Exergoeconomic Approach Research Articles

Energy, exergy and exergoeconomic analyses and ANN-based three-objective optimization of a supercritical CO2 recompression Brayton cycle driven by a high-temperature geothermal reservoir

The use of CO2-based power cycles to harness high-temperature geothermal resources is an interesting application that has been little explored. Therefore, to obtain a more holistic understanding of these systems, in this work, a supercritical CO2 recompression Brayton cycle is assessed. For comparison, the performances of a recuperative cycle and a recompression cycle with intercooling were also computed. Detailed mathematical models were developed and then, artificial neural network-based surrogate models were adopted to conduct multi-objective optimization. Results of the baseline simulations show that, the high temperature recuperator and the turbine are the most important components from both exergy and exergoeconomic approaches. The optimizations reveal that the intercooled cycle is superior to the other layouts in all the cases while the recuperative cycle is not feasible with reinjection temperatures greater or equal to 150 °C. When the reinjection temperature is constrained to 150 °C, the intercooled cycle attains 4472.70 kW, 62.10 % and 14.42 $/GJ for net power, exergy efficiency and product unit cost, respectively, whereas without this constraint, it achieves 5394.09 kW, 61.83 %, 11.79 $/GJ. In conclusion, the adoption of advanced layouts of the CO2 cycle is beneficial for this application from both technical and economic points of view.

Optimization and experimental study on the effect of graphite bars on the productivity of conical solar distiller: Exergo-economic approach

This work aims to enhance productivity and reduce the production cost of conical solar distillers using green and inexpensive materials. Conical solar stills are characterized by their cover is always exposed to the same solar radiation in all locations and do not create shading. Different graphite bars are installed at various distances in the still basin, acting as corrugated surfaces and energy storage materials to increase the interface area, reduce energy losses, and enhance the overall performance. Three conical stills were designed and tested to investigate the effect of changing the distances (0 to 30 mm) between the graphite rods on the production rate at the same climatic conditions of El Oued, Algeria. Furthermore, energy, exergy, economic, and exergoeconomic approaches were conducted to assess the viability of the proposed distillers. Results showed that reducing the distances between graphite bars increases the production rate due to the increased interfacial space with basin water and the storage of excess heat absorbed during the day. The energy and exergy efficiencies of the proposed conical solar distillers incorporated with graphite bars improved by 46.23–90.46 % and 181–321 % respectively, compared with the traditional conical still. Based on the exergo-economic approach, the annual energy and exergy outlets improved by 45.65–90.46 % and 187.5–439 % respectively, compared to the traditional conical still. The cost of the yield and payback period decreased by 40.41–74.91 % and 28.8–42.8 % respectively, compared to the traditional conical still. Finally, incorporated graphite rods with conical solar stills represent a good option for obtaining high performance with economic benefit.

Exergo-economic approach for comprehensive evaluation of the performance of industrial-scale milk and coffee beverage process lines

This study aimed to perform comprehensive analyses of the performance of the industrial-scale production of three different beverages (whole milk, black coffee, and milk coffee) in carton aseptic and glass bottle packaging process lines from raw material to the secondary packed final product by using innovative exergo-economic approach to promote a detailed data for a sustainable, performance-efficient production and economy in beverage industry. System performance efficiencies (energy and exergy) for the whole of production lines and individual processing steps were determined, and the exergo-economic performance of the industrial productions of three different beverages was compared. The maximum overall exergy efficiencies for glass bottle and carton aseptic packaging lines were as 52.57 % and 55.90 %, respectively, in whole milk production whereas the minimum overall exergy efficiencies were for these lines were 47.39 % and 48.67 %, respectively, for milk coffee production. For whole milk, the process steps having the minimum exergy efficiency were the filling step in carton aseptic (23.14 %±1.25) and the seperation step (26.90 %±1.09) in glass bottle packaging lines. For black coffee and milk coffee productions, the process step with the highest improvement potential was the homogenization/deaeration step for both carton aseptic and glass bottle packaging lines. The highest exergy destruction costs were obtained for the milk coffee; 72.52±0.03$/MJ for carton aseptic package and 63.82±1.85$/MJ for glass bottle. The most cost-efficient process was determined to be the black coffee in the carton aseptic packaging line due to the minimum product cost rate (89.71±2.39 $/MJ). It is thought that this study contributes valuable information on the approach of the comparing the performance of different production lines using exergo-economic evaluation.

