A Literature Review on Methods and Metrics for the Analysis of Outdoor Air Displacement Conditions in the Urban Environment

The ongoing pandemic has driven the attention of both policy makers and professionals of the building sector towards the need for proper ventilation of the indoor environment. Despite accurate ventilation control only being available with mechanical ventilation systems, in several countries worldwide the renovation of indoor air relies mainly on natural solutions. In this context, in the design of new or renovated buildings, conventional natural ventilation rates are typically assumed to be in agreement with available technical standards, sometimes regardless of the actual external conditions. For instance, local wind speed and direction, as well as buoyancy-driven air displacements, are not considered, even if they can significantly affect the ventilation efficacy for the designed buildings. Moreover, the local outdoor temperature and the presence of pollutants are rarely accounted for, even though they can represent interesting inputs not only for naturally ventilated buildings but also for mechanical ventilation systems. In the framework described above, this review paper aims to provide an overview of the current state-of-the-art of the research regarding air displacement and conditions in the urban context, focusing on the main methods, parameters and metrics to consider in order to ensure a deeper and more accurate modelling of natural ventilation potential in the urban built environment. The analysis of the literature includes both experimental and numerical studies. As regards the latter ones, the features of the chosen urban areas—real or parametric ones—the adopted turbulence models and the indexes calculated as simulation outputs were analysed, with the purpose of defining a common framework to support future extensive numerical studies.