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[Display omitted] • Thermal decoupling of methanation and electrolysis is an effective solution. • Power-to-Gas feasibility is strictly related on oxygen selling and local grants. • Highly efficient natural gas production with 75% conversion efficiency. • Optimization suggests reducing the capacity of the methanation reactor. This work presents a numerical analysis of a fully renewable Power-to-Gas system driven by photovoltaic and anaerobic digestion technologies, to produce synthetic renewable natural gas. The anaerobic digester is supplied by municipal wastes and it produces biogas, including about 35 % of carbon dioxide. This carbon dioxide is separated by means of an upgrading unit and it is combined in a three stage multi-tubular methanation reactor with the hydrogen produced by solid oxide electrolysis. A novel control strategy is developed to achieve a stable, safe, and efficient operation of the reactor. Suitable zero-dimensional and one-dimensional steady state models are developed in MatLab for the solid oxide electrolyzer and the methanation reactor. Such MatLab models are subsequently integrated into TRNSYS environment to perform the dynamic simulation for one year of operation of the whole system. A suitable thermoeconomic analysis is also implemented, also considering the possibility of selling the oxygen produced by the electrolyzer for industrial purposes. The results show that the proposed system achieves a primary energy saving of 30.33 GWh per year with 6,330 t CO2eq per year saved. The economic profitability of the is also very good, showing a Simple Payback of 2.63 years. The income due to the selling of oxygen plays a crucial role in this result. The overall efficiency of the system is equal to 0.75, that is extremely high when compared to similar layouts. The results from the thermoeconomic optimization show that the lowest Simple Payback value, i.e. less than 2 years, is obtained when the capacity of the methanation reactor is reduced by five times. [ABSTRACT FROM AUTHOR]

• Novel layout to be easily adopted by existing residential districts. • The novel layout can reduce the primary energy consumption of the residential district. • A primary energy saving index of 38 % and payback period of 2.2 years is achieved. • Power to heat strategy increases the district self-consumed electricity by 15%. • The power to heat strategy is able to further exploit the excess renewable electricity. This paper aims at reducing both electricity and space heating demands of residential districts. It specifically investigates the emerging paradigm, based on renewable energy communities, for existing residential districts. In particular, a novel renewable energy community layout is analyzed. This layout integrates a district heating network and the power to heat control strategy. The proposed system is designed to prevent any major refurbishment inside the apartments, using the existing high temperature space heating system. This arrangement is compared with more conventional renewable energy community layouts. Detailed dynamic models for both the residential district and the proposed layouts are developed using the TRNSYS software. Results show that renewable energy community is an extremely profitable paradigm for promoting the use of renewables at residential buildings scale. Moreover, the layout integrating energy community, district heating network, and Power-to-Heat strategy achieves the best results with a payback period of 2.2 years and a primary energy saving of 38 %. [ABSTRACT FROM AUTHOR]

• The one-dimensional mechanism models of the system's key components are developed. • The system's optimal operating conditions are explored by steady-state simulation. • Comparison of the system performance in fuel cell co-flow and counter-flow modes. • The dynamic thermoelectric response characteristics of the system are investigated. Methane reforming solid oxide fuel cell system has received widespread attention due to its high efficiency and environmental friendliness. However, the multi-domain coupling of the solid oxide fuel cell hybrid with methane reforming reactor poses a significant challenge to the mechanistic modeling which is essential for efficiency evaluation and dynamic characterization of the system. To this end, the object-oriented language Modelica is used to describe the one-dimensional distributed parameter responses of methane reforming reactor and solid oxide fuel cell to investigate the responses of power output, heat, and reaction gas concentration. Steady-state and dynamic simulations are carried out to explore the optimal operating conditions of the system and the transient characteristics of the system thermoelectric coupling in solid oxide fuel cell co-flow and counter-flow modes. The results show that the maximum system efficiency is 58.37 % and 59.21 % for solid oxide fuel cells in the co-flow and counter-flow modes, respectively, based on the system safety constraints. The component with the largest exergy loss in the system is the solid oxide fuel cell, with exergy losses of 11.76 kW and 10.89 kW for co-flow and counter-flow, respectively. In the co-flow mode, the positive-electrolyte-negative layer temperature increases along the cell length. In the counter-flow mode, the positive-electrolyte-negative layer temperature increases and then decreases along the length and its temperature. The average value of the temperature gradient in the positive-electrolyte-negative layer is higher in the counter-flow mode than in the co-flow mode, and the non-uniformity of the solid oxide fuel cell temperature is higher, which tends to reduce its lifetime. The reversal of the water–gas shift reaction proceeds at the outlet of the reforming reactor and the solid oxide fuel cell inlet. In the dynamic simulations, with the step change in current, the transient behavior of the solid oxide fuel cell internal variables differs significantly in the co-flow and counter-flow modes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nonlinear dynamic model of a green ammonia synthesis system is developed. • Start-up of H 2 and N 2 subsystems and warm start-up of ammonia reactor are studied. • System dynamic responses under fluctuations of renewable energy are also analyzed. • Bed temperature, H 2 /N 2 ratio and pressure are well maintained by PID controllers. • Buffer tank decreases the reactor variation and is important for pressure control. Green ammonia production system driven by renewable electricity will be under frequent dynamic operation due to the fluctuation of renewable energy. The nonlinear dynamic model of a green ammonia synthesis system is developed and the dynamic responses of PEM (proton exchange membrane) electrolysis subsystem, PSA (Pressure swing adsorption) subsystem and ammonia synthesis subsystem during the start-up process and under the fluctuation of renewable electrical current are analyzed. The start-up dynamic results show that the hydrogen production rate of PEM electrolysis system is positively correlated to the current. The nitrogen output of PSA system is affected by the adsorption time, adsorption pressure, bed length, and air velocity. A start-up period of 300 min from the warmed-up state to the design state can maintain the temperature rise rate of the ammonia synthesis reactor at approximately 40 K/h. The dynamic results under step fluctuations of electrical current show that the PEM electrolysis subsystem and the PSA subsystem response fast compared to the ammonia synthesis reactor and buffer tanks. Using large buffer tanks to smooth the fluctuation allows the system to slide with the variation of renewable current to some extent, resulting in a higher outlet ammonia fraction when the current increases. Different volume ratios of the hydrogen tank to the nitrogen tank volume can lead to different variations of the hydrogen/nitrogen ratio. PID controllers can effectively maintain the bed temperatures, hydrogen/nitrogen ratio, and pressure of the ammonia synthesis reactor at their set points despite fluctuations in renewable electrical current. Buffer tanks are necessary to compensate for the imbalance between the flow rate fluctuation caused by current change and the flow rate regulation caused by PID controllers. [ABSTRACT FROM AUTHOR]

