Energies

21 pages, 9661 KiB

Open AccessArticle

Monitoring the Geometry Morphology of Complex Hydraulic Fracture Network by Using a Multiobjective Inversion Algorithm Based on Decomposition

by Liming Zhang, Lili Xue, Chenyu Cui, Ji Qi, Jijia Sun, Xingyu Zhou, Qinyang Dai and Kai Zhang

Energies 2021, 14(16), 5216; https://doi.org/10.3390/en14165216 - 23 Aug 2021

Viewed by 2168

Abstract

The fracturing technique is widely used in many fields. Fracture has a greater impact on the movement of fluids in formations. Knowing information about a fracture is key to judging its effect, but detailed information about complex fracture networks is difficult to obtain. [...] Read more.

The fracturing technique is widely used in many fields. Fracture has a greater impact on the movement of fluids in formations. Knowing information about a fracture is key to judging its effect, but detailed information about complex fracture networks is difficult to obtain. In this paper, we propose a new method to describe the shape of a complex fracture network. This method is based on microseismic results and uses the L-system to establish a method for characterizing a complex fracture network. The method also combines with decomposition to construct a new method called the multiobjective fracture network inversion algorithm based on decomposition (MOFNIAD). The coverage of microseismic monitoring results and the degree of fitting of production data are the two objective functions of the inversion fracture network. The multiobjective fracture network inversion algorithm can be optimized to obtain multiple optimal solutions that meet different target weights. Therefore, this paper established a multischeme decision method that approached the ideal solution, sorting technology and AHP to provide theoretical guidance for finding a more ideal fracture network. According to the error of microseismic monitoring results, we established two cases of fracture to verify the proposed method. Judging from the results of the examples, the fracture network finally obtained was similar to actual fractures. Full article

► Show Figures

Figure 1

32 pages, 9435 KiB

Open AccessArticle

Minimization of Output Voltage Ripple of Two-Phase Interleaved Buck Converter with Active Clamp

by Yeu-Torng Yau, Kuo-Ing Hwu and Jenn-Jong Shieh

Energies 2021, 14(16), 5215; https://doi.org/10.3390/en14165215 - 23 Aug 2021

Cited by 4 | Viewed by 2450

Abstract

A control technique combining pulse width modulation (PWM) and pulse amplitude modulation (PAM) is presented herein to reduce the output voltage ripple of the converter as little as possible. Such a converter requires a two-stage cascaded structure. The first stage is the buck-boost [...] Read more.

A control technique combining pulse width modulation (PWM) and pulse amplitude modulation (PAM) is presented herein to reduce the output voltage ripple of the converter as little as possible. Such a converter requires a two-stage cascaded structure. The first stage is the buck-boost converter, which is used to adjust the output voltage of the second power stage, whereas the second stage is the two-phase interleaved buck converter, which is used to reduce the output voltage ripple. In theory, the two phases of the second stage operate under the condition of individual duty cycles of 50% with a phase difference of

180^{°}

between the two, and hence, the currents in the two phases are cancelled for any period of time, thereby making the output voltage of the converter almost voltage-free. Moreover, in order to improve the overall efficiency further, the proposed soft-switching technique based on an active clamp is presented and applied to these two stages to render the main and auxiliary switches turned on with zero-voltage switching (ZVS). Finally, the operating principles and control strategies of the proposed converter are described, and then, their effectiveness is verified by experimental results. Full article

► Show Figures

Figure 1

14 pages, 1853 KiB

Open AccessArticle

Quantitative Evaluation Methods of Cluster Wind Power Output Volatility and Source-Load Timing Matching in Regional Power Grid

by Yongqian Liu, Yanhui Qiao, Shuang Han, Yanping Xu, Tianxiang Geng and Tiandong Ma

Energies 2021, 14(16), 5214; https://doi.org/10.3390/en14165214 - 23 Aug 2021

Cited by 8 | Viewed by 1829

Abstract

The quantitative evaluation of cluster wind power output volatility and source-load timing matching is vital to the planning and operation of the future power system dominated by new energy. However, the existing volatility evaluation methods of cluster wind power output do not fully [...] Read more.

The quantitative evaluation of cluster wind power output volatility and source-load timing matching is vital to the planning and operation of the future power system dominated by new energy. However, the existing volatility evaluation methods of cluster wind power output do not fully consider timing volatility, or are not suitable for small sample data scenarios. Meanwhile, the existing source-load timing matching evaluation indicator ignores the impact of wind power permeability on the timing matching degree between wind power output and load. Therefore, the authors propose quantitative evaluation methods of cluster wind power output volatility and source-load timing matching in regional power grid. Firstly, the volatility-based smoothing coefficient is defined to quantitatively evaluate the smoothing effect of wind-farm cluster power output. Then, the source-load timing matching coefficient considering wind power permeability is proposed to quantitatively evaluate the timing matching degree of regional wind power output and load, and the corresponding function model of volatility-based smoothing coefficient and source-load timing matching coefficient is established. Finally, the validity and applicability of the proposed methods are verified by MATLAB software based on the actual power output of 10 wind farms and actual grid load in a certain grid dispatching cross-section of northeast China. The results demonstrated that the proposed volatility-based smoothing coefficient can accurately represent the smoothing effect of wind farm cluster power output while maintaining the volatility continuity of wind power output time series and without affect from the data sample size. The source-load timing matching coefficient can accurately characterize the difference in the timing matching degree between wind power output and grid load under different wind power permeability and the influence degree on grid load. Full article

(This article belongs to the Section A: Sustainable Energy)

► Show Figures

Figure 1

14 pages, 1728 KiB

Open AccessArticle

The Analysis of Power Transformer Population Working in Different Operating Conditions with the Use of Health Index

by Patryk Bohatyrewicz and Andrzej Mrozik

Energies 2021, 14(16), 5213; https://doi.org/10.3390/en14165213 - 23 Aug 2021

Cited by 10 | Viewed by 2516

Abstract

The management of the power transformer population is a complex process, as the grid companies operate thousands of devices. For this issue, the health index method can be applied to facilitate asset management. The algorithm can be used not only in the technical [...] Read more.

