This document has been a long time coming. As described by @jljcolorado, Lidia Morawska, co-chair of the group that published the new WHO airborne model, was previously cut off by John Conly when making the case that #COVIDisAirborne to WHO. /3
Air purifier manufacturers say HEPA should always be the filter of choice, and their product's proprietary filter delivers. Which HEPA? ISO 35H at 99.95% or ISO 40H at 99.99%? Why not ISO 50U? That's 10x better at 99.999%. Why stop there? Go for ISO 70U at 99.99999%! /1
The answer is, single-pass filtration efficiency DOESN'T MATTER except in specific cases like Powered Air Purifying Respirators (PAPR), clean rooms, operating theaters, or nuclear laboratory exhaust—HEPA's original purpose. /2
For portable/in-room air cleaners, all that matters is the Clean Air Delivery Rate (CADR) for a target particle size and type, within acceptable for sound power and frequency characteristics for the people in the room. /3
Four years into this and we can't keep duct-taping in-room filter solutions for clean air. It's just filter(s) and a fan. We need open-source, optimized design, certifiable product, efficient, repairable using commodity filters and commodity components. /1
We need air cleaners assembled and distributed by not-for-profit community-based social enterprise. No more lock-in to proprietary filters. Verified replacement commodity filtration performance for safety. /2
Low income with donated CR boxes will pay over time in electrical costs for the duct-taped solution for clean air.
Power utilization for Smoke CADR, same filters:
Conventional CR Box: 4 CADR/W. (77 W)
PC fan array air cleaner: 24 CADR/W. (8 W)
/3
1/ Levoit Core 400S versus Austin Air HM400 in a challenge to see which portable air cleaner removes submicron salt particle aerosols the fastest! Which do you think will win, and by how much? Poll in next tweet below...
2/ Which has a higher CADR (Clean Air Delivery Rate):
Levoit Core 400S, or Austin Air HM400?
See if you can find the manufacturer's claims for both, and then come back and vote:
[sarcasm] Not only is the Austin Air bigger and far heavier, it also draws way more power, is much louder, and more expensive. It couldn't possibly be *worse* than the Levoit, right? Right?
When an IAQ report for an elementary school states the acceptable industry CO2 guideline is 700 ppm above ambient, or 1200 ppm, ask why the professional is using Std 62.1-2016 Informative Appendix D that was DELETED in 2018 because of misuse and outdated 1950's data.
@O_S_P_E 's calculator will give a target steady state CO2 value based on Standard 62.1 minimum acceptable outdoor air ventilation rates. Hint: It's not 1200 ppm for an elementary classroom. Link: https://t.co/V1DwupuJ3xospe-calc.herokuapp.com
Key phrases identifying that the deleted Informative Appendix D was used:
-Target of 700 ppm CO2 above ambient
-ambient is 300-500 ppm
-majority of occupants be satisfied with respect to human bioeffluents
-uses 1.2 MET, 15 CFM (7.5 L/s), 0.31 L/min
I agree both COVID and climate have engineering solutions, but disagree that engineering is *the* approach for climate that will drive an economic boom, because it overlooks the underlying geological reason for the industrial revolution:
Energy. /1
Yes, engineering was the response to social need. As it was with aqueducts, for example.
However the enormous geological endowment of concentrated solar energy in fossil fuels is behind all expansion since the industrial revolution. /2
Like all life that encounters ample energy supply, humans went (and continue to) go bananas, and appear to be collectively unable to wean ourselves off it, engineering or otherwise. /3