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Author: Torio, Herena ×

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Now showing 1 - 5 of 5
  • Publication
    Exergy analysis of solar thermal systems: A necessary complement to conventional energy analysis?
    ( 2011)
    Torio, Herena
    ;
    Schmidt, Dietrich
    Current analysis and optimization methods of energy use in buildings are based on the assessment of primary energy flows, where all energy conversion steps from the extraction of energy sources (e.g. fuels) to the final demands to be supplied are assessed. The primary energy approach aims at limiting the use of fossil fuels for providing a given demand, leading to reduce energy demands and maximize the use of renewable energy sources. It is based, thus, on a distinction between renewable and fossil energy sources, being renewable energy flows often disregarded in the final balance. Thereby, an assessment of the efficiency of renewable energy use cannot be obtained from such analyses. Exergy is a thermodynamic magnitude defined as the maximum theoretical work obtainable from the interaction of a system with its environment as the equilibrium state is reached between both. Exergy analysis allows for the detection and quantification of the improving potential of complex energy systems and has been widely used for the optimization of thermodynamic systems since the middle of the last century. Exergy analysis shows the true thermodynamic efficiency of an energy system. All energy flows, renewable or not, are regarded in the exergy balances, thereby allowing the assessment of the efficiency of renewable energy use in a given energy system. Low temperature energy demands in buildings such as space heating and cooling have low quality, i.e. low exergy content. Low temperature renewable energy systems (e.g. solar thermal systems) are able to lower significantly the quality of the supplied energy in buildings, thereby increasing the exergy efficiency of energy supply. In the present paper results from exergy analysis of a solar thermal unit for supplying part of the domestic hot water and space heating demands of a multi-family dwelling are presented and compared to conventional primary and final energy assessments. Differences and added value of exergy analysis as compared to conventional primary energy assessment for solar thermal systems is investigated by comparing the conclusions and insight gained from both methods. The quality of solar thermal heat varies greatly depending on outdoor conditions and on the dynamic behavior of the solar thermal unit, i.e. on inlet and outlet collector temperatures. Therefore, dynamic energy and exergy simulations are required for an accurate and meaningful comparison of such analyses. Furthermore, different configurations and operation modes for the solar thermal system are investigated, allowing to achieve deeper understanding about the differences and information provided by each of the two analyses methods investigated.
  • Publication
    Projektverbund LowEx: Deutsche Beteiligung und Koordinierung des ECBCS Annex 49: Low Exergy Systems for High-Performance Buildings and Communitites
    (Fraunhofer IBP, 2011)
    Schmidt, Dietrich
    ;
    Torio, Herena
    ;
    Schurig, Marlen
    ;
    Kallert, Anna
    Dieser Bericht stellt die Abschlussdokumentation des Forschungsvorhabens "Deutsche Beteiligung und Koordinierung des ECBCS Annex 49: Low Exergy Systems for High-Performance Buildings and Communitites" dar, welches im Rahmen des deutschen Forschungsvorhabens "LowEx Heizen und Kühlen mit Niedrigexergie" des Bundesministeriums für Wirtschaft und Technologie (BMWi) gefördert wurde. Schwerpunkte des Vorhabens war die Koordinierung und Durchführung einer internationalen kooperativen Forschungsarbeit im Rahmen der Internationalen Energieagentur (IEA) und des Energy Conservation in Buildings and Community Systems Programme (ECBCS). Somit ist dieser Bericht im Wesentlichen die deutsche Übersetzung der englischsprachigen Kurzfassung des Abschlussberichtes des ECBCS Annex 49.
  • Publication
    Low exergy systems for high performance buildings and communities
    ( 2011)
    Torio, Herena
    ;
    Schmidt, Dietrich
    As a consequence of the latest reports on climate change and the needed reduction in CO2 emissions, huge efforts must be made in the future to conserve high quality, or primary energy, resources. A new dimension will be added to this problem if countries with fast growing economies continue to increase their consumption of fossil energy sources in the same manner as they do now. Even though there is still considerable energy saving potential in the building stock, the results of the finished IEA ECBCS Annex 37, Low Exergy Systems for Heating and Cooling of Buildings, show that there is an equal or greater potential in exergy management. This implies working with the whole energy chain, taking into consideration the different quality levels involved, from generation to final use, in order to significantly reduce the fraction of primary or high-grade energy used and thereby minimise exergy consumption. New advanced forms of technology need to be implemented. At the same time, as the use of high quality energy for heating and cooling is reduced, there is more reason to apply an integral approach, which includes all other processes where energy/exergy is used in buildings. In recent years, we have made substantial progress in the development of new and integrated techniques for improving energy use, such as heat pumps, co-generation, thermally activated building components, and methods for harvesting renewable energy directly from solar radiation, from the ground and various other waste heat sources. The results obtained in research projects on optimised exergy use in buildings are promising and elucidate a huge potential for introducing new components, techniques and system solutions to create low exergy built environments. The exergy conversion, e.g. heat or electricity production, plays a crucial role in possible future activities in the overall system optimisation of the entire energy system within a building. New solutions can be obtained by taking advantage of the design of entire quarters or community structures into consideration. Then, by coupling a group of buildings or by the possible use of new energy sources (e.g. the use of water in old coal mines to heat and cool entire cities a more efficient use of energy is possible.