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In this paper, the cooling, thermal and electrical energy storages are integrated into the combined cooling, heating, and power (CCHP) system to improve its energy utilization efficiency. Eight scenarios with or without electrical energy storage (EES) are investigated for the CCHP system. Furthermore, a non-dominated sorting genetic approach using elite crossover is presented for the eight scenarios. The elite crossover enables the individuals with non-domination rank 1 to converge towards the Pareto front of each scenario, and the other crossover helps the individuals with larger ranks to search in wide regions. In addition, an elimination strategy is used to exclude the individuals in crowded regions, which is beneficial for obtaining diversified solutions for each scenario instead of similar ones. For the four scenarios where selling electricity to grid is allowed, their energy, economy and environment function values are higher than those of the separate production scenarios, and the two scenarios with EES are 1.5997% and 2.6495%, respectively, higher than the two scenarios without EES. For the four scenarios where selling electricity to grid is forbidden, the two scenarios with EES can provide feasible solutions while the others fail. The two scenarios with EES achieve 72.1202% and 80.5804% total growths, respectively, for the separate production scenarios. • This paper studies dispatch of combined cooling, heating, and power (CCHP) system. • The cooling, thermal and electrical energy storages are integrated into the CCHP system. • Eight scenarios are investigated to improve the energy utilization efficiency of CCHP. • A non-dominated sorting genetic approach using elite crossover is presented for CCHP. • The scenarios with electrical energy storages achieve relatively high total growths. [ABSTRACT FROM AUTHOR]

In the traditional combined cooling, heating, and power (CCHP) systems, the frequently changed user loads result in unfavorable supply-demand matching characteristics, which weakens the practical operational regulation performance. In this work, the thermochemical recuperation (TCR) with syngas storage method is proposed to optimize the system regulation characteristics and enhance the waste heat recovery. Various building energy load scenarios are also adopted to comprehensively evaluate the modified CCHP system operation characterizes. Meanwhile, with the consideration of reasonable operation regulation of syngas storage and multi-energy demands supplementary between different buildings, the coordinated system energy scheduling capacity are deeply explored to investigate the practical system application feasibility. The results indicate that under the designated operating conditions, the cooling/heating-to-power output ratios have been adjusted from 2.45 and 2.73 to 0.24–2.55 and 0.64–2.85, respectively. Additionally, with the efficient operation regulation process of TCR and syngas storage, the annual average energy utilization efficiency of the hotel, hospital, office and shopping center will be increased by 3.88%, 3.85%, 4.50% and 3.98%. Besides, through the synergistic complementary of syngas storage and adjustment between shopping center and hospital, the annual average syngas storage utilization rate of the shopping center can be increased from 16.99% to 97.41%, with the annual fuel consumption reduction of 5.78% in hospital scenario. This paper provides a combined TCR and syngas storage regulation method for the CCHP system, which enhances the system energy output flexibility and waste heat recovery capabilities in the distributed energy system application. • A coupling method of thermochemical recuperation and syngas storage is proposed. • The off-design condition thermodynamic model of the system is established. • The dynamic operation of the system in the long-term regulation process are analyzed. • The characteristics of syngas storage complementary coordination capability is explored. [ABSTRACT FROM AUTHOR]