The management of the power transformer population is a complex process, as the grid companies operate thousands of devices. For this issue, the health index method can be applied to facilitate asset management. The algorithm can be used not only in the technical assessment of the individual units, but also to determine the relationships within the whole population. In this paper, the presented health index method consists of periodic oil diagnostics, including the physicochemical properties, dissolved gas analysis, and furfural content, and further assessment in terms of the criticality of the device to determine the technical condition. The algorithm was specifically designed to reflect even the smallest changes of the input parameters in the final score. The performance of the health index was tested on 620 oil analyses from 220 transformers divided into four subpopulations based on the service conditions. The results have proven to be largely dependent on the criticality level and the operating conditions of the device. The analysis of the study group has shown the influence of corrective maintenance on the mean value of the health index score. Full article

(This article belongs to the Special Issue Experimental and Numerical Analysis of Thermal Ageing in Power Transformers)

► Show Figures

Figure 1

13 pages, 3978 KiB

Open AccessArticle

A Coordinated Optimal Strategy for Voltage and Reactive Power Control with Adaptive Amplitude Limiter Based on Flexible Excitation System

by Yuwei Peng, Jiancheng Zhang, Chengxiong Mao, Hongtao Xiong, Tiantian Zhang and Dan Wang

Energies 2021, 14(16), 5212; https://doi.org/10.3390/en14165212 - 23 Aug 2021

Cited by 2 | Viewed by 1614

Abstract

The flexible excitation system (FES) is a kind of novel excitation system with two channels for damping control. Besides the basic functions of traditional excitation systems, flexible excitation systems can provide reactive power support for the terminal voltage, and the large-capacity FES can [...] Read more.

The flexible excitation system (FES) is a kind of novel excitation system with two channels for damping control. Besides the basic functions of traditional excitation systems, flexible excitation systems can provide reactive power support for the terminal voltage, and the large-capacity FES can improve the voltage stability and power-angle stability of synchronous generator units. However, with the increase in system capacity and the complication of control objectives, the difficulty of controller design will be increased. The randomness and fluctuation of new energy resources such as photovoltaic and wind turbines may cause disturbance and fault to the power system, which requires the coordinated control strategy for the FES to achieve stability in voltage and power angle. In this paper, the basic characteristics of FES are analyzed, and the mathematic model of the single machine infinite bus (SMIB) system based on FES is derived. The coordinated control strategy based on decoupling control of stator and rotor is proposed according to the optimal objectives of voltage stability and power-angle stability, and the linear optimal excitation control (LOEC) is adopted with the adaptive amplitude limiter (AAL) determined by fuzzy rules. The MATLAB/Simulink platform is established and the results verify the superiority of the proposed LOEC + AAL control strategy in large disturbance working conditions, which showed better robustness. The proposed coordinated control strategy provides an effective solution for industrial application and performance improvement of FES. Full article

► Show Figures

Figure 1

14 pages, 1129 KiB

Open AccessArticle

Railway Vehicle Energy Efficiency as a Key Factor in Creating Sustainable Transportation Systems

by Małgorzata Ćwil, Witold Bartnik and Sebastian Jarzębowski

Energies 2021, 14(16), 5211; https://doi.org/10.3390/en14165211 - 23 Aug 2021

Cited by 21 | Viewed by 3682

Abstract

Railway transit forms the backbone of sustainable transportation systems, which are necessary to limit the effects of global warming. In this paper, the authors seek to determine whether there is a statistically significant difference in energy consumption between distinct railway vehicle types. Firstly, [...] Read more.

Railway transit forms the backbone of sustainable transportation systems, which are necessary to limit the effects of global warming. In this paper, the authors seek to determine whether there is a statistically significant difference in energy consumption between distinct railway vehicle types. Firstly, the energy consumption measurement methods in the railway transportation sector are described and compared to each other in respect to precision and cost. Secondly, the use of energy consumption as a criterion in rolling stock tenders with the associated norm is analysed, particularly with regard to the life-cycle cost of railway vehicles. In the next part real life data on energy consumption of six distinct passenger electrical railway vehicle types is presented and analysed in order to compare the efficiency of different types of rolling stock. The differences in energy efficiency between rolling stock types may be used to improve the procurement process ensuring train operating companies obtain less energy-consuming vehicles. Full article

(This article belongs to the Special Issue Energy Consumption Patterns in Sustainable Supply Chains)

► Show Figures

Figure 1

10 pages, 217 KiB

Open AccessArticle

Risk Management Scenarios for Investment Program Delays in the Polish Power Industry

by Stanisław Tokarski, Małgorzata Magdziarczyk and Adam Smoliński

Energies 2021, 14(16), 5210; https://doi.org/10.3390/en14165210 - 23 Aug 2021

Cited by 20 | Viewed by 2407

Abstract

The introduction of the Green Deal in 2019 by the European Commission poses a significant challenge for EU member states whose power generation is based primarily on fossil fuels. In Poland, nearly 80% of the electricity is produced from fossil fuels. This paper [...] Read more.

The introduction of the Green Deal in 2019 by the European Commission poses a significant challenge for EU member states whose power generation is based primarily on fossil fuels. In Poland, nearly 80% of the electricity is produced from fossil fuels. This paper presents an analysis of the risks related to the delays in the accomplishment of investment programs in the Polish power industry. Three scenarios were prepared for balancing the deficiency of about 3 GW of power and 20 TWh of electricity in the national power grid in the years 2031–2040, which may emerge as a result of the delayed accomplishment of investment programs, particularly in nuclear energy. The first scenario presents a variant entailing the rapid phasing out of coal and the replacement of the decommissioned power units with new gas-powered units, where the missing power volume would be partially balanced by import, and partially through gas-based production in the new power units. The second scenario assumes that the missing power would be balanced by retaining the existing, older coal-powered units, whereas the required electricity would be compensated by import. The third scenario involves the production of the missing volume of electricity using coal with CO₂ capture in existing or new coal-powered units. Full article

(This article belongs to the Special Issue Risk Management in the Energy Sector)

19 pages, 4191 KiB

Open AccessArticle

Experimental Assessment of the Performance and Emissions of a Spark-Ignition Engine Using Waste-Derived Biofuels as Additives

by Joaquim Costa, Jorge Martins, Tiago Arantes, Margarida Gonçalves, Luis Durão and Francisco P. Brito

Energies 2021, 14(16), 5209; https://doi.org/10.3390/en14165209 - 23 Aug 2021

Cited by 4 | Viewed by 2484

Abstract

The use of biofuels for spark ignition engines is proposed to diversify fuel sources and reduce fossil fuel consumption, optimize engine performance, and reduce pollutant emissions. Additionally, when these biofuels are produced from low-grade wastes, they constitute valorisation pathways for these otherwise unprofitable [...] Read more.

