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Energies, Volume 13, Issue 15 (August-1 2020) – 283 articles

Cover Story (view full-size image): Distributed multi-rate PHiL test using a grid-forming converter as power interface can extend the capabilities of smart grid laboratories in a quasi-static operating regime. A cost-efficient setup is demonstrated by re-purposing an existing converter and a remotely located digital real-time simulator between the DTU Lyngby and Risø campuses. View this paper.
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Article
Influence of the Thermometer Inertia on the Quality of Temperature Control in a Hot Liquid Tank Heated with Electric Energy
Energies 2020, 13(15), 4039; https://doi.org/10.3390/en13154039 - 04 Aug 2020
Cited by 3 | Viewed by 854
Abstract
This paper presents the medium temperature monitoring system based on digital proportional–integral–derivative (PID) control. For industrial thermometers with a complex structure used for measuring the temperature of the fluid under high pressure, the accuracy of the first-order model is inadequate. A second-order differential [...] Read more.
This paper presents the medium temperature monitoring system based on digital proportional–integral–derivative (PID) control. For industrial thermometers with a complex structure used for measuring the temperature of the fluid under high pressure, the accuracy of the first-order model is inadequate. A second-order differential equation was applied to describe a dynamic response of a temperature sensor placed in a heavy thermowell (industrial thermometer). The quality of the water temperature control system in the tank was assessed when measuring the water temperature with a jacketed thermocouple and a thermometer in an industrial casing. A thermometer of a new design with a small time constant was also used to measure temperature. The quality of water temperature control in the hot water storage tank was evaluated using a classic industrial thermometer and a new design thermometer. In both cases, there was a K-type sheathed thermocouple inside the thermowell. Reductions in the time constant of the new thermometer are achieved by means of a steel casing with a small diameter hole inside which the thermocouple is precisely fitted. The time constants of the thermometers were determined experimentally with a jump in water temperature. A digital controller was designed to maintain the preset temperature in an electrically heated hot water tank. The function of the regulator was to adjust the power of the electrical heater to maintain a constant temperature of the liquid in the tank. Full article
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Article
How Does the Electricity Demand Profile Impact the Attractiveness of PV-Coupled Battery Systems Combining Applications?
Energies 2020, 13(15), 4038; https://doi.org/10.3390/en13154038 - 04 Aug 2020
Cited by 3 | Viewed by 1078
Abstract
Energy storage is a key solution to supply renewable electricity on demand and in particular batteries are becoming attractive for consumers who install PV panels. In order to minimize their electricity bill and keep the grid stable, batteries can combine applications. The daily [...] Read more.
Energy storage is a key solution to supply renewable electricity on demand and in particular batteries are becoming attractive for consumers who install PV panels. In order to minimize their electricity bill and keep the grid stable, batteries can combine applications. The daily match between PV supply and the electricity load profile is often considered as a determinant for the attractiveness of residential PV-coupled battery systems, however, the previous literature has so far mainly focused on the annual energy balance. In this paper, we analyze the techno-economic impact of adding a battery system to a new PV system that would otherwise be installed on its own, for different residential electricity load profiles in Geneva (Switzerland) and Austin (U.S.) using lithium-ion batteries performing various consumer applications, namely PV self-consumption, demand load-shifting, avoidance of PV curtailment, and demand peak shaving, individually and jointly. We employ clustering of the household’s load profile (with 15-minute resolution) for households with low, medium, and high annual electricity consumption in the two locations using a 1:1:1 sizing ratio. Our results show that with this simple sizing rule-of-thumb, the shape of the load profile has a small impact on the net present value of batteries. Overall, our analysis suggests that the effect of the load profile is small and differs across locations, whereas the combination of applications significantly increases profitability while marginally decreasing the share of self-consumption. Moreover, without the combination of applications, batteries are far from being economically viable. Full article
(This article belongs to the Special Issue Assessment of Photovoltaic-Battery Systems)
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Article
Optimal PV Parameter Estimation via Double Exponential Function-Based Dynamic Inertia Weight Particle Swarm Optimization
Energies 2020, 13(15), 4037; https://doi.org/10.3390/en13154037 - 04 Aug 2020
Cited by 9 | Viewed by 1163
Abstract
Parameters associated with electrical equivalent models of the photovoltaic (PV) system play a significant role in the performance enhancement of the PV system. However, the accurate estimation of these parameters signifies a challenging task due to the higher computational complexities and non-linear characteristics [...] Read more.
Parameters associated with electrical equivalent models of the photovoltaic (PV) system play a significant role in the performance enhancement of the PV system. However, the accurate estimation of these parameters signifies a challenging task due to the higher computational complexities and non-linear characteristics of the PV modules/panels. Hence, an effective, dynamic, and efficient optimization technique is required to estimate the parameters associated with PV models. This paper proposes a double exponential function-based dynamic inertia weight (DEDIW) strategy for the optimal parameter estimation of the PV cell and module that maintains an appropriate balance between the exploitation and exploration phases to mitigate the premature convergence problem of conventional particle swarm optimization (PSO). The proposed approach (DEDIWPSO) is validated for three test systems; (1) RTC France solar cell, (2) Photo-watt (PWP 201) PV module, and (3) a practical test system (JKM330P-72, 310 W polycrystalline PV module) which involve data collected under real environmental conditions for both single- and double-diode models. Results illustrate that the parameters obtained from proposed technique are better than those from the conventional PSO and various other techniques presented in the literature. Additionally, a comparison of the statistical results reveals that the proposed methodology is highly accurate, reliable, and efficient. Full article
(This article belongs to the Special Issue Nano-Structured Solar Cells 2020)
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Article
IoT-Based Smart Plug for Residential Energy Conservation: An Empirical Study Based on 15 Months’ Monitoring
Energies 2020, 13(15), 4035; https://doi.org/10.3390/en13154035 - 04 Aug 2020
Cited by 4 | Viewed by 849
Abstract
The study examines the implications of educating prosumers regarding Internet of Things (IoT) use and monitoring to reduce power consumption in the home and encourage energy conservation, sustainable living, and behavior change. Over 15 months, 125 households and household owners received training regarding [...] Read more.