Experimental optimization of conical solar distillers using graphite pin fins as sensible heat storage materials: Energy, exergy, and exergo-economic approach

Fresh water and energy are essential for the development and prosperity of societies. Solar stills are easy to build, operate, and maintain, but their disadvantage is low daily productivity. This work aims to optimize and enhance the performance of conical solar stills by integrating innovative graphite pin fins that function as extended surfaces and sensible energy storage in the distillation basin. Graphite is inexpensive, available locally, natural properties, and has good thermal characteristics and heat capacity. Four different alternates spacing between the graphite pin fins ranging from 10 to 70 mm have been investigated and optimized to achieve maximum daily water production. Three identical conical solar distillers were designed, manufactured, and tested, under the same weather conditions in El Oued city, Algeria (33.3676◦ N and 6.8516◦ E). Energy, economy, exergy, and exergo-economics approach were performed to evaluate the economic feasibility of modified conical distillers. The results showed that reducing the distance between the pin fins leads to a decrease in the productivity of the distiller due to the increase in the shadow area. Among the pin fin distances evaluated, the 50 mm distance achieved the highest daily water production with reasonable economic feasibility. Adding graphite pin fins to conical distiller basin increases daily productivity and thermal efficiency by 52.16–90.78% and 33.44–63%, respectively. The production cost and payback time of the modified conical distillers with pin fins are reduced by 35.49–79.72% and 35.48–79.72%, respectively compared to the traditional conical stiller.

Thermodynamic and economic performance comparison of biomass gasification oxy-fuel combustion power plant in different gasifying atmospheres using advanced exergy and exergoeconomic approach

Regarding the growing concern about carbon emission and environmental pollution, biomass has received extensive attention as renewable energy because of environmentally friendly and carbon-neutral. To enhance the utilization of biomass energy and reduce carbon emission, a biomass gasification oxy-fuel combustion power system is established. Advanced exergy and exergoeconomic analyses are applied to evaluate the system in different gasifying atmospheres of air, steam, and air/steam. The air, steam, and air/steam systems have exergy destruction of 155.9 MW, 163.2 MW, and 199.5 MW, and exergy efficiency of 43.47%, 49.48%, and 40.17%. The operating cost of the air, steam, and air/steam system is 305556.4 $/h, 393550.0 $/h, and 276284.8 $/h, and the annualized cost is 64.1 M$, 74.7 M$, and 63.9 M$, respectively. The thermodynamic improvement potential is 25.97% for the air system, 32.29% for the steam system, and 24.91% for the air/steam system. The avoidable cost ratios of the three systems are above 70%, suggesting a high cost-saving potential. The results reveal the effects of gasifying agents on the biomass gasification power system. Strategies are proposed for system improvement based on the advanced exergy and exergoeconomic analysis.

Thermodynamic and exergo-economic analyses and multi-objective optimization of an innovative and efficient geothermal-assisted power and hydrogen cogeneration system

This paper presents an efficient integration of a flash-binary geothermal system with a double-pressure Kalina cycle and a proton exchange membrane electrolyzer unit. The main objective is to generate power and hydrogen simultaneously. A comprehensive thermodynamic analysis is conducted, encompassing mass, energy, and exergy assessments, along with an exergo-economic approach, to thoroughly evaluate system performance. The operation of the system is examined under varying conditions, and trends in the assessment indexes are predicted accordingly. The designed system achieves notable results, producing 1018 kW of net power and 0.1119 kg/h of hydrogen. The thermal and exergetic efficiencies are found to be 14.34 % and 45.59 %, respectively, based on the thermodynamic approach. From an economic perspective, the payback period is estimated to be 2.51 years, while the sum unit cost of products is calculated at 8.94 $/GJ. Furthermore, a detailed exergy analysis highlights that the Kalina cycle's condenser contributes the most to exergy destruction, accounting for approximately 129.6 kW. Through a parametric study, it is revealed that the pressure of the production well significantly influences the performance indicators, and the price of electricity sold has a substantial impact on the system's payback period and net present value. Moreover, the application of a multi-objective optimization strategy leads to the identification of the system's optimal state through an exergo-economic assessment. This optimization yields an exergy efficiency of around 49.75 % and a sum unit cost of products of 8.56 $/GJ.

