meter can only read the total amount of energy consumption rather than analyze the internal load components for users. Nonintrusive load monitoring (NILM), as a vital part of smart power utilization techniques, can provide load [...] Read more.
In a real interactive service system, a smart meter can only read the total amount of energy consumption rather than analyze the internal load components for users. Nonintrusive load monitoring (NILM), as a vital part of smart power utilization techniques, can provide load disaggregation information, which can be further used for optimal energy use. In our paper, we introduce a new method called linear-chain conditional random fields (CRFs) for NILM and combine two promising features: current signals and real power measurements. The proposed method relaxes the independent assumption and avoids the label bias problem. Case studies on two open datasets showed that the proposed method can efficiently identify multistate appliances and detect appliances that are not easily identified by other models. Full article
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Open AccessArticle
A High-Performance Stochastic Fractal Search Algorithm for Optimal Generation Dispatch Problem
Energies 2019, 12(9), 1796; https://doi.org/10.3390/en12091796
Received: 19 April 2019 / Revised: 6 May 2019 / Accepted: 7 May 2019 / Published: 11 May 2019
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Abstract
This paper proposes applications of a modified stochastic fractal search algorithm (MSFS) to solve the economic load dispatch problem (ELD) in which valve-point effects, prohibited operating zones, power losses in all conductors, multi-fuel sources and other constraints of power system are taken into [...] Read more.
This paper proposes applications of a modified stochastic fractal search algorithm (MSFS) to solve the economic load dispatch problem (ELD) in which valve-point effects, prohibited operating zones, power losses in all conductors, multi-fuel sources and other constraints of power system are taken into consideration. The proposed method is first developed in the study by performing two modifications on two procedures of new solution generation from conventional stochastic fractal search (SFS). The first modification is used to change the strategy of producing new solutions of the first and the second update procedures while the second one is to newly update the worst solutions in the first update process and the best solutions in the second update process. These modifications have major influence on the solution search performance of the proposed method. All improvements of the proposed method can be illustrated by solving and analyzing results from various test systems with different system scales including 3-unit, 6-unit, 10-unit, and 20-unit systems. Comparison of results obtained by MSFS, SFS, and other existing methods indicates that the proposed MSFS method is more effective and robust than compared methods in terms of solution quality, high-quality solution search stability and convergence process. Consequently, the proposed method should be used as a very favorable optimization method for the ELD problem and it should be tried for other optimization problems in electrical engineering. Full article
(This article belongs to the Special Issue Applications of Heuristic Methods to Electrical Power Engineering)
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Open AccessArticle
Magnetic Field during Wireless Charging in an Electric Vehicle According to Standard SAE J2954
Energies 2019, 12(9), 1795; https://doi.org/10.3390/en12091795
Received: 23 April 2019 / Revised: 6 May 2019 / Accepted: 8 May 2019 / Published: 11 May 2019
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Abstract
The Society of Automotive Engineers (SAE) Recommended Practice (RP) J2954 (November 2017) was recently published to standardize the wireless power transfer (WPT) technology to recharge the battery of an electric vehicle (EV). The SAE J2954 RP establishes criteria for interoperability, electromagnetic compatibility (EMC), [...] Read more.
The Society of Automotive Engineers (SAE) Recommended Practice (RP) J2954 (November 2017) was recently published to standardize the wireless power transfer (WPT) technology to recharge the battery of an electric vehicle (EV). The SAE J2954 RP establishes criteria for interoperability, electromagnetic compatibility (EMC), electromagnetic field (EMF) safety, etc. The aim of this study was to predict the magnetic field behavior inside and outside an EV during wireless charging using the design criteria of SAE RP J2954. Analyzing the worst case configurations of WPT coils and EV bodyshell by a sophisticated software tool based on the finite element method (FEM) that takes into account the field reflection and refraction of the metal EV bodyshell, it is possible to numerically assess the magnetic field levels in the environment. The investigation was performed considering the worst case configuration—a small city car with a Class 2 WPT system of 7.7 kVA with WPT coils with maximum admissible ground clearance and offset. The results showed that the reference level (RL) of the International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines in terms of magnetic flux density was exceeded under and beside the EV. To mitigate the magnetic field, the currents flowing through the WPT coils were varied using the inductor-capacitor-capacitor (LCC) compensation instead of the traditional series-series (SS) compensation. The corresponding calculated field was compliant with the 2010 ICNIRP RL and presented a limited exceedance of the 1998 ICNIRP RL. Finally, the influence of the body width on the magnetic field behavior adopting maximum offset was investigated, demonstrating that the magnetic field emission in the environment increased as the ground clearance increased and as the body width decreased. Full article
(This article belongs to the Special Issue Wireless Power for Electric Vehicles)
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Open AccessArticle
Configuration Optimization and Performance Comparison of STHX-DDB and STHX-SB by A Multi-Objective Genetic Algorithm
Energies 2019, 12(9), 1794; https://doi.org/10.3390/en12091794
Received: 16 March 2019 / Revised: 17 April 2019 / Accepted: 7 May 2019 / Published: 11 May 2019
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Abstract
Based on the thermohydraulic calculation model verified in this study and Non-dominated Sorted Genetic Algorithm-II (NSGA-II), a multi-objective configuration optimization method is proposed, and the performances of shell-and-tube heat exchanger with disc-and-doughnut baffles (STHX-DDB) and shell-and-tube heat exchanger with segmental baffles (STHX-SB) are [...] Read more.