To better make use of the waste heat in distributed data centers, a new design of integrated waste heat recovery system that can meet different needs including heating for users and data center cooling is introduced. The system can switch among different operation modes including waste heat recovery mode, natural cooling mode, composite cooling mode and refrigeration mode based on the ambient temperature. The integrated waste heat recovery system is experimented in the enthalpy-difference laboratory, and the experimental results show well consistency compared with the modeling results. The operation strategies to switch among different modes are determined based on the experimental and modeling results. The paper introduced PUE (Power Usage Effectiveness) and ERE (Energy Reuse effectiveness) to comprehensively evaluate the cooling and energy reutilization effectiveness of the system. According to the evaluation result, the integrated waste heat recovery system has well performed energy effectiveness, environmental and economic effect. The ERE values of using the integrated waste heat recovery system in Chinese typical climate cities including Harbin, Beijing, Xi'an, Shanghai and Guangzhou are 0.87, 1.02, 1.04, 1.17 and 1.29 respectively. Using this system at 96 kW distributed data center instead of CRAC (computer room air conditioning) system can save 152.7 MWh electricity, 56.4 tons of standard coal, and 244.7 tons of CO 2 emission in Beijing annually. The payback periods of this new system in different climate regions in China are all within 3 years. • An integrated data center cooling and waste heat recovery system is proposed. • Operation performance of the system is verified by experiment and modeling. • Energy Reuse Factor in Beijing is 1.02, and payback period is within 3 years. [ABSTRACT FROM AUTHOR]

In this paper, one MOEA/D variant using two crossover strategies (MOEA/D-TCS) and two constraint handling methods are proposed to deal with four combined cooling, heating, and power (CCHP) scenarios in summer and winter. MOEA/D-TCS maintains a balance between global search and local search by combining a modified spiral updating position of whale optimization algorithm and the simulated binary crossover of genetic algorithm, and it is able to obtain a wide and even Pareto set for each CCHP scenario. The two constraint handling methods enable infeasible solutions to get rid of infeasible regions over a short period of time, guaranteeing that the reserved solutions of MOEA/D-TCS satisfy all constraints. Experimental results show that each CCHP scenario with the battery has lower energy consumption, operation cost and carbon dioxide emission than the corresponding CCHP scenario without the battery, and hence the battery is helpful to the improvements of the flexibilities and efficiencies of energy cascade utilization for the CCHP systems in summer and winter. Also, MOEA/D-TCS performs better than the other seven multi-objective evolutionary algorithms and achieves larger hypervolumes and coverage rates for four CCHP scenarios. • The optimal dispatch of combined cooling, heating, and power is studied. • The battery is added to the combined cooling, heating, and power system. • A MOEA/D with two crossover strategies is presented for OD-CCHP. • The scenarios with the battery achieve small objective function values. • The improved MOEA/D outperforms the other methods for four OD-CCHPs. [ABSTRACT FROM AUTHOR]

Schematic illustration of the double-layer PDRC coating. [Display omitted] • The idea of introducing masking layer for double-layer PDRC coating is proposed. • PDRC coating achieves high solar reflectivity (94.0%) at a thin thickness. • The PDRC coating reduces the indoor temperature of container room by 5.0 °C. • The prepared PDRC coating can realize large-scale long-time outdoor applications. The realization of spontaneous sub-ambient cooling in daytime typically requires the solar reflectance and thermal emittance of passive daytime radiative cooling (PDRC) material to be > 90%. Toward real-world applications, however, to achieve high optical performance and excellent durability, PDRC coating is often cost-prohibitive due to its high thickness (500 μm or higher). To solve the contradiction between high optical performance and thin thickness of PDRC coating, the idea of introducing masking layer for PDRC coating is proposed in this paper to prepare the water-based double-layer PDRC coating and explore its long-term outdoor application potential. The PDRC coating can achieve high solar reflectance (94.0%) and "atmospheric transparent spectrum window" emittance (93.0%), while the thickness and cost are only 40% and 60% of existing water-based PDRC coating. The PDRC coating shows efficient cooling performance when applied as the external coating of large temporary buildings, with maximum temperature reduction of 20.8 °C and 5.0 °C on the roof/indoor, which are equal to or greater than recorded values. The 150-day large-scale outdoor application shows that the coating has excellent durability, which offers a reference for the long-term outdoor application of PDRC coating. The application of the PDRC coating on rooftops of containers can achieve a cooling energy savings of up to 15.3% compared to conventional steel roofs, translating to an annual energy savings of 413.2 MJ and a reduction of approximately 114 kg in carbon dioxide emissions, which provide compelling evidence for the ability of PDRC coating to mitigate carbon emissions and address global climate change. [ABSTRACT FROM AUTHOR]

