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Age of air and air exchange efficiency in idealized city models
epartment of Mechanical Engineering, The University of Hong Kong, Hong Kong.
University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för inomhusmiljö.
epartment of Mechanical Engineering, The University of Hong Kong, Hong Kong.
2009 (English)In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 44, no 8, 1714-1723 p.Article in journal (Refereed) Published
Abstract [en]

Wind can provide relevantly clean external (rural) air into urban street network, i.e. city ventilation. The local mean age of air denotes the time it takes for the external air to reach a location after entering the urban canopy layer. The air exchange efficiency denotes the efficiency of flushing the street network with external air. However, difficulties exist in calculating the local mean age of air in a city due to open boundaries. The traditional experimental homogeneous emission method is adapted here in a CFD method to predict the urban local age of air and analyze the air exchange efficiency for city ventilation. Three simple city models are considered, including a round city model, a square city model and a long rectangular city with one main street parallel to the approaching wind or with two crossing streets. The difference in the city shape results in significant difference in the local mean age of air. In the round city of one narrow street, two inflows through street openings converge close to the city centre and exits through the street roof, so the air close to the city centre is relatively old and the air exchange efficiency is low (30%). For a round city with two crossing streets, a slightly non-parallel wind to the main street generates younger air and the higher air exchange efficiency in the city.

Place, publisher, year, edition, pages
Elsevier , 2009. Vol. 44, no 8, 1714-1723 p.
Keyword [en]
Air exchange efficiency; CFD; Homogeneous emission method; Local mean age of air; Urban morphology
National Category
Energy Systems
Identifiers
URN: urn:nbn:se:hig:diva-3981DOI: 10.1016/j.buildenv.2008.11.013ISI: 000265171300019Scopus ID: 2-s2.0-61749103944OAI: oai:DiVA.org:hig-3981DiVA: diva2:208752
Available from: 2009-03-19 Created: 2009-03-19 Last updated: 2016-10-27Bibliographically approved

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CiteExportLink to record
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Cite
Citation style
  • apa
  • harvard-cite-them-right
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
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Language
  • sv-SE
  • en-GB
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  • nn-NB
  • de-DE
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