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Clean Air Delivery Systems

There are three primary clean air delivery systems employed in cleanrooms.

The first concept is to use primary air handling units to provide air to ducted terminal HEPA filters. The air is conditioned depending on the cleanroom requirements in the primary units and the re-circulated air is supplied in a duct through the filter mounted in the ceiling. The return air is then brought back to the central air handling units either through a plenum return or a ducted return.

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The second approach is a plenum supply and/or ducted return or plenum return approach. In this case the cleanroom ceiling is positively pressurized to drive the air through the HEPA filters. The air is then returned through a raised floor or through return walls back to a different plenum or a ducted return to the central air handlers. Plenum supplies are prevalent in class 100, class 10 and class 1 application where 100% filter coverage is required. All plenum systems require an extremely tight seal, for this reason gel seal grids with knife edge filters are typically used. Sometimes the rooms create the supply plenum and other times modular plenums are employed.

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The third approach to cleanroom air systems is the use of fan filters or small modular fans to drive single or multiple filters. Fan filters are typically placed in a cleanroom ceiling either dry seal or gel seal depending on how the return system is designed and the fan filters drive the air through the cleanroom to the return. Fan filters draw their conditioned air off of a plenum typically isolated from the building and supplied with conditioned make up air conditioned to meet the requirements of the job. Fan filters have some advantages in smaller applications as well as a low initial cost for start ups and are good for projects where cleanrooms may be expanded or relocated in the future. Fan filters typically have draw backs in terms of sound levels, static pressure capacity and service ability as they create a service level at the ceiling and because each filter has a fan; multiple fans may require service over time. Fan filters are also built with less durable fan delivery systems than most central systems and require the cleanroom envelope to be opened to contamination for service.

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