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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]

This study presents the modelling and dynamic simulation of a high penetration wind diesel power system (WDPS) consisting of a diesel generator (DG), a wind turbine generator (WTG), consumer load, dump load and a battery energy storage system (BESS). First the WDPS architecture and the models of the WDPS components are described. The WDPS is simulated in wind-only (WO) mode where the DG is not running and the WTG supply active power and in wind-diesel (WD) mode where both DG and WTG supply power. The simulation results are given showing graphs of the main electric variables in the WDPS (system frequency and voltage and active power in each component) and main battery variables (current, voltage and state of charge). The results in the WO mode show how the BESS, under the command of a proportional-integral-derivative (PID) controller, supplies/stores active power to regulate the isolated system frequency. The WD control enables the BESS to smooth the load and wind power variations, so that the isolated system power quality is improved. Also it is shown in the WD mode a peak shaving application where the control orders the BESS to supply active power temporarily to support system frequency in a DG overload situation. [ABSTRACT FROM AUTHOR]

A ground source heat pump system (GSHPS) utilizes a relatively stable underground temperature to achieve energy-saving for heating and cooling in buildings. However, continuous long-term operation will reduce the soil temperature in winter, resulting in a decline in system performance. In this research, in order to improve the system performance of a GSHPS, a ground heat pump system integrated with solar thermal storage was developed. This solar-assisted ground heat pump system (SAGHPS) can both maintain the balance of the soil temperature effectively and achieve higher system performance than the conventional system. In this paper, in order to examine the characteristics of the system, a dynamic simulation was conducted under various conditions. The results of our case study provide specific operation data such as heat exchange rate, heat source temperature, and heat pump COP. As a result, the heat pump COP of SAGHPS was 4.7%, 9.3% higher than that of the GSHPS. [ABSTRACT FROM AUTHOR]

Sustainable solutions for energy saving in buildings are assuming increasing interest both in the research and the industrial community. In this view, cool roof systems demonstrated to be interesting and effective solutions which role in energy saving for cooling and mitigating local and global warming is already acknowledged. In these recent years, several studies were carried out in order to quantify their thermal-energy effect with varying boundary conditions, while global climate analytical models were proposed with the purpose to evaluate the effect of high albedo solutions in terms of radiative forcing and CO 2eq offset. This work concerns the combined analysis of thermal-energy and environmental effect of cool roof (high albedo) clay tiles with low visual impact, specifically optimized in order to preserve traditional residential buildings. In particular, dynamic simulation models and field monitoring of a real residential village were developed and the effect of such tiles is analyzed in terms of energy saving for cooling and of CO 2eq avoided emissions due to the energy efficient intervention, coupled with the effect in climate change mitigation. This aspect is specifically considered by applying an analytical method elaborated in previous works, where the effect of high albedo surfaces in terms of CO 2eq offset is quantified with varying orientation, inclination, solar reflectance and geographical details. The combined analysis showed how an overall annual CO2 emissions’ offset is achievable by coupling single-building and global assessment methodologies. In particular, the energy saving contribution saved around 141 tonnes of CO 2eq per year, and the global warming analytical model showed that the albedo increase allowed to offset about 772 tonnes of CO 2eq per year. This prototypical study showed how local energy analysis should be coupled to global analysis in order to have an exhaustive view of building retrofit strategies’ sustainability. [ABSTRACT FROM AUTHOR]

In an adiabatic compressed air energy storage process (A-CAES), heat storage tank operation is a key factor that determines the overall energy performance of the process. To highlight energy issues linked to a correct tank design in the specific case of an A-CAES system, a two-dimensional thermal numerical model was developed. Thermal efficiencies of the tank are presented with abacus defined from the four dimensionless numbers defining the thermal behavior of the reservoir. Cycling effects are explored with a realistic case study corresponding to an A-CAES system design to deliver an electrical power of 250 MWel for 4 h, the daily peak demand. Extended beyond the thermal reservoir, A-CAES thermodynamic analysis combined with the dynamic simulation makes it possible to generate a direct quantitative link between reservoir sizing and A-CAES global efficiency. [ABSTRACT FROM AUTHOR]

• A new energy system is developed and examined using dynamic modelling to meet the needs of a two-story structure. • To decrease the size of the plant, including the PVT size and fuel consumption, the PCM is incorporated into the building. • Fuel consumption and prices are reduced by 17.24% and 8.57%, respectively, using the suggested approach. • Exergy efficiency, unit product cost, and CO 2 emission of 64.3 %, 0.26 $/kWh, and 0.21 kg/kWh are obtained respectively at optimum point. The buildings energy sector is expected to account for 40% of total world energy consumption and 40% participation on total carbon dioxide emissions, according to the International Energy Agency reports. The present study proposes a novel integrated system to meet all loads of the house's energy requirements. The system employs a heat storage tank rather than pricey batteries, which helps to keep the total cost of the system as low as feasible. Also, the system is developed for an on-grid operation, being capable to sell surplus energy to the grid helping to reduce the payback time. Dynamic modeling is conducted to analyze the system performance to provide heating, cooling and power demands of a case study building, for which two scenarios of with and without Phase Change Material (PCM) incorporation is considered. The influence of critical design factors is investigated, after which a tri-objective optimization is carried out. It was found that, the integration of PCM energy storage would reduce the annual heating and cooling demands of the building by 25.6%. As a result, the exergy efficiency of the proposed system increases by 13 % and the product cost is reduced by 8.57%. Based on the obtained yearly average results, the proposed building energy system yields exergy efficiency, unit product cost, and CO 2 emission of 64.3 %, 0.26 $/kWh, and 0.21 kg/kWh, respectively. [ABSTRACT FROM AUTHOR]

