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Energies, Volume 15, Issue 1 (January-1 2022) – 393 articles

Cover Story (view full-size image): Public concern about environmental problems such as global climate change has recently grown, and various technologies have been considered. There is especially an increasing amount of interest in eco-friendly mobility that contributes to the reduction of global warming, and the eco-friendly mobility market is increasing rapidly. As eco-friendly mobility develops, the traction system of mobility is taking an electrical form. Therefore, mutual interference due to vibration and noise between each part is a problem. In this paper, we predict the vibration and noise caused by the electromagnetic vibration source based on the electromagnetic characteristic analysis of the traction motor, which is the core of the traction system, and understand its effects. View this paper
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29 pages, 10390 KiB  
Article
Joint Research on Aerodynamic Characteristics and Handling Stability of Racing Car under Different Body Attitudes
by Zhe Zhang, Qiang Wang, Shida Song, Chengchun Zhang, Luquan Ren and Yingchao Zhang
Energies 2022, 15(1), 393; https://doi.org/10.3390/en15010393 - 5 Jan 2022
Cited by 4 | Viewed by 5146
Abstract
With the rapid development of FSAE, the speed of racing cars has increased year by year. As the main research content of racing cars, aerodynamics has received extensive attention from foreign teams. For racing cars, the aerodynamic force on the aerodynamic device ultimately [...] Read more.
With the rapid development of FSAE, the speed of racing cars has increased year by year. As the main research content of racing cars, aerodynamics has received extensive attention from foreign teams. For racing cars, the aerodynamic force on the aerodynamic device ultimately acts on the tires through the transmission of the body and the suspension. When the wheel is subjected to the vertical load generated by the aerodynamic device, the ultimate adhesion capacity of the wheel is improved. Under changing conditions, racing wheels can withstand greater lateral and tangential forces. Therefore, the effects of aerodynamics have a more significant impact on handling stability. The FSAE racing car of Jilin University was taken as the research object, and this paper combines the wind tunnel test, the numerical simulation and the dynamics simulation of the racing system. The closed-loop design process of the aerodynamics of the FSAE racing car was established, and the joint study of aerodynamic characteristics and handling stability of racing car under different body attitudes was realized. Meanwhile, the FSAE car was made the modification of aerodynamic parameter on the basis of handling stability. The results show that, after the modification of the aerodynamic parameters, the critical speed of the car when cornering is increased, the maneuverability of the car is improved, the horoscope test time is reduced by 0.525 s, the downforce of the car is increased by 11.39%, the drag is reduced by 2.85% and the lift-to-drag ratio is increased by 14.70%. Moreover, the pitching moment is reduced by 82.34%, and the aerodynamic characteristics and aerodynamic efficiency of the racing car are obviously improved. On the basis of not changing the shape of the body and the aerodynamic kit, the car is put forward to shorten the running time of the car and improve the comprehensive performance of the car, so as to improve the performance of the car in the race. Full article
(This article belongs to the Section E: Electric Vehicles)
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22 pages, 4222 KiB  
Article
Comparative Life-Cycle Assessment of Liquefied Natural Gas and Diesel Tractor-Trailer in China
by Shuhan Hu and Hongyuan Chen
Energies 2022, 15(1), 392; https://doi.org/10.3390/en15010392 - 5 Jan 2022
Cited by 3 | Viewed by 3451
Abstract
Many countries, especially China, have extensively promoted liquefied natural gas (LNG) to replace diesel in heavy-duty vehicles for to achieve sustainable transport aims, including carbon peaks and neutrality. We developed a life-cycle calculation model for environmental load differences covering vehicle and fuel cycles [...] Read more.
Many countries, especially China, have extensively promoted liquefied natural gas (LNG) to replace diesel in heavy-duty vehicles for to achieve sustainable transport aims, including carbon peaks and neutrality. We developed a life-cycle calculation model for environmental load differences covering vehicle and fuel cycles to comprehensively compare the LNG tractor-trailer and its diesel counterpart in China on a full suite of environmental impacts. We found that the LNG tractor-trailer consumes less aluminum but more iron and energy; emits less nitrogen oxide, sulfur oxide, nonmethane volatile organic compounds, and particulate matter but more greenhouse gases (GHG) and carbon monoxide (CO); and causes less abiotic depletion potential, acidification potential, and human toxicity potential impacts but more global warming potential (GWP) and photooxidant creation potential (POCP) impacts. Poor fuel economy was found to largely drive the higher life-cycle GHG and CO emissions and GWP and POCP impacts of the LNG tractor-trailer. Switching to the LNG tractor-trailer could reduce carbon dioxide by 52.73%, GWP impact by 44.60% and POCP impact by 49.23% if it attains parity fuel economy with its diesel counterpart. Policymakers should modify the regulations on fuel tax and vehicle access, which discourage improvement in LNG engine efficiency and adopt incentive polices to develop the technologies. Full article
(This article belongs to the Collection Energy Transition towards Carbon Neutrality)
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21 pages, 4816 KiB  
Article
Dielectric Properties of Electrical Insulating Liquids for High Voltage Electric Devices in a Time-Varying Electric Field
by Peter Havran, Roman Cimbala, Juraj Kurimský, Bystrík Dolník, Iraida Kolcunová, Dušan Medveď, Jozef Király, Vladimír Kohan and Ľuboš Šárpataky
Energies 2022, 15(1), 391; https://doi.org/10.3390/en15010391 - 5 Jan 2022
Cited by 27 | Viewed by 3944
Abstract
The motivation to improve components in electric power equipment brings new proposals from world-renowned scientists to strengthen them in operation. An essential part of every electric power equipment is its insulation system, which must have the best possible parameters. The current problem with [...] Read more.
The motivation to improve components in electric power equipment brings new proposals from world-renowned scientists to strengthen them in operation. An essential part of every electric power equipment is its insulation system, which must have the best possible parameters. The current problem with mineral oil replacement is investigating and testing other alternative electrical insulating liquids. In this paper, we present a comparison of mineral and hydrocarbon oil (liquefied gas) in terms of conductivity and relaxation mechanisms in the complex plane of the Cole-Cole diagram and dielectric losses. We perform the comparison using the method of dielectric relaxation spectroscopy in the frequency domain at different intensities of the time-varying electric field 0.5 kV/m, 5 kV/m, and 50 kV/m. With the increasing intensity of the time-varying electric field, there is a better approximation of the Debye behavior in all captured polarization processes of the investigated oils. By comparing the distribution of relaxation times, mineral oil shows closer characteristics to Debye relaxation. From the point of view of dielectric losses at the main frequency, hydrocarbon oil achieves better dielectric properties at all applied intensities of the time-varying electric field, which is very important for practical use. Full article
(This article belongs to the Special Issue Modeling and Design of Electrical Machines and Devices in High Temperature)
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10 pages, 3569 KiB  
Article
First-Principles Study of Amorphous Al2O3 ALD Coating in Li-S Battery Electrode Design
by Jake A. Klorman, Qing Guo and Kah Chun Lau
Energies 2022, 15(1), 390; https://doi.org/10.3390/en15010390 - 5 Jan 2022
Cited by 5 | Viewed by 3225
Abstract
The Li-S battery is exceptionally appealing as an alternative candidate beyond Li-ion battery technology due to its promising high specific energy capacity. However, several obstacles (e.g., polysulfides’ dissolution, shuttle effect, high volume expansion of cathode, etc.) remain and thus hinder the commercialization of [...] Read more.
