Engineering notes
CO2 sensors on an AHU and in a meeting room
Where to put a CO2 sensor for demand-controlled ventilation. Range, output, return-air location.
Return air, not the supply grille
Demand-controlled ventilation reads CO2 in the return or in the occupied zone. A sensor on the supply grille reads outdoor air after the mixing box and does not see the room. 0–2000 ppm is enough for offices; lock the output to the DDC input (0–10 V or 4–20 mA).