Using of Double Skin Facade (DSF) became a very demanding trend in most kind of buildings, since it provides natural light, creates a connection between indoor inhabitants and the external environment without getting affected by harsh weather conditions. The verification of the balance equations to be used in a dynamic simulation software and the assessment of the active double-skin facade thermal performance in terms of energy recovery savings are the two main items of this study. For this purpose the software DIGITHON has been used. By comparing measured data of exit air temperature from a certain facade with calculated results, validation has been attained to use it in terms of buildings integrated with DSF. Highlighting benefits of using facade as a thermal energy recovery item during heating seasons on HVAC system is presented with respect to four European climatic zones for each orientation. Average pre-heat efficiency has been studied and illustrated on a seasonal scale. [ABSTRACT FROM AUTHOR]

As a result of the increased penetration of intermittent renewable energy sources, Combined Heat and Power (CHP) units are being looked upon as one of the sources that might provide for the ever growing need for electrical flexibility. However, CHP units are often considered as must-run units on the grid for their main purpose is generally to cover the heat demand of an adjoining District Heating Network (DHN). This paper demonstrates how a CHP–DHN system may be used as a frequency reserve without excessively compromising the lifetime of the CHP, using either a specific storage tank or the DHN's thermal inertia in order to compensate for the resulting heat imbalance. In the latter case, it is shown that a buffer tank, although smaller than a specific Thermal Energy Storage (TES), is required due to restrictions for acceptable DHN temperature gradients. In both approaches, the size of the tank has been mapped out considering frequency reserve's duration and capacity. The results show that a simplistic static model of the DHN is sufficient for the design of a specific TES, while a detailed dynamic simulation is required when the DHN is used as storage, to prevent overestimating the flexibility of the CHP–DHN system. This research could be used to assess the potential for improving CHP–DHN systems flexibility, using them as frequency reserves, and to design the required storage or buffer tanks. • A control strategy to use a CHP-DHN system as a frequency reserve is proposed. • Dedicated storage tanks and/or DHN thermal inertia are used. • The DHN can be used as heat storage, but a buffer tank is required. • A detailed dynamic DHN model is needed to determine the DHN flexibility. • The flexibility of the CHP–DHN system was determined for 370 MW CHP. [ABSTRACT FROM AUTHOR]

This paper presents the conceptual design for a two-step thermochemical cycle producing hydrogen continuously, even off-sun, with the concentrated solar energy as the heat source. For a case study, the two-step iron oxide cycle (Fe3O4/FeO) is selected to illustrate the design concept. Two reactors, one storage tank and the solar collector comprise the system. Molten wustite (FeO) is accumulated in the storage tank on-sun. The FeO is not only involved in the reactions but also acts as the heat transfer medium, obtaining the energy from the solar insolation and delivering energy to support the thermal decomposition of magnetite (Fe3O4). In this way, the temperature limitation (<800 K) of molten salt is solved, and the intermittency problem of variable insolation is circumvented. A simple feedback scheme is used to control the flow rate between the storage tank and the reactors in order to minimize the temperature fluctuations. For the wustite hydrolysis reaction, the volumetric flow rate of water is regulated to control the temperature in the reactor. We derived the kinetics of the two-step iron oxide cycle from previous experimental reports. We simulated the dynamics of the system over 50 days with mass and energy balances. The simulation results show that the storage tank temperature will be stationary at 2250 K. After five days, the decomposition temperature at 2100 K, and the hydrogen production stabilized at 7 kg/min. Admitting the difficulty of high temperature operation, this design is still promising due to the high efficiency of two-step cycle itself, the process intensification of the FeO acting as the reactant/product/heat transfer medium (no need of heat exchangers), and the continuous operation/production of hydrogen. [ABSTRACT FROM AUTHOR]

How do the new building façade components work under real climatic conditions? The question is especially related to the dynamic behaviour of new and complex components such as the ventilated walls, the Phase Change Material, or others that use nano-technologies and aerogels. One of the objectives of the undergoing research activity, namedAbitare Mediterraneo, is the evaluation of their thermal behaviour through the use of an outdoor test cell, in order to reproduce under the real external conditions the performance of these components, and consequently define the main thermal parameters such as the attenuation factor and the thermal inertia, characterising the component; moreover, the results will be used to write new algorithms for dynamic simulation tools allowing an appropriate evaluation of the complex behaviour of the whole building at a real scale condition. The new test cell is realised in Florence, Italy. The design starts from the study of the experience of the existing PASSYS test cells, overtaking the main weakness of the building structure and of the heat-flux sensors. [ABSTRACT FROM PUBLISHER]

Highlights: [•] A new dynamic simulation code for building energy performance analysis is presented. [•] The thermal behavior of each building element is modeled by a thermal RC network. [•] The physical models implemented in the code are illustrated. [•] The code was validated by the BESTEST standard procedure. [•] We investigate residential buildings, offices and stores in different climates. [ABSTRACT FROM AUTHOR]

