Airflow TrackingAirflow tracking is a return fan control strategy in which the return fan speed is modulated to maintain return airflow at a setpoint. During the fully recirculating modes listed above, it would make sense for the offset used in return fan control to be 0 CFM. It is probably best to demonstrate this recirculating mode death spiral by watching it play out on a BAS graphic. This allows for more consistent building pressure control during Occupied Mode and avoids the Recirculating Mode Death Spiral from ever occurring during Unoccupied Mode. Stay tuned as I walk through at least five more case studies where the AHU recirculating mode death spiral has reared its head.