Abstract
The objective of this study is to investigate the characteristics of airborne spread of exhaled droplet nuclei between two occupants in a space conditioned by a horizontal air distribution method, known as stratum ventilation. Experiments were conducted in a full-scale climate chamber. Two breathing thermal manikins were used to simulate a standing infected person and a standing exposed person, respectively. Tracer gas (N2O) was added into the air exhaled by the infected manikin. The tracer gas concentrations in the air inhaled by the exposed manikin and at the ventilation exhaust were continuously monitored. ACH was kept at 2 h-1. The variables in the experiments include the positioning of the manikins, the distance between manikins, and the room air temperature. The horizontal supply airflow to the breathing zone strongly intensifies the mixing between the flow of exhalation and the room air, which reduces the exposure risk of occupants at close proximity and flattens the risk-distance curves. The homogenization of concentration weakens considerably the importance of the relative positioning and location of the infected and exposed persons. All those characteristics of airborne transmission may not be maintained, however, if the horizontal supply jet does not interact directly with the occupants. The findings from this study are intended to contribute for better understanding of airborne transmission indoors.
Highlights
The indoor air quality has concentrated more and more attention for past decades since it is closely concerned with the human health
Many previous studies have focused on investigating the airborne transmission between occupants in rooms conditioned by commonly used total volume air distribution methods, including displacement ventilation (DV), mixing ventilation (MV) and under floor air distribution (UFAD)
The results from Nielson’s showed that at proximity the susceptible exposure index could reach to seven times higher than that in the remote distance
Summary
The indoor air quality has concentrated more and more attention for past decades since it is closely concerned with the human health. Many previous studies have focused on investigating the airborne transmission between occupants in rooms conditioned by commonly used total volume air distribution methods, including displacement ventilation (DV), mixing ventilation (MV) and under floor air distribution (UFAD). Mui et al [7] numerically modelled the dispersion of exhaled droplet nuclei between an infected manikin and an exposed manikin under MV and DV in an empty room. He et al [8] studied the transmission behaviours of exhaled aerosols between two occupants under MV, DV and UFAD. There has been little discussion regarding stratum ventilation (SV) in this field
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