Abstract: The share of renewable energies in electricity and heat supply besides the conventional energy resources gains more importance. Accordingly, the efficiency and flexibility of modern thermal power plants should be further improved. To design such a system, it is necessary to generate detailed computer models that can accurately predict the power plant behaviour during fast transients, part loads and start-up procedures. In this work, a dynamic simulation model for a subcritical three-pressure-stage HRSG (heat recovery steam generator) is built, employing the advanced processing simulation software Aspen Plus Dynamics®. The simulation results obtained from the HRSG model are validated towards the dynamic measurements during warm start-up procedure. The capability of processing simulation software used to estimate the dynamic behaviour of real HRSG is demonstrated. The HRSG model shows high accuracy at different part loads with a maximum relative error of about 5%. The good agreement suggests that the HRSG model is very reliable and is capable to predict the operational processes. [Copyright &y& Elsevier]

Highlights: [•] A novel dynamic model for thermocline thermal energy storage systems is presented. [•] Adaptive grid technique used. [•] Accuracy is improved while using an order of magnitude fewer states and equations. [•] Effects of numerical diffusion are minimized. [•] Model more accurate under temperature (and density) inversion. [ABSTRACT FROM AUTHOR]

In order to make distributed generation systems for apartment buildings economically viable, it is essential to develop an efficient and low-cost heat supply system. We are developing a new cogeneration system (Neighboring CoGeneration system: NCG system). The key concept of this system is to install a heat storage unit for the hot water supply, floor heating, and bath heating in each house, and to connect the heat storage units by a single-loop hot water pipe. The system leads to time leveling of the total heat supply and reduced installation costs. Furthermore, it is expected that the cogeneration can operate according to electrical demand because of the large heat storage capacity of the system. In this study, a dynamic simulation model is developed to evaluate the performance and environmental load-reduction effect of the NCG system for 50 households. The results show that the NCG system can supply sufficient heat for peak demand in winter and reduce annual CO2 emissions by 23% on average. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 42(8): 745-757, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.20376 [ABSTRACT FROM AUTHOR]

Abstract: The paper is focused on the dynamic simulation of a Photovoltaic/Thermal collector (PVT) integrated in a high-temperature Solar Heating and Cooling (SHC) system. The system is based on the following main components: concentrating parabolic PVT (photovoltaic thermal) collectors, a double-stage LiBr-H2O absorption chiller, storage tanks, auxiliary heaters, balance of plant devices. The PVT is made-up by a parabolic dish concentrator and a triple-junction receiver. The polygeneration system provides electricity, space heating and cooling and domestic hot water for a given building, whose simulation is also included in the model. In particular, PVT produces electric energy, which is in part consumed by the building loads (lights and equipments), in part by the system parasitic loads, whereas the eventual excess is sold to the public grid. Simultaneously, the PVT provides the heat required to drive the absorption chiller. The system was simulated by means of a zero-dimensional transient model, that allows the evaluation of temperature profiles and also heat/electrical energy flows for whatever period of the year. It is also possible to evaluate the overall energetic and economic performance on whatever time basis (day, week, month, year, etc.). The economic results show that the system under investigation can be profitable, if a proper funding policy is available. The paper also includes an extensive parametric analysis aiming at evaluating the set of design and operating parameters (solar field area, tank volumes, set point temperatures, etc.) that maximize the energetic and/or economic performance of the system. [Copyright &y& Elsevier]

Abstract: Energy saving through incorporation of automation techniques in buildings is usually too complicated and costly and it is necessary to protect environment. Presently, there is no single directive and standard method to estimate and validate the energy consumption process in industrial buildings for heating to maintain a comfortable environment for working. The purpose of this study was to find and develop a practical method for analysis and calculation of thermal energy consumptions and saving in buildings. The energy required for heating in an industrial building in Kosice, Slovakia was studied using measurements, calculations and dynamic simulations. The energy needed for heating was determined according to the Slovakian and Austrian national standard methods using the simplified calculation method that is applied for non-residential buildings and the ESP-r and BuilOpt-VIE simulation programs. The repeatability of the experimental data and possibility of rapid assessments in an optimized process using these methods were studied. It was found that the clear definitions of the heat consumers inside the building, including all machinery and occupants, are very important for evaluation of energy needed for heating. Using dynamic simulation, it is not possible to reproduce actual temperatures at various heights without prior knowledge of the exact functionality of the heating and cooling systems. The simulations results also indicated that integration of lighting, heat recovery and door opening automation can significantly reduce the heating energy consumption. [Copyright &y& Elsevier]

Highlights: [•] First paper dealing with numerical dynamic simulation of thermal-lag Stirling engine. [•] Observation on different operating modes, such as rotating, swinging, swinging-to-rotate, and swinging-to-decay modes. [•] Study of influential factors affecting the operating modes. [•] Optimal geometrical or operating parameters of the baseline case for maximum engine power are found. [ABSTRACT FROM AUTHOR]

Abstract: The discontinuous nature of the solar energy forces to study the dynamic behavior of solar plants to characterize their operations, to deepen their process understanding and to improve the performance and maintenance. The present paper focuses on the dynamic simulation and control of concentrating solar plants with the aim to define a reasonably simplified layout as well as to highlight the main issues to characterize the process dynamics of these energy systems and their related energy storages. Detailed first-principles mathematical models of key unit operations are developed, implemented, and integrated into commercial codes to improve the reliability of the plant dynamic simulation as well as the prevision accuracy. The case of Archimede concentrating solar power plant with the related two-tanks direct thermal energy storage technology is investigated. [Copyright &y& Elsevier]

