If you’re going to build a cleanroom that needs to maintain a specific temperature requirement, but the outside environment around it is at a higher temperature (for example if you’re putting a cleanroom in an open warehouse that has no temperature or humidity control), the cleanroom envelope has to withstand the difference. So you need an R-value in the wall to ensure the heat doesn’t transfer through. You also need a structure that will stop moisture from transferring.
Everything depends on the amount of air cleanliness that is required; the number of filters you need, the amount of CFM that you need – everything is a result of that decision. Therefore, that decision sets the tone for every other decision that has to do with designing and constructing a clean room. And it adds the cost up front, as well as the operational cost.
Every time you go down a class, or up a class, for instance from an ISO 8 (class 100,000) to an ISO 7 (class 10,000), that’s going to take twice as much air. The cost of filtering and moving air is a significant cost of operating a clean room. This process translates all the way down through to the number of filters that you need, the amount of return air space that you need, the amount of air conditioning you need to cool that return air and so forth. And this multiplies itself as you go through the process.
One of the most important factors that you have to determine when constructing a cleanroom is what size of particle you will need to filter out. Is it any size particle? Is it a specific size or range of particles? Most often you find that people look at the cleanroom classification and they go to the lowest level particle count to determine what classification they need.
There are basically three different air flow systems in cleanrooms: pressurized plenum, ducted supply and ducted return, and ducted supply and open return. Pressurized plenum essentially means you pump the air into the plenum, push it through the filters and down on into the cleanroom. With a ducted supply and ducted return, you’re doing just that; you’re ducting the air delivered to the cleanroom and you’re ducting the air back out of the cleanroom. This last design is prevalent in a pharmaceutical cleanroom arrangement where you have to control the air. The most efficient from a cost and operational standpoint, is the ducted supply and open return. This involves ducting the air into the cleanroom though you let the air flow into an open return, which is essentially an return air plenum.
Cleanroom door selection is an interesting topic because from a cleanliness standpoint, the decisions are somewhat easy. In a pharmaceutical environment you’re concerned about cracks or crevices in the door and how microbial growth can result from that. But the decision process for a cleanroom door is more influenced by what you need from the entry and exit of people, personnel and materials, than on how a door relates to the cleanliness level.
Making a decision on ceiling systems, like the wall systems, is dictated by what your cleanliness classification is and what you’re worried about from a cleaning agent standpoint. But then you have to add one more factor to that, which is how much weight the ceiling will need to support.
Windows are an important component of cleanrooms. One of the most important things in a cleanroom environment is to allow personnel to see inside the cleanroom, without making unnecessary trips inside, since you want to limit the amount of people entering the environment.
The type of cleanroom wall surface used is dictated by a lot of things, including the cleanliness required of the cleanroom, whether static electricity is an issue, or the type of cleaners that will be used to clean your cleanroom.
There are four basic mechanisms in which fibrous air filters remove contamination from the airstreams.
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