The Li-S battery is exceptionally appealing as an alternative candidate beyond Li-ion battery technology due to its promising high specific energy capacity. However, several obstacles (e.g., polysulfides’ dissolution, shuttle effect, high volume expansion of cathode, etc.) remain and thus hinder the commercialization of the Li-S battery. To overcome these challenges, a fundamental study based on atomistic simulation could be very useful. In this work, a comprehensive investigation of the adsorption of electrolyte (solvent and salt) molecules, lithium sulfide, and polysulfide (Li2Sx with 2 ≤x≤ 8) molecules on the amorphous Al2O3 atomic layer deposition (ALD) surface was performed using first-principles density functional theory (DFT) calculations. The DFT results indicate that the amorphous Al2O3 ALD surface is selective in chemical adsorption towards lithium sulfide and polysulfide molecules compared to electrolytes. Based on this work, it suggests that the Al2O3 ALD is a promising coating material for Li-S battery electrodes to mitigate the shuttling problem of soluble polysulfides. Full article
(This article belongs to the Special Issue Advance in Lithium-Sulfur Battery)
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38 pages, 5910 KiB  
Article
OC6 Phase Ia: CFD Simulations of the Free-Decay Motion of the DeepCwind Semisubmersible
by Lu Wang, Amy Robertson, Jason Jonkman, Jang Kim, Zhi-Rong Shen, Arjen Koop, Adrià Borràs Nadal, Wei Shi, Xinmeng Zeng, Edward Ransley, Scott Brown, Martyn Hann, Pranav Chandramouli, Axelle Viré, Likhitha Ramesh Reddy, Xiang Li, Qing Xiao, Beatriz Méndez López, Guillén Campaña Alonso, Sho Oh, Hamid Sarlak, Stefan Netzband, Hyunchul Jang and Kai Yuadd Show full author list remove Hide full author list
Energies 2022, 15(1), 389; https://doi.org/10.3390/en15010389 - 5 Jan 2022
Cited by 26 | Viewed by 5352
Abstract
Currently, the design of floating offshore wind systems is primarily based on mid-fidelity models with empirical drag forces. The tuning of the model coefficients requires data from either experiments or high-fidelity simulations. As part of the OC6 (Offshore Code Comparison Collaboration, Continued, with [...] Read more.
Currently, the design of floating offshore wind systems is primarily based on mid-fidelity models with empirical drag forces. The tuning of the model coefficients requires data from either experiments or high-fidelity simulations. As part of the OC6 (Offshore Code Comparison Collaboration, Continued, with Correlation, and unCertainty (OC6) is a project under the International Energy Agency Wind Task 30 framework) project, the present investigation explores the latter option. A verification and validation study of computational fluid dynamics (CFD) models of the DeepCwind semisubmersible undergoing free-decay motion is performed. Several institutions provided CFD results for validation against the OC6 experimental campaign. The objective is to evaluate whether the CFD setups of the participants can provide valid estimates of the hydrodynamic damping coefficients needed by mid-fidelity models. The linear and quadratic damping coefficients and the equivalent damping ratio are chosen as metrics for validation. Large numerical uncertainties are estimated for the linear and quadratic damping coefficients; however, the equivalent damping ratios are more consistently predicted with lower uncertainty. Some difference is observed between the experimental and CFD surge-decay motion, which is caused by mechanical damping not considered in the simulations that likely originated from the mooring setup, including a Coulomb-friction-type force. Overall, the simulations and the experiment show reasonable agreement, thus demonstrating the feasibility of using CFD simulations to tune mid-fidelity models. Full article
(This article belongs to the Special Issue Numerical Analysis, Field Testing and Experimental Assessment of Offshore Wind Turbines)
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38 pages, 6700 KiB  
Review
A Review of Modelling of the FCC Unit—Part II: The Regenerator
by Thabang W. Selalame, Raj Patel, Iqbal M. Mujtaba and Yakubu M. John
Energies 2022, 15(1), 388; https://doi.org/10.3390/en15010388 - 5 Jan 2022
Cited by 8 | Viewed by 3786
Abstract
Heavy petroleum industries, including the Fluid Catalytic Cracking (FCC) unit, are among some of the biggest contributors to global greenhouse gas (GHG) emissions. The FCC unit’s regenerator is where these emissions originate mostly, meaning the operation of FCC regenerators has come under scrutiny [...] Read more.
Heavy petroleum industries, including the Fluid Catalytic Cracking (FCC) unit, are among some of the biggest contributors to global greenhouse gas (GHG) emissions. The FCC unit’s regenerator is where these emissions originate mostly, meaning the operation of FCC regenerators has come under scrutiny in recent years due to the global mitigation efforts against climate change, affecting both current operations and the future of the FCC unit. As a result, it is more important than ever to develop models that are accurate and reliable at predicting emissions of various greenhouse gases to keep up with new reporting guidelines that will help optimise the unit for increased coke conversion and lower operating costs. Part 1 of this paper was dedicated to reviewing the riser section of the FCC unit. Part 2 reviews traditional modelling methodologies used in modelling and simulating the FCC regenerator. Hydrodynamics and kinetics of the regenerator are discussed in terms of experimental data and modelling. Modelling of constitutive parts that are important to the FCC unit, such as gas–solid cyclones and catalyst transport lines, are also considered. This review then identifies areas where the current generation of models of the regenerator can be improved for the future. Parts 1 and 2 are such that a comprehensive review of the literature on modelling the FCC unit is presented, showing the guidance and framework followed in building models for the unit. Full article
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24 pages, 3254 KiB  
Review
Prospects for the Development of the Russian Rare-Earth Metal Industry in View of the Global Energy Transition—A Review
by Alexey Cherepovitsyn and Victoria Solovyova
Energies 2022, 15(1), 387; https://doi.org/10.3390/en15010387 - 5 Jan 2022
Cited by 23 | Viewed by 5352
Abstract
Global energy transition trends are reflected not only in oil and gas market dynamics, but also in the development of related sectors. They influence the demand for various types of metals and minerals. It is well-known that clean technologies require far more metals [...] Read more.