An effective quantification of the energy absorbed and supplied by latent heat thermal energy storage (LHTES) units is critical to maximise their use within thermal systems. An effective control of the charging and discharging processes of these units demands an accurate estimation of the state-of-charge (SoC). However, a direct and reliable SoC estimation requires incorporating internal sensors to monitor the temperature gradient of the phase change material (i.e. the storage medium), resulting in higher instrumentation costs and technical specifications. These issues may be relieved by adopting state observers for SoC estimation to drastically reduce the number of measurements. This paper bridges this gap by presenting a novel and direct method for estimating the SoC of LHTES units, both for heating and cooling applications, based on a non-linear state observer. The observer is based on a simple one-dimensional dynamic model of the thermal store and the thermophysical properties of the storage medium and the heat transfer fluid, which are usually provided by manufacturers. This enables the estimation of the internal temperatures of the LHTES unit and, in turn, SoC calculation. The observer implementation is simple as it requires three measurements only as input variables (i.e. the mass flow rate and the input and output temperatures of the heat transfer fluid). The SoC estimation approach is assessed through dynamic simulations of two LHTES units: one for a heating application and one for a cooling application. The results show that the SoC can be estimated with root mean square and mean absolute errors of less than 4.6% and 3.62%, respectively, compared with experimental measurements. • The specific latent heat value of phase change materials is dynamically modelled using probability density functions. • A non-linear observer estimates the temperature of a phase change material in thermal energy storage units. • The state-of-charge of latent heat thermal energy storage units is calculated using the observer outputs. • A calculation method of the state-of-charge is proposed to reduce the computation time. • Implementation and verification of non-linear observers and state-of-charge calculation method is performed using MATLAB. [ABSTRACT FROM AUTHOR]

• A resonance tube-coupled FPS-CCP system is proposed. • A novel time-domain unsteady model of the FPS-CCP system is developed and verified. • Evolvement of onset process is successfully achieved. • A cooling capacity of 1000 W at 110 K and electric power of 800 W with a global exergy efficiency of 29.4% is obtained. This paper proposes a novel resonance tube-coupled free-piston Stirling engine-based combined cooling and power (FPS-CCP) system for future application in scavenging unconventional natural gas from coal mines and oil fields. Unlike the traditional duplex Stirling system, the proposed system employs a resonance tube to couple an engine and a cryocooler. In addition, a linear alternator is introduced to facilitate startup and meet multiple demands, resulting in flexible adjustments and even higher exergy efficiency. A novel time-domain unsteady model based on thermoacoustic theory was developed to investigate the onset behavior of the (FPS-CCP) system. The proposed model successfully predicted the onset temperature and onset frequency. Results indicated that within the calculation range, the resonance tube with either a larger diameter or a shorter length leads to a lower onset temperature. Furthermore, the system performance under the steady-oscillating state was studied in terms of the typical operation characteristics and energy flow distribution. When the heating temperature is 833 Kand the mean pressure of helium gas is 5 MPa, the proposed system can provide a cooling capacity of 1000 W at 110 K and an electric power of 800 W with a global exergy efficiency of 29.4%, demonstrating an efficient power matching among the subsystems. [ABSTRACT FROM AUTHOR]