Abstract: Dynamic simulation results for a thermal energy storage (TES) unit used in a parabolic trough concentrated solar power (CSP) system are presented. A two-tank-direct method is used for the thermal energy storage. While previous works have been focused largely on controlling the outlet temperature of the solar collector as a single unit, this work emphasizes the storage component, its interaction with the other components of the system, and how it can be leveraged to control power output in addition to collector outlet temperature. The use of storage gives the system the ability to provide power at a constant rate despite significant disturbances in the amount of solar radiation available. It can also shift times of power generation to better match times of consumer demand. By contrast, a CSP system without storage undergoes large fluctuations in power output, particularly during intermittent cloud cover. Adding a storage system increases the solar share of the power plant by as much as 47% for a base load thermal power output of 1MW. This reduces the supplementary fuel requirement by as much as 43%. [Copyright &y& Elsevier]

Abstract: With a view towards better efficiency in renewable energy utilisation, particularly solar energy, the authors study a long-term solar thermal energy storage based on water absorption by a lithium bromide aqueous solution. After a description of the process, the system dynamic simulation model is detailed and used to investigate the influence of certain parameters (heat exchanger size, solution flow rate, absorption percentage) and operating conditions (heat supply temperature to the building, crystallisation ratio, heat need) on the system performance (storage density, thermal efficiency, etc.). The analysis of simulations made for a low-consumption building in Chambéry shows that the solution flow rate is a critical parameter in the process performance. It also appears that crystallisation in the solution storage tank increases the storage density more than three times. The simulation results are used in the design of a prototype that is under experimentation for validation of the model. [Copyright &y& Elsevier]

Abstract: The paper suggests a multi-criteria approach for the energy refurbishment of historical buildings, proposing methodologies for the performance analysis, coupling several experimental and numerical studies. The target consisted in a rigorous evaluation procedure, in order to guarantee the necessary reliability of a numerical model of the system “building envelope/technical plants”, on which testing the technical and economical convenience of energy retrofit solutions. The paper collects the long work carried out by several Institutions during the last years, on Building “Palazzo dell’Aquila Bosco-Lucarelli”, a historical building located in Benevento (Southern Italy), currently analyzed in order to define the technical adoption of possible improving actions. The carried out studies, beyond the proposition of an operational methodology, are aimed to evidence a best-practice specified for the Italian territorial context, which has several historical buildings needing restoration. Carefully applied investigations, based on various methodologies and through several instrumentations, allowed the definition of a numerical model correspondent to the real building, defined also comparing the results with the historical requests of gas and electricity. Moreover, dynamic energy simulations tested the effectiveness, singularly and coupled, of several solutions for the building energy optimization. A significant potentiality of energy and economic optimization has been demonstrated. [Copyright &y& Elsevier]

In cold climatic regions such as those located across Canada, it is necessary to implement heating system technology that is ultra-efficient and that has near-zero rates of emissions. Such systems would satisfy consumers' energy needs and also comply with environmental standards, especially because the systems would account for more than 80% of residential energy use. This paper investigates two complementary efficient systems that can support these heating systems; ground-source heat pumps (GSHPs) and organic Rankine cycle systems (ORCs). The study proposes to couple these two systems in a parallel configuration. A dynamic simulation model created in TRNSYS platform has been deployed to assess the performance of the combined ORC-GSHP based micro-cogeneration system. This former provides heating to a residential house during the heating mode as needed. It has the capacity to switch to a charging mode, during which the ORC system is directly coupled to the ground heat exchanger (GHE), which works as a thermal energy storage and supplies energy to the GSHP. The feasibility of this combined system arrangement, and its comparison with a conventional GSHP system are examined for use in residential buildings in three cities across the varied climatic regions within Canada, namely Edmonton (AB), Halifax (NS), and Vancouver (BC). Results showed that the proposed micro-cogeneration system recorded less energy use of over 80%. The addition of the ORC system had a definite effect on the performance of the GSHP in that it decreased the operating hours from 11–58% compared to the conventional GSHP case and maintained consistently higher COP values. These results may help to specify viable ORC-GSHP based micro-co/trigeneration systems in cold climatic applications and should be useful for prototype design and development. [ABSTRACT FROM AUTHOR]

[Display omitted] • Biomass power plant model integrated with thermochemical heat storage was created. • Fluidized bed using Ca(OH) 2 /CaO stores surplus electricity from renewable energy. • Overall energy efficiency was 9.79% for the base case (output: 1 MW el). • Steam flow rate is most important parameter for flexible power generation. • Energy storage efficiency is dramatically improved by recycling steam. In this study, a biomass power plant integrated with thermochemical heat storage (TCS) using Ca(OH) 2 /CaO particles reacted in a fluidized bed reactor was proposed. In the strategy of power generation, organic Rankine cycle (ORC) was worked by the heat from biomass combustion in normal operation. In charging time, the electricity from the power grid was stored by dehydration reaction in the daytime although the turbine output was not changed, and the amount of biomass combustion decreased compared to normal operation time. In discharging time, the heat from hydration reaction was converted to electricity through the ORC in the evening and the turbine output increased to respond to the increase of the electricity demand. The designed process was evaluated from energy efficiencies and the flexibility of the power generation by dynamic simulation. Results show energy storage efficiency and overall energy efficiency equaled 58.5% and 9.79% (only ORC: 11.4%) for base case, respectively. The energy storage efficiency increased by increasing the heat recovery from steam after a reactor, and it led to the decrease of the biomass combustion in charging time. It was found that the inlet gas flow rate into the reactor had the largest influence on energy efficiencies by changing the parameters such as fluidized bed volume, inlet gas conditions into the reactor, and heat supply into the reactor. In addition, the increase of the turbine output and discharging time were flexibly changed in discharging time by changing operational parameters. Therefore, it is possible to add flexibility to biomass power plants by integrating TCS. [ABSTRACT FROM AUTHOR]