scheme of the on-grid photovoltaic HVAC system. [Display omitted] • Modeling of split-type HVAC systems, VRF, and Chiller with thermoaccumulation; • Energy performance analysis of photovoltaic air conditioning systems; • Compatibility between thermal load and photovoltaic generation in offices; • Energy thermoaccumulation systems contribute to an increase in energy performance; • Photovoltaic air conditioning systems proposed reduced grid dependence by 87%; This article presents the air-conditioning performance analysis of an office building with thermal zones for the transient simulation of photovoltaic solar systems in a tropical climate. The study focuses on the correlation between air conditioning consumption and photovoltaic generation. The objective is to maximize the self-consumption of locally produced photovoltaic energy. The simulation and numerical analysis of the annual energy flow using a time interval resolution of 2 min was introduced as a novelty of the work to demonstrate the implementation of the proposed climatization technologies. The procedure developed was tested through 4 case studies where photovoltaic energy generation was scaled to meet the annual consumption demand of different air conditioners and considering the southern hemisphere climate conditions. The performance of the cases studied was evaluated considering an energetic point of view through metering of self-sufficiency and self-consumption of conditioners and a financial vision through indicators of Net Present Value, Internal Rate of Return, and Payback Period. It was possible to reduce energy by 96% at peak hours compared to the reference scenario using energy demand side management. From the energy point of view, the proposed cases proved to be viable. Regarding the economic aspects, the instances with the renewal of the splits and the central Variable Refrigerant Flow system presented the best financial indexes between 6 and 7 years of payback and internal rate of return of 22% and 21%, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • 2D dynamic models for rSOC and methanol synthesis are developed in COMSOL. • Dynamic models are run jointly by MATLAB call with fluctuating PV power supply. • Multi-physics analysis and operation optimization on full PMPS are conducted. • Techno-economic comparison of PMPS and PHPS is conducted. • The roundtrip efficiency and levelized cost are 78% and 0.49 $/t CH 3 OH, respectively. Power-to-Methanol-to-Power System (PMPS) has a great potential for fluctuating renewable power storage and flexible power generation. In this study, a dynamic-cycle model of PMPS is developed by coupling reversible solid oxide cells with methanol synthesis process. The system stores energy from fluctuating photovoltaic power in the form of methanol during the day and generates electricity at night using the methanol fuel generated in the daytime. It is found that reducing the CO 2 ratio in co-electrolysis from 60% to 30% increases CH 3 OH production by 64% and doubles electricity efficiency due to the increased H 2 supply to methanol synthesis section. While in the fuel cell, reducing methanol supply rate from 500 to 200 SCCM increases power generation capacity by 110% with longer generating duration, and the electricity efficiency is improved from 30% to 61%. Besides, the optimized PMPS presents a round-trip efficiency of 78%, along with high conversion rates of carbon (97%) and hydrogen (84%), significantly exceeding that of the Power-to-Hydrogen-to-Power System (PHPS, the round-trip efficiency of 45%) under similar cell's inputs. Furthermore, our techno-economic analysis shows that the levelized fuel cost (0.49 $ t−1 CH 3 OH) and levelized generating capacity cost (0.22 $ /kWh) of PMPS are about 10% (4.8 $ t−1 H 2) and 74% of the PHPS, mainly due to the 16% lower capital expenditure of PMPS. [ABSTRACT FROM AUTHOR]

• The dynamic model of different kinds of air-to-water heat pumps is presented. • Single-stage (SSHP), multi-stage (MSHP) and inverter-driven (IDHP) units are considered. • The detailed energy loss modelling linked to on-off cycling is shown. • Heat pump control algorithms can be optimized by means of the developed models. • Cycling losses have a significant influence on SSHPs seasonal energy performance. In this paper, the impact of on-off cycling losses on the seasonal energy performances of three reversible air-to-water heat pumps having equivalent thermal performance at full load but different power modulation capacity is discussed by means of a series of dynamic simulation models. The analysis of the heat pump performance at partial load, the development and comparison of different control algorithms for heat pumps and, finally, the modeling and evaluation of the degradation effect due to the heat pump on-off cycles at partial load conditions are numerically investigated by means of a series of innovative TRNSYS models not available in the software standard library. The models are able to take into account the variation of the heat pump performance at partial load conditions for multi-stage, inverter-driven and single-stage devices. The findings of this paper point out that the energy losses introduced during the start-up transient of the heat pump has a significant impact on the overall energy performance of the system only for single-stage units, which perform on-off cycles during the whole season, with a decrease of the seasonal performance factor (SPF) up to 12%. On the other hand, modulating heat pumps (i.e. multi-stage and inverter-driven units) avoid carrying out on-off cycles and, of course, cycling losses for a significant part of the season according to their enhanced modulation capacity. It is shown how the accurate dynamic simulation of heat pump-based systems is a useful tool for HVAC designers in order to optimize their control system parameters, with the aim to reduce the compressor maximum hourly number of cycles. [ABSTRACT FROM AUTHOR]

• Estimated cost of solar fuels via supercritical water gasification of algae is 2.5 USD/L. • Fast-ramping Fischer–Tropsch units will be critical for solar-driven gas-to-liquids. • A predictive dispatch scheduler for the FT unit brings cost savings of 19%. This paper evaluates the annual dynamic performance and techno-economic feasibility of a solar fuels process driven by concentrated solar power (CSP). The process integrates solar supercritical water gasification (SCWG) of microalgae, syngas storage, and downstream Fischer–Tropsch (FT) synthesis, to produce renewable drop-in liquid transport fuels. Performance curves for key components, derived from design-point and off-design simulations in steady-state flowsheet models established in the previous work of the authors, are incorporated into a dynamic energy-based model of the overall plant in OpenModelica. Control units are implemented to model the high-level state transitions of the plant relating to ramp-up and ramp-down of solar-SCWG and FT units as well as syngas storage and dispatch. There is significant uncertainty about the achievable ramping time for FT plant, owing to the dynamics of the synthesis of long-chain hydrocarbons in the FT reactor, so this is modelled as a variable-duration ramp-up with no useful product output. A perfect one-day-ahead forecast scheduler is developed to regulate the supply of solar syngas to the FT unit to minimise these ramp-up events. The levelised cost of fuel (LCOF) for the plant is minimised using a genetic algorithm to adjust the solar multiple and syngas storage capacity of the plant, with weather data and location of Geraldton in Western Australia. The optimal configuration has a solar multiple of ∼4 and syngas storage of ∼20 h, and achieves an LCOF of ∼3.5 AUD/L (∼2.5 USD/L) and capacity factor of ∼72%. Sensitivity analysis shows that the price of the farmed microalgae feedstock has the strongest influence on the LCOF. The one-day-ahead syngas dispatch scheduler contributes an LCOF reduction of 19% compared to an immediate dispatch strategy. The importance of the FT ramping time in these simulations suggests that fast-ramping FT reactors (e.g. microchannel reactors) will be essential for the techno-economic success of solar-gasified FT fuels, and motivates further research and development on this topic. [ABSTRACT FROM AUTHOR]

Highlights • The coupling correlation within organic Rankine cycle is revealed by dynamic test. • A system-level model is simulated by imposing the real-time experimental parameters. • The average overshoot of the evaporation pressure of 48 kPa is captured by the model. • The model predicts that the max desired power output is 1874.7 W with efficiency of 6.94%. Abstract This paper aims to reveal the coupling correlation of the ORC related system, and verify the boundaries and feasibilities of the system-level modeling. A kW-scale ORC test rig with a self-made expansion valve is set up for the dynamic test under three common freedoms, namely the mass flow rate of working fluid, heat source and cooling source. By imposing the same real-time experimental conditions, the system-level dynamic simulation is performed on the Modelica/Dymola software. The test rig and dynamic model are of high-accuracy and reliable after examining the heat balances and error propagation of the measurement uncertainties, as well as calibrating with theoretical analysis. Results show that the internal disturbance of mass flow rate of working fluid significantly affect the states parameters. The external disturbance of mass flow rate of cooling source has a less effect on the states parameter, while the states parameters are insensitive to the external disturbance of mass flow rate of heat source. The simulation results are in agreement with the experimental results. The average overshoot of the outlet temperature of cooling source is 0.7 °C, and the average overshoot of the evaporation pressure is 48 kPa, which coincide with the results from the experiment under the disturbance of working fluid mass flow rate. It shows the potential of such simulation model to be a guided model, which also predicts that the maximum desired power output of the ORC test rig is about 1874.7 W, with the thermal efficiency of 6.94%. [ABSTRACT FROM AUTHOR]

Highlights • Dynamic modelling of combined-cycle gas turbine power plant with thermal storage. • Cascaded latent heat storage integration strategies to plant operation processes. • Complete system dynamic simulations of the plant with cascaded latent heat storage. • Quantified analysis of stored and released thermal energy for different strategies. Abstract The combined-cycle gas turbine (CCGT) power plants are often required to provide the essential fast grid balance service between the load demand and power supply with the increase of the intermittent power generation from renewable energy sources. It is extremely challenging to ensure CCGT power plants operating flexibly and also maintaining its efficiency at the same time. This paper presents the feasibility study of a CCGT power plant combined with the cascaded latent heat storage (CLHS) for plant flexible operation. A 420 MW CCGT power plant and a CLHS dynamic models are developed in Aspen Plus based on a novel modelling approach. The plant start-up processes are studied, and large amount of thermal energy can be accumulated by CLHS during the start-up. For load-following operation, extensive dynamic simulation study is conducted and the simulation results show that the extracted exhaust gas can be used for thermal energy storage charging, and the stored heat can be discharged to produce high temperature and high pressure steam fed to the steam turbine. Besides, the stored heat can also be used to maintain the heat recovery steam generator (HRSG) under warm condition to reduce plant restart-up time. The simulation results demonstrate that the integration of CLHS with CCGT power plant is feasible during the start-up, load-following and standstill operations. [ABSTRACT FROM AUTHOR]

