Cleanroom Design FAQs: Single Pass & Recirculating Design

Question: What is the difference between a single pass and a recirculating cleanroom?

There’s really not an enormous difference between a single pass and a recirculating cleanroom, it just has to do with the preciseness of how you control the return. In any cleanroom you’re taking the air and you’re pushing it down through the room, and then you’re transferring it out of the room. Now the difference between a single pass and a recirculating cleanroom is what you do with that air once its purged out of the room. For instance, are you just going to control the return back to the plenum, or are you going to let that air wash into the surrounding areas? The decision based on which design you use has to deal with the preciseness of your control.

If you’re controlling temperature and humidity very tightly, you want to use a recirculating system so that once you’ve conditioned that air you’re not letting it escape. The good thing about a single pass cleanroom is once you’ve purged the air out of it, you’re allowing that air to then recirculate through the surrounding area and actually serve to clean up that surrounding area. Essentially this amounts to taking a mini-environment and making it a larger environment. How you make the decision on whether to use a single pass and recirculating clean room depends more on the tightness or preciseness of the control of the temperature and humidity than it does on the tightness or control of the particle count.

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