Calculateur de Lois d'Affinité de Ventilateur — Formule

Fan Laws (Affinity Laws for Fans)

The fan laws are identical in form to the pump affinity laws. They predict how fan performance changes with rotational speed.

Fan Laws for Speed Change

Q2/Q1 = N2/N1 (airflow scales linearly)

SP2/SP1 = (N2/N1)² (pressure scales with speed squared)

BHP2/BHP1 = (N2/N1)³ (power scales with speed cubed)

A small 10% speed reduction cuts power by 27%, making variable-speed fans highly efficient for part-load operation.

Exemple Résolu

A fan at 1200 RPM moves 10,000 CFM at 2.0" w.g. using 5 HP. Speed increased to 1500 RPM.

  1. Speed ratio = 1500 / 1200 = 1.25
  2. Q2 = 10000 × 1.25 = 12,500 CFM
  3. SP2 = 2.0 × 1.25² = 2.0 × 1.5625 = 3.13 in. w.g.
  4. BHP2 = 5 × 1.25³ = 5 × 1.9531 = 9.77 HP