Anemometers are instruments dedicated to measuring air and gas velocity, essential for HVAC, ventilation, safety, process control, air quality, and meteorology applications. There are several main technologies, each optimized for specific ranges and operating conditions: hot-wire anemometers, vane anemometers, Pitot tube anemometers, ultrasonic anemometers, and vortex anemometers. The choice depends on the velocity range, the required accuracy, the duct geometry, the gas temperature, and the presence of particulate matter.
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Hot wire anemometers
Hot-wire anemometers use a thin metal wire (typically platinum or tungsten) heated to a controlled temperature; the airflow cools the wire by convection, reducing its electrical resistance. The electronics maintain a constant wire temperature (or current) and measure the required power, from which it calculates the flow velocity according to King's equations or dedicated equations. They are particularly accurate at low velocities (0,01-2 m/s), ideal for measuring ambient air flow and ventilation vent flow rates. The dynamic response is excellent (hundredths of a second), but the wire is fragile and deteriorates in the presence of particulate matter.
Propeller anemometers
Vane anemometers use a lightweight propeller (typically 60-100 mm in diameter) mounted on a low-friction bearing; the airflow rotates the propeller at a speed proportional to the flow velocity. An optical or magnetic sensor counts the revolutions per second, and the electronics calculate the linear velocity. They are robust and suitable for medium-high speeds (1-30 m/s standard, up to 80 m/s with special propellers). They are used for measurements on ventilation vents, air ducts, paint booths, and HVAC system maintenance. Propellers of various sizes are used depending on the typical speed of the application.
Pitot probes
Pitot probes measure the difference between the total (stagnation) pressure of the flow and the static pressure; the velocity is derived from Bernoulli's formula: v = √(2 ΔP/ρ), where ρ is the air density. The typical Pitot probe is a metal tube (stainless steel) with two ports: an axial one for the total pressure, a lateral one for the static pressure. It is connected to a low-pressure differential pressure gauge (typical range 0-1000 Pa or 0-2500 Pa). Pitot probes are used for velocity measurements in large-section air ducts, in fan and compressor testing, and in the aeronautical industry.
HVAC Applications
HVAC applications are diverse: balancing air conditioning systems (checking supply and return air flow rates across all vents in a building); testing air handling units; checking extractor hoods in professional kitchens (with the minimum required capture velocity for food and environmental safety); checking paint booths (checking vertical extraction velocity to avoid solvent dispersion); commissioning clean rooms (checking air velocity under HEPA filters, compliant with ISO 14644); energy efficiency inspections of air conditioning systems; and maintenance of industrial ventilation systems.
Features and functions
Modern anemometers integrate: simultaneous measurement of speed, flow rate (with input of duct dimensions), temperature, humidity, and pressure; time averaging and statistical functions; alarm thresholds; memory for hundreds of measurements; USB/Bluetooth data output; PC software for archiving and generating balancing reports; interchangeable probes (hot wire, propeller, miniature probes for small spaces, Pitot); calculation of average flow rate on grilles for measurements on large outlets.
Reference standards
The main standards are: ISO 5167 (for flow measurement with Pitot tubes and other restrictors); ISO 7726 (for ergonomics and indoor climate); EN 12599 (testing and commissioning of building ventilation systems); ASHRAE 111 (USA, HVAC commissioning). Anemometers are calibrated in reference wind tunnels with ISO 17025 traceability. Typical calibration frequency is annual.
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