When we re-opened after COVID we were nervous about the ventilation in the partially underground fablab. So we built a CO2 sensor to monitor the CO2 build-up in the lab, which is a good proxy for ventilation. For more details on the link between COVID safety, ventilation and CO2 measurement see the HCSP web site (in French).
The CO2 level sensor, uses a MH-Z14A sensor linked to an ESP8266-based Wemos Mini (the same one that was already reading temperature and humidity), which uses wifi to send the reading over MQTT to our openhab based smartlab.
This is then displayed on the web panel
And also displayed on the ceiling mounted LED strip.
As we don’t spend all our time looking at these displays, at 850ppm a loud voice says “CO2 alert; the space must be ventilated” and we then have to open the two doors to allow fresh air to replace the CO2 in the fablab. So far, so good.