The study examines the implications of educating prosumers regarding Internet of Things (IoT) use and monitoring to reduce power consumption in the home and encourage energy conservation, sustainable living, and behavior change. Over 15 months, 125 households and household owners received training regarding IoT plug equipment, usage monitoring, and energy reduction. A face to face survey was then conducted regarding power consumption reductions, frequency of monitoring, and user satisfaction compared to the previous year. The study found that participating households used around 5% less energy compared to average households. The reduction rate was found to have increased when more appliances were connected to smart plugs and their power usage was monitored more frequently. Power usage also fell in a greater level when participants were more satisfied with being given smart plugs and related education. Moreover, energy reduction rates increase when smart plugs were used for cooling and heating appliances as well as video, audio, and related devices. The results suggest that this program can be used to reduce energy use, which can be beneficial for smart homes and smart cities. The study demonstrates the importance of education from the perspective of energy conservation and related policies. Full article
(This article belongs to the Special Issue IoT and Sensor Networks in Industry and Society)
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Article
Does Energy Price Induce China’s Green Energy Innovation?
Energies 2020, 13(15), 4034; https://doi.org/10.3390/en13154034 - 04 Aug 2020
Cited by 3 | Viewed by 867
Abstract
This paper aims to comprehensively analyze the relationship between energy price and green energy innovation in China, and first studies the impact of energy price on China’s green energy innovation, then further investigates the moderating role of energy price distortion in the price–innovation [...] Read more.
This paper aims to comprehensively analyze the relationship between energy price and green energy innovation in China, and first studies the impact of energy price on China’s green energy innovation, then further investigates the moderating role of energy price distortion in the price–innovation relationship, especially in the context of lagging energy marketization level in the process of China’s transition from planned economy to the market economy. Based on the data of 30 provinces in China from 2003 to 2017, this paper provides a measurement of green energy innovation capacity through the number of “alternative energy production” and “energy conservation” patents. Our results show that energy price has a significantly positive impact on China’s green energy innovation, no matter the number of green energy patent applications or the number of green energy patent grants is used as the proxy of green energy innovation capacity. However, there exists heterogeneity related to the influence of energy price on green energy innovation. Specifically, energy price has a noticeable role in promoting green energy innovation in central and western China, but not in eastern China. Further research results show that energy price distortion significantly reduces the inducing effect of energy price on green energy innovation. Meanwhile, the distortion degrees of energy price in the central and western regions of China are significantly lower than that in the eastern region, which explains to a large extent why the inducing effect of energy price on innovation is more prominent in the central and western regions. Full article
(This article belongs to the Special Issue Global Market for Crude Oil)
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Article
Occupancy Prediction Using Differential Evolution Online Sequential Extreme Learning Machine Model
Energies 2020, 13(15), 4033; https://doi.org/10.3390/en13154033 - 04 Aug 2020
Viewed by 739
Abstract
Despite increasing energy efficiency requirements, the full potential of energy efficiency is still unlocked; many buildings in the EU tend to consume more energy than predicted. Gathering data and developing models to predict occupants’ behaviour is seen as the next frontier in sustainable [...] Read more.
Despite increasing energy efficiency requirements, the full potential of energy efficiency is still unlocked; many buildings in the EU tend to consume more energy than predicted. Gathering data and developing models to predict occupants’ behaviour is seen as the next frontier in sustainable design. Measurements in the analysed open-space office showed accordingly 3.5 and 2.7 times lower occupancy compared to the ones given by DesignBuilder’s and EN 16798-1. This proves that proposed occupancy patterns are only suitable for typical open-space offices. The results of the previous studies and proposed occupancy prediction models have limited applications and limited accuracies. In this paper, the hybrid differential evolution online sequential extreme learning machine (DE-OSELM) model was applied for building occupants’ presence prediction in open-space office. The model was not previously applied in this area of research. It was found that prediction using experimentally gained indoor and outdoor parameters for the whole analysed period resulted in a correlation coefficient R2 = 0.72. The best correlation was found with indoor CO2 concentration—R2 = 0.71 for the analysed period. It was concluded that a 4 week measurement period was sufficient for the prediction of the building’s occupancy and that DE-OSELM is a fast and reliable model suitable for this purpose. Full article
(This article belongs to the Section Sustainable Energy)
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Article
Design, Implementation, and Evaluation of Open Power Quality
Energies 2020, 13(15), 4032; https://doi.org/10.3390/en13154032 - 04 Aug 2020
Cited by 1 | Viewed by 640
Abstract
Modern electrical grids are transitioning from a centralized generation architecture to an architecture with significant distributed, intermittent generation. This transition means that the formerly sharp distinction between energy producers (utility companies) and consumers (residences, businesses, etc.) are blurring: end-users both produce and consume [...] Read more.
Modern electrical grids are transitioning from a centralized generation architecture to an architecture with significant distributed, intermittent generation. This transition means that the formerly sharp distinction between energy producers (utility companies) and consumers (residences, businesses, etc.) are blurring: end-users both produce and consume energy, making energy management and public policy more complex. The goal of the Open Power Quality (OPQ) project is to design and implement a low cost, distributed power quality sensor network that provides useful new forms of information about modern electrical grids to producers, consumers, researchers, and policy makers. In 2019, we performed a pilot study involving the deployment of an OPQ sensor network at the University of Hawaii microgrid for three months. Results of the pilot study validate the ability of OPQ to collect accurate power quality data in a way that provides useful new insights into electrical grids. Full article
(This article belongs to the Section Smart Grids and Microgrids)
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Article
Energy Price Policies and Food Prices: Empirical Evidence from Iran
Energies 2020, 13(15), 4031; https://doi.org/10.3390/en13154031 - 04 Aug 2020
Viewed by 907
Abstract
During the last decade, the rising trend in energy prices and its potential effect on food prices have become a controversial issue between policy-makers and economists. Therefore, research addressing the relationship between food and macroeconomic variables, such as energy prices, will be useful [...] Read more.
