Combined Cooling, Heating And Power System Research Articles

Demand flexibility and its impact on a PEM fuel cell-based integrated energy supply system with humidity control

The development of efficient energy systems and renewable alternative energy sources has attracted substantial attention owing to the rise in environmental deterioration and energy usage. A combined cooling, heating, and power (CCHP) system can fully use different types of energy with low emissions and offers a viable solution to address these issues. Demand flexibility is a key issue in collaborating with different types of supplies and demands for optimal system operation. In this study, a proton-exchange membrane fuel cell driven CCHP system with humidity control is proposed to fully investigate the impact of demand flexibility on system operation. A novel flexible load regulation strategy was designed for the proposed system. The results show that flexible load regulation can reduce the thermal storage capacity by 25%. Supplement heating and cooling do not need operate in winter and summer. With flexible regulation, the heating load can be reduced by 15.69% in winter, and the cooling and dehumidification loads can be reduced by 30.71% and 6.09% in summer. The reductions in hydrogen consumption can reach 1.98% and 7.51% during winter and summer. The proposed method can simultaneously increase the exergy efficiency and reduce carbon emission, as well as the economy cost.

Exergy, exergoeconomic, and exergoenvironmental analyses of novel solar- and biomass-driven trigeneration system integrated with organic Rankine cycle

This study proposes a combined cooling, heating, and power (CCHP) system driven by biomass and solar energy integrated with an organic Rankine cycle (ORC). Its exergy, exergoeconomic, and exergoenvironmental performances are investigated. First, the thermodynamic parameters of each material and energy flow for the proposed CCHP system are simulated using Aspen Plus. Second, the exergy and exergoeconomic performances of the system are investigated, and an exergoenvironmental analysis of the system is performed. The results show that the unit exergy costs (UEC) of domestic hot water, electricity generated by an internal combustion engine (ICE) and the ORC, and chilled/heated water under summer/winter conditions are 2.742/2.742, 6.713/6.629, 12.930/12.930, and 27.100/12.530 MW/MW, respectively, with corresponding unit exergoeconomic costs (UEEC) of 41.11/41.11, 124.40/139.20, 181.80/181.80, and 507.10/302.60 USD/MWh, respectively. Meanwhile, the corresponding environmental impact rates per exergy unit are 0.616/0.616, 2.988/3.023, 0.030/0.030, and 6.567/3.072 mPts/MJ, respectively. The results highlight the urgency to prioritize improvements to the solar collector performance to reduce the UEC of electricity generated by the ORC. The absorption chiller/heater, heat exchanger, and ICE exhibit significant potential for enhancing their exergoeconomic performance. Additionally, the gasifier, ICE, and ORC can be optimized to mitigate their environmental impact with relatively minimal exertion.

Novel design of a CCHP system to boost nearly zero-carbon building concept

The accumulation of carbon dioxide in the atmosphere is responsible for global warming. To address this issue, this study develops and optimizes a novel and economically viable combined cooling, heating, and power (CCHP) system for an educational building with minimal CO2 emissions. The main components of the system include a gas turbine cycle, a molten carbonate fuel cell, a heating system, an electric chiller, and an absorption chiller. Optimization is conducted based on a 4E (energy, exergy, economic, and environmental) analysis using TRNSYS and MATLAB software. The optimized CCHP system has a unit product cost of $52.44/h with an overall exergy efficiency of 44.34 %, generating 0.39 kg of CO2/kWh. Furthermore, the objective of a nearly zero-carbon system is achieved by integrating carbon capture and storage (CCS) into the original CCHP system. A novel cryogenic carbon capture unit is implemented to capture CO2 from the flue gas. Integrating CCS reduces CO2 emissions by up to 91 %, presenting a cost-effective approach to carbon offset. Although there is a modest increase in operational costs ($53.46/h) and a slight decrease in exergy efficiency (43.3 %), these trade-offs are necessary to attain an environmentally responsible system. Overall, the optimized CCHP system with the integrated CCS shows potential as an energy-efficient solution for the selected educational building while reducing CO2 emissions.

