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AbstractOne variation of exergy analysis, specific fuel consumption (SFC) analysis, was modified according the advanced exergy analysis, where exergy destructions within each component were split into endogenous/exogenous and avoidable/unavoidable parts, and by combining the energy-savings effects of each component. The modified analysis approach can help locate not only the weak points at the component level but also certain bottlenecks from the topology viewpoint, which may indicate adding or deleting some components, or enhancing the thermodynamic interactions between different process or subsystems. The modified approach was then applied to a conventional coal-fired power plant. The detailed spatial distribution of SFC within the current system at different partial-load conditions were deeply discussed at both component and process levels. Further splitting of SFC and the energy-saving effects of each process are also obtained and discussed. The results show that combustion and heat-and-mass transfer processes have the largest SFC. Heat-and-mass transfer process and the vent process have the greatest avoidable SFCs. The closer the component to the final product, the larger its influence on the overall performance, and, thus, a small improvement to these components may lead to a large reduction in the overall fuel consumption. More effective energy-saving measures of coal-fired power plants should focus on the match of heat transfer at intermediate-and-low temperature level and the breakage of the isolation of heat transfer subsystems, especially enhancing the interaction between the air preheating process and feedwater preheating process.

AbstractThe mineral fixation of CO2 has a significant but highly varying relevance in carbon capture and storage (CCS) models. One reason is the impact of the minerals’ concentrations, but the choice of the thermodynamic database on which the geochemical model calculations are based, has probably an equivalent or even more important impact on the model results.In this example, natural groundwater and a mineral assemblage consisting of calcite, dolomite, albite, and K-feldspar in two different concentrations were used to perform scenario simulations with the geochemical model PHREEQC. The four different thermodynamic datasets phreeqc.dat, wateq4f.dat, llnl.dat, and minteq.dat were used to calculate the amount of CO2 which could be fixed through the reactions with the described minerals.In the simulations using low reactive mineral concentrations (1–2.5 wt%), the range of the amount of fixed CO2 in the mineral and dissolved phases lies between 0.29 and 0.31 mol/kgw for the four chosen thermodynamic databases, which reflects the complete transformation of albite and K-feldspar to secondary minerals in all the simulations and only minor differences in the amounts of dissolved calcite and dolomite. On the other hand, the amount of fixed CO2 shows a variance of between 1.51 and 2.17 mol/kgw when using high reactive mineral concentrations (10–25 wt%). Especially the transformation of the K-feldspar depended significantly on the chosen thermodynamic database which affected the calculated product minerals of the reaction. Using the phreeqc.dat, the wateq4f.dat, and the minteq.dat databases, the amount of CO2 fixation due to its reaction with K-feldspar is up to six times larger than the amount calculated with the llnl.dat database.It is currently not clearly possible to decide which thermodynamic database should be used to receive the most realistic modeling results. Consequently, the uncertainty in the modeling results due to varying thermodynamic databases should be regarded in addition to the uncertainty resulting from factors like the heterogeneous distribution of mineral phases in the aquifers. It still has to be discussed whether a risk-based approach offers a secure way of modeling CCS related scenarios or whether worst-case scenarios have to be applied.

Abstract Improving building thermal performance is important if the UK is to meet the 80% emission reduction target by 2050. Aiming to provide insights into UK building thermal performances, relevant national policies were highlighted and a one-day workshop was run. Real-time responses of industrial stakeholders were collected using Poll Everywhere. The stakeholder perspectives on challenges, barriers, thermal performances and other concerns were reported. It showed that (i) a whole-house retrofit plan was necessary; (ii) improving thermal performances would be challenging but achievable; and (iii) industrial stakeholders were concerned about building performance, legislation, drivers, cost, professional development, technology alternatives and future vision. It was concluded that industrial consultation should be continued to assist thermal performances of buildings in the UK.

AbstractDuring the last decade, housing construction in Mexico has increased dramatically, despite the economic and financial crises, it is one of the main drivers of the Mexican economy; the government has supported programs to develop social housing in order to assist low-income families. This type of initiatives has allowed low-income people to own a place to live, but it has also promoted the spread of housing developments with house models of similar characteristics in the very diverse geographical and climatic zones of Mexico. Even though some of the dwellings have few differences depending on the region they belong to, they do not reflect climatic adaptations. The correct selection of the envelope materials is one of the first and most effective passive strategy that must be considered in the design of a housing. However, just selecting the materials by knowing their thermal properties is not enough to make an appropriate decision about the construction system. For this reason, we need a tool like Ener-Habitat, which allows a quick assessment of thermal and energy performance of a building system consisting of several layers, through the time-dependent calculation of heat transfer, suitable for high thermal mass materials, such as those generally used in Mexico and the climates of Mexico with high solar radiation and large temperature swing during the day. The study propose a method to analyze the cost and energy benefit of building systems, and as example analyzes some walls building systems, in a hot-dry climate city of Mexico, during the air conditioning season. This tool allows, at early stages of architectural design, quick assessments for decision taking on the building systems choice, in relation with better energy performance. Ener-Habitat was created by researchers from six academic institutions in Mexico and was funded by the National Council for Science and Technology and the Ministry of Energy of Mexico.