Thermo-economic assessment and optimization of a multigeneration system powered by geothermal and solar energy

A novel multigeneration system using dual renewable energy sources (i.e., geothermal and solar) is introduced, analyzed, and optimized. The integration of a geothermal line, a solar tower, a steam Rankine cycle, two organic Rankine cycles, an ejector refrigeration cycle, a thermoelectric generator unit, and a reverse osmosis subsystem forms the entire system. The outputs of this energy-conversion system are heating load, cooling load, electricity, and freshwater. Regarding methodology, the energy, exergy, and exergoeconomic approaches are implemented to assess the system from thermodynamic and economic viewpoints. Moreover, an optimization process based on exergy efficiency and the total unit cost of products is executed to determine the system’s optimal decision variables. The results obtained from the optimization process show that the proposed system is able to achieve 25.4% exergy efficiency and 34.1 $/GJ total unit cost of products, exhibiting 48% and 43% improvement compared to a base case study. Furthermore, the methodology is demonstrated on a case study where the system operates at its optimum condition in a specific location. Having monthly average values of direct normal irradiation for this spot, the average hourly performance of the system is evaluated for each month. Based on the obtained results, the minimum and maximum freshwater production rates are 3.06 kg/s and 3.84 kg/s, respectively. It can be estimated that a range of 1224 to 1536 individuals, varying from month to month, can receive the produced freshwater.

Application of nanomaterial based alkaline electrolyzer for hydrogen production in renewable energy-driven system: Multi-criteria assessment, environmental and exergoeconomic approaches

An alkaline electrolyzer is a traditional equipment to generate hydrogen. Improving the yield of electrolyzers has recently captured much attention. In this regard, the utilization of carbon-coated nanomaterial structures is a state-of-art method. On the other hand, considering the current crisis of fossil energies, the exploitation of renewables and green technologies is necessary and unavoidable. Additionally, the design and development of integrated energy systems with two or more output products and the maximum usage of thermal losses to enhance productivity can increase the flexibility and acceptability of the energy system. In this regard, the current paper develops a framework for the performance of a new solar and biomass energies-driven multigeneration system (MGS). The main units installed in MGS are three electric energy generation units based on a gas turbine process, a solid oxide fuel cell unit (SOFCU) and an organic Rankine cycle unit (ORCU), a biomass energy conversion unit to useful thermal energy, a seawater conversion unit into useable freshwater, a unit for converting water and electricity into hydrogen energy and oxygen gas via a nanomaterial-based alkaline electrolyzer, a unit for converting solar energy into useful thermal energy (based on Fresnel collector), and a cooling load generation unit. The planned MGS has a novel structure and layout that has not been considered by researchers in previous papers. The current article is based on presenting a multi-aspect evaluation in order to investigate thermodynamic-conceptual, environmental and exergoeconomic analyzes. The outcomes indicated that the planned MGS can produce about 6.31 MW of electrical power and 0.49 MW of thermal power. Furthermore, MGS is able to produce various products such as potable water (∼0.977 kg/s), cooling load (∼0.16 MW), hydrogen energy (∼1.578 g/s) and sanitary water (∼0.957 kg/s). The overall energy and exergy productivities were measured as 78.13% and 47.72%, respectively. Also, the total investment and unit exergy costs were 47.16 USD per hour and 11.07 USD per GJ, respectively. Further, the content of carbon dioxide released from the planned system was equal to 10.59 kmol per MWh. A parametric study has been also developed to identify influencing parameters.

Analysis of Desalination Performance with a Thermal Vapor Compression System

Multi-effect distillation with thermal vapor compression (MED-TVC) is a highly energy-efficient desalination technology that can provide a reliable and sustainable source of high-quality water, particularly in areas with limited energy infrastructure and water resources. In this study, a numerical model based on exergoeconomic approach is developed to analyze the economic performance of a MED-TVC system for seawater desalination. A parallel/cross feed configuration is considered because of its high energy efficiency. In addition, a parametric study is performed to evaluate the effects of some operational parameters on the total water price, such as the top brine temperature, seawater temperature, motive steam flow rate, and number of effects. The obtained results indicate that the total water price is in the range of 1.73 USD/m3 for a distilled water production of 55.20 kg/s. Furthermore, the exergy destructions in the effects account for 45.8% of the total exergy destruction. The MED effects are also identified to be the most relevant component from an exergoeconomic viewpoint. Careful attention should be paid to these components. Of the total cost associated with the effects, 75.1% is due to its high thermodynamic inefficiency. Finally, the parametric study indicates that adjusting the top brine temperature, the cooling seawater temperature, the motive steam flow rate, and the number of effects has a significant impact on the TWP, which varies between 1.42 USD/m3 and 2.85 USD/m3.

