CO2 is a direct gas measurement in the SEN66 stack. In buildings, it is most useful as an occupancy and ventilation signal: people exhale CO2, ventilation removes it, and the slope of the trace tells you whether the room is accumulating or recovering.
Accuracy still depends on conditions. A sensor buried behind furniture, placed next to a supply diffuser, or located in direct breath plumes will tell a different story from one placed in the occupied breathing zone. Automatic baseline correction also assumes the room periodically sees outdoor-like air; permanently occupied or poorly ventilated rooms need more caution.
Ventilation interpretation should focus on shape: buildup rate during occupancy, peak level, decay after doors open or HVAC changes, and whether the room returns to baseline. A single number is less informative than the curve.
For commercial work, CO2 telemetry can support facilities decisions, but it is not the whole compliance package. Standards and certifications still care about design rates, commissioning, reporting, maintenance, and project documentation.
References
- Sensirion SEN66 datasheet (PDF)
- ASHRAE Standard 62.1 - Ventilation for Acceptable Indoor Air Quality www.ashrae.org
- Persily (LBNL) - Indoor CO₂ and ventilation eta-publications.lbl.gov
