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Comment by alexpw | Hacker News Reader

> An updated design, also known as a Comparetto Cube, [1] uses four filters and a cardboard base that can sit directly on the floor.

I never understood the purpose of the bottom filter in the Corsi-Rosenthal Box, so it felt like a waste of a filter, but I'm a big fan of the Comparetto Cube (no put intended). And 4 packs of filters are readily available -- 20x20x2 is suggested for the Comparetto Cube.

[edit] Also, thank you. I couldn't recall the Corsi-Rosenthal name/link, but thought of the wiki immediately.

[1] https://www.thisoldhouse.com/green-home/22231148/diy-air-fil...

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> I never understood the purpose of the bottom filter in the Corsi-Rosenthal Box

It's for when the box fan is not sitting on the floor - either raised up on feet (which many have), sitting in a window, or hung somewhere. That said, you're right - 4 packs are easier to come by and probably work nearly as well in the real world.

I have been focused on HVAC / air purification recently.

Its amazing to me that these designs are less than two years old when the tech has been available for decades.

One of the biggest problems with the C-R and comparetto is that they are large and hideous to look at.

I have been working on a design that makes the C-R or comparetto or a smaller version than the 20" something that can be attractive enough to hang in the corner of a room as both an air purifier and room lighting.

Something that I remind myself of, often, (assuming it is true) is that airplanes were invented prior to putting wheels on baggage.

It’s true. I don’t think popular, consumer grade luggage for the middle class had wheels until the 1970s. And if you watch for these kind of details in popular culture, I don’t think you even see wheeled baggage in the movies until the early 1980s. I couldn’t tell you the reason, but I think this was one of those status, income and class things: "I can afford to have someone carry my bags around."

It's easy to add "legs" to the C-R device - a few dollars at most in wood dowels and no tools, for example. Maximizing filter area is really important because flow vs static pressure for a fan like this is usually logarithmic...and static pressure rapidly rises as the filters get used (their efficiency goes up, but flow drops.) That's one reason you see a lot of squirrel fans used in air filtration units; they can generate much more static pressure.

In theory, if you mounted it fan-down and placed some towel or blankets underneath, you could also dampen a fair amount of the noise coming from the fan.

It's probably more effective and cheaper to get thicker filters. A 20x20x5 filter has five times the filter surface area of a 20x20x1 filter, but costs $36 - about 2-3x as much as a 20x20x1. Two 20x20x5 filters would provide twice the filter surface area.

But...these solutions were all intended mostly for emergency situations where purpose-built air filtration units were in really constrained supply. Folks should really just buy a regular air filtration unit that uses much less electricity and is quieter, especially if it auto-adjusts speed depending upon need.

> Folks should really just buy a regular air filtration unit that uses much less electricity and is quieter

This post is about how one of these made with a ceiling fan can be much quieter than a regular air filtration unit: "Testing my prototype, it has a CADR of ~180 CFM and is only 33dB. By contrast, the Wirecutter's top-recommended air purifier has a CADR of 233 CFM at 54 dB or 110 CFM at 36 dB. With some tweaks it should be able to match the commercial purifier's performance, without being louder."

> especially if it auto-adjusts speed depending upon need

I see how that works for wildfire smoke, but how would it work for covid?

virus in the air is dependent on effective filtration, rather than bulky particulate matter by volume.. the virus is highly contagious (few particles matter a lot)

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