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The temporal stability and spatial homogeneity of current density are key factors in Polymer Electrolyte Fuel Cell (PEFC) performance and durability. Temporal and spatial variations of relative humidity, fuel concentration, and water droplets in the channels are the principal causes of non-homogeneous current density. A dynamic pseudo-3D model was previously proposed by the authors and has been extended and improved to perform the long-term and intensive simulations of PEFC with low computational cost, which allows to study of the performances homogeneity with different experimental configurations and flow field topologies. The model considers important phenomena in the homogeneity analysis, such as gases and liquid water movement in diffusion layers and flow field, electrochemical reactions, and others. Model validation has been performed using experimental data obtained from a 25 cm 2 cell with a single serpentine, which has allowed studying the model transient response and spatial representation. The simulations have been used to study the homogeneity and stability of 36 setups of PEFC, varying the rib/channel width ratio, the stoichiometric ratio, and the number of parallel serpentine channels. The results show the importance of a properly flow field design to control gas flow, remove the channels' liquid water, and keep a homogeneous feeding. The study evaluated a set of channel configurations that show the improved temporal voltage stability and current density spatial homogeneity. The results show the impact of channel gas speed and ratio channel/rib width in liquid droplets removal and the proper fuel spatial distribution; and how configurations with a lesser number of channels in serpentine design require a lower stoichiometric ratio to perform better temporal and spatial uniformity. In the case of the cell configurations simulated, the optimum design was achieved using between 5 and 7 parallel serpentine channels and a channel/rib ratio 3/5. • Pseudo-3D model of PEM fuel cell oriented to study the performance uniformity. • Temporal stability and spatial homogeneity studied for different flow field setups. • The methodology allows long-term simulations with low computational cost. • Stoichiometry is a key factor removing liquid water and increasing cell stability. • Balance of the number of channels and stoichiometry to proper liquid water removal. [ABSTRACT FROM AUTHOR]

Deaerator is one of the most important equipment for steady state and dynamic operation of power plants. The deaerator energy storage utilization process is one of the most essential ways to enhance the variable load rate of power plants. The purpose of this study is to improve the dynamic simulation performance of the deaerator during unit load changes by constructing a more reasonable deaerator model, aiming to provide guidance for practical operations. In this paper, a thermal mass microelement algorithm is proposed for the heat transfer between droplets and steam in the deaerator, followed by segmental modeling of the deaerator. By comparing with the operation data of a power plant, the steady state operation error of the deaerator model is within 0.6 %. Subsequently, the unit load variation process is simulated and the dynamic variation accuracy of the model proposed in this paper is enhanced by 1–2 % compared to the lumped parameter model. The dynamic characteristics of the deaerator are obtained by simulating the step and ramp changes of the deaerator boundary conditions and the deaerator start-up process. In addition, during the simulation of condensate throttling, the maximum power of the unit using the deaerator model in this paper is 0.2–1.5 MW larger than that of the lumped parameter model. • A thermal mass microelement algorithm for heat exchange between droplets and steam in deaerator is proposed. • A more rational deaerator model is established. • Compared to the lumped parameter model, the proposed model enhances the accuracy of the dynamic simulation by 1–2 %. • The maximum power in the proposed model during condensate throttling is 0.2–1.5 MW greater than that in the lumped model. [ABSTRACT FROM AUTHOR]

Decarbonising the industrial sector is a key part of climate change mitigation targets, and Solar Heat for Industrial Process (SHIP) is a promising technology to achieve this. However, one of the drawbacks of SHIP systems is that they rely on an intermittent energy source. Therefore, sensible energy storage has emerged as a potential solution. In addition, solid byproducts have been proposed as a low-cost but effective material for thermal energy storage (TES). This work presents a SHIP system model coupled with a copper slag-packed-bed TES (PBTES) model using air as heat transfer fluid. The TES has been implemented to preheat the makeup water of the tank where steam is generated. A system design was carried out using a parametric analysis to find a solar field size and a corresponding TES volume. The resulting system was simulated, and the operating variables were analysed in detail. The results show that it is possible to generate 20% more energy due to the storage system. Additionally, a techno-economic analysis indicates that the SHIP with PBTES system results in a payback period of 14 years and a savings of C O 2 emissions of 30 t C O 2. • Integration of a SHIP system with copper slag packed-bed TES • Dynamic simulation and analysis of the system's main variables • System performance assessment and control improvement • Techno-economic analysis of the entire system and carbon savings • SHIP system with TES presents a payback of 14 years and annual savings of 30 tCO2 [ABSTRACT FROM AUTHOR]

As one of the effective measures to reduce energy consumption of high-speed railway, train operation control has gained much attention because of its cost-effectiveness. Conventional approaches to eco-driving generally rely on single-mass train models and lack a thorough investigation into the vehicle cruising process, which can overlook real-world operation conditions and hinder further improvements in energy efficiency. To address these issues, this paper proposes a comprehensive framework for optimizing the cruising speed of high-speed trains (HSTs) based on track conditions to reduce energy consumed by motion resistances (ECMR). Firstly, a multibody dynamics simulation model of the HST is developed and validated to accurately evaluate ECMR under a range of operation scenarios. Simulation results show that the impact of speed on ECMR varies considerably according to track characteristics. Subsequently, a neural network is constructed to derive the regressive relationship between operation conditions and ECMR. On this basis, an optimization model for the cruising speed under different track conditions is formulated to minimize the ECMR of a railway segment with a given operation time. Finally, the effectiveness of the model is validated through case studies, which demonstrate that ECMR can be reduced by up to 27.85% compared to traditional control strategies. The proposed optimization method can be integrated with current train speed profiles to further enhance energy efficiency. This framework has broad applicability for addressing engineering problems related to train operation optimization. [Display omitted] • Energy consumed by motion resistances (ECMR) of high-speed trains (HSTs) is studied. • A dynamic model of the HST is developed to characterize ECMR under various scenarios. • A strong correlation between speed and track properties on ECMR is observed. • A unified framework is built to optimize the cruising speed for energy conservation. • Up to 27.85% of ECMR can be reduced through the cruising speed optimization. [ABSTRACT FROM AUTHOR]

Gas–electricity integrated energy systems (GE-IES) offers a promising solution for enhancing energy efficiency and accommodating renewable energy sources. Accurate dynamic simulation is essential for optimizing and controlling GE-IES. However, the presence of various local controllers introduces prominent discrete characteristics, posing challenges for the dynamic simulation of the GE-IES. This paper investigates the dynamic simulation method in GE-IES with discrete characteristics. Firstly, we propose an adaptive step size simulation method based on quantized state system theory. This method maintains the event-driven characteristics of the quantized state integration algorithms, while enhancing computational speed through adaptive step size adjustments. Secondly, we establish an event-driven simulation framework that facilitates interactions of different subsystems during the dynamic simulation, improving the compatibility with various models and solving algorithms. Finally, we validate the accuracy, efficiency, and scalability of the proposed method and the framework using two typical GE-IES cases with different scales. Simulation results demonstrate the effectiveness on the dynamic simulation of GE-IES and highlight the feasibility of natural gas networks in consuming and storing surplus renewable energy. • An adaptive step size, 2nd/3rd-order quantized state system simulation method is proposed. • A comprehensive event-driven simulation framework incorporating both state-discretized and time-discretized methods is established. • Improved performance is achieved in simulating gas–electricity integrated energy systems with discrete characteristics. • The effectiveness in analyzing operation strategy and fault dynamics is verified. [ABSTRACT FROM AUTHOR]

Utilizing LNG cold energy for power generation is critical for improving energy efficiency of LNG supply chain. Current studies on power generation systems that use LNG cold energy primarily focus on steady-state simulations and optimizing key parameters. However, there is a notable gap in research regarding dynamic simulations to understand the dynamic behaviors of these systems. To address this, a dynamic model for a dual-stage series ORC system that harnesses LNG cold energy was proposed focusing on its dynamic responses. A comparative analysis of its stability under two different control strategies were conducted identifying the cascade control strategy as the superior method. The effects of various parameters, such as LNG temperature, mass flow, and composition, along with exhaust gas pressure, temperature, and composition, on the stability and dynamic response of the system were investigated. The results indicate that fluctuations in LNG mass flow have the most significant impact on system stability, while exhaust gas pressure has the least. Additionally, most parameters effectively returned to their setpoints after disturbances when managed by the cascaded control strategy. This research provides valuable insights into the operational characteristics of the dual-stage ORC, demonstrating its potential for sustainable power generation by leveraging the recovery of LNG cold energy. • Dynamic model of dual-stage ORC utilizing LNG cold energy is proposed. • Dynamic behaviors of proposed system have been investigated. • Cascade control system improves stability and dynamic response of the ORC system. • Variation of LNG mass flow rate influences stability of ORC system significantly. [ABSTRACT FROM AUTHOR]

