diffrentcolours | Air Filtration

A couple of weeks I went to an event at the venue where my local Queer Club takes place. Obviously we wore masks. There were about 40 people in attendance. I took CO2 readings with my Aranet4 Home, did some estimates of the room volume, and measured the flow rate of the filter box they have there.

Both in terms of raw CO2 numbers (which ignore air filtration) and Air Changes Per Hour (which ignore room population and activity) the numbers were pretty dismal. But I got enough data to try modelling the room using co2room, a Python script I wrote.

Given the number of people in the room and the volume, I worked out the natural ventilation rate of the building by tweaking until the resultant curve fit the readings from the Aranet.

Then I fixed that, and tried changing the number of people in the room. At 40 people, 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'll feed back to the venue that they shouldn't expect the filter to be useful with more than 30 people tops in the room, and see if I can donate a bigger one to them - the 20" box I'm working on should allow up to 70 in there.