Highlights • Innovative design of a synergistic hybrid solar natural gas power plant. • Utilizes natural gas for steam superheating for efficient power production. • Design is more flexible, reliable, and efficient than stand-alone solar thermal plant. • Detailed dynamic, systems-level model coupled with robust controls developed. • Annual results showing the synergy between the two energy sources, with solar to electric efficiency improving by 71.9%. Abstract Solar power is considered among the leading renewable energy technologies. Abundant supply, flexibility of installation, and decreasing cost makes it an interesting renewable energy resource. However, there are challenges associated with the reliability of solar power due to its intermittent nature. This work demonstrates the synergies that exist in integrated hybrid systems, where a dispatchable fuel is used in conjunction with concentrated solar power. In this simulation-based study, a parabolic trough solar concentrator is used to collect solar energy. The heat collected from the solar field is used to generate steam in a Rankine cycle. The system also utilizes natural gas combustion in the steam generator to provide supplemental steam when the solar intensity is reduced due to cloud cover or at night. Natural gas is also used for superheating the steam, which allows the system to produce higher temperatures and achieve increased thermodynamic cycle efficiencies. This flexible design produces 100 MW at nominal conditions, while it is capable of producing a maximum of 140 MW when sufficient solar energy is available. The novel contributions of this work include a complete, systems-level, dynamic model of a hybrid solar plant. The model is complete with a control system that smoothly transitions the plant from pure natural gas mode at night to solar hybrid mode during the day. It evaluates innovative design features such as flexible fuel operation, steam superheating to boost efficiency, and preheating by solar or waste heat. Furthermore, this work demonstrates that by hybridizing a solar system with a dispatchable energy source, both the reliability and efficiency of the solar power production are increased. The annual solar-to-electric efficiency increases from 15.2% to 26.13% with hybridization, which indicates that utilization of the solar energy is effectively increased. [ABSTRACT FROM AUTHOR]

Highlights • Proposed a novel photovoltaic water pumping system approach for feed, milk production. • Proved the approach with dynamic simulations of water and electricity demand. • The approach yields positive economic improvement, energy and emission reduction. • Scale and production of feeds proportions has significant influence on the results. Abstract As dairy consumption grows, domestic dairy farms face challenges in reducing the cost of feeds and the production of high-quality milk for market demands. This paper aims to introduce and integrate solar energy into the milk production chain to investigate its economic performance. By collecting data on milk production processes from 11 dairy farms in China, we quantified electricity usage and costs of milk production to identify the best and worst cases. Crop yields response to the water demand and the electricity requirements of the dairy farms were considered. The study simulated scenarios of self-sufficiency at 20%, 80%, and 100%, in the identified farms by integrating a photovoltaic water pumping (PVWP) system to provide both power and water for alfalfa and other feeds' irrigation and subsequent milk production. We evaluated annual discounted cost, revenue and net profit under each scenario and case. The results showed that a dairy farm with an integrated PVWP system and self-sufficient feeds would lead to value add-ins, such as electricity saving with solar energy generation, economic cost saving of crops, and CO 2 emission reduction. The analysis on return on investment (ROI) and internal rate of return (IRR) revealed that not all the self-sufficient feeds can bring positive marginal profit. Among the investigated scenarios and cases, the dairy farm marked out by the highest ROI with 3.12 and IRR with 20.4%, was the farm where the integrated PVWP system was used to reach 20% self-sufficiency (self-production of only alfalfa). The other scenarios and cases with higher levels of self-sufficiency showed lower ROIs and IRRs. This indicates that high self-production levels of feeds decrease the total profit due to high investment cost. Sensitivity analyses of crop price and operational cost were conducted for ROI with single and double factor approaches. Scale and production of feeds proportions should be carefully considered in improving the economic performance of dairy milk production. [ABSTRACT FROM AUTHOR]

Highlights • A CCHP system primed by Maisotsenko combustion turbine cycle was proposed. • Performance comparison with that based on conventional gas turbine cycle was made. • Dynamic system simulations were conducted using the TRNSYS platform. • Different climate regions were considered with the results compared. • The loading profiles affected the relative performances of the two CCHP systems. Abstract Buildings are the significant primary energy consumption and pollutant emission contributors in a modern city. Distributed multi-generation systems such as combined cooling, heating and power (CCHP) systems are considered an alternative to fulfil the energy saving requirements in the building sectors. In this study, a CCHP system primed with Maisotsenko combustion turbine cycle (MCTC) was considered with its performance compared with that primed with a simple gas turbine with recuperator (SGTR). With dynamic models of the CCHP systems constructed using TRNSYS, a design optimisation was conducted using genetic algorithm to determine the system component size and number based on the best year-round cost saving. A study case which consisted of building complexes in a district scale was used for investigation under two climatic conditions. The simulation results showed that the relative performances of both CCHP systems depended on the load profiles which differed from the situations when both prime movers were used solely for power generation. In a heating-dominated application, the performance of the MCTC-primed CCHP system was better than the SGTR-primed one only during the summer period and that the year-round performance was inferior to the latter one. Last but not the least, a parameter study was conducted which showed the benefit reduction of CCHP system with the decreasing of public grid price and increasing fuel gas price. [ABSTRACT FROM AUTHOR]

• Thermal performance of the proposed hot water storage was evaluated experimentally. • Proposed solution shows a 19% less total thermal loss than the centralised system. • Circulating pump in this solution consumes 11 times lower energy than centralised one. • The LCC of proposed solution is 6.1% lower than that of the centralised system. • Centralised system requires higher operating costs but a lower control system cost. The retrofit solution for domestic hot water (DHW) system in existing buildings requires to ensure the long-term energy security and efficiency as well as to minimise occupants' disturbance, construction works and installation costs. In this regard, the present study performs a techno-economic evaluation on a novel retrofit solution for DHW production in a pilot building. The proposed solution appoints a substantial role to the thermal energy storage through a 2-pipe hot water network utilisable for both DHW and heating purposes. The first storage level is provided by a centralised buffer storage supplied by a PV-BESS-driven heat pump while the second level consists of decentralised modular tanks installed in each dwelling for the production and storage of hot water. Firstly, experimental thermal performance of the proposed decentralised storages is investigated. By developing a dynamic simulation code, the energy efficiency of the proposed solution is compared to that of the existing system in the pilot building as well to that of a typical centralised system as a benchmark solution. Finally, economic analysis of the retrofit solution is performed to address capital expenditures of the system, including purchasing and installation costs, as well as its life cycle cost (LCC). The obtained results indicate that the proposed system reduces the annual energy consumption for DHW production more than 7,200 kWh, with respect to the existing DHW system. Furthermore, it is shown that, in the proposed system, the fraction of thermal loss from piping network decreases by 31.5%, compared to a typical DHW centralised system. Economic assessment of the proposed solution implies that this system, in terms of both mechanical and electrical components, requires 13.7% lower initial investment than a typical centralised system. However, the cost of control systems in this system is higher since it is inherently a control-based system. [ABSTRACT FROM AUTHOR]

• It is the basis for integrated energy system scheduling based on flow-regulation. • A hydraulic-thermal coupling dynamic model for heating network is proposed. • The modified forward–backward iteration is proposed for model calculation. • The exact hydraulic and thermal dynamic processes of heating network are obtained. • A data-driven hydraulic-thermal dynamic model is proposed for fast calculation. The district heating is expected to play a crucial role in the decarbonization of integrated energy systems within the context of attaining carbon neutrality. The literature review reveals a research gap in the investigation of models that account for the hydraulic-thermal coupling dynamic characteristics of heating networks in integrated energy systems, particularly those based on the flow-regulation mode. This discrepancy may affect the safety of the heating networks and contribute to the inefficient scheduling of integrated energy systems, which motivates this study. In this study, it refutes the harsh hypotheses in previous studies, making it more closely related to the real hydraulic and thermal conditions of heating networks. A mechanism-driven model is proposed, which involves the coupled hydraulic and thermal dynamic characteristics of heating networks. The modified forward–backward iteration as a calculation method is carried out, which is embedded with the method of characteristic and upwind difference. A data-driven hydraulic-thermal dynamic model is proposed for fast calculations. For model validation and case analysis, three heating networks in the integrated energy systems are utilized. The simulation results indicate that 1) The hydraulic and thermal average relative errors between the measured data and the simulation results are 0.396% and 0.091%, respectively, validating the effectiveness of the proposed dynamic mechanism model; 2) Compared to the current quasi-dynamic model, the proposed dynamic mechanism model could reflect the characteristics of heating networks more accurately and simulates the dynamic processes with higher resolution. These results demonstrate that the fluctuations of water head and pipe flow can reach 61.24 ∼ 237.53 m and −4.26 ∼ 32.16 kg/s, respectively. The average temperature difference between the two models is around 0.264 °C; 3) Compared to the forward–backward iteration, the modified forward–backward iteration has a superior convergence performance and calculation accuracy; 4) Compared to the quasi-dynamic model, the proposed data-driven model increases the overall accuracy of hydraulic-thermal calculations and significantly reduces the amount of time required. The average calculation time of the data-driven model is 0.0349 s, while those of the quasi-dynamic model and the proposed mechanism model are 352.92 s and 624.13 s, respectively. In conclusion, the proposed mechanism model of hydraulic-thermal coupling calculation and the related data-driven model are suitable for the dynamic simulations of heating networks in integrated energy systems. [ABSTRACT FROM AUTHOR]

