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Lots of people looking to measure CO2 in buildings to assess ventilation, so here's a few thoughts.
You should be looking for CO2 below 1000ppm, and ideally around 800ppm BUT thereâs a bit more to it 1/9
You should be looking for CO2 below 1000ppm, and ideally around 800ppm BUT thereâs a bit more to it 1/9
CO2 is a proxy for ventilation and itâs not perfect. The CO2 is in human exhaled breath. In an indoor space it builds up with time. It will reach a higher value with more occupants and be reduced when the fresh air ventilation rate is higher. 2/9
This means to understand if the ventilation is adequate, you need to measure with the normal number of people in the space. If you measure with less people you will get a lower reading which could give a false impression that the ventilation is OK. 3/9
The amount of CO2 exhaled depends on the people. Children have a lower emission rate than adults, and increased physical activity increases the emission rate. In most spaces you wouldnât notice a big difference between people but it could matter in some spaces. 4/9
Where you measure is important. Check there are no other CO2 sources in the space - if you measure in your kitchen by the gas hob youâll get a false reading 5/9
Try to place sensors in the occupied zone of a room but not too close to a person (you donât want to directly measure their breath) or not by a vent or open window where the ventilation could be better than the middle of room. 6/9
Transient effects also matter. The CO2 builds up and decays quickly when a room has a high airflow rate, but much more slowly in a poorly ventilated space. A single low reading doesnât tell you the whole picture. 7/9
Watch the concentration change with time and wait until it settles down. If after 30 min itâs still slowly rising, the ventilation is poor. If you have a meter that allows you to download, you can plot the data with time. 8/9
If the CO2 goes above 1000ppm for very short periods donât panic - this is probably more people in a room for a short time. If itâs regularly above 1000-1500ppm I would take steps to increase flow or reduce occupancy. 9/9