A highly efficient, low-carbon CCHP system and its comprehensive optimization for an integrated medical and nursing complex

As the global population ages, the demands imposed by medical treatment and care for the elderly are becoming increasingly pressing. To reduce energy consumption and systemic defects in the process of integrating medical treatment and care for the elderly, the authors of this study designed a highly efficient, flexible and low-carbon combined cooling, heating, and power (CCHP) system for the integration of medical and nursing complexes by using a multi-level model of optimization. The complex was modeled in DeST software to obtain the cooling and heating loads, and the general algebraic modeling system software and mixed-integer linear programming (MILP) were used for the collaborative optimization of the choice of equipment, capacity allocation, and operational strategy. The results showed that the proposed system could reduce the total consumption of electric power by 40.95 % when a semiconductor wall was installed on floors 8–12 of the complex for elderly care. The energy management strategy of the system was also optimized by using the vehicle-to-building subsystem in a novel wind–solar–storage and heat pump-based combined cooling, heating, and power system. The rates of reduction in emissions of CO2 and NOx, and the rate of reduction in primary energy consumption of the Wind–Solar–Storage and Heat Pump (WSSH)–CCHP system were 96.5 %, 99.1 %, and 95.6 %, respectively. Finally, the heat pump-assisted liquid-gap membrane distillation (HP-LGMD) subsystem were optimized in MATLAB. The resulting gained output ratio, flux, thermal efficiency of the system, and energy consumed for water production were 0.0269, 4.22 kg/m2, 17.07 %, and 46.88 %, respectively. The proposed system is highly energy efficient, is capable of economical scheduling, and can use energy cascading, which provides guidance on sustainable development of environment and energy.

Control strategy design and performance analysis of a low carbon and high ratio green energy CCHP (LCHRG-CCHP) system

In order to solve the compatibility of combined cooling, heating and power (CCHP) system with green energy and the coupling problem with energy storage equipment, the system structure (LCHRG-CCHP system) proposed in this paper for the low-carbon and high-green energy compatible optimization research of the integrated energy system integrating green energy and flexible hybrid energy storage. Aiming at the high compatibility and low carbon emission of CCHP system to green energy, the traditional CCHP system, the combination of CCHP system and green energy, the combination of CCHP system and green energy and short-term energy storage, and the combination of CCHP system and green energy and long-term and short-term energy storage are compared. The intelligent optimization algorithm combining improved sine dung beetle optimizer and linear support vector machine algorithm (MDBO-LSVM) is used to solve the problem. The results show that in the CCHP system, the coupling of short-term energy storage and long-term energy storage can effectively improve the compatibility of the system with green energy. The proportion of green energy in the system proposed in this paper is increased by 13.32 %, which can reach an average of 23.91 %, while the carbon emissions are reduced by 37.34 %, which effectively improves the energy utilization rate.

Thermodynamic Analysis of a Cogeneration System Combined with Heat, Cold, and Electricity Based on the Supercritical CO2 Power Cycle

The supercritical CO2 power cycle driven by solar as a new generation of solar thermal power generation technology has drawn significant attention worldwide. In this paper, a cogeneration system derived from a supercritical CO2 recompression Brayton cycle is proposed, by considering the recovery of waste heat from the turbine outlet. The absorption refrigeration cycle is powered by the medium-temperature waste heat from the turbine outlet, while the low-temperature waste heat is employed for heating, achieving the cascaded utilization of the heat from the turbine outlet. As for the proposed combined cooling, heating, and power (CCHP) system, a dynamic model was built and verified in MATLAB R2021b/Simulink. Under design conditions, values for the energy utilization factor (EUF) and exergy efficiency of the cogeneration system were obtained. Moreover, the thermodynamic performances of the system were investigated in variable cooling/heating load and irradiation conditions. Compared with the reference system, it is indicated that the energy utilization factor (EUF) and exergy efficiency are 84.7% and 64.8%, which are improved by 11.5% and 10.3%. The proposed supercritical CO2 CCHP system offers an effective solution for the efficient utilization of solar energy.

