Scale fan performance to a new speed or air density. Fan laws extend the affinity laws with a density correction — pressure and power scale with ρ₂/ρ₁.
Turbomachinery · Fan ScalingAir density — click preset to fill both ρ₁ and ρ₂ (or set individually)
Change ρ₂ for altitude/temperature correction — if same as ρ₁, no density correction
Fan laws with density correction:
Pressure unit equivalences (1 Pa = ...):
Standard air density at sea level:
| Condition | T [°C] | ρ [kg/m³] | vs 20°C |
|---|---|---|---|
| Cold winter air | 0 | 1.293 | +7.4% |
| Standard HVAC | 20 | 1.204 | — |
| Warm supply | 40 | 1.127 | −6.4% |
| Hot supply | 60 | 1.060 | −12% |
| 1 000 m altitude | 8.5 | 1.112 | −7.6% |
| 2 000 m altitude | 2.0 | 1.007 | −16% |
Fan laws are the extension of affinity laws to include gas density changes. When ρ₂ = ρ₁ (same gas, same conditions), the fan laws reduce to the pump affinity laws. The density correction is critical in HVAC: a fan designed for winter air (0°C, 1.293 kg/m³) running in summer (35°C, 1.146 kg/m³) delivers ~11% less pressure at the same speed.