Are you looking for a project where you could substantially improve
indoor air quality, with benefits both to general health and reducing
pandemic risk?

I’ve written
a bunch
about
air
purifiers
over the past few years, and its frustrating how bad commercial
market is.

The most glaring problem is the widespread use of HEPA filters. These
are very effective filters that, unavoidably, offer significant
resistance to air flow. HEPA is a great option for filtering air in
single pass, such as with an outdoor air intake or a biosafety
cabinet, but it’s the wrong set of tradeoffs for cleaning the air
that’s already in the room. Air passing through a HEPA filter removes
99.97% of particles, but then it’s mixed back in with the rest of the
room air. If you can instead remove 99% of particles from 2% more
air, or 90% from 15% more air, you’re delivering more clean air. We
should compare in-room purifiers on their Clean Air
Delivery Rate (CADR), not whether the filters are HEPA.

Next is noise. Let’s say you do know that CADR is what counts, and
you go looking at purifiers. You’ve decided you need 250 CFM, and you
get something that says it can do that. Except once it’s set up in
the room it’s too noisy and you end up running it on low, getting just
75 CFM. Everywhere I go I see purifiers that are either set too low
to achieve much or are just switched off. High CADR with low noise is
critical.

Then consider filter replacement. Th