Comment by etchalon
3 years ago
A E12 filter filters out 99.5% of particles above 0.3 microns.
An H13 filter filters out 99.95% of particles above 0.3 microns.
Assuming a volume of 10000 particles above 0.3 microns:
An E12 filter will leave 50 particles.
An H13 filter will leave 5 particles.
That's a 10x difference.
The only point the author was making with the 0.9005 vs 0.90005 example was that if you're only processing 10% of the air, then the efficiency of your filter doesn't matter. The entire section honestly would have been better without numbers, because they cause some amount of confusion and they don't really help make the point since it's obvious. If your room's air is recycled with outside air fully over the course of one day, and your filters take ten days to work through the volume of air in your room, then the efficiency of your filter doesn't matter.
That's it. Yes, one filter is 10x as efficient. It doesn't matter because in this example they aren't moving enough air relative to the room size/leakiness for it to matter.
Saying, "OK, but as a total percent of the air in your home at any given time, the difference is tiny" is … weird. It's still a 10x difference.
Using small numbers to make the difference look small doesn't hide that.
Sorry, you’re still missing the point.
If you are taking air, running it once through a filter, and using the air that comes out for an application that needs very few particles, then a 99.99% filter is “10x” as efficient as a 99.9% filter in the sense that the air coming out will have 1/10 as many particles. For example, a 99% efficient face mask is “10x” as efficient as a 90% efficient mask (assuming both fit perfectly, which they don’t, although a PAPR approximates a perfect fit).
But an air purifier doesn’t do this at all. It continuously sucks in air, removes particles from it, and sends the filtered air right back into the room to mix with all the other air. The performance of a 95% filter in this context is barely distinguishable from that of a hypothetical 100% filter. Your characterization would have the 100% air purifier being “infinitely” more efficient.
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So? We're talking about practical effectiveness here. The difference really only matters if you only have one chance to filter the air, like the filter in a ventilation system bringing air into a cleanroom (the article goes into this).
Since the air purifier intakes and exhausts in the same space (meaning filtered air gets re-filtered), all the slightly worse filter means it that you'd need to run it for a couple more minutes to get the room down to a similar concentration of particulate per unit volume... So the difference in particulate concentration would likely not be anywhere near 10x at steady state, it would be much smaller (but depends how much air leaks into the room from outside, the particulate content of the outside air, the volume of air you're getting through the purifier per unit time, etc.)