This research compares an existing 4th generation heating and cooling network with a novel 5th generation heating and cooling network, driven by renewables. The networks are designed to cover the energy demand of a large shopping center. The existing network uses the thermal energy recovered from a trigenerative reciprocating engine coupled with an absorption chiller, to supply the heating and cooling networks. The proposed renewable 5th generation network consists of two neutral rings: the first one is the cold sink for the water-to-water heat pumps, installed in the substations; the second one is the hot sink for the heat pumps installed in the substations. One of the main novelties of the proposed layout consists in the use of a heat exchanger between these two rings. This heat exchanger recovers the heat rejected by the condensers of the heat pumps operating in cooling mode, supplying the evaporators of the heat pumps operating in heating mode. A photovoltaic field equipped with a lithium-ion battery partially matches the electricity demand of the network. The models of the shopping center and the existing and proposed networks are developed in TRNSYS environment. The proposed system achieves promising results: renewable electricity matches roughly 89% of the shopping mall electricity load can be covered by renewable power. • Novel paradigm to be easily adopted by existing residential districts. • The proposed novel paradigm is able to significantly reduce the primary energy consumption of the residential district. • Very promising results with a primary energy saving index of 38% and payback period of 2.2 years. • The power to heat strategy is able to further exploit the renewable electricity not directly exploited by the renewable energy community [ABSTRACT FROM AUTHOR]

Electric-Steam Integrated Energy Systems (ES-IES) have garnered considerable attention in industrial applications due to their high energy utilization efficiency and energy density. Nonetheless, the limited thermal storage capacity of the steam system impacts the stability of ES-IES, posing a challenge for its implementation in scenarios with a high proportion of renewable energy sources. To address this limitation, this study demonstrates how the integration of a Steam Accumulator (SA) can enhance the stability of ES-IES through a dynamic simulation-based approach. Firstly, a novel method for simulating the steam system is introduced. This method utilizes a resolution-adaptive strategy based on the central implicit difference format to balance simulation accuracy and speed. Furthermore, a simulation framework for ES-IES is delineated, detailing the solution order of subsystems and system coupling interface parameter interaction method. Meanwhile, a comprehensive model and solution for the SA are proposed, aligning well with the aforementioned ES-IES simulation methods in terms of accuracy and complexity. Finally, case study demonstrated that equipping SA in ES-IES can effectively reduce its fault-recovery time by 57.9%, highlighting the efficacy of SA in promoting system stability and security. • A steam accumulator dynamic model and solution. • A novel steam system dynamic simulation approach. • An ES-IES simulation framework. • Fault-state ES-IES operation stability improvement. [ABSTRACT FROM AUTHOR]

The supercritical CO 2 Brayton cycle has promising prospects for application in hypersonic vehicles owing to its performance and compactness. However, the extreme thermal environment in aircrafts and limited cold sources make the transient characteristics of the Brayton cycle unclear. In this study, dynamic models of supercritical CO 2 Brayton cycle were established. The heat exchanger model was based on the supercritical moving boundary method proposed in our previous work and the finite volume method, whereas the modeling of the turbomachinery was based on the performance map approach. Proportional-integral-derivative (PID) controller modules were introduced to enable closed-loop control of various parameters to meet different working conditions. The transient characteristics of the heat exchanger and Brayton cycle model were validated using literature data. Dynamic models for both simple and recuperated layouts were developed to study the transient behavior in aerospace scenarios with sudden thermal load increases, cold-source limitations, and combined disturbances. Under the given conditions, results indicate that both sudden increases in thermal load and cold-source limitations cause a decrease in the thermodynamic performance, with a reduction in thermal efficiency of 0.7 and 2.2%, respectively. When these conditions were combined, the performance further deteriorated, with the thermal efficiency decreasing from 14.4 to 9.5%. This condition can result in compressor over speeding and failure of the PID controller. The simulation results for the two layouts show that the recuperated layout has a 34.8% higher power output at the cost of increasing the total weight by 29.7%. The dynamic models proposed in this study provide valuable insights into the behavior of Brayton cycle systems in hypersonic vehicles, aiding system design, evaluation, and control strategy development. • Transient characteristics of the supercritical CO 2 Brayton cycle need clarification. • Dynamic models used to study transient behavior in SCO 2 -CBC in aerospace scenarios. • Thermal load increases, cold-source limits, and combined disturbances considered. • Recuperated and simple layouts have contrasting advantages of cycle performance. • Valuable insights for improving the design of CBCs for hypersonic vehicles obtained. [ABSTRACT FROM AUTHOR]

The temperature has a significant effect on the lifespan and the safety of the batteries which are one of the core components of electric vehicles. A well-designed battery thermal management system is required to adjust the temperature of the batteries within an appropriate range for thermal safety, and further minimize the energy consumption for energy savings. However, these two goals form a tradeoff. Typically, increased energy consumption for cooling results in safer batteries thermally. To examine this tradeoff, firstly, a linear electro-thermal model is built to evaluate the thermal dynamics of the operating battery-cooling module. The linear model accounts for the heat generation based on internal resistance, and the heat transfer based on a resistance–capacitance model. Such linear model reduces the computation of the model simulation to dynamically catch up with the change of temperatures and to implement control strategies on the cooling system in a short time. Based on this model, a model predictive control (MPC) framework is proposed to design thermal control methods, which considers both thermal safety and energy saving. The weight of these two goals can be adjusted to explore the tradeoff between them. Finally, we investigate the performance of the MPC framework by applying the Urban Dynamometer Driving Schedule (UDDS) to the battery module. The simulation results show that the electro-thermal model is effective for battery thermal dynamics evaluation. Additionally, the tradeoff between the two goals is demonstrated by the simulation. • A fast temperature prediction and closed-loop thermal control framework is proposed. • An electro-thermal model of an active-liquid-cooling battery module is developed. • A thermal prevention control strategy is proposed. [ABSTRACT FROM AUTHOR]

Intelligent design and operation optimization allow energy systems to take advantage of the flexibility that multi-generation provides. This study proposes a basic solar-driven system integrated with thermal energy storage for round-the-clock energy harvesting. A modified configuration is then designed incorporating innovative multi-heat recovery approaches to increase the capacity and product diversity of the basic system. The modified system is able to cover vital urban utilities such as electricity, fresh water, cooling, and hydrogen throughout the day. To overcome the time-consuming procedure of dynamic techno-economic simulation as well as the limitation of commercial engineering equation solvers for tri-objective optimization, a deep learning approach is developed to reduce the computational complexity and improve the analysis accuracy. In this regard, the trained neural networks play an intermediary role in coupling the developed code with the MATLAB optimization toolbox. A comparison between the modified and conventional configurations indicates that implementing the multi-heat recovery approach results in a 29% increase in power generation while only increasing the overall system cost by 1.97%. From an economic perspective, the Sankey diagram depicts that the storage unit with a cost rate of 12.25 $/h accounts for 6.77% of the plant's cost rate, which enables the system to operate continuously. According to the sensitivity analysis and contour plots, the number of collectors significantly affects the total cost rate and fresh water production capacity while it has no tangible effect on the exergy efficiency. • A novel multigeneration system with thermal energy storage is designed. • A modified configuration with heat recovery is introduced to boost the capacity. • The comparative study indicates a 17.6% improvement in the power generation. • A dynamic simulation code is developed based on meteorological data. • A deep learning techno-economic optimization is applied to the system. [ABSTRACT FROM AUTHOR]

