Effect of flow disturbance induced by walking on the performance of personalized ventilation coupled with mixing ventilation

Abstract

The aim of this work is to investigate the effect of a walking occupant disturbance, on the performance of personalized ventilation (PV). A computational fluid dynamics (CFD) model of an office space with two people was developed. The first occupant was seated while using the PV (4 L/s). The second occupant was walking along a linear path parallel to the PV jet direction. A dynamic mesh was adopted to model the walking motion. The flow field was validated experimentally in a chamber equipped with stationary and walking manikins. The validated CFD model was used to assess the PV jet during the disturbance. Moreover, tracer gas was used to evaluate the breathable air quality of the PV user. CO2 was used to model passive contaminants in the space, while SF6 represented a local contamination source (walking occupant).Results showed that the walking disturbance deteriorated the PV efficiency. When the occupant was at its closest to the seated occupant and PV, turbulence intensities increased to 21%. This enhanced entrainment of contaminants into the jet, causing a decrease of εv by 72% and 56% for CO2 and SF6. When the occupant is at the end of the trajectory, the negative pressure at the back deflected the PV jet away from the breathing zone. This decreased εv by 60% and 45% for CO2 and SF6. A safe distance of 85 cm between the occupants was recommended to preserve air quality. Moreover, using a wider PV of 18.5 cm diameter (15 L/s) increased εv significantly.