Based on the thermohydraulic calculation model verified in this study and Non-dominated Sorted Genetic Algorithm-II (NSGA-II), a multi-objective configuration optimization method is proposed, and the performances of shell-and-tube heat exchanger with disc-and-doughnut baffles (STHX-DDB) and shell-and-tube heat exchanger with segmental baffles (STHX-SB) are compared after optimization. The results show that, except in the high range of heat transfer capacity of 16.5–17 kW, the thermohydraulic performance of STHX-DDB is better. Tube bundle diameter, inside tube bundle diameter, number of baffles of STHX-DDB and tube bundle diameter, baffle cut, number of baffles of STHX-SB are chosen as design parameters, and heat transfer capacity maximization and shell-side pressure drop minimization are considered as common optimization objectives. Three optimal configurations are obtained for STHX-DDB and another three are obtained for STHX-SB. The optimal results show that all the six selected optimal configurations are better than the original configurations. For STHX-DDB and STHX-SB, compared with the original configurations, the heat transfer capacity of optimal configurations increases by 6.26% on average and 5.16%, respectively, while the shell-side pressure drop decreases by 44.33% and 19.16% on average, respectively. It indicates that the optimization method is valid and feasible and can provide a significant reference for shell-and-tube heat exchanger design. Full article
(This article belongs to the Special Issue Heat Exchangers for Waste Heat Recovery)
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Open AccessArticle
Optimal Design of a Novel ‘S-shape’ Impeller Blade for a Microbubble Pump
Energies 2019, 12(9), 1793; https://doi.org/10.3390/en12091793
Received: 13 April 2019 / Revised: 3 May 2019 / Accepted: 8 May 2019 / Published: 11 May 2019
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Abstract
The newly designed impeller blade, a so-called novel ‘S-shape’ blade, used for microbubble pumps has been introduced to enhance pump performance. Unlike a conventional blade having separated blades, like cantilever-shape blades, the newly designed impeller has a continuous blade, thus having a relatively [...] Read more.
The newly designed impeller blade, a so-called novel ‘S-shape’ blade, used for microbubble pumps has been introduced to enhance pump performance. Unlike a conventional blade having separated blades, like cantilever-shape blades, the newly designed impeller has a continuous blade, thus having a relatively robust structure as compared to a conventional impeller. The optimal blade design of the ‘S-shape’ blade has been demonstrated to obtain a higher pump efficiency. To analyze the three-dimensional flow field inside the pump by numerical simulation, a general analysis code, ANSYS CFX, is employed in the present work. The computed pump efficiency has a maximum error of 4 percent compared to the experimental data. The optimal design of the pump impeller blade is based on geometric constraints considering blade manufacturing, and uses three design variables: the number of blades, the blade thickness and the radius of the blade rib. The response surface method, a global optimization method, is employed to optimize the pump impeller blade. Throughout the blade optimization of the ‘S-shape’ blade, it is found that the chief influence on the pump efficiency is the number of the impeller blades. Pump efficiency, an object function, is increased by up to 35.3 percent, which corresponds to a 3.7 percent increase compared to the reference one. It is no use to say that the ‘S-shape’ blade having a continuously connected blade has more rigid characteristics. The larger pressure increases of the optimized pump along with the volute casing wall is observed from the middle position of the rotational direction, which comes from the increase of momentum energy due to larger circulating flow inside each blade passage as compared to the reference one. The detailed flow field inside the pump blades is also analyzed and compared. Full article
(This article belongs to the Section Energy and Environment)
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Open AccessArticle
Investigation of Thermal Comfort Responses with Fuzzy Logic
Energies 2019, 12(9), 1792; https://doi.org/10.3390/en12091792
Received: 20 April 2019 / Revised: 2 May 2019 / Accepted: 8 May 2019 / Published: 11 May 2019
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Abstract
In order to reduce the energy consumption of buildings a series of new heating, ventilation and air conditioning strategies, methods, and equipment are developed. The architectural trends show that office and educational buildings have large glazed areas, so the thermal comfort is influenced [...] Read more.
In order to reduce the energy consumption of buildings a series of new heating, ventilation and air conditioning strategies, methods, and equipment are developed. The architectural trends show that office and educational buildings have large glazed areas, so the thermal comfort is influenced both by internal and external factors and discomfort parameters may affect the overall thermal sensation of occupants. Different studies have shown that the predictive mean vote (PMV)—predictive percentage of dissatisfied (PPD) model poorly evaluates the thermal comfort in real buildings. At the University of Debrecen a new personalized ventilation system (ALTAIR) was developed. A series of measurements were carried out in order to test ALTAIR involving 40 subjects, out of which 20 female (10 young and 10 elderly) and 20 male (10 young and 10 elderly) persons. Based on the responses of subjects related to indoor environment quality, a new comfort index was determined using fuzzy logic. Taking into consideration the responses related to thermal comfort sensation and perception of odor intensity a new the fuzzy comfort index was 5.85 on a scale from 1–10. Full article
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