Thermodynamic analysis of a CCHP system with hydrogen production process by methane reforming enhanced by solar-assisted chemical looping adsorption

Combined cooling, heating and power (CCHP) systems integrated with renewable energy can greatly alleviate the fossil energy crisis and greenhouse effect. This work proposes a novel CCHP system, which consists of a solar-assisted sorption enhanced chemical looping steam methane reforming (SE-CL-SMR) hydrogen generation subsystem, a solid oxide fuel cell-gas turbine (SOFC-GT) subsystem, a dual-effect Li-Br absorption chiller/heat pump (DAC/H) subsystem, and a domestic hot water (DHW) subsystem. The impacts of the reformer temperature, pressure, the ratios of steam to carbon, calcium oxide to carbon, and nickel oxide to calcium oxide on the system’s methane conversion rate, hydrogen yield, hydrogen purity, and CO2 capture efficiency are also explored. While ensuring the hydrogen production effect and considering the lowest energy consumption, the optimal reforming temperature, reforming pressure, ratios of S/C, CaO/CH4 and NiO/CaO of the CCHP system are 560 °C, 1 atm, 3, 1 and 0.5, respectively. The system’s energy and exergy analysis is performed under the optimized operating condition. In comparison with the data of reference, the findings demonstrate that the system’s overall power generation efficiency is 53.23 %, the total energy utilization rate is 74.32 %, and the exergy efficiency is 52.87 %.

Thermo-economic analysis of an integrated combined heating, cooling, and power unit with dish collector and organic Rankine cycle

In recent years, the integration of renewable resources into simultaneous production systems has resulted in a substantial reduction in fuel consumption when compared to the conventional methods. This study focuses on the design and modeling of a CCHP (combined cooling, heating, and power) system for the campus of Faculty of New Sciences and Technologies, University of Tehran. The system harnesses the primary energy and heat derived from a dish collector and natural gas, while electricity generation is facilitated by a Brayton cycle. Additionally, two organic Rankine cycles recover the waste heat and generate supplementary electricity downstream of the system. The total efficiency of this system attained 79%, and the total exergy efficiency of the CCHP reached 48%. When examining the economic sector, noteworthy savings can be observed, compared to a centralized power generation system. This can be attributed to a 37% reduction in fuel consumption, resulting from the adoption of the dish collector as the primary supplier. Overall, this is a novel setup that involves two stages of ORC, along with a dish collector and combustion chamber that supply the microturbine. The proposed system in this article could be a guide for novel commercial and residential systems in the future.

Comprehensive performance assessment of a novel biomass-based CCHP system integrated with SOFC and HT-PEMFC

The combination of biomass gasification and fuel cell is a promising way to enhance the system energy efficiency and decrease the fossil fuel consumption. In this study, a new biomass-based combined cooling, heating and power (CCHP) system considering high temperature proton exchange membrane fuel cell (HT-PEMFC) and solid oxide fuel cell (SOFC) is proposed. Syngas from biomass gasifier is utilized by SOFC and HT-PEMFC for power generation, waste heat derived from SOFC and HT-PEMFC are recovered by ORC and absorption chiller for electricity and cooling production, respectively. Energetic, exergetic, economic and environmental investigations are performed to illustrate system comprehensive performances. The results demonstrated that power generation ratio of SOFC to HT-PEMFC is 2.32, exergy and energy efficiency of CCHP system are 25.06% and 49.48%, respectively. Levelized cost of production and CO2 emission rate of multi-products are 0.069$/(kW·h) and 0.673kg/(kW·h), respectively. Moreover, steam to biomass ratio and equivalent ratio show different effects on system performances due to the distinction of syngas composition. Operating temperature of SOFC has a great influence on system exergy and energy efficiency, with increasing by 11.18% and 16.97% respectively. In general, this novel system provides a new pathway for integrating biomass with different fuel cell technologies.

