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Heating buildings have a huge heat capacity and have abilities to accept fluctuating heat supply from renewables. Creating a low-order scalable model that describes the thermal dynamics of coupled heat transfer, charge, and discharge processes among heating buildings is essential to unlocking the thermal storage potential of building mass and achieving space heating decarbonization. White-box models tend to be too complex and black-box models lack scalability. Thus, a low-order gray-box model with uncertain lumped parameters is proposed based on comprehensive heat transfer analyses and necessary assumptions. Thermal mass in heating buildings is divided into four independent heat storage units. The building envelope that can be heated directly or not is regarded as a different heat storage unit. To reduce the search space dimension of model identification, the decision variables are downsized to essential model parameters based on the sensitivity analysis. Moreover, a progressive dimension reduction method is introduced to further improve the probability that the optimization algorithm converges to a global minimum. Case studies show that the calibrated model with global optimal solutions of uncertain model parameters has a good performance on the prediction of the average temperature of indoor air, the average absolute error is only 0.1 °C. • A low-order gray-box model with uncertain parameters is built for heating buildings. • Thermal mass in heating buildings is divided into four independent heat storage units. • Uncertain model parameters can be reduced based on the sensitivity analysis. • The progressive dimension reduction method is proposed to find a global optimum. [ABSTRACT FROM AUTHOR]

The application of phase change materials (PCMs) in renewable energy storage and building temperature regulation is considered an effective method to reduce the use of fossil fuels and carbon emissions. However, issues concerning the utilization of PCMs in high-humidity environments remain to be addressed to fill the gap in real-world applications. This paper establishes a simplified novel two-zone model, comprehensively considering the natural convection on the surface of the PCP in high-humidity environments, as well as the formation, movement, and evaporation of water films on the surface. Subsequently, numerical solutions and experimental validation are conducted, and the influence of high-humidity environments on the heat and moisture transfer is elucidated. The results indicate that a high-humidity environment can significantly suppress the sensible heat transfer with a ratio range of latent heat to sensible heat typically around 1–4. Furthermore, the increase in the height of PCP leads to an increase in the proportion of sensible heat transfer. On the contrary, increasing the thermal conductivity of the PCM can amplify the latent heat transfer. The results can help further study the thermal storage and the dehumidification potential of phase change units in application on a large scale under high humidity conditions. [Display omitted] • A simplified model for PCM thermal storage prediction in high humidity environments is established. • The variation of water film on the PCP surface is considered. • Sensitivity analysis for PCM thermal storage in high humidity environments is investigated. • A high-humidity environment can lead to a ratio range of latent heat to sensible heat typically around 1–4. [ABSTRACT FROM AUTHOR]

Clean energy development for multiple productions interests many countries and companies. Hence, this paper presents an innovative solar-driven trigeneration arrangement equipped with a thermal energy storage unit (TESU); the whole system comprises parabolic dish collectors, a modified Rankine cycle, and a double-effect absorption chiller. The system is designed to enhance the integrity performance compared to previous designs. Heat loss recovery is performed using an internal heat exchanger to improve the Rankine cycle's performance. The operating framework of the arrangement contains three steady modes: solar mode associated with the state without applying TESU, storage mode corresponding to the state without solar energy using TESU, and solar-storage mode capable of storing energy in addition to launching the combined cycles. The prediction of the sensitivity of the net output power, heating capacity, input energy, power to heating and cooling ratios, and energy and exergy efficiencies is conducted in solar mode. Furthermore, the thermoeconomic analysis is carried out in solar mode to determine the equipment's financial aspect. Referring to the results, the overall energy efficiencies of the modes introduced before are equal to 97.23%, 81.98%, and 40.23%, and the corresponding exergy efficiencies are 15.53%, 14.47%, and 8.58%. Also, the exergoeconomic factor of the solar subsystem is 70.77%. [Display omitted] • Modeling a CCHP system based on a modified Rankine cycle, a double absorption chiller, parabolic dish collectors and a TSU. • Improving the trigeneration system's performance by eliminating the examined models' weaknesses. • Analyzing solar dish collector systems' thermodynamic and exergoeconomic. [ABSTRACT FROM AUTHOR]

