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An integrated numerical model that describes the operation of a renewable-energy-based system for a building's heating, cooling, and domestic hot water needs is described in this study. The examined energy system includes a vapor compression multi-source heat pump, PVT collectors, borehole thermal energy storage, and water tanks. Energy balance equations for the collectors and the tanks are coupled with correlations for the heat pump and the piping losses within a thermal network approach. The non-linear system of equations that arises is solved by employing in-house software developed in Python v. 3.7.3. The performance of the numerical tool is validated against measurements collected during the pilot operation of such a system installed in Athens (Greece) for two 5-day periods (summer and winter). It is shown that the proposed model can predict, both qualitatively and quantitatively, the building's energy system performance, whereas limited deviations from the experimental findings are mostly observed when highly transient phenomena occur. The numerical tool is designed with flexibility in mind and can be easily adapted to accommodate additional energy-system configurations and operational modes. Thus, it can be utilized as a supporting decision tool for new energy systems' designs and the optimization of existing ones. [ABSTRACT FROM AUTHOR]

The variability and inhomogeneity of solar energy limits the development of solar heating systems (SHS) in many fields. In order to improve the utilization efficiency of SHS, this paper takes three typical cities (Xi'an, Dunhuang, Lhasa) as the research object, studies the operation state of SHS in student dormitory buildings, and puts forward a corresponding optimization strategy. The research shows that the reduction of water supply temperature will improve the operation efficiency and energy saving effect of a spontaneous combustion heat pump and that there is an optimal volume of heat storage water tank (HSWT), which can make the energy saving effect of SHS run better. The optimization of the SHS shows the water supply temperature is 35 °C, and the optimal volume of HSWT is 15 m3 in the "Resource-general area (Ⅲ)" represented by Xi'an, 25 m3 in the "Resource-rich area (Ⅱ)" represented by Dunhuang, and 40 m3 in the "Resource-richer area (Ⅰ)" represented by Lhasa. With the increase in the abundance of solar energy resources in the region, the optimal volume of HSWT also increases. Meanwhile, the solar energy contribution rate of the three regions in descending order is 61.3% (Lhasa), 32.8% (Dunhuang), and 25.9% (Xi'an). After optimization, the contribution of SHS increased by about 5%. The research results will help improve the efficiency of SHS in cold areas of China and make the system more efficient and energy efficient during operation. [ABSTRACT FROM AUTHOR]

Solar heating technology has the advantages of being high efficiency, energy-saving, and environment protecting; however, the instability of solar energy and its mismatch with the variation characteristics of building heat load have caused great difficulties in the design and the efficient operation strategy of a solar system. A heat storage tank is an important part of a solar hot water system. In order to improve system efficiency, this paper proposes a flat plate PCM storage tank, establishes a mathematical model, and conducts experimental verification under different working conditions. Experiments show that in the heat storage process, the phase change material (PCM) only accounts for less than 20% of the space of the PCM storage tank, and its heat storage can reach 50% of the total heat storage of the tank. In the discharge process, the water temperature of the ordinary tank decreases by 20 °C within 1.5 h, and the phase change process lasts approximately 3 h, with the water temperature remaining at 45~50 °C during this period. In the natural cooling process, the heat discharge of the two water tanks at night was similar, while the temperature of the ordinary water tank decreased by 12 °C and that of the phase change water tank decreased by 7 °C. By simulating the dynamic simulation model of the composite solar phase change thermal storage combined with an air-cooled heat pump system, the results show that the solar heating system with a PCM storage tank (SHS-PCM) saves 34% more energy than a solar heating system with a common tank (SHS-without PCM), and the volume of the PCM storage tank is reduced to 1/5 of the ordinary tank. The investment payback period method of energy saving reconstruction is used to analyze the economy of the SHS-PCM and the SHS-without PCM, the initial investment cost of the SHS-PCM is CNY 9858 higher than the SHS-without PCM, but the annual operation cost is saved by CNY 12,100, and the project investment payback period is 0.81 years, which has energy-saving potential and economic benefits. [ABSTRACT FROM AUTHOR]