Global energy transition trends are reflected not only in oil and gas market dynamics, but also in the development of related sectors. They influence the demand for various types of metals and minerals. It is well-known that clean technologies require far more metals than their counterparts relying on fossil fuels. Nowadays, rare-earth metals (REMs) have become part and parcel of green technologies as they are widely used in wind turbine generators, motors for electric vehicles, and permanent magnet generators, and there are no materials to substitute them. Consequently, growth in demand for this group of metals can be projected in the near future. The topic discussed is particularly relevant for Russia. On the one hand, current trends associated with the global energy transition affect the country’s economy, which largely depends on hydrocarbon exports. On the other hand, Russia possesses huge REM reserves, which may take the country on a low-carbon development path. However, they are not being exploited. The aim of this study is to investigate the prospects for the development of Russia’s rare-earth metal industry in view of the global energy transition. The study is based on an extensive list of references. The methods applied include content analysis, strategic management methods and instruments, as well as planning and forecasting. The article presents a comprehensive analysis of the global energy sector’s development, identifies the relationship between the REM market and modern green technologies, and elaborates the conceptual framework for the development of the REM industry in the context of the latest global tendencies. It also contains a critical analysis of the current trends in the Russian energy sector and the plans to develop the industry of green technologies, forecasts future trends in metal consumption within based on existing plans, and makes conclusions on future prospects for the development of the REM industry in Russia. Full article
(This article belongs to the Special Issue Sources and Markets of New Energy Minerals for Renewable Energy Generation and Storage)
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16 pages, 4789 KiB  
Article
A Comparative Study of Equivalent Circuit Models for Electro-Chemical Impedance Spectroscopy Analysis of Proton Exchange Membrane Fuel Cells
by Lei Zhao, Haifeng Dai, Fenglai Pei, Pingwen Ming, Xuezhe Wei and Jiangdong Zhou
Energies 2022, 15(1), 386; https://doi.org/10.3390/en15010386 - 5 Jan 2022
Cited by 22 | Viewed by 4358
Abstract
Electrochemical impedance spectroscopy is one of the important tools for the performance analysis and diagnosis of proton exchange membrane fuel cells. The equivalent circuit model is an effective method for electrochemical impedance spectroscopy resolution. In this paper, four typical equivalent circuit models are [...] Read more.
Electrochemical impedance spectroscopy is one of the important tools for the performance analysis and diagnosis of proton exchange membrane fuel cells. The equivalent circuit model is an effective method for electrochemical impedance spectroscopy resolution. In this paper, four typical equivalent circuit models are selected to comprehensively compare and analyze the difference in the fitting results of the models for the electrochemical impedance spectroscopy under different working conditions (inlet pressure, stoichiometry, and humidity) from the perspective of the fitting accuracy, change trend of the model parameters, and the goodness of fit. The results show that the fitting accuracy of the model with the Warburg element is the best for all under each working condition. When considering the goodness of fit, the model with constant phase components is the best choice for fitting electrochemical impedance spectroscopy under different inlet pressure and air stoichiometry. However, under different air humidity, the model with the Warburg element is best. This work can help to promote the development of internal state analysis, estimation, and diagnosis of the fuel cell based on the equivalent circuit modeling of electrochemical impedance spectroscopy. Full article
(This article belongs to the Collection Batteries, Fuel Cells and Supercapacitors Technologies)
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21 pages, 2798 KiB  
Review
Bio-Based Waste’ Substrates for Degraded Soil Improvement—Advantages and Challenges in European Context
by Malgorzata Kacprzak, Iwona Kupich, Anna Jasinska and Krzysztof Fijalkowski
Energies 2022, 15(1), 385; https://doi.org/10.3390/en15010385 - 5 Jan 2022
Cited by 24 | Viewed by 3366
Abstract
The area of degraded sites in the world is constantly expanding and has been a serious environmental problem for years. Such terrains are not only polluted, but also due to erosion, devoid of plant cover and organic matter. The degradation trends can be [...] Read more.
The area of degraded sites in the world is constantly expanding and has been a serious environmental problem for years. Such terrains are not only polluted, but also due to erosion, devoid of plant cover and organic matter. The degradation trends can be reversed by supporting remediation/reclamation processes. One of the possibilities is the introduction of biodegradable waste/biowaste substrates into the soil. The additives can be the waste itself or preformed substrates, such composts, mineral-organic fertilizers or biochar. In EU countries average value of compost used for land restoration and landfill cover was equal 4.9%. The transformation of waste in valuable products require the fulfillment of a number of conditions (waste quality, process conditions, law, local circumstances). Application on degraded land surface bio-based waste substrates has several advantages: increase soil organic matter (SOM) and nutrient content, biodiversity and activity of microbial soil communities and change of several others physical and chemical factors including degradation/immobilization of contaminants. The additives improve the water ratio and availability to plants and restore aboveground ecosystem. Due to organic additives degraded terrains are able to sequestrate carbon and climate mitigate. However, we identified some challenges. The application of waste to soil must comply with the legal requirements and meet the end of use criteria. Moreover, shorter or long-term use of bio-waste based substrate lead to even greater soil chemical or microbial contamination. Among pollutants, “emerging contaminants” appear more frequently, such microplastics, nanoparticles or active compounds of pharmaceuticals. That is why a holistic approach is necessary for use the bio-waste based substrate for rehabilitation of soil degraded ecosystems. Full article
(This article belongs to the Special Issue Biodegradable Waste as an Element of the Circular Economy–Smart Solutions)
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22 pages, 1299 KiB  
Review
Waste Heat Recovery Technologies Revisited with Emphasis on New Solutions, Including Heat Pipes, and Case Studies
by Paul Christodoulides, Rafaela Agathokleous, Lazaros Aresti, Soteris A. Kalogirou, Savvas A. Tassou and Georgios A. Florides
Energies 2022, 15(1), 384; https://doi.org/10.3390/en15010384 - 5 Jan 2022
Cited by 28 | Viewed by 6524
Abstract
Industrial processes are characterized by energy losses, such as heat streams rejected to the environment in the form of exhaust gases or effluents occurring at different temperature levels. Hence, waste heat recovery (WHR) has been a challenge for industries, as it can lead [...] Read more.
Industrial processes are characterized by energy losses, such as heat streams rejected to the environment in the form of exhaust gases or effluents occurring at different temperature levels. Hence, waste heat recovery (WHR) has been a challenge for industries, as it can lead to energy savings, higher energy efficiency, and sustainability. As a consequence, WHR methods and technologies have been used extensively in the European Union (EU) (and worldwide for that matter). The current paper revisits and reviews conventional WHR technologies, their use in all types of industry, and their limitations. Special attention is given to alternative “new” technologies, which are discussed for parameters such as projected energy and cost savings. Finally, an extended review of case studies regarding applications of WHR technologies is presented. The information presented here can also be used to determine target energy performance, as well as capital and installation costs, for increasing the attractiveness of WHR technologies, leading to the widespread adoption by industry. Full article
(This article belongs to the Special Issue Applications and New Technologies of Waste Heat Recovery)
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13 pages, 2150 KiB  
Article
Numerical Simulation of Operating Parameters of the Ground Source Heat Pump
by Filip Bartyzel, Tomasz Wegiel, Magdalena Kozień-Woźniak and Marek Czamara
Energies 2022, 15(1), 383; https://doi.org/10.3390/en15010383 - 5 Jan 2022
Cited by 2 | Viewed by 4740
Abstract
Due to the growing demand for new ecological, low-emission heat sources, there is a need to develop new tools for simulating the operating parameters and costs of the implemented solutions. The article analyses the existing solutions for the simulation of heat pump operation [...] Read more.