The use of biofuels for spark ignition engines is proposed to diversify fuel sources and reduce fossil fuel consumption, optimize engine performance, and reduce pollutant emissions. Additionally, when these biofuels are produced from low-grade wastes, they constitute valorisation pathways for these otherwise unprofitable wastes. In this study, ethanol and pyrolysis biogasoline made from low-grade wastes were evaluated as additives for commercial gasoline (RON95, RON98) in tests performed in a spark ignition engine. Binary fuel mixtures of ethanol + gasoline or biogasoline + gasoline with biofuel incorporation of 2% (w/w) to 10% (w/w) were evaluated and compared with ternary fuel mixtures of ethanol + biogasoline + gasoline with biofuel incorporation rates from 1% (w/w) to 5% (w/w). The fuel mix performance was assessed by determination of torque and power, fuel consumption and efficiency, and emissions (HC, CO, and NOx). An electronic control unit (ECU) was used to regulate the air–fuel ratio/lambda and the ignition advance for maximum brake torque (MBT), wide-open throttle (WOT)), and two torque loads for different engine speeds representative of typical driving. The additive incorporation up to 10% often improved efficiency and lowered emissions such as CO and HC relative to both straight gasolines, but NOx increased with the addition of a blend. Full article

(This article belongs to the Special Issue Valorization of Wastes for Energy Production by Thermal and Biological Processes)

► Show Figures

Figure 1

26 pages, 52099 KiB

Open AccessArticle

Crowdsourcing Urban Air Temperature Data for Estimating Urban Heat Island and Building Heating/Cooling Load in London

by Kit Benjamin, Zhiwen Luo and Xiaoxue Wang

Energies 2021, 14(16), 5208; https://doi.org/10.3390/en14165208 - 23 Aug 2021

Cited by 17 | Viewed by 3219

Abstract

Urban heat island (UHI) effects significantly impact building energy. Traditional UHI investigation methods are often incapable of providing the high spatial density of observations required to distinguish small-scale temperature differences in the UHI. Crowdsourcing offers a solution. Building cooling/heating load in 2018 has [...] Read more.

Urban heat island (UHI) effects significantly impact building energy. Traditional UHI investigation methods are often incapable of providing the high spatial density of observations required to distinguish small-scale temperature differences in the UHI. Crowdsourcing offers a solution. Building cooling/heating load in 2018 has been estimated in London, UK, using crowdsourced data from over 1300 Netatmo personal weather stations. The local climate zone (LCZ) scheme was used to classify the different urban environments of London (UK). Inter-LCZ temperature differences are found to be generally consistent with LCZ temperature definitions. Analysis of cooling degree hours in July shows LCZ 2 (the densest urban LCZ in London) had the highest cooling demand, with a total of 1550 cooling degree hours. The suburban related LCZs 5 and 6 and rural LCZs B and D all had about 80% of the demand of LCZ 2. In December, the rural LCZs A, B and D had the greatest heating demand, with all recording around 5750 heating degree hours. Urban LCZs 2, 5 and 6 had 91%, 86% and 95% of the heating demand of LCZ D, respectively. This study has highlighted both advantages and issues with using crowdsourced data for urban climate and building energy research. Full article

(This article belongs to the Special Issue Resilience and Climate Adaptability of Buildings and Urban Areas)

► Show Figures

Figure 1

26 pages, 2531 KiB

Open AccessReview

Review of Wind Turbine Icing Modelling Approaches

by Fahed Martini, Leidy Tatiana Contreras Montoya and Adrian Ilinca

Energies 2021, 14(16), 5207; https://doi.org/10.3390/en14165207 - 23 Aug 2021

Cited by 25 | Viewed by 6062

Abstract

When operating in cold climates, wind turbines are vulnerable to ice accretion. The main impact of icing on wind turbines is the power losses due to geometric deformation of the iced airfoils of the blades. Significant energy losses during the wind farm lifetime [...] Read more.

When operating in cold climates, wind turbines are vulnerable to ice accretion. The main impact of icing on wind turbines is the power losses due to geometric deformation of the iced airfoils of the blades. Significant energy losses during the wind farm lifetime must be estimated and mitigated. Finding solutions for icing calls on several areas of knowledge. Modelling and simulation as an alternative to experimental tests are primary techniques used to account for ice accretion because of their low cost and effectiveness. Several studies have been conducted to replicate ice growth on wind turbine blades using Computational Fluid Dynamics (CFD) during the last decade. While inflight icing research is well developed and well documented, wind turbine icing is still in development and has its peculiarities. This paper surveys and discusses the models, approaches and methods used in ice accretion modelling in view of their application in wind energy while summarizing the recent research findings in Surface Roughness modelling and Droplets Trajectory modelling. An An additional section discusses research on the modelling of electro-thermal icing protection systems. This paper aims to guide researchers in wind engineering to the appropriate approaches, references and tools needed to conduct reliable icing modelling for wind turbines. Full article

(This article belongs to the Special Issue Challenges for Renewable Energy Production in Cold Climates 2020)

► Show Figures

Figure 1

26 pages, 4683 KiB

Open AccessArticle

Solar-Based DG Allocation Using Harris Hawks Optimization While Considering Practical Aspects

by Suprava Chakraborty, Sumit Verma, Aprajita Salgotra, Rajvikram Madurai Elavarasan, Devaraj Elangovan and Lucian Mihet-Popa

Energies 2021, 14(16), 5206; https://doi.org/10.3390/en14165206 - 23 Aug 2021

Cited by 21 | Viewed by 3251

Abstract

The restructuring of power systems and the ever-increasing demand for electricity have given rise to congestion in power networks. The use of distributed generators (DGs) may play a significant role in tackling such issues. DGs may be integrated with electrical power networks to [...] Read more.

The restructuring of power systems and the ever-increasing demand for electricity have given rise to congestion in power networks. The use of distributed generators (DGs) may play a significant role in tackling such issues. DGs may be integrated with electrical power networks to regulate the drift of power in the transmission lines, thereby increasing the power transfer capabilities of lines and improving the overall performance of electrical networks. In this article, an effective method based on the Harris hawks optimization (HHO) algorithm is used to select the optimum capacity, number, and site of solar-based DGs to reduce real power losses and voltage deviation. The proposed HHO has been tested with a complex benchmark function then applied to the IEEE 33 and IEEE 69 bus radial distribution systems. The single and multiple solar-based DGs are optimized for the optimum size and site with a unity power factor. It is observed that the overall performance of the systems is enhanced when additional DGs are installed. Moreover, considering the stochastic and sporadic nature of solar irradiance, the practical size of DG has been suggested based on analysis that may be adopted while designing the actual photovoltaic (PV) plant for usage. The obtained simulation outcomes are compared with the latest state-of-the-art literature and suggest that the proposed HHO is capable of processing complex high dimensional benchmark functions and has capability to handle problems pertaining to electrical distribution in an effective manner. Full article

(This article belongs to the Topic Optimisation, Optimal Control and Nonlinear Dynamics in Electrical Power, Energy Storage and Renewable Energy Systems)

► Show Figures

Figure 1

13 pages, 4479 KiB

Open AccessArticle

Innovative Techniques in Underground Mining for the Prevention of Gas Dynamic Phenomena

by Martina-Inmaculada Álvarez-Fernández, María-Belén Prendes-Gero, Juan-Carlos Peñas-Espinosa and Celestino González-Nicieza

Energies 2021, 14(16), 5205; https://doi.org/10.3390/en14165205 - 23 Aug 2021

Cited by 5 | Viewed by 1694

Abstract

In the last decades, rigorous research has been carried out with the end of understanding the gas dynamic phenomenon and although different preventive techniques have been employed, even today there are numerous accidents even with the loss of life. This work analyses an [...] Read more.