Research activity in the field of combined cooling heating power (or trigeneration) systems with high renewable energy source (RES) contributions has increased rapidly over the last few years, in line with the European Union legislation about energy communities. However, technical challenges arise regarding the synergetic, sustainable and optimal integration of RES in local energy systems. In the present study, the operation of a trigeneration system located in the student residences of Democritus University of Thrace in Greece is examined. The system involves a combination of highly promising renewable and storage technologies, including solar thermal energy and biomass for heat generation, hot water tanks for thermal energy storage, absorption refrigeration for cooling, along with Organic Rankine Cycle and photovoltaic systems for electricity generation. System modeling and simulation have been implemented in Dymola environment with the use of Modelica equation-based modeling language. The accuracy of the model response has been validated against available measurements. Specific design and control measures have been proposed, simulated in a transient fashion and evaluated in terms of (i) RES generation, (ii) solar fraction and (iii) temporal flexibility. The measures examined, including the placement of a Li-ion battery, resulted in an increase of 24.6% in the heating demand solar contribution and of 7.9% in the renewable energy generated for the electricity demand, over the examined periods. [ABSTRACT FROM AUTHOR]

Utilizing biological processes for hydrogen production via gasification is a promising alternative method to coal gasification. The present study proposes a dynamic simulation model that uses a one-dimensional heat-transfer analysis method to simulate a biohydrogen production system. The proposed model is based on an existing experimental design setup. It is used to simulate a biohydrogen production system driven by the waste heat from an integrated gasification combined cycle (IGCC) power plant equipped with carbon capture and storage technologies. The data from the simulated results are compared with the experimental measurement data to validate the developed model's reliability. The results show good agreement between the experimental data and the developed model. The relative root-mean-square error for the heat storage, feed-mixing, and bioreactor tanks is 1.26%, 3.59%, and 1.78%, respectively. After the developed model's reliability is confirmed, it is used to simulate and optimize the biohydrogen production system inside the IGCC power plant. The bioreactor tank's time constant can be improved when reducing the operating volume of the feed-mixing tank by the scale factors of 0.75 and 0.50, leading to a 15.76% and 31.54% faster time constant, respectively, when compared with the existing design. [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]

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 present work focuses on the development of a detailed dynamic model of an existing parabolic trough solar power plant (PTSPP) in Spain. This work is the first attempt to analyse the dynamic interaction of all parts, including solar field (SF), thermal storage system (TSS) and power block (PB), and describes the heat transfer fluid (HTF) and steam/water paths in detail. Advanced control circuits, including drum level, economiser water bypass, attemperator and steam bypass controllers, are also included. The parabolic trough power plant is modelled using Advanced Process Simulation Software (APROS). An accurate description of control structures and operation strategy is necessary in order to achieve a reasonable dynamic response. This model would help to identify the best operation strategy due to DNI (direct normal irradiation) variations during the daytime. The operation strategy used in this model has also been shown to be effective compared to decisions made by operators on cloudy periods by improving power plant performance and increasing operating hours. [ABSTRACT FROM AUTHOR]

Dynamic simulation provides an efficient approach for improving the efficiency of parabolic trough power plants and control circuits. In the dynamic simulation, the possibilities and operating conditions of the plant are evaluated regarding materials, processes, emissions, or economics. Several studies related to the dynamic simulation of the parabolic trough technology are summarised and discussed in this work. This study is the first research that presents a thorough description of the advanced control circuits used in the solar field and thermal storage system of a parabolic trough power plant. This power plant was implemented using advanced process simulation software (APROS). The dynamic model was built based on the real specifications of the power plant. [ABSTRACT FROM AUTHOR]

A centralized solar hybrid heating and cooling system satisfying the thermal, cooling and sanitary water demands of a typical Italian small district composed of six residential buildings situated in Naples (southern Italy) is modelled, simulated and analysed through the software TRNSYS over a period of 5 years. The plant is based on the operation of solar thermal collectors coupled with seasonal borehole storage; the solar field is also composed of photovoltaic solar panels connected with electric energy storage. An adsorption chiller powered by solar energy is adopted for cooling purposes, while a condensing boiler is used as an auxiliary unit. The performance of the proposed system has been assessed from energy, environmental and economic points of view and contrasted with the operation of a typical Italian heating and cooling plant, highlighting the following main results: saving of primary energy consumption up to 40.2%; (decrease of equivalent CO2 emissions up to 38.4%; reduction of operating costs up to 40.1%; and simple pay-back period of about 20 years. [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]

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]

