On the impact of the urban environment on the potential of natural ventilation.

Knowledge and estimation of the wind speed and air flow characteristics, in a city, is of vitalimportance for passive cooling applications and especially in the design of naturallyventilated buildings. This study is referred to the analysis of the wind characteristics in urbancanyons as a function of the free stream wind. The impact on the airflow rate calculation isdiscussed for an urban canyon. The goal of this study is to get a better insight of the impact ofthe urban environment on the ventilation effectiveness. For this reason a large number of dataare collected including air temperature, wind speed and direction above and at various heightsinside ten urban canyons in Athens. Two ventilation techniques are considered: single sidedand cross ventilation and three different cases are studied regarding the incidence angle of thefree stream wind to the canyon axis: (a) vertical incidence, (b) parallel incidence and (c)oblique wind. Finally a model is proposed for the simple calculation of the wind speed andair flow characteristics in urban canyons.