Custom Fan Filter Unit Sizing
As the leader in custom engineered Fan Filters Units (FFUs), we are often presented with the challenge of fitting a FFU in a restricted height area. As the semiconductor equipment market continues to pack more equipment in less space, the challenge of getting clean air to the key zones while staying within the space allotted is increasingly challenging.
The following blog presents various options, along with the pros and cons of low profile HEPA/ULPA/PTFE fan filter units
There are two forms of Fan Filter Units (FFUs) than can be used in low profile applications and each has it’s place depending on the customers goal for air cleanliness and air uniformity, while fitting in the height available.
1) Standard FFUs (Fan plenum on top of a HEPA/ULPA FILTER)
2) Side Blower/distribution membrane
Low Profile FFU
Standard 9” overall height Airflotek Euro
In our standard 9” FFU the uniformity of a 2’X4’ PTFE version is +4.8%/-4.4% @ 98 FPM. (6 spots measured with a Velgrid and using the Relative Standard Deviation uniformity calculation method) All results stated in the following slides are in relation to these numbers.
Shorten the FFU to 8”
The FPM drops by 3% to 95 FPM while the uniformity is negatively affected only slightly to +4.5%/-6.5%, still within most customer uniformity specifications.
Shorten the FFU to 7”
The FPM drops by 6% to 92 FPM while the uniformity is increasingly negatively affected to +8.1%/-5.9%, still within most customer uniformity specifications.
Shorten the FFU to 6.25”, leaving the fan ¼” from the top of the filter
The FPM drops by 8% to 90 FPM while the uniformity is further negatively affected to +7.0%/-5.2%, still within most customer uniformity specifications.
For Low Profile FFUs
Mixed height FFU (different heights for the fan section and main body of FFU
The standard layout for a Fan Filter Unit requires a minimum of 5” of height, plus an additional 2 ¾” above the FFU for air inlet. In some applications it is necessary to make HEPA/ULPA filter air to the side and blow it into a distribution chamber with a CEG membrane across the bottom. In this manner a total height of 2” can be achieved in the area where the filtered air exits. Getting the specified uniformity out of this technique often requires development time, but it can be made to deliver uniformity to meet most applications.