Abstract The transient cooling process of an underground water pit thermal storage with inclined sidewalls is investigated in this paper. An experimental device was designed in order to validate the mathematical model proposed. Materials properties have been assumed constant with temperature, except for the water’s density that has been treated using the Boussinesq approximation. The simulations of temperature distributions are proved well by comparison with the experimental results. Results show that the water temperature decreasing next to the tank walls by the heat losses from the top and sidewalls of the tank, which creates a downward flow along the tank wall. At the center of the tank, a slight upward flow is generated, which lifts the warmer water at the bulk of the tank to a higher level. In this way, the buoyancy-driven flow gradually builds up the thermal stratification in the tank. The Nusselt number values show that comparing with the upper surface of the storage tank, there is more radical heat exchange at the bottom and inclined sidewalls. The maximum velocity appears near the top part of the inclined sidewalls, and its value decreases as the cooling continues.

AbstractThis paper describes a new2nd generation linear focus solar simulator test bench. The test bench is used for the non-destructive calorimetric measurement of relative optical efficiency of parabolic trough receivers. Compared to the predecessor, the test bench has been optimized for faster measurement, better long term stability and easier operation. The test bench optics is an elliptical shaped glass mirror trough with flat end mirrors. The receiver and six solar simulator lamps, metal halide lamps with 2.5 kWeeach are located in their respective focal lines. Absorbed power is measured via temperature increase of the water flowing through the receiver and the mass flow rate. By comparison to the absorbed power of a reference receiver, the optical efficiency of a sample can be determined relative to the optical efficiency of the reference receiver.

Abstract The complete cycle of specific processes related to the geological storage of CO 2 is investigated in detail at Ketzin since 2004. The scientific monitoring program targets different depths of the involved area and addresses the safety and reliability of the storage. The surface monitoring comprises long-term soil CO 2 flux measurements and soil gas analyses. Annual mean values of soil CO 2 fluxes ranged from 2.4 to 3.4 µmol m -2 s -1 before the injection started (2005-2008) and from 2.3 to 3.5 µmol m -2 s -1 during and after CO 2 injection (2009-2016) and thus do not indicate an upward migration of the injected CO 2 .

AbstractEven though the integration of renewable energies in new buildings is technically easy, the rise of solar thermal systems in the French market of energy renovation is limited by recurring constraints of implementation related to the installation of the storage tank. This is the reason why the Integrated Solar Collector (ISC) constitutes a very promising concept to develop. For both new buildings and renovation of the existing buildings, the ISC gives the opportunity to reduce the cost of installation and operation comparatively to a conventional Solar Domestic Hot Water System, because of their simplicity and passive operating process (without pump, nor controller). This second advantage is extremely important for the development prospects of the solar thermal market which is currently slowed down by the level of investment. The third advantage of our new ISC is the possibility of successful architectural integration, contrary to the currently available solutions with the storage installed on the roof.We developed a new concept of ISC adapted to the energy renovation with a multidisciplinary approach. Its design took into account various aspects: architectural integration (storage bellow the collector), energy performance (solar heat transfer at the bottom of the storage, fully insulated storage) and technological constraints (freezing risk). The project made it possible to study on the one hand its global performance (stratification, solar fraction) and on the other hand the free convective heat transfers inside the storage cavity. The approach used both numerical (architectural draft and design of the prototype, global modelling, and velocity / temperature fields) and experimental tools (test of heat, PIV on a cavity heated at the bottom, test of the prototype). The first prototype of ISC puts forward very satisfactory energy performances. Improvements are possible by enhancing thermal stratification in the storage system. Concerning the heat pipes operation against gravity, the project highlighted the current lack of technological solution adapted to our needs. The study of the building integration showed the architectural opportunities given during the renovation (new volumes) and the technical constraints which were solved (weight, storage insulation, freezing).

Abstract Copper is a common impurity in photovoltaic silicon. While reported to precipitate instantly in n-type Si, copper causes light-induced degradation (Cu-LID) in p-type Si. Recently, partial recovery of Cu-LID was observed after only few minutes of dark annealing at 200 °C. In this contribution, we investigate the effects of the dark anneal on Cu-LID-limited minority carrier lifetime both experimentally and by simulations. Surprisingly, after initial recovery, the dark anneal results in further degradation corresponding to a many-fold increase in recombination activity compared to the degraded state after illumination. This anneal-induced degradation can potentially cause additional losses in accidentally Cu-contaminated devices when exposed to elevated temperatures, for example during recovery and regeneration treatments of solar cells. Transient ion drift measurements confirmed that the anneal-induced degradation cannot be attributed to residual interstitial Cu after illumination. After hundreds of hours of annealing, the samples showed another recovery. To analyze these experimental results, a comparison to simulations is performed at the end of the paper.