Once you’ve decided that building a cleanroom is required for the development of your products the first question that must be answered is which class of clean room is needed.
The current standard US and Canada is the ISO classification system ISO 14644-1. The lower the ISO class the requirements for cleanliness go up.
Second, once the classification is identified this will determine your layout and design. For example, ISO 8 does not require you to enter through an airlock, while ISO 6 does.
Cleanrooms maintain particulate-free air using an HVAC system which is at the core of every clean room. The system uses either HEPA or ULPA filters using an air flow principle known as the Laminar principle. The principle uses air which is forced in a single direction in a constant stream. The stream forces the air into filters in the room so they may be recirculated over and over again removing the particulates from the air.
Third, for the clean rooms to maintain its ISO level the air in the room will need to be swapped out over and over every hour throughout the day How many times will depend on the ISO level you wish to maintain. This is known as the ACH (Air changes per hour)
Fourth, once the ACH is established we can figure out air flow required within the clean room space. There are many factors to consider here but for our purposes we will ignore some of these for the moment, so we end up with a more simplified formula:
(Room Volume in cubic feet) x (ACH) ÷ 60 = CFM (Required Air flow cubic feet per minute)
For Example: Your space is 10Wx10Lx8H. Room volume is Length x Width x Height or 800 Cubic Feet. You want to maintain an ISO Level 6. You can plug in the ACH of 150. Your final formula is:
800 x 150 ÷ 60 = 2,000CFM
The CFM will help determine the number of filters would be required based on their capacity giving you the basic framework to determining what your space will look like.