Individual control of the frequency of intermittent personalized ventilation and its effect on cross-contamination in an office space

Abstract

The transmission of respiratory diseases is influenced to a great extent by the ventilationin the space, mainly localized ventilation near the infection source (i.e. the infected person): One of the strategies that has been proven efficient in providing occupants with protection indoor are source control strategies. Personalized Ventilation (PV) is such strategy that delivers conditioned clean air towards the breathing zone of the user, thus providing protection while procuring acceptable levels of thermal comfort. In recent studies, PV applications varied the supplied cool clean air intermittently, mimicking natural outdoor conditions in order to enhance occupants’ thermal comfort and improve energy efficiency. Such system operation is referred to as Intermittent PV (I-PV). The highly turbulent oscillatory jet may however promote the dispersion of contaminants, especially when the user is infected. Furthermore, the individual preferences of IPV frequency also affects the contaminants’ transport. To the authors’ knowledge, such effect has not been tackled in literature. Therefore, this work investigates the impact of individually controlling the frequency of an I-PV system on cross-contamination between occupants in an office space. An infected person is considered seated in a tandem (i.e. back-to-face) position with respect to a healthy person, located at a distance of 1.5 m. This seating configuration is usually the most critical when using PV. The contamination source is the breathing of the infected person. The IPV is considered to operate at an average flowrate of 10 l/s, with a minimum of 4 l/s. The IPV users are free to control the frequency of flow delivery in a range of [0.3 Hz – 1 Hz]. A validated computational fluid dynamics (CFD) model of an office space equipped with IPV and background mixing ventilation is used to assess the cross-contamination between the occupants. A comparison between IPV frequencies is conducted to highlight the influence of IPV frequency control on contaminants dispersion and the resulting exposure level of the healthy occupant.