Yaneer Bar-Yam
AndrewMeffan@yaneerbaryam Better engineering for indoor air quality is costly up-front but once in place is highly cost-effective. HEPA are low-cost but still have the issue of being turned down or off to reduce noise. I use multiple HEPAs but in a relatively noisy clinical setting. For schools or offices, quieter systems will get more consistent use.
Dustin D. Wind@AndrewMeffan @yaneerbaryam Fans that are turning over a lot of air will almost unavoidably give off a hum that some might consider loud. If a system is extremely quiet, I'd worry that it may be because it's not actually cleaning the air nearly as fast as people's droplets are "dirtying" it. Rapid air turnover is essential.