As a promising large-scale physical energy storage technology, the main challenge of compressed CO 2 energy storage currently is the issue of low-pressure CO 2 high-density storage. To address that issue, a novel trans -critical compressed CO 2 energy storage system based on 13X zeolite variable temperature adsorption (TSA-TC-CCES) is proposed in this paper. Based on the principle of 13X zeolite adsorption gas storage, combined with the temperature swing adsorption (TSA) method and contact heat exchange scheme, it realizes low-pressure CO 2 high-density storage and real-time internal circulation of heat. Under the design conditions, the adsorption tower volume, system round-trip efficiency, energy storage density, energy efficiency, and energy cycle efficiency are 360.55 m3, 89.19%, 6.29 kW ⋅ h/m3, 70.8%, and 93.53%, respectively. The sensitivity analysis results indicate that energy storage density and round-trip efficiency decrease with increasing adsorption temperature while growing with increasing desorption temperature. The increase in storage pressure positively affects energy storage density, while the increasing storage temperature harms energy storage density. The release pressure at the critical point causes abrupt changes in system performance. • A trans -critical compressed CO 2 energy storage system based on 13X zeolite temperature swing adsorption is proposed. • The contact heat exchange solution enables instant internal circulation of heat, eliminating the need for heat storage media. • This system utilizes temperature fronts to control the reheat temperature and compressor inlet temperature. [ABSTRACT FROM AUTHOR]

Abstract As energetic systems become more and more complex, it is necessary to develop strategies for analyzing the influence of the parameters as well as their couplings. This approach is even unavoidable when the optimization procedure is based on multi-criteria. In the present work, we propose an analysis strategy for multi-criteria optimization applied to inter-seasonal solar heat storage for residential building energy needs, including heating and domestic hot water. The modeling is based on simplified equations of the components, while keeping the main physical and coupling phenomena. A sensitivity study is applied to the corresponding energetic system in order to identify the most relevant parameters and couplings interacting on the various output objectives. Several simulations are performed to investigate a multi-objective optimization and various figure representations are presented to refine the analysis. Highlights • Dynamical system study including inter-seasonal and short-term energy storages. • System analysis to insure heating and domestic hot water demands. • Achievement of sensitivity analysis for parameters and coupling parameters. • Investigation of weighted multi-criteria optimization. • Implementation of combined analysis to promote a general efficient methodology. [ABSTRACT FROM AUTHOR]

This research presents technical and cost-minimised design to decarbonise the heating network by using large-scale heat pump and thermal heat storage. In this paper, real hourly heat-consumption and heat-production cost data for the city of Aarhus, Denmark are used for calculating techno-economic feasibility of coupling the heating network with electrical grid. An optimum solution is suggested for the entire network with least amount of backup generation capacity, thermal heat storage capacity, natural gas boiler capacity and levelised cost of energy. Aarhus constitutes 5% of the Denmark's total heat demand and 4% of electrical load demand. This can be fulfilled with 160 MW of rated wind generation capacity, 35 MW of solar PV generation capacity, 45 MW of backup generation capacity, 221 MW of natural gas boiler capacity and 3.4 GWh of thermal heat storage capacity. The levelised cost of energy shows that, the coupling between the electrical grid and heating sector reduces the cost by more than 50% to 45  € /MWh. However, the cost-minimised design is possible with wind/solar mix of 85% and renewable energy penetration of 100%. Sensitivity analysis concedes that, the 100% decarbonisation of heating sector relies heavily upon the cost assumed for wind generation and solar PV generation, instead of the operation and maintenance cost for heat pump. Furthermore, the reduction in cost for wind generation and solar PV generation leads to the decrease in levelised cost of energy. Whereas, the reduction in cost for heat pump, thermal heat storage capacity and natural gas boiler capacity leads to an increase in renewable energy penetration. Sensitivity analysis further reveals that, increasing thermal heat storage capacity and the cost of selling excess renewable energy does not have major impact upon the levelised cost of energy and can be instrumental for the economic viability of fossil-free future. [ABSTRACT FROM AUTHOR]

