Cleanroom fan filter coverage is an important consideration when designing and constructing a cleanroom. Fan filter coverage is largely determined by cleanroom air flow requirements. A room with faster air change rates requires more airflow, thus will also require additional fan filter units to achieve the desired air flow velocity and room air change rates.
Learn more: Fan Filter Features and Style Comparison
The formula for calculating sufficient Fan/Filter Unit (FFU) coverage to meet your ISO requirement is determined by the expected air changes per hour, cubic feet of the room, and CFM of each fan filter unit.
No. of FFUs = (Air Changes per Hour ⁄ 60) × (Cubic feet in room ⁄ 650)
*The value “650” refers to the cubic feet/minute (CFM) of a typical 2′ x 4′ loaded FFU at medium speed.
Each of the ISO classes has a range for air changes per hour, depending on the application and room design.
Air Classification Charts: FS209E and ISO Cleanroom Standards and Airflow Tables
In general, an ISO 7 classification requires roughly 60-90 air changes per hour. In the case of an ISO 7 room measuring 10′ x 10′ x 10′, the minimum number of FFUs required is 2, and the maximum required is 3.
ISO 7 Cleanroom Maximum Fan Filter Unit Calculation:
Minimum # of FFUs: (60/60) x (1000/650) = 1.54
Maximum # of FFUs: (90/60) x (1000/650) = 2.31
Discussion: An ISO 7 room is more forgiving than (for example) ISO 5, however the 10-foot ceiling warrants a rounding up of the calculation fractions.
In general, an ISO 5 classification requires roughly 240-480 air changes per hour. In the case of an ISO 5 room measuring 12′ x 12′ x 7′, the minimum number of FFUs required is 7, and the maximum required is 13.
ISO 5 Cleanroom Fan Filter Coverage Calculations:
Minimum # of FFUs: (240/60) x (1008/650) = 6.20
Maximum # of FFUs: (480/60) x (1008/650) = 12.41
Note: The cleanliness standards of an ISO 5 room may warrant a rounding up of the calculation fractions to avoid under-performance.
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