Urban heat island affects cities climate and results in higher air temperature with respect to the surrounding rural zones. Anthropogenic heat released by human activities exacerbates this phenomenon which impacts on environmental and energy fields. Air conditioning is commonly used to achieve comfort indoor conditions in the warmer urban climate but it is also one of the serious cause of the urban heat islands. The heat rejected by the condensers of air conditioning systems, increases the air temperature next to the buildings in which they are installed. In this paper a system consisting of a ground-source heat pump, a low temperature thermal network and a series of electric heat pumps, is analysed. The thermal grid is the heat source/sink for the water to water electric heat pumps that are installed at each end-user of a multi-purpose six floors building located in Naples (Southern of Italy). In cooling mode the condenser heat is discarded in the ground by the ground source heat pump that operates between the lower temperature thermal grid and the borefield. In the heating period the thermal network is heated by the ground source heat pump, that draws energy from the ground. The models simulating the energy conversion systems, the low temperature thermal network and the building, are implemented in the dynamic simulation software TRNSYS 17. A first advantage of the proposed configuration is the avoided interaction with the outside air and the corresponding mitigation of the urban heat island phenomenon. A second one is the higher coefficient of performance of the water to water electric heat pumps, operating with a lower temperature gap with respect to the case in which the electric heat pumps interact with the outside air. Furthermore, the interaction with thermal grid allows high seasonal performance due to the low fluctuation of the temperature with respect to the air. Finally this energy efficient system could be simply installed not only in the new buildings, but also in refurbishments. The proposed system is compared with a conventional one installed in each dwelling consisting of an air to water air conditioner for cooling operation and a boiler for heating. Interesting global and local environmental advantages are obtained. [ABSTRACT FROM AUTHOR]

In this work, a dynamic model of a high-temperature integrated solar combined cycle power plant is presented. The system includes a three-pressure combined cycle power plant coupled to parabolic trough solar collectors. Thermal storage, a heat solar steam generator, pumps, heat exchangers, and several controllers are also included in the system. Solar energy is used to produce additional steam to be supplied to the steam turbine of the combined cycle power plant. The integrated solar combined cycle system is based on the heat transfer fluid arrangement, exploiting solar energy to produce steam. The analysis is developed by a dynamic simulation model including detailed algorithms for the calculation of the performances of system components. Special control strategies are included in the model in order to accurately manage the steam production of the heat solar steam generator. The paper presents a thermo-economic and environmental comparison between the integrated solar combined cycle and a conventional combined cycle, powered by fossil fuels, based on dynamic simulations. A case study, referred to a plant with a maximum power of around 100 MW, located in Almeria (Southern Spain), is presented and discussed. A parametric analysis was also performed to show the effect of the variation of total solar field reflector area on the system performance. For the case under evaluation, a simple pay-back of 15 years was found, for a solar field aperture area of 80 000 m 2 ; however, the parametric analysis suggests that a smallest solar field area should be used under the hypotheses of the case study. [ABSTRACT FROM AUTHOR]

The main challenges of wastewater treatment plants are high-energy demand and sludge disposal. A hybrid system for sewage sludge drying is proposed in this work to face both these issues. The developed layout is based on the integration of two renewable energy sources, biogas from anaerobic digestion of sludge and solar energy in order to increase sustainability and energy self-sufficiency of the plant. Biogas is used to fuel a combined heat and power system and solar energy is exploited through a parabolic trough collector field. Electrical energy produced by the combined heat and power is used to cover the plant demand, whereas thermal energy coming from the combined heat and power unit and solar field is employed to run an anaerobic digestion process and for thermal drying of the residual sludge. The considered case study is based on data collected for an existing wastewater treatment plant. The proposed system is studied through data obtained from the scientific literature, suppliers of the considered equipment and properly developed sub-models of the various components, to assess its feasibility and the overall energy, environmental and economic performance. The system is dynamically simulated and daily, weekly and yearly results are presented. For the considered desiccant flow temperatures, the solar collector field achieves a thermal efficiency of about 56.0%, while for the combined heat and power unit it is about 44.0%, which is slightly higher than the nominal one, due to the preheating of combined heat and power unit intake air. The integration of solar energy with the combined heat and power system leads to a primary energy saving of about 14.6% with respect to the existing plant, where the sludge is not digested and neither thermally dried. The economic analysis shows that the Simple Pay Back period of the system is less than 3.40 years. [ABSTRACT FROM AUTHOR]

This paper presents the design of a novel high-temperature solar assisted triple-pressure level combined cycle power plant. The system includes innovative high-temperature flat plate evacuated solar thermal collectors, a double stage lithium bromide/water absorption chiller, pumps, heat exchangers, storage tanks, mixers, diverters, controllers and a triple-pressure combined cycle power plant. This novel layout uses high-vacuum non-concentrating flat plate solar thermal collectors driving a double effect absorption chiller, leading to an overall high coefficient of performance for the solar cooling section. The provided cooling energy is used to cool gas turbine inlet air to enhance system efficiency and electrical capacity. This effect is mainly performed during central hours of the day when the conventional gas-fired combined cycles dramatically suffer for efficiency and capacity reduction, as a consequence of the corresponding increase of external air temperature. Such increase is related to the higher availability of solar radiation. This technology may be a viable solution, especially for hot and dry areas, in terms of primary energy savings and increased revenues. This prototypal system was numerically analysed for a combined cycle with a rated electrical power of 99 MWe and an electrical efficiency of 56%, developing a dynamic simulation model and detailed thermo-economic optimizations. Special attention is also paid to the design of novel control strategies aiming at maximizing the solar cooling effect. The results of the dynamic simulations show a very high average thermal efficiency of the solar collectors, equal to 34%. Implications of the performed work allowed an increase of the power output up to 5.5% and a satisfactory payback period equal to 10.7 years. [ABSTRACT FROM AUTHOR]

Renewable energy (RE) penetration growth without energy storage system (ESS) is restricted due to its poor dispatchability. Compressed air energy storage system (CAES) is one of the promising ESS technologies. But, low energy density and high mechanical inertia confined its application as a bulk ESS. In this paper, a novel hybrid thermal-compressed supercritical carbon dioxide energy storage (T-CCES) system is proposed to address CAES shortcomings. In this system, a stratified water thermal energy storage (TES) is employed to store both released heat of compression process and high-frequency reluctant power of a wind farm (which cannot be followed by CCES) using electrical heaters. A dynamic simulation is performed to evaluate system characteristics in steady wind generation condition and in a real wind generation condition. Stochastic simulation of the proposed system integrated with a real wind farm is also fulfilled to assess its characteristics and performance by considering uncertainties using sparse polynomial chaos expansion. Additionally, global sensitivity analysis via Sobol’ indices is conducted to identify the most important parameters of the system. Results show that the system can store wind power during off-peak hours and smoothly releases it into the grid with 57.55% round-trip efficiency (RTE) and 84.1 kWh/m 3 energy density. Uncertainty quantification results indicate that the system can properly work under uncertainties with standard deviation of 55.72–58.16% RTE and 83.7–86.5 kWh/m 3 energy density. Moreover, results show that the random production of wind turbine has a negligible effect on performance characteristics of the T-CCES which makes it a promising solution for integration with wind farms. [ABSTRACT FROM AUTHOR]

