Many demand oriented ventilation systems are facing one common problem. They are designed for operation with some nominal air flow volume that correspond to air flow velocities of a few meters per second in the duct. This is the sunny side of the life for the most ventilation systems, since the air flow is easily and precisely controlled by simple and affordable means like common VAV (Variable Air flow Volume) controllers.
Though, there are periods when just a tiny fraction of this nominal air flow volume is required. Let´s point some examples for such demand oriented ventilation systems.
During such operation periods the air flow velocities shall be measured deep below one meter per second. Here the most popular control methods hopelessly struggle against massively increasing imprecision.
Getting out of the imprecision trap at low air flow velocity measurement.
Some of the air flow velocity measurement methods seem to solve the low velocity imprecision problem and perform well at the higher velocity end of range as well.