Exergy

The climate condition affects the performance of the combined-cycle power plants. The efficiency of the combined
cycle is significantly influenced by the temperature, pressure and humidity of the air. When the ambient air
temperature increases, the density of the air decreases, and it leads to a reduction of power generated by the gas
turbine. In this work, the energy and exergy analysis of a commercial gas turbine, with inlet air cooling, was
performed. The effects of fogging system on gas-turbine performance studied. For this aim, the energy and exergy
balances were obtained for each piece of equipment. Calculations have been made for four different cases for the
regarded gas turbine system. Furthermore, exergetic efficiency, exergy destruction rates and improvement
potentials were obtained, and the results of the study demonstrated graphically. It is concluded that the net power
output of the gas turbine system increased at lower inlet temperatures and exergy destruction rates occurred from
highest to lowest as combustion chamber (CC), gas turbine (GT) and air compressor (AC), respectively.

This paper presents a thermodynamic and exergoeconomic analysis of a recently-retrofitted Passivhaus non-domestic building. The selected case study, a Community Centre located in London, underwent a deep-energy retrofit in 2011, becoming the first ‘non-domestic Passivhaus’ retrofit in the country. As the building was retrofitted per Passivhaus standards, which is based solely on First Law analysis, a thermodynamic investigation can provide a novel means by which to assess its exergy efficiency and cost-effectiveness. As such, the aim of this paper is to conduct a comprehensive exergy and exergoeconomic analysis, presenting novel performance indicators for the pre-retrofit and post retrofit Passivhaus building. First law outputs show that the improvement presents high levels of energy savings (75.6%), reductions in carbon emissions (64.5%), and occupant thermal comfort improvement (28.8%). Second law outputs present a reduction in primary exergy input reduction of 56.4% and exergy destructions of 60.4%, leading to improve building exergy efficiency from 9.8% to 18.0%. Nevertheless, exergoeconomically the building did not perform as expected due to high capital cost and exergy destructions cost rates. These results give an insight into the thermodynamic impact of the Passivhaus approach, providing a critical assessment of the strengths and limitations of the standard under both thermodynamic laws.

The paper describes a systematic framework that uses exergoeconomic theory integrated into ‘building energy retrofit’ (BER) design. An exergoeconomic module, based on the SPECO method, has been embedded into ‘EXRETOpt’, a recently developed retrofit-oriented exergy simulation tool based on EnergyPlus. Both active and passive technologies were analysed using two calibrated archetype non-domestic buildings as case studies (an office and a primary school). A novel cost-benefit indicator which accounts for building exergy destruction cost, retrofit annual capital cost, and project annual revenue is presented. This indicator is employed to account for best exergoeconomic performance technologies and to further develop deep BER packages. Compared to typical practice, exergoeconomics combined with cost-benefit provides a powerful tool for exploration and design improvement of building energy systems. In both cases, final product cost for heating and cooling processes were substantially reduced. In addition, the office case presented improvements in energy use by 67%, CO2 emissions by 53%, thermal comfort by 22%, exergy destructions by 42%, and the overall building exergy efficiency was improved from 14.8% to 20.0%. The school case presented similar results with an improvement of building exergy efficiency from 8.2% to 11.1%, and the potential to generate income due to current government incentives.

The undertaking of building energy retrofits is essential for the reduction of energy use and carbon emissions at a national level. Nowadays, a number of construction methods and energy technologies that are available to practitioners require that the appropriate retrofit solution is identified to ensure long-term project success. A significant limitation of conventional methods that may be used to examine this (e.g. scenario by scenario) is that only a limited number of design scenarios can be evaluated which limits the potential for identifying the “best” designs. Furthermore, while the building sector has a large thermodynamic potential where most of the buildings' energy demands (especially space conditioning) can be met by low-grade sources, the associated exergy analysis method is rarely used in architectural practice.
The following paper presents a simulation-based exergy optimization model, which aims to assess the impact of a diverse range of retrofit measures. Two non-domestic UK archetype case studies (a typical office and a primary school) are used to test the feasibility of the proposed framework. The objective optimization functions in this study are building energy use, exergy destructions throughout the building energy supply chain, and improvement of occupants’ thermal comfort levels. Different measures combinations based on retrofitting the insulation levels of the envelope and the application of different HVAC systems configurations (VAV, VRF, ground-source heat pump, air-source heat pump, district heating/cooling systems) are assessed. A large range of optimal solutions were achieved highlighting the framework capabilities. This approach can be extended by using the outputs in cost-benefit analysis and in thermoeconomic optimization.

