Air Velocity Sensors Explained: How They Work & Where to Use Them
An air velocity sensor measures how fast air is actually moving through a duct or opening — a direct measurement that drives airflow control, energy calculations, and system commissioning. Jaideo Automation supplies the Air Velocity Sensors range.
How an Air Velocity Sensor Works
Most HVAC air velocity sensors use a heated element (hot-wire or thermal dispersion principle) — as air flows past the sensing element, it cools the element at a rate proportional to air velocity. The sensor measures that cooling rate and converts it into a velocity or flow reading, output as a signal a building automation system can read and act on.
Why Measure Air Velocity Rather Than Just Pressure
While a differential pressure switch infers airflow status indirectly through pressure signature, an air velocity sensor measures velocity directly. This matters for applications needing accurate airflow values rather than just a threshold alarm — variable air volume (VAV) control, outdoor air measurement for ventilation compliance, and energy monitoring all depend on knowing the actual velocity, not just whether flow crossed a setpoint.
Applications
- Variable air volume (VAV) systems — modulating airflow to match zone demand requires continuous velocity feedback
- Outdoor air measurement — confirming minimum ventilation rates are being delivered for indoor air quality compliance
- Duct airflow monitoring — verifying design airflow is actually being achieved after installation
- Energy calculations — airflow data feeds into energy consumption and efficiency reporting
Where Air Velocity Sensors Are Installed
Typically mounted directly in the ductwork at a point with stable, well-developed airflow — away from bends, dampers, or other turbulence sources that would distort the reading. Multiple sensor points across a duct cross-section are sometimes used for larger ducts to get an accurate average reading.
How This Fits Into Your BMS
Air velocity data feeds directly into building automation system control loops — for VAV box modulation, economizer control, and demand-controlled ventilation strategies covered in our CO2, Enthalpy & Occupancy Sensors guide.
Frequently Asked Questions
How does an air velocity sensor measure airflow?
Most air velocity sensors use a heated element that cools as air flows past it, with the cooling rate converted into a velocity reading proportional to how fast the air is moving.
Why use an air velocity sensor instead of a pressure switch?
An air velocity sensor measures airflow directly and continuously, which is needed for applications like VAV control and outdoor air measurement that require actual velocity values, not just a threshold alarm.
Where should air velocity sensors be installed in ductwork?
Air velocity sensors should be installed at a point with stable, well-developed airflow, away from bends, dampers, or other sources of turbulence that would distort the reading.