HEPA fan filter units are HEPA filters with motor fan assembly attached. They are used to provide air filtration in cleanrooms. HEPA stands for High Efficiency Particulate Air filter. HEPA filters remove 99.97% of particles 0.3 microns or larger.
Figure 1. HEPA fan filter unit (top view)
The HEPA fan filter units are typically placed in negative pressure plenum above the cleanroom ceiling. The fan-motor assembly pushes the air through the HEPA filter into the cleanroom (Figure 1). If there is no plenum, then the HEPA fan filter units are typically ducted to the air return walls (Figure 2). In one pass cleanrooms such as softwall cleanrooms the HEPA fan filter units draw air from the surrounding non classified space (Figure 3).
Figure 2. HEPA fan filter units in recirculating cleanroom Figure 3. Ducting running to HEPA fan filter units in recirculating cleanroom Figure 4. HEPA fan filter units in one pass softwall cleanroom
Prior to development of HEPA fan filter unit cleanrooms used custom air handlers and ducted HEPA ceiling modules to filter the air. This was more expensive, less flexible, and had a longer lead time. In addition, these design cleanrooms have to be rebalanced frequently.
Figure 5. Cleanroom with customer air handler and HEPA ducted ceiling modules.
HEPA fan filter unit technical variants
Voltage: HEPA fan filter units are typically available in 115V, 230V and 277V. The higher voltage units are selected to lower current draw and energy usage. Another option to reduce cleanroom energy is usage to upgrade the HEPA fan filter unit AC motor to lower energy DC motor (LEDC variant).
Sizes: 2’x4’ HEPA fan filter units are the most common size for cleanrooms. 2’x2’ HEPA fan filter units are typically used for smaller rooms that do not require the full CFM of a 2’x4’ unit. A recent new development is the 4’x4’ HEPA which provides the same CFM as two 2’x4’ HEPA fan filter units at a slightly lower cost.
HEPA vs. ULPA filter: An alternative to the HEPA fan filter unit is ULPA Ultra Low Particulate Air filter for class 100 / ISO-5 cleanrooms. HEPA filters remove 99.97% of particles 0.3 microns or larger. ULPA filters remove 99.999% effective at removing particles 0.12-micron diameter or large.
Special features on HEPA Fan filter units
RSR – room side replaceable (allows HEPA filter to be replaced without removing the fan-motor assembly. More expensive then standard HEPA fan filter units, these are most commonly used in pharmaceutical cleanroom (who change their HEPA filters annually).
Test port – allow for annual field testing of HEPA filter for leaks. This used to be a very common test / feature but is not used very much today.
Indicator light – a red LED showing that filter is clogged or a green LED showing that motor is operating. Given the long life/reliability of properly used HEPA fan filter units, annual cleanroom particle testing this feature is not very common.
Remote speed control – allow speed adjustment without using physical speed control rheostat mounted on HEPA Fan filter unit. This requires a control panel hard wired to a solid state speed controller of each HEPA fan filter unit in the cleanroom. Another options is hand held remote control device and solid state speed controller with infrared or wireless communication capability on each FFU. Both are ex
HEPA fan filter units are a big user of cleanroom power and contributor to heat load. The higher the cleanroom class the more HEPA fan filter units will be required. An ISO6 /class 1000 cleanroom will require 9 times the number of HEPA fan filter units as an ISO6/class 100k cleanroom. That is because an ISO6 cleanroom has 180 air changes per hour while an ISO8 cleanroom has only 20 air changes per hour.
Figure 6. Air Changes per hour – cleanroom classification
Summary: HEPA fan filter units are HEPA filters with motor fan assembly attached. They are used to provide air filtration in cleanrooms. HEPA stands for High Efficiency Particulate Air filter. The HEPA fan filter units are placed in cleanroom plenum. Technical options include different voltages, size, ULPA vs. HEPA, indicator lights, testing ports and remote control. HEPA fan filter units replaced custom air handlers and HEPA ducted ceiling modules due to their lower cost, shorter lead times, and superior performance.
Property American Cleanroom Systems 2023
The author Anthony Chien has worked at American Cleanroom Systems for past 11 years. He has more than 40 years of cleanroom experience. Anthony has a BS and MS in Electrical Engineering specializing in semiconductor manufacturing from the University of Illinois. American Cleanroom Systems is a design build modular cleanroom manufacturer based in Rancho Santa Margarita CA. It is expert in ISO-5 through ISO-8 (class 100 to class 100k) modular cleanrooms for pharmaceutical cleanrooms, medical device cleanrooms, and industrial cleanrooms.
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