Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Ceiling Air Purifier

jefftk.com

Post reply on HN
Print view View original

121–130 of 163 posts

Re: Ceiling Air Purifier

#121

Post by danans »

malfist wrote: post #35
itsoktocry wrote: post #31

Earlier quoted context omitted.

> I've had HVAC techs tell me not to use those thick filters unless your system is designed for it. Yeah, it will also shorten the lifespan of the motor since it has to work harder. But is the cleaner air trade-off worth it? I think so.

I've always heard this, but I don't know that that's true. The thing that dies first on an HVAC system isn't the motor, it lasts a long damn time, it's the capacitor, or contactor or some other fault not really related to the motor work load. Plus, your "motor" isn't an engine, it's not variable speed, it only has one "hardness" that it works at. It might push less air with the thicker filter, but it's not going to r…

> Plus, your "motor" isn't an engine, it's not variable speed, it only has one "hardness" that it works at.

Many newer AC motors are variable speed or at least multi-speed.

Re: Ceiling Air Purifier

#122

Post by danans »

bombcar wrote: post #41
malfist wrote: post #35

Earlier quoted context omitted.

I've always heard this, but I don't know that that's true. The thing that dies first on an HVAC system isn't the motor, it lasts a long damn time, it's the capacitor, or contactor or some other fault not really related to the motor work load. Plus, your "motor" isn't an engine, it's not variable speed, it only has one "hardness" that it works at. It might push less air with the thicker filter, but it's not going to r…

It's usually a misunderstanding of how furnaces "work" - the blower motor does its thing and doesn't really "spin up or spin down" depending on the load - it just moves more or less air. The problem is (especially with older furnaces; modern ones have safety features to prevent this) that if you have too much back-pressure you don't get enough airflow over the heat exchanger (or air conditioner coils) and it can crac…

> The problem is (especially with older furnaces; modern ones have safety features to prevent this) that if you have too much back-pressure

An everyday way in which people induce this scenario is by shutting the heating vents in particular rooms because they get too hot. Even on the newer furnaces, this results in the automatic controls shutting off the burner when the pressure and temperature gets too high, and then the fan starts pushing around cold air.

A secondary negative effect of this is that it pressurizes the ducts causes them to leak more, resulting in reduced efficiency, and also quicker failure.

A well designed system which has been configured to deliver the correct amount of heat to each room doesn't experience the same issues. Unfortunately, most older homes and even newer production built homes have poorly designed HVAC systems.

Heat pumps don't experience as many of these issues because they just don't get air as hot, and instead rely on higher throughput of lower temperature air to heat spaces, but that makes them far more reliant on good duct system design.

Re: Ceiling Air Purifier

#123

Post by rapunkill »

kolencherry wrote: post #55
sha256sum wrote: post #6

Great idea. What's worked for me is simply taking a 20"x20"x1" filter and sliding it into the back cover of a standard $25 Lasko box fan. Cheap, easy option for air filtration in the home.

Yes! This is the basis for the Corsi-Rosenthal Box [1]. Five 20"x20"x1" filters and a box fan, with duct tape to seal the edges. Not the prettiest, but it's effective. [1] https://en.wikipedia.org/wiki/Corsi%E2%80%93Rosenthal_Box

Not a new idea[1] I'm surprised it even has a name [1] https://www.youtube.com/watch?v=Uzpn09OIyqw

Re: Ceiling Air Purifier

#124

Post by KennyBlanken »

alexpw wrote: post #71
kolencherry wrote: post #55

Earlier quoted context omitted.

Yes! This is the basis for the Corsi-Rosenthal Box [1]. Five 20"x20"x1" filters and a box fan, with duct tape to seal the edges. Not the prettiest, but it's effective. [1] https://en.wikipedia.org/wiki/Corsi%E2%80%93Rosenthal_Box

> 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, tha…

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.

Re: Ceiling Air Purifier

#125

Post by jefftk »

KennyBlanken wrote: post #124
alexpw wrote: post #71

Earlier quoted context omitted.

> 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, tha…

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 ge…

> 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?

Re: Ceiling Air Purifier

#126

Post by hinkley »

bredren wrote: post #120
hinkley wrote: post #91

Earlier quoted context omitted.

Tends to burn out the motor though. Vornado used to sell an air filter that took two 10x20” house filters. Before I discovered that model I was trying to build my own using computer case fans (my intent was to hide the loud box under furniture). Home Depot used to carry those in the 1500 classification which was great, but those are getting harder to come by too, and even the regional chain that had them doesn’t as m…

> Tends to burn out the motor though. Do you have data on this? Adding a fan shroud to the Corsi-R supposedly does not increase energy usage or motor temperature: https://www.texairfilters.com/how-to-improve-the-efficiency-... I'm looking for data on the power usage and motor temperature difference from a 20" Hurricane in normal operation, with a 20" merv 14 on the back, a C-R and a Comparetto.

Same author https://www.texairfilters.com/a-variation-on-the-box-fan-wit... chose 4 filters due to higher throughput.

He has an addendum at the bottom where they tested the fans and saw no problems with a single filter. I... don't understand how they come to those conclusions based on the charts in the paper. All of the fans were >10ºC hotter and one model went up by 20. 15C is a lot for cheap, planned obsolescence consumer electronics.

Re: Ceiling Air Purifier

#127

Post by donthellbanme »

bredren wrote: post #119
alexpw wrote: post #71

Earlier quoted context omitted.

> 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, tha…

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…

No post body was provided.

Re: Ceiling Air Purifier

#128

Post by jryb »

Pxtl wrote: post #113
blagie wrote: post #52

I think people are missing the point. YES this is bad engineering for a finished product: - The fan is not designed for high static pressure. It won't do well pulling air through filters. - It's ugly. It will get uglier as filters get dirty. - It's expensive to replace filters. - Etc. But it's not a finished, industrial project. It's a prototype. Those sorts of issues are universal for prototypes. They're easy to add…

If we're looking for a finished product, we're leaving a tool on the shelf -- filters aren't the only option. Pipe the air through a duct flooded with deadly UV-C and sterilize the air instead of just filtering it.

This also creates ozone though, which is detrimental to human health. Review here: https://link.springer.com/article/10.1007/s11356-017-9239-3

Re: Ceiling Air Purifier

#129

Post by TurkishPoptart »

TedDoesntTalk wrote: post #8
sha256sum wrote: post #6

Great idea. What's worked for me is simply taking a 20"x20"x1" filter and sliding it into the back cover of a standard $25 Lasko box fan. Cheap, easy option for air filtration in the home.

That’s a great idea. What kind of filter do you use?

Is that enough for allergens, smoke, and pet dander? I don't care about virus filtration (which is not going to happen anyway, if it's something I'm making out of cardboard and duct-tape)

Re: Ceiling Air Purifier

#130

Post by TurkishPoptart »

kolencherry wrote: post #55
sha256sum wrote: post #6

Great idea. What's worked for me is simply taking a 20"x20"x1" filter and sliding it into the back cover of a standard $25 Lasko box fan. Cheap, easy option for air filtration in the home.

Yes! This is the basis for the Corsi-Rosenthal Box [1]. Five 20"x20"x1" filters and a box fan, with duct tape to seal the edges. Not the prettiest, but it's effective. [1] https://en.wikipedia.org/wiki/Corsi%E2%80%93Rosenthal_Box

How is this significantly better than the parent comment of attaching one filter to a box fan?
Post reply on HN