Combined heat and power (CHP) plants based on gas engines feature overall efficiencies of 90%, response times of less than 2 min, tolerate multiple starts per day and can be deployed as decentralised generators. A decoupling heat storage device between the plant and the heat sink can improve operation flexibility, but increases investment costs. The cost-optimal sizing of plant and storage against time dependent electricity prices is a non-trivial optimisation problem. In this study, we investigate how the optimal design depends on various boundary conditions. We sweep residential and industrial heat demand profiles (5 kW–100 MW peak), electricity price levels and variance and fuel prices. We pair a linear plant model with heat sink and price combinations and use a fast heuristic algorithm to find power, storage size and operating pattern for maximised annual profit over 8760 h. Brake-even is reached with a surplus of 0.03–0.14 €/kWh on today's spot market price (fuel 0.08 €/kWh). Design results for plants ≥ 1 MW power are similar. Future optimal designs are up to 30% larger than today's and profits increase. The design is generally robust on expected price changes due to the flat optimum. The results provide a valuable basis for designing profitable plants today and in future. [ABSTRACT FROM AUTHOR]

This paper (Part B) presents the results of sensitivity, baseline performance, and levelized cost of energy analyses of a recently proposed Pumped Thermal Energy Storage and Bottoming System (Bot-PTES) that uses ammonia as the working fluid. The system model was outlined in Part A of this two-part paper. This analysis focuses on the effects of hot thermal storage utilization, system pressure, and evaporator/condenser size on the system performance. It also presents the estimated performance for a proposed baseline Bot-PTES. Results of this analysis showed that all selected parameters had significant effects on efficiency, with the evaporator/condenser size having the largest effect over the selected ranges. Results for the baseline case showed stand-alone energy storage efficiencies between 51 and 66% for varying power levels and charge states, and a stand-alone bottoming efficiency of 24%. The resulting efficiencies for this case were low compared to competing technologies; however, the dual-functionality of the Bot-PTES enables it to have higher capacity factor, leading to $91–197/MWh levelized cost of energy compared to $262–284/MWh for batteries and $172–254/MWh for Compressed Air Energy Storage. [ABSTRACT FROM AUTHOR]

M-TES (Mobile Thermal Energy Storage) technology is explored in this paper for transportation of industrial surplus heat for use in LTDH (low temperature district heating network). LTDH has promising potential in utilizing low grade heat, on the other hand, 20%–50% of industry generated surplus heat is often released to the ambient environment. M-TES is used to match thermal energy supply and demand that occur at different locations and that are shifted in time. In this paper, design of M-TES is conducted, optimization in operating strategies is performed, sensitivity analysis on levelized cost is studied, and environmental impact of CO 2 emissions due to transportation is evaluated. The results of the study show an array of transportation means and storage operating strategies under which M-TES is technically, economically and environmentally sound for transportation of industrial surplus heat for use in LTDH network. [ABSTRACT FROM AUTHOR]

High-temperature aquifer thermal energy storage system usually shows higher performance than other borehole thermal energy storage systems. Although there is a limitation in the widespread use of the HT-ATES system because of several technical problems such as clogging, corrosion, etc., it is getting more attention as these issues are gradually alleviated. In this study, a sensitivity analysis of recovery efficiency in two cases of HT-ATES system with a single well is conducted to select key parameters. For a fractional factorial design used to choose input parameters with uniformity, the optimal Latin hypercube sampling with an enhanced stochastic evolutionary algorithm is considered. Then, the recovery efficiency is obtained using a computer model developed by COMSOL Multiphysics. With input and output variables, the surrogate modeling technique, namely the Gaussian-Kriging method with Smoothly Clopped Absolute Deviation Penalty, is utilized. Finally, the sensitivity analysis is performed based on the variation decomposition. According to the result of sensitivity analysis, the most important input variables are selected and confirmed to consider the interaction effects for each case and it is confirmed that key parameters vary with the experiment domain of hydraulic and thermal properties as well as the number of input variables. [ABSTRACT FROM AUTHOR]

