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An exergy analysis is performed to analyse the possibilities of fuel saving in the cryogenic distillation process, which is the main method of air separation. It is shown that more than half of the exergy loss takes place in the liquefaction unit and almost one-third in the air compression unit. Minor exergy losses are taking place in the distillation unit and the main heat exchanger. The major cause of exergy loss is the use of compressors and to a lesser extent the use of turbines. Especially, the relatively low rational efficiency of the turbines operating in the cryogenic region is striking. Improvements are suggested which save one-fourth of the exergy loss. For more substantial reductions of the exergy losses in air separation alternative processes have to be used or developed.

Abstract This paper aims to compare the energy efficiency and CO 2 emissions of four different range extender engine solutions deployed in the same baseline series hybrid vehicle, under a combination of driving scenarios aiming to be representative of typical driving instead of standard cycles. Baseline vehicle is roughly based on Chevy VOLT/Opel Ampera. The baseline internal combustion engine is replaced by an over-expanded cycle engine, Wankel engine and microturbine, with respective generator and exhaust after treatment. Weight savings are compensated by introducing additional battery modules, maintaining the original baseline vehicle curb weight. Vehicle Specific Power (VSP) is used for driving cycle analysis and as explanatory variable for energy consumption and CO 2 emissions variations. Upstream fuel energy and CO 2 emissions of gasoline/diesel and electricity are regarded. Average VSP correlates with variation of the percentage of engine off, potential regenerative braking energy and eco/boost operation. Positive wheel energy correlates with energy consumption and electric autonomy adequately. The vehicle with the lightest engine (Wankel) and largest battery shows to be the most efficient in urban driving (when the engine does not have to work), while the vehicle with the highest efficient engine (over-expanded) and with dual eco/boost setting is the most efficient during the charge sustaining operation and in annual combined use.

Recent needs of reducing pollutant emissions of internal combustion engines have pushed the development of non-conventional ignition systems. One of the most promising techniques appears to be the so-called Turbulent Jet Ignition (TJI) system, in which a jet of high-energy reactive gases is generated by means of a pilot combustion in a pre-chamber and used to initiate the main combustion event in the cylinder. Considering the complex nature of some phenomena typical of TJI systems, 3D CFD studies are essential to provide a detailed analysis for an efficient design. In this study, numerical simulations of an active pre-chamber TJI system applied to a lean operating methane engine were performed to provide a thorough analysis of the combustion process that characterizes such a technology. The numerical model was validated against experimental measurements carried out on an optically accessible single cylinder spark-ignition engine equipped with the pre-chamber prototype. The numerical simulations provided an insight view of both physical and chemical phenomena occurring inside the pre-chamber otherwise difficult to achieve by experiments alone. The evolution of some species of interest was analyzed in order to study the main charge ignition process, as well as the overall combustion progress. The results show that the main charge ignition is made possible by the large amount of energy and active radicals released from the pre-chamber and this ensures an overall stable and faster combustion in lean conditions. The performance improvements of the TJI system with respect to a traditional spark-ignition engine were evaluated in terms of efficiency and pollutant emission levels.

Experimental study we present is a full-scale energy recovery system able to extract, by means of a water sourced heat pump, the leftover thermal bioenergy available in a Sequencing Batch Biofilter Granular Reactor (SBBGR) within the wastewater treatment process. Heat pump compressor engine was powered by a 5.1 kW Photovoltaic plant, thermal energy being recovered is accumulated by two phase change materials tanks (PCM) for heat and cold latent energy storage whose capacity is 0.3 and 0.5 m3 respectively, thermal energy excess was dissipated through evaporator and condenser devices. Thermal energy extracted from SBBGR ranged from 0 to 14.5 kWh as function of environmental temperature and temperature set point of SBBGR. It was largely affected by environmental temperature during radiation and no deterioration of SBBGR performances were recorded during energy extraction even at lowest temperature set point (i.e. 15 °C). Results obtained demonstrated that SBBGR technology, thanks to its particular process scheme, allows wastewater heat extraction within the treatment process operation, making it actually the only wastewater treatment system able to exchange energy at low temperature (15 °C) without prejudice to treatment performances and, at the same time, to operate a thermal regulation of the treatment reactors, integrating the optimization of thermo-dependent biological processes with energy recovery systems.