Binalarda ve diğer birçok endüstriyel alanda yaygın olarak kullanılan kompakt ısı değiştiricilerinin
seçiminde önemli kriterler ısı transferi ve basınç düşüşü performansı, maliyet, kompaktlık ve etkenlik
olarak sıralanabilir. Bununla birlikte son yıllarda enerji kullanımına yönelik yapılan çalışmalar farklı
sistemlerdeki enerji kullanılabilirliğinin yani ekserjinin de değerlendirilmesi gerektiğini ortaya
koymaktadır. Aynı zamanda ikinci yasa yaklaşımı, bir optimizasyon problemi olan ısı değiştirici
tasarımında da yer almaktadır.
Yapılan çalışmada 650-670 kompaktlık oranına sahip üç farklı tipteki ısı değiştirici 0.027-0.16 ısıl
kapasite oranlarında deneysel olarak incelenmiştir. İnceleme sonuçları kullanılarak ısı değiştiricilerinde
gerçekleşen ekserji yıkımı hesaplanmıştır. Ekserji yıkım değerleri açısından ısı değiştiricileri
karşılaştırılmıştır. Karşılaştırma sırasında ısı değiştiricilerin ısı transferi yüzey alanlarının dağılımı,
tersinmezlik değerleri, tersinmezliğin sıcaklık ve basınç bileşenleri ve ekserji verimleri kullanılmıştır.
Heat transfer and pressure drop performance, cost, compactness and effectiveness can be listed as
important criteria for selection of widely utilized compact heat exchangers in buildings and a lot of
other industrial areas. Nevertheless, recent studies intended for energy usage presents that usability
of the energy, namely exergy, should be evaluated for various systems. The second law approach is
also used for heat exchanger design which is an optimization problem.
In this work, three different type heat exchangers having 650-670 compactness ratios were
experimentally investigated between 0.027-0.16 heat capacity ratios. Exergy destruction occurred in
the heat exchangers were calculated using the investigation results. Distribution of heat transfer
surface area of the heat exchangers, irreversibility rates, temperature and pressure components of the
irreversibility and exergy efficiency were used for comparison.

Prinsloo, G.J., Dobson, R.T., Mammoli, A.A. 2016. Model based design of a novel Stirling solar micro-cogeneration system with performance and fuel transition analysis for rural African village locations. Solar Energy 133, p 315-330 doi:10.1016/j.solener.2016.04.014