Sustainable and environmentally-friendly multi-generation system of power, cooling, and hydrogen; Multi-objective optimization using particle swarm algorithm

Guaranteeing long-term sustainability and developing environmentally friendly systems can be addressed with multi-generation systems that use renewable energy sources. Accordingly, a parabolic trough solar collector field was used to drive an organic Rankine cycle-ejector refrigeration integration, a modified organic Rankine cycle by regenerator, and a proton exchange membrane electrolyzer to produce power, cooling, and hydrogen. The energy, exergy, and exergoeconomic approaches were applied to assess the designed system's feasibility. The Pentane-Butane zeotropic mixture was utilized to enhance the performance of the organic Rankine cycle-ejector refrigeration integration. Finally, multi-objective optimization is performed to reach the system's optimum operating conditions. The obtained results at the base conditions revealed that the designed plant could yield 1501 kW total net power, where 192.9 kW was produced by the modified organic Rankine cycle. Also, the cooling load and hydrogen production were obtained at about 433 kW and 3.71 kg/h. Moreover, the system reached 6.68% exergetic efficiency with 5.17 years payback period at the optimum state. According to the obtained results, the proposed plant can be feasible for construction that could help sustainable development plans.

Exergy and Exergy-Economic Approach to Evaluate Hybrid Renewable Energy Systems in Buildings

Hybrid renewable energy systems (HRES) combine two or more renewable energy systems and are an interesting solution for decentralized renewable energy generation. The exergy and exergo-economic approach have proven to be useful methods to analyze hybrid renewable energy systems. The aim of this paper is to present a review of exergy and exergy-economic approaches to evaluate hybrid renewable energy systems in buildings. In the first part of the paper, the methodology of the exergy and exergo-economic analysis is introduced as well as the main performance indicators. The influence of the reference environment is analyzed, and results show that the selection of the reference environment has a high impact on the results of the exergy analysis. In the last part of the paper, different literature studies based on exergy and exergo-economic analysis applied to the photovoltaic-thermal collectors, fuel-fired micro-cogeneration systems and hybrid renewable energy systems are reviewed. It is shown that the dynamic exergy analysis is the best way to evaluate hybrid renewable energy systems if they are operating under a dynamic environment caused by climatic conditions and/or energy demand.

Techno-economic investigation and dual-objective optimization of a stand-alone combined configuration for the generation and storage of electricity and hydrogen applying hybrid renewable system

In this study, a solar driven co-generation structure of hydrogen and electricity is techno-economically investigated to be installed in the Farakhi village. In addition, a combined renewable configuration is also designed and integrated to the proposed system so as to provide required direct current for utilization in solid oxide electrolyzer. The presented scheme is modeled and simulated by MATLAB, ASPEN HYSYS, and HOMER Pro software. Economic, exergy as well as exergoeconomic approaches are applied to determine and to monitor the performance of the system and also to specify prominent factors through sensitivity analysis. The annual capital cost, yearly maintenance cost, and yearly operating cost of system were 15584.784 $/year, 455.062 $/year, and 245113 $/year, respectively. The system produced 29.2 ton of hydrogen per year, with a LCOP of 8.94 $/kg H2. The yearly cost of the system (ACS) was determined to be 261153 $/year. The largest amount of exergy destruction was related to reactor of the SOEC sub-unit with a value of 22.9 kW, which accounts for 47.33% of the total exergy destruction in the system. Moreover, the greatest share in the irreversibility of the whole combined renewable configuration was related to photovoltaic modules with a value of 86.62% and then biogas generator with a value of 8.03%. The largest and least values of exergoeconomic factor belonged to the solar collectors (100%) and reactor (9.91%), respectively. Ultimately, the economic, exergy, and exergoeconomic parametric analyses were carried out to generalize the results of the presented study to other geographical locations. The values of current density, operating temperature of SOEC, voltage of SOEC and temperature of fluids leaving the thermoelectric generator at the optimum point were determined to be 0.337 A/cm2, 791.5 °C, 1.212 V, and 197.5 °C, respectively.

Dynamic exergy and economic assessment of the implementation of seasonal underground thermal energy storage in existing solar district heating

In this paper, an exergoeconomic approach is proposed to assess the impact of the integration of a Borehole Thermal Energy Storage (BTES) in the existing district heating of the city of Chateaubriant in France. To do so, a dynamic simulation is run over ten years of operation. The model includes a new approach for cost calculation of short-term thermal storage, which is extended to seasonal BTES. The analysis of the system operation at yearly and daily scales revealed several issues. Hence, without redesigning the existing installation, it was found that a non-comprehensive control strategy results in an increase of fossil fuel share by 1.2%. At the BTES scale, from an exergoeconomic point of view, the charging stage is found particularly sensitive to the dynamic. For example, charging the BTES at low temperature increases of the specific cost of the heat stored. Hence, it is shown that some exergoeconomic indicators, like the specific cost of stored heat, could be relevant for designing and operating heating systems with borehole thermal energy storage.