In the last decades, rigorous research has been carried out with the end of understanding the gas dynamic phenomenon and although different preventive techniques have been employed, even today there are numerous accidents even with the loss of life. This work analyses an alternative and innovative method of fracturing and degassing coal, by generating CO₂ with a pyrotechnic device called PYROC (Pyrotechnic Break Cartridges). Medium-scale tests of generation of CO₂ into coal samples are carried out and their effect is analysed comparing the initial and final permeabilities of the coal samples once the generation of CO₂ has finished. These permeabilities are calculated by injecting methane. Besides, the influence of different parameters as the length of the boreholes, the pressure of the gas or the initial permeability of the coal have been analysed with a numerical simulation of one face of one of the sublevels of a mine. The results show that the method increases the safety in mining operations because it fractures and degasses the coal, increases the permeability of the coal in the borehole of injection from 9.5 mD to 31 mD, decreases the methane gas pressure below pre-detonation levels for 1 min, achieves decompressed lengths between 8 and 10 m ahead of the face with pressures of injection of 50 MPa, relaxes the total length of the borehole for initial coal permeability values equal to or greater than 0.002 mD, and allows to work with low permeable coals with high induced stresses and high methane concentrations. Full article

(This article belongs to the Special Issue Innovative Techniques in Underground Excavation)

► Show Figures

Figure 1

21 pages, 3306 KiB

Open AccessArticle

Bumpless Transfer of Uncertain Switched System and Its Application to Turbofan Engines

by Penghui Sun, Xi Wang, Shubo Yang, Bei Yang, Huairong Chen and Bin Wang

Energies 2021, 14(16), 5204; https://doi.org/10.3390/en14165204 - 23 Aug 2021

Cited by 4 | Viewed by 2064

Abstract

Nonlinear control problems in turbofan engines are challenging. No single nonlinear controller can achieve desired control effects in a full flight envelope, but in the case of multiple controllers, there exist problems in the bumpless transfer between different controllers. To this end, this [...] Read more.

Nonlinear control problems in turbofan engines are challenging. No single nonlinear controller can achieve desired control effects in a full flight envelope, but in the case of multiple controllers, there exist problems in the bumpless transfer between different controllers. To this end, this paper presents a bumpless transfer mechanism for an uncertain switched system based on integral sliding mode control (ISMC), and the mechanism can be used for the speed control of turbofan engines. The uncertain switched system is used to describe the turbofan engine dynamics. Then, the ISMC controller is derived for subsystems of the uncertain switched system. A resetting scheme is introduced for the ISMC controller to ensure the continuity of control inputs during the controller transition, as well as the bumpless transfer. In view of the transient behavior caused by controller switching, the global stability of the switched system is analyzed using the multiple Lyapunov function approach and average dwell time condition. Simulation results validate that the designed resetting scheme can ensure the continuity of control input signals and avoid the instability caused by high-frequency controller switching, and increase the control effectiveness of the proposed ISMC method within the full flight envelope. Full article

(This article belongs to the Topic Power System Modeling and Control)

► Show Figures

Figure 1

18 pages, 6622 KiB

Open AccessArticle

Experimental Investigation of Neat Biodiesels’ Saturation Level on Combustion and Emission Characteristics in a CI Engine

by Vikas Sharma, Abul K. Hossain and Ganesh Duraisamy

Energies 2021, 14(16), 5203; https://doi.org/10.3390/en14165203 - 23 Aug 2021

Cited by 13 | Viewed by 2321

Abstract

The fuel qualities of several biodiesels containing highly saturated, mono, and poly unsaturated fatty acids, as well as their combustion and exhaust emission characteristics, were studied. Six biodiesel samples were divided into two groups based on their fatty acid composition, including group 1 [...] Read more.

The fuel qualities of several biodiesels containing highly saturated, mono, and poly unsaturated fatty acids, as well as their combustion and exhaust emission characteristics, were studied. Six biodiesel samples were divided into two groups based on their fatty acid composition, including group 1 (coconut, castor, and jatropha) and group II (palm, karanja, and waste cooking oil biodiesel). All fuels (in both groups) were tested in a single-cylinder off-road diesel engine. Castor and karanja biodiesel, both rich in mono-unsaturation level, have a high viscosity of about 14.5 and 5.04 mm²/s, respectively. The coconut and palm biodiesels are rich in saturation level with cetane numbers of 62 and 60, respectively. In both groups, highly saturated and poly-unsaturated methyl esters presented better combustion efficiency and less formation of polluted emissions than mono-unsaturation. At full load, coconut and palm biodiesel displayed 38% and 10% advanced start of combustion, respectively, which reduced ignition delay by approximately 10% and 3%, respectively. Mono-unsaturated methyl esters exhibited a higher cylinder pressure and heat release rate, which results in higher NOx gas emissions. The group II biodiesels showed about 10–15% lower exhaust emissions owing to an optimum level of fatty acid composition. Our study concluded that highly saturated and poly-unsaturated fatty acid performed better than mono-unsaturated biodiesels for off-road engine application. Full article

► Show Figures

Figure 1

25 pages, 547 KiB

Open AccessReview

Towards Optimal Management in Microgrids: An Overview

by Álex Omar Topa Gavilema, José Domingo Álvarez, José Luis Torres Moreno and Manuel Pérez García

Energies 2021, 14(16), 5202; https://doi.org/10.3390/en14165202 - 23 Aug 2021

Cited by 20 | Viewed by 3931

Abstract

A microgrid is a set of decentralized loads and electricity sources, mainly renewable. It can operate connected to and synchronized with a traditional wide-area synchronous grid, i.e., a macrogrid, but can also be disconnected to operate in “island mode” or “isolated mode”. When [...] Read more.

