The Cuboid: A DIY air purifier that's better than a box-fan (2021)
dynomight.net
dynomight.net
https://www.texairfilters.com/a-variation-on-the-box-fan-wit...
-EDIT- I should also mention that you don't need 5 filters for this (MERV 13 is expensive), you can use 4 and a piece of cardboard for the 6th side that is touching the ground.
4 x 1" filters, each with a surface area of 10 square megamicrons, provide a total of 40 square megamicrons when assembled into a box.
A single 1 x 4" filter strapped to a fan gives a total of 10 square megamicrons.
How are those the same surface area?
Ah! I get it, because of the pleating. I guess it depends on whether the greater incoming airflow interferes with itself once it gets squeezed between pleats.
If there’s a belt from the motor to the fan you’re in for a good time.
Probably uncertainty over how effective fans are when immediately obstructed, and maybe concerns about particles possibly getting deflected backwards if a filter messes with a smooth, laminar flow.
This is, if we think of two kinds of airflow:
1. [laminar flow](https://en.wikipedia.org/wiki/Laminar_flow ), which is like a smoothly flowing river;
2. [turbulent flow](https://en.wikipedia.org/wiki/Turbulence ), which is like erratic flow inside a mixer;
then it seems like a box-fan might effect a laminar-flow further away from the blades (under normal circumstances), but could it be more turbulent near the blades?
The boxed-in design seems to try to dodge assumptions about how air flows near the blades, reducing uncertainty about how turbulent-flows might screw with it.
Or even all the excess dust kicked up from a digging out old things we didn’t know he still had…
I leave the fan duct fan running on low (right at the midpoint of the speed dial so technically medium I guess) 24/7 in my kitchen out of eye site because it's so quiet.
So, in my experience, much quieter, quiet enough that people don't notice it running all the time. I have the dial in reach though so I can crank it all the way if something burns on the stove, clears the air out shockingly fast.
I got some sound proof panels and crappily bungee corded them around the fan and it didn't have a noticeable effect. I think if I put more effort into the sound baffles it would reduce the sound, but the whole setup without baffles is quiet enough I haven't bothered.
They have just thrown 3 filters on top of the box fan with lots of gaps on the side. Air will mostly follow the path of lease resistance and not go through the filters. You need a filter that is the same size, 20x20, as the box fan and then the filter(s) will need to be sealed, via duct tape or so, around the fan for it to be effective.
Ideally you want to use a 4” thick filter, so a 20x20x4 filter and then just seal the outside. It provides huge surface area for the filter and the air flow is almost the same as the fan without the filter. I have a setup like that and it can really move air. The filter you have are much thinner.
Now, I have no idea why you’re seeing the same results between taped and non-taped, it makes no sense and is indeed surprising.
If you time and inclination, you may want to look into a 20x20x4 HEPA filter and try it.
The internet would welcome any new designs you might have. I'm sure OP would be happy to have started a build-off.
Most of the box fan filters I've seen these days look like this cuboid fan- as in, they have four filters, a base, and a fan. Many also include some cardboard curved corners to improve airflow and reduce noise. I kind of assumed that's what we were comparing until I saw the image.
Like these from another thread: https://cleanaircrew.org/box-fan-filters/
This is not a perfect device, but it will capture more particulate than nothing.
If you add even a little bit of duct to extend approximately 3 duct diameters on the outlet it will make the fan a lot more efficient by allowing the airflow to stabilize and lower buffeting noise at the outlet. There athere are some of the centrifugal fans that include a noise suppressor for more money that's basically a short duct that's double walled and perforated on the inside.
I suspect the pleated nature of the filter means that the static pressure drop isn't all that much. Haven't got a manometer to measure it though.
I often reference this manufacturer when designing a duct system and selecting filter sizes. This is for their MERV10 filter. MERV8 is lower initial pressure. They have a velocity vs pressure chart on page 4. At 50 FPM it's down to about 0.03 in. w.c.
https://www.glasfloss.com/product/zl-hv/
I think a centrifugal could still be an advantage for noise while having a reasonable dimension, but your feedback is sincerely appreciated.
A 10x increase in surface area would mean far far less powerful fans are needed, and the filters could last a decade before needing to be replaced.
I personally prefer to use two filters on each side, one as a "pre-filter" (cheaper carbon/charcoal, MERV ~10ish), with better (higher MERV, ~13 if possible) rated filters underneath. You can then replace the prefilters more often, but the filters underneath won't require replacement nearly as much.
I wrote about building them with hot glue on my blog[0] -- shameless plug! :)
0 - https://dantonio.info/projects/10-minute-corsirosenthal-box/
[1]https://adhesives.specialchem.com/selection-guide/hot-melt-a...
Some details about AHAM's CADR calculation are here: https://frdmtoplay.com/nagivating-air-purification/
"What is the best DIY Air Filter?"
EDIT: I built one for my workshop but in my house with all the windows/doors closed it seems that I can get by with a much smaller filter, there's not that much smoke/particles that keep getting in IMO.
