Co-occupant's exposure to exhaled pollutants with two types of personalized ventilation strategies under mixing and displacement ventilation systems

Abstract

Personalized ventilation (PV) system in conjunction with total ventilation system can provide cleaner inhaled air for the user. Concerns still exist about whether the normally protecting PV device, on the other hand, facilitates the dispersion of infectious agents generated by its user. In this article, two types of PV systems with upward supplied fresh air, namely a chair-based PV and one kind of desk-mounted PV systems, when combined with mixing ventilation (MV) and displacement ventilation (DV) systems, are investigated using simulation method with regard to their impacts on co-occupant's exposure to the exhaled droplet nuclei generated by the infected PV user. Simulation results of tracer gas and particles with aerodynamic diameter of 1, 5, and 10 μm from exhaled air show that, when only the infected person uses a PV, the different PV air supplying directions present very different impacts on the co-occupant's intake under DV, while no apparent differences can be observed under MV. The findings demonstrate that better inhaled air quality can always be achieved under DV when the adopted PV system can deliver conditioned fresh air in the same direction with the mainly upward airflow patterns of DV.

Airborne spread of expiratory droplet nuclei between the occupants of indoor environments: A review

“…Studies finding that DV and UFAD perform better than MV demonstrated that the vertical diluting function of DV and UFAD can reduce the horizontal dispersion of exhaled flows and can thus reduce the risk of cross‐infection. This finding was found to be valid not only for tracer gas but also for small particles <5 μm in diameter …”

“…Past studies that have evaluated the influence of MV, DV, and UFAD on airborne transmission reported some inconsistent findings. Some studies suggested that DV and UFAD are better at reducing the risk of cross‐infection than MV, whereas other studies show that MV performs better than DV and UFAD. Studies finding that DV and UFAD perform better than MV demonstrated that the vertical diluting function of DV and UFAD can reduce the horizontal dispersion of exhaled flows and can thus reduce the risk of cross‐infection.…”

“…However, they are low‐resolution in both space and time. As an alternative, CFD methods employing computational thermal manikins and well‐established mathematical models for the transport of tracer gas/particles can provide a high‐resolution whole‐field flow and concentration data . However, CFD simulations must be experimentally validated and they are very dependent on the knowledge of the practitioners.…”

A time-based analysis of the personalized exhaust system for airborne infection control in healthcare settings

“…The experiments done in this study represent such scenarios, and all the experimental conditions are with 90% recirculated air. Even though in most of the previous work, the given definition of iF was used in situations where the concentration in background supply air is zero (Li et al 2013), the definition of iF is equally valid in the present situation with 90% recirculated air because the measured background concentration is not due to pollutants from other sources except the infected manikin.…”

Particle Tracking Velocimetry for indoor airflow field: A review

“…The performance of ventilation and air distribution systems not only influences the indoor air quality directly [11,12], but also strongly affects the total energy consumptions in buildings [13]. Among the evaluation indices referring to ventilation and air distribution systems, there are airflow patterns (such as trajectory, impingement, separation, circulation, reattachment, buoyancy, vortices etc) and airflow field (temperature, velocity and pressure).…”