CovidVentilation

Some thoughts and numbers on ventilation during COVID

How far should our windows be open?

• When someone sneezes, coughs or sings, they create aerosols that linger in the air for hours.
• The purpose of ventilation is to carry those droplets out of the building before someone breathes them in.
• The time to do that needs to be small compared to the service duration to be useful.
• Assuming that we want the air changed 5 times per hour and the church is 20 metres wide, this means an average air flow of 100m/hour or 0.1km/hr
• So the fraction of the wall that needs to be open is 0.1 divided by the outside wind speed in km/hr.
• If the average height is 5 metres, then the required opening can be calculated in cm as 500 times that, 50/(wind speed in km/hr). Five cm for a 10kph wind.

Can a carbon dioxide meter help us determine ventilation?

• https://twitter.com/mdc_martinus/status/1401278363449409539?s=20 Belgian Coronavirus Commissioner making CO2 meters mandatory in all indoor venues.

• https://theconversation.com/belgium-has-mandated-carbon-dioxide-monitors-in-certain-venues-to-help-fight-covid-but-how-useful-are-they-162734 Commentary on the above.

• https://www.irishtimes.com/news/world/europe/belgium-imposes-ventilation-rules-for-businesses-to-combat-new-covid-surge-1.4612101

• https://kildare-nationalist.ie/2021/07/04/how-co2-monitors-could-play-key-role-in-reopening-indoor-dining-in-ireland/

• https://www.rte.ie/news/coronavirus/2021/0709/1234155-hospitality-ventilation/

• https://www.sciencedaily.com/releases/2021/04/210407143809.htm

• Meters being installed in Irish schools.

• The Age on ventilation.

COSMOS article

• Ventilating complaints about air standards.pdf

• Virus is airborne; ventilation is key.
• Purifier airflow rates of 3 litres of air per second per person are needed.
  • This comes to 10.8 cubic metres per hour per person.
  • Samsung AX7500K Air Purifier $999 is rated as CADR 701m³/hr (Clean Air Delivery Rate)
• A fallback ventilated system (for a naturally ventilated building) comes into operation when the detected levels of CO2 in the air rise above about 800 parts per million, so it could reliably improve air quality.