• A novel reversible solid oxide fuel cells system for grid stabilization. • A two-staged methanation subsystem utilizes the H 2 from SOEC operating and CO 2. • A control strategy of 7 modes (M1 – M7) operation is proposed. • M2 and M6 are optimal in terms of energy efficiency and system risk. • Dynamic simulations are conducted to investigate the system. The power to gas concept is promising for the next generation of electrochemical energy storage and grid stabilization technologies. The fuel produced from electricity-driven fuel production can be an efficient energy carrier for excessive grid power. Here, a reversible solid oxide cell(s) system integrated with methane synthesis (ReSOC-MS) is proposed for the grid stabilization application at Mega Watts class. CH 4 can be synthesized at grid surplus conditions and can be a transportation friendly energy carrier. A control strategy is proposed for this combined system, based on the grid state and H 2 tank state of the system for the normal solid oxide fuel cell (SOFC) mode and solid oxide electrolysis cell (SOEC) mode. Simulation results of these two operational modes demonstrate that the ReSOC-MS can achieve 85.34% power to gas efficiency in SOEC mode and 46.95% gas to power efficiency in SOFC mode. Dynamic simulations of stepping grid state for 5000 s operation show that the power to gas efficiency can be higher than 70%, thereby successfully demonstrating the capability of grid-balancing and methane production. [ABSTRACT FROM AUTHOR]

• Injection of air from compressed air energy storage to a gas turbine was simulated. • The aim is to increase the GT's ramp rate without increasing the rate of TIT change. • Dynamic simulation was performed for various scenarios of increasing load. • A genetic algorithm was used to optimize the air injection schedule. • It was confirmed that the system integration and control would work well. Manufacturers are trying to increase ramp rates to improve the operational flexibility of gas turbines. However, higher ramp rates lead to rapid variation in the combustion gas temperature and shorten the life of the turbine. To increase the rate without reducing the life, this study considers the use of a compressed air energy storage (CAES). Injecting pressurized air that is stored in CAES into the combustor of a gas turbine increases the power output of the gas turbine without increasing fuel supply. Therefore, the ramp rate of the turbine can be increased while suppressing the temperature change of the combustion gas. The injection schedule was optimized through a dynamic simulation to increase the ramp rate. A genetic algorithm was used in the optimization of the schedule. The optimized schedule turned out to be a simple form consisting of a linear increase and decrease in the injection flow rate. Furthermore, despite the increased ramp rate, the fluctuation of turbine inlet temperature could be maintained under a safe level due to the optimized compressed air injection. [ABSTRACT FROM AUTHOR]

Highlights • Dynamic simulation model of a novel vehicle to net zero energy building layout. • System environmental and thermo economic analysis coupled with electric vehicle. • Investigation of the electric vehicle charging effects on the system performance. • The system is economically feasible only with a small capacity storage system. • Electric vehicle allows one a significant equivalent CO 2 emissions reduction. Abstract This paper analyses the energy, environmental and economic performance of a future scenario where electric vehicles are connected to efficient buildings powered by building integrated flat-plate photovoltaic/thermal collectors, equipped with electric energy storage. The produced renewable electricity and thermal energy are exploited for building electrical and thermal applications. The surplus of produced electricity is stored into the electrical battery and used to charge the electric vehicle. The proposed system is modelled and dynamically simulated within the TRNSYS environment, where special attention is paid to the design of suitable system control strategies, aiming at optimizing the exploitation of the solar energy for electricity and heating purposes. To this aim, a sensitivity analysis is also carried out to find out the optimal system configuration. A case study analysis, relative to the weather zone of Naples (South Italy), is conducted to evaluate the energy, economic and environmental feasibility of the investigated scenario. Simulation results show that, with respect to a reference system, a remarkable reduction of electricity from the grid is achieved, corresponding to a primary energy saving equal to 57.66%. A reduction of 51.63% of CO 2 emissions and a simple pay payback period equal to 11.64 years are achieved. [ABSTRACT FROM AUTHOR]

• Thermal energy demand evaluation for buildings with high-energy performance. • Application of the Degree Days method for the evaluation of building heating load. • Several dynamic building simulations located in different cities were considered. • A comparison of the results obtained using different weather data sets was done. • Reliable relationships for preliminary of heating demand assessment were provided. The weather is one of the main factors to consider when designing a building because it represents the most important boundary condition to affect the dynamic behaviour of the building. In the literature, many studies use the degree day to predict building energy demand. However, linking the results obtained from a generic building simulation tool with defined degree days, will not give reliable energy evaluation. The goal of this study is to demonstrate that the assessment of building energy demand through the use of the degree day is correct only if the determination of the climate index is a function of the same weather data. The relationship between Heating Degree-Day and heating energy performance was identified by determining some simple correlations, in order to obtain a preliminary evaluation of energy demands. The authors used Heating Degree Days based on three climate data-sets, developing different relationships and feedback. For the extraction of these correlations, numerous dynamic simulations on non-residential buildings characterized by high-energy performance were carried out. From the analysis of the results, it is clear that the relationships with higher correlation coefficients (higher than 0.9) are those that are a function of the degree calculated from the same climatic file used during the simulations. The proposed methodology, validated in this work for an Italian case study can be extended to any country and can be used to improve the reliability of any decision support tool based on climatic indexes. [ABSTRACT FROM AUTHOR]

Highlights • The U-value impact on the thermal performance of residential buildings was analyzed. • 192000 buildings were randomly generated and evaluated using dynamic simulation. • Six geometry-based indexes were correlated with the buildings performance. • Higher U-values can decrease energy consumption in lower latitudes. • Higher and wider U-value intervals increase the geometric freedom for lower latitudes. Abstract Contrarily to what happens in northern European countries, buildings in the Mediterranean region are prone to overheating. Consequently, it is important to better understand the role that the thermal transmittance of the building envelope elements has on air-conditioning consumptions. This paper analyzes the effect of different U -values on building design in the Mediterranean area. 192 000 residential buildings were randomly generated for sixteen distinct locations and the energy consumption was assessed for each. It was found that in northern Mediterranean locations, as U -values decreased, energy consumption also decreased. However, in warmer climates, low thermal transmittances tended to significantly increase energy consumption. Hence, the lower the latitude, the higher the U -values should be, in order to prevent increasing the cooling demands. Additionally, geometry-based indexes were correlated with the building's energy performance. For high U -values, it was found that bigger buildings worsen the energy performance and larger windows tended to improve it. For low U -values, bigger north-facing windows were beneficial. There is an adequate interval of values for which the geometry has a lower impact, which is wider and higher for lower latitudes, thus meaning that not only does the building performance improve but architects are also freer to explore alternative designs. [ABSTRACT FROM AUTHOR]

Highlights • Development of an innovative building integrated air based solar thermal collector. • Dynamic modelling and experimental validation of the whole building/device system. • Solar collectors are integrated in the façades of an office building. • Active/passive effects on the building are analysed for several boundary conditions. • Interesting energy and comfort results are achieved. Abstract In this paper the design and the energy performance investigation of a new flat-plate solar thermal air collector prototype is presented. The adoption of cost-effective materials and simple design solutions represent the main novelties of the proposed device when compared to existing commercial collectors. In addition, the prototype is suitably designed to be integrated into the building envelope (façade), which is a key feature for the market uptake of building integrated solar thermal systems. The paper includes the description of the dynamic simulation model, developed for the energy and economic performance analyses of the whole building-prototype system. The simulation model, implemented with a computer code written in MatLab, is able to predict both active (hot air production for building space heating) and passive (winter free heating and summer overheating) effects due to the building integration of the proposed solar collector. By such tool, indoor comfort investigations can also be carried out. The dynamic simulation models of both the building and the collector prototype were successfully validated. In order to show the features of the developed simulation code, a suitable case study was carried out. It refers to an office space, part of a high-rise multi-use building, simulated as located in three different weather zones (Freiburg, Naples and Almeria). The examined solar collector is modelled as vertically integrated into the building façade, and three different orientations (East, South-East and South) were taken into account. Interesting results for the energetic, economic and occupants comfort points of view are obtained. By taking into account an initial cost of the system of about 5 k€, the primary energy savings achieved by the proposed system against the traditional buildings range between 1.9 and 8.0 MWh/y (depending on the selected weather zone and backup system). The shortest payback for all the investigated weather zones is obtained for Naples, which is equal to 6.2 years. [ABSTRACT FROM AUTHOR]

