What is a Cleanroom Fan Filter Unit?

A cleanroom fan filter unit (FFU) uses HEPA filtration to protect products and personnel inside the cleanroom from unwanted particles and germs. The HEPA filter (or ULPA filter) in the FFU is constructed of delicate tightly woven fibers to catch sub-micron particles. In a typical cleanroom, the fan powered hepa filter mounts on top of the ceiling grid and scrubs air clean as the motor pulls air from outside the cleanroom, pushes it through the HEPA filter and into the cleanroom.The downward top-to-bottom flow of air into the cleanroom provides laminar airflow - a single pass unidirectional flow of air--starting from the ceiling and exiting near the floor--to help flush out other contaminants that may be introduced inside the cleanroom. The clean filtered air being pushed into the cleanroom also creates a positive pressure environment to help keep unwanted contaminants from drifting inside the cleanroom.

Cleanroom ratings range from Class 1 to Class 100,000—lower clean room ratings indicate fewer contaminants and higher air change rates, and therefore may require more FFUs to reach the desired cleanliness classification.

Disadvantages of Bench Top Replaceable Fan Filter Units

Components of a standard top-side replaceable fan filter unit

Terra manufactures and stocks HEPA filter fan units for every application. Each design offers advantages for specific applications. Standard FFUs offer the lowest cost option and are ideal for small scale and less critical cleanroom operations. However they have an unfortunate disadvantage when installed to a cleanroom. In order to change the filter, the bulky unit must be entirely pulled out of the ceiling bay. Climbing up to remove the bulky FFU can be difficult, dirty, and hazardous. The procedure may require tall ladders, multiple people, personal protective equipment, and perhaps worst of all, shutting down the cleanroom.

The cleanroom filter replacement process for top-side replaceable FFUs can put a complete stop on your cleanroom operations because the room suddenly lacks a functional ceiling. Dust and contaminating particles can pour in freely from the outside compromising the cleanroom’s cleanliness rating. In most cases, cleanroom operations halt until filters are changed and all HEPA filter blowers return to functional status.

Once the fan filter modules are placed back into the ceiling, depending on the required cleanliness classification, the cleanroom may need to undergo multiple step cleaning procedures with germicidal, fungicidal and sporicidal surfactants. Once these steps are complete, the air change rates can then be re-checked and recertified to fully restart cleanroom production. For critical operations, this type of shutdown could not only cost a fortune from lost time, but compromise cGMP operating standards and safety.

instal image 1 instal image 2 instal image 3 Removing a top-side replaceable fan filter unit from a ceiling grid to change the HEPA filter

Benefits of a Room-Side Replaceable Fan Filter Unit

rsr tab HEPA filter retaining bracket in a room-side replaceable FFU

Room-side replaceable (RSR) FFUs drastically simplify filter replacement to keep your cleanroom operations running smoothly. The HEPA filter of an RSR FFU is designed to be replaced from within the cleanroom, without dismantling the entire FFU. Filter replacement may still require a cleanroom ladder, but can be completed by 1 person; simply twist the retaining tabs to change out the filter, rather than pulling the entire FFU apart from the ceiling grid. With the fan filter unit still fixed to the ceiling, as long as other FFUs are running while one filter is being changed, the room can maintain positive pressure and keep outside contaminants from entering the space. This simplifies the filter changing process and minimizes downtime of your cleanroom operation.

Air change rates can then be tested after a filter change to double check conformance to the desired ISO Class. For more stringent cleanliness requirements, an inspector may still need to audit and recommission the space before the room can be made operational.

Multiply Savings on Room-side Replaceable Fan Filter Units

For most cleanroom applications, room-side replaceable FFUs offer great savings by simplifying the filter replacement process to spare downtime and financial burdens. These savings multiply for cleanrooms with large networks of fan filter units.

To make filter changes even easier and avoid unexpected cleanroom shutdowns, Terra offers a filter replacement alarm to monitor the HEPA fan filter unit’s back pressure and issue an alarm when the filter is due for replacement. Challenge ports are also available to simplify filter leak testing of the cleanroom hepa filters.

Filter replacement alarm monitors the HEPA fan filter unit’s back pressure and issues alarm at user-specified set-point
Challenge port simplifies filter leak testing

To find out more about fan filter unit and cleanroom air filter designs Terra offers, chat with one of our cleanroom experts online, or call us to speak with one of our cleanroom specialists.