Clean Air Map - Greatly Improve Your CO2 Monitor
A brilliant way to improve the functionality of your Mini CO2 monitor is to help map out the adequacy of indoor air in your community - check out this fantastic mapping system 'Clean Air Map' by Raven.
We've spoken with the amazing people running this site and are looking forward to collaborating with them more closely in the future.
Check out their work, sign up to the Clean Air Map yourself and get mapping:
You'll need a CO2 monitor to gather the data. Check out our Mini CO2 monitors below and use discount code CLEANAIRMAP20 to receive a 20% discount:
In schools and other shared indoor spaces, the key to a safe environment is to keep the windows open whenever people are present. This allows any continuously-exhaled pathogens that are carried within the CO2 in the air. CO2 in the air is constantly diluted and expelled outdoors, however when you are inside it is building up, due to exhaled breath. We do not recommend intermittent opening of the windows (e.g. 5 min. of every hour).
With the windows in a fixed position, and as long as the wind conditions don’t change, a "steady-state" is reached quickly. This means that the amount of exhaled CO2 is approximately equal to the amount of CO2 that leaves through the windows, so that the CO2 level in the room stays approximately constant. It is this approximately constant level that we need to keep below the desired target, e.g. 700 ppm. The graph below shows real data from a school in Spain. The bluish periods correspond to periods of transition, when people arrive or leave the room, or when something is changed with the ventilation (a window is open, in one of the 2 days shown).
If the steady state of CO2 is too high, then you have to open the windows a little more. If CO2 is lower than the limit and people are too cold/too hot, then you can close the windows a little. If you cannot find a way to keep CO2 low enough while keeping people thermally comfortable, then alternative actions are needed, e.g. air cleaning through filtration, reducing the number of people using the space, etc.
As shown in that example, opening 3 windows in a classroom only 15 cm was nearly sufficient to stay around 700 ppm. Thus typically it is not needed to keep all windows fully open. Importantly, the amount of window opening needed will depend on each particular building and room, and meteorological conditions (especially wind). Wind tends to increase the ventilation rate, and on windy days a similar CO2 level should be achievable with smaller window openings. A shared CO2 monitor (e.g. as a project for school students that visit different classrooms multiple times a day) can be used to quickly learn the amount of opening needed for a given indoor space as a function of wind conditions.
Ventilating corridors in schools (and other multi-room buildings) is very important, as otherwise they transfer exhaled air between classrooms.