Multi-objective optimization and evaluation of hybrid combined cooling, heating and power system considering thermal energy storage

Introducing thermal energy storage (TES) and solar energy effectively reduces fossil fuel consumption and greenhouse gas emissions in combined cooling, heating, and power (CCHP) systems. This study establishes a two-layer optimization framework to obtain the optimal configuration of the CCHP system coupling solar and thermal energy storage. The outer layer uses component sizes as decision variables to optimize the system's annual economic economy, annual carbon dioxide emissions, and annual primary energy consumption; the inner layer uses equipment output as decision variables to optimize the operation and maintenance costs. Firstly, the representative typical scenes were obtained using the k-means algorithm to reduce the computational complexity. Then, the multi-objective chaos optimization (MOCGO) algorithm is combined with mixed-integer linear programming (MILP) to obtain the established optimization model's configuration scheme and optimal operating strategy. TOPSIS is to rank the best Pareto solutions. Finally, a large hotel is a case study. The optimization results indicate that the proposed two-layer optimization model can achieve the optimal configuration scheme and scheduling strategy for hybrid CCHP. Compared to the rule-based multi-objective one-layer optimization model, the proposed two-layer optimization model can achieve maximum improvements of 30.63 %, 37.94 %, and 38.16 % in economic, energy, and environmental performance. Compared with the rule-based single-objective one-layer optimization model, the proposed two-layer optimization model can achieve maximum improvements of 34.95 %, 35.81 %, and 37.55 % in economic, energy, and environmental performance, respectively. In addition, TES can substantially increase the optimal performance of the two-layer optimization model.

Performance analysis and application of a novel combined cooling, heating and power system integrated with multi-energy storage system

The dynamic fluctuations of user energy demand places the combined cooling, heating and power (CCHP) system in a perpetual state of off-design operation, leading to significant performance deterioration. Integrating an energy storage system with the CCHP system is an effective approach to this issue. However, conventional methods often segregate the storage of cooling load, heating load and power of CCHP system, limiting their conversion and resulting in suboptimal utilization and low efficiency. Therefore, this study proposes a novel CCHP system integrated with multi-energy storage system, allowing flexible release cooling load, heating load and power to meet diverse user load profiles. Mathematical modeling, thermodynamic analysis and environmental assessment are conducted. The case study demonstrates that the proposed system surpasses the conventional CCHP system in exergy efficiency ηex, primary energy rate PER, primary energy saving ratio PESR, carbon dioxide emission reduction ratio CDERR and cost saving ratio CSR of the proposed system increase by 3.1 %, 13.6 %, 9.0 %, 6.2 % and 8.4 %, respectively. The proposed system effectively balances user energy demand and energy supplied by the CCHP system, efficient utilization of diverse energies, significantly enhancing off-design performance, and yielding high efficiency, energy saving, and reduced carbon emissions.

Exergy and exergoeconomic analyses of multi-energy complementary system based on different natural gas and biogas co-firing ratios considering carbon tax

This study analyzes the exergy and exergoeconomic performances of a combined cooling, heating, and power (CCHP) system powered by natural gas and biogas. First, the exergy of the energy and material flows in the investigated co-firing CCHP system is obtained. In addition, the exergy loss and exergy loss distribution ratios of each component as well as the exergy efficiency of the entire system are investigated. Furthermore, the effects of the co-firing ratio of natural gas and biogas on the exergy and exergoeconomic performances are analyzed. Meanwhile, a carbon tax is considered in the exergoeconomic analysis. The results show that the gasifier, two-stage LiBr-H2O absorption chiller, and internal combustion engine indicate the largest exergy loss and exergy loss distribution ratios under different co-firing ratios. The exergy efficiency of the entire system decreases by 3.81% and 4.93% as the co-firing ratio decreases from 1:1–1:10 (natural gas: biogas) in the summer and winter, respectively. The unit exergoeconomic cost (UEC) of multiple products decrease with the co-firing ratio. Finally, a sensitivity analysis is performed to reveal the effects of the co-firing ratio and natural gas price on the UEC of multiple products.

