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Pumped thermal energy storage (PTES) technology offers numerous advantages as a novel form of physical energy storage. However, there needs to be a more dynamic analysis of PTES systems. This paper proposes a dynamic simulation model of the PTES system using a multi-physics domain modeling method to investigate the dynamic response of key system parameters during the system's start-up and variable operating conditions. Additionally, the impact of equipment parameters on system characteristics was analyzed. Furthermore, a comparative analysis was conducted to assess the variation in system characteristics when considering the different working medium properties. The results show that the system cavity volume should be selected as 5 m3, and the initial pressure of the system during the charge/discharge period should be selected as 2.1 MPa and 3.8 MPa, respectively. The system runs to the design operating conditions during the start-up process in about 1400 s. In the process of variable operation conditions, the power load in the charge/discharge period can be increased or reduced from the rated value by gas filling or venting, and the system characteristics change accordingly. The simulation model and research findings will offer theoretical insights for optimizing the design of the PTES system. • A dynamic simulation physical model of the PTES system was proposed. • The dynamic changes in system characteristics were analyzed. • The TES tank's thermal inertia and heat management of the PTES system were analyzed. • The effects of main equipment parameters on system characteristics were analyzed. • System characteristics were compared when using different gas properties. [ABSTRACT FROM AUTHOR]

Abstract Integration of a latent heat energy storage into a solar heating system has become a well-known engineering practice that can bridge the mismatch between the heat demand of the served building and heat supply from the solar heating system. However, control schemes, energy performance analysis, characterization and optimization of such a system under the Tibet climatic/altitude conditions still remain a challenge. This research aims to investigate a PCM-integrated solar heating system applicable to Tibet which is unique in terms of the altitude, solar radiation, atmospheric pressure and water boiling temperature etc. The whole process involves (1) identification of the unique features of Tibet climate and altitude and relevant requirements to the solar system; (2) design of a PCM-integrated solar heating system based on a selected building in Lhasa and planning the potential control strategies appropriate to such a system; (3) analysis of the system's energy performance under different operational schemes; and (4) recommendation of the most appropriate system operational scheme and design strategy. A dynamic simulation model was established and applied to study the energy performance of such a system, in which the solar energy usage rate is defined as the performance evaluation index. It is found that the operational scheme 'A' has the best energy saving effect, followed by operational schemes B and C. The system presents a more favorite energy performance between 9:00 h–18:00 h, compared to other time slots in a typical winter day. Change in operational schemes creates a significant impact on the energy saving effect of the system. The results help wide and fast deployment of the PCM-integrated solar heating system and enable the determination of the best performing operational scheme and associated performance data appropriate to Tibet or similar regions in the world, thus making a significant contribution to the saving of fossil fuel energy consumption and reduction of the carbon emission on the regional and global scales. Highlights • Energy performance and operational schemes of a Tibet-focus SHS-PCM was investigated. • Operational scheme A is the best and C is the worst in terms of energy saving rate. • Daytime heating achieved a higher energy efficiency compared to the full day heating. • Energy saving rates for three schemes are 64%, 50% and 46% for the full day heating. • Energy saving rates for three schemes are 92%, 79% and 24% for daytime heating. [ABSTRACT FROM AUTHOR]

Although, the horizontal thermally stratified storage tanks (TSST) are nowadays the most popular, especially in the domestic solar water heaters, most of the literature is oriented towards the vertical tanks. Recently, a smart adaptive model for TSST was proposed, where the grid segments size and location changes automatically according the different variations in the tank. It showed good agreement with experimental work, however the model and its validation was presented for the vertical configuration only. In this work, the adaptive-grid model is extended to the horizontal cylindrical tank orientation while accounting for the changes in grid segments cross-section during moving in the vertical direction as to be aligned with the thermocline region; the proposed model is validated with experimental data available in the literature. The results show an excellent agreement with the literature and yield a significant reduction in the number of nodes needed for the modeling (∼32.7% reduction) when compared to other horizontal tank models while accounting for the changes tank geometry in the vertical direction. [ABSTRACT FROM AUTHOR]

The aim of the paper is to simulate multi-tank storage with the thermocline moving from tank to tank and compare the results against single tank storage. No analysis of this nature has previously been performed. The results lend added impetus to developing this new type of thermal energy storage, especially as heat losses through insulation have already been reduced a minimum. Dividing a seasonal thermal energy storage tank into smaller tanks reduces the negative effect of heat transfer through the thermocline. The work is a continuation of the concept already proposed in available literature of using multiple solar energy stores, but we focus mainly on developing a dynamic model of a system of this type and presenting the results of a time and thermocline dependent simulation. The study also encompassed examination of the thickness of thermal insulation of the storage tanks, with definitions of its critical size. Our study revealed that the use of multi-tank thermal energy storage reduces heat loss through the thermocline. This is illustrated mainly by changes in water temperature in the upper part of the tank, which fluctuates across a much smaller range than for a single tank. In the single tank system, the temperature drops below 60 °C, whereas for the multi-tank system it always remains above 64 °C. In addition, in the multi-tank solution the loss caused by the thermocline occurs in only one tank, leaving 3/4 of the storage system unaffected by thermocline loss. • The concept of multi tank seasonal thermal energy storage is examined. • The examination is based on the dynamic modeling. • Results are compared with the single tank thermal energy storage systems. • The examined system is more efficient due thermocline losses limitation. [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]

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: 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: 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]

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]