This paper describes the performance of a hybrid renewable energy system (HRES) integrated with a combined heat and power cogenerative smart microgrid as remote area power supply (RAPS) in deregulated district energy systems. The research focus on 100% renewables follows on from the ideas of the international energy society (ISES) 100% renewable energy drive, the IEEE smart villages initiative, international renewable energy alliance (IREA), the smart electric power alliance (SEPA) and the alliance for rural electrification (ARE). The proposed hybrid biogas based sun tracker concentrated solar hybrid renewable domestic hot water and power generation system. This alternative energy system design is suitable for space heating, household lighting and cooling refrigeration loads in smart villages, eco-estates, game-farms and remote islands. The study highlights the benefits of embedded generation in integrated and interactive smartgrid configurations for decentralised and district energy systems. International development initiatives such as the Alliance for Rural Electrification and the IEEE Smart Village program have been calling on engineers from developing countries to assist in reducing energy poverty through the design and development of custom designed small-scale sustainable renewable energy solutions. This paper describes the thermodynamic and electrical modeling, simulation and synthesis of a novel kit-based concentrating solar power combined heat and power or hybrid solar cogeneration system. It describes the decentralized solar co-generation system based on a combined cycle Stirling micro-CHP system that includes a low maintenance linear free piston Stirling engine with waste heat recovery, ideal for small business, residential or domestic solar home systems. The concentrating solar combined cycle power and energy system has been designed as a cost-effective community shared solar micro-combined heat and power unit to help enable solar energy utilization within the physical and socio-economic reality of isolated rural areas. This modular plug-and-play unit intends to serve as a stand-alone 100% renewable energy solar powerpack in rural microgrid energy distribution network applications where it will deliver around 3 kW of heat and 1 kW of electricity in distributed generation configurations. The focus of this paper is on the model based design approach in which the main components of the proposed solar micro-combined heat and power system have been systematically modeled on the TRNSYS and Matlab Simulink simulation platforms. This discrete digital modeling approach follows the design guide of the National Renewable Energy Laboratory Village Power Program wherein computer models are used to predict system performance. The TRNSYS model application is extended to meet compulsory World Bank and Development Agency funding and humanitarian investment requirements in terms of providing energy reform and fuel transition projections as part of proving the suitability of newly proposed solar technologies for remote area power applications. The proposed computer model applies statistical weather data to explore the performance, feasibility and fuel transition effects for the solar micro-combined heat and power system in terms of electricity and hot-water generation as well as fuel wood replacement at various locations in Southern Africa. The results show the annual power and hot water generation capability of the system for various sites across Southern Africa, and demonstrates a significant potential in reducing fuel wood usage for villages in these areas. This technology and analysis principles would also be valuable in environmental CO2 sequestration analysis, energy sustainability studies, techno-economic analysis as well as cost benefit studies for greenhouse gas (GHG) mitigation and adaptation technologies. Africa is a developing countries situated in one of the most vulnerable continents to climate variability. Climate change threatens food security and water stress from droughts and floods as well as potential extinction of plant and animal species, calling for nature conservation to reverse wood-land degradation, deforestation and erosion.
This universal distributed generation Stirling engine generation system is ideal for decentralized pre-paid energy co-operatives and pay-as-you-go solar home business models towards empowering remote off-grid villages and indigenous communal living in village communities through indigenous local sustainable energy sources. Energy production from thermodynamic micro-CHP system forms the core of a smart energy system infrastructure that makes up the rural energy system able to serve rural village communities-sustainably. It is intended to ensure sustainable rural development by providing sustainable energy that could displace traditional fossil fuels. The system uses indigenous energy resources, and with added photovoltaic PV or wind energy generation to ensure fossil fuel displacement in replacing fuels such as kerosene, paraffin, candles and wood fuel that cause human health issues and illness due to smoke inhalation. Such hybrid biofuel or biogas solar system provide a sustainable green energy solution and household home heating or district heating solution based on zero-net-energy 100% renewables. It is offered as a humanitarian aid technology to help service coalitions in support of entrepreneurial ventures into engineering for change in remote isolated off-grid rural communities at the bottom of the pyramid.
Follow on work describes the cyber-physical system aspects with smartgrid energy management and control modeling for coordination and optimization of the overall village power system. The integrated community solar and community microgrid solutions are novel in the context of thermo-electrical cogeneration, virtual power plants and hierarchical control structures for remote rural islanded village applications. Hybrid photovoltaic PV, eolica wind, small hydro and biogas cogeneration (poly-generation, tri-generation or hybrid-generation) in multi-carrier pico-grid, nano-grid or micro-grid dispatch can be used for power n energy delivery to drive appliances such as direct current DC LED lighting, fridges, radio, satellite TV, entertainment systems, and sanitation in islanded network configurations. This includes a flexible smart energy management in smart-grid architecture, data analytics and smart-meter instrumentation that includes machine-learning and artificial intelligence with mathematical and economic optimization in demand management, automated demand response, demand management and flexible controllable load curtailment. The intelligent energy management system aspects include customer engagement in control automation, intelligent self-learning, predictive optimization, energy profile or load forecasting, solar forecasting and battery energy storage integration in managing energy reserves. With smart-meter dashboard analytics, this will ensure renewable energy integration in dispersed generation with energy storage (battery, fuel-cell, tank) to ensure practical energy management that deals with the uncertainty, variability, flexibility and energy security in small-scale heat and power microgrids.
Highlights include customer engagement and cooperation in community solar energy utilization in physical & socio-economic reality of isolated rural areas; Localized rural electric power solution to ensure self-sufficient prosumer based energy in community smartgrids; Digital numerical modeling of custom designed kit-based concentrated solar tracker Stirling CSP micro-CHP system; Simulation prediction of CSP system performance in isolated rural African contexts to improve resource coordination and energy preservation; Analysis on fuel transition projections & rural energy generation reform; Need for hot water geyser type energy storage and dispatch; Demonstration of the personalized approach to power supply within sociological relevance and sustainability merit of customized community solar technology.
http://www.sciencedirect.com/science/article/pii/S0038092X16300378
https://www.researchgate.net/publication/301659032_Model_based_design_of_a_novel_Stirling_solar_micro-cogeneration_system_with_performance_and_fuel_transition_analysis_for_rural_African_village_locations