Due to the growing demand for new ecological, low-emission heat sources, there is a need to develop new tools for simulating the operating parameters and costs of the implemented solutions. The article analyses the existing solutions for the simulation of heat pump operation parameters, describes the requirements for a modern building—nZEB and proposes a simulation tool based on thermodynamic parameters of the refrigerant. The script allows for deriving simple linear equations that can be used for the overall simulation of a system in which the heat pump is a key part and the efficiency of the entire system depends on its performance. The developed numerical script allows for reproducing the Linde refrigeration cycle and the parameters of its characteristic points. To calibrate the simulation, historical data obtained from the SOPSAR system were used. These data were pre-cleaned (peaks and other obvious measurement errors were removed). The obtained numerical model in combination with ground and air temperatures, anticipated hot water consumption and energy losses of the building can be used to simulate the annual performance and energy consumption of the heat pump. The obtained linear models have an RSMD error of 8% compared to historical data from SOPSAR system for all sets of simulated temperatures. Full article
(This article belongs to the Special Issue Computational Thermal, Energy, and Environmental Engineering)
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19 pages, 5607 KiB  
Article
Chlorine Corrosion in a Low-Power Boiler Fired with Agricultural Biomass
by Danuta Król, Przemysław Motyl and Sławomir Poskrobko
Energies 2022, 15(1), 382; https://doi.org/10.3390/en15010382 - 5 Jan 2022
Cited by 15 | Viewed by 2619
Abstract
The selection of appropriate heat-resistant materials which are at the same time resistant to atmospheres rich in chlorine and its compounds is one of the most important current construction problems in steel boiler elements when using biomass fuels of agricultural origin. In the [...] Read more.
The selection of appropriate heat-resistant materials which are at the same time resistant to atmospheres rich in chlorine and its compounds is one of the most important current construction problems in steel boiler elements when using biomass fuels of agricultural origin. In the research presented here, an area was identified in the furnace of a 10 kW boiler where there was a potential risk of chlorine corrosion. This zone was determined based on numerical analysis of the combustion process; it is the zone with the highest temperatures and where the gas atmosphere conducive to the formation of chlorine corrosion centers. Subsequently, tests were carried out in the process environment of the combustion chamber of a 10 kW boiler (the fuel was barley straw) by placing samples of eight construction materials in a numerically-designated zone. These included samples of steel (coal boiler St41K, heat-resistant H25T and H24JS, and heat-resistant valve 50H21G9N4) as well as intermetallic materials based on phases (FeAl, Fe3Al, NiAl, and Ni3Al). The samples remained in the atmosphere of the boiler furnace for 1152 h at a temperature of 750–900 °C. After this time, the surfaces of the samples were subjected to SEM microscopy and scanning analysis. The results showed that the St41K boiler steel was not suitable for operation under the assumed conditions, and that a thick layer of complex corrosion products was visible on its surface. The least amount of corrosion damage was observed for the samples of 50H21G9N4 steel and intermetallic materials. Full article
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14 pages, 4047 KiB  
Article
Prediction and Optimization of the Cost of Energy Resources in Greek Public Hospitals
by Paraskevi N. Zaza, Anastasios Sepetis and Pantelis G. Bagos
Energies 2022, 15(1), 381; https://doi.org/10.3390/en15010381 - 5 Jan 2022
Cited by 7 | Viewed by 2950
Abstract
The continuous operation and the specialized conditions needed for safely delivering healthcare services make hospitals among the most expensive buildings. Several studies in different countries have investigated the potential role and contribution of macroscopic indices of hospitals in total energy requirements. In this [...] Read more.
The continuous operation and the specialized conditions needed for safely delivering healthcare services make hospitals among the most expensive buildings. Several studies in different countries have investigated the potential role and contribution of macroscopic indices of hospitals in total energy requirements. In this work, we tried to investigate the energy requirements of Greek hospitals in terms of cost. We collected data from all public hospitals in Greece over a 2 year period (2018–2019) and evaluated the contribution of various factors in the total energy cost. The data revealed large variability by region and by hospital, even regarding structures of the same category and size. The analysis also showed that structural and operational data of each hospital differently influence the hospitals’ energy requirements. Using regression methods, we developed two models for calculating annual energy costs. One only contains hospital structural data (number of beds, type of hospital, number of employees, and the non/use of alternative energy sources such as natural gas), and it reached an R² of 0.84. The second model contains not only structural but also operational data from each hospital (number of the internal patients, number of surgeries and number of medical imaging tests), and it reached an R² of 0.87. The former model is easier to compute since it only relies on data that can be easily gathered, but the latter has slightly better performance. These tools can help the Ministry of Health and hospitals’ management to identify the factors that contribute to the energy cost in order to plan targeted interventions, be well-prepared regarding budgeting, and be able to progressively measure, monitor, and improve the environmental footprint of hospitals by investing in renewable energy resources. Full article
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16 pages, 3027 KiB  
Article
Self-Heating of Biochar during Postproduction Storage by O2 Chemisorption at Low Temperatures
by Aekjuthon Phounglamcheik, Nils Johnson, Norbert Kienzl, Christoph Strasser and Kentaro Umeki
Energies 2022, 15(1), 380; https://doi.org/10.3390/en15010380 - 5 Jan 2022
Cited by 4 | Viewed by 3607
Abstract
Biochar is attracting attention as an alternative carbon/fuel source to coal in the process industry and energy sector. However, it is prone to self-heating and often leads to spontaneous ignition and thermal runaway during storage, resulting in production loss and health risks. This [...] Read more.
Biochar is attracting attention as an alternative carbon/fuel source to coal in the process industry and energy sector. However, it is prone to self-heating and often leads to spontaneous ignition and thermal runaway during storage, resulting in production loss and health risks. This study investigates biochar self-heating upon its contact with O2 at low temperatures, i.e., 50–300 °C. First, kinetic parameters of O2 adsorption and CO2 release were measured in a thermogravimetric analyzer using biochar produced from a pilot-scale pyrolysis process. Then, specific heat capacity and heat of reactions were measured in a differential scanning calorimeter. Finally, a one-dimensional transient model was developed to simulate self-heating in containers and gain insight into the influences of major parameters. The model showed a good agreement with experimental measurement in a closed metal container. It was observed that char temperature slowly increased from the initial temperature due to heat released during O2 adsorption. Thermal runaway, i.e., self-ignition, was observed in some cases even at the initial biochar temperature of ca. 200 °C. However, if O2 is not permeable through the container materials, the temperature starts decreasing after the consumption of O2 in the container. The simulation model was also applied to examine important factors related to self-heating. The results suggested that self-heating can be somewhat mitigated by decreasing the void fraction, reducing storage volume, and lowering the initial char temperature. This study demonstrated a robust way to estimate the cooling demands required in the biochar production process. Full article
(This article belongs to the Special Issue Advances in Solid Fuels Conversion to Enable the Global Energy Transitions)
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18 pages, 16864 KiB  
Article
Simulation and Flow Analysis of the Hole Diaphragm Labyrinth Seal at Several Whirl Frequencies
by Xiang Zhang, Yinghou Jiao, Xiuquan Qu, Guanghe Huo and Zhiqian Zhao
Energies 2022, 15(1), 379; https://doi.org/10.3390/en15010379 - 5 Jan 2022
Cited by 6 | Viewed by 2633
Abstract
The seal is designed to reduce leakage and improve the efficiency of gas turbine machines, and is an important technology that needs to be studied in gas turbine design. A series of seals were proposed to try to achieve this goal. However, due [...] Read more.
