Reducing the exposure risk in hospital wards by applying stratum ventilation system

Occupancy-aided ventilation for both airborne infection risk control and work productivity

“…The rebreathed fraction based airborne infection risk evaluation is developed based on the assumption that the pathogen distribution in the indoor air is uniform (Equations (2) , (4) ). However, the pathogen distribution is inevitably non-uniform [ 9 ]. This assumption has been widely used and is regarded as acceptable for mixing ventilation [ 18 ].…”

“…When the ventilation system employs advanced air distribution which delivers fresh and clean air effectively to the breathing zone, e.g. , displacement ventilation and stratum ventilation [ 9 , 21 ], the assumption of uniform distribution of airborne pathogens might cause large errors, and new evaluation methods are required to account for the effects of the non-uniformly distributed airborne pathogens on the airborne infection risk [ 32 ]. Moreover, the airborne infection risk evaluation requires the number of infectors, while it is challenging to deterministically obtain the number of infectors unless the epidemical data are available.…”

“…Ventilation, as one of engineering controls, plays a crucial role in reducing airborne infection risk [ 3 ]. Ventilation (natural ventilation or mechanical ventilation) is widely used for thermal comfort [ 8 ] and indoor air quality [ 9 ]. Regarding indoor air quality, ventilation replaces contaminated indoor air with clean air to dilute the pathogens in aerosols and lower the inhaled dose [ 9 ].…”

Recent research on expiratory particles in respiratory viral infection and control strategies: A review

“…The air undergoes good mixing within the occupied zone, then starts to lift upwards similar to DV ( Yang et al., 2019 ) Can facilitate rapid mixing of air in the occupied zone, with the space above the occupied zone stratified to prevent the return of contaminants; Close to occupants for easy control The high-speed supply jet promotes resuspension of particles from the floor and into the breathing zone ( Bolashikov & Melikov, 2009 ) Impinging jet ventilation (IJV) A jet of air is supplied downwards with high momentum at a certain height, then strikes and spreads over the floor, forming a very thin shear layer with a far reach. The exhaust is generally near the ceiling level ( Karimipanah & Awbi, 2002 ; Yang et al., 2019 ) Fresh air can be delivered directly to the occupied zone due to thermal stratification; Heated air can be supplied in winter, which has sufficient momentum to overcome the buoyancy force generated by heat sources ( Yang et al., 2019 ) Because of the discomfort of the draught, the application is suggested in scenarios where occupants remain in fixed positions ( Haghshenaskashani & Sajadi, 2018 ) Confluent jet ventilation (CJV) Circular jets are delivered in parallel directions in the same plane, coalescing at a certain distance downstream and moving as a single jet ( Cho et al., 2008 ) Confluent jets have slower velocity decay than other jet forms due to less entrainment of the ambient air, therefore the momentum is conserved better and the confluent jets can penetrate further in the occupied zone ( Andersson et al., 2018 ) Wall attached ventilation (WAV) Fresh air is delivered from the linear slot inlet, attached to the sidewall or column surface due to the Coanda effect, moving downwards, impinging and spreading over the floor ( Li et al., 2019 ) Can be used in both cooling and heating mode; Simple to install ( Li et al., 2019 ) Stratum ventilation (SV) Clean air is delivered horizontally, forming the lowest air temperature and highest air velocity at the breathing zone ( Lu et al., 2020 ) Forms a fresh air layer and reduces contaminant concentration in the breathing level ( Lu et al., 2020 ) Supplied air temperature and contaminant source position can affect the performance of SV ( Tian et al., 2010 ) Piston ventilation / Laminar airflow …”

“…Meanwhile, all three ventilation systems can operate in heating mode. Stratum ventilation (SV) delivers clean air horizontally into the breathing zone ( Lu et al., 2020 ), while Piston ventilation (or laminar airflow) can supply clean air vertically or horizontally across the whole room and swipe airborne virus away in a “washing effect” ( Yang et al., 2019 ). Strictly speaking, Protected occupied zone ventilation (POV) is not a type of TVAD, as it separates the indoor space into several subzones through downward-plane jets with low turbulence, which can effectively reduce short-range cross-infection ( Cao et al., 2014 ).…”