A novel approach to enhance outdoor air quality: Pedestrian ventilation system

Higher population density has altered the citiesʹ old landscape with dense areas consisting of high-rise buildings. As a result, detrimental phenomena appeared inside modern cities that threatened the inhabitantʹs health and comfort. Among these phenomena, the Urban Heat Island (UHI) is known as the most harmful side effect of the urbanization which affects the Outdoor Air Quality (OAQ). In addition to the reduction of wind velocity within the urban canopies, the accumulated pollution decreases the OAQ and renders the pedestrian areas to hazardous level. According to earlier researches, the UHI generally shows more intensity in higher aspect ratio (the height of building to street breadth) canopies which mostly exist in high-density areas. These buildingsʹ canopies have typically higher pollution concentration than low-rise residential building canopies due to lower air exchange rate and heavy traffic load. The situation becomes worst under the stable atmospheric stratification condition when the canopy ground is colder than the ambient air. Many passive strategies have been proposed to enhance the OAQ. However, the variety of the UHI makes the passive mitigation strategies ineffective in some cases. In this paper a novel approach, the pedestrian ventilation system (PVS), is proposed to ventilate building canopy under various atmospheric stability conditions: stable, neutral, and unstable. The capability of this system to enhance the pedestrian level health and comfort parameters (i.e. velocity, temperature and air exchange rate) has been studied using Computational Fluid Dynamics (CFD) simulation. The results of the simulations confirm that the PVS can significantly improve the flow regime of the buildingsʹ canopy.