Influence of mixed and displacement air distribution systems' design on concentrations of micro-particles emitted from floor or generated by breathing

Abstract

Particles deposited on surfaces and floors can be reintroduced into air through re-suspension; thus constituting a threat to humans’ health. The ventilation system configuration should reduce indoor air particle concentrations and ensure minimal deposition and re-deposition fractions over surfaces and floors. The purpose of this work is to compare the effectiveness of different mixed and displacement air distribution system configurations in removing re-suspended particles from indoor occupied space for two main scenarios of particle generation: floor emissions and particle generated at the breathing level. The performance was investigated using configurations with variable inlet/outlets sizes and locations by evaluating breathing level air quality. A computational fluid dynamics (CFD) model was developed to predict the flow field and particle transport in the space using ANSYS Fluent software. The model was validated by experimentation. Good agreement was achieved between the CFD and experimental values of planer normalized concentration at different heights with a maximum relative error in the order of 10%. This was followed by a parametric study conducted to determine the most influential design parameters in enhancing indoor air quality: the relative inlet/outlet location, the number of exhausts and the suction velocity. Mixed ventilation configuration with top supply and two floor return vents at walls’ middle (reversed displacement ventilation) presented the best performance in case of floor generation by creating an effective symmetrical suction covering the majority of floor area while DV provided the worst performance. Accordingly, recommendations on switching operation between displacement and mixed ventilation were provided in case of activities involving high floor resuspension as dusting and vacuuming. © 2019 Elsevier Ltd