A microgrid is a set of decentralized loads and electricity sources, mainly renewable. It can operate connected to and synchronized with a traditional wide-area synchronous grid, i.e., a macrogrid, but can also be disconnected to operate in “island mode” or “isolated mode”. When this microgrid is able to manage its own resources and loads through the use of smart meters, smart appliances, control systems, and the like, it is referred to as a smart grid. Therefore, the management and the distribution of the energy inside the microgrid is an important issue, especially when operating in isolated mode. This work presents an overview of the different solutions that have been tested during the last few years to manage microgrids. The review shows the variety of mature and tested solutions for managing microgrids with different configurations and under several approaches. Full article

► Show Figures

Graphical abstract

17 pages, 5434 KiB

Open AccessArticle

Hydrodynamic Modeling of Oil–Water Stratified Smooth Two-Phase Turbulent Flow in Horizontal Circular Pipes

by Qi Kang, Jiapeng Gu, Xueyu Qi, Ting Wu, Shengjie Wang, Sihang Chen, Wei Wang and Jing Gong

Energies 2021, 14(16), 5201; https://doi.org/10.3390/en14165201 - 23 Aug 2021

Viewed by 2644

Abstract

In the petrochemical industry, multiphase flow, including oil–water two-phase stratified laminar flow, is more common and can be easily obtained through mathematical analysis. However, there is limited mathematical analytical model for the simulation of oil–water flow under turbulent flow. This paper introduces a [...] Read more.

In the petrochemical industry, multiphase flow, including oil–water two-phase stratified laminar flow, is more common and can be easily obtained through mathematical analysis. However, there is limited mathematical analytical model for the simulation of oil–water flow under turbulent flow. This paper introduces a two-dimensional (2D) numerical simulation method to investigate the pressure gradient, flow field, and oil–water interface height of a pipeline cross-section of horizontal tube in an oil–water stratified smooth flow. Three Reynolds average N–S equation models (

k - ε

,

k - ω

, SST

k - ω

) are involved to simulate oil–water stratified smooth flow according to the finite volume method. The pressure gradient and oil–water interface height can be computed according to the given volume flow rate using the iteration method. The predicted result of oil–water interface height and velocity profile by the model fit well with several published experimental data, except that there is a large error in pressure gradient. The SST

k - ω

turbulence model appears higher accuracy for simulating oil–water two-phase stratified flow in a horizontal pipe. Full article

► Show Figures

Figure 1

16 pages, 4637 KiB

Open AccessArticle

Analysis of the Operation of an Unheated Wooden Church to the Shaping of Thermal and Humidity Conditions Using the Numerical Method

by Grzegorz Nawalany, Paweł Sokołowski and Małgorzata Michalik

Energies 2021, 14(16), 5200; https://doi.org/10.3390/en14165200 - 23 Aug 2021

Cited by 7 | Viewed by 1812

Abstract

The article deals with the problem of the effects of using a wooden church on thermal and humidity conditions forming inside. Religious services in the studied site were provided several times a year. The building was not used in the remaining time. The [...] Read more.

The article deals with the problem of the effects of using a wooden church on thermal and humidity conditions forming inside. Religious services in the studied site were provided several times a year. The building was not used in the remaining time. The analysis of the effects of the frequency of religious services and the number of people at the services on the formation of temperature and humidity conditions in the wooden church is provided in this paper. The effect of the presence of people in the church on CO₂ concentration fluctuations was also studied. Analysis of the results showed that external conditions have the greatest effect on internal microclimate substitutions. The presence of people affects temporary fluctuations in internal parameters. Both the number of people attending the service and the time of year are important. An indoor air temperature amplitude of 9.4 °C was recorded during the winter period. The CO₂ level in the church during the service exceeded the limit value of 1000 ppm, reaching 1800 ppm in the extreme case, which could result in decreased comfort for people. The high CO₂ concentration may have been caused by a lack of effective ventilation in the building. The obtained simulation results showed a high agreement of the theoretical data with the measurement results (correlation 0.91). The analysis of three simulation variants showed that the people attending the services have a significant share in the gains of thermal energy inside the church. In order to meet the assumptions for variant 1, there are no requirements to start the heating system, assuming a similar schedule of services. Full article

► Show Figures

Figure 1

23 pages, 13690 KiB

Open AccessArticle

Study of a Bi-Vertical Axis Turbines Farm Using the Actuator Cylinder Method

by Laurie Jégo and Sylvain S. Guillou

Energies 2021, 14(16), 5199; https://doi.org/10.3390/en14165199 - 23 Aug 2021

Cited by 7 | Viewed by 2041

Abstract

Vertical axis turbines, which extract kinetic energy from currents, can produce electricity independently from a current’s direction. Hence, this type of turbines raises interest for harvesting energy from tidal currents, where flow changes direction during flood and ebb tides, and where currents present [...] Read more.

Vertical axis turbines, which extract kinetic energy from currents, can produce electricity independently from a current’s direction. Hence, this type of turbines raises interest for harvesting energy from tidal currents, where flow changes direction during flood and ebb tides, and where currents present large variation of direction during tide. Methods for representing vertical axis turbines in tidal farms should be implemented in order to predict correctly power production with an acceptable time cost. The Actuator Cylinder (AC) is one of them. Numerical results in terms of wakes, with the study of velocity profiles, and efforts are compared to experiences, as well as showed that the method is sufficiently accurate and for a reasonable computing time, which is of prime importance for tidal turbines farms studies. The Actuator Cylinder method is implemented in ANSYS Fluent in a 2D stationary resolution. The method is then applied to a double levels of two counter-rotating rotors marine turbine designed by Hydroquest. Wake and power production of a single turbine and several farm configurations are studied under different current conditions (magnitude and direction). Full article

(This article belongs to the Special Issue Tidal Turbines)

► Show Figures

Figure 1

26 pages, 8938 KiB

Open AccessArticle

On the Accuracy of uRANS and LES-Based CFD Modeling Approaches for Rotor and Wake Aerodynamics of the (New) MEXICO Wind Turbine Rotor Phase-III

by Shantanu Purohit, Ijaz Fazil Syed Ahmed Kabir and E. Y. K. Ng

Energies 2021, 14(16), 5198; https://doi.org/10.3390/en14165198 - 23 Aug 2021

Cited by 14 | Viewed by 3775

Abstract

This work presents a comparison study of the CFD modeling with two different turbulence modeling approaches viz. unsteady RANS and LES, on a full-scale model of the (New) MEXICO rotor wind turbine. The main emphasis of the paper is on the rotor and [...] Read more.