The seal is designed to reduce leakage and improve the efficiency of gas turbine machines, and is an important technology that needs to be studied in gas turbine design. A series of seals were proposed to try to achieve this goal. However, due to the complex fluid dynamic performance of the seal-rotor system, the seal structure can obtain both the best leakage performance and best rotordynamic performance. This paper presents a detailed flow analysis of the hole diaphragm labyrinth seal (HDLS) at several whirl frequencies and several rotation speeds. The pressure drop, velocity, turbulence kinetic energy and leakage performance of the HDLS were discussed by simulations. An interesting exponential–type relationship between rotation speeds and leakage flow at different whirl frequencies was observed by curve fitting technology. A reverse flow rate was proposed to describe such an unusual phenomenon. Such a relationship can be used to further establish the leakage model of the HDLS and other similar seals. Full article
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20 pages, 351 KiB  
Article
On the Assessment of e-Banking Websites Supporting Sustainable Development Goals
by Witold Chmielarz and Marek Zborowski
Energies 2022, 15(1), 378; https://doi.org/10.3390/en15010378 - 5 Jan 2022
Cited by 8 | Viewed by 2484
Abstract
The main aim of this article was to test the authors’ proprietary method (i.e., the conversion method applied to evaluate e-banking services that support sustainable development goals in households, communities, and society). The authors’ conversion method can be applied with the aim of [...] Read more.
The main aim of this article was to test the authors’ proprietary method (i.e., the conversion method applied to evaluate e-banking services that support sustainable development goals in households, communities, and society). The authors’ conversion method can be applied with the aim of maintaining a balance between households, producers, and public administration services in line with the principles of sustainable development of the information society in Poland. To achieve this goal, the authors identified the differences between the results obtained using the conversion method and the results produced by other methods such as TOPSIS, Promethee II, and PROSA involving the same group of respondents. A hypothesis was made about the existence of significant differences in the results obtained as part of the studies. The research was carried out on a sample of nearly 830 ratings concerning the 27 most popular electronic banks in Poland. As part of the survey, the respondents assessed 18 characteristics (attributes) of the selected banks using a simplified Likert scale. The study was conducted during the pandemic in Poland in 2020. The authors compared the results achieved in the case of the TOPSIS, Promethee II, and PROSA methods and the ones obtained with the application of the conversion method. Then, the ratings of the e-banking websites were arranged in descending order, and the distances between the positions in the rankings obtained by the conversion method and other methods were calculated. In addition, the R2 correlation coefficients were calculated for all combinations of the results received using individual methods. The results showed the greatest differences both in the absolute distances between the positions obtained in the ranking and the lowest value of the R2 correlation coefficient in the case of the conversion method in relation to the other methods. The limitation of the present research resulted from the fact that the study sample included respondents who were all members of the academic environment. The students analyzed in the study were part of a group supporting globalization processes where e-business solutions are widely used. However, the purchases of goods and services both local and foreign made by this group were often limited in scope and value due to a lack of funds. The research results indicate a potential need for improvement of the conversion method. Full article
(This article belongs to the Special Issue Sustainable Development: Policies, Challenges, and Further)
13 pages, 1423 KiB  
Article
Biogas Generation from Maize and Cocksfoot Growing in Degraded Soil Enriched with New Zeolite Substrate
by Mariola Chomczyńska, Małgorzata Pawłowska, Oliwia Szczepaniak and Ewelina Duma
Energies 2022, 15(1), 377; https://doi.org/10.3390/en15010377 - 5 Jan 2022
Cited by 2 | Viewed by 1821
Abstract
Degraded lands are potential areas for obtaining biomass which can serve as an energy source after its conversion into biogas. Thus, the studies on biogas production from maize and cocksfoot biomasses obtained from degraded soil supplemented with additions of new zeolite substrate (Z-ion [...] Read more.
Degraded lands are potential areas for obtaining biomass which can serve as an energy source after its conversion into biogas. Thus, the studies on biogas production from maize and cocksfoot biomasses obtained from degraded soil supplemented with additions of new zeolite substrate (Z-ion as the nutrient carrier) and on arable soil (reference soil) were carried out during batch digestion tests. It was found that the biogas and biomethane potentials and specific energy of the test species growing in degraded soil enriched with Z-ion additions (1% and 5% v/v in the cases of cocksfoot and maize, respectively) did not differ significantly from the values of these parameters that were found for the plants growing in arable soil. The application of Z-ion to the degraded soil (especially in a dose of 5% v/v) resulted in an increase in the nitrogen content and decrease (below the lower optimum value) in the C/N ratio in the plant biomass. However, these changes did not negatively influence the final values of the biogas or methane potentials or the specific energy found for the maize biomass. Therefore, the study results indicated the usefulness of Z-ion substrate for improving the growth conditions for energy crops in degraded soils and, as a consequence, obtaining a plant feedstock suitable for the digestion process. Full article
(This article belongs to the Topic Anaerobic Digestion Processes)
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15 pages, 3574 KiB  
Article
Experimental Validation of a Hydrostatic Transmission for Community Wind Turbines
by Biswaranjan Mohanty and Kim A. Stelson
Energies 2022, 15(1), 376; https://doi.org/10.3390/en15010376 - 5 Jan 2022
Cited by 11 | Viewed by 2340
Abstract
Hydrostatic transmissions are commonly used in heavy-duty equipment for their design flexibility and superior power density. Compared to a conventional wind turbine transmission, a hydrostatic transmission (HST) is a lighter, more reliable, cheaper, continuously variable alternative for a wind turbine. In this paper, [...] Read more.
Hydrostatic transmissions are commonly used in heavy-duty equipment for their design flexibility and superior power density. Compared to a conventional wind turbine transmission, a hydrostatic transmission (HST) is a lighter, more reliable, cheaper, continuously variable alternative for a wind turbine. In this paper, for the first time, a validated dynamical model and controlled experiment have been used to analyze the performance of a hydrostatic transmission with a fixed-displacement pump and a variable-displacement motor for community wind turbines. From the dynamics of the HST, a pressure control strategy is designed to maximize the power capture. A hardware-in-the-loop simulation is developed to experimentally validate the performance and efficiency of the HST drive train control in a 60 kW virtual wind turbine environment. The HST turbine is extensively evaluated under steady and time-varying wind on a state-of-the-art power regenerative hydrostatic dynamometer. The proposed controller tracks the optimal tip-speed ratio to maximize power capture. Full article
(This article belongs to the Special Issue Advancement in Wind Turbine Technology)
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27 pages, 3409 KiB  
Review
Methods of Thermal Treatment of Radioactive Waste
by Leon Fuks, Irena Herdzik-Koniecko, Katarzyna Kiegiel, Agnieszka Miskiewicz and Grazyna Zakrzewska-Koltuniewicz
Energies 2022, 15(1), 375; https://doi.org/10.3390/en15010375 - 5 Jan 2022
Cited by 12 | Viewed by 4772
Abstract
Throughout the world, and especially in the European Union, numerous technologies for the thermal treatment of radioactive waste are available or being developed. These technologies can be applied to a large range of different radioactive waste streams, including non-standard types of waste that [...] Read more.