Intelligent day-ahead optimization scheduling for multi-energy systems

Concerning energy waste and rational use, this paper studies the optimal scheduling of day-ahead energy supply and the community’s demand with a combined cooling, heating, and power (CCHP) system in summer. From the perspective of bilateral costs and renewable energy use, this paper examines the impact of energy storage systems integrated into cogeneration systems. The Gurobi solver is used to optimize the residential community’s supply and demand sides of the traditional CCHP system (T-CCHP) and the CCHP system with energy storage (CCHP-ESS) under insufficient solar power. Subsequently, two optimal arrangements for energy consumption on the user side under these systems are suggested. In the optimization model, energy storage is added to the T-CCHP system on the energy supply side. On the user side, the energy use scheme is optimized considering the user’s comfort. The innovation point of this study is that the optimization of comprehensive energy in the park involves both supply and demand. The impact of increasing energy storage is discussed on the energy supply side, and the impact of optimization of the energy use plan on costs is discussed on the user side.

Bargaining‐based energy sharing framework for multiple CCHP systems with a shared energy storage provider

AbstractIn the present day, when centralized energy storage technology is becoming increasingly mature, the cooperative energy sharing framework between the combined cooling, heating, and power (CCHP) systems and a shared energy storage provider (SESP) can effectively promote the local consumption of renewable energy and reduce the social energy cost. In this study, the optimal operation models of CCHP and SESP are first developed by considering the electric energy trading of the CCHP and the SESP. Then the CCHP–SESP cooperative operation model is established based on Nash bargaining theory, followed by equating it into two subproblems of coalition social energy cost minimization and electric energy trading payment negotiation. The alternating direction method of multipliers approach is introduced to solve the energy‐sharing problems in a distributed way. Numerical simulation results show the effectiveness of the proposed energy‐sharing framework. Simulation results show that the proposed bargaining‐based energy‐sharing framework can significantly reduce the social energy cost and improve the utilization rate of energy storage resources.

Design and analysis of solar hybrid combined cooling, heating and power system: A bi-level optimization model

The planning and operation optimization of hybrid combined cooling, heating and power (CCHP) systems is the prerequisite and foundation for its advantages such as economy, energy saving, and high efficiency. This study constructed a bi-level optimization model of a hybrid CCHP system. Firstly, an upper-level capacity planning model of the hybrid CCHP system is constructed considering system economy, energy, and environmental performance. Secondly, a lower-level operation optimization model is proposed, considering the operation and maintenance cost of the system. Thirdly, a multi-objective honey badger algorithm (MOHBA) is developed based on the characteristics of the studied problem and the features of the bi-level optimization model. Finally, the optimization results indicate that the hybrid CCHP can save 32.79 % of the total cost, 49.74 % of primary energy, and 60.18 % of carbon emissions compared to the separation production (SP) system. In addition, compared with improving the strength Pareto evolutionary algorithm (SPEA2), non-dominated sorting genetic algorithm-II (NSGA-II), multi-objective evolutionary algorithm based on decomposition (MOEAD), and multi-objective particle swarm optimization (MOPSO), the proposed MOHBA can provide superior optimization results. The proposed bi-level planning model achieves improved economic, energy, and environmental performance of the hybrid CCHP system compared to the single-level planning model for the given operation modes.