This work presents a comparison study of the CFD modeling with two different turbulence modeling approaches viz. unsteady RANS and LES, on a full-scale model of the (New) MEXICO rotor wind turbine. The main emphasis of the paper is on the rotor and wake aerodynamics. Simulations are carried out for the three wind speeds considered in the MEXICO experiment (10, 15, and 24 ms⁻¹). The results of uRANS and LES are compared against the (New) MEXICO experimental measurements of pressure distributions, axial, radial, and azimuth traverse of three velocity components. The near wake characteristics and vorticity are also analyzed. The pressure distribution results show that the LES can predict the onset of flow separation more accurately than uRANS when the turbine operates in the stall condition. The LES can compute the flow structures in wake significantly better than the uRANS for the stall condition of the blade. For the design condition, the mean absolute error in axial and radial velocity components along radial traverse is less than 10% for both the modeling approaches, whereas tangential component error is less than 2% from the LES approach. The results also reveal that wake recovers faster in the uRANS approach, requiring further research of the far wake region using both CFD modeling approaches. Full article

(This article belongs to the Special Issue Advancement in Wind Turbine Technology)

► Show Figures

Figure 1

18 pages, 1298 KiB

Open AccessArticle

Energy Efficiency and Decarbonization in the Context of Macroeconomic Stabilization

by Anna Misztal, Magdalena Kowalska, Anita Fajczak-Kowalska and Otakar Strunecky

Energies 2021, 14(16), 5197; https://doi.org/10.3390/en14165197 - 23 Aug 2021

Cited by 9 | Viewed by 2875

Abstract

Decarbonization is an activity aimed at reducing greenhouse gas emissions to limit climate change and global warming. Ensuring macroeconomic stabilization is the basis for ecological action. The question is whether macroeconomic stabilization helps companies, institutions and countries act for decarbonization. This article presents [...] Read more.

Decarbonization is an activity aimed at reducing greenhouse gas emissions to limit climate change and global warming. Ensuring macroeconomic stabilization is the basis for ecological action. The question is whether macroeconomic stabilization helps companies, institutions and countries act for decarbonization. This article presents research on the impact of components of macroeconomic stabilization on decarbonization and energy efficiency in the largest greenhouse gas emitters in the European Union from 1990 to 2020. We focus on the following countries, France, Germany, Italy, Poland and Spain. The contribution to knowledge is using the pentagon of macroeconomic stabilization to assess macroeconomic stabilization’s impact on decarbonization and energy efficiency. According to the correlation coefficients, the Ordinary Least Squares and the Seemingly Unrelated Regression method, there is a statistically significant impact of components of macroeconomics stabilization on decarbonization and energy efficiency. Moreover, our models show a different strength and direction of relationships between the explained and explanatory variables. Research results confirm the necessity to coordinate the macroeconomic with environmental policy. We think that it is essential to use effective tools of economic support (European Union Emissions Trading System, environmental taxes) and greater pressure from European Union institutions on countries that emit harmful substances. Full article

(This article belongs to the Special Issue Financial Development and Energy Consumption Nexus)

► Show Figures

Figure 1

21 pages, 6746 KiB

Open AccessArticle

A Machine Learning-Based Gradient Boosting Regression Approach for Wind Power Production Forecasting: A Step towards Smart Grid Environments

by Upma Singh, Mohammad Rizwan, Muhannad Alaraj and Ibrahim Alsaidan

Energies 2021, 14(16), 5196; https://doi.org/10.3390/en14165196 - 23 Aug 2021

Cited by 104 | Viewed by 8871

Abstract

In the last few years, several countries have accomplished their determined renewable energy targets to achieve their future energy requirements with the foremost aim to encourage sustainable growth with reduced emissions, mainly through the implementation of wind and solar energy. In the present [...] Read more.

In the last few years, several countries have accomplished their determined renewable energy targets to achieve their future energy requirements with the foremost aim to encourage sustainable growth with reduced emissions, mainly through the implementation of wind and solar energy. In the present study, we propose and compare five optimized robust regression machine learning methods, namely, random forest, gradient boosting machine (GBM), k-nearest neighbor (kNN), decision-tree, and extra tree regression, which are applied to improve the forecasting accuracy of short-term wind energy generation in the Turkish wind farms, situated in the west of Turkey, on the basis of a historic data of the wind speed and direction. Polar diagrams are plotted and the impacts of input variables such as the wind speed and direction on the wind energy generation are examined. Scatter curves depicting relationships between the wind speed and the produced turbine power are plotted for all of the methods and the predicted average wind power is compared with the real average power from the turbine with the help of the plotted error curves. The results demonstrate the superior forecasting performance of the algorithm incorporating gradient boosting machine regression. Full article

(This article belongs to the Special Issue Electrical Engineering for Sustainable and Renewable Energy II)

► Show Figures

Figure 1

12 pages, 2387 KiB

Open AccessArticle

Power Enhancement of a PV Module Using Different Types of Phase Change Materials

by Ali Shaito, Mohammad Hammoud, Fadel Kawtharani, Ali Kawtharani and Hilal Reda

Energies 2021, 14(16), 5195; https://doi.org/10.3390/en14165195 - 23 Aug 2021

Cited by 9 | Viewed by 2556

Abstract

Photovoltaic (PV) systems are well-known systems that convert solar energy into electrical energy. Increases in operating temperature induce a drop in conversion efficiency and, thus, in the output power produced by the panel. This paper investigates the effectiveness of using Phase Change Materials [...] Read more.

Photovoltaic (PV) systems are well-known systems that convert solar energy into electrical energy. Increases in operating temperature induce a drop in conversion efficiency and, thus, in the output power produced by the panel. This paper investigates the effectiveness of using Phase Change Materials (PCMs) in cooling PV modules. Due to its high storage density with limited temperature fluctuations, the latent heat storage in a PCM is an important factor. This depends on the thermophysical properties of PCMs such as the melting point, specific heat capacity, latent heat, density, etc. This paper aims to make a comparison between four types of PCM with different melting points and physical properties. Indoor experimental studies were performed using five prototypes. A halogen lamp was used as a solar simulator to ensure that experiments were carried out under the same irradiance. The first prototype was the reference, which consisted of a PV panel, a stand, and an electric circuit without PCMs. Four other prototypes were investigated, consisting of a PV panel with a container added at the rear face, with each having different types of PCM: sodium sulfate decahydrate, sodium phosphate dibasic dodecahydrate, decanoic acid, and calcium chloride hexahydrate, respectively. The results clearly show the effect of PCMs’ properties on PV temperature profile and power generation. Full article

► Show Figures

Figure 1

11 pages, 1413 KiB

Open AccessArticle

Small-Scaled Production of Blue Hydrogen with Reduced Carbon Footprint

by Yuriy Zagashvili, Aleksey Kuzmin, George Buslaev and Valentin Morenov

Energies 2021, 14(16), 5194; https://doi.org/10.3390/en14165194 - 22 Aug 2021

Cited by 11 | Viewed by 3066

Abstract

This article reviews a method of hydrogen production based on partial non-catalytic oxidation of natural gas in an original synthesis gas generator. The working principles of the unit are similar to those of liquid-propellant rocket engines. This paper presents a description of the [...] Read more.