Throughout the world, and especially in the European Union, numerous technologies for the thermal treatment of radioactive waste are available or being developed. These technologies can be applied to a large range of different radioactive waste streams, including non-standard types of waste that present specific waste management challenges. Thermal treatment can result in a significant reduction in volume and hazard, which are beneficial for safe storage and disposal. Thermal treatment also removes organic material that can form complexing agents and increase the mobility of radionuclides in the landfill. In the paper, basic thermal techniques are presented, and some examples of the installations are shown. Common knowledge of these methods may result in an increased public acceptance of nuclear energy in a country just introducing it, as Poland is. Full article
(This article belongs to the Special Issue Storage and Disposal Options for Nuclear Waste)
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22 pages, 11806 KiB  
Article
Extending DC Bus Utilization for Induction Motors with Stator Flux Oriented Direct Torque Control
by Tomas Esparza Sola, Huang-Jen Chiu, Yu-Chen Liu and Arief Noor Rahman
Energies 2022, 15(1), 374; https://doi.org/10.3390/en15010374 - 5 Jan 2022
Cited by 9 | Viewed by 2153
Abstract
This paper presents a method to extend the DC bus utilization on an induction motor (IM) by using a combination of Space-Vector Modulated Direct Torque Control (DTC–SVM) and conventional DTC. The scheme proposed in this paper exploits the advantages of both control methods. [...] Read more.
This paper presents a method to extend the DC bus utilization on an induction motor (IM) by using a combination of Space-Vector Modulated Direct Torque Control (DTC–SVM) and conventional DTC. The scheme proposed in this paper exploits the advantages of both control methods. During the linear region, it allows for a low torque ripple and low current harmonic distortion (THD). During the overmodulation region, it allows for the fastest torque response up to the six-step operation region. In both regions, there is complete independence of the motor parameters. The paper describes a way to provide a smooth transition between the two control schemes. Non-linearities affect the stator flux angle estimation, which leads to the inability to decouple torque and flux. To overcome this problem, a novel PI-based control scheme as well as a simplification on the decoupling terms’ calculation are proposed. Simulation and experimental results are presented to verify the feasibility of the proposed method. Full article
(This article belongs to the Special Issue Design and Control of Electrical Motor Drives II)
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24 pages, 2032 KiB  
Article
Multi-Agent Real-Time Advanced Metering Infrastructure Based on Fog Computing
by Ivan Popović, Aleksandar Rakić and Ivan D. Petruševski
Energies 2022, 15(1), 373; https://doi.org/10.3390/en15010373 - 5 Jan 2022
Cited by 10 | Viewed by 3380
Abstract
This effort to make the power grid more intelligent is tightly coupled with the deployment of advanced metering infrastructure (AMI) as an integral part of the future vision of smart grid. The goal of AMI is to provide necessary information for the consumers [...] Read more.
This effort to make the power grid more intelligent is tightly coupled with the deployment of advanced metering infrastructure (AMI) as an integral part of the future vision of smart grid. The goal of AMI is to provide necessary information for the consumers and utilities to accurately monitor and manage energy consumption and pricing in real time. Immediate benefits are enhanced transparency and efficiency of energy usage and the improvement of customer services. Although the road map toward successful AMI deployment is clearly defined, many challenges and issues are to be solved regarding the design of AMI. In this paper, a multi-agent AMI based on the fog-computing approach is presented. Architecture follows structural decomposition of AMI functionalities encapsulated in a form of local and area-specific service components that reside at the different tiers of hierarchically organized AMI deployment. Fog computing concepts provide the framework to effectively solve the problems of creating refined and scalable solutions capable of meeting the requirements of the AMI as a part of future smart grid. On the other hand, agent-based design enables concurrent execution of AMI operations across the distributed system architecture, in the same time improving performance of its execution and preserving the scalability of the AMI solution. The real-time performance of the proposed AMI solution, related to the periodic and on-demand acquisition of metering data from the connected electricity meters, was successfully verified during one year of pilot project operation. The detailed analysis of the performance of AMI operation regarding data collection, communication and data availability across the deployed pilot AMI, covering several transformer station areas with diverse grid topologies, is also presented. Full article
(This article belongs to the Special Issue Challenges and Research Trends of Smart Grids and Distribution Network)
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19 pages, 3753 KiB  
Article
The Impact of Alumina Nanofluids on Pool Boiling Performance on Biphilic Surfaces for Cooling Applications
by Ricardo Santos, Ana Sofia Moita, Ana Paula C. Ribeiro and António Luís N. Moreira
Energies 2022, 15(1), 372; https://doi.org/10.3390/en15010372 - 5 Jan 2022
Cited by 6 | Viewed by 1706
Abstract
This work aims to study the impact of nanofluids with alumina particles on pool boiling performance. Unlike most studies, which use a trial-and-error approach to improve boiling performance parameters, this study details the possible effects of nanoparticles on the effective mechanisms of boiling [...] Read more.
This work aims to study the impact of nanofluids with alumina particles on pool boiling performance. Unlike most studies, which use a trial-and-error approach to improve boiling performance parameters, this study details the possible effects of nanoparticles on the effective mechanisms of boiling and heat transfer. For this purpose, biphilic surfaces (hydrophilic surfaces with superhydrophobic spots) were used, which allow the individual analysis of bubbles. Surfaces with different configurations of superhydrophobic regions were used. The thermophysical properties of fluids only vary slightly with increasing nanoparticle concentration. The evolution of the dissipated heat flux and temperature profiles for a nucleation time frame is independent of the fluid and imposed heat flux. It can be concluded that the optimal concentration of nanoparticles is 3 wt%. Using this nanoparticle concentration leads to lower surface temperature values than those obtained with water, the reference fluid. This is due to the changes in the balance of forces in the triple line, induced by increased wettability as a consequence of the deposited particles. Wherefore, smaller and more frequent bubbles are formed, resulting in higher heat transfer coefficients. This effect, although relevant, is still of minor importance when compared to that of the use of biphilic surfaces. Full article
(This article belongs to the Special Issue Industrial Applications of Nanofluids in the Energy Sector)
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31 pages, 13954 KiB  
Article
A Smart Energy Recovery System to Avoid Preheating in Gas Grid Pressure Reduction Stations
by Piero Danieli, Massimo Masi, Andrea Lazzaretto, Gianluca Carraro and Gabriele Volpato
Energies 2022, 15(1), 371; https://doi.org/10.3390/en15010371 - 5 Jan 2022
Cited by 6 | Viewed by 2540
Abstract
Preheating is often required to prevent hydrate formation during the pressure reduction process in a natural gas distribution network’s pressure reduction station. This paper examines an energy recovery method to avoid the cost and energy consumption of this preheating. The primary aim is [...] Read more.