Highlights • A credit rating based multi-leader multi-follower game is proposed. • A best response algorithm is designed to obtain the unique equilibrium strategy. • The impact level of transmission losses on trading behaviors is discussed. Abstract In this paper, we investigate the problem of credit rating management in energy trading among microgrids subject to transmission losses and wheeling cost. The main concern is how to constrain the default behaviors of retailers to enable all the consumers and retailers to be actively involved in the energy trading. By endowing retailers as leaders and consumers as followers, we establish a multi-leader multi-follower dynamic game model and propose a scorecard model based on logistic regression to evaluate retailers' credit ratings. The concept of trust degree is then introduced for all the retailers as a punitive measure to relate their credit ratings with the reduction in the profit. With such a strategy, we can theoretically show that a unique equilibrium exists for the dynamic game model. Moreover, a best response algorithm is proposed to make the consumers and retailers achieve the equilibrium iteratively. Numerical simulations are provided to demonstrate the effectiveness and efficiency of the proposed method. It is found that default behaviors of selfish retailers can be greatly constrained with only a slight degradation of the interests of other participants, thereby promoting the establishment of a trustworthy trading market. We also discuss the influence level of transmission losses on trading behaviors of retailers and consumers. [ABSTRACT FROM AUTHOR]

Highlights • A detailed dynamic simulation model for a coal-fired power plant is developed. • The integration of a steam accumulator into the water-steam cycle is presented. • Charging the energy storage leads to a (minimum) load reduction of up to 7.0%. • Discharging the energy storage leads to an additional net power of up to 4.3%. • The integrated energy storage enhances the frequency control supply by ±2.8%. Abstract Improving the flexibility of conventional power plants is one key challenge for the transformation of the energy system towards a high share of renewable energies in electricity generation. Flexible and dispatchable power plants will contribute to this ongoing transformation process as they compensate the fluctuating electricity generation from renewable energy sources such as wind and photovoltaics. In this context, dynamic simulation models offer an efficient tool to evaluate flexibility measures and the resulting highly transient power plant operation. In this paper, the buildup of a dynamic power plant model using the modeling language Modelica in the simulation environment Dymola is presented. The detailed dynamic power plant model is validated successfully against measurement data from the underlying coal-fired reference power plant. The paper then focuses on the integration of a steam accumulator – also known as a Ruths storage – into the power plant process in order to increase its flexibility. The results of the dynamic simulations show that charging the steam accumulator leads to a reduction of the net power up to 7.0%. By discharging the Ruths storage an additional net power of 4.3% can be activated very quickly. Thus, the storage integration leads to an improved load flexibility with regard to a temporary reduction of the minimum load as well as to the possibility of performing a load change at a constant firing rate (e.g. to participate on the quarter-hourly intraday markets). Furthermore, the integrated energy storage enhances the provision of primary control reserve significantly by ±2.8%. [ABSTRACT FROM AUTHOR]

Highlights • A novel natural gas-diesel dual-fuel rotary engine was proposed and studied. • Fuel spray characteristics under rotary engine working conditions were obtained. • Dynamic simulation model was validated in detail for diesel rotary engine. • Mixture formation process and combustion characteristics were analyzed. • Blending natural gas could effectively improve the total combustion rate. Abstract To further improve the performance of diesel rotary engine, a novel natural gas-diesel rotary engine was proposed and studied in this paper. Based on a spray experimental setup, the diesel spray characteristics under diesel rotary engine working conditions were obtained and analyzed. Thereafter it was used to validate the spray model for diesel rotary engine modeling and simulation. The effect of different natural gas blending ratios on mixture formation and combustion process in the natural gas-diesel rotary engine were investigated. Simulation results showed that for fuel-air mixing process, the natural gas movement process was susceptible to the airflow motion. However, the diesel distribution range was obviously enlarged under the influence of high-speed unidirectional flow. At assisted ignition timing, the stratified distributed diesel made the combustion process mainly occured at the front and middle of the combustion chamber. Besides, the flame propagation speed was accelerated with natural gas blending ratio increasing, which effectively improved the total combustion rate. Compared to single-fuel mode, when natural gas blending ratio increased to 20%, the maximum combustion pressure increased by 24.17%. Meanwhile, soot and CO decreased obviously, but NO and CO 2 also increased. [ABSTRACT FROM AUTHOR]

Highlights • Easily define a mixture of molten salt and non-condensable gas for rigorous dynamic simulation. • Enables system-wide thermal and hydrodynamic analysis for energy storage processes. • New experimental data on operating a thermal energy storage facility using molten salt. • The heat exchanger performance is influenced by trapped non-condensable gas. • Anomalous sudden changes in the hydrodynamic losses uncovered. Abstract Thermal energy storage (TES) plays a crucial role improving the efficiency of solar power utilization. Molten salt (MS) has gained a strong position as a thermal fluid in applications where solar power is stored and used overnight to provide dispatchable energy production. Novel process and operating concepts are being developed for TES systems that require reliable engineering tools. System-wide dynamic simulation provides a virtual test bench and analysis tool for assisting in process and control design and operational issues. Proper characterization of the thermal fluids in simulation tools is critical for successful simulation studies. In this paper, we report the experimental and modelling work related to counter-current heat exchange and free drainage test runs in CIEMAT's multi-purpose MS test loop at Plataforma Solar de Almería in Spain. We present a general method to define MS and non-condensable gas within a homogeneous pressure-flow solver. We present modelling of an indirect MS TES system connected to a thermal oil loop through TEMA type heat exchangers, model calibration with half of the experimental data, and finally, validation simulations against rest of the data. All these experimental data are previously unpublished. The model predicts the system behaviour with good agreement regarding temperatures, pressures, flow rates and liquid levels. The simulations suggest that the heat exchangers' shell sides suffer from trapped non-condensable gas which significantly affects heat transfer, heat loss to ambient air and hydrodynamic losses. Our results contribute to thermal-hydraulic, system-wide modelling and simulation of MS processes. Furthermore, the results have practical implications for MS TES facilities with respect to system design, analysis and operation. [ABSTRACT FROM AUTHOR]

Highlights • Market model with renewables as an economically-driven investment option. • Development of policy scenarios for renewable expansion and security of supply. • New market design with optimal adaption of conventional power to renewables. • Simulation of renewables that are able to generate base-loadable electricity. • Cost comparison for governments to reach energy goals. Abstract We explore the impact of renewable energy under free market conditions on the security of energy supply using data for the German electricity market. We design a fundamental electricity market model, where renewable energy capacity is not driven by expansion goals, but is dynamically modeled as an economically-driven investment option. Furthermore, we analyze the economics of five policy scenarios designed to secure both electricity supply and renewable energy expansion. Our analysis demonstrates that renewable energy expansion leads to conventional power plant shut-downs (due to economic losses) and, as a result, to energy shortages. We find that the application of a fixed feed-in tariff mechanism for renewable energy (i.e. a fixed payment for the provided energy) is an appropriate instrument to simultaneously achieve renewable energy expansion and uninterrupted energy supply. However, when internalizing the external costs of electricity generation, the scenario of a free market for renewable energy together with subsidies for conventional power plants becomes the most cost efficient option. [ABSTRACT FROM AUTHOR]

Highlights • Double U-tube borehole heat exchangers are studied by 3D finite element simulations. • Simulation results are validated by comparing 3D and 2D borehole thermal resistance. • Equations to evaluate the mean fluid temperature of a double U-tube borehole are given. • Results hold for any borehole length, shank spacing, conductivity and working condition. • Results improve thermal-response-tests evaluation and borehole-fields hourly simulation. Abstract The design of ground-coupled heat pump systems requires the knowledge of the mean temperature T fm of the working fluid in borehole heat exchangers. This quantity is usually approximated by the arithmetic mean of inlet and outlet temperature. The approximation yields an overestimation of the thermal resistance of the heat exchanger in thermal response tests, as well as errors in the estimation of the outlet fluid temperature in the dynamic simulation of ground-coupled heat pumps. Recently (Applied Energy 206, 2017, 1406–1415), Zanchini and Jahanbin determined, by finite element simulations, correlations that allow an immediate evaluation of T fm in any working condition, with reference to double U-tube boreholes with length 100 m and shank spacing 85 mm. In this paper, the analysis presented there is extended to double U-tube boreholes with any length, between 50 and 200 m, and any shank spacing, between 65 and 105 mm. The results hold for every thermal conductivity of the sealing grout between 0.9 and 1.6 W/(m K), every volume flow rate between 12 and 24 L per minute, every diameter of the BHE and every working condition (heating, cooling, thermal response test), both in quasi-stationary and in transient regime. [ABSTRACT FROM AUTHOR]

