alt Hacker NewsHEPA filters are counterproductive in standard air purifiers. Air purifiers pump their cleaned air directly into the dirty air of the room. It doesn't matter if that cleaned air is extremely clean, because it's immediately mixed with dirty air. What actually matters is how much clean air you produce: the "clean air delivery rate" (CADR).
The more effective the filter the more it restricts airflow. If a filter is only 99% effective instead of 99.99% but allows double the airflow, it provides nearly double the CADR. To benefit from HEPA you need a clean side and dirty side, like in a clean-room setup.
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A reasonable compromise is achieved by an air purifier that has the outlet on top because it’s blowing the filtered air well away from the inlet side and generally circulates the air in the room.
I used to work in the cleanest room in the state, that wasn’t a lab, back when I lived in Adelaide, and top-inlet button-outlet in a raised floor data centre is how the air handling units in the main data hall worked, so you can simulate that to a certain extent.
> The more effective the filter the more it restricts airflow.
This isn’t the whole story. Surface area and flow rate are factors.
A residential home is aiming to improve air quality, rather than grow flawless silicon ingots etc.
What you wanna say is it might be more efficient with more CADR per minute with less filtration than less CADR an a higher filtration.
But a HEPA filter is better than no filter. Even if would be more effective with another.
(Also depends on size of hepa filter and room to clean. Large enough filter and small enough space and Hepa can clean all the air)
Any air purifier should be able to cycle the air in a normal room often enough that it should be quite clean in a short time.
If the purifier can filter the air more quickly than air leaves the room it'll still reduce the amount of pollutants in the air. Most people aren't going to create a "clean side" and "dirty side" setup for filtering the air in a room.
If you only use 99% it means there are small particles you can't catch. Being faster is meaningless if you can never clean the air.
Air purifiers are designed to run 24/7 and all they do is catch particles. Eventually all the particles will be caught. The one I got also detects if there is a lot of particles and will spin faster accordingly.
You don't need to seperate the clean and dirty air. Mixing them isn't as efficient but it should still be roughly 63% efficient (1-1/e).