Preheating is often required to prevent hydrate formation during the pressure reduction process in a natural gas distribution network’s pressure reduction station. This paper examines an energy recovery method to avoid the cost and energy consumption of this preheating. The primary aim is to assess the techno-economic feasibility of an energy recovery system based on the Ranque–Hilsch vortex tube coupled to a heat exchanger for large-scale application to the gas grid. To this end, a techno-economic model of the entire energy recovery system was included in an optimisation procedure. The resulting design minimises the payback period (PP) when the system is applied to the pressure reduction stations belonging to a particular gas grid. The pressure reduction stations always operate at an outlet pressure above atmospheric pressure. However, available performance models for the Ranque–Hilsch vortex tube do not permit prediction at backpressure operation. Therefore, a novel empirical model of the device is proposed, and a cost function derived from several manufacturer quotations is introduced for the first time, to evaluate the price of the Ranque–Hilsch vortex tubes. Finally, a nearly complete set of pressure reduction stations belonging to the Italian natural gas grid was chosen as a case study using actual operating parameters collected by each station’s grid manager. The results indicate that the environmental temperature strongly affects the technical and economic feasibility of the proposed energy recovery system. In general, pressure reduction stations operating at an ambient temperature above 0 °C are economically desirable candidates. In addition, the higher the energy recovery system convenience, the higher the flow rate and pressure drop managed by the station. In the Italian case study, 95% of preheating costs could be eliminated with a PP of fewer than 20 years. A 40% preheating cost saving is still possible if the maximum PP is limited to 10 years, and a small but non-negligible 3% of preheating costs could be eliminated with a PP of fewer than 4.5 years. Full article
(This article belongs to the Special Issue Advances in Natural Gas Engineering)
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18 pages, 447 KiB  
Review
Forecasting of Wind and Solar Farm Output in the Australian National Electricity Market: A Review
by John Boland, Sleiman Farah and Lei Bai
Energies 2022, 15(1), 370; https://doi.org/10.3390/en15010370 - 5 Jan 2022
Cited by 2 | Viewed by 2775
Abstract
Accurately forecasting the output of grid connected wind and solar systems is critical to increasing the overall penetration of renewables on the electrical network. This is especially the case in Australia, where there has been a massive increase in solar and wind farms [...] Read more.
Accurately forecasting the output of grid connected wind and solar systems is critical to increasing the overall penetration of renewables on the electrical network. This is especially the case in Australia, where there has been a massive increase in solar and wind farms in the last 15 years, as well as in roof top solar, both domestic and commercial. For example, in 2020, 27% of the electricity in Australia was from renewable sources, and in South Australia almost 60% was from wind and solar. In the literature, there has been extensive research reported on solar and wind resource, entailing both point and interval forecasts, but there has been much less focus on the forecasting of output from wind and solar systems. In this review, we canvass both what has been reported and also what gaps remain. In the case of the latter topic, there are numerous aspects that are not well dealt with in the literature. We have added discussion on the value of forecasts, rather than just focusing on forecast skill. Further, we present a section on how to deal with conditionally changing variance, a topic that has little focus in the literature. One other topic may be particularly important in Australia at the moment, but may become more widespread. This is how to deal with the concept of a clear sky output from a solar farm when the field is oversized compared to the inverter capacity, resulting in a plateau for the output. Full article
(This article belongs to the Special Issue Advances in Wind and Solar Farm Forecasting)
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17 pages, 60236 KiB  
Article
Improving Energy Efficiency by Utilizing Wetted Cellulose Pads in Passive Cooling Systems
by Ebrahim Morady, Madjid Soltani, Farshad Moradi Kashkooli, Masoud Ziabasharhagh, Armughan Al-Haq and Jatin Nathwani
Energies 2022, 15(1), 369; https://doi.org/10.3390/en15010369 - 5 Jan 2022
Cited by 4 | Viewed by 2397
Abstract
The effectiveness of using wetted cellulose pads on improving the performance of two conventional passive cooling systems has been evaluated. First, an experimental design was developed to determine the impact of using a wetted cellulose pad on the temperature and velocity of the [...] Read more.
The effectiveness of using wetted cellulose pads on improving the performance of two conventional passive cooling systems has been evaluated. First, an experimental design was developed to determine the impact of using a wetted cellulose pad on the temperature and velocity of the airflow. A cellulose pad (7090 model) with a cross-sectional area of 0.5 × 0.5 m2 and three different thicknesses of 10, 15, and 30 cm were selected and tested. The results indicated that using wetted cellulose pads with thicknesses ranging from 10–30 cm decreased the outlet airflow temperature from 11.3 to 13.7 °C on average. For free airflow at velocity 3.5 m/s, the outlet airflow velocity from the wetted cellulose pad decreased to 0.9, 0.7 and 0.6 m/s, respectively, for cellulose pads with thicknesses of 10, 15, and 30 cm. By applying experimental results on a psychrometric chart, the humidity ratio of outlet airflow was obtained between 40–70%. The study established airflow velocity as the critical parameter in passive cooling systems. With the novel concept of combining wetted cellulose pads for passive cooling systems (i.e., wind catchers and induced ventilation), there is good potential to reduce the energy requirements for thermal comfort in buildings in regions with a hot and arid climate. Full article
(This article belongs to the Section A3: Wind, Wave and Tidal Energy)
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15 pages, 3841 KiB  
Article
Possibility of Advanced Modified-Silica-Based Porous Materials Utilisation in Water Adsorption Processes—A Comparative Study
by Karol Sztekler, Agata Mlonka-Mędrala, Nezar H. Khdary, Wojciech Kalawa, Wojciech Nowak and Łukasz Mika
Energies 2022, 15(1), 368; https://doi.org/10.3390/en15010368 - 5 Jan 2022
Cited by 6 | Viewed by 2287
Abstract
Due to a high risk of power outages, a heat-driven adsorption chillers are gaining the attention. To increase the efficiency of the chiller, new adsorbents must be produced and examined. In this study, four newly developed silica–based porous materials were tested and compared [...] Read more.
Due to a high risk of power outages, a heat-driven adsorption chillers are gaining the attention. To increase the efficiency of the chiller, new adsorbents must be produced and examined. In this study, four newly developed silica–based porous materials were tested and compared with silica gel, an adsorber commonly paired with water. Extended sorption tests using mercury intrusion porosimetry, gas adsorption, and dynamic vapor sorption were performed. The morphology of the samples was determined using a scanning electron microscope. The thermal properties were defined using simultaneous thermal analysis and a laser flash method. Metal organic silica (MOS) nanocomposites analysed in this study had thermal properties similar to those of commonly used silica gel. MOS samples have a thermal diffusivity coefficient in the range of 0.17–0.25 mm2/s, whereas silica gel of about 0.2 mm2/s. The highest water adsorption capacity was measured for AFSMo-Cu and equal to 33–35%. For narrow porous silica gel mass uptake was equal about 25%. In the case of water adsorption, it was observed that the pore size of the sorbent is essential, and adsorbents with pore sizes higher than 5 nm, are most recommended in working pairs with water. Full article
(This article belongs to the Special Issue Adsorption Desalination and Cooling Systems: Advances in Design, Modeling and Performance)
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20 pages, 8634 KiB  
Article
Development and Test of a Novel Electronic Radiator Thermostat with a Return Temperature Limiting Function
by Michele Tunzi, Dorte Skaarup Østergaard and Svend Svendsen
Energies 2022, 15(1), 367; https://doi.org/10.3390/en15010367 - 5 Jan 2022
Cited by 3 | Viewed by 1983
Abstract
Automated hydronic balancing in space heating systems is crucial for the fourth-generation district heating transition. The current manual balancing requires labor- and time-consuming activities. This article presents the field results of an innovative electronic radiator thermostat tested on two Danish multi-family buildings. The [...] Read more.