[Display omitted] • Thermochemical heat storage using Ca(OH) 2 /CaO in a fluidized bed reactor was modeled. • Variable renewable energy fluctuation can be absorbed by using steam as fluidizing gas. • The energy efficiencies for nitrogen were higher than that for steam. • The simulated data agreed with the experimental data, albeit not perfectly. A simplified dynamic model of a Ca(OH) 2 /CaO–containing fluidized bed reactor was developed by combining a continuously stirred tank reactor model in the solid phase with a series of continuously stirred tank reactors in the gas phase for mass transport. The heat supplied to the thermochemical heat storage system was allowed to fluctuate to evaluate the absorption of variable renewable energy fluctuation. In addition, the performance of the fluidized bed was assessed using nitrogen or steam as the fluidizing gas. For nitrogen, the fluctuation of bed temperature increased with the increasing time step of heat change. The bed temperature was affected by the magnitude of the fluctuation of the supplied heat more strongly for nitrogen than for steam, mainly because the rate of dehydration under these conditions was more strongly dependent on temperature than in the case of steam. The thermochemical heat storage efficiency (calculated by considering reaction heat) and energy storage efficiency (calculated by considering reaction heat and sensible heat) equaled 14.1% and 34.1% for steam and 29.9% and 62.7% for nitrogen, respectively. The differences between the efficiencies for steam and nitrogen were ascribed to the latent heat of H 2 O. Sensitivity analysis showed that both efficiencies increased with increasing heat supply because of the concomitant decrease in the time required to heat the system to the reaction temperature. During this time, thermochemical heat storage did not occur, which resulted in lower efficiency. Therefore, the fluctuation from variable renewable energy can be absorbed by using thermochemical heat storage. [ABSTRACT FROM AUTHOR]

This work presents a dynamic analysis of an anaerobic digestion plant, in which concentrating photovoltaic/thermal collectors are used to match a part of both heating and power demand of the process. The system is supplied by the organic fraction of municipal solid waste. The system also includes a thermal storage tank and an auxiliary heating system. An up-grade section is also included, to produce biomethane, suitable for injection into the natural gas pipeline network. For such hybrid solar-biomass system, a comprehensive simulation model was developed in MATLAB®, calculating the time-dependent production of biomethane as a function of the operating temperature within the digester. The model, based on differential equations and thermal balances, accounts for both thermal and biological phenomena occurring within the process, taking into consideration the geometrical and structural characteristics of the system. The consistent Anaerobic Digestion Model 1 is used to model the biological process, evaluating the biogas production as a function of a series of operating variables: the digester operating temperature, mass flowrate and temperature of the hot water entering the digester, ambient temperature, mass flowrate and composition of the organic waste in input. The model also calculates the electric consumption of the upgrading process, used to convert the biogas into biomethane. Such model was integrated into the simulation platform of the overall plant, developed in TRNSYS, evaluating the energy, environmental and economic performance of the entire system. A case study is presented, showing the dynamic performance of the system under evaluation: for such case, a primary energy saving of 24% was found, with respect to a conventional digester; around 20% of the overall thermal energy demand is met by solar energy; finally, a promising payback time of about 3 years was estimated. [ABSTRACT FROM AUTHOR]

• DEMO IHTS system. • Dynamic model. • MATLAB®/Simulink. • HITEC molten salt. • Mass and energy flow. This study is carried out within the DEMOnstration Balance of Plant (DEMO BoP) development activities. Despite the pulsed operation of the Tokamak reactor, a steady energy output of the DEMO BoP need to be ensured. To fulfil this requirement, a two-tank Intermediate Heat Transport and Storage System (IHTS) with HITEC molten salt as a heat transfer fluid is applied. The focus of the study is the development of a dynamic simulation model for the DEMO IHTS using MATLAB®/Simulink. The customized programme block is developed for MATLAB®, which is used for the simulation of the temperature dependences of HITEC parameters. The influence of tank geometry and molten salt temperature on the temperature decrease in the IHTS tanks in due course of service maintenance is studied. The simulation of fluid filling level as well as mass and energy flows through the IHTS during the pulse and dwell operation is carried out. [ABSTRACT FROM AUTHOR]