This study analyzes the energy sustainability of citrus residues conversion and valorization through fluidized bed gasification plant. An energy analysis of the integration into a real citrus juice factory of a combined heat and power system (CHP), coupled with a citrus residues air-steam gasification unit, is presented. Energy and biomass assessments are estimated by matching the gasification unit performance with the syngas request of the CHP unit through an integrated simulation model. Results show that the integration of a gasification-CHP system into the juice industrial cycle could supply 7,875 MWh/year of electricity, corresponding to 88% of the factory's demand. About 82% of the heat produced in the CHP unit is used to dry the citrus residues, while about 1,086 MWh/year are available for the heat request of the juice production process. This allow saving 27,906 MWh/year of non-renewable primary energy, reducing the specific non-renewable primary energy consumption of about 46% the factory's carbon dioxide impact could be decreased of about 45%.

Abstract The goal of this work has been to document the efficiency of domestic hot water (DHW) distribution systems and to propose more energy efficient and environmentally friendly solutions for DHW systems based on analyses of existing conditions. In the article, measurements from 13 apartment buildings and two institutions are presented, i.e. consumption of DHW, heat loss from circulation lines and efficiency of the DHW system. The heat load and the cooling of the district heating water for DHW are documented as well. Possibilities for improving the DHW system include new types of circulation pipes, which have the potential of a 40% reduction of heat losses. In addition to the reduction of heat losses inside the building, a low return temperature from the hot water system will have a large impact on the heat losses from the district heating network when the building is being heated by district heating. It is likely that the production and distribution of DHW in buildings will constitute a dominant share of both the present, and in particular, the future energy design requirements of buildings. The results of this project could influence not only future buildings, but also existing buildings when renovation of installations take place.

Abstract In order to obtain data on the behaviour of green facades in buildings as a passive system for energy savings in dry Mediterranean Continental climate a long-term work has been performed. This paper presents the first results of two actions developed during 2009. First, the growth of four different climbing plants as well as their ability to provide shadow was studied. Second, monitoring for a year of a real green facade was carried out. The results confirmed the great capacity of green facades to produce shade, reducing the heat on the facade wall of the building. It was also verified that a microclimate between the wall of the building and the green curtain are created, characterized by slightly lower temperatures and higher relative humidity. This means that the green screen acts as a wind barrier and confirms the evapotranspiration effect of the plants. On the other hand, these results did not allow withdrawing conclusions about the insulation effect of green facades.

he feasibility of individual natural gas fired boiler-based heating systems in the retrofitting of buildings constructed in the 50–60 s in Bilbao (northern Spain) is evaluated in this paper. A holistic approach through dynamic simulations using TRNSYS is employed for the purpose. An existing dwelling previously monitored and used to validate the model applied is selected as a case study. 54 different scenarios are evaluated, which arise from the combination of 3 different envelope options, 2 types of heat production units, 3 heat production temperatures and 3 comfort temperature set-points. The cases are evaluated in terms of energy results, economic aspects, and the influence of user behaviour. Regarding the latter, the influence of the potential rebound effect is also evaluated. The results show energy savings nearby 10% when condensing boilers are compared with high efficiency boilers. In relation to hot water production temperature, energy savings between 5 and 10% are found when the temperature is lowered from 60 to 50 °C. The greatest impact on energy consumption is related to the occupants’ behaviour: reductions up to 89% are achieved if the indoor temperature set-point is lowered 2 °C. This is reinforced with the results related to the rebound effect, which show significant differences on energy consumption values. These evidences demonstrate that the user behaviour is an essential feature to be considered in studies regarding buildings energy performance. As a consequence, the holistic approach herein employed emerges as a key tool to be applied in further works related with the topic The author G. Diarce wants to thank the financial support of the Basque Government, through the Department of Education, Universities and Research’s Personnel Research Training Program (2012 call).