• A multi-energy absorption system is proposed for combined cooling and heating. • Multiple sets of indoor terminals are driven by a single set of absorption machine. • Annual operating cost for a typical household is reduced by 25.5–46.8%. • Carbon reduction ratio reaches 41–44% compared with traditional methods. • Annual carbon emission per household for cooling and heating reduces below 3000 kg. Under the background of carbon neutrality, efficient and low-carbon cooling and heating in rural areas away from the centralized network is a meaningful topic. In this paper, a multi-energy complementary absorption system is proposed to provide space heating in winter and cooling in summer. The system utilizes renewable energy that is abundant in rural areas, including solar and biomass, and balances the energy supply through natural gas replenishment. By adopting the cooling/heating medium circulation, multiple sets of indoor terminals are driven by a single set of absorption machine and outdoor unit. It is found that as long as the renewable energy ratio is higher than 0.2, the economic performance of the proposed system will be outstanding over the existing methods. When applied in Beijing, the annual operating cost for a typical household is reduced by 25.5–46.8% compared with traditional gas furnace/compression heat pump combined with air conditioner. Moreover, even when the proposed system is driven solely by natural gas, the carbon emission is reduced by 16–20% compared with traditional methods. When the renewable energy ratio is 0.4, the carbon reduction ratio reaches 41–44%, and the annual carbon emission for cooling and heating of a typical household reduces below 3000 kg. It is expected that by solving the problem of load and concentration variation during the year-round operation, the proposed system has great application potential in cold winter and hot summer areas away from the centralized cooling or heating network. [ABSTRACT FROM AUTHOR]

• An operation strategy based on energy complementarity was proposed for interactive CCHP system. • The heat to power ratios of three typical load demand were analyzed and abstracted. • The interactive operation strategy shows better performance in all cases. • The interaction mechanism between different CCHP systems was analyzed. • The impact of the third user was investigated to extend the operation strategy in multi-users. The interactive operation of multiple combined cooling, heating, and power (CCHP) systems can improve the performance of regional integrated energy systems by exploiting the spatiotemporal complementarity of loads. The interaction of various energy networks in the interactive combined cooling, heating, and power (ICCHP) system introduces new challenges to the optimization of the operation strategy. An interactive operation strategy based on the energy complementarity characteristics of the following electric load, following thermal load, and following hybrid electric–heating load operation strategies is proposed in this paper. To investigate the interaction effect on the system performance and the effect mechanisms when it operates interactively between different users, the load heat-to-power ratio of users was first classified and abstracted. Then, the performances of the ICCHP between two users with different loads and between two users with the same loads are analyzed separately. Finally, the effect of a third user was investigated to expand the application of the interactive operating strategy to the multi-user mode. The results showed that the interaction between CCHP systems with different loads can make use of the complementarity between different loads and the energy complementarity of operation strategies, which greatly improves the performance of the ICCHP system. CCHP systems with the same loads can only rely on the energy complementarity of the operation strategies, leading to less improvement in performance. In addition, the performance of the ICCHP system will be significantly improved in the three-CCHP interactive mode if the performance of the third building is higher in independent operation. [ABSTRACT FROM AUTHOR]

• A novel strategy to ensure flexibility of hybrid CCHP system is proposed. • A new indicator is developed to assess the flexibility of CCHP system. • A collaborative optimization model of system design and operation is constructed. • Flexibility reserve actively defenses uncertain external conditions. • The grid interaction and underused fuel are reduced up to 99% and 84%, respectively. Flexible combined cooling, heating and power (CCHP) systems actively resist the variable factors from both sides of load and renewable energies. In order to fully utilize the flexibility potential of the CCHP system, this paper divides the system with the energy supply process in an analytical viewpoint of flexibility and proposes a novel operational strategy of following system flexibility to schedule energy dispatch. An indicator called flexibility index is proposed and employed to evaluate the flexibility of CCHP system, which comprehensively reflects system design and operational performance. The flexibility index assesses the contribution of energy storage devices in reducing the underutilized fuel consumption and decreasing grid dependence. A multi-objective optimization model is constructed to improve the economic performance and flexibility of the CCHP system. The results in a case study demonstrate the proposed strategy can use flexibility components to cover 93.75% and 99.31% of load scenarios in cooling and heating seasons, respectively. Compared with traditional strategies of following electric load and following thermal load, the proposed method reduces the dependence on the electric grid by 98.04% and 99.61%, respectively, and declines the underused fuel consumption by 79.79% and 84.05%, respectively. The carbon emissions because of the efficient energy management are reduced by 8.30% and 21.30%, respectively. [ABSTRACT FROM AUTHOR]