• Comprehensive dynamic model for SC-CAES systems is established for the first time. • Transient characteristics with control under parameter steps are explored in depth. • Both volume effect and thermal inertia are considered for system dynamic study. Compressed air energy storage systems are often in off-design and unsteady operation under the influence of external factors. A comprehensive dynamic model of supercritical compressed air energy storage system is established and studied for the first time. In this model, important factors, including volume effect and thermal inertia, are considered for system dynamic simulation which used to be ignored in the past. The transient characteristics and control methodology are mainly focused in this work. The exergy efficiency of transient processes is detected to better understand the dynamic process. Specifically, firstly the response characteristics of system power, mass flow rate, thermal storage temperature/outlet water temperature, and exergy efficiency under the step of key regulation parameters are studied in depth. And then a control framework is well built and studied. The result shows that the influence of the volume effect on the system dynamic characteristics is concentrated in the early time, and mainly affecting the mass flow rate and then the power. The influence of thermal inertia on the system dynamic characteristics takes a long time, mainly affecting thermal storage temperature and the outlet temperature. With the new-built controller, during energy charging, under 10% step-down command of load, the power can quickly reach equilibrium for about 10 s, while thermal storage temperature can be controlled in about 8 s. During the energy discharging period, the combination control mode can achieve shorter load equilibrium time and smaller load overshoot. [ABSTRACT FROM AUTHOR]

An innovative adsorber plate heat exchanger (APHE), which is developed for application in adsorption heat pumps, chillers and thermal energy storage systems, is introduced. A test frame has been constructed as a representative segment of the introduced APHE for applying loose grains of AQSOA-Z02. Adsorption kinetic measurements have been carried out in a volumetric large-temperature-jump setup under typical operating conditions of adsorption processes. A transient 2-D model is developed for the tested sample inside the setup. The measured temporal uptake variations with time have been fed to the model, through which a micro-pore diffusion coefficient at infinite temperature of 2 E−4 [m2s−1 and an activation energy of 42.1 [kJ mol−1 have been estimated. A 3-D model is developed to simulate the combined heat and mass transfer inside the APHE and implemented in a commercial software. Comparing the obtained results with the literature values for an extruded aluminium adsorber heat exchanger coated with a 500 μm layer of the same adsorbent, the differential water uptake obtained after 300 s of adsorption (8.2 g/100 g) implies a sound enhancement of 310%. This result proves the great potential of the introduced APHE to remarkably enhance the performance of adsorption heat transformation appliances. • An innovate stainless steel adsorber plate heat exchanger (APHE) is introduced. • Representative APHE-segment is experimentally tested with AQSOA–Z02 loose grains. • 2-D and 3-D Simulations carried out on the representative segment and the APHE. • Diffusion coefficient at infinite temperature (D ∞) and (E a) are obtained. • Performance of the introduced APHE outreaches coated aluminium heat exchangers. [ABSTRACT FROM AUTHOR]

Biomass combined heat and power plants (CHPPs) can operate target-specifically because of their controllability while supporting decarbonization in district heating. The transition from the German Renewable Energies Act funding, which has promoted biomass CHPPs but is now about to expire, to direct marketing, is a major economic challenge for many biomass-heating grids. To successfully accomplish it, the flexible operation of biomass CHPPs, compared to the previous baseline-operation, is becoming an increasingly important requirement if participation in the electricity markets is to remain profitable. This paper presents a techno-economic assessment of flexible CHPP operation in a modeled district heating system with a CHPP, a peak load boiler and a thermal heat storage. The simulation model compares two cases - a natural gas and a wood-chip gasifier CHPP. The analysis of the results investigates the parameters that need to be adapted to make biomass-fired CHPP heating grids more efficient compared to fossil-fired CHPP heating grids in a flexible operating scenario. It highlights the technical and economic superiority of a fossil-fired CHPP in flexible operation in comparison to the wood gasifier system. The introduction of a CO 2 -tax on natural gas as a fuel, currently under discussion in Germany, would increase the competitiveness of the wood gasifier. • Simulation model of a district heating system. • Model units are wood or natural CHP plant, peakload boiler and heat storage. • Three scenarios for CHP plant dispatch under consideration of electricity prices. • Focus on dynamic differences of the CHP plant operation strategy. • Results show limitations in operational flexibility of the wood gas CHP plant. [ABSTRACT FROM AUTHOR]

Double reheat is a potential technique to increase the efficiency of coal-fired power plants. Large penetration of renewable power requires coal-fired power plants to operate flexibly. The thermal inertia of a double-reheat boiler is extremely high due to its complicated flow, strong coupling and numerous devices, which seriously restrict the operational flexibility of double-reheat coal-fired power plants. In this study, dynamic simulation models and temperature control systems of a double-reheat boiler are developed via GSE software and then validated to understand the heat storage change law. An improved control model considering heat storage changes is proposed. The flexibility of original and improved control strategies is compared. It turns out that steam temperatures in the boiler system with the original control exceed the allowable ranges when the load cycling rate is 1.5% Pe0 min−1. By contrast, steam temperatures in the boiler system with the improved control remain within the allowable ranges when the load cycling rate is 3.0% Pe0 min−1. The response time with the improved control is shorter than that with the original control. This study is expected to provide a detailed reference for improving the flexibility of double-reheat power plants. • Dynamic models and control system of a tower double reheat boiler are developed. • Heat storage characteristics of the double reheat boiler are studied. • An improved control considering heat storage is proposed. • The response time shortens after the improved control is applied. • Load-cycling rate with the improved control increases to 3.0% Pe0 min−1. [ABSTRACT FROM AUTHOR]

