Anemometer Measurement in Air Exhaust and Ventilation Systems:
Air vents significantly disrupt the relatively uniform airflow distribution inside ducts: high‑velocity zones form at the surface of open vents, while low‑velocity zones appear in surrounding areas, and vortices are generated across the grille. Depending on the grille design, the airflow cross‑section becomes relatively stable at a distance of approximately 20 cm in front of the grille. Under such conditions, large‑diameter rotary vane anemometer probes are commonly used for testing. A larger measuring aperture averages out uneven flow velocities and calculates representative mean values over a wider area.
Anemometer Measurement with Volumetric Flow Funnels at Suction Openings
Even without grille interference at suction inlets, airflow is disordered in direction and the flow cross‑section remains highly non‑uniform. This is caused by local negative pressure inside the duct, which draws air into the chamber in a funnel‑shaped pattern. No qualified measuring position exists in the immediate vicinity of the suction port to meet standard testing requirements.
Methods such as grid traversal measurement with averaging functions cannot deliver reliable volumetric flow data. Only duct testing or funnel measurement methods ensure repeatable results. Measuring funnels of different specifications are available to suit various working conditions. A measuring funnel creates a stable, standardized flow cross‑section at a set distance upstream of the flap valve. After centering and fixing the probe at this cross‑section, the measured velocity reading is multiplied by the funnel correction coefficient to calculate the extracted volumetric flow rate.
