Wind Tunnel
Study for Estimating Outdoor Ventilation in a Dense
Low-Rise Building Area
Bin
Su
School
of Architecture and Landscape Architecture, UNITEC Institute of
Technology,
Auckland, New Zealand
Abstract
To accurately estimate the
natural ventilation of outdoor spaces surrounded by low-rise buildings
using a wind tunnel requires
correct representation of the natural wind regime combined with
appropriately scaled building models and testing method.
Existing outdoor ventilation studies are largely based on wind
speed and estimated air change rates.
Wind speeds mainly influence: peoples’ comfort, safety in
pedestrian areas, the heat transfer between outdoor surfaces and airflow,
and evaporation from wet surfaces. Studies
of air change rates in outdoor spaces (for regions below surrounding roof
height) are mainly related to the dispersion and/or removal of pollutants,
moisture and hot air. This paper considers the application of wind tunnel
studies to estimate the ventilation of outdoor spaces.
It also considers the role of CO2 as a tracer gas for
such studies. It concludes that to accurately estimate the ventilation of
outdoor areas by means of a wind tunnel analysis, the natural wind
properties in the wind tunnel model must be correctly related to the local
terrain category. Buildings
themselves can be represented by low cost small scale models constructed
from expanded polystyrene. The CO2 tracer gas method is a safe, low cost and
efficient quantitative test method for estimating the ventilation of
outdoor spaces using a wind tunnel.
Key words:
natural outdoor
ventilation, wind tunnel study, CO2 tracer gas, air change
rate, pollutant dispersion, low-rise building.
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