This article reviews a method of hydrogen production based on partial non-catalytic oxidation of natural gas in an original synthesis gas generator. The working principles of the unit are similar to those of liquid-propellant rocket engines. This paper presents a description of the operation and technical characteristics of the synthesis gas generator. Its application in the creation of small-scaled plants with a capacity of up to 5–7 thousand m³/h of hydrogen is justified. Hydrogen production in the developed installation requires a two-stage method and includes a technological unit for producing a hydrogen-containing gas. Typical balance compositions of hydrogen-containing gas at the synthesis gas generator’s outlet are given. To increase the hydrogen concentration, it is proposed to carry out a two-stage steam catalytic conversion of carbon monoxide contained in the hydrogen-containing gas at the synthesis gas generator’s outlet using a single Cu–Zn–cement-containing composition. Based on thermodynamic calculations, quasi-optimal modes of natural gas partial oxidation with oxygen are formulated and the results of material balance calculation for the installation are presented. In order to produce “blue” hydrogen, the scheme of carbon dioxide separation and liquefaction is developed. The conclusion section of the paper contains the test results of a pilot demonstration unit and the recommendations for improving the technology and preventing soot formation. Full article

(This article belongs to the Special Issue Adsorption Technology to Optimize Hydrogen Production Processes: From Fundamental Research to Process Design)

► Show Figures

Figure 1

19 pages, 8612 KiB

Open AccessArticle

Instability Control of Roadway Surrounding Rock in Close-Distance Coal Seam Groups under Repeated Mining

by Yu Xiong, Dezhong Kong, Zhanbo Cheng, Zhijie Wen, Zhenqian Ma, Guiyi Wu and Yong Liu

Energies 2021, 14(16), 5193; https://doi.org/10.3390/en14165193 - 22 Aug 2021

Cited by 20 | Viewed by 2984

Abstract

In order to solve the problems of roadway stability and easy instability under repeated mining of close-distance coal seam groups, the mechanism and control technology of surrounding rock instability under repeated mining were studied via indoor testing, field testing, physical similarity simulation experiment, [...] Read more.

In order to solve the problems of roadway stability and easy instability under repeated mining of close-distance coal seam groups, the mechanism and control technology of surrounding rock instability under repeated mining were studied via indoor testing, field testing, physical similarity simulation experiment, and numerical simulation. The results show that the surrounding rock of roadway has low strength, low bearing capacity, and poor self-stabilization ability, and it is vulnerable to engineering disturbances and fragmentation. Affected by the disturbance under repeated mining, the roadway surrounding rock cracks are developed and the sensitivity is strong, and it is prone to large-scale loose and destroyed. The location of the roadway is unreasonable, and the maximum principal stress of the roadway is 3.1 times of the minimum principal stress, which is quite different. Thus, under a large horizontal stress, the surrounding rock undergoes long-range expansion deformation. On the basis of this research, the direction and emphasis of stability control of roadway surrounding rock under repeated mining of coal seam groups in close-distance are shown. A repair scheme (i.e., long bolt + high-strength anchor cable + U-shaped steel + grouting) is proposed, and reduces the risk of roadway instability. Full article

(This article belongs to the Special Issue Rock Burst Disasters in Coal Mines)

► Show Figures

Figure 1

15 pages, 4579 KiB

Open AccessArticle

Diagnostic Protocol for Thermal Performance of District Heating Pipes in Operation. Part 1: Estimation of Supply Pipe Temperature by Measuring Temperature at Valves after Shutdown

by Peter Lidén, Bijan Adl-Zarrabi and Carl-Eric Hagentoft

Energies 2021, 14(16), 5192; https://doi.org/10.3390/en14165192 - 22 Aug 2021

Cited by 3 | Viewed by 1724

Abstract

This study evaluates temperatures measured at district heating (DH) valves in manholes and their usability for non-destructively assessing the thermal performance of buried DH pipes. The study was conducted as a field test in which part of a DH network was shut down [...] Read more.

This study evaluates temperatures measured at district heating (DH) valves in manholes and their usability for non-destructively assessing the thermal performance of buried DH pipes. The study was conducted as a field test in which part of a DH network was shut down and the temperature decline in the valves was analysed in terms of absolute temperature and thermal response time from the DH pipe to the top of the valve. The calculated and measured supply pipe temperatures by the drainage valves were in good agreement, with 1% deviation. The valve measurement analysis from this study shows that the drainage valve has good potential to serve as a measurement point for assessing the thermal status of a DH network. However, the shutdown valve measurements were greatly affected by the manhole environment. Full article

(This article belongs to the Special Issue Recent Advances in District Heating)

► Show Figures

Figure 1

22 pages, 1628 KiB

Open AccessArticle

The Use of Robotic Process Automation (RPA) as an Element of Smart City Implementation: A Case Study of Electricity Billing Document Management at Bydgoszcz City Hall

by Andrzej Sobczak and Leszek Ziora

Energies 2021, 14(16), 5191; https://doi.org/10.3390/en14165191 - 22 Aug 2021

Cited by 31 | Viewed by 6038

Abstract

Smart cities are an extremely important, multi-faceted subject, both in terms of their practical aspects and in terms of research. This is expressed, among other things, in the multitude of approaches to this concept. These approaches differ based on the emphasis placed on [...] Read more.

Smart cities are an extremely important, multi-faceted subject, both in terms of their practical aspects and in terms of research. This is expressed, among other things, in the multitude of approaches to this concept. These approaches differ based on the emphasis placed on individual aspects: some focus more on technology, and others put more weight on social issues, while still others value sustainable development issues. Currently, an important topic of discussion about the development of the smart city—the importance of which has become even greater in the context of the COVID-19 pandemic—is the digital transformation of the city. The use of robotic process automation (RPA) tools can be a part of such a transformation, as such tools, using advanced software, enable the automation of those tasks carried out thus far by humans. Although such an approach has, to date, been widespread in the case of enterprises (in particular, those operating in the financial and BPO/SSC sectors, but less often in the utilities sector, the first applications of these solutions in the context of process automation for cities are also beginning to emerge in various parts of the world. This article is based on a case study approach. The implementation conditions (including the constraints) of such an approach, the benefits achieved, and the lessons learned (which can be important for other local government units) are outlined using the example of the Bydgoszcz city hall’s (Poland) electricity billing document management. The results of the case study presented here lead to the conclusion that the use of RPA tools enables, very quickly and at relatively low cost, measurable results to be achieved that are related to the processing of electricity billing documentation for the city of Bydgoszcz. This allows the assertion to be made that robotic process automation can be taken into consideration as one of the tools used to build smart cities. Full article

(This article belongs to the Special Issue ICT in Smart Cities Development Management)

► Show Figures

Figure 1

26 pages, 8723 KiB

Open AccessArticle

Characterization of Supplementary Cementitious Materials and Fibers to Be Implemented in High Temperature Concretes for Thermal Energy Storage (TES) Application

by Laura Boquera, David Pons, Ana Inés Fernández and Luisa F. Cabeza

Energies 2021, 14(16), 5190; https://doi.org/10.3390/en14165190 - 22 Aug 2021

Cited by 6 | Viewed by 2403

Abstract

Six supplementary cementitious materials (SCMs) were identified to be incorporated in concrete exposed to high-temperature cycling conditions within the thermal energy storage literature. The selected SCMs are bauxite, chamotte, ground granulated blast furnace slag, iron silicate, silica fume, and steel slag. A microstructural [...] Read more.