Microcogeneration systems guarantee the reduction of primary energy consumption and greenhouse gas emissions in residential sector, by reducing fossil fuels demand and grid losses with respect to conventional energy conversion systems. Energy, environmental and economic benefits can be obtained sharing the cogenerated thermal and electric energy among different end-users to increase the operating hours of the microcogeneration plant with respect to the scenario in which energy demand of each end-user is satisfied by a single cogeneration system. This paper analyses a microcogeneration system used to satisfy electric, space heating and domestic hot water demands of two separate residential buildings located in Spain in a load sharing approach. It consists of a natural gas fuelled internal combustion engine with a thermal and electric power of 12.5 kW and 5.5 kW, respectively. An auxiliary boiler with a nominal thermal power of 24 kW, is also included. The domestic hot water and the heating requirements are managed by means of two different thermal energy storages. The proposed energy conversion systems were experimentally analysed in a test facility in Vitoria Gastéiz (Spain). The models representing the components and the buildings have been implemented in TRNSYS 17. The energy, environmental and economic performance of proposed system are compared with those achieved by a traditional system based on separated energy production. The results highlight that the load sharing between users with different load profiles leads to better environmental and thermo-economic results with respect to the conventional system. The microcogeneration plant works for about 3000 hours per year achieving a primary energy saving of 12.1% and a reduction of equivalent CO 2 emissions equal to 27.8%. The payback period of the analysed solution is equal to 11.9 years unless economic support mechanisms are considered. The results of this study show that the introduction of a microcogeneration system in load sharing approach leads to energy, environmental and economic benefits even considering two separate residential buildings, occupied by users with different behaviour. [ABSTRACT FROM AUTHOR]

The pressure drop between the gas transportation grid and local networks can be exploited to generate electricity by means of a turbo expander. However, a lack of performance indicators leads to incomprehension and underestimation of the actual benefits in terms of energy savings and carbon emission reductions, thus limiting the diffusion of such smart, energy-saving technology. For this reason, in this study, key performance indicators are proposed for natural gas pressure regulation stations with energy recovery. The waste energy recovery index is introduced by considering the possibility of system thermal integration and a reference theoretical sideways process, where a Joule-Thompson expansion occurs. Furthermore, the reduction of greenhouse gas emissions is evaluated through the carbon emission recovery index that quantifies the environmental benefits of the energy saving action. Different key performance indicator values have been calculated by means of custom prediction models based on system characteristics. Finally, in order to assess the accuracy of such models, a parallel simulation is conducted using UniSim® Design Suite software. Here, the two system configurations are implemented: one related to the case study and one related to the reference sideways process. The results show that the model successfully predicts the heat needs of pressure reduction stations and, for a typical system configuration, characterised by an expansion ratio of 4.8, a maximum waste energy recovery of about 69% could be achieved when the system is operating at nominal conditions. Proposed KPIs turned out to be a helpful tool to manage design development and system operations. Moreover, the simplicity of the performance indexes makes them easy to implement in software for process control and simple to interpret for system operators. [ABSTRACT FROM AUTHOR]

This work focuses on a dynamic simulation model for the energy, economic and environmental analysis of an innovative polygenerative system layout based on a building integrated photovoltaic thermal system coupled to an adsorption chiller and to an electricity storage system. The thermal energy of building integrated photovoltaic thermal collectors is exploited in order to produce solar space heating and cooling and domestic hot water. Auxiliary electric air-to-water heat pumps/chillers and a gas-fired condensation boiler are included in the system model in order to integrate the demands of heating, cooling and domestic hot water production. The electricity produced by building integrated photovoltaic thermal collectors is used to satisfy the building needs. The eventual extra-production is delivered to the grid or stored in lead-acid batteries. By means of the developed dynamic simulation model (implemented in TRNSYS environment) the energy system performance on the whole building can be analysed in terms of heating/cooling energy, electricity and domestic hot water demands. In particular, both the passive and active energy effects of the investigated collectors can be assessed. The model includes a suitable tool for the comparison of the innovative system layout vs. traditional reference building-plant systems. For energy, economic and environmental impact optimization purposes, sensitivity analyses can be performed by varying the main system design parameters with respect to the value of reference case ones. In order to show the potentiality of the developed simulation model, several new case studies are developed. They refer to a 3-floor office building located in four different Italian weather zones. Simulation results show that the obtained SPBs, the primary energy saving for electricity and domestic hot water production, and the equivalent carbon dioxide avoided emissions range between 10.6–11.3 years, 58.5–68.8% and 76.3–90.2%, respectively. [ABSTRACT FROM AUTHOR]

In this paper, a detailed numerical analysis of a Combined Cooling, Heating and Power system is presented, aiming at determining its optimal operating strategy in a real industrial application. The system layout includes a reciprocating engine, fuelled by natural gas, heat exchangers for waste-heat recovery, pumps, storage tanks, a single-effect water lithium bromide absorption chiller, a cooling tower, a back-up vapour-compression electric chiller, mixers and valves. A dynamic simulation model of the whole system was developed in TRNSYS. A case study was analysed, referred to a real industrial application, where the system under evaluation should be installed in the near future, providing electricity, mainly used for the production process, and space cooling. Real measured data were used to estimate the electric energy demand of the factory. A detailed building simulation model was used to calculate heating and cooling demands. A detailed economic analysis was carried out, aiming at evaluating: (i) the optimal size of the Combined Cooling, Heating and Power system; (ii) the optimum control strategy, from a thermo-economic point of view, comparing three different cases: Base-Load operation, electric load tracking and a new hybrid strategy based on the simultaneous tracking of electric and thermal-loads. The results showed that the optimal capacity of the system was lower than that selected by the designers of the real unit to be installed. The hybrid control strategy obtained the best profitability, achieving a simple pay-back period equal to 3.8 years, compared to 4.1 years achieved in case of electric-load tracking. [ABSTRACT FROM AUTHOR]

• Micro heat pipe array-based BIPVT module enables efficient heat utilization. • A novel model of the BIPVT module and energy supply system was established. • Highly efficient combination of BIPVT and heat pump utilization is achieved. • Summarized the energy-saving features of BIPVT building in different seasons. • The novel BIPVT buildings achieve nearly zero energy standards. Building integrated photovoltaic–thermal (BIPVT) technology is an efficient form of solar energy utilization, which realizes self-energy supply and holds good development prospects. In this paper, a novel BIPVT module based on micro heat pipe array and BIPVT near-zero energy building are proposed. A matching multi-energy complementary energy supply system is also proposed for this building. The building and energy supply system models were built using TRNSYS. The load characteristics of BIPVT buildings were studied by analyzing the heat transfer process of BIPVT components. The energy-saving rate of the building was also calculated using the method of near-zero energy building evaluation index. The accumulated cooling load and heating load of the buildings throughout the year show that those of the BIPVT buildings are 8.6% higher than those of the benchmark building. Comparison of the energy consumption results shows that the annual cumulative energy consumption of the BIPVT building is 32.3% lower compared to the benchmark building's. In addition, 61.2% of the energy required for year-round refrigeration, heating, and electricity can be supplied by this system. The energy consumption index of the BIPVT building is 70.26 kWh / (m2 • a). Compared with the benchmark building, the BIPVT building energy saving rate is 76.6% and the building energy efficiency improvement rate is 32.3%. [ABSTRACT FROM AUTHOR]

To enable the heat pump water heater maintain efficient operation under diverse circumstances, a novel PV/T-air dual source heat pump water heater (PV/T-AHPWH) has been proposed in this study. In the PV/T-AHPWH system, a PV/T evaporator and an air source evaporator connect in parallel and operate simultaneously to recover energy from both solar energy and environment. A dynamic model is presented to simulate the behavior of the PV/T-AHPWH system. On this basis, the influences of solar irradiation, ambient temperature and packing factor have been discussed, and the contributions of air source evaporator and PV/T evaporator are evaluated. The results reveal that the system can obtain efficient operation with the average COP above 2.0 under the ambient temperature of 10 °C and solar irradiation of 100 W/m 2 . The PV/T evaporator can compensate for the performance degradation of the air source evaporator caused by the increasing condensing temperature. As the evaporating capacity in PV/T evaporator remains at relatively low level under low irradiation, the air source evaporator can play the main role of recovering heat. Comparing the performance of dual source heat pump system employing PV/T collector with that utilizing normal solar thermal collector, the system utilizing PV/T evaporator is more efficient in energy saving and performance improvement. [ABSTRACT FROM AUTHOR]