• An innovative slim decentralised plug-and-play tank is proposed for DHW production. • Model calibration is performed by experimental data in charge/discharge process. • Retrofit solution cuts required annual energy in half of which 82% is RES quota. • Optimised charging scheme reduces the total annual electrical energy by 5.2 %. • A degree increment in draw-off temperature increases annual CO 2 emission by 103 kg. The present study deals with a multi-objective analysis of an innovative decentralised system to produce and store domestic hot water (DHW), emphasising on the combined effects of the technological aspect, control strategy and user's behaviour. The proposed system, by relying on thermal energy storage, decouples energy production and demand while shaves peaks in the energy demand and, at the same time, provides more autonomy to users through local storages. To identify subtle interactions in components of DHW system, dynamic simulations are carried out by establishing a coupled TRNSYS-MATLAB code, calibrated and validated by experimental measurements. The energy analysis implies that the proposed system cuts the required annual electrical energy in half, of which up to 82% of needed primary energy is supplied from renewable sources, compared to previous electrical-decentralised system. The optimisation of the results through applying control strategies indicates that adopting a three-time charging scheme is advantageous in terms of providing a more stable temperature profile as well as a higher hot water temperature. Compared to an available-by-demand operation, this scheme reduces the required total annual electricity by 5.2 % and enhances total thermal loss from components up to 4.0%. Furthermore, a sensitivity analysis on the results emphasises the striking role of the user behaviour in electrical energy consumption either via draw-off temperature or adjusting the pre-defined temperature for activation of the built-in auxiliary heater. [ABSTRACT FROM AUTHOR]

A novel methodology for optimizing thermal storage for biomass boiler heating systems is presented in this paper. Biomass boiler heating systems have gradually gained popularity in residential, commercial, and large-scale district heating plants due to the lower carbon footprint of biomass energy. One unanswered question in this field was the size of the thermal energy storage (TES) tank with respect to different boiler capacities and different types of heat demand profiles. Different standards and recommendations (based only on boiler capacities) have been proposed by various organizations around the world with large deviations on the sizing of the TES tank, but without a clear technical basis for these recommendations. These inconsistencies impede the effective design and deployment of biomass boiler heating systems. This study used a dynamic process simulation system based on field data from a 25-kW wood pellet boiler with radiant floor heating. By running the simulation for different boiler capacities (N) and different types of heat demand profiles (i.e. low, medium, high, intermittent, and variable), the optimum TES tank volume can be estimated by evaluating the TES tank discharge efficiency, boiler on-time, boiler off-time, and maximum boiler output temperature. Linear correlations between optimum TES tank volume and boiler nominal capacity for different types of heat demand profiles were obtained. The results showed that the medium building heat demand (45% N) required the smallest TES tank volume while intermittent building demand requires the largest. High building demand (60% N) generates the highest TES tank discharge efficiency (up to 99%) but also requires large storage volume. From the economic point of view, it is recommended to size the thermal energy storage system such that the average building heat demand is around 45% of boiler nominal capacity. [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]

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 capability to dynamically plan, predict, and control indoor conditioning allows to adapt to individual preferences of inhabitants and enables demand side management. While former mainly improves thermal comfort of inhabitants so does latter unlock ecological and financial opportunities mostly for energy utilities. Commonly, dynamic indoor conditioning is based on piece-wise constant indoor temperature constraints. This paper's contribution is the presentation of additional constraints: in particular ones expressed relative to the nominal behavior of a hydronic heating system. This allows to simultaneously harness the relevant process variables in particular during the pre-loading and post-loading phases of a load reduction. The findings are based on data sets acquired on 10 inhabited, residential buildings in Stockholm over a whole year. One of the findings is that building models need to be adaptable if predictive control is applied in practice. This adaptability is assured by a novel concept, i.e. a so called model manager on which the control is relying for the selection of the most accurate model. Centralized optimal control of buildings connected to a district heating network is challenging in practice due to a high computational load. In order to reduce it, the herein presented method elaborates plans only every hour instead of at every control step for optimal control. Since these plans cannot be optimal due to the lack of regular update a hitherto unknown cascaded control logic has been developed that corrects planning errors and other disturbances. Capabilities are demonstrated and compared to conventional controllers in dynamic simulations of a multi-zoned building. The herein presented method is to our knowledge the first to provide all flexibility desired by energy utilities and inhabitants alike through harnessing the consequences of transitions. [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]

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]

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]

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]

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: 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: 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] • 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]

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]

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]