Thoughts about HEPA is as a standard. A lower percentage removed can happen in two ways. One is probabilistic, where the same particle might or might not get trapped. Managing probabilistic capture, total circulation and fan stats (airflow vs static pressure) is probably a good idea. Introducing determinsitic non-captures (where there are a a class of particles not captured), can be a problem, as those will not be affected by the purifier. But that is engineering that requires only dilligence.
Another way of putting it is that it makes more sense to use higher airflow, lower static pressure fans, and the filters should work with that.
I agree that the correct measure is particulates where people breathe, not simply exhaust particulates.
Introducing deterministic non-captures (where there are a a class of particles not captured), can be a problem, as those will not be affected by the purifier.
With something like a MERV 14 HVAC filter there aren’t any particle sizes that it deterministically doesn’t capture, though it does have lower efficiency at some sizes (75% at worst performing size).
Thoughts about HEPA is as a standard. A lower percentage removed can happen in two ways. One is probabilistic, where the same particle might or might not get trapped. Managing probabilistic capture, total circulation and fan stats (airflow vs static pressure) is probably a good idea. Introducing determinsitic non-captures (where there are a a class of particles not captured), can be a problem, as those will not be affected by the purifier. But that is engineering that requires only dilligence.
Another way of putting it is that it makes more sense to use higher airflow, lower static pressure fans, and the filters should work with that.
I agree that the correct measure is particulates where people breathe, not simply exhaust particulates.
With something like a MERV 14 HVAC filter there aren’t any particle sizes that it deterministically doesn’t capture, though it does have lower efficiency at some sizes (75% at worst performing size).