Thermal energy storage system in concentrating solar power plants can guarantee sustainable and stable electricity output in case of highly unstable solar irradiation conditions. In this paper, the lumped parameter method is used to develop the models of different thermal energy storage systems. In order to improve the reliability as well as the prediction accuracy of developed models, the charging/discharging process is firstly simulated, and then the dynamic characteristics of thermal energy storage systems are fully tested by imposing 15% step disturbance of mass flow. The results show that the charging/discharging characteristics of the three different thermal energy storage systems are almost the same, which have little to do with the storage mediums used in the systems. Besides, for the representative 1MWe solar parabolic trough power plant, a 15% step up disturbance of oil mass flow will result in a small increase (1.8% and 1.3% respectively) on the outlet temperature of oil and molten salt. On the other side, a 15% step down disturbance of oil mass flow will lead a 2.7% and 2.2% decrease on the outlet temperature of oil and molten salt respectively. In order to verify the validity of the proposed models, the simulation results are compared with both the design points and representative experimental data from the 1MWe solar parabolic trough power plant. The results show that the maximum relative error is not more than 1% when comparing with the design points and the maximum relative error is not more than 12% when comparing with the representative experimental data. Conclusions of this paper are good references for system design, control and commissioning of concentrating solar power plants. • Thermal energy storage can provide sustainable and stable electricity output. • Lumped parameter method is used to build the model of thermal energy storage. • The dynamic characteristics are tested by a 15% step disturbance of mass flow. • A 15% step-up will result in a 1.3% increase in molten salt outlet temperature. • A 15% step down will result in a 2.2% decrease in molten salt outlet temperature. [ABSTRACT FROM AUTHOR]

The addition of thermal energy storage and natural gas as a complementary energy source improves the flexibility, reliability, and value of concentrated solar power (CSP) plants. Nevertheless, due to the transient nature of solar energy, transitions from solar-only mode and natural-gas mode to hybrid solar-natural gas mode is quite challenging, especially when the plant is equipped with thermal storage. Thus, it is important to develop proper dynamic modeling and control schemes to accurately simulate such transitions. The objective of this study is to address this subject by demonstrating a dynamic model with reliable control schemes for a highly integrated hybrid parabolic trough-natural gas plant equipped with thermal energy storage. The specific goal is to study the dynamics of adding thermal storage to the hybrid plant. It is found that the developed control schemes assist smooth transitions between different operational modes and effective utilization of thermal storage and natural gas to maintain steady power production and steam mass flow rates under different solar conditions. The results demonstrate that the integration of storage regulates power production by solar energy and natural gas during the day time. It also enables an increase in the solar fraction of the hybrid plant while it causes a small decrease in thermodynamic efficiency. The analysis shows that the hybrid plant with the storage has a substantially lower specific CO 2 emission (0.320 tonne/MWh) than single natural gas plant (0.413 tonne/MWh) although it has a higher levelized cost of electricity ($86.32/MWh against $74.92/MWh). The hybrid plant with storage demonstrates a promising potential for reliable and clean production of electricity, although research and development should be conducted to lower its cost. • A hybrid parabolic trough-natural gas plant with thermal storage is simulated. • A detailed dynamic model with reliable control schemes is developed. • The control schemes assist smooth transitions between different operational modes. • Thermal storage regulates power produced by solar and natural gas throughout days. • The hybrid plant shows promising potential for flexible and clean power production. [ABSTRACT FROM AUTHOR]

• Optimization of dynamic poly-generation system is conducted for building application. • A hybrid simulation model is newly developed to improve conventional methods. • Capacity optimization based on a meta-model is carried out with a genetic algorithm. • A multi-criteria evaluation has been performed with sensitivity and feasibility analysis. A decentralized small-scale poly-generation system has attracted lots of attention nowadays. In this study, the poly-generation system is optimized and evaluated for the building application. To reduce the high computational cost of dynamic simulation and multi-objective global optimization process, a hybrid simulation model has been newly proposed. The new hybrid model is developed with the validation and verification of each system component. Based on the developed model, the meta-model is optimized for improving the multi-criteria indices (energy, environment, and economy). For the optimization, the critical design variables are selected as the rated electrical power of the prime mover, the volume of thermal storage system, the cooling/heating capacity ratio supplied by electrically driven systems, and maximum heat power from the storage system. As a result of optimization and decision making, the most effective point from Pareto frontier is determined. In addition, sensitivity analysis and feasibility evaluation are conducted to investigate the effectiveness of the poly-generation system when integrated with the building in South Korea. The results show that primary energy consumption is reduced by 22.9%, CO 2 emissions by 14.2%, and annualized total cost by 6.0%, respectively. Through the specific economic investigation, the payback year is calculated as 6.2. Finally, the performance that greatly affects multi-criteria indices is further discussed in terms of utilization rate, load coverage, and self-sufficiency ratio. [ABSTRACT FROM AUTHOR]

To overcome non-programmability issues that limit the market penetration of renewable energies, the use of thermal energy storage has become more and more significant in several applications where there is a need for decoupling between energy supply and demand. The aim of this paper is to present a multi-node physics-based model for the simulation of stratified thermal energy storage, which allows the required level of detail in temperature vertical distribution to be varied simply by choosing the number of nodes and their relative dimensions. Thanks to the chosen causality structure, this model can be implemented into a library of components for the dynamic simulation of smart energy systems. Hence, unlike most of the solutions proposed in the literature, thermal energy storage can be considered not only as a stand-alone component, but also as an important part of a more complex system. Moreover, the model behavior has been analyzed with reference to the experimental results from the literature. The results make it possible to conclude that the model is able to accurately predict the temperature distribution within a stratified storage tank typically used in a district heating network with limitations when dealing with small storage volumes and high flow rates. [ABSTRACT FROM AUTHOR]

