The Influence of Street Canyon Design on Hospital Air Quality

This study considers air exchange between outdoor and indoor environments in the context of a hospital room with single-sided natural ventilation. Computational fluid dynamics (CFD) simulations are used to examine the trade-off between outdoor pollutant ingress and indoor contaminant dilution, and the influence of the street canyon design. Two street-canyon aspect ratios were investigated (Height/Width=0.5 and 1) with roof angles of zero and 26.6º. An open window was located on the on the leeward side connecting to an interior room. ANSYS Fluent 15 was used to model airflow in the indoor and outdoor spaces and employed a k-omega turbulence model. A tracer was released in the outdoor location between the buildings and concentrations determined inside the open window. A second tracer released inside the building was used to establish concentrations at the pedestrian level outside. Increasing canyon width reduced the residence time of the outdoor pollutant and reduces ingress. Flat roofs for both ratios drew the tracer to the leeward side of the building due to negative pressures. However, pitched roofs created more complex systems that reduced contaminant in the canyon due to unsteady vortices. Contaminants released inside the room result in proportionally higher concentrations outside for narrow canyons.