You may be over-engineering things. Since there's no specific cutoff or precise value you need before calling a break, you could probably work out what rate thi

You may be over-engineering things. Since there's no specific cutoff or precise value you need before calling a break, you could probably work out what rate things would increase at per typical person given the volume of the room and then just have a timer. Something like "Calm - 120 people-minutes, Energetic - 60 people-minutes, so three people really going for it means we take a break every 20". Maybe this isn't enough for you, but I know it's easy for me to get trapped in a rabbit hole of how to solve things in a specific way and at times I need to pull back and say "what am I actually trying to solve". I had this with co2 monitors, getting fairly into which one to get then I realised I can deal with this by just regularly opening the window. I don't need a specific number. edit - Air exchange may happen pretty quickly, depending on the room and surroundings, so it could be as easy as "every X minutes we take a moment to open the door and window".