HEPA filters for Critical Environments including Cleanrooms and Clean Spaces are somewhat more specialized than standard HVAC HEPA filters. We’ve provided resources below for you to consider when selecting your cleanroom HEPA filter. Click for more information on:
HEPA Filter Types for Cleanroom Applications
- Minipleat HEPA Filters are available in efficiencies of 99.99% on 0.3 microns and 99.99% on 0.12 microns and are ideal for applications such as Clean Benches, Ceiling Grid Systems, and Horizontal Flow Wall Modules. Under conditions of 100 Feet Per Minute filter face velocity, the pressure drop of a Minipleat HEPA filter is comparable to a 6 inch deep HEPA filter with corrugated aluminum separators. Because of the close pleating of the shallower unit, both filters have a comparable amount of filter media, and therefore similar life cycles. The Minipleat HEPA is often used where overhead space is limited.
- Ducted Terminal HEPA Filter Modules are used where supply air is being introduced into the Cleanroom or Clean Space through ductwork and the existing air handling unit has sufficient fan static pressure to. Modules are supplied with a duct collar that should be the same diameter as the supply air duct drops serving the space.
- HEPA Fan Filter Units are self-contained units that have a blower built into the housing, to draw air from a supply air duct or plenum, and push it through the HEPA filter into the space. These units are typically equipped with a Variable Speed motor and controller to allow for field balancing during installation, and for adjustments over time.
Considerations When Selecting Cleanroom HEPA Filters
- Roomside Replaceable or Standard Units?
For Cleanroom applications your best choice is Roomside Replaceable HEPA Filter Terminal Units. A Roomside Replaceable HEPA Modules allows for HEPA filter replacement within the housing, and does not require breaking the ceiling barrier and risking contamination inside the Cleanroom. First Cost for these units is typically higher than for Non-Roomside Replaceable units but the replacement Cost is typically lower due to reduced labor cost and reduced HEPA filter cost.
- Fan Powered HEPA Filter Units or Ducted Terminal Modules?
When your Air Handling equipment is not capable of overcoming the resistance of a HEPA filter, a Fan Powered module may be the best choice. This unit requires electrical circuits and will generate more noise than a simple ducted module but in retrofit applications, it may reduce project costs. Non-fan powered HEPA filter modules are suited to applications where there is sufficient air handling unit fan static to push the air through the HEPA filter. For Cleanrooms with a ceiling plenum, HEPA filter modules without duct collars, or Minipleat HEPA filters are the perfect choice.
- Noise Levels associated with Fan Powered HEPA Filter Units can be a point of concern for some projects. HEPA Corporation has developed an excellent solution to this problem. HEPA Corporation STEALTH™100 Fan Filter Units are the low noise, energy saving choice for all applications where sound levels and worker comfort are essential. Advanced STEALTH™100 technology allows these units to last up to three times longer than other units, require only 100 watts at full speed and run at 90 FPM while providing a minimum of 99.999% filtration efficiency. Nominal noise level is 51-53 dbA at 90 FPM. The variable speed control allows the user to fine tune airflow to suit specific requirements.
- Energy Required to produce airflow through each HEPA Filter
Choosing the best HEPA filter for your project should also include selecting the one that uses the least energy since Cleanrooms are large energy consumers. HEPA Corporations HEPA Pleat II® Minipleat product line is an excellent choice when energy is a key factor. By moving beyond the industry depth barrier and introducing 5” and 7-1/2” deep Minipleats, the pressure drop for these filters is lower, saving you energy. These energy values can be calculated for comparison using the following formula:
(Airflow(CFM)) ((Pressure Drop (w.c))
(Fan Efficiency) (6,356)
- Test Ports, Aerosol Injection Ports and Balancing Dampers are an important set of options to consider. Most manufacturers offer room side test ports to measure pressure drop, and aerosol injection ports to inject the challenge medium for in-place HEPA filter leak testing. Adjustment of the balancing dampers, if installed, can also be made from the room side. These are important items that can make your periodic Cleanroom Certification and Testing much easier.
- Prefilters and Final Filters should be installed upstream of any HEPA filters to protect and extend the life of the HEPA. Prefilters can be Pleated Filters or Multi-ply Ring Panel filters with a MERV rating of at least 8. Final Filters can be either a High Efficiency Box Filter, a High Efficiency Pocket Filer or a Minipleat Filter with a MERV rating of at least 13. You must take into account the clean and final pressure drops of each filter in the system when sizing your air handling equipment to ensure proper airflow balance throughout the life of the filter.
When to Change a HEPA Filter
Your HEPA filter is designed to provide High Purity air to the space it is serving. Over time, HEPA filters accumulate dirt load and can sustain penetrations from the particles presented against them. As the filter loads, it becomes more efficient and the pressure against it increases. This can start to cause small to large penetrations in the media. These penetrations can be detected during a periodic in-place leak test.
Smaller penetrations can often be sealed with a Silicone Gel, as long as the total penetration area does not exceed the recommended upper limits for the application or the manufacturer. If there are leaks detected around the frame of the HEPA filter, or if the filter does not pass the leak test in any other way, the filter should be replaced.
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