System-level dynamic models of power plants are valuable tools for the assessment and prediction of plant performance, decisions on the design configuration, and the tuning of operating procedures and control strategies. In this work, the development of an integrated power plant model is presented. This model is validated against steady-state data from a subcritical power plant with reheat and regenerative cycles. The coal-fired power plant model studied has nominal power generation of 605 MW and efficiency of 38.3%. Traditional, regulatory control architectures are incorporated into and tuned with the dynamic power plant model. Dynamic simulation shows that the plant model is stable for sudden changes in coal load, and the controllers are able to maintain the controlled variables at their set points. In this two-part publication, we present the complete workflow of data collection, model development and validation, control tuning, dynamic optimization formulation and solution, and supervisory control architecture for a coal-fired subcritical power plant. Part I focuses on elements of model development and analysis, illustrating the advantages of acausal, object-oriented modeling in power plant simulation. Part II illustrates the use of this model for efficiency optimization under transient part-load operation. [ABSTRACT FROM AUTHOR]

In this study we combine the experimental measurement data and the theoretical model of ejector to determine CO 2 ejector component efficiencies including the motive nozzle, suction chamber, mixing section, diffuser as well as the total ejector efficiency. The ejector is modeled utilizing the distributed-parameter method, and the flow passage is divided into a number of elements and the governing equations are formulated based on the differential equation of mass, momentum and energy conservation. The efficiencies of ejector are investigated under different ejector geometric parameters and operational conditions, and the corresponding empirical correlations are established. Moreover, the correlations are incorporated into a transient model of transcritical CO 2 ejector expansion refrigeration cycle (EERC) and the dynamic simulations is performed based on variable component efficiencies and fixed values. The motive nozzle, suction chamber, mixing section and diffuser efficiencies vary from 0.74 to 0.89, 0.86 to 0.96, 0.73 to 0.9 and 0.75 to 0.95 under the studied conditions, respectively. The response diversities of suction flow pressure and discharge pressure are obvious between the variable efficiencies and fixed efficiencies referring to the previous studies, while when the fixed value is determined by the presented correlations, their response differences are basically the same. [ABSTRACT FROM AUTHOR]

In this study, a solar cooling system of 100 kW is analyzed parametrically in dynamic basis for the city of Athens, Greece. The objective of this study is the design of a sustainable system, using energetic, exergetic and financial criteria. The examined system includes evacuated tube collectors, storage tank and a single stage absorption chiller operating with LiBr-H 2 O working pair. Different combinations of collecting areas and storage tank volumes are tested in order to determine the most suitable cases exergetically. These optimum cases are evaluated financially and finally the system with the higher financial indexes is selected as the most suitable. More specifically, the collecting area is analyzed from 150 m 2 to 600 m 2 and the storage tank from 6 m 3 to 16 m 3 . Finally, 450 m 2 of evacuated tube collectors with a 14 m 3 storage tank was proved to be the optimum solution financially with 15 years payback period and 67 k€ net present value. [ABSTRACT FROM AUTHOR]

Absorption systems offer an alternative way to substitute energy economically in mechanical compression systems in the field of refrigeration and air conditioning. The aim of this article is to investigate the transient performance of a single effect absorption chiller using the pair LiBr/H 2 O when the overall heat transfer coefficients are varied in time by updating the thermo-physical properties and convective coefficients. A thermodynamic model was developed based on conserving mass and energy and considers, so as to determine the overall heat transfer coefficients of the heat exchangers of a chiller and the correlations of the convective coefficients of the processes of refrigeration by absorption (desorption, absorption, condensation and evaporation). This model when tested for real operating conditions and considering the overall coefficients of heat transfer were constant throughout the process showed relative errors were less than 15% in the chilled water circuit and under 2% in cold water. This difference drops significantly when the variable overall coefficients are considered throughout the process, these errors being approximately 5% and 0.3%, there being a percentage fall in all water circuits. [ABSTRACT FROM AUTHOR]

The dynamic model of a poly-generation system based on a biogas-fed solid oxide fuel cell (SOFC) plant is presented in this paper. The poly-generation plant was developed in the framework of the FP7 EU-funded project SOFCOM ( www.sofcom.eu ), which consists of a fuel-cell based polygeneration plant with CO 2 capture and re-use. CO 2 is recovered from the anode exhaust of the SOFC (after oxy-combustion, cooling and water condensation) and the Carbon is fixed in the form of micro-algae in a tubular photobioreactor. This work focuses on the dynamic operation of the SOFC module running on steam-reformed biogas. Both steady state and dynamic operation of the fuel cell stack and the related Balance-of-Plant (BoP) has been modeled in order to simulate the thermal behavior and performance of the system. The model was validated against experimental data gathered during the operation of the SOFCOM proof-of-concept showing good agreement with the experimental data. The validated model has been used to investigate further on the harsh off-design operation of the proof-of-concept. Simulation results provide guidelines for an improved design of the control system of the plant, highlighting the feasible operating region under safe conditions and means to maximize the overall system efficiency. [ABSTRACT FROM AUTHOR]

This work aimed to numerically study the influence of injection strategy on mixture formation and combustion process in a port injection natural gas rotary engine. On the base of a 3D dynamic simulation model which was established in our previous work, some critical information was obtained, which was difficult to obtain through experiment, in terms of the flow field, the fuel distribution, the temperature field and the concentration fields of some intermediates. Simulation results showed that for mixture formation, the movements of fuel in injection stage were mainly controlled by the intensity of the vortex I for injection timing, and the value of jet flux for injection duration respectively. With retarded injection timing, the decreasing intensity of the vortex I resulted in less fuel moving toward the back of the combustion chamber. With the extension in injection duration, the decreasing value of jet flux resulted in more fuel staying at the back of the combustion chamber. For combustion process, the overall combustion rate for injection strategy which had an injection timing of 390 °CA (BTDC) and injection duration of 51.5 °CA (case ID4) was the fastest. This was mainly due to the fact that the accumulation area of fuel was at the middle and front of the combustion chamber. Meanwhile, fuel concentration near the leading and trailing spark plugs was conducive for the flame kernel formation. Compared with the injection strategy which had an injection timing of 450 °CA (BTDC) and an injection duration of 55 °CA (case IT1), the improved combustion rate of case ID4 had a 23% increase in the peak pressure, but also a certain increase in NO emissions. [ABSTRACT FROM AUTHOR]

The heat transfer performances of evaporators and condensers significantly affect the efficiency of household refrigerators. For enhancing heat transfer of the condensers and evaporators, a novel dual energy storage (DES) refrigerator with both heat storage condenser (HSC) and cold storage evaporator (CSE) is proposed. The performance comparison of three kinds of energy storage refrigerators: HSC refrigerator, CSE refrigerator and DES refrigerator is analyzed by establishing dynamic simulation models. According to the simulation results, the DES refrigerator combines the advantage of HSC refrigerator and CSE refrigerator, it has more balanced operational cycle and higher evaporation pressure and temperature. The DES refrigerator shows a best energy saving performance among the three energy storage refrigerators with largest off-time to on-time ratio of 4.3 and the electrical consumption saving can reach 32%, which is greater than the sum (28%) of the other two kinds of energy storage refrigerators. [ABSTRACT FROM AUTHOR]

