Research and Developmentin

City University of Hong Kong

Research and Development

Air flow and ventilation in urban area

Presented byProf. Edmund Choi

Wind FlowWind flow in city areas can produce problems. Wind flow in city areas can produce problems. Different problems are experienced at the two Different problems are experienced at the two extreme ends of the wind flow.extreme ends of the wind flow.

••Not enough wind Not enough wind air ventilation issuesair ventilation issues

••Strong wind Strong wind wind loading problemswind loading problems

Not having enough air flow

•• Wider spread of dense Wider spread of dense developmentsdevelopments

•• Taller and taller buildingsTaller and taller buildings•• ““WallWall--likelike”” developmentsdevelopments•• Larger heat island effectLarger heat island effect

•• All these will result in making the summer more unAll these will result in making the summer more un--bearable and more concerns on the air ventilation in bearable and more concerns on the air ventilation in city areascity areas

Air Ventilation Study

•• Team Clean in 2003:Team Clean in 2003:-- For Government to For Government to consider stipulating Air Ventilation Assessment consider stipulating Air Ventilation Assessment for all major development or redevelopment for all major development or redevelopment proposals in future planningproposals in future planning

•• Objective is to have a comfortable, healthy and Objective is to have a comfortable, healthy and sustainable living environment, and to promote sustainable living environment, and to promote better layout of building blocks in the citybetter layout of building blocks in the city

Air ventilation studies

To better understand the problem, generic and To better understand the problem, generic and case studies are carried outcase studies are carried out

•• Effect of building geometryEffect of building geometry•• Height/width ratio and relative heights of Height/width ratio and relative heights of

buildingsbuildings

•• Gaps between buildingsGaps between buildings

•• Podiums and their heights Podiums and their heights

Air ventilation studies

Generic and case studiesGeneric and case studies

•• Building groupsBuilding groups•• Layout of building groupsLayout of building groups

•• Street width, and depth/width ratioStreet width, and depth/width ratio

•• Enhancing air ventilation Enhancing air ventilation

Air ventilation studiesCFD study on street canyon with varying width/heightCFD study on street canyon with varying width/height

Air ventilation studiesWeak wind region behind podiums of different heightsWeak wind region behind podiums of different heights

Air ventilation studiesCFD study on building Height and down wash effectCFD study on building Height and down wash effect

Building Height=15m Building Height=30m Building Height=60m

Building Height=90m Building Height=120m

Air ventilation studiesPermeable podium and sky garden

Air ventilation studiesEnhancing air ventilation Enhancing air ventilation -- Permeable podiumPermeable podium

Air ventilation studiesEnhancing air ventilation Enhancing air ventilation -- Effect of sky garden/duct floorEffect of sky garden/duct floor

Air ventilation studiesWind tunnel studies on Wind tunnel studies on

street width/podium height/tower heightstreet width/podium height/tower height

Air ventilation studiesFlow in street networks

Air ventilation studiesFlow in street networkFlow in street network

High surrounding buildingsHigh surrounding buildings

Low surrounding buildingsLow surrounding buildings

Air ventilation studiesWeak wind region behind building group of

varying heights

Air ventilation study Air ventilation assessment on a housing estatesAir ventilation assessment on a housing estates

Wind tunnel studyWind tunnel study

Air ventilation study Air ventilation assessment on a housing estatesAir ventilation assessment on a housing estates

Wind tunnel studyWind tunnel study

B

C

A

Wind

Wind

BA

Air ventilation studies

Wind tunnel study of effect of topography on wind Wind tunnel study of effect of topography on wind flowflow

•• Blockage effect of hills and mountainsBlockage effect of hills and mountains

•• Funnelling effect of valleys and channelsFunnelling effect of valleys and channels

Topographic effect in Hong Kong

Directions WSW, Wind blowing over Victoria Peak areaDirections WSW, Wind blowing over Victoria Peak area

Hong Kong Island WSW

0100200300400500600700800900

1000

0 1000 2000 3000 4000 5000 6000

Wind

Wind Profile

Terrain Profile

0 0.5 1.0

Victoria Peak552m

Topographic effect on wind directionShing Mun River Valley

Wind sectors inside & outside the valleyWind sectors inside & outside the valley

E

Inner areawind sectorson site

S

Nouter ringun-obstructedwind sectors

W

Effect oftopography

Directional probability Directional probability distribution inside the distribution inside the valley will be different valley will be different from that of the unfrom that of the un--obstructed windobstructed wind

R & D on Wind Loading

•• Wind loading on unWind loading on un--usual shaped buildingusual shaped building

•• Structure with curved surfaceStructure with curved surface

•• Structure having protrusions on building envelopStructure having protrusions on building envelop

Thank You