Last night I went to an event at the venue where my local Queer Club takes place. I took CO2 readings with my #Aranet, did some estimates of the room volume, and measured the flow rate of the filter box they have there.
In terms of raw CO2 numbers (which ignore air filtration) and Air Changes Per Hour (which ignore room occupancy) the numbers were pretty dismal.
But I got enough data to try modelling the room using co2room [codeberg.org], a Python script I wrote.
I worked out the natural ventilation rate of the building by tweaking until the resultant curve fit the readings from the Aranet.
At 40 people last night, the "effective CO2 rate" (i.e. the CO2 readings you'd get if you were ventilating rather than filtering) topped out around 1000ppm, which is above my risk threshold.
However, at my Queer Club event which has only about 20 people, even though it runs for longer it tops out at about 500ppm.
I will feed back to the venue that they probably want a max capacity of 30 if they expect their filter box to be effective. And offer them one of the CR boxes I'm building - at full whack, they should filter enough air to allow up to 70 people.