Participants of the COP 26 summit have agreed to limit global temperature rise to 1.5 K by 2050. Out of the many strategies envisaged to meet the targets of COP 26, the 'Sector Coupling' process aims to use renewable electricity in residential heating, chemical industry, and transportation sectors. Several studies predict that de-central energy systems will play a significant role in the future. Among the proposed sector coupling strategies in de-central energy systems, the Power to Gas (PtG) process producing chemical energy carriers like Substitute Natural Gas (SNG) from renewable power is gaining acceptance. Numerical models of de-central energy systems are needed to analyse sector coupling under fluctuating renewable energy generation and changing gas demand. This study introduces a numerical model of a decentral energy system that includes a novel methanation concept developed at the Engler Bunte Institut of KIT called 3 Phase Methanation. Here, H 2 from electrolysis and CO 2 from DAC or other biomass-based sources are passed through a slurry bubble column reactor. The slurry is a suspension of the catalyst in a liquid heat transfer medium where the heat of the reaction is dissipated. The 3-Phase methanation process is modelled in this study using the axial dispersion method. Earlier studies describing experimental campaigns conducted on the pilot plant in KIT have proven that the reactor core is nearly isothermal with stable product gas compositions even if the load changes are instantaneous. In this study, it is shown that the numerical model can replicate the experimental results. Following modelling and validation, the numerical model of the PtG plant is integrated with the other components to simulate the de-central energy system. The simulation results demonstrate the dynamic output of all the components and, in particular, the response provided by the PtG plant. This model can be adapted to simulate sector coupling in future de-central energy systems and analyse aspects like long-term energy storage, GHG minimisation and cost-optimal operation. • The power to gas (PtG) process helps in decarbonisation through sector coupling. • Dynamic simulation of energy systems with PtG plants is the focus of this work. • A novel 3 Phase methanation capable of dynamic operation is introduced. • A numerical model is developed for decentral energy systems with dynamic PtG plants • The model can be customised for future decentral energy systems. [ABSTRACT FROM AUTHOR]

The paper analyzes the introduction of a photovoltaic system satisfying electric, space heating and cooling demand of an office building located in southern Italy. The electric load is due to an electric heat pump, used to satisfy space heating and cooling load, a pure electric demand (personal computers, printers, lighting, etc.) and an electric vehicle charged during working hours. Dynamic simulations to evaluate the energy and environmental performance of the analyzed system considering different photovoltaic peak powers (4.5–9.0 kW), electric vehicle distance per day (40–120 km) and charging mode is carried out. The solar based system shows primary energy saving and equivalent carbon dioxide emission reduction higher than 40% in comparison to the reference conventional system based on a natural gas fired boiler, an electric chiller and a diesel car. The results highlight that the solar energy system is more competitive when DC charging system is provided. [ABSTRACT FROM AUTHOR]

This paper presents new approach for determining buildings technical system energy performance. This new methodology describes a mathematical model for accurately predicting indoor temperature and heat losses of the space heating and domestic hot water system components. The entire model is described by system of ordinary differential equations which can be solved using standard numerical techniques. The innovative aspect of the method is the integral approach in mathematical modeling of buildings energy needs and technical systems heat loss, taking into account heat accumulation in all considered parts (building envelope + technical system). Such approach allows a detailed insight of the system behavior for chosen working conditions. This model can serve for energy performance calculations in a wide variety of buildings types and their technical systems. The calculation example is given for family house, equipped with conventional space heating and domestic hot water heating system, with the time step of 1 min and for characteristic day of each month within a year. The results are compared against those obtain from EN ISO 13790 and standard series EN 15316. The comparison shows significant differences in determination of the annual delivered energy to the heating system (33%), as a consequence of difference in estimation of the energy need for heating (15%) and calculation of the technical systems recoverable heat losses utilization factor, which seems to be underestimated. The delivered energy to the space heating and domestic hot water heating system differs 25%, while the energy delivered to the generation system differs 4%. [ABSTRACT FROM AUTHOR]

• Dynamic model of SOFC-Engine hybrid system was developed. • Individually developed components were integrated into one system. • The model was simulated based on the start-up scenario. • The dynamic behavior of components was analyzed. A dynamic simulation model of a hybrid power generation system of a solid oxide fuel cell and a homogeneous charge compression ignition engine was developed to investigate the behavior of the system during the start-up process. The stack, reformer, catalytic burner, and heat exchanger were implemented as dynamic models based on physical equations. For the engine, an experimental data-based mapping model was developed. The dynamic model was simulated on a Matlab/Simulink platform. Individually developed component models were assembled as an integrated system model and operated at the system level. The hybrid system was designed to generate approximately 4 kW of electricity from the SOFC stack and 1 kW from the engine, resulting in a total system power of 5 kW, with an electrical efficiency of 50.6%. The integrated model was operated using a four-step start-up procedure for 50 h, during which the temperature and composition of the stream were observed in time. Based on this, the dynamic behavior of the system was analyzed at each stage throughout the entire start-up process from ambient to high operating temperature. Validation of key results suggests a close resemblance between the model and an actual system. Therefore, the proposed model is expected to exceed the limitations of the existing static model analysis method. [ABSTRACT FROM AUTHOR]

A dynamic simulation model of a novel solar–geothermal polygeneration system and the related exergetic and exergoeconomic analyses are presented in this paper. The plant is designed in order to supply electrical, thermal and cooling energy and fresh water for a small community, connected to a district heating and cooling network. The hybrid system is equipped with an Organic Rankine Cycle fueled by medium-enthalpy geothermal energy and by a Parabolic Trough Collector solar field. Geothermal brine is also used for space heating and cooling purposes. Finally, geothermal fluid supplies heat to a Multi-Effect Distillation unit, producing also desalinized water from seawater. Dynamic simulations were performed in order to design the system. The overall simulation model, implemented in TRNSYS environment, includes detailed algorithms for the simulation of system components. Detailed control strategies were included in the model in order to properly manage the system. An exergetic and exergoeconomic analysis is also implemented. The exergetic analysis allows to identify all the aspects that affect the global exergy efficiency, in order to suggest possible system enhancements. The accounting of exergoeconomic costs aims at establishing a monetary value to all material and energy flows, then providing a reasonable basis for price allocation. The analysis is applied to integral values of energy and a comparison of results between summer and winter season is performed. Results are analyzed on different time bases presenting energetic, exergetic, economic and exergoeconomic performance data. Results show that global exergy efficiency varies between 40% and 50% during the “Thermal Recovery Mode” operation and between 16% and 20% during the “Cooling mode” operation. It was also found that electricity, chilled water, cooling water and desalinated water exergoeconomic costs vary respectively in the ranges 0.1475–0.1722 €/kW h, 0.1863–0.1888 €/kW h ex , 0.01612–0.01702 €/kW h ex and 0.5695–0.6023 €/kW h ex . [ABSTRACT FROM AUTHOR]

Desiccant-based air handling units can provide significant operational advantages and can use solar energy as the main heat source. Hereinafter a plant equipped with a silica-gel desiccant wheel is analyzed for two Italian locations (Benevento and Milano). A parametric study involving collectors types, surfaces, tilt angles and installation site has been performed. The proposed system has been compared with a conventional HVAC unit, through dynamic simulations. In terms of energy and environmental analysis, solar desiccant systems should always be preferred to conventional ones, even when the solar thermal energy surplus is fully dissipated. A maximum primary energy saving of about 10% and 20% with flat plat and evacuated tube collectors, respectively, occurs in both locations. The savings increase up to about 58% and 72% in Benevento and 43% and 58% in Milano, when the solar heat excess is completely used for further energy demands. One observes that systems with evacuated tube collectors are preferable where the available space for the solar field is small, instead with larger surfaces flat plate collectors are advantaged. In terms of economic analysis, the shortest payback periods are 6 and 8 years for Benevento and Milano, respectively. [ABSTRACT FROM AUTHOR]

This paper presents experimental and numerical analyses of a novel high-temperature solar cooling system based on innovative flat-plate evacuated solar thermal collectors (SC). This is the first solar cooling system, including a double-effect absorption chiller, which is based on non-concentrating solar thermal collectors. The aim of the paper is prove the technical and economic feasibility of the system, also presenting a comparison with a conventional technology, based on concentrating solar thermal collectors. To this scope, an experimental setup has been installed in Saudi Arabia. Here, several measurement devices are installed in order to monitor and control all the thermodynamic parameters of the system. The paper presents some of the main results of this experimental campaign, showing temperatures, powers, energies and efficiencies for a selected period. Experimental results showed that collector peak efficiency is higher than 60%, whereas daily average efficiency is around 40%. This prototypal solar cooling system has been numerically analysed, developing a dynamic simulation model aiming at predicting system performance. For a representative operating period, numerical data were compared with the experimental one, showing an excellent accuracy of the model. A similar system, equipped with Parabolic Trough solar thermal collectors (PTC) was also simulated in order to compare the novel solar collectors with such reference technology. For both systems a detailed thermo-economic model has been implemented in order to perform such comparison also from the economic point of view. Results showed that the rated energy performance of the prototypal solar cooling system featuring new collectors is better than that of the reference system. In particular, the difference between the novel and the reference solar cooling system becomes more and more significant, when considering the effects of dust and defocusing related to the tracking mechanism of concentrating collectors in harsh environments. Finally, from the economic point of view, results showed that the novel prototype was able to achieve a good profitability. [ABSTRACT FROM AUTHOR]