During the last decade, the rising trend in energy prices and its potential effect on food prices have become a controversial issue between policy-makers and economists. Therefore, research addressing the relationship between food and macroeconomic variables, such as energy prices, will be useful in providing information for the design of appropriate economic policies. This study uses data from Iran to examine the impacts (short- and long-term) of exchange rate and energy prices on food prices. Iran is a good case study as in recent years its consumers have faced a rapid increase in both fuel and food prices. The variables employed in this study are the prices of ten food products, exchange rate (the value of Iranian rial per US dollar), and petroleum prices. All data in this study are from the Statistical Centre of Iran (SCI). We employ the panel unit root test, Pedroni co-integration tests, Pooled Mean Group (PMG), Mean Group (MG), and Dynamic Fixed Effects (DFE) estimation techniques, applied to a panel of monthly prices for ten food products for the period of March 1995 to February 2018. Results show that in both the short- and long-run, food prices would increase in response to an increase in energy prices. Findings also suggest that the appreciation of the United States Dollar (USD) in terms of the Iranian rial exerts a positive and significant impact on food prices in the long run. Full article
(This article belongs to the Special Issue Energy Policy and Policy Implications 2020)
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Article
Modelling and Measurement of a Moving Magnet Linear Motor for Linear Compressor
Energies 2020, 13(15), 4030; https://doi.org/10.3390/en13154030 - 04 Aug 2020
Viewed by 661
Abstract
For the purpose of efficiency improvement, a linear motor that performs a linear reciprocating motion can be employed to directly drive the piston in a reciprocating refrigeration compressor without crankshaft mechanism. This also facilitates the modulation of cooling capacity as the stroke and [...] Read more.
For the purpose of efficiency improvement, a linear motor that performs a linear reciprocating motion can be employed to directly drive the piston in a reciprocating refrigeration compressor without crankshaft mechanism. This also facilitates the modulation of cooling capacity as the stroke and frequency can be readily varied in response to heat load. A novel design of moving magnet linear motor for linear compressor was analyzed in the paper. A finite element analysis (FEA) model was built to simulate the characteristics of the linear motor. Current and displacement signals were measured from a test rig and were defined in the transient FEA model. Transient motor force was simulated with the FEA model and good agreements are shown between the results from the FEA model and interpolated shaft force from static force measurements. Major Losses, such as copper loss and core loss were also computed. Motor efficiency decreased from 0.88 to 0.83 as stroke increased from 9 mm to 12 mm, while the pressure ratio remained unchanged. Comparisons were made between the present moving magnet linear motor and moving coil linear motors. Generally, the moving magnet linear motor demonstrates higher efficiency than moving coil motors, which have significantly higher copper loss. The present moving magnet design with simple structure could be further optimized to improve motor efficiency. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Article
Combined Diagnostic Analysis of Dynamic Combustion Characteristics in a Scramjet Engine
Energies 2020, 13(15), 4029; https://doi.org/10.3390/en13154029 - 04 Aug 2020
Cited by 4 | Viewed by 979
Abstract
In this work, the dynamic combustion characteristics in a scramjet engine were investigated using three diagnostic data analysis methods: DMD (Dynamic Mode Decomposition), STFT (Short-Time Fourier Transform), and CEMA (Chemical Explosive Mode Analysis). The data for the analyses were obtained through a 2D [...] Read more.
In this work, the dynamic combustion characteristics in a scramjet engine were investigated using three diagnostic data analysis methods: DMD (Dynamic Mode Decomposition), STFT (Short-Time Fourier Transform), and CEMA (Chemical Explosive Mode Analysis). The data for the analyses were obtained through a 2D numerical experiment using a DDES (Delayed Detached Eddy Simulation) turbulence model, the UCSD (University of California at San Diego) hydrogen/oxygen chemical reaction mechanism, and high-resolution schemes. The STFT was able to detect that oscillations above 50 kHz identified as dominant in FFT results were not the dominant frequencies in a channel-type combustor. In the analysis using DMD, it was confirmed that the critical point that induced a complete change of mixing characteristics existed between an injection pressure of 0.75 MPa and 1.0 MPa. A combined diagnostic analysis that included a CEMA was performed to investigate the dynamic combustion characteristics. The differences in the reaction steps forming the flame structure under each combustor condition were identified, and, through this, it was confirmed that the pressure distribution upstream of the combustor dominated the dynamic combustion characteristics of this scramjet engine. From these processes, it was confirmed that the combined analysis method used in this paper is an effective approach to diagnose the combustion characteristics of a supersonic combustor. Full article
(This article belongs to the Special Issue Scramjet and Ramjet Combustion)
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Article
Aerodynamic Drag Analysis of Autonomous Electric Vehicle Platoons
Energies 2020, 13(15), 4028; https://doi.org/10.3390/en13154028 - 04 Aug 2020
Cited by 2 | Viewed by 869
Abstract
Vehicle platooning has been proposed as one of the potential technologies for intelligent transport systems to improve transportation and energy efficiency in urban cities. Despite extensive studies conducted on the platooning of heavy-duty trucks, literature on the analysis of urban vehicle platoons has [...] Read more.
Vehicle platooning has been proposed as one of the potential technologies for intelligent transport systems to improve transportation and energy efficiency in urban cities. Despite extensive studies conducted on the platooning of heavy-duty trucks, literature on the analysis of urban vehicle platoons has been limited. To analyse the impact of platooning in urban environments, this paper studies the influence of intervehicle distance, platoon size and vehicle speed on the drag coefficient of the vehicles in a platoon using computational fluid dynamics (CFD). Two vehicle models—a minibus and a passenger car—are analysed to characterise the drag coefficients of the respective platoons. An analysis of energy consumption is conducted to evaluate the energy savings with platooning using a longitudinal dynamics simulation. The results showed a reduction in the average drag coefficient of the platoon of up to 24% at an intervehicle distance of 1 m depending on the number of vehicles in the platoon. With a larger intervehicle distance of 4 m, the reduction in the drag coefficient decreased to 4% of the drag coefficient of the isolated vehicle. Subsequently, energy savings with platooning were calculated to be up to 10% depending on the driving cycle, intervehicle distance and platoon size. Full article
(This article belongs to the Special Issue Intelligent Transportation Systems)
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Article
Detailing the Self-Discharge of a Cathode Based on a Prussian Blue Analogue
Energies 2020, 13(15), 4027; https://doi.org/10.3390/en13154027 - 04 Aug 2020
Cited by 1 | Viewed by 1050
Abstract
Prussian Blue analogues (PBAs) are a promising class of electrode active materials for batteries. Among them, copper nitroprusside, Cu[Fe(CN)5NO], has recently been investigated for its peculiar redox system, which also involves the nitrosyl ligand as a non-innocent ligand, in addition to [...] Read more.