Evaluating the efficiency of CCHP systems in Xinjiang Uygur Autonomous Region: An optimal strategy based on improved mother optimization algorithm

A novel approach is presented in this research to improve the design of a combined cooling, heating, and power (CCHP) system. The focus of the study is on a gas turbine system that can provide efficient power, cooling, and heating. The efficacy of the proposed technique is evaluated based on four parameters, namely energetic, exergetic, economic, and environmental features. To achieve superior and optimal results, an Improved Mother Optimization Algorithm (IMOA), a recently developed metaheuristic algorithm, is employed. This study provides a comprehensive guide for enhancing the performance, efficiency, and sustainability of CCHP systems. A practical case study was conducted to evaluate the proposed methodology in rural areas of Xinjiang Uygur Autonomous Region, China, over a period of one year. The simulation results reveal that the Gas Engine (GE) and the boiler components play a significant role in utilizing fuel energy, contributing 65 % and 35 %, respectively to the overall utilization. The analysis of the destruction rate of profile highlights that heat dissipation, mechanical losses, and electrical losses are the primary sources of energy losses within the system. When comparing the proposed IMOA with existing techniques, it is evident that the IMOA achieves a noteworthy 10 % reduction in energy consumption and a remarkable 15 % increase in overall efficiency of system. Furthermore, in terms of environmental impact, the IMOA leads to a substantial 20 % reduction in carbon dioxide (CO2) emissions compared to traditional optimization methods. The economic analysis results demonstrate that the IMOA-based approach not only improves cost-effectiveness by 25 %, but also yields an estimated return on investment (ROI) that is 18 % higher than alternative optimization techniques. Moreover, the proposed method with minimum fuel usage of 0.200 L/h, compared with Improved Butterfly Optimizer (IBO) with 0.201 L/h, Modified Mayfly (MM) algorithm with 0.205 L/h, Developed Owl Search (DOS) algorithm with 0.211 L/h, and Improved Owl Search (IOS) algorithm methods with 0.207 L/h, provides better results.

Optimizing cooling, heating, and power systems for PEMFC using a multi-objective optimization

Combined cooling, heating, and power (CCHP) systems are attractive solutions for providing multiple energy services from a single fuel source. However, designing and operating CCHP systems optimally is challenging due to the complex thermodynamic and economic interactions among the system components. Multi-objective optimization is a powerful technique to find the best trade-off solutions among conflicting objectives. In this paper, an improved version of the World Cup Optimizer (IWCO), a metaheuristic algorithm inspired by the soccer tournament, has been proposed to solve the multi-objective optimization problem of a CCHP system. The IWCO algorithm enhances the exploration and exploitation capabilities of the original WCO algorithm by introducing a new selection mechanism and a new mutation operator. The performance of the IWCO algorithm has been validated by comparing it with other well-known multi-objective optimization algorithms on several benchmark functions. The results show that the IWCO algorithm outperforms the other algorithms in terms of convergence rate and solution quality. We then apply the IWCO algorithm to optimize a CCHP system with three objectives: minimizing the total annual cost, minimizing the total greenhouse gas emissions, and maximizing the system efficiency. The CCHP system consists of a fuel cell, a micro gas turbine, and an absorption chiller. A Pareto front is used to represent the optimal trade-off solutions among the three objectives. The results show that the IWCO algorithm can provide a variety of Pareto-optimal solutions, which can help decision-makers in designing and operating CCHP systems. The results indicate that the IWCOA produces the most favorable optimization outcomes, achieving energy efficiency rates of 78.7 % and a maximum annual reduction of greenhouse gas emissions totaling 5.2e7 g. Additionally, it manages to decrease the yearly cost to 4.139e3 $. These findings provide a valuable means of assessing the effectiveness of different fuel cell technologies based on their operational characteristics. They underscored the considerable potential of the IWCOA in improving the operational efficiency and environmental footprint of CCHP systems, thus making significant contributions to the progress of sustainable energy technology.

