Learn About Air Purification and Filtration

Ceiling HEPA Filter Terminology

February 10, 2017 |

Clean room Fan Powered HEPA unitIf you look up at the ceiling of a cleanroom, operating room, anteroom, or pharmacy you will likely see a diffuser with a HEPA filter in it.  These rooms require high purity air filters and the most reliable way of delivering that to a space is through a terminal diffuser HEPA.  These filters have several different terms that are used frequently that you should know when replacing filters, or servicing a space that use them.


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Housing: This is the part of the Ceiling HEPA module that the actual filter sits in.  Sometimes it is an integral part of the filter and other times, such as in room side replaceable units, it gets left in the ceiling during filter changes.

 Ducted: This means that the supply air is delivered through ductwork, which is usually tied into a larger HVAC system or on its own dedicated make-up air unit.

 Fan Powered:  These units have a fan attached to the filter housing that provides the airflow that goes through the HEPA filter.  Typically the air s drawn from the interstitial space above the room, because of this there is usually a prefilter on top of the unit to keep the fan clean that will need to be changed regularly.  Fan Powered units are very popular in small rooms, when retrofitting a space, or when using a modular cleanroom.

Room Side Replaceable (RSR): Indicates that the HEPA filter panel can be changed from inside the space without having to take the housing out as well.  These are highly recommended for nearly all application, especially when certification or changing of the filters will have to be done regularly. 

 Bow Tie, Guillotine, or Isolation Damper:  Cutting off airflow to individual ceiling HEPA filters may be needed for testing, certification, or decontamination procedures and these are the three most common options.  Bow-tie dampers offer an inexpensive system that has the poorest seal dampers should be avoided.  Guillotine dampers function with two plates that move like a guillotine to ensure a high seal integrity.  Isolation dampers will provide the best seal to ensure no airflow gets to the HEPA and it is isolated from airflow, they are commonly offered in “low-leak” which is ≤0.029 cfm per inch of diameter at 10” w.c. and “bubble-tight” which will not leak at 10” w.c. Bubble-tight dampers should be used in ASME N510-1995 spaces.

 Service Ports or Test Ports: Quick-disconnects that facilitate easy testing and certification of the filter module.  Typically an injection port will be plumbed to a dispersion ring/plate that gives even distribution of the challenge aerosol to the HEPA filter so testing can be done accurately. 

 Panel: Typically just the HEPA filter itself and it would be installed into a housing.

 HEPA Diffuser: There can be a couple different things this could mean a couple different things.  The housing on a Room-Side-Replaceable unit offers the diffuser portion of the ceiling HEPA system.  In some cases when attempting to save money a HEPA diffuser can be a HEPA filter with a diffusion plate/grill that is integral part of frame so an additional housing isn’t needed.

 Penetration:  Efficiency ratings get a little confusing, because per the IEST standards that HEPAs are tested to do not test the capture efficiency, they test what the filter doesn’t capture – or what is allowed to penetrate the filter.  Even though you may have a 99.99% HEPA it will be labeled as having a penetration of 0.01 or less, similarly an ULPA filter that would be called 99.9999% or (Four 9’s) will be labeled as having a penetration of 0.0001 or less.

 For all your ceiling HEPA filter questions, or if you need replacements contact us and we are here to help.

Tags: HEPA Clean Room

Written by Ben Klawitter