Six supplementary cementitious materials (SCMs) were identified to be incorporated in concrete exposed to high-temperature cycling conditions within the thermal energy storage literature. The selected SCMs are bauxite, chamotte, ground granulated blast furnace slag, iron silicate, silica fume, and steel slag. A microstructural characterization was carried out through an optical microscope, X-ray diffraction analysis, and FT-IR. Also, a pozzolanic test was performed to study the reaction of SCMs silico-aluminous components. The formation of calcium silica hydrate was observed in all SCMs pozzolanic test. Steel slag, iron silicate, and ground granulated blast furnace slag required further milling to enhance cement reaction. Moreover, the tensile strength of three fibers (polypropylene, steel, and glass fibers) was tested after exposure to an alkalinity environment at ambient temperature during one and three months. Results show an alkaline environment entails a tensile strength decrease in polypropylene and steel fibers, leading to corrosion in the later ones. Full article

(This article belongs to the Special Issue Performance and Optimization of Solar Thermal Energy Storage Systems)

► Show Figures

Figure 1

16 pages, 3972 KiB

Open AccessArticle

The Application of Disturbance-Observer-Based Control in Breath Pressure Control of Aviation Electronic Oxygen Regulator

by Rui Pan, Guiping Lin, Zhigao Shi, Yu Zeng and Xue Yang

Energies 2021, 14(16), 5189; https://doi.org/10.3390/en14165189 - 22 Aug 2021

Cited by 7 | Viewed by 2608

Abstract

The electronic oxygen regulator (EOR) is a new type of aviation oxygen equipment which uses electronic servo control technology to control breathing gas pressure. In this paper, the control method of EOR was studied, and the dynamic model of the aviation oxygen system [...] Read more.

The electronic oxygen regulator (EOR) is a new type of aviation oxygen equipment which uses electronic servo control technology to control breathing gas pressure. In this paper, the control method of EOR was studied, and the dynamic model of the aviation oxygen system was established. A disturbance-observer-based controller (DOBC) was designed by the backstepping method to achieve the goal of stable and fast breath pressure control. The sensitivity function was proposed to describe the effect of inspiratory flow on breath pressure. Combined with the frequency domain analysis of the input sensitivity function, the parameters of the DOBC were analyzed and designed. Simulation and experiment studies were carried out to examine the control performance of DOBC in respiratory resistance and positive pressurization process under the influence of noise and time delay in the discrete electronic control system, which could meet the aviation physiology requirements. The research results not only verified the rationality of the application of DOBC in the breath control of EOR, but also proved the effectiveness of the control parameters design method according to the frequency domain analysis, which provided an important design basis for the subsequent study of EOR. Full article

(This article belongs to the Special Issue Advances in Fluid Power Systems)

► Show Figures

Figure 1

14 pages, 4179 KiB

Open AccessArticle

Estimation of Heat Loss Coefficient and Thermal Demands of In-Use Building by Capturing Thermal Inertia Using LSTM Neural Networks

by Martín Pensado-Mariño, Lara Febrero-Garrido, Estibaliz Pérez-Iribarren, Pablo Eguía Oller and Enrique Granada-Álvarez

Energies 2021, 14(16), 5188; https://doi.org/10.3390/en14165188 - 22 Aug 2021

Cited by 4 | Viewed by 2409

Abstract

Accurate forecasting of a building thermal performance can help to optimize its energy consumption. In addition, obtaining the Heat Loss Coefficient (HLC) allows characterizing the thermal envelope of the building under conditions of use. The aim of this work is to study the [...] Read more.

Accurate forecasting of a building thermal performance can help to optimize its energy consumption. In addition, obtaining the Heat Loss Coefficient (HLC) allows characterizing the thermal envelope of the building under conditions of use. The aim of this work is to study the thermal inertia of a building developing a new methodology based on Long Short-Term Memory (LSTM) neural networks. This approach was applied to the Rectorate building of the University of Basque Country (UPV/EHU), located in the north of Spain. A comparison of different time-lags selected to catch the thermal inertia has been carried out using the CV(RMSE) and the MBE errors, as advised by ASHRAE. The main contribution of this work lies in the analysis of thermal inertia detection and its influence on the thermal behavior of the building, obtaining a model capable of predicting the thermal demand with an error between 12 and 21%. Moreover, the viability of LSTM neural networks to estimate the HLC of an in-use building with an error below 4% was demonstrated. Full article

► Show Figures

Figure 1

15 pages, 2754 KiB

Open AccessArticle

Effect of Cleaning the Annular Space on the Adhesion of the Cement Sheath to the Rock

by Marcin Kremieniewski, Sławomir Błaż, Stanisław Stryczek, Rafał Wiśniowski and Andrzej Gonet

Energies 2021, 14(16), 5187; https://doi.org/10.3390/en14165187 - 22 Aug 2021

Cited by 10 | Viewed by 2118

Abstract

Drilling boreholes in gas zones and in zones with the possibility of migration or gas exhalation requires a high index of well tightness. An important parameter determining the effectiveness of sealing the annular space is the adhesion of the cement sheath to the [...] Read more.

Drilling boreholes in gas zones and in zones with the possibility of migration or gas exhalation requires a high index of well tightness. An important parameter determining the effectiveness of sealing the annular space is the adhesion of the cement sheath to the rock formation. Low values of adhesion of the cement sheath to the rock formation and to the casing surface result in the formation of uncontrolled gas flows. The lack of adhesion also reduces the stabilization of the pipe column. To obtain the required adhesion, the annular space should be properly cleaned. Thorough removal of filter cake from the drilling fluid increases adhesion and reduces gas migration from the annular space. Therefore, in this work, the authors focus on determining the effect of cleaning the annular space on the adhesion of the cement sheath to the rock formation. The results of the research work allow for further research on the modification of spacers and cement slurries in order to obtain the required increase in adhesion. The article presents the issues related to the preparation of the borehole for cementing by appropriate cleaning of the rock formation from the residue of the mud cake. During the implementation of the works, tests of cleaning the rock surface are performed. The obtained results are correlated with the results of adhesion on the rock–cement sheath cleaned of the wash mud cake contact. When analyzing the obtained test results, a relationship is found between the cleaning of the rock surface and the adhesion of the cement sheath to it. Full article

(This article belongs to the Special Issue Fundamentals of Enhanced Oil Recovery)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Energies, Volume 14, Issue 16 (August-2 2021) – 501 articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI