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An Exergetic Analysis and Potential for Improving the Rational Energy Use in Dwellings
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
2008 (English)In: Proceedings of the 8th Symposium on Building Physics in the Nordic Countries / [ed] C. Rode, Danish Society of Engineers, IDA , 2008, 613-620 p.Conference paper (Refereed)
Abstract [en]

The quality of a certain amount of energy is defined as the relative exergy content of this energy. Most of our buildings with their heating and cooling systems today are built for conversion of high quality energy sources to low quality use with destruction of the available exergy as a result. Globally we have a huge potential for transforming our processes to more efficient use of the exergy and also for feeding our processes directly from renewable energy sources without the use of high quality energy sources. Exergy analysis is also important as an innovation driver in buildings and building systems. This work is carried out within the frame of IEA Annex 49 Low Exergy Systems for High-Performance Buildings and Communities. The scope of the annex is to improve, on a community and building level, the design of energy use strategies, taking into account the different qualities of energy sources, from generation and distribution to consumption within in the built environment. In particular, this is carried our by the method of exergy analyses to provide assessment of the thermodynamic features of any process and to achieve a clear, quantitative indication of both the irreversibilities and potential for matchmaking between the resources used and the end-use energy flows. The paper contains a systematic survey of the exergy consuming processes for building and building appliances, their role in exergy balance, the level of energy quality needed in primary process and the potential for developing processes towards improved exergy efficiency. The work presented here gives a listing of the important processes in buildings with a discussion of their nature from an exergy point of view. The methodology for analysis is exemplified for a limited number of processes, dealing with the energy use and exergy destruction in processes, the potential for exergy  saving and the discussion on the technical and economical feasibility.

Place, publisher, year, edition, pages
Danish Society of Engineers, IDA , 2008. 613-620 p.
Keyword [en]
Exergy, energy, efficiency, buildings, appliances
National Category
Civil Engineering
URN: urn:nbn:se:kth:diva-25404ISBN: 978-87-7877-265-7OAI: diva2:357975
8th Nordic Building Physics Symposium, Copenhagen, June 16-18 2008.
QC 20101020Available from: 2010-10-20 Created: 2010-10-20 Last updated: 2012-02-08Bibliographically approved
In thesis
1. Exergy Analysis in Buildings: A complementary approach to energy analysis
Open this publication in new window or tab >>Exergy Analysis in Buildings: A complementary approach to energy analysis
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Though mandatory to be pursued, improved energy efficiency is not the only target to reach. The quality of energy has to be assessed as well. Most of the overall energy use in residential building is for low temperature heat, i.e. temperatures relatively close to the outdoor conditions. From a thermodynamic point of view, this is a degraded form of energy with low potential to be converted into work. On the other hand energy demand is mostly met with high quality energy, such as electricity and natural gas. There is a mismatch between supply and demand, which is not clearly shown by the sole energy analysis. Target of this thesis is to analyze the energy use in buildings from the point of view of its quality, to provide effective theoretical and calculation tools to investigate this mismatch, to assess its magnitudo and to propose improvements aiming at a more rational use of the energy. The idea behind the quality is clarified with the concept of exergy.

The potential for improvement in space heating is shown. In no heating system the overall exergy efficiency is above 20%, with fossil fuels. Using direct electricity heating results in exergy efficiency below 7%. Most of the household appliances processes have low-exergy factors but still are supplied with electricity. This results in poor exergy efficiencies and large exergy losses.

Systems are poorly performing because little consideration is explicitly given to energy quality. Policies to lower the energy demand, though vital as first step towards an improved use of energy, should not neglect the exergy content.

The problem is then shifted to find suitable supplies. Electricity can be exploited with low exergy losses with high-COP heat pumps. Use of fossil fuels for heating purposes should be avoided. District heating from cogeneration and geothermal proves to be a suitable solution at the building level. The issues connected to its exploitation forces to shift the boundary layers of the analysis from the building level to the community level. A rational use of energy should address the community level. The system boundaries have to be enlarged to a dimension where both the energy conversion and use take place with reduced energy transportation losses. This is a cost-effective way to avoid the waste of the exergy potential of the sources with exergy cascade and to make it possible the integration of with renewable sources. Exergy efficiency of the buildings is a prerequisite for a better of energy in this field.

Place, publisher, year, edition, pages
Stockholm: Byggvetenskap, 2009. viii, 35 p.
Meddelande. Inst. för byggnadsteknik, 1651-5536
Exergy; Energy; Building systems performance; Built environment.
urn:nbn:se:kth:diva-11537 (URN)978-91-7415-519-8 (ISBN)
2009-12-11, Seminarierummet, Brinelsvägen 34, KTH- Inst. för Byggvetenskap, 16:00 (English)
IEA ECBCS Annex 49: Low Exergy Systems for High Performance Buildings and CommunitiesESF Cost C24: Analysis and Design of Innovative Systems for Low-EXergy in the Built Environment: COSTeXergy
Available from: 2009-11-25 Created: 2009-11-19 Last updated: 2010-10-20Bibliographically approved

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