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Energy and sustainable building

By : Elisa C. Boelman, Hideo Asada

In this paper, the exergy concept is explained and related to buildings by means of design and research examples. The concept is explained and applied to show that the thermal exergy requirements of systems near environmental temperature are very low. This implies that low-grade heat sources (e.g. solar or waste-heat near environmental temperature) could be thermodynamically better suited for use in buildings, since their temperatures better match the temperature levels often required in buildings An example of previous research is presented to illustrate how the concept of exergy consumption can be used to show how energy is degraded through energy conversion steps in and around a fluorescent tube. From an energy viewpoint, most of the electricity going into the tube is converted into heat. An exergy analysis, however, yields more intuitive results: although most of the exergy is consumed by energy conversion in the tube, most of the exergy output accounts for light: in exergy terms, the fluorescent tube is a lighter, not a heater. The exergy analysis also shows that the light emitted by the tube subsequently degrades into heat and is eventually dissipated, through absorption in the indoor surfaces. The exergy concept enables us to compare different types of energy - such as electricity, visible radiation and heat - on a common basis, and show explicitly what is consumed as a result of energy resource degradation.

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