Indoor air quality monitoring with KNX

Air quality has moved from a niche concern to a mainstream design parameter. Tenants ask about it; LEED and WELL credits depend on it; productivity studies link it to cognitive performance. KNX air quality sensors integrate naturally with the rest of the building.

What to measure. CO2 is the headline metric: it correlates with occupancy and ventilation effectiveness. Setpoints around 1000 ppm trigger increased ventilation in most schemes. VOCs (volatile organic compounds) catch cleaning chemicals, off-gassing furniture, and cooking. Humidity affects comfort and condensation risk. PM2.5 (fine particulate matter) became a concern with wildfire smoke and is now standard in higher-end installations.

Sensor placement. Place sensors at breathing height (1.2 to 1.5 m above floor), away from windows, vents, and doors. One sensor per zone of similar use; do not assume one sensor represents an entire open-plan floor. Calibration drift is real; budget for re-calibration or replacement every 2 to 5 years depending on the sensor.

Response logic. CO2 above 1000 ppm: ramp ventilation up. CO2 above 1500 ppm: switch to maximum ventilation and notify facility staff. Humidity above 65 percent: enable dehumidification (or, if the HVAC plant cannot dehumidify, alert). PM2.5 above 35 micrograms per cubic meter: increase filter levels and recommend keeping windows closed.

Display. A simple traffic-light indicator (green / amber / red) on a touch panel or a small dedicated display in each room is more effective than precise numbers. Most occupants want to know whether the air is fine, and only an interested few want exact ppm.

Logging. Send the readings to the visualization server for historical charts. A trend chart of last week's CO2 by room is what a facility manager needs to fine-tune setpoints. Over time, the data also supports continuous commissioning of the HVAC system.