CovidVentilation - The Psalter

Some thoughts, numbers and reading on ventilation during COVID

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. For a 20kph wind, 2.5cm should do.
Warren wrote on 1 Oct 2021:
As we move into late Spring and Summer (I could not support it earlier in the heart of winter), I do now support David’s proposition on air flow. If we do recommence any onsite worship, we should advise people attending that all our windows and entrance doors will be wide open during worship. There would be no A/c or fans used, and attendees and worship leadership would need to be aware there will of course be increased traffic noise and complex noise. And social distancing will still be a good protection. With all these riders applied to any and all our worship, it will restrict us for some time on attendance numbers. We could not expect all our congregation being able to worship at their preferred times, or together, for a much longer time.

The volume of our church auditorium is about 1500 cubic metres.
One person takes about 15 breaths per minute, each of 0.5 litres, with expired air being about 5% CO2, giving about 20 litres of carbon dioxide per hour, or 0.02 cubic metres. After an hour this would raise the CO2 concentration by 0.02/1500*1,000,000 or 13ppm. (Parts per million.) With acceptable concentrations of 400ppm above ambient of 400ppm at the end of a one hour service, we would be good for 30 people.

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 or 7500 m³/hr (Clean Air Delivery Rate) for 70 people
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.

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Collected by DavidMorgan