Abstract
A new design method is proposed to calculate outdoor air ventilation rates to control respiratory infection risk in indoor spaces. We propose to use this method in future ventilation standards to complement existing ventilation criteria based on the perceived air quality and pollutant removal. The proposed method makes it possible to calculate the required ventilation rate at a given probability of infection and quanta emission rate. Present work used quanta emission rates for SARS-CoV-2 and consequently the method can be applied for other respiratory viruses with available quanta data. The method was applied to case studies representing typical rooms in public buildings. To reduce the probability of infection, the total airflow rate per infectious person revealed to be the most important parameter to reduce the infection risk. Category I ventilation rate prescribed in the EN 16798-1 standard satisfied many but not all type of spaces examined. The required ventilation rates started from about 80 L/s per room. Large variations between the results for the selected case studies made it impossible to provide a simple rule for estimating the required ventilation rates. Consequently, we conclude that to design rooms with a low infection risk the newly developed ventilation design method must be used.
Highlights
People around the world suffer multiple airborne respiratory in fections each year; this is creating suffering and significant socioeconomic costs
The results show that lower individual probability levels of 3% and 1% are more achievable in larger rooms; in the large classroom a Cate gory II ventilation rate is enough for 3%
While quanta emission rates were increased by 30%, required ventilation rates increased by 33–50% and on average by 39% in the rooms studied
Summary
People around the world suffer multiple airborne respiratory in fections each year; this is creating suffering and significant socioeconomic costs. Available information on COVID-19 shows that transmission of this disease has been associated with the close proximity for which general ventilation is not an efficient solution, as well as when ventilation is inadequate especially in crowded spaces The latter is supported by the evidence from superspreading events where ventilation with outdoor air was measured or estimated to be as low as 1–2 L/s per person [17,18,19] which is lower by a factor of 5–10 lower than the commonly prescribed 10 L/s per person in existing standards [20,21]. Acceptable risk level is calculated from event reproduction number This newly developed equation can be applied to design rooms with low infection risk that in some cases can be feasible, but in some cases not, as demonstrated by a number of case studies conducted in public buildings. The study is limited to general ventilation with fully mixing air distribution and effects on spatial concentration differences at different locations in the rooms are not analysed
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