In museums, hygrothermal conditions must be carefully controlled by HVAC system to avoid artwork degradation. Higher energy requirements are needed for the maintenance of the suitable thermal environment. Moreover, a comfortable thermal sensation is needed for a positive museum experience. In light of current policies on energy efficiency, we propose an original procedure for the concurrent achievement of three goals: artwork preservation, energy efficiency, and human thermal comfort. This procedure is based on the application of multi-objective optimization and aims at correctly choosing temperature and relative humidity setpoints, through the use of dynamic simulations and evaluation of three indexes as objectives. This strategy can be particularly effective in museums hosted in historic buildings, where envelope and HVAC refurbishment is often forbidden or discouraged due to the architectural constraints. Furthermore, the retrofit action is almost costless. A case study is presented: first, a monitoring campaign in an Italian museum has been used for the validation of dynamic simulation models of the building-HVAC system; then, the validated models have been used to show that improvements of artwork lifetime, human thermal comfort and reduction of energy requirements of the HVAC system are possible, if currently-used hygrothermal setpoints (based on technical standards and guidelines) are replaced with those identified by the optimization problem. [ABSTRACT FROM AUTHOR]

Due to the rapid rise of power consumption of data centers in recent years, much work has been done to develop energy-efficient design, controls and diagnosis of their cooling systems, while the energy system simulation is used as an effective tool. However, existing models of information technology (IT) equipment of data centers cannot well represent the effects of IT equipment design and operation status on the data center cooling demand, and this hinders the development of the energy saving cooling technologies of data centers. To address this issue, this paper introduces a power consumption model of IT equipment in data centers with coefficients and modeling script provided for immediate use in data center energy system simulation. This energy model can be used to simulate energy performance of typical IT equipment in data centers under real-time dynamic operation conditions conveniently and effectively without the need of data other than the specifications of a data center design and IT equipment manuals. Its use with a commonly used building simulation program is demonstrated with a building model of a typical large office in a subtropical area. The results show that the model can represent the change of power consumption of data centers with different IT equipment designs and operation appropriately. [ABSTRACT FROM AUTHOR]

In this paper, the energy performance of an energy self-sufficient residential building, located in the outskirt of L’Aquila city, in central Italy, is presented. The aim of this study is to demonstrate that even a self- sufficient building, that represents a still uncommon construction in the Mediterranean area, can have optimization margins. The analysis is performed via calibrated model carried out with EnergyPlus™ engine coupled with DesignBuilder. The results of this study show a substantial discrepancy between the high efficiency of the envelope, and the poor performance of the heating system. Therefore, five possible scenarios, that differ for the technological plant, were hypothesized. Based on the total thermal energy consumption of the heating system as it is, equal to 29.9 kWh/m 2  y, the proposed multi-scenario analysis allows to identify a solution that ensures energy savings up to 67.1%. In this study, these results indicate that a proper a priori study of building’s thermal load by considering different plant typologies could help to choose the better solutions for realizing efficient buildings. [ABSTRACT FROM AUTHOR]

Rapid deployment of health service infrastructure is underway to meet the growing needs of populations in sub-Saharan Africa, however the energy infrastructure needed to support high quality services has tended to lag. Understanding the electrical and thermal energy needs of health centers constructed with local building methods and materials and operating outside of the jurisdiction of heating, ventilation and air conditioning (HVAC) codes is complicated by a lack of appropriately scaled and configured energy system design frameworks and validation data for dynamic simulations. In this work we address this gap by linking the thermal envelope performance of health center buildings under heating and cooling loads with measured indoor air temperature, meteorological conditions, and operational electricity demand. A resistance-capacitive type energy balance model is parameterized using typical health center architectural data for sub-Saharan Africa (floor plans from Uganda and Lesotho) and heat transfer characteristics; to achieve this energy flows between HVAC equipment, internal loads, and ambient conditions are simulated on an hourly time step with indoor temperature thresholds representative of thermostat settings. A typical meteorological year dataset for Lesotho is used as a case study, validated with indoor temperature measurements and power metering at four health center sites spanning a daily patient load ranging from 15 to 450 per day over rural and urban communities. High resolution electricity measurements from smart meters installed at the clinics are used to close the energy balance and form the basis of a probabilistic method for forecasting long term hourly electricity demand in African health centers. These data and the corresponding method have relevance to energy system design for health clinics across sub-Saharan Africa, especially those featuring intermittent renewable generation. The integration of these two modeling approaches constitutes a novel tool for sizing and costing energy infrastructure to meet operational demand at health centers in both urban and rural areas of developing countries. [ABSTRACT FROM AUTHOR]

The operational flexibility of a thermal power plant has played an essential and promising role in accommodating the increment of variability in the supply and demand sides in China. The rapid activation of thermal storage in entire coal-fired power plant lies at the heart for the strategy. Understanding the thermodynamic characteristics of the power unit in the transient process quantitatively remains a challenge. In this study, dynamic simulations of an entire 660 MW supercritical coal-fired power plant were conducted via GSE software, and the models were validated in the steady state and transient processes. Then, five different measures were introduced to regulate the extraction steam of high-pressure heaters for operational flexibility. The dynamic characteristics of the main thermodynamic parameters and output power were described and compared. Moreover, the operational flexibility of these measures was discussed. It turns out that: among the five measures, the change degrees of pressure, flowrate, and temperature in main devices increase with the increment in the number of throttled valves and/or the degree of feedwater bypass. The feedwater temperature at steady state reduces by 94.6 °C at most, and the maximum temperature change rate of metal slabs in HP heaters is −44.6 °C min −1 . The dynamic process for output power under different measures has two different ramp stages, namely, a rapid stage and a slow stage. Furthermore, compared with other measures, 100% throttling extraction steam of #1, #2, and #3 HP heaters has the best operational flexibility, that is, the maximum average power ramp rate in a minute, power capacity, and energy capacity are 6.19% of rate power per minute, 48.40 MW, 5.58 MW h, respectively. The average power ramp rate, power capacity and energy capacity increase with the increment in the number of throttled valves and/or the degree of feedwater bypass. This work is expected to provide a detailed reference on the use of turbine thermal storage to improve the operational flexibility of coal-fired power plants. [ABSTRACT FROM AUTHOR]

The increased impact from fluctuating energy sources like wind and photovoltaics significantly affects the operational regime of conventional power plants. In the near future, even former base load power plants such as the large-scale lignite plants in Germany will need to start and shut down to balance the electricity system. As frequent starts were not in the focus of optimisation in the past, an extensive potential can be expected to reduce start-up costs and environmental impacts. In order to investigate such optimisation potentials, a comprehensive dynamic simulation model has been developed including process components such as boiler and water-steam cycle but also the power plants control system along with start-up sequence control. After successfully reproducing a reference start of the power plant, the model has been used to identify restrictions for faster start-ups, less fuel consumption and less emission while keeping the thermal and mechanical stress, caused by higher ramp rates, within acceptable bounds. [ABSTRACT FROM AUTHOR]

Due to its advantages of small size, wide adaptability and high reliability, thermoelectric power generation (TEG) technology is attracting more and more attention in the application prospects of distributed energy, waste heat recovering and clean electricity supply. However, the promotion of the TEG is hindered by its low energy conversion efficiency which has become the most urgent problem in the TEG system. In order to achieve higher efficiency, a novel cascaded thermoelectric generator system (CTEG) with three-stage thermoelectric generators and its dynamic models based on the energy conservation equation, unsteady heat conduction theory and fluid dynamics were proposed and built. Through experimental data and numerical results, the system dynamic performance and the key parameters which affect the characteristics of the TEG system were analyzed. The results show that the efficiency of the new cascaded TEG system is greatly improved by 21.56% compared with the system with single-stage TEG. Furthermore, this study puts forward guidance for system improvement, and it is encouraging that a more appropriate system configuration could be an important means to further increase the system efficiency. Moreover, this dynamic simulation model can be used in the system design and operating improvement. [ABSTRACT FROM AUTHOR]

This study concerns the development of a data-based compact model for the prediction of the fluid temperature evolution in district heating (DH) pipeline networks. This so-called "reduced-order model" (ROM) is obtained from reduction of the conservation law for energy for each pipe segment to a semi-analytical input–output relation between the pipe outlet temperature and the pipe inlet and ground temperatures that can be identified from training data. The ROM basically is valid for generic pipe configurations involving 3D unsteady heat transfer and 3D steady flow as long as heat-transfer mechanisms are linearly dependent on the temperature field. Moreover, the training data can be generated by physics-based computational "full-order" models (FOMs) yet also by (calibration) experiments or field measurements. Performance tests using computational training data for a single-pipe configuration demonstrate that the ROM (i) can be successfully identified and (ii) can accurately describe the response of the outlet temperature to arbitrary input profiles for inlet and ground temperatures. Application of the ROM to two case studies, i.e. fast simulation of a small DH network and design of a controller for user-defined temperature regulation of a DH system, demonstrate its predictive ability and efficiency also for realistic systems. Dedicated cost analyses further reveal that the ROM may significantly reduce the computational costs compared to FOMs by (up to) orders of magnitude for higher-dimensional pipe configurations. These findings advance the proposed ROM as a robust and efficient simulation tool for practical DH systems with a far greater predictive ability than existing compact models. • A data-based input–output reduced-order model (ROM) is developed. • A significant computational cost reduction from the ROM is achieved while preserving high prediction accuracy. • Application of the ROM on practical system operations is demonstrated. [ABSTRACT FROM AUTHOR]