Prussian Blue analogues (PBAs) are a promising class of electrode active materials for batteries. Among them, copper nitroprusside, Cu[Fe(CN)5NO], has recently been investigated for its peculiar redox system, which also involves the nitrosyl ligand as a non-innocent ligand, in addition to the electroactivity of the metal sites, Cu and Fe. This paper studies the dynamics of the electrode, employing surface sensitive X-ray Photoelectron spectroscopy (XPS) and bulk sensitive X-ray absorption spectroscopy (XAS) techniques. XPS provided chemical information on the layers formed on electrode surfaces following the self-discharge process of the cathode material in the presence of the electrolyte. These layers consist mainly of electrolyte degradation products, such as LiF, LixPOyFz and LixPFy. Moreover, as evidenced by XAS and XPS, reduction at both metal sites takes place in the bulk and in the surface of the material, clearly evidencing that a self-discharge process is occurring. We observed faster processes and higher amounts of reduced species and decomposition products in the case of samples with a higher amount of coordination water. Full article
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Review
Recent Advances in the Critical Heat Flux Amelioration of Pool Boiling Surfaces Using Metal Oxide Nanoparticle Deposition
Energies 2020, 13(15), 4026; https://doi.org/10.3390/en13154026 - 04 Aug 2020
Cited by 5 | Viewed by 1132
Abstract
Pool boiling is an effective heat transfer process in a wide range of applications related to energy conversion, including power generation, solar collectors, cooling systems, refrigeration and air conditioning. By considering the broad range of applications, any improvement in higher heat-removal yield can [...] Read more.
Pool boiling is an effective heat transfer process in a wide range of applications related to energy conversion, including power generation, solar collectors, cooling systems, refrigeration and air conditioning. By considering the broad range of applications, any improvement in higher heat-removal yield can ameliorate the ultimate heat usage and delay or even avoid the occurrence of system failures, thus leading to remarkable economic, environmental and energy efficiency outcomes. A century of research on ameliorating critical heat flux (CHF) has focused on altering the boiling surface characteristics, such as its nucleation site density, wettability, wickability and heat transfer area, by many innovative techniques. Due to the remarkable interest of using nanoparticle deposition on boiling surfaces, this review is targeted towards investigating whether or not metal oxide nanoparticles can modify surface characteristics to enhance the CHF. The influence of nanoparticle material, thermo-physical properties, concentration, shape, and size are categorized, and the inconsistency or contradictions of the existing research results are recognized. In the following, nanoparticle deposition methods are presented to provide a worthwhile alternative to deposition rather than nanofluid boiling. Furthermore, possible mechanisms and models are identified to explain the amelioration results. Finally, the present status of nanoparticle deposition for CHF amelioration, along with their future challenges, amelioration potentials, limitations, and their possible industrial implementation, is discussed. Full article
(This article belongs to the Special Issue Advances in Heat Transfer Enhancement)
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Article
RANS Simulation of the Effect of Pulse Form on Fluid Flow and Convective Heat Transfer in an Intermittent Round Jet Impingement
Energies 2020, 13(15), 4025; https://doi.org/10.3390/en13154025 - 04 Aug 2020
Cited by 1 | Viewed by 644
Abstract
The of effect pulse form (rectangular, sinusoidal and triangular) on the fluid flow and heat transfer of an intermittent jet impingement was studied numerically. It was shown in a non-steady-state jet, both an increase and decrease in heat transfer are possible compared with [...] Read more.
The of effect pulse form (rectangular, sinusoidal and triangular) on the fluid flow and heat transfer of an intermittent jet impingement was studied numerically. It was shown in a non-steady-state jet, both an increase and decrease in heat transfer are possible compared with steady-state jet for all investigated pulse forms. For small distances between the pipe edge and obstacle (H/D ≤ 6) in the pulsed jet, heat transfer around the stagnation point increases with increasing pulse frequency, while for H/D > 8 an increase in frequency causes a heat transfer decrease. A growth in the Reynolds number causes a decrease in heat transfer, and data for all frequencies approach the steady-state flow regime. The numerical model is compared with the experimental results. Satisfactory agreement on the influence of the form and frequency of pulses on heat transfer for the pulsed jet on the obstacle surface is obtained. Full article
(This article belongs to the Special Issue Enhancement of Heat Transfer in Power Plants)
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Article
Examining the Impact of Daylighting and the Corresponding Lighting Controls to the Users of Office Buildings
Energies 2020, 13(15), 4024; https://doi.org/10.3390/en13154024 - 04 Aug 2020
Cited by 5 | Viewed by 893
Abstract
Daylight utilization significantly contributes to energy savings in office buildings. However, daylight integration requires careful design so as to include variations in daylight availability and maintain a balance between factors such as lighting quality and heat gain or loss. Designers with proper planning [...] Read more.
Daylight utilization significantly contributes to energy savings in office buildings. However, daylight integration requires careful design so as to include variations in daylight availability and maintain a balance between factors such as lighting quality and heat gain or loss. Designers with proper planning can not only improve the visual environment and create higher-quality spaces, but simultaneously minimize energy costs for buildings. The utilization of photosensors can exploit the benefits of daylighting by dimming the lighting system, so that no excessive luminous flux is produced, thus leading to energy savings as well as visual contentment. However, the human factor is crucial for the proper function of a lighting control system. Without its acceptance from the users, energy savings can be minimized or even negligible. The objective of this paper is to present a post-occupancy evaluation regarding occupant satisfaction and acceptance in relation to daylighting in offices equipped with automated daylight controls. In addition, the response of the users was compared with lighting measurements that were performed during the post-occupancy evaluation. Three case studies of office buildings with installed daylight-harvesting systems were examined. The age of the occupants was a crucial factor concerning their satisfaction in relation to the lighting levels. Aged users were more comfortable with lighting levels over 500lx, while young users were satisfied with 300lx. The impact of different control algorithms was outlined, with the integral reset algorithm performing poorly. The acceptance of the users for the closed loop systems maintained the expected energy savings of the daylight harvesting technique. Most of the occupants preferred to use daylight as a light source combined with artificial light but having the control to either override or switch it on and off at will. The results shown that a post-occupancy survey along with lighting measurements are significant for making an office environment a humancentric one. Full article
(This article belongs to the Special Issue Building Energy Audits-Diagnosis and Retrofitting)
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Article
Assessment of Energy Storage from Photovoltaic Installations in Poland Using Batteries or Hydrogen
Energies 2020, 13(15), 4023; https://doi.org/10.3390/en13154023 - 04 Aug 2020
Cited by 6 | Viewed by 1058
Abstract
This paper presents a series of economic efficiency studies comparing three different investment variants: without energy storage, with energy stored in batteries and hydrogen installation with a PEM fuel cell stack for a location in Poland. To reach a target, the current solar [...] Read more.