A dynamic simulation study in TRNSYS environment has been carried out to evaluate energy and economic performance of a novel heating and cooling system based on the coupling between a low or medium-enthalpy geothermal source and an Air Handling Unit, including a Desiccant Wheel. During summer season, a Downhole Heat Exchanger supplies heat to regenerate the desiccant material, while a certain amount of geothermal fluid is continuously extracted by the well in order to maintain high operating temperatures. Simultaneously, the extracted geothermal fluid drives an absorption chiller, producing chilled water to the cooling coil of the Air Handling Unit. Conversely, during the winter season, geothermal energy is used to cover a certain amount of the space heating demand. In both summer and winter operation modes, a geothermal energy is also used to supply Domestic Hot Water. A case study was analyzed, in which an existing low-enthalpy geothermal well (96 °C), located in Ischia (an island close to Naples, Southern Italy), is used to drive the geothermal system. Results showed that the performance of the proposed system is significantly affected by the utilization factor of Domestic Hot Water. In fact, considering a range of variation of such parameter between 5% and 100%, Primary Energy Saving increase from 77% to 95% and Pay-Back Period decreases from 14 years to 1.2 years, respectively. The simulations proved the technical and economic viability of the proposed system. In fact, a comparison with similar systems available in literature pointed out that the layout proposed in this work is characterized by better energy and economic performance, especially in the best scenario. Finally, a sensitivity analysis showed that the system performance is mainly affected by the nominal geothermal flow rate and by natural gas cost. [ABSTRACT FROM AUTHOR]

This paper sets out to make a dynamic analysis of a single-effect, lithium bromide–water (LiBr/H 2 O) absorption chiller. A mathematical model has been developed based on conserving mass, energy, and species, which considers the correlations of the convective coefficients of absorption refrigeration processes so as to determine the overall heat transfer coefficients of the heat exchangers of chillers. The implementation of this mathematical model was built on the Matlab platform, and resolved the system of non-linear equations by making explicit use of the finite difference method. The model has the ability to simulate and predict the behavior of internal and external parameters such as temperature, concentrations and pressures when these are subjected to disruptions in the power supply and thermal load. The largest absolute differences found when validating the model by means of the experimental numerical values in the water circuits were approximately 1.0 °C, 0.7 °C and 0.2 °C for hot, chilled and cold water, respectively. In terms of relative error, these divergences represent a maximum of 5% and a minimum of 0.3%. The model showed good results when subjected to disturbances in the load and power source, as it reproduced the behavior of the temperature parameters and the Coefficient of Performance (COP), in line with the comparisons made with the data provided by the manufacturer, the COP being approximately 0.7 for operating conditions. [ABSTRACT FROM AUTHOR]

The energy markets deregulation coupled with the rapid spread of unpredictable energy sources power units are stressing the necessity of improving traditional power plants flexibility. Cyclic operation guarantees high profits in the short term but, in the medium-long time, cause a lifetime reduction due to thermo-mechanical fatigue, creep and corrosion. In this context, Combined Cycle Power Plants are the most concerned in flexible operation problems. For this reason, two research groups from two Italian universities have developed a procedure to estimate the devices lifetime reduction with a particular focus on steam drums and superheaters/reheaters. To assess the lifetime reduction, it is essential to predict the thermodynamic variables trend in order to describe the plant behaviour. Therefore, the core of the procedure is the power plant dynamic model. At this purpose, in this paper, three different dynamic models of the same single pressure Combined Cycle Gas Turbine are presented. The models have been built using three different approaches and are used to simulate plant behaviour under real operating conditions. Despite these differences, the thermodynamic parameters time profiles are in good accordance as presented in the paper. At last, an evaluation of the drum lifetime reduction is performed. [ABSTRACT FROM AUTHOR]

To ensure that air separation unit can bear high ramp rate and flexible operations when integrated into oxy-combustion power plant, this paper focuses on the investigations of plantwide control design and operating strategy for double-column air separation unit without or with liquid oxygen storage drum through dynamic simulation. It is found that three air separation unit types (normal, oversize, and downsize) with the proposed control structure configured with logic control loops (strategies 1, 2, and 3) can achieve 5%/min of high ramp rate and flexible operations such as peak and off-peak or/and energy storage. Compared between the latter two logical controls, strategy 2 would be better because its oxygen product qualities can be maintained closer to their targets. Three integrated patterns between air separation unit and oxy-combustion boiler are proposed to improve operating flexibility, among which oversize case would be more suitable for oxy-combustion power plant since its energy saving (20.33 MW) is larger and operating strategy is more flexible than those in downsize (10.76 MW) and normal cases. Process control for flexible operations would be an opportunity for engineering, and comprehensive dynamic model with specified control system provides possibility to integrate air separation unit with full-train oxy-combustion power plants. [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]

This paper outlines a complete bioenergy flow incorporating bioresource procurement, feedstock supply, conversion technologies and energy consumption to industrialize the development and utilization of bioenergy. An input–output optimization simulation model is developed to introduce bioenergy industries into the regional socioeconomy and energy production and consumption system and dynamically explore the economic, energy and environmental benefits. 16-term simulation from 2010 to 2025 is performed in scenarios preset based on bioenergy industries, carbon tax-subsidization policy and distinct levels of greenhouse gas emission constraints. An empirical study is conducted to validate and apply the model. In the optimal scenario, both industrial development and energy supply and demand are optimized contributing to a 8.41% average gross regional product growth rate and a 39.9% reduction in accumulative greenhouse gas emission compared with the base scenario. By 2025 the consumption ratio of bioenergy in total primary energy could be increased from 0.5% to 8.2%. Energy self-sufficiency rate could be increased from 57.7% to 77.9%. A dynamic carbon tax rate and the extent to which bioenergy industrial development could be promoted are also elaborated. Regional economic development and greenhouse gas mitigation can be potentially promoted simultaneously by bioenergy utilization and a proper greenhouse gas emission constraint. The methodology presented is capable of introducing new industries or policies related to energy planning and detecting the best tradeoffs of economy–energy–environment. [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]

Architects and urban planners have been relying on geometry-based indices to design more energy efficient buildings for years. The advantage of such indices is their ease of use and capability to capture the relation of a few geometric variables with the building’s performance. However, such relation is usually found using only a few simple building models and considering only a few climate regions. This paper presents the analysis of six geometry-based building indices to determine their adequacy in eight different climate regions in Europe. For each location, three residential building design programs were used as building specifications. Two algorithms were employed to randomly generate and assess the thermal performance of three sets of 500 alternative building models. The results show that geometry-based indices only correlate with the buildings’ thermal performance according to specific climate regions and building design programs. [ABSTRACT FROM AUTHOR]

The paper investigates the introduction of a MCHP (Micro Combined Heat and Power) system in buildings with low energy demand with respect to the current building stock. A load sharing approach between a multifamily residential building and an office one is taken into account. Dynamic simulations are carried out in order to evaluate the thermo-economic performance of the analyzed system. Particular attention is given to the estimation of the electric load of the different users, as the economic profitability of a MCHP system is strongly influenced by the amount of self-consumed electricity. In order to analyze the influence of climatic conditions, two different geographical locations in Italy (Naples and Turin, having 1034 and 2617 heating degree days, respectively) are considered. The results of this study indicate that the installation of MCHP systems in buildings with low energy demand allows to increase the percentage of self-consumed electricity reducing the bidirectional electricity flow between the users and the external grid, as well as the impact on the grid itself due to the large diffusion of distributed generation systems. Moreover this study shows that the load sharing approach between users with different load profile leads to better energy, environmental and economic results with respect to a conventional system. The climatic conditions play an important role on the MCHP operational hours and hence on the thermo-economic performance of the system. The primary energy saving of the system located in Turin is equal to 8.8% with respect to 6.2% of the system located in Naples. Also the environmental performance, evaluated in terms of equivalent CO 2 avoided emissions, are better in Turin (8.3%) than in Naples (6.7%). The economic analysis shows acceptable values of the pay-back period in presence of economic support mechanisms. The findings of this study show that the introduction of a MCHP system in load sharing approach leads to thermo-economics advantages even considering the lower heating needs of well-insulated buildings. [ABSTRACT FROM AUTHOR]