This study presents a comparison of the optimisation of building energy retrofit strategies from two different perspectives: an energy/economic-based analysis and an exergy/exergoeconomic-based analysis. A recently retrofitted community centre is used as a case study. ExRET-Opt, a novel building energy/exergy simulation tool with multi-objective optimisation capabilities based on NSGA-II is used to run both analysis. The first analysis, based on the 1st Law only, simultaneously optimises building energy use and design’s Net Present Value (NPV). The second analysis, based on the 1st and the 2nd Laws, simultaneously optimises exergy destructions and the exergoeconomic cost-benefit index. Occupant thermal comfort is considered as a common objective function for both approaches. The aim is to assess the difference between the methods and calculate the performance among main indicators, considering the same decision variables and constraints. Outputs show that the inclusion of exergy/exergoeconomics as objective functions into the optimisation procedure has resulted in similar 1st Law and thermal comfort outputs, while providing solutions with less environmental impact under similar capital investments. This outputs demonstrate how the 1st Law is only a necessary calculation while the utilisation of the 1st and 2nd Laws becomes a sufficient condition for the analysis and design of low carbon buildings.

In this study, energy, exergy and cost analyses of a continuous type hybrid photoelectrochemical hydrogen production system are performed, and the comparative results are presented. The proposed system has the advantage to eliminate generating waste by converting by-products into commercially viable products. In addition to hydrogen, the system generates Cl2 and NaOH as useful commodities which are desired by various industries. The proposed system is designed to have an annual production capacity of 2.8 kg hydrogen per square meter of heliostat with a production cost of $1/kg hydrogen produced. In addition to converting the by-products into usable commodities, the system emits no pollutants during operation.

http://arc.aiaa.org/doi/abs/10.2514/1.J053467?journalCode=aiaaj

Aircraft have evolved into extremely complex systems that require adapted methodologies and tools for an efficient
design process. A theoretical formulation based on exergy management is proposed for assessing the aeropropulsive
performance of future aircraft configurations. It consists of the combination of a momentum balance and a fluid flow
analysis involving the first and second laws of thermodynamics. The exergy supplied by the propulsion system and its
partial destruction within the control volume is associated with the aircraft mechanical equilibrium. Characterization
of the recoverable mechanical and thermal outflows is made along with the identification of the irreversible
phenomena that destroy their work potential. Restriction of the formulation to unpowered configurations yields
connections to some well-known far-field drag expressions and shows that their underlying theory can be related to
exergy considerations. Because the exergy balance does not rely on the distinction of thrust and drag, it is especially
suitable for the performance evaluation of highly integrated aeropropulsive concepts like boundary-layer ingestion.

In the present article thermodynamic evaluation of the
separator pressure to increase the thermal and exergy efficiency in parallel cycle geothermal power plants have been studied analytically. Also, two different views on efficiency have been considered; thermal efficiency and exergy efficiency. Both views anticipate very close optimum flashing pressure and in this pressure, exergy efficiency is between 2.5 to 5 times more than thermal efficiency. In addition, both views predict an increase of 28-35 percent for the efficiency of parallel double flash-binary power plants than the efficiency of parallel single flash-binary power plants.

In developing countries, the four-stroke single-cylinder gasoline engine finds wide use. Motorcycles, tricycles and household machines like vegetable grinding machines are but a few of the machinery which run on this engine. Researchers have found that this engine is inefficient and consumes a lot of fuel, in light of sustainability and energy efficiency, this study aimed to perform an exergy analysis of a single-cylinder 4-stroke gasoline engine to determine how best its efficiency can be improved. Parameters such as brake thermal power, exergy efficiency, the quantity of exergy destruction and the component of the engine which is the most influential on its efficiency were determined while varying the engine's torque. A G200K1 Honda engine was used as the study material. At the lowest tested torque of 9.4Nm, a corresponding brake power output of 2.4609kW and efficiency of 17.07% was measured, while at a higher torque 9.70Nm, a corresponding brake power output of 2.5395kW and efficiency of 17.62% was measured. It was also found that for every 1.06% rise in torque there is a corresponding 1.80% rise in brake power and exergy efficiency. It was concluded from the findings that the bulk of energy waste in the system comes from the high-temperature gas released from the engine's exhaust. For the overall efficiency of four-stroke single-cylinder gasoline engines to be improved, the exergy destruction due to combustion should be minimised by optimizing the combustion temperature and reducing heat loss from the combustion chamber.