This paper presents a series of economic efficiency studies comparing three different investment variants: without energy storage, with energy stored in batteries and hydrogen installation with a PEM fuel cell stack for a location in Poland. To reach a target, the current solar potential in Poland, the photovoltaic (PV) productivity, the capacity of the energy storage in batteries as well as the size of the hydrogen production system were calculated. The solar potential was determined using archival meteorological data and the Krieg estimation method. A laboratory scale PV system (1 kW) was used to estimate the decrease in real solar installation power during the last 10 years of operation. All analyses were made for a 100 kW photovoltaic array located in Poland using static and dynamic methods of investment project assessment, such as Simply Bay Back Period (SPBP) or Net Present Value (NPV). The results showed that the SPBP amounted to 8.8 years and NPV 54,896 € for non-storage systems. Whereas, for systems with energy stored the economic indexes were, as follow: SPBP = never, NPV = 183,428 € for batteries and SPBP = 14.74 years, NPV = 22,639 € for hydrogen/fuel cell installation. Storage in hydrogen is more advantageous than batteries due to the smaller investment outlays. Full article
(This article belongs to the Special Issue Assessment of Photovoltaic-Battery Systems)
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Article
Education for Sustainable Energy: Comparison of Different Types of E-Learning Activities
Energies 2020, 13(15), 4022; https://doi.org/10.3390/en13154022 - 04 Aug 2020
Viewed by 825
Abstract
This paper reports a comparison of results obtained by using different e-learning strategies for teaching a biogas topic in two courses of the chemical engineering degree at the University of Granada. Particularly, four different asynchronous e-learning activities were carefully chosen: (1) noninteractive videos [...] Read more.
This paper reports a comparison of results obtained by using different e-learning strategies for teaching a biogas topic in two courses of the chemical engineering degree at the University of Granada. Particularly, four different asynchronous e-learning activities were carefully chosen: (1) noninteractive videos and audio files; (2) reading papers and discussion; (3) virtual tour of recommended websites of entities/associations/organizations working in the biogas sector; (4) PowerPoint slides and class notes. Students evaluated their satisfaction level (assessment) and teachers gave scores for evaluation exams (scores). We discuss the results from a quantitative point of view to suggest recommendations for improving e-learning implementations in education for sustainable energy. For dependent variables, reached scores and satisfaction assessment, we find the differences between means for students in two different academic years are no significant. In addition, there are no significant differences between means depending on the type of course. Significant differences appear for scores and satisfaction assessment between different activities. Finally, we deeply analyze the relationship between score and satisfaction assessment. The results show a positive correlation between assessment of e-learning activities and the score level reached by students. Full article
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Article
Optimal Management of the Desalination System Demand in Non-Interconnected Islands
Energies 2020, 13(15), 4021; https://doi.org/10.3390/en13154021 - 04 Aug 2020
Viewed by 750
Abstract
The high energy consumption of desalination systems represents a significant opportunity for the application of demand response schemes, particularly for the case of Non-Interconnected Island (NII) systems. In particular, the optimal management of the desalination demand can be proven quite beneficial in increasing [...] Read more.
The high energy consumption of desalination systems represents a significant opportunity for the application of demand response schemes, particularly for the case of Non-Interconnected Island (NII) systems. In particular, the optimal management of the desalination demand can be proven quite beneficial in increasing the Renewable Energy Sources’ (RES) penetration, which is one of the main objectives in the day-ahead scheduling of the electricity system in Greek NIIs. This paper proposes a detailed representation of the desalination system, taking into account all the relevant constraints for the system’s operation. The mathematical representation of the aforementioned operation is incorporated in the day-ahead scheduling (DAS) for the case of Greek NII systems in order to define the optimal operational scheduling of a desalination system. The proposed optimisation procedure is applied for the desalination system installed in the Greek island of Kythnos. The results of the analysis indicate that the DAS problem shall be fully aware of the capabilities of the desalination system in order to allow specific water flows (in and out of specific reservoirs) at specific hours of the day, allowing the optimal exploitation of the available RES produced energy. Full article
(This article belongs to the Section Smart Grids and Microgrids)
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Article
The “INNOVARE” Project: Innovative Plants for Distributed Poly-Generation by Residual Biomass
Energies 2020, 13(15), 4020; https://doi.org/10.3390/en13154020 - 04 Aug 2020
Viewed by 850
Abstract
The valorization of residual biomass plays today a decisive role in the concept of “circular economy”, according to which each waste material must be reused to its maximum extent. The collection and energy valorization at the local level of biomass from forest management [...] Read more.