Thermo-mechanical energy level approach integrated with exergoeconomic optimization for realistic cost evaluation of a novel micro-CCHP system

Conventional exergoeconomic analysis suffers from a lack of solid conceptual meaning behind its auxiliary cost equations defined for the needed components. To provide a logical relation between auxiliary cost equations, here a modified exergoeconomic analysis is used, which integrates the energy level of each stream with the conventional exergoeconomic analysis. Since the energy level of a component stems from a temperature (known as thermal term) and pressure (known as mechanical term) difference between its inlet and outlet streams, modifying the unit cost of the streams by their energy level significantly affects the overall unit cost of product. Hence, in this study, a new integral micro-CCHP (combined cooling, heating, and power) system driven by geothermal source and working with different zeotropic mixtures is proposed and evaluated economically by employing the recommended modified exergoeconomic approach. Later, due to the existing conflicting trend between energy efficiency, exergy efficiency, and modified total unit cost associated with the products, a multi-objective optimization tool is used to merge several optimal design points into an equilibrium point as the final optimal point. Several similar benchmarks (in terms of applications or sketch) are selected and the superiorities of the devised micro-CCHP system over them in terms of thermodynamics and thermoeconomics have been demonstrated. After optimization, the net power, cooling load, and heating load are improved by 106.77%, 142.83%, and 49.78%, respectively. This improvement in all products has led to a meaningful enhancement of 24.91% in energy efficiency, 15.42% in exergy efficiency, and 9% in the total unit cost of product (TUCP) (in both modified and conventional cost approaches). The best representative optimal point has the optimal energy efficiency, exergy efficiency, and TUCP of 61.61%, 44.46%, and 0.63 $/kWh, respectively.

Optimal equipment arrangement of a total site for cogeneration of thermal and electrical energy by using exergoeconomic approach

The optimal equipment arrangement for a system for cogeneration of thermal and electrical energy for a total site is determined with exergoeconomic analysis. A steam power plant can operate concurrently in a dual-use mode producing steam and electricity. It is important to know the potential for cogeneration before designing and optimizing a central utility system in order to establish on site fuel demand targets. In the current study, two case studies with different backpressure steam turbines arrangement are considered and, if extra power generation is needed, designs with a system of condensing and gas turbines are examined. The minimum exergy destruction rate, maximum exergy efficiency, minimum total capital cost rate and minimum exergy destruction cost rate for these arrangements are investigated with exergoeconomic analysis. Finally, selected backpressure steam turbines arrangement in conjunction with the gas turbine system are introduced for finding the optimum arrangement of the cogeneration system in the total site with an exergoeconomic approach.

A novel working fluid selection and waste heat recovery by an exergoeconomic approach for a geothermally sourced ORC system

A novel working fluid selection methodology is proposed for organic Rankine cycles (ORCs) coupled with low-grade geothermal sources by employing an existing dataset of an operating binary geothermal plant that works with n-pentane. Thermodynamic and thermoeconomic aspects of power production are combined to evaluate 29 different single-component working fluid candidates from different chemical branches in four-step elimination methodology. In terms of working fluid classification from physical point of view, results indicate that there is a direct relationship between vapor expansion ratio (VER) and net work output for dry working fluids. On the other hand, it is shown that isentropic fluids behave differently from dry fluids. Based on the proposed methodology, R113 is selected as a new working fluid for the existing plant instead of n-pentane. Results indicate that by applying the proposed methodology, it is possible to increase first and second law efficiencies of plant 0.59% and 3.18%, respectively, while reducing the levelized electrical cost (LEC) around 11% in comparison to base plant outputs with n-pentane. Furthermore, a case study is presented in addition the plant level analysis by implementing a hypothetical waste heat recovery cycle, configurated with proposed methodology, in order to reduce exergy losses originating from brine re-injection. It is shown that it may be possible to further reduce the LEC around 1% and increase the overall efficiencies 0.1% for the first law and 0.26% for the second law. However, it is necessary to be deliberate about these final results since they also demonstrate the sensitivity of LEC to the increases in second law efficiency rather than levelized capital investments.

