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Article: Age of air and air exchange efficiency in idealized city models

TitleAge of air and air exchange efficiency in idealized city models
Authors
KeywordsAir exchange efficiency
CFD
Homogeneous emission method
Local mean age of air
Urban morphology
Issue Date2009
PublisherPergamon. The Journal's web site is located at http://www.elsevier.com/locate/buildenv
Citation
Building And Environment, 2009, v. 44 n. 8, p. 1714-1723 How to Cite?
AbstractWind 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. © 2008 Elsevier Ltd. All rights reserved.
Persistent Identifierhttp://hdl.handle.net/10722/58986
ISSN
2015 Impact Factor: 3.394
2015 SCImago Journal Rankings: 2.121
ISI Accession Number ID
Funding AgencyGrant Number
Hong Kong SAR GovernmentHKU 7145/07E
Funding Information:

The work described in this paper was supported by a grant entitled as CityVent - A Theory of Ventilation of a Dense and High-Rise City by Wind and Buoyancy Forces from the Research Grants Council of the Hong Kong SAR Government (Project No. HKU 7145/07E). The valuable comments by Prof James Axley, School of Architecture; School of Forestry & Environmental Studies, Yale University, USA, on the manuscript is also gratefully acknowledged.

References

 

DC FieldValueLanguage
dc.contributor.authorHang, Jen_HK
dc.contributor.authorSandberg, Men_HK
dc.contributor.authorLi, Yen_HK
dc.date.accessioned2010-05-31T03:40:55Z-
dc.date.available2010-05-31T03:40:55Z-
dc.date.issued2009en_HK
dc.identifier.citationBuilding And Environment, 2009, v. 44 n. 8, p. 1714-1723en_HK
dc.identifier.issn0360-1323en_HK
dc.identifier.urihttp://hdl.handle.net/10722/58986-
dc.description.abstractWind 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. © 2008 Elsevier Ltd. All rights reserved.en_HK
dc.languageengen_HK
dc.publisherPergamon. The Journal's web site is located at http://www.elsevier.com/locate/buildenven_HK
dc.relation.ispartofBuilding and Environmenten_HK
dc.subjectAir exchange efficiencyen_HK
dc.subjectCFDen_HK
dc.subjectHomogeneous emission methoden_HK
dc.subjectLocal mean age of airen_HK
dc.subjectUrban morphologyen_HK
dc.titleAge of air and air exchange efficiency in idealized city modelsen_HK
dc.typeArticleen_HK
dc.identifier.openurlhttp://library.hku.hk:4550/resserv?sid=HKU:IR&issn=0360-1323&volume=44&issue=8&spage=1714&epage=1723&date=2009&atitle=Age+of+air+and+air+exchange+efficiency+in+idealized+city+modelsen_HK
dc.identifier.emailLi, Y:liyg@hkucc.hku.hken_HK
dc.identifier.authorityLi, Y=rp00151en_HK
dc.description.naturelink_to_subscribed_fulltext-
dc.identifier.doi10.1016/j.buildenv.2008.11.013en_HK
dc.identifier.scopuseid_2-s2.0-61749103944en_HK
dc.identifier.hkuros161293en_HK
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-61749103944&selection=ref&src=s&origin=recordpageen_HK
dc.identifier.volume44en_HK
dc.identifier.issue8en_HK
dc.identifier.spage1714en_HK
dc.identifier.epage1723en_HK
dc.identifier.isiWOS:000265171300019-
dc.publisher.placeUnited Kingdomen_HK
dc.identifier.scopusauthoridHang, J=35240092500en_HK
dc.identifier.scopusauthoridSandberg, M=35585315900en_HK
dc.identifier.scopusauthoridLi, Y=7502094052en_HK

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