Historically, the HVAC industry was using air filters primarily for the purposes of keeping the HVAC systems clean. A secondary purpose was to protect people served by the HVAC equipment. In the early eighties, when the HVAC industry responded to the energy crisis by introducing drastic energy conservation measures, poor indoor air quality was the result. Today, the HVAC industry is switching gears.. It has akready reviewed and revised many of the early conservation measures and also modernized it's air filtration practices. It now focuses it's air filtration efforts primarily on building occupant protection, assuming that as long as the occupants are provided with adequately clean air, the equipment is protected against dust build-up automatically.

The American Society of Heating, Refrigeration and Air Conditioning Engineers, (ASHRAE) is the organization that writes HVAC industry standards. Presently, there are two standards related to air filtration, 52 and 62. The old ASHRAE Standard 52.76, Method of Testing Air Cleaning Devices used in General Ventilation fo Removing Particulate Matter, also known as Standard 52.1, is being replaced by a new standard 52.2, Method of Testing General Ventilation Air Cleaning Devices for Removal Efficiency by Particle Size. Standards 62.1989, Ventilation for Acceptable Indoor Air Quality is also being revised and replaced by new Standard 62.1989R.

The old Standard 52.76 was sufficient for the historical purpose of air filters: that of protecting the HVAC equipment; however it is NOT adequate for protecting people served by the HVAC equipment. It specifies a method of testing to determine atmospheric dust spot efficiency, which is determined on a light-transmission basis. This method is not reliably objective and therefore it does not yeild acceptably consistent results. The standard also specifies another method of comparing filters according to their dust weight arrestance. This method also has it's problems. It does not recognize how many dust particles have been "arrested" because the particle size distribution of dust used in the test can never be the same size. If the test dust sample contains more larger particles, the arrestance appears to be higher, if the particles are smaller, the weight of the "arrested" particles will be considerably lower, and the arrestance will appear to be lower. This inconsistency may invite less than completely honest presentation of test results, especially by those filter providers who feel the pressures of competition.

These difficulties with the old standard, combined with the fact that filters in general are more efficient when catching larger particles, forced ASHRAE to re-think it's approach to air filtration. The new approach is one that would be more responsive to the needs of people rather than to the HVAC equipment. It would also be more objective and would utilize modern laser technology. About three years ago, an ASHRAE Standard Project Committee was formed to prepare a new Standard 52.2 At this point, the standard has already been developed and reviewed by the public. It's release is expected in late 1997 or 1998.

Changing Standards
Parallel with this development, ASHRAE has made changes to it's Standard 62.1989. The new Standard 62.1989R has also been developed and reviewed by the public. However, since this covers a much broader spectrum of issues, and has therefore received many more public review comments, it's release is expected in late 1998 or early 1999.

The significance of the new Standard 62-1989R is that it covers many more aspects of indoor air quality, including the filtration of air. For the first time, the standard sets the requirements for dust removal efficiency that must be achieved by filters in all HVAC equipment, large and small. It requires filters to remove at least 60% of particles of 3.0 microns in size, when filter efficiency is established by the procedures specified in Standard 52.2.

EDL decided to have their products tested according to the new Standard 52.2 by an independent ASHRAE recognized laboratory. Attached are the results obtained from Research Triangle Institute last spring. They confirm compliance of all 2" Dynamic filter products with ASHRAE Standard 62.1989R. However, the attached performance results should be considered as preliminary since Engineering Dynamics Ltd., (manufacturer of Dynamic filters) was one of the first companies to have their products tested by the new method which is rather complex and still needs some refining.

Apples & Oranges
It is important to note that definition of efficiency by the new Standard 52.2 is vastly different from the definitions of atmospheric dust spot efficiency in the old Standard 52.76. Therefore it would be grossly inappropriate to compare the percentage value of filter efficiency obtained by the old method with the percentage value of filter efficiency measured by the new method.

Outstanding Issues
As much as ASHRAE has made a giant leap ahead in the area of air filtration, there are still several outstanding issues that need to be addressed before the industry has all the tools to effectively protect people served by HVAC systems. One issue has to do with norms of dust particle counts that need to be established for people with different degrees of tolerance to dust. The next issue has to do with a measurement of filter performance that would reflect more accurately the situations in which filters are normally used. Both the old and new standards 52 measure single-pass efficiency, but many HVAC systems recirculate return air that has already been filtered on previous passes. A multi-pass efficiency standard is needed for the development of more effective filtration strategies for buildings with different occupation requirements. The last issue has to do with a special feature that is unique to electronic filters. They agglomerate small dust particles into larger ones. In fact this makes them more efficient at the smaller sizes than the new standard 52.2 could possibly measure. This concern has already been brought forward by the National Air Filtration Association (NAFA).

Although there is still work to be done in the area of air filtration, ASHRAE is urging the industry to start using the new Standards 52 and 62 now, before their official release. ASHRAE believes that the general public should benefit from the latest development as soon as possible.

Dynamic Air Cleaners Inc.
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