Exergoeconomic Evaluation and Optimization of Reverse Brayton Refrigerator

Abstract In this article, by using exergoeconomic approach, an economic evaluation of reverse Brayton cycle-based refrigerator has been performed for 10 kW range cooling capacity at 65 K. One of the typical application domains of this refrigerator at the considered heat load is cooling of high-temperature superconductor for future power transmission lines that are in the developmental phase in different parts of the world. Multi-objective optimization and sensitivity analysis have been performed to investigate the sources of cost attached to the exergy destruction. Based on exergoeconomic evaluation parameters, recommendations have been provided for deciding the cost-effective design parameters for refrigerators. The significant finding of this analysis is that, for the basic reverse Brayton cryocooler, component performance, the turbine being the major one, needs to be improved to meet the economic criteria of 25 $/W as enumerated in the cryogenic road map for high-temperature superconductor cooling. The exergoeconomic design applied on the reverse Brayton refrigerator for high-temperature superconductor cables cooling can be adapted for other applications such as recondensation and liquefied natural gas cold energy utilization.

Thermodynamic and exergoeconomic analysis of a novel solar-assisted multigenerational system utilizing high temperature phase change material and hybrid nanofluid

The goal of this article is to propose and analyze a novel solar driven multigenerational system producing electricity, cooling, hydrogen and fresh water. The system consists of parabolic dish collector with hybrid nanofluids, re-compression sCO2 Brayton cycle, proton exchange membrane (PEM) electrolyzer, desalination unit and double effect lithium-bromide/water absorption cycle. To achieve high system performance and to meet the energy demand in the absence of solar flux, a thermal energy storage system has been used having high temperature phase change material (PCM). This system is able to continue system operation after the sunset and also ensure the stable fluid temperature at the turbine inlet. The performance of the proposed system is assessed by varying the different input parameters such as; inlet temperature, mass flow rate, direct normal irradiation (DNI), wind speed and turbine inlet temperature (TIT). In addition to the energy and exergy analysis, exergoeconomic approach is used to calculate the cost rate and exergo-economic factor of all the components of the integrated system. The results indicate that the overall energy and exergy efficiencies of the proposed system are 31.59% and 30.02%, respectively; while production of fresh water and cooling load are 1.564 kg/s and 196.1 kW, respectively. The exergoeconomic results show that Levelised cost of electricity and total cost rate of exergy destruction are 0.1387 $/kWh and 530 $/hr., respectively with payback period of 9.5 years. Moreover, single- and multi-objective optimizations are carried out to determine the optimal design using a genetic algorithm method in EES (engineering equation solver). Total cost rate and overall exergy efficiency are the two desired objectives to be optimized.

Exergy-based evaluation of a waste heat driven polygeneration system with CO<SUB align="right">2 as the working fluid

A waste heat driven polygeneration system that couples a supercritical power cycle with a transcritical refrigeration cycle is proposed and evaluated in this study. The stand-alone system using carbon dioxide as the working fluid produces power, refrigeration, and heating capacities simultaneously. Three scenarios of the system with different ambient temperatures (25-35°C) are optimised using exergoeconomic approach to obtain the lowest average cost of the products. The obtained results show that the average product cost is the highest ($113/GJ) for the scenario with the ambient temperature of 30°C, while the product cost is reduced to $82/GJ when the ambient temperature is 35°C. Moreover, the pressure for merging the sub-systems influences the performance of the system significantly, and the variations of the operating conditions differ among the scenarios by increasing the merging pressure. Besides, a multi-objective optimisation is implemented for supporting decision-makers to find the optimal solutions.

Exergy-based evaluation of a waste heat driven polygeneration system with CO<SUB align="right">2 as the working fluid

A waste heat driven polygeneration system that couples a supercritical power cycle with a transcritical refrigeration cycle is proposed and evaluated in this study. The stand-alone system using carbon dioxide as the working fluid produces power, refrigeration, and heating capacities simultaneously. Three scenarios of the system with different ambient temperatures (25-35°C) are optimised using exergoeconomic approach to obtain the lowest average cost of the products. The obtained results show that the average product cost is the highest ($113/GJ) for the scenario with the ambient temperature of 30°C, while the product cost is reduced to $82/GJ when the ambient temperature is 35°C. Moreover, the pressure for merging the sub-systems influences the performance of the system significantly, and the variations of the operating conditions differ among the scenarios by increasing the merging pressure. Besides, a multi-objective optimisation is implemented for supporting decision-makers to find the optimal solutions.