[Display omitted] • This study evaluates energy consumption options in France using dynamic ARDL. • Explores the impact of changes in disaggregated energy consumption on CO 2 emissions. • The results show that nuclear energy can be a real option for France against gas supply cuts. • The KRLS approach validates the robustness of the dynamic ARDL simulations outcomes. The study explores the influences of potential changes in energy consumption on carbon dioxide (CO 2) emissions, focusing on disaggregated energy consumption sources. In this manner, the study considers France as the leading nuclear energy-consuming country in Europe, includes yearly data between 1970 and 2021, and performs the dynamic autoregressive distributed lag (DYNARDL) model. In addition, the Kernel-based regularized least squares (KRLS) is used for robustness check. The results reveal that (i) cointegration exists between the disaggregated energy consumption indicators and CO 2 emissions; (ii) nuclear, natural gas, oil, and coal energy have a statistically significant effect on CO 2 emissions, while renewable energy is not statistically significant; (iii) nuclear power has a decreasing effect on CO 2 emissions; (iv) positive (i.e., increasing) shocks to nuclear reduce CO 2 emissions, even if they are 300 % in the case of counterfactual shocks; (v) any positive (i.e., increasing) shocks to coal have a drastically increasing effect on CO 2 emissions, even if they are 25 % in the case of counterfactual shocks; (vi) the KRLS approach confirms the robustness of the results. Thus, this study suggests that France should continue to rely on nuclear power for electricity generation and that French policymakers should reduce electricity exports to European Union countries to provide an alternative against the Russian natural gas shock by preventing a reduction in energy supply. [ABSTRACT FROM AUTHOR]

This paper proposes a novel solid oxide steam electrolyser with in-situ hydrogen storage by integrating a magnesium hydride (MH) section with proton-conducting solid oxide electrolysis cell (SOEC) section. Dynamic simulation results show that it takes 1950 s to fully charge the MH section with a 56% H 2 storage efficiency without any flow recirculation, when the electrolyser is operated at 1.4 V and 4 atm, yielding a current density of 4956.40 A/m 2 . The evolution of temperature, H 2 partial pressure and reaction of Mg powder through the charging process are analysed. It is found that the exothermic H 2 absorption process of MH section can enhance the performance of the electrolysis process of SOEC section. The effects of operating parameters including operating pressure, electrolysis voltage, and cooling air temperature on the performance of the novel design are investigated by sensitivity studies. Results show that it is beneficial to operate the electrolyser at elevated pressure for shorter absorption time and higher H 2 storage efficiency. Increasing the operating voltage can shorten the absorption time, but lower H 2 storage efficiency. An optimal cooling air temperature is found at 521 K when the electrolyser is operated at 1.4 V and 4 atm. [ABSTRACT FROM AUTHOR]

System inertia reduction, driven by the integration of renewables, imposes significant challenges on the primary frequency control. Electrification of road transport not only reduces carbon emission by shifting from fossil fuel consumption to cleaner electricity consumption, but also potentially provide flexibility to facilitate the integration of renewables, such as supporting primary frequency control. In this context, this paper develops a techno-economic evaluation framework to quantify the challenges on primary frequency control and assess the benefits of EVs in providing primary frequency response. A simplified GB power system dynamic model is used to analyze the impact of declining system inertia on the primary frequency control and the technical potential of primary frequency response provision from EVs. Furthermore, an advanced stochastic system scheduling tool with explicitly modeling of inertia reduction effect is applied to assess the cost and emission driven by primary frequency control as well as the benefits of EVs in providing primary frequency response under two representative GB 2030 system scenarios. This paper also identifies the synergy between PFR provision from EVs and “smart charging” strategy as well as the impact of synthetic inertia from wind turbines. [ABSTRACT FROM AUTHOR]

Due to their non-deterministic behaviour, renewable energies are defined as non-dispatchable energies and are largely coupled with energy storage systems to overcome the problem of matching energy production and demand. Hence, in the energy efficiency and conservation field there is growing interest towards energy storage systems, especially when combined with the demand side management (DSM) concept, representing DSM the possibility of shaping end user electricity consumption. In this work an existing installation of a thermal energy storage (TES) system coupled with heat pumps in an industrial building is presented and a dynamic simulation model is built to represent its behaviour. Simulations are performed to show the load shifting potential of such storage and costs and energy use are assessed for different configurations, in order to evaluate the viability of this TES application. In particular the demand side strategy considered is aimed at shifting energy demand for cooling to weekend daytime to recover surplus PV electricity or otherwise to off peak hours to profit from lower electricity tariffs. It is found that the use of TES implies increased energy demand, while costs can decrease when electricity tariffs with a considerable difference between on peak and off peak rates are applied. Furthermore the integration with renewable sources for electricity production, such as PV panels, makes the installation of TES economically interesting independently of the electricity tariff in place. However the more relevant aspect for the overall economic feasibility of such installation is the initial capital investment. [ABSTRACT FROM AUTHOR]

The transition from fossil fuels to green renewable resources presents a key challenge: most renewables are intermittent and unpredictable in their nature. Energy storage has the potential to meet this challenge and enables large scale implementation of renewables. In this paper we investigated the dynamic performance of a specific Adiabatic Compressed Air Energy Storage (A-CAES) plant with packed bed thermal energy storage (TES). We developed for the first time a plant model that blends together algebraic and differential sub-models detailing the transient features of the thermal storage, the cavern, and the compression/expansion stages. The model allows us to link the performance of the components, in particular those of the thermal storage system, with the performance of the whole A-CAES plant. Our results indicate that an A-CAES efficiency in the range 60–70% is achievable when the TES system operates with a storage efficiency above 90%. Moreover, we show how the TES dynamic behaviour induces off-design conditions in the other components of the A-CAES plant. Such device-to-plant link of performance is crucial: only through integration of TES model in the whole A-CAES model is possible to assess the benefits and added value of thermal energy storage. To the authors’ knowledge the present study is the first of this kind for an A-CAES plant. [ABSTRACT FROM AUTHOR]

As renewable energies are incorporated in larger shares in the electricity grid and district heating and cooling networks, the integration of storage solutions becomes more important. Thermal Energy Storage is an effective way to store heat and utilize the synergies between different energy carriers. Stratified storage tanks are a promising technology because of their low cost, simplicity and reliability. However, the modeling of the thermocline region in a stratified tank remains a challenge. There is a need to develop a fast and accurate 1D model for simulations and optimizations of TES. In this paper, a new discretization scheme is applied to the vertical axis of the storage tank. Orthogonal Collocation accurately represents the temperature profiles inside the storage tank with less points than the traditional multinode model, therefore running faster. Oscillations appear in the temperature profiles computed with orthogonal collocation if the thermocline represented is too steep and a low number of discretization points is used. But if a realistic thermocline is used as initial condition, the model performs well. Thus, it is appropriate to represent the real behavior of a storage tank, where uniform temperature conditions are avoided. Orthogonal Collocation on Finite Elements runs even faster and represents a good perspective for optimization studies. The model developed in this paper is validated with real data from a solar thermal plant with storage. A continuous and smooth model is also developed for natural convection inside the storage tank. The limitations of the model are discussed and perspectives on the modeling of natural convection for optimization models are given. • Orthogonal collocation is suggested for the 1D storage tank model discretization. • The proposed model runs faster than the multinode model for the same accuracy. • Orthogonal collocation on finite elements is suggested for optimization studies. • The storage tank model is validated with real plant data. • A continuous and smooth model for natural convection is developed. [ABSTRACT FROM AUTHOR]