The valorization of residual biomass plays today a decisive role in the concept of “circular economy”, according to which each waste material must be reused to its maximum extent. The collection and energy valorization at the local level of biomass from forest management practices and wildfire prevention cutting can be settled in protected areas to contribute to local decarbonization, by removing power generation from fossil fuels. Despite the evident advantages of bioenergy systems, several problems still hinder their diffusion, such as the need to assure their reliability by extending the operating range with materials of different origin. The Italian project “INNOVARE—Innovative plants for distributed poly-generation by residual biomass”, funded by the Italian Ministry of Economic Development (MISE), has the main scope of improving micro-cogeneration technologies fueled by biomass. A micro-combined heat and power (mCHP) unit was chosen as a case study to discuss pros and cons of biomass-powered cogeneration within a national park, especially due to its flexibility of use. The availability of local biomasses (woodchips, olive milling residuals) was established by studying the agro-industrial production and by identifying forest areas to be properly managed through an approach using a satellite location system based on the microwave technology. A detailed synergic numerical and experimental characterization of the selected cogeneration system was performed in order to identify its main inefficiencies. Improvements of its operation were optimized by acting on the engine control strategy and by also adding a post-treatment system on the engine exhaust gas line. Overall, the electrical output was increased by up to 6% using the correct spark timing, and pollutant emissions were reduced well below the limits allowed by legislation by working with a lean mixture and by adopting an oxidizing catalyst. Finally, the global efficiency of the system increased from 45.8% to 63.2%. The right blending of different biomasses led to an important improvement of the reliability of the entire plant despite using an agrifood residual, such as olive pomace. It was demonstrated that the use of this biomass is feasible if its maximum mass percentage in a wood matrix mixture does not exceed 25%. The project was concluded with a real operation demonstration within a national park in Southern Italy by replacing a diesel genset with the analyzed and improved biomass-powered plant and by proving a decisive improvement of air quality in the real environment during exercise. Full article
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Article
Defining Transmission System Operators’ Investment Shares for Phase-Shifting Transformers Used for Coordinated Redispatch
Energies 2020, 13(15), 4019; https://doi.org/10.3390/en13154019 - 04 Aug 2020
Viewed by 701
Abstract
The implementation of network codes within the framework of European Transmission System Operators (TSOs), involves redesigning the process of executing remedial actions aimed at maintaining the power system on a daily basis. One of the key elements of this redesign is the co-optimisation [...] Read more.
The implementation of network codes within the framework of European Transmission System Operators (TSOs), involves redesigning the process of executing remedial actions aimed at maintaining the power system on a daily basis. One of the key elements of this redesign is the co-optimisation of all accessible measures, bringing a cost-optimal result and providing network security for the entire Capacity Calculation Region (CCR). This specifically means that the currently installed Phase Shifting Transformers (PSTs) are expected to be utilised for the benefit of the whole CCR, with no special priority to any issues incurred by the owner. Therefore, this paper addresses any questions regarding the rules of financing (investment shares per TSO) to be applied for future PST installations. The investment shares are calculated based on the exemplary implementation of a new European procedure – cost-sharing of remedial actions. Consequently, another long-term application of this process is postulated. In order to support the claims with numerical evidence, two scenarios with new PST investments are analysed. The conclusions drawn show that the largest investment burden can be imposed upon zones different from the area of which the new PST installation has taken place. As a result, joint TSOs’ investments may be a potential solution to financing new devices used for future coordination of remedial actions. Full article
(This article belongs to the Section Energy Economics and Policy)
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Article
Assessment of MOV Deterioration under Energized Conditions
Energies 2020, 13(15), 4018; https://doi.org/10.3390/en13154018 - 04 Aug 2020
Viewed by 505
Abstract
Metal oxide varistors (MOVs) are widely used to protect electrical and electronic devices that are very vulnerable to surges due to the low insulation level of the equipment. MOVs deteriorate gradually due to manufacturing defects, mechanical and thermal stress, or repeated protective operations [...] Read more.
Metal oxide varistors (MOVs) are widely used to protect electrical and electronic devices that are very vulnerable to surges due to the low insulation level of the equipment. MOVs deteriorate gradually due to manufacturing defects, mechanical and thermal stress, or repeated protective operations against surges. These defects result in the thermal runaway of MOV and finally lead to the explosion and electric fire of electrical and electronic devices due to a short circuit and a line-to-ground fault. Therefore, the reliable assessment of the condition of MOV deterioration is required for electrical and electronic equipment. However, when most accelerated degradation tests for the MOV have been performed to date, an 8/20 μs standard surge current is applied under de-energized conditions, which is unlike the actual operating environment. In this study, a surge generator was designed to apply a surge current to MOVs to monitor their deterioration. Three different types of leakage currents were measured to analyze the change rates of their electrical characteristics of MOVs by comparing them with the reference voltage variation. Furthermore, the condition assessment of MOV deterioration under energized and de-energized conditions was investigated. Full article
(This article belongs to the Special Issue Power Conditioning and Power Protection for Electronic Systems)
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Article
Forecasting Day-Ahead Hourly Photovoltaic Power Generation Using Convolutional Self-Attention Based Long Short-Term Memory
Energies 2020, 13(15), 4017; https://doi.org/10.3390/en13154017 - 04 Aug 2020
Cited by 3 | Viewed by 770
Abstract
The problem of Photovoltaic (PV) power generation forecasting is becoming crucial as the penetration level of Distributed Energy Resources (DERs) increases in microgrids and Virtual Power Plants (VPPs). In order to improve the stability of power systems, a fair amount of research has [...] Read more.
The problem of Photovoltaic (PV) power generation forecasting is becoming crucial as the penetration level of Distributed Energy Resources (DERs) increases in microgrids and Virtual Power Plants (VPPs). In order to improve the stability of power systems, a fair amount of research has been proposed for increasing prediction performance in practical environments through statistical, machine learning, deep learning, and hybrid approaches. Despite these efforts, the problem of forecasting PV power generation remains to be challenging in power system operations since existing methods show limited accuracy and thus are not sufficiently practical enough to be widely deployed. Many existing methods using long historical data suffer from the long-term dependency problem and are not able to produce high prediction accuracy due to their failure to fully utilize all features of long sequence inputs. To address this problem, we propose a deep learning-based PV power generation forecasting model called Convolutional Self-Attention based Long Short-Term Memory (LSTM). By using the convolutional self-attention mechanism, we can significantly improve prediction accuracy by capturing the local context of the data and generating keys and queries that fit the local context. To validate the applicability of the proposed model, we conduct extensive experiments on both PV power generation forecasting using a real world dataset and power consumption forecasting. The experimental results of power generation forecasting using the real world datasets show that the MAPEs of the proposed model are much lower, in fact by 7.7%, 6%, 3.9% compared to the Deep Neural Network (DNN), LSTM and LSTM with the canonical self-attention, respectively. As for power consumption forecasting, the proposed model exhibits 32%, 17% and 44% lower Mean Absolute Percentage Error (MAPE) than the DNN, LSTM and LSTM with the canonical self-attention, respectively. Full article
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Article
New Multifunctional Isolated Microinverter with Integrated Energy Storage System for PV Applications
Energies 2020, 13(15), 4016; https://doi.org/10.3390/en13154016 - 04 Aug 2020
Cited by 1 | Viewed by 632
Abstract
This paper proposes a novel multifunctional isolated microinverter which is able to extract the maximum available power from a solar photovoltaic module and inject it into the power grid, while simultaneously charging a battery energy storage system (BESS). The proposed microinverter integrates a [...] Read more.