• Prototype for district heating network modelling and result visualization. • Co-simulation of buildings, district heating network, and heat generation plant. • Large-scale simulation of a dynamic district heating network. • Animation of temperature propagation in a district heating network. • Evaluation of the supply reliability in failure scenarios. With the increasing complexity of district energy systems, both researchers and enterprises require ever more complex modelling and simulation methods. This has resulted in the need for new approaches that can be taken to create large-scale simulations as well as new methods to clearly visualize their dynamic simulation results. This study presents a prototype of a simulation framework for large-scale simulations of district energy systems that offers three main advantages compared to the state of the art: (i) scalable simulation models are made possible; (ii) a novel heating network model generation tool was developed that can be used to create models for the IDA ICE simulation environment; and (iii) the dynamic results of the simulation of the heating network and the buildings can be visualized as animations in QGIS, which makes it possible to clearly visualize the superimposed result layers of the buildings and the network. The prototype was tested in a two-part case study. In the first part of the study, the extent of the district heating network model size was examined, and decoupling methods were applied to 1531 customers. The second part of the study involved a failure scenario, which evaluated the effects of a malfunction at the heat generation plant on the 469 connected buildings. One significant finding was that the temperature progression in the network reacts comparatively quickly, while the room air temperature in well-insulated buildings with larger thermal storage masses cool more slowly. Another finding was that IDA ICE allows fast and accurate simulations with up to 8200 customers or 36,000 pipes in meshed heating networks without parallelization techniques. [ABSTRACT FROM AUTHOR]

This work presents an optimization strategy and the cost-optimal design of an off-grid building served by an energy system involving solar technologies, thermal and electrochemical storages. Independently from the multi-objective method (e.g., utility function) and algorithm used (e.g., genetic algorithms), the optimization of this kind of systems is typically characterized by a high-dimensional variables space, computational effort and results uncertainty (e.g., local minimum solutions). Instead of focusing on advanced optimization tools to handle the design problem, the dimension of the full problem has been reduced, only considering the design variables with a high "effect" on the objective functions. An off-grid accommodation building is presented as test case: the original six-variable design problem consisting of about 300,000 possible configurations is reduced to a two-variable problem, after the analysis of 870 Monte Carlo simulations. The new problem includes only 220 possible design alternatives with a clear benefit for the multi-objective optimization algorithm. The energy-economy Pareto frontiers obtained by the original and the reduced problems overlap, showing the validity of the proposed methodology. The No-RES (no renewable energy sources) primary energy consumption can be reduced up to almost 0 kWh/(m2yr) and the net present value (NPV) after 20 years can reach 70 k€ depending on the number of photovoltaic panels and electrochemical storage size. The reduction of the problem also allows for a plain analysis of the results and the drawing of handy decision charts to help the investor/designer in finding the best design according to the specific investment availability and target performances. The configurations on the Pareto frontier are characterized by a notable electrical overproduction and a ratio between the two main design variables that goes from 4 to 8 h. A sensitivity analysis to the unitary price of the electrochemical storage reveals the robustness of the sizing criterion. [ABSTRACT FROM AUTHOR]

Ulaanbaatar (Mongolia) is the coldest capital city in the world with approximately 98% of its heating demand satisfied by means of coal-burning stoves. This leads to enormous air pollutant emissions, with Ulaanbaatar being one of the top five most polluted cities in the world. In this study, an innovative solar hybrid heating system for the Mongolian scenario was used, which was based on the operation of a solar field composed of four series-connected evacuated tube heat pipe collectors, coupled with a thermal energy storage. The solar hybrid heating system was simulated and analyzed using the software TRNSYS. The simulations were designed to satisfy the heating demand of a typical single-family detached house located in Ulaanbaatar and were carried out with and without considering the soiling effects on the solar system operation. The overall performance of the proposed plant was compared with those associated with different fossil fuel-based Mongolian conventional heating systems, in order to assess the potential energy, environmental and economic benefits. The results highlighted that the proposed plant allowed for the obtainment of significant reductions in terms of primary energy consumption (up to 34.6%), global CO2 equivalent emissions (up to 52.3%), and operating costs (up to 49.6%), even if the expected return on the investment could be unacceptable. [ABSTRACT FROM AUTHOR]

Strong convergence problems may arise during the dynamic simulation of the phase transitions of adsorption systems subjected to larger and/or random fluctuations of the boundary conditions, which do not follow the conventional cycle sequence (e.g., adsorptive thermal storage systems). This sequence could even be reversed at some instants and its stages not completed. Such convergence problems preclude solving those phase transitions, and thus the successful dynamic simulation of the adsorption systems. A set of numerical procedures for solving those problems is proposed, consisting of a small group of new conditions to be added to the conventional numerical algorithms. Its successful use is demonstrated in the dynamic simulation of a thermal energy storage system provided with an adsorption module, modeled in two distinct but coupled platforms (TRNSYS and MATLAB), for which the convergence difficulties are identified and described. Results indicate successful convergence by applying the proposed methodology, in contrast with the original algorithm, attesting for its capability to overcome the convergence problems that occur during the system's dynamic simulation. This set of numerical recipes can be adapted for other systems' algorithms, or to serve as a basis for its successful dynamic simulation, thus showing a promising and enlarged range of use. [ABSTRACT FROM AUTHOR]