Automated hydronic balancing in space heating systems is crucial for the fourth-generation district heating transition. The current manual balancing requires labor- and time-consuming activities. This article presents the field results of an innovative electronic radiator thermostat tested on two Danish multi-family buildings. The prototypes had an additional return temperature sensor on each radiator and an algorithm was used to accurately control valve opening to ensure automated hydronic balancing. The results highlighted that the new thermostat performed as expected and helped secure the cooling of district heating temperatures —defined as the difference between supply and return temperature—4–12 °C higher during the test compared to results obtained in 2020, when the prototypes were replaced with state-of-the-art thermostats in the first building. The measurements from the other building illustrated how only two uncontrolled radiators out of 175 could contaminate the overall return temperature. The remote connection of the thermostats helped pinpoint the faults in the heating system, although the end-users were not experiencing any discomfort, and secure, after fixing the problems, a return temperature of 35 °C. Future designs may consider integrating a safety functionality to close the valve or limit the flow in case of damage or malfunction to avoid a few radiators compromising the low-temperature operation of an entire building before the cause of the problem has been identified. Full article
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18 pages, 2947 KiB  
Article
Modeling Multivalued Dynamic Series of Financial Indexes on the Basis of Minimax Approximation
by Zahid Mamedov, Irina Vygodchikova, Ayaz Aliev, Lira Gurieva and Natalia Rud
Energies 2022, 15(1), 366; https://doi.org/10.3390/en15010366 - 5 Jan 2022
Cited by 1 | Viewed by 1841
Abstract
In this article, the problem of modeling a time series using the Minimax method is considered. The expediency of using Minimax to identify points of change in trends and the range of changes in the graphical figures of technical analysis is justified. Spline [...] Read more.
In this article, the problem of modeling a time series using the Minimax method is considered. The expediency of using Minimax to identify points of change in trends and the range of changes in the graphical figures of technical analysis is justified. Spline approximation of the dynamic process with range constraints was performed to improve the quality of the model. Investors are advised to refrain from making hasty decisions in favor of holding reliable shares (such as PJSC Novatek shares), rather than selling them. The purchase of new shares should be carefully analyzed. Through an approximation of the dynamic number of the applicable optimization problem of minimizing the maximum Hausdorff distances between the ranges of the dynamic series and the values of the approximating function, the applied approach can provide reliable justification for signals to buy shares. Energy policy occupies the highest place in the list of progress ratings according to news analytics of businesses related to the energy sector of the economy. At the same time, statistical indicators and technologies of expert developments in this field, including intellectual analysis, can become an important basis for the development of a robotic knowledge program in the field under study, an organic addition to which is the authors’ methodology of development in energy economics as in energy policy. This paper examines the model of approximation of the multivalued time series of PJSC Novatek, represented as a series of ranges of numerical values of the indicators of financial markets, with constraints on the approximating function. The authors consider it advisable for promising companies to apply this approach for successful long-term investment. Full article
(This article belongs to the Special Issue Innovative Economic Technologies and Policies in the Energy Sector)
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18 pages, 5822 KiB  
Article
Mixed H2/H∞ Optimal Voltage Control Design for Smart Transformer Low-Voltage Inverter
by Wei Hu, Yu Shen, Zhichun Yang and Huaidong Min
Energies 2022, 15(1), 365; https://doi.org/10.3390/en15010365 - 5 Jan 2022
Cited by 2 | Viewed by 1729
Abstract
The smart transformer has been widely applied for the integration of renewables and loads. For the smart transformer application, the voltage control of low-voltage inverter is important for feeding the load. In this paper, a multi-objective optimization control design approach which comprehensively considers [...] Read more.
The smart transformer has been widely applied for the integration of renewables and loads. For the smart transformer application, the voltage control of low-voltage inverter is important for feeding the load. In this paper, a multi-objective optimization control design approach which comprehensively considers all aspects of indexes, such as linear quadratic (LQ) index, H∞ norm, and closed-loop poles placement, is proposed based on the linear matrix inequality (LMI) solution. The proposed approach is able to alleviate the weight of the designer from the tedious design process of the multiple resonant controllers and the selection of the weighting matrix for the LQ control. Besides that, some excellent performances such as fast recovering time, low total harmonic distortion (THD) and high robustness are achieved by the proposed approach. The THD are 0.5% and 1.7% for linear and non-linear loads, respectively. The voltage drop for linear load step is reduced to 10 V. The proposed approach is applied to a 5 kVA three-phase inverter to yield an optimal control law. Results from the simulation and experiment presented herein will illustrate and validate the proposed approach. Full article
(This article belongs to the Special Issue Smart Transformers and Their Role in Smart Grids)
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15 pages, 12654 KiB  
Article
Bio-Crude Production from Protein-Extracted Grass Residue through Hydrothermal Liquefaction
by Saqib Sohail Toor, Ayaz Ali Shah, Kamaldeep Sharma, Tahir Hussain Seehar, Thomas Helmer Pedersen and Lasse Aistrup Rosendahl
Energies 2022, 15(1), 364; https://doi.org/10.3390/en15010364 - 5 Jan 2022
Cited by 9 | Viewed by 2652
Abstract
In the present study, the protein-extracted grass residue (press cake) was processed through hydrothermal liquefaction under sub and supercritical temperatures (300, 350 and 400 °C) with and without using a potassium carbonate catalyst. The results revealed that bio-crude yield was influenced by both [...] Read more.
In the present study, the protein-extracted grass residue (press cake) was processed through hydrothermal liquefaction under sub and supercritical temperatures (300, 350 and 400 °C) with and without using a potassium carbonate catalyst. The results revealed that bio-crude yield was influenced by both temperature and the catalyst. The catalyst was found to be effective at 350 °C (350 Cat) for enhancing the bio-crude yield, whereas supercritical state in both catalytic and non-catalytic conditions improved the quality of bio-crude with reasonable HHVs (33 to 36 MJ/kg). The thermal behaviour of bio-crude was analysed and higher volatile contents (more than 50% under the range of 350 °C) were found at supercritical conditions. The overall TOC values in the residual aqueous phase varied from 22 to 38 g/L. Higher carbon loss was noticed in the aqueous phase in supercritical conditions. Furthermore, GCMS analysis showed ketones, acids and ester, aromatics and hydrocarbon with negligible nitrogen-containing compounds in bio-crude. In conclusion, the catalytic conversion of grass residue under subcritical conditions (350 Cat) is favourable in terms of high bio-crude yield, however, supercritical conditions promote the deoxygenation of oxygen-containing compounds in biomass and thus improve HHVs of bio-crude. Full article
(This article belongs to the Special Issue Hydrothermal Liquefaction for Aviation and Maritime Sustainable Fuels)
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