This paper proposes a novel multifunctional isolated microinverter which is able to extract the maximum available power from a solar photovoltaic module and inject it into the power grid, while simultaneously charging a battery energy storage system (BESS). The proposed microinverter integrates a novel DC–DC power converter and a conventional DC–AC power converter. The DC–DC power converter is able to send electrical energy to the secondary side of a high-frequency transformer and to the BESS, using only two power switches. Throughout this paper, the converter topology, the operation modes, the control algorithms, and the development of a laboratory prototype of the proposed microinverter are described in detail. Moreover, simulation and experimental results are presented to demonstrate the feasibility of the proposed solution. Full article
(This article belongs to the Special Issue Assessment of Photovoltaic-Battery Systems)
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Article
Vectorized Mathematical Model of a Slip-Ring Induction Motor
Energies 2020, 13(15), 4015; https://doi.org/10.3390/en13154015 - 04 Aug 2020
Viewed by 557
Abstract
The paper deals with the modeling of a slip-ring induction motor. Induction motors are very often used in industry and their suitable model is needed to reduce control and operating costs. The identification process of self and mutual inductances of the stator and [...] Read more.
The paper deals with the modeling of a slip-ring induction motor. Induction motors are very often used in industry and their suitable model is needed to reduce control and operating costs. The identification process of self and mutual inductances of the stator and rotor, and mutual inductances between them in the function of the rotor rotation angle is presented. The dependence of each inductance on the rotor rotation angle is determined experimentally. The inductance matrix is then formulated. Taking the magnetic energy of the inductances and kinetic energy of the rotor into account, the Lagrange function is defined. Next, the motor motion equations are obtained. After making some algebraic transformations and using the dimensionless variables, the motion equations of electric circuits and of the mechanical equation are written separately in the forms facilitating their solution. The solution was obtained using the Simulink model for the stator and rotor currents in the form of vectors. The simulation was controlled by MATLAB script. The results of the simulation are presented in the form of basic variables time courses and compared with some values calculated with the use Steinmetz model of induction motor. The work is followed by two appendices, which contain procedures for determining the inverted inductance matrix. Full article
(This article belongs to the Section Electric Vehicles)
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Article
Carbon Dioxide Mixtures as Working Fluid for High-Temperature Heat Recovery: A Thermodynamic Comparison with Transcritical Organic Rankine Cycles
Energies 2020, 13(15), 4014; https://doi.org/10.3390/en13154014 - 04 Aug 2020
Cited by 2 | Viewed by 590
Abstract
This study aims to provide a thermodynamic comparison between supercritical CO2 cycles and ORC cycles utilizing flue gases as waste heat source. Moreover, the possibility of using CO2 mixtures as working fluids in transcritical cycles to enhance the performance of the [...] Read more.
This study aims to provide a thermodynamic comparison between supercritical CO2 cycles and ORC cycles utilizing flue gases as waste heat source. Moreover, the possibility of using CO2 mixtures as working fluids in transcritical cycles to enhance the performance of the thermodynamic cycle is explored. ORCs operating with pure working fluids show higher cyclic thermal and total efficiencies compared to supercritical CO2 cycles; thus, they represent a better option for high-temperature waste heat recovery provided that the thermal stability at a higher temperature has been assessed. Based on the improved global thermodynamic performance and good thermal stability of R134a, CO2-R134a is investigated as an illustrative, promising working fluid mixture for transcritical power cycles. The results show that a total efficiency of 0.1476 is obtained for the CO2-R134a mixture (0.3 mole fraction of R134a) at a maximum cycle pressure of 200 bars, which is 15.86% higher than the supercritical carbon dioxide cycle efficiency of 0.1274, obtained at the comparatively high maximum pressure of 300 bars. Steam cycles, owing to their larger number of required turbine stages and lower power output, did not prove to be a suitable option in this application. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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Article
Converting a Water Pressurized Network in a Small Town into a Solar Power Water System
Energies 2020, 13(15), 4013; https://doi.org/10.3390/en13154013 - 04 Aug 2020
Cited by 2 | Viewed by 790
Abstract
The efficient management of water and energy is one challenge for managers of water pressurized systems. In a scheme with high pressure on the environment, solar power appears as an opportunity for nonrenewable energy expenditure reduction and emissions elimination. In Spain, new legislation [...] Read more.
The efficient management of water and energy is one challenge for managers of water pressurized systems. In a scheme with high pressure on the environment, solar power appears as an opportunity for nonrenewable energy expenditure reduction and emissions elimination. In Spain, new legislation that eliminates old taxes associated with solar energy production, a drop in the cost of solar photovoltaic modules, and higher values of irradiance has converted solar powered water systems into one of the trendiest topics in the water industry. One alternative to store energy (compulsory in standalone photovoltaic systems) when managing pressurized urban water networks is the use of head tanks (tanks accumulate water during the day and release it at night). This work intends to compare the pressurized network running as a standalone system and a hybrid solution that incorporates solar energy supply and electricity grids. The indicator used for finding the best choice is the net present value for the solar power water system lifespan. This study analyzed the possibility of transferring the energy surplus obtained at midday to the electricity grid, a circumstance introduced in the Spanish legislation since April 2019. We developed a real case study in a small town in the Alicante Province, whose findings provide planning policymakers with very useful information in this case and similar case studies Full article
(This article belongs to the Special Issue Assessment of Photovoltaic-Battery Systems)
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Article
Development of an Elevation–Fresnel Linked Mini-Heliostat Array
Energies 2020, 13(15), 4012; https://doi.org/10.3390/en13154012 - 04 Aug 2020
Viewed by 817
Abstract
Heliostats are critical components of solar tower technology and different strategies have been proposed to reduce their costs; among them diminishing their size to reduce wind loads or linking nearby heliostats mechanically, to reduce the overall number of actuators. This document aims to [...] Read more.
