Boy you're quite the contrarian. Congratulations. Did I say 0% effective? Talking about primary use here. You're right, though, that cloth or coffee filter is better than nothing.
You’re right that it’s better than nothing, but it’s a far cry from “better than an expensive HEPA filter.” The best efficacy I’ve seen claimed in rigorous testing is 87%, compared with well over 99% for a good HEPA filter: https://www.nytimes.com/wirecutter/reviews/best-air-purifier...
You're making statements with no backing, logic, or argument behind them.
2) The percent of material removed by a filter per unit time is the product of (1) filter efficiency with (2) what percentage of a room's air passes per unit time.
4) "Airborne" is generally via microscopic droplets. The CDC's guidance changed from large droplet transmission (which is relatively short-distance and short-time) to airborne. This doesn't mean individual viruses are floating around with any H20.
5) No one credible believes 1 virus particle is likely to infect you, except by very bad luck. Most citations give claims in the 100-1000 particle range. Low initial infectious dose also /appears/ to correspond to less aggressive infections. This has not been rigorously proven (and it's hard to do), but has a strong theoretical basis:
- One virus particle is unlikely to make it past the mucous layer, unless you're super-unlucky.
- If it does, your innate immune system can usually handle minor infections before they escalate.
- If it can't, your adaptive immune system has more time to respond. You're looking at a few days before it kicks in. With a lower initial infectious dose, you'll still have that much less virus when it kicks in.
If you'd like to contradict any of this, please provide citations. I'll read them. I'm glad to be proven wrong. Perhaps I'll learn something.
> Better than 90% filtration at 1 micrometer and up.
What means it's probably useless against any airbone virus. But it's pretty great against particle pollution, in case you want to use it in a private space.
I would think a paper filter filters a lot better than cloth at least. The problem is breathing through it of course (as opposed to around). I searched and see some projects on the internet where people are trying to use them. Seems like a worthwhile idea to me.
If you are taking air, running it once through a filter, and using the air that comes out for an application that needs very few particles, then a 99.99% filter is “10x” as efficient as a 99.9% filter in the sense that the air coming out will have 1/10 as many particles. For example, a 99% efficient face mask is “10x” as efficient as a 90% efficient mask (assuming both fit perfectly, which they don’t, although a PAPR approximates a perfect fit).
But an air purifier doesn’t do this at all. It continuously sucks in air, removes particles from it, and sends the filtered air right back into the room to mix with all the other air. The performance of a 95% filter in this context is barely distinguishable from that of a hypothetical 100% filter. Your characterization would have the 100% air purifier being “infinitely” more efficient.
I wish analysis like this would stop using tests of the filter material to make any judgement about the purifier.
If the air passed through the filter precisely once and then ended up in your room, it would be valid. But it doesn't - the air passes many times through the filter, and mixes with the room air again and again each time.
That means it is far less important to get 99.9% filtration, and far more important to get more cubic feet passing through the filter each minute. That dramatically changes the optimal design.
To see why, imagine a room of 1000 cubic feet. Now filter one of those cubic feet, and put it back into the same room. A good 99.9% filter has just removed 0.0999% of the dirt. A bad 90% filter with double the airflow removed 0.18% of the dirt. The bad filter is much better!
Except that field data shows they don’t because they are not used precisely as required - which means the filter doesn’t work effectively if at all and then it becomes infectious waste that isn’t treated and disposed of correctly.
Human system effects dominate - as the field data shows. It’s like HCQ - works in a lab, not in the real world.
Might be useful in tightly controlled medical settings with adequate filtered ventilation. But there’s no hard evidence beyond that at this stage.
I guess the difference is whether the bacteria die and produce endotoxins on your HEPA filter which is circulating air though your house, or if the bacteria die in your carpet or on your countertop where it is more likely to be cleaned in the next 6 months and less likely to be recirculated as breathing air.
Regardless, I agree with you. If the filter prevents you from breathing X% bacteria and y% of bacteria produce endotoxins then your choices are
-Breathe in that extra x% bacteria and have them produce xy endotoxins directly in your lungs
-Kill the bacteria but breather in their xy endotoxins that are dispersed in the air.
> > A filter which captures 70% of particles with an air flow of 100cfm will capture the same amount of virus as a filter which captures 100% of particles with an air flow of 70cfm. Both will clean the room just as fast.
> It will not clean the room just as fast, it will take longer to clean the room.
Here are two different models:
A. Air moves sequentially. First you filter all of the air once, then you filter all of it another time etc. In this model, a filter with 100% efficacy will get everything in a single pass, and the CFM determines how long that pass takes, while a filter with lower efficacy will never get it all, but will get pretty close after a few passes. In this model you want high filtration.
B. Air moves randomly. At each minute, the purifier selects air from the room at random, filters it, and spits it back out. In this model, a filter with 100% efficacy at 70 CFM is exactly equivalent to a filter with 70% efficacy at 100 CFM, and you will often want to trade off efficacy for flow.
I think real rooms are generally much closer to (B) than (A), though of course somewhere in the middle?
"In order to be effective, the activated charcoal filter would have to be a minimum of five pounds to have any statistically significant effect, he said."
It's really shocking how ineffective things like pitcher filters are when compared to a quality cartridge filter. The pitcher filters really do practically nothing.
The cheap activated charcoal filters are bullshit.
You can't absorb things without absorbant mass. The black plastic sponge has hardly any mass at all, period.
I however do not have a good solution. I've DIY'd my own filter with charcoal pellets, but I've been unable to test it, and I'm somewhat unhappy with the design anyway.
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