Economic, energy and environmental analysis and evaluation of hybrid CCHP system considering different buildings: A two-level optimization model

Combined cooling, heating and power (CCHP) integrated energy systems can realize the gradient utilization of energy and the coordination and complementarity of multiple energy sources, which is the primary choice for solving the energy crisis and alleviating the environmental pressure. However, most current design and operational optimizations for CCHP are performed under rule-based operational strategies. This paper constructs a two-level alternating optimization framework for the planning-operation of the CCHP system with an embedded scheduling strategy. The upper-level solves for the optimal capacity configuration of the system to optimize energy, economic and environmental performance, and the lower-level solves for the operating capacity of the equipment system to optimize the operation and maintenance cost. In order to obtain the optimal configuration scheme and scheduling strategy for the system, a novel multi-objective weIghted meaN oF vectOrs (MOINFO)-mixed integer linear programming (MILP) method is proposed. The optimization results suggest that the hybrid CCHP for three buildings (market, office, and restaurant) under the two-level optimization model can achieve better economic, energy, and environmental performance than the rule-based single-level optimization model. Generally, for the market, office and restaurant, the two-Level model achieves maximum economic, energy and environmental performance improvements of 29.12%, 29.88%, and 42.13%; 38.32%, 19.56%, and 34.68%; and 47.37%, 30.93%, and 45.47%, respectively.

4E analysis and parameter study of a solar-thermochemical energy storage CCHP system

The combination of calcium looping and concentrating solar power (CSP) is a promising energy conversion technology that can greatly increase the share of solar energy used in combined cooling, heating and power (CCHP) systems. This paper designs a CCHP system based on solar energy and thermochemical energy storage. The system runs all day through day and night modes. Under basic working conditions, the energy and exergy efficiencies of the system could reach 56.92 % and 35.94 %, respectively. The system is evaluated by multiple approaches including parametric sensitivity analysis and 4E (energy, exergy, economy and environment)) analyses. The results demonstrate that the system could produce 2618.09 MW of electricity, 305.56 MW of heat and 523.88 MW of cooling capacity per day, respectively. At the same time, the reductions of CO2 emissions and fossil fuel consumption could reach 2222.76 tons and 696.41 m3 per day, respectively. Furthermore, the increasing mass flow of main turbine inlet could increase both the system efficiency and the exergy efficiency. Thus, it is beneficial to reduce the environmental impact but with the increasing investment cost. In the meanwhile, the exergoeconomic factor and exergoenvironment factor of the system were 55.65 % and 0.139, respectively. Besides, as the extraction flow rate of the intermediate pressure turbine increases, the energy efficiency increases but the exergy efficiency descends. This is unfavorable to reducing the environmental impact, yet it could decrease the investment cost of the system. These results reveal that the hybrid system has the characteristics of high efficiency and emission reduction in energy storage, power generation, heating and cooling, and has great development potential.

Innovative environmental impact index function to determine the optimal operating point of the trigeneration (CCHP) using landfill gas

In this paper, a numerical study of a combined cooling, heating, and power (CCHP) system and landfill is conducted simultaneously to increase the overall system efficiency and reduce the emission of some greenhouse gases such as methane and carbon dioxide emanating from solid waste landfills. A dimensionless function is defined to cover the demand growth for electricity, heating, and cooling in recent years. The variability of methane production in the landfills source during the period of operation, the growth of demands, and the optimal operating point of the CCHP system during thirty years from an energy, exergy, economic, and environmental (4E) perspective led to the use of genetic algorithms for determining optimal system parameters. For this purpose, the functions of exergy efficiency, total annual cost (TAC), and dimensionless function of environmental impacts are used. Optimization is performed as three-objective and two-objective without environmental function. The positive effect of dimensionless function in reducing environmental effects by 1.56 % and economic parameters by 1 % compared to two-objective optimization is shown by the results. The results of this study show that by using the defined functions, a power of 561 kW with an average exergy efficiency of 55.26 % can be generated during its service life and TAC of 2 billion/year $ by a landfill with a solid waste capacity of 900 ton/day.