On the Air Flow in Urban Canyons for Ventilation
Purposes
Ch.Georgakis
and M. Santamouris
Group of Building Environmental Physics,
University of Athens, Building Physics 5, University Campus, 157 84
Athens, Greece
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Abstract
The work described in this paper formed part of the
European UrbVent project on urban ventilation. Measurements of wind speed,
wind direction, and air temperature were made at four different heights,
inside a pedestrian street canyon in the centre of Athens, Greece, and at
the top of the canyon. In addition, infrared radiation on the canyon façades
was measured. Experimental
data were collected at intervals of 30 seconds. The dimensions of the
canyon were: height/width=2.3, length/height=50/23=2.2 with an orientation
of 12 degrees from North. Measurements were made under normal summer
weather conditions. Results revealed that there was a significant
difference between the surface temperatures of the canyon façades and
that the heat island effect varied up to 5°C.
For ambient flow perpendicular to the main axis of the canyon, the
air flow inside the canyon is characterized by a single vortex driven by
the ambient air flow. In this case, the air velocity inside the canyon was
strongly correlated with the velocity above the buildings. When the air
flow outside the canyon was parallel to the main axis of the canyon, the
measured wind speed and direction inside the canyon were strongly
correlated with the conditions outside the canyon.
Key words: Wind speed,
wind direction, air temperature, surface temperature, urban canyons,
street canyons, vortex, heat island.
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