Preparing airflow intelligence
Calibrating industrial-grade components and rendering the next section.
How inlet and outlet conditions impact actual installed performance versus catalog curves.
One of the most common causes of fan underperformance in the field is the failure to account for system effect factors (SEF) during design. Fan performance curves are measured under ideal laboratory conditions — real installations rarely match these.
System effect occurs when the velocity profile entering or leaving the fan is non-uniform. Elbows, transitions, or dampers placed too close to the fan inlet create swirl and turbulence that reduce effective pressure. AMCA Publication 201 provides standardized SEF calculation methods.
A 90° elbow directly at the fan inlet can reduce fan performance by 15–25%. The recommended minimum straight duct length before the fan inlet is 2.5–5 duct diameters depending on elbow configuration.
Outlet system effect occurs when the fan discharges into a plenum or abrupt expansion without adequate duct length for velocity pressure recovery, reducing system efficiency.
For Aerotech's AX-Series axial fans, the adjustable pitch mechanism allows field correction of performance shortfalls caused by system effect — compensating for up to 10–15% SEF penalty without motor replacement.
Engineers should always perform a system effect analysis during the design phase, adding SEF penalties to the calculated system resistance before selecting the fan to ensure operation at the best efficiency point.
