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Article: City ventilation of Hong Kong at no-wind conditions

TitleCity ventilation of Hong Kong at no-wind conditions
Authors
KeywordsCity ventilation rate
Slope flow
Surface temperature
Thermal buoyancy
Wall flow
Issue Date2009
PublisherPergamon. The Journal's web site is located at http://www.elsevier.com/locate/atmosenv
Citation
Atmospheric Environment, 2009, v. 43 n. 19, p. 3111-3121 How to Cite?
AbstractWe hypothesize that city ventilation due to both thermally-driven mountain slope flows and building surface flows is important in removing ambient airborne pollutants in the high-rise dense city Hong Kong at no-wind conditions. Both spatial and temporal urban surface temperature profiles are an important boundary condition for studying city ventilation by thermal buoyancy. Field measurements were carried out to investigate the diurnal thermal behavior of urban surfaces (mountain slopes, and building exterior walls and roofs) in Hong Kong by using the infrared thermography. The maximum urban surface temperature was measured in the early noon hours (14:00-15:00 h) and the minimum temperature was observed just before sunrise (5:00 h). The vertical surface temperature of the building exterior wall was found to increase with height at daytime and the opposite occurred at nighttime. The solar radiation and the physical properties of the various urban surfaces were found to be important factors affecting the surface thermal behaviors. The temperature difference between the measured maximum and minimum surface temperatures of the four selected exterior walls can be at the highest of 16.7 °C in the early afternoon hours (15:00 h). Based on the measured surface temperatures, the ventilation rate due to thermal buoyancy-induced wall surface flows of buildings and mountain slope winds were estimated through an integral analysis of the natural convection flow over a flat surface. At no-wind conditions, the total air change rate by the building wall flows (2-4 ACH) was found to be 2-4 times greater than that by the slope flows due to mountain surface (1 ACH) due to larger building exterior surface areas and temperature differences with surrounding air. The results provide useful insights into the ventilation of a high-rise dense city at no-wind conditions. © 2009 Elsevier Ltd. All rights reserved.
Persistent Identifierhttp://hdl.handle.net/10722/59059
ISSN
2015 Impact Factor: 3.459
2015 SCImago Journal Rankings: 1.999
ISI Accession Number ID
Funding AgencyGrant Number
Hong Kong Special Administrative Region, China7145/07E
CIBSE HK Branch
Funding Information:

The work described was supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region, China (Project No. HKU 7145/07E) and a CIBSE HK Branch grant. We thank Mr Leung Wing Kam for assisting us in the measurements. Special thanks to Xie Xiaojian, Hang Jian, Gong Jian, Luo Zhiwen, Gao Xiaolei, Liu Li and Wu Jiayi for taking infrared photos during the 24 h measurements. We are also grateful to the Peak Tower of Hong Kong for providing necessary on-site support.

References

 

DC FieldValueLanguage
dc.contributor.authorYang, Len_HK
dc.contributor.authorLi, Yen_HK
dc.date.accessioned2010-05-31T03:42:11Z-
dc.date.available2010-05-31T03:42:11Z-
dc.date.issued2009en_HK
dc.identifier.citationAtmospheric Environment, 2009, v. 43 n. 19, p. 3111-3121en_HK
dc.identifier.issn1352-2310en_HK
dc.identifier.urihttp://hdl.handle.net/10722/59059-
dc.description.abstractWe hypothesize that city ventilation due to both thermally-driven mountain slope flows and building surface flows is important in removing ambient airborne pollutants in the high-rise dense city Hong Kong at no-wind conditions. Both spatial and temporal urban surface temperature profiles are an important boundary condition for studying city ventilation by thermal buoyancy. Field measurements were carried out to investigate the diurnal thermal behavior of urban surfaces (mountain slopes, and building exterior walls and roofs) in Hong Kong by using the infrared thermography. The maximum urban surface temperature was measured in the early noon hours (14:00-15:00 h) and the minimum temperature was observed just before sunrise (5:00 h). The vertical surface temperature of the building exterior wall was found to increase with height at daytime and the opposite occurred at nighttime. The solar radiation and the physical properties of the various urban surfaces were found to be important factors affecting the surface thermal behaviors. The temperature difference between the measured maximum and minimum surface temperatures of the four selected exterior walls can be at the highest of 16.7 °C in the early afternoon hours (15:00 h). Based on the measured surface temperatures, the ventilation rate due to thermal buoyancy-induced wall surface flows of buildings and mountain slope winds were estimated through an integral analysis of the natural convection flow over a flat surface. At no-wind conditions, the total air change rate by the building wall flows (2-4 ACH) was found to be 2-4 times greater than that by the slope flows due to mountain surface (1 ACH) due to larger building exterior surface areas and temperature differences with surrounding air. The results provide useful insights into the ventilation of a high-rise dense city at no-wind conditions. © 2009 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/atmosenven_HK
dc.relation.ispartofAtmospheric Environmenten_HK
dc.rightsCreative Commons: Attribution 3.0 Hong Kong License-
dc.subjectCity ventilation rateen_HK
dc.subjectSlope flowen_HK
dc.subjectSurface temperatureen_HK
dc.subjectThermal buoyancyen_HK
dc.subjectWall flowen_HK
dc.titleCity ventilation of Hong Kong at no-wind conditionsen_HK
dc.typeArticleen_HK
dc.identifier.openurlhttp://library.hku.hk:4550/resserv?sid=HKU:IR&issn=1352-2310&volume=43&issue=19&spage=3111&epage=3121&date=2009&atitle=City+ventilation+of+Hong+Kong+at+no-wind+conditionsen_HK
dc.identifier.emailLi, Y:liyg@hkucc.hku.hken_HK
dc.identifier.authorityLi, Y=rp00151en_HK
dc.description.naturepostprint-
dc.identifier.doi10.1016/j.atmosenv.2009.02.062en_HK
dc.identifier.scopuseid_2-s2.0-67349236046en_HK
dc.identifier.hkuros172748en_HK
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-67349236046&selection=ref&src=s&origin=recordpageen_HK
dc.identifier.volume43en_HK
dc.identifier.issue19en_HK
dc.identifier.spage3111en_HK
dc.identifier.epage3121en_HK
dc.identifier.eissn1873-2844-
dc.identifier.isiWOS:000266896000010-
dc.publisher.placeUnited Kingdomen_HK
dc.identifier.scopusauthoridYang, L=13806737800en_HK
dc.identifier.scopusauthoridLi, Y=7502094052en_HK

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