beshaya
commented
3 years ago Hm, good point. I suppose that if a filter is 85% efficient at capturing the particles, you could treat it as 85% of a hepa filter.
I.e. to get 5 ACH equivalent, you need 5 / 0.85 = 5.9 ACH with a MERV 13.
That does seem useful to expose in the calcuator.
Is your feature request related to a situation you're trying to understand with microCOVID? Please describe. Trying to understand the impact of filters with various MERV ratings on risk reduction, given that several public places / transit types use them.
(Not super important, but this specifically came up with my trying to gauge the risk of visiting the Meow Wolf exhibit, which uses MERV13 filters)
Describe the solution you'd like Either add a risk reduction factor to the filters on the calculator for MERV13+ filters, or explain on the Blog / White Paper pages why those are insufficient.
Additional context The blog and white paper are pretty dismissive of MERV-rated filters:
However:
"Research shows that the particle size of SARS-CoV-2 is around 0.1 micrometer (µm). However, the virus generally does not travel through the air by itself. These viral particles are human-generated, so the virus is trapped in respiratory droplets and droplet nuclei (dried respiratory droplets) that are larger than an individual virus. Most of the respiratory droplets and particles exhaled during talking, singing, breathing, and coughing are less than 5 µm in size. CDC recommends using the highest efficiency ventilation filters possible, without having detrimental effects on overall HVAC system performance. ASHRAE has similar guidance; however, they recommend a minimum filtration efficiency target of MERV 13, provided there are not substantial negative impacts on the HVAC system performance and occupant comfort. A MERV 13 filter is at least 50% efficient at capturing particles in the 0.3 µm to 1.0 µm size range and 85% efficient at capturing particles in the 1 µm to 3 µm size range. Collectively these particles are capable of remaining airborne for hours and are most associated with deep lung penetration. A MERV 14 filter is at least 75% and 90% efficient, respectively, at capturing those same particles. Efficiencies for MERV 15 and MERV 16 filters are even higher. Thus, the recommended filters are significantly more efficient at capturing particles of concern than a typical MERV 8 filter, which is only around 20% efficient in the 1 µm to 3 µm size range and is not rated for capture efficiency of the smaller 0.3 µm to 1.0 µm particles."