MERV is the soon to be crazy Uncle that we will be showing the door. It was a fun run, and you did some good things, but it’s time for a better test standard to be used. With the global economy becoming more real every day having a simple, cost-effective, and global filter testing standard to replace MERV and ASHRAE 52.2 is a reality. This standard is ISO 16890.
It’s not that MERV was horrible, it was a significant improvement over the 52.1 Arrestance method, but there were areas where it fell short that will be corrected with the ISO standard.
Accuracy - It is important that a test method be repeatable and consistent, which has been an issue for 52.2 since it started. There are a lot of moving pieces and procedures within that standard and, even with recent changes, there is a wide acceptable margin of tolerances. This creates different labs giving the same filter different a Minimum Removal Efficiency Value.
Real-World - ASHRAE 52.2 relies heavily on particles larger than 3 microns, these particles are less than 0.20% (Yes, 1/5 of 1 percent) of all particles in the air. Also, the particle size of ASHRAE dust which is used to determine Dust Holding Capacity is 100 times larger than the average particle size found in ambient air - which renders a dust holding capacity test mostly useless. Also, the Appendix J is still optional, so most filters that would lose efficiency during actual use opt-out of the Appendix J test - This means filters are being sold as “MERV-13” but are known to drop to MERV-11 or lower after a short time in use.
Difference between values - The scale used in ASHRAE 52.2 ranges from 1–16 but the difference in particulate removal is not consistent between the numbers. For example the difference between 8 and 11, however 8 is considered “Medium Efficiency” while 11 is the start of “High Efficiency” The chart below illustrates the fractional efficiency curves of a filters that would be classified at 8 and 11, notice how they are almost overlapping on the smaller particle sizes.
ISO 16890 will address these issues by creating a process that is more simple, easier to duplicate with fewer steps, use more real-world applicable information, and have real discernible differences between ratings. There will be four practical components to ISO 16890 and they are as follows:
1) The testing will be weighted to the efficiency of filters on smaller particles instead of larger particles. Small sub-micron particles make up over 99% of airborne particles and are the most detrimental to Human Health.
2) IPA Vapor Discharge will be mandatory. This will offer a consistent real-world efficiency as the synthetic coarse-fiber media will be reported accurately to their real-world efficiencies.
3) Dust Holding Capacity will be done with ISO fine, which is a more real-world particle size distribution than ASHRAE dust. Also, this will be done after the filter is discharged with the IPA Vapor which will also provide more real-world representation of a filter’s ability to hold particulate.
4) Efficiency Values will be determined based on particle sizes that are more commonly used - most notably PM-1 which 99% of all particles fall under, and PM-2.5 which is what the EPA monitors. These values will take into account the real-world efficiency loss experienced by cheaper filters using coarse synthetic fiber media. This is the biggest advantage from a building owner/manager perspective because under 52.2 these filters are being promoted at a higher particulate removal efficiency than what they provide for most of their life.
It’s been over 15 years since ASHRAE 52.2 came into existence and made us look more critically at air filters, and ISO 16890 is the next step in the progression of getting useable real-world relevant information. The next step in this progression would be to add an energy testing standard. Europe had an energy use test standard with their EN779 standard, and now that ISO 16890 has been published work on a global energy use standard has begun.