Yaneer Bar-Yam
Heidrun WiesenmüllerStill a long way to go, but I've noticed something similar here in Germany.
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.
EdgeAnd Corsi boxes. And open windows.
@yaneerbaryam For those who don't have money to drop on an expensive "official" device for air filtration, a Corsi-Rosenthal box can be a relatively-affordable godsend. Four furnace filters and a box fan, and it cleans air much faster than many "official" devices that cost 10x as much.
https://cleanaircrew.org/box-fan-filters/
https://cleanaircrew.org/box-fan-filters/
DIY box fan filters – Corsi-Rosenthal box - Clean Air Crew
Also known as a Corsi-Rosenthal box, this DIY method of building your own air filter with MERV13 furnace filters and a box fan are an easy and cost-effective way to help clear indoor air from airborne virus particles, wildfire smoke, pollen, dust, and more! If you can seal a box, you can build one (or
@MySideIsHumanity I agree completely. Be aware that the relative filtration rates mean that at the time average level the Corsi-Rosenthal Box has to be 4X ACH to achieve the same level of filtration. So the 10X lower cost means that it is about 2.5X more cost effective.
@yaneerbaryam Indeed. I guess I'm smitten by the concept because I've come across too many "official" devices that blow (and thus have cleaned) air at a rate comparable to 2 or 3 people breathing.
@MySideIsHumanity One use of Corsi Rosenthal boxes that is not much appreciated is that they can be put in windows to clean air from the outside if there is high density of people / cars outside. People tend to think that outdoor air is clean when it is not necessarily so.
At least the geometry is good for this, but still the filtering efficiency would be good to improve.
@yaneerbaryam Indeed, air quality is all relative - swimming in a lake is generally safer than swimming in a sewer due to dilution, but swallowing water while swimming in a non-chlorinated pool with a bunch of kids can still get you sick.
It's really sad that many people incorrectly assume that "being outside = safe", and go to outdoor concerts and sporting events packed with people in close proximity.
Paul Briley 🇪🇺@yaneerbaryam @MySideIsHumanity
#corsirosenthalbox is legitimate way to clean air & is as efficient as HEPA air filtration & in most instances is quieter at doing it with higher CADR
https://news.3m.com/2022-02-24-3M-scientists-This-Corsi-Rosenthal-box-movement-is-legit?utm_term=corp-brd-en_us-ba-corsirosenthalbox-osm-mtpl-na-learn-is-feb22-na
#corsirosenthalbox is legitimate way to clean air & is as efficient as HEPA air filtration & in most instances is quieter at doing it with higher CADR
https://news.3m.com/2022-02-24-3M-scientists-This-Corsi-Rosenthal-box-movement-is-legit?utm_term=corp-brd-en_us-ba-corsirosenthalbox-osm-mtpl-na-learn-is-feb22-na
@paul_briley @MySideIsHumanity We should correct for the filtering efficiency. CADR is not a like for like comparison as we require a certain ACH for a particular room and that has to be combined with filtration rate (i.e. 80% compared to 99.97%. See other comments.
David Elfstrom@yaneerbaryam @paul_briley @MySideIsHumanity CADR is an experimentally tested particle removal value independent of filtration efficiency and reflects the equivalent outdoor air exchange rate. No further adjustments are needed to calculate the equivalent air changes per hour.
@DavidElfstrom @paul_briley @MySideIsHumanity Let's discuss so it will be clear. I sent my number by DM so we can discuss.
@DavidElfstrom @paul_briley @MySideIsHumanity
Please also clarify why we would need any particular filtration rate if this were true. For example why not 50% or 10%?
Clean Air Stars@yaneerbaryam @paul_briley @DavidElfstrom @MySideIsHumanity For infection control purposes there may be a lower bound of required efficiency where the additional mixing of air containing particles with infectious virions accompanied with inadequate filtering may increase the average risk to participants throughout the space. Eg Dyson with a HEPA filter but ~6% single pass efficiency due to ~15x flow multiplier
@cleanairstars @paul_briley @DavidElfstrom @MySideIsHumanity
We are on the same side. Speculative statements don't constitute science. Please provide information that would explain the different regimes and the behavior that connects them.
@yaneerbaryam @paul_briley @DavidElfstrom @MySideIsHumanity There is some protection for each occupant related to their distance from the emitter that would be a function of particle/virus concentration & airflow patterns plus time for viability decay (a function of time, humidity, temp, & presence of UV). Quantifying these in any meaningful way that adequately represents the variables present in each unique situation, is not going to be easy
@yaneerbaryam @MySideIsHumanity @paul_briley @DavidElfstrom Therefore it will not be straightforward understanding the impact that high mixing with low (inadequate) outside air or filtered recirculated air will have, or how we determine what “inadequate” filtration single pass efficiency actually is. It would be a continuum. Assuming same mixing, 0% filter efficiency with no outside air will increase *average* risk across the room, 99.97% filter efficiency will decrease risk.
@yaneerbaryam @MySideIsHumanity The interesting thing about #CorsiRosenthalBox is that by using multiple filters the average face velocity of the filter is far below the ASHRAE 52.2 test condition.
It turns out that single pass efficiency of 0.3-1 micron is 80% at these low velocities, compared to the minimum 50% efficiency requirement for MERV-13.
@DavidElfstrom @MySideIsHumanity Great, that is about what I read. So for 80% that gives us a factor of 0.2 remaining after a filtering pass and .2^5 = 0.0003 that would put the 99.97% filtration at 5 filtering passes. Is that your point? I said 4X but it is about 5X?
If the rate was 0.5 then we would have to have about 8X.
@yaneerbaryam @MySideIsHumanity both in-room HEPA and a CR box, as well as outdoor air ventilation, act on mixed room air. All that's needed is the single pass efficiency to convert airflow to equivalent clean air rate. A CR box with 1000 m3/h airflow is approximately equivalent to a HEPA with 800 m3/h airflow. This is verified by test chamber particle removal.
@DavidElfstrom @MySideIsHumanity Happy to discuss and clarify. I will send you my phone number by DM.
@MySideIsHumanity @DavidElfstrom @yaneerbaryam this below made me wonder whether the single pass efficiency for the Filtrete 1900 in this configuration is even higher, or whether the particle meter is too cheap or not meant to be used in a high velocity air stream. Has anyone tested this in a more reliable way?
@MySideIsHumanity @yaneerbaryam just be aware that off the shelf retail solutions don’t necessarily need to be expensive. You can see for yourself here and include DIYs to get an upfront cost comparison http://filters.cleanairstars.com
Professor Kerstin Sailer@yaneerbaryam I really wish this was true. It's unfathomable to me that universities wouldn't follow their own #science and so far have failed (on the whole) to implement a #MaskMandate #Covid #LongCovid
Lady In The Studio@yaneerbaryam virtually no masks here in southern Tasmania and covid rife