TL;DR
FFU noise is usually a worn bearing in the centrifugal fan, a loose fan wheel, or panel resonance from fan imbalance. Check fan bearing condition and panel mounting before replacing the fan motor.
What you might see
- rattling or humming noise from one or more FFUs
- vibration transmitted to the ceiling grid
- noise level increasing over several weeks
- particle count slightly elevated below the noisy FFU
Likely causes
Fan motor bearing wear from extended operating hours
Fan wheel imbalance from fiber or particle accumulation on the blades
Loose mounting screw allowing the FFU housing to vibrate against the ceiling grid
FFU motor capacitor degradation causing speed hunting and noise
Required tools
- Torque driver for mounting screws
- Replacement fan motor assembly
- Dry cloth for blade cleaning
- Handheld particle counter for post-maintenance check
Safety first
- The FFU fan operates continuously. Power off and confirm zero rotation before reaching inside the housing.
- HEPA filter face media is fragile. Do not touch the filter face or place tools on the filter surface during FFU maintenance.
Procedure
- 1
Identify the noisy FFU by placing a hand lightly on each FFU housing while the system is running. Increased vibration transmission identifies the fault unit.
- 2
Power off the identified FFU from the local switch. Listen as it spins down. A bearing that grinds during spin-down confirms bearing wear.[1]
- 3
Remove the FFU filter housing following the manufacturer's procedure. Inspect the fan wheel for particle or fiber buildup. Clean the blades with a dry cloth.
- 4
Check all mounting screws at the ceiling grid. Tighten any loose screw to the specified torque.
- 5
Spin the fan wheel by hand with power off. Roughness or resistance indicates a worn bearing. Replace the fan motor assembly.[1]
- 6
Reinstall the filter and power on the FFU. Verify noise is reduced before leaving the area.
- 7
Check the particle count below the repaired FFU after 30 minutes of operation to confirm the HEPA filter seal was not disturbed during maintenance.
Sources
Terra Universal Terra Universal hardwall cleanroom Cleanroom Equipment / FFU general technical documentation, Terra Universal
Terra Universal cleanroom FFU general maintenance and fan replacement procedures (general)
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Pressure differential loss is usually an FFU speed reduction, an exhaust air increase, or a wall panel seal failure. Check FFU face velocity and room seal integrity before adjusting any fan speed.
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