The ground truth for cascading failure in power system can only be obtained through a detailed dynamic model involving nonlinear differential and algebraic equations whose solution process is computationally expensive. This has prohibited adoption of such models for cascading failure simulation. To solve this, we propose a fast cascading failure simulation approach based on implicit Backward Euler method (BEM) with stiff decay property. Unfortunately, BEM suffers from hyperstability issue in case of oscillatory instability and converges to the unstable equilibrium. We propose a predictor–corrector approach to fully address the hyperstability issue in BEM. The predictor identifies oscillatory instability based on eigendecomposition of the system matrix at the post-disturbance unstable equilibrium obtained as a byproduct of BEM. The corrector uses right eigenvectors to identify the group of machines participating in the unstable mode. This helps in applying appropriate protection schemes as in ground truth. We use Trapezoidal method (TM)-based simulation as the benchmark to validate the results of the proposed approach on the IEEE 118-bus network, 2383-bus Polish grid, and IEEE 68-bus system. The proposed approach is able to track the cascade path and replicate the end results of TM-based simulation with very high accuracy while reducing the average simulation time by ≈ 10 − 35 fold. The proposed approach was also compared with the partitioned method, which led to similar conclusions. • Fast dynamic cascading failure simulation approach using Backward Euler method (BEM). • Hyperstability of BEM addressed through a new predictor–corrector (PC) approach. • Adaptive Center of Inertia (COI) frame for faster convergence of Newton iterations. • Comprehensive comparison of proposed BEM-PC approach against state-of-art. • BEM-PC replicates cascade path and end-results with ≈ 10 − 35 -fold average speedup. [ABSTRACT FROM AUTHOR]

• A method to support investment decisions for smart shading devices is proposed. • PROMETHEE II multi-criteria is coupled to EnergyPlus to study smart building aspects. • Criteria related to energy, finance, environment, occupants' well-being are defined. • More expensive smart options are repaid through enhanced comfort and energy savings. In the framework of the current energy transition, the building sector is experiencing a smart revolution, recognizing how the adoption of advanced control strategies and smart management systems can increase buildings energy efficiency and improve occupants' comfort. As a key element for smart buildings, solar shading devices coupled with effective control systems need to be strategically assessed. The investment decision-making process for selecting the proper shading systems is influenced by the existence of potential conflicts from economic, environmental, social, and energy standpoints, thus asking to be supported by innovative methodological approaches able to include all these aspects in the decisional framework. To this purpose, the work aims to propose a multi-disciplinary methodological framework to support decision-makers in ranking a set of solar shading device and relative control strategy, integrating energy dynamic simulations with multi-criteria decision analysis techniques. The analysis focuses on office buildings, recognizing their huge impact in terms of energy consumptions and the need to guarantee proper indoor conditions to increase employees' productivity and well-being. To test the applicability of the multi-step methodology for this building category, the proposed approach is applied to an office building located in the North-West of Italy, aiming to assess and compare different alternative combinations of shadings devices and management strategies. The advanced features of building energy modelling and simulation and the application of PROMETHEE II (Preference Ranking Organization METHod for Enrichment Evaluation II) method as multi-criteria analysis allows to provide recommendations to decision-makers to identify the systems to be installed, able to guarantee the best trade-off between internal comfort, operational energy, and environmental costs for the building under investigation. [ABSTRACT FROM AUTHOR]

• Proposition of heat-up efficiency to evaluate start-up procedures energetically. • Thermal parameters for electrolysis systems with up to 1 MW el are presented. • Efficiency when only using heating is always lower than partial-load heat-up. • Introduction of a new dimensionless heat-up number for electrolyzers. • Dimensionless heat-up number enables general estimation of time constants. Dynamically-operated water electrolyzers enable the production of green hydrogen for cross-sector applications while simultaneously stabilizing power grids. In this study, the start-up phase of polymer electrolyte membrane (PEM) water electrolyzers is investigated in the context of intermittent renewable energy sources. During the start-up of the electrolysis system, the temperature increases, which directly influences hydrogen production efficiency. Experiments on a 100 kW el electrolyzer, combined with simulations of electrolyzers with up to 1 MW el , were used to analyze the start-up phase and assess its implications for operators and system designers. It is shown that part-load start-up at intermediate cell voltages of 1.80 V yields the highest efficiencies of 74.0 % LHV compared to heat-up using resistive electrical heating elements, which reaches maximum efficiencies of 60.9 % LHV. The results further indicate that large-scale electrolyzers with electrical heaters may serve as flexible sinks in electrical grids for durations of up to 15 min. [ABSTRACT FROM AUTHOR]

Due to the strengthening of regulations and codes on building energy performance, as well as with the application of national legislations regarding energy management and efficiency, existing industrial facilities are using thermal refurbishment and renovation as impetus for increasing their overall energy efficiency. This paper analyzes a building envelope refurbishment for a case study of an existing historical industrial facility. Critical parameters affecting energy performance of industrial buildings were identified by reviewing relevant literate. Two retrofit scenarios were developed and dynamic thermal simulation using EnergyPlus was implemented to evaluate the potential for improvement. Thereby the impact of interior loads was considered, determined by measurements conducted on factory machines, occupancy and lighting operation patterns. However, information regarding constructions of the existing facility and installed technical building services is limited. There is also uncertainty in the quantification of natural ventilation air change rate for such buildings. To overcome these limitations a study of various material databases was carried out, in order to assess data for building envelope composition. Input values for missing data were provided based on literature, allowing a fair comparison between refurbishment alternatives. Simulation results showed that the heating demand of the facility could be reduced up to 52%, indicating a significant potential for energy savings. Beyond that, thermal performance against summer overheating also depicted considerable improvements as regards to hours exceeding thermal comfort levels. [ABSTRACT FROM AUTHOR]

Design criteria for a residential nZEB in Mediterranean climate are discussed. The integrated design procedure focuses on the problem of a large number of available building variants concerning the building envelope. The aim is to search the ones that minimize winter and summer energy demand without compromising thermal comfort. The adopted methodological approach combines the use of dynamic energy simulation tool (EnergyPlus), based on a one-dimensional conduction finite difference solution method, and a constrained multi-objective optimization algorithm. For four cities (Madrid, Nice, Naples, Athens), several passive strategies are compared: thermal properties of the building envelope, adoption of phase change materials with different melting temperatures, cool roof solutions, several window/wall ratio values, some external and internal shading systems. The results allow to evidence that it is difficult to understand the best trade-off between summer and winter performance, by assuring high standard of thermal comfort when the aim is to reach NZEB objectives in Mediterranean climate. However, some guidelines are indicated, starting from the discussed results. [ABSTRACT FROM AUTHOR]

• Introduce pipeline FDFR function to obtain linear gas flow constraints. • Proposed FRF method decouples system constraints into linear and nonlinear ones. • FRF modeling and solution method greatly improves the computational efficiency. • Develop a leakage diagnosis algorithm based on bilayer optimization. • Location errors in single and multiple leakages cases are within 1%. Timely diagnosing leakages is significant for the safety and reliability of gas pipeline systems, where an efficient and accurate modeling and solution method is critical to identify the leakage rate and location. Here, a frequency response function-based modeling method for dynamic gas flow in pipelines is proposed. Based on the frequency-domain flow resistance of pipelines and Fourier Transform, original dynamic flow model is transformed into the frequency response function model consisting of linear lumped transmission constraints, nonlinear frequency response function, and nonlinear pipeline resistance characteristics, which are efficiently solved according to their different mathematical properties. Dynamic simulation cases show the proposed modeling and solution method greatly improves the computational efficiency keeping the accuracy. Besides, taking the difference between measurements and simulation results under leakage condition as objective, an iterative bilayer optimization algorithm is proposed based on the mathematical categorization of system constraints to efficiently diagnose leakages. Four leakage diagnosis cases in single pipeline and pipeline network with measurement noise and transient boundary conditions are studied to validate the leakage diagnosis method. Absolute location errors in the results are all within 1%, demonstrating the accuracy and robustness of the proposed method for single leakages and multiple leakages occurring successively or simultaneously. [ABSTRACT FROM AUTHOR]

The transient performance of solar thermal power plants is critical to the system design and optimization. This study numerically investigates the dynamic efficiencies of an open-loop air receiver and a thermal energy storage unit. One-dimensional dynamic models of the air receiver and thermal energy storage were developed using the Modelica language with a graphical user interface and the Dymola solver to provide comprehensive thermal simulation at low computational cost. An air receiver and thermal energy storage experimental platforms were built to validate the simulation models. The simulation results compare well with the experimental data, so the models can be used to predict the variations of air receiver and thermal energy storage efficiencies. The models were then combined into a receiver and thermal energy storage system model with control schemes. The schemes control the air receiver outlet air temperature at relatively stable values while the thermal energy storage automatically switches between charging, discharging and stand-by modes. [ABSTRACT FROM AUTHOR]