Widespread commercialization of PCM-based latent heat storage systems is limited by the low melting and solidification rates during the phase transition process. In this study, fins are used to enhance the phase change process. A parametric study is conducted to understand the effect of fins on the thermal performance of vertically- and horizontally-oriented rectangular storage tanks. Throughout simulations, the fin volume, and thereby the mass of PCM in the tank, were kept constant. It was observed that the horizontal enclosures can take advantage of the development of strong natural convection flow until near the end of the melting process, whereas with vertical counterparts the strength of the convection currents was diminished during the shrinkage stage. The results suggest that longer and thinner fins are more beneficial for enhancing the melting rate than shorter and thicker fins. It was concluded that for horizontal enclosures with fin lengths of 25 and 35 mm, increasing the number of fins does not necessarily shorten the melting time. The maximum melting time reduction compared to the 3-fin vertical enclosure with a fin length of 25 mm (chosen as our benchmark case) was 75.1% when nine 45-mm-long fins are used in a horizontal enclosure. • Melting of PCM in vertically and horizontally oriented enclosures is investigated. • Different configurations of fins are employed to enhance thermal storage. • Energy storage rate in horizontal enclosure outperforms the vertical enclosure. • Longer and thinner fins are more beneficial than shorter and thicker fins. • Nusselt number decreases with the increase in fin number. [ABSTRACT FROM AUTHOR]

Reliable access to electricity is still a serious problem for remote villages, however, abundant solar radiation and biomass have the potentials to provide energy supply in a sustainable way. This paper focuses on the optimal design and techno-economic analysis of the stand-alone hybrid energy system for a typical rural village in the northwest of China. Based on the estimation of local renewable energy potential and the investigation of heat and power consumption patterns, a mixed-integer linear programming optimization model is presented with the aim of minimum total annualized cost. The techno-economic analysis of different system configurations is conducted and compared. Particularly, the levelized cost of energy production and levelized cost of energy consumption is proposed to evaluate the economic-cost of energy from both supply and demand-side respectively. Furthermore, sensitivity analysis and scenario analysis is conducted to demonstrate the influences of the variations and uncertain environmental policy on total system cost and performance. The results demonstrate that the PV/biomass-CHP/diesel generator/gas boiler/battery/thermal energy storage hybrid energy system is the most economical option with a total annualized cost of 652 × 103 $. The levelized cost of energy consumption (0.355 $/kWh) is greater than that of energy production (0.275 $/kWh), implying a great potential for local electrification and more flexible heat/power output equipment. • Stand-alone hybrid energy system with biomass-CHP for remote areas. • Novel levelized cost of energy evaluated from both supply and demand perspectives. • Techno-economic analysis of hybrid energy systems with different configurations. • Sensitivity analysis to investigate the impacts of market price variations and environmental policy uncertainty. [ABSTRACT FROM AUTHOR]

Recycling heat from local industrial processes is one of the suitable and strategic opportunities for district heating all over the world. However, in northern China, the majority of low-grade energy has been wasted, the main difficulties are of an institutional and commercial character. The rapid development of renewables and constant promotion of time-of-use tariff policy has provided new chances for power-to-heat implementation and thermal energy storage. In this study, a general configuration optimization framework of additional waste heat recovery and storage (WHRS) devices is proposed, which is based on the cost-benefit analysis. Due to the implicit nature of such an optimization problem, conventional economic dispatch, two-stage branch evaluation, linear programming solver, and two kinds of advanced optimization algorithms (i.e., Genetic Algorithm and Pattern Search) have been integrated systematically. Moreover, case studies and sensitivity analyses are conducted to verify the feasibility of the proposed optimization model and to reveal the effects of uncertain economic parameters, respectively. The results show that the average time-consuming of Pattern Search is only 4.9% of the GA optimizations. When introducing additional WHRS devices with optimal configurations, the total operating costs decreased by 6.9% and the cost proportion of gas boiler declines remarkably from 8.6% to 2.0%. Image 1 • Formulate a general solving strategy based on the two-stage branch evaluation. • The feasible region can be expanded from discrete points to a continuous domain. • Simplify MINLP to a group of LP problems that can be solved quickly and precisely. • The effects of uncertain economic parameters are revealed by sensitivity studies. [ABSTRACT FROM AUTHOR]