Heliostats are critical components of solar tower technology and different strategies have been proposed to reduce their costs; among them diminishing their size to reduce wind loads or linking nearby heliostats mechanically, to reduce the overall number of actuators. This document aims to describe the development of a linked array of mini-heliostats which move together in an elevation–Fresnel configuration. This configuration consists of an array of mirrors rotating around linked parallel axes, in a linear Fresnel style with an added elevation mechanism allowing all axes to incline simultaneously in the plane North–South–Zenith; that is equivalent to an array of N linked mini-heliostats moved by only two drives instead of 2N. A detailed analytical study of the Sun-tracking performance of this kind of heliostat arrays was carried out, and an 8-mirror prototype based on optical and mechanical analyses was designed, built and tested. Even though the mirrors are flat, the array produced a rather compact radiative flux distribution on the receiver. The flux distribution is compatible with a slope error of the order of 1 mrad. Peak and mean concentration ratios reached 6.89 and 3.94, respectively. Full article
(This article belongs to the Section Solar Energy and Photovoltaic Systems)
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Article
A Nonlinear Autoregressive Distributed Lag (NARDL) Analysis of West Texas Intermediate Oil Prices and the DOW JONES Index
Energies 2020, 13(15), 4011; https://doi.org/10.3390/en13154011 - 04 Aug 2020
Viewed by 721
Abstract
The paper features an examination of the link between the behaviour of oil prices and DowJones Index in a nonlinear autoregressive distributed lag nonlinear autoregressive distributed lag (NARDL) framework. The attraction of NARDL is that it represents the simplest method available of modelling [...] Read more.
The paper features an examination of the link between the behaviour of oil prices and DowJones Index in a nonlinear autoregressive distributed lag nonlinear autoregressive distributed lag (NARDL) framework. The attraction of NARDL is that it represents the simplest method available of modelling combined short- and long-run asymmetries. The bounds testing framework adopted means that it can be applied to stationary and non-stationary time series vectors, or combinations of both. The data comprise a monthly West Texas Intermediate (WTI) crude oil series from Federal Reserve Bank of St Louis (FRED), commencing in January 2000 and terminating in February 2019, and a corresponding monthly DOW JONES index adjusted-price series obtained from Yahoo Finance. Both series are adjusted for monthly USA CPI values to create real series. The results of the analysis suggest that movements in the lagged real levels of monthly WTI crude oil prices have very significant effects on the behaviour of the DOW JONES Index. They also suggest that negative movements have larger impacts than positive movements in WTI prices, and that long-term multiplier effects take about 9 to 12 months to take effect. Full article
(This article belongs to the Special Issue Multivariate Modelling of Fossil Fuel and Carbon Emission Prices)
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Article
Design of an Equivalent Consumption Minimization Strategy-Based Control in Relation to the Passenger Number for a Fuel Cell Tram Propulsion
Energies 2020, 13(15), 4010; https://doi.org/10.3390/en13154010 - 03 Aug 2020
Cited by 2 | Viewed by 695
Abstract
In this paper, a new control strategy for a fuel cell supercapacitor tramway is tested on a real drive cycle. The control algorithm is based on the equivalent consumption minimization strategy, weighted for the vehicle passenger number. Its implementation is presented by highlighting [...] Read more.
In this paper, a new control strategy for a fuel cell supercapacitor tramway is tested on a real drive cycle. The control algorithm is based on the equivalent consumption minimization strategy, weighted for the vehicle passenger number. Its implementation is presented by highlighting the customization for a specific drive cycle, located in Reggio Calabria, one of the main cities of southern Italy. The heart of the paper concerns the fuel cell hybrid powertrain, where energy source and DC/DC converter models are formalized and numerically designed; in addition, all the drivetrain components are taken into account through appropriate relations. By means of the drive cycle characteristics, in terms of morphology, vehicle features, and speed, the main components are properly selected, with the aim of avoiding under- and over-sizing issues. A specific case study is analyzed, considering the passenger variation at each tramway stop. Satisfying results are achieved in the simulation campaign: 2.9 kg of hydrogen is consumed for a round trip, with a quasi-constant fuel cell efficiency of more than 50%, while the supercapacitor SOC ranges in a wide interval, between 35% and 95%. Full article
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Article
Application of IoT and BEMS to Visualise the Environmental Performance of an Educational Building
Energies 2020, 13(15), 4009; https://doi.org/10.3390/en13154009 - 03 Aug 2020
Cited by 2 | Viewed by 1326
Abstract
This paper presents the application of Internet of Things (IoT) Technology and Building Energy Management System (BEMS) within the Marylebone Campus of the University of Westminster, located in central London, to improve the environmental performance of the existing building as well as enhance [...] Read more.
This paper presents the application of Internet of Things (IoT) Technology and Building Energy Management System (BEMS) within the Marylebone Campus of the University of Westminster, located in central London, to improve the environmental performance of the existing building as well as enhance the learning experience on energy and sustainability. Sixty IoT sensors connected to minicomputers were planned to be deployed within three floors of the building to continuously measure the real-time environmental parameters, such as dry-bulb temperature, relative humidity, illuminance level, carbon dioxide, and sound levels. Experimental workshops were also arranged with undergraduate and post-graduate students at their classrooms using IoT sensors, portable Bluetooth sensors and online questionnaires to increase awareness of the effect of environmental and behavioural changes on energy saving through real-time visualisation. Users’ subjective feedback on their workplace was also collected through Post Occupancy Evaluation (POE) questionnaire surveys. The results show the effectiveness of IoT systems and BEMS in supplying the building users and management with high-resolution, low-cost data acquisition systems highlighting the existing challenges and future scopes. The study also documents the process and the improvement in students’ awareness of environmental and energy performance of their building through IoT data visualizations and POE. Full article
(This article belongs to the Special Issue Smart Building, Smart Cities, Home Automation and IoT)
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