Renovation of existing buildings is important in the work toward increased energy efficiency and reduced environmental impact. The present paper treats energy renovation measures for a Swedish district heated multi-family house, evaluated through dynamic simulation. Insulation of roof and façade, better insulating windows and flow-reducing water taps, in combination with different HVAC systems for recovery of heat from exhaust air, were assessed in terms of life cycle cost, discounted payback period, primary energy consumption, CO 2 emissions and non-renewable energy consumption. The HVAC systems were based on the existing district heating substation and included mechanical ventilation with heat recovery and different configurations of exhaust air heat pump. Compared to a renovation without energy saving measures, the combination of new windows, insulation, flow-reducing taps and an exhaust air a heat pump gave up to 24% lower life cycle cost. Adding insulation on roof and façade, the primary energy consumption was reduced by up to 58%, CO 2 emissions up to 65% and non-renewable energy consumption up to 56%. Ventilation with heat recovery also reduced the environmental impact but was not economically profitable in the studied cases. With a margin perspective on electricity consumption, the environmental impact of installing heat pumps or air heat recovery in district heated houses is increased. Low-temperature heating improved the seasonal performance factor of the heat pump by up to 11% and reduced the environmental impact. [ABSTRACT FROM AUTHOR]

In this paper, a novel solar thermal polygeneration (STP) system for production of cooling, clean water and domestic hot water is modeled and analyzed for the weather conditions of United Arab Emirates (UAE). The system comprises of solar collectors for production of thermal energy, single stage LiBr–H 2 O absorption chiller (VAC) for providing air conditioning to office cabins and membrane distillation (MD) modules for clean water production along with domestic hot water generation as by-product. The performance of STP is analyzed with three different solar collectors – flat plate collectors (FPC), evacuated tube collector (ETC) and compound parabolic collector (CPC). The system is modeled and dynamically simulated using TRNSYS software for optimization of various design parameters like slope of the collectors, mass flow rate through the collector loop, storage capacity and area of collectors. Combined and system efficiency of the STP system has been determined for optimum conditions. Economic benefits are analyzed for different collectors and fuel costs savings. A lowest payback period of 6.75 years is achieved by STP with evacuated tube collector field having gross area of 216 m 2 . STP system has cumulative savings of $520,000 over the life time of the project through roof top solar collector installation. In terms of environmental benefits, 109 metric tons/year of CO 2 emissions would be avoided and hence the overall payback period would be reduced by 8% based on cost saving through carbon credits. Economic and environmental benefits were aided by steady system performances of absorption chiller (35 kW), membrane distiller (80 l/day) and heat recovery system (1.2 m 3 /h) throughout the year. The complete simulation results of the STP system is utilized for the development, installation and testing of a polygeneration system at RAKRIC. [ABSTRACT FROM AUTHOR]

Thermal cooling systems are particularly attractive in locations supplied by district heating based on cogeneration heating plants (CHP). Moreover, solar thermal energy is a major renewable source for the provision of thermal energy, fulfilling demands for space heating, domestic hot water, process heat, and cooling. This energy source can be suitably used also in Nordic Countries. The presented paper focuses on two configurations of a cooling solar-driven thermal system for an office building located in Finland. Dynamic simulation approach has been used through TRNSYS software. In particular, the configurations differ from the connection between the hot storage tank, the solar collectors and the chiller. Particularly, in the first configuration only the tank can supply the chiller (Case 1), while in the second, the chiller can be supplied either by the tank or the solar collectors directly (Case 2). System performance indexes, in case of district heating as main building heating supply system in winter and as auxiliary heating system for the chiller in summer, have been evaluated as a function of the tank and solar thermal field sizes. Results show that Case 2 has better performance than Case 1, because of the versatility shown in summer. Particularly, when the solar irradiance is low, Case 2 solutions perform far better than Case 1 solutions, benefitting from the direct connection between the solar collectors and the chiller. This study has highlighted also the potential of this technology in cold climate areas supplied by means of DH based on CHP plants. Indeed, the adoption of such cooling technology, in addition to reduce both heating and cooling consumed energy and to shave summer electricity peaks, can potentially allow some CHP plants to operate also in summer, fulfilling the future energy networks aims: being able to provide electricity, heat and cooling energy. [ABSTRACT FROM AUTHOR]

As reported in the scientific literature and mentioned in building energy performance legislation, the thermal inertia of the opaque building envelope can have a significant positive impact on the reduction of summer indoor overheating, of space cooling peak load and of electricity consumption. At the early stages of the envelope design, there is a need to use simplified as well as effective parameters to correctly characterize the thermal performance of the opaque envelope under dynamic conditions. In this work, a new methodology to describe the dynamic thermal behavior of opaque components is proposed. The approach is based on the harmonic parameters specified in ISO 13786 but it also takes into account realistic boundary conditions for different orientations and solar absorptance values. New equivalent thermal parameters are determined by means of dynamic simulations. The use of these parameters to assess the conduction heat flow rate by means of a simplified model is validated through a comparison with the results of a dynamic simulation. The method presented in the article represents an improvement with respect to the parameters usually applied at the early design stage to thermally characterize the opaque envelope of the building under dynamic conditions. In fact, it allows simplified but reliable performance parameters referring to actual boundary conditions to be obtained. The application potential of the proposed methodology lies in the drawing-up of catalogues and technical standards that supply the values of the new equivalent thermal parameters for different technical solutions. [ABSTRACT FROM AUTHOR]

In the last decades, increasing attention has been paid to the enhancement of energy performance and comfort conditions of historic buildings, where the necessity to preserve architectural heritage does not allow typical invasive retrofit interventions. The need for a replicable methodology for improving the sustainability of historic buildings based on the integration of energy efficiency solutions with renewable technologies is here addressed, by riding over the constraints imposed by architectural preservations, rather taking advantage of heritage architectural peculiarities. The case study is represented by Palazzo Gallenga Stuart, a historical university building located in central Italy. The optimization of the building energy efficiency has been pursued through two strategies specifically prototyped for application in historic buildings, i.e. innovative cool tiles with the same appearance of traditional historic tiles, and a geothermal heat pump system with water storage tanks positioned in the under-ground unoccupied areas of the building previously used as archives, also preventing the use of external units spoiling the building façade. Four retrofit scenarios were analyzed and compared from a both technical and economical point of view. The results showed that the application of the innovative cool tiles lead to a maximum cooling energy saving of 14.0% and 3.8% in the classrooms of the top floor and in the whole building, respectively. Furthermore, the installation of a more effective energy plant leads to an average energy saving of 64.3% and 67.0% in terms of heating and cooling demand, respectively. The combination of the two effects leads to an average energy saving of 64.0% for heating and 69.2% for cooling. Additionally, the cost-benefit analysis showed a payback time of 5 years. This work shows the important environmental benefit achievable by researching around smart and innovative integrated systems for energy saving in historic buildings having a great potential in reducing energy demand and carbon emissions, in ancient European countries in particular. [ABSTRACT FROM AUTHOR]

This study investigates the impact of the design of a heat recovery steam generator (HRSG) on its dynamic behaviour under the boundary condition of a gas turbine start-up. For that purpose, a validated HRSG model with three pressure stages and reheater section is modified by replacing the once-through evaporator in the high pressure circuit with a natural circulation evaporator, including the associated control circuits. Both models are designed to supply equal steam mass flows with equal steam parameters (temperature, pressure) at full load, which enables a balanced assessment of the two technologies. After an extensive description of the modelling approach and its practical realisation, detailed simulation results for start-up procedures from warm and hot initial conditions are presented. Differences in the transient behaviour of the HRSGs are highlighted and discussed. In industrial practice, frequent start-ups cause increased material fatigue, which in turn has an adverse effect on the operating lifetime of a power plant. Hence, the present work is complemented by an analysis of the temperature gradients in the most critical components with respect to thermal stress. Results generally show similar responses of the high pressure systems to gas turbine start-up with the exception of accelerated pressure build-up in the once-through evaporator. Greater temperature deviations are observed in the natural-circulation HRSG across the wall of the high-pressure drum. [ABSTRACT FROM AUTHOR]