Wind Tunnel Study for Estimating Outdoor Ventilation in a Dense Low-Rise Building Area

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.