Troubleshooting System Performance

In most cases where fan systems fail to perform as predicted, the fan is not the problem. Always look for other possible causes in a systematic approach to troubleshooting. Remember fan ratings are derived from laboratory tests in ideal conditions, and site installations are rarely like this! Was proper allowance made for the "system effect" of any less-than-ideal situation at the design stage?

LOW AIRFLOW
Check correct fan rotation. (Fans running in reverse may only deliver 50-70% of normal flow and centrifugal fans still move air in the correct direction through the duct system even in reverse.)
Check for obstructions in duct or blocked filters.

Check for restriction at fan inlet such as slack flexible connection, a bend too close or inadequately sized duct (as demonstrated here)

Check for restrictions at the fan outlet
closer than 2D.
This weathercap for instance will
severely affect fan performance!

Is there turbulent flow into the fan?  Here are some commonly encountered installation problems and their solutions -

Is there leakage in the duct system?   The fan may be passing the correct air quantity even if terminal measurements indicate a deficiency.

EXCESSIVE NOISE
Inappropriate installation will result in excessive air noise.
Obstructions close to fan inlet will produce air turbulence and high noise levels.
Lack of vibration isolation can cause normal operating noise to be transmitted and even amplified into the structure.
Some slow speed and single-phase motors produce electrical noise, which can at times be a nuisance.

Fans are conventionally rated assuming spherical radiation of sound waves in "free field" conditions. This is a theoretical condition that makes no allowance for the effect of the surrounding environment. Actual installed sound levels depend on this effect and will usually vary from the "dB(A) @3m" figure catalogued. For example the noise level in a reverberant factory with fans installed in a high roof can be up to 10dB above the catalogued dB(A) @ 3m.




Please contact us if you are experiencing difficulties with any of our fans.