2600 sq ft home, filter is on the floor on the most open area of the house, which covers about 1/2 of the total space (39' Dome Home, 2 story plus a half story master, the area from the living room / dining room / kitchen to the master is all open area)
My air quality meter showed me in the low warning area for PM2.5 and PM10 before I started using this, half a day after starting it up I am in the good range across the board, plus the climate is more uniform throughout the house and I'm sleeping better from the gentle breeze and mild white noise.
I don't know if it would work as well in a boxier home, but a lot of people have said that it does for them as well, so it's probably worth it if you have $65 to burn and the space for the filter cube setup thing.
- Tape (free).
- Two pieces of packaging foam (free).
Not that those are expensive, but I'm not sure why the link says they are free.
So people will build heirloom-quality furniture pieces for "free" with "scraps."
But, as a DIYer myself, a lot of things do accumulate for Actually Free, you just have to watch out for good materials.
As filters age, they change colour. Mine start white and turn dark grey when old.
However, I noticed that even the outlet side got darker. That made me wonder if a 'blocked' filter was actually allowing more small particulates through (for example perhaps because all the surface area that a bit of PM2.5 could electrolytically stick to has already been stuck to).
Does this sound plausible? Anyone got test results for small particulates of different materials and how the filter performs as it ages?
Next time I’ll get one with washable prefilters even if the final one is disposable.
MERV 3 is really really minimal filtering. Your furnace almost certainly is designed to take better filters than that.
As can be seen, this is an issue during the heating season, not the cooling season - which is when many people are fighting smoke. If you actually pay attention to home maintenance, you can go for the better filter in the summer, and drop down to the minimum or close to it during the winter.
I’m actually very curious about more intelligent systems. Those that can:
- bring in outside air on occasion to freshen things up
- negotiate the best way to cool a home depending on outside air. It drives me mad when my AC kicks on and it’s actually colder outside.
All HRV's do that. "single room recuperator" from aliexpress is in every flat after renovation in Lithuania.
You’ll draw in a lot of dirty outside air with that setup if you don’t block/reduce outside air intake. It will still go through a filter, but it’s going to cause the filter to dirty very quickly.
The extra effectiveness might also come from the Cuboid fan being elevated off the floor. With the box fan standing on the floor and pointing horizontally, it has an additional solid boundary restricting intake air. The vertical pointing fan in the Cuboid does not have this restriction.
A proper test would use the same fan in both designs. The non-Cuboid fan would be oriented upwards and mounted on stilts. Multiple trials should be done with the results averaged. He omitted a chart showing both particles counts vs. time of both approaches, which would be the most important figure to include.
Can recommend.
Or don't let the perfect be the enemy of the good -- buy 10x box fans for cheaper, because they're manufactured and shipped in the millions of units.
If it's not going to catch on fire, why are we worrying about the longevity of something that costs $30?
They should list a CFM at Inches of Water Column in the 1/4 to 1/2" range to be considered "high static" pressure.
Those blowers from the other comment are like for your iron smelter.
I mean, if you read colander reviews on Amazon, you'll find people who somehow lost a hand to it.
Historically, Amazon doesn't seem to care.
The design should also fix the worst parts of using a box fan:
1. Make less noise.
2. Use less electricity.
https://www.amazon.com/Adaptive-Sound-Technologies-LectroFan...
Hooked it up to a wifi power switch. Old meets new.
That level of noise is pretty bad for most of the rest.
I'm currently dreaming up a ceiling fan replacement that has a much lower profile and also cleans the air with a standard furnace filter.
Post: https://www.jefftk.com/p/ceiling-air-purifier
HN Discussion: https://news.ycombinator.com/item?id=31590773
For CO2, the ZGm053U has been a great device. But now I would like to measure all the dust I see in a dark room with a bright flashlight.
I can imagine many theoretical reasons like sourcing and availability but are there things beyond actual conjecture here
https://www.usa.philips.com/c-m-ho/air-purifier-and-air-humi...
For many people on HN they won't get it. $500 isn't a lot for an appliance right? For many that's two months groceries...
It runs silently at lowest and humidifies the air too.
It uses one container of water per day.
I filter the tap water so it doesn't clog up the filter.
I disable the ionisation feature which makes particles stick to the walls and furniture.
Box fans with HEPA filters are a good immediate and emergency solution but have their drawbacks, mainly:
1) The fan and filter fights against particles coming in from outside, through small cracks under the doors, windows etc. So the higher the outdoor air pollution, the more the fan needs to fight against it. At extremely high pollution levels they will get into problems maintaining healthy air indoors.
2) Sealing the gaps and making your house/room more air tight, increases CO2 levels significantly which leads to drowsyness and decreased mental performance. So you always work with a trade-off.
3) Often you need to run the fans on highest level to be effective which creates quite a high level of noise.
4) Ideally you want something demand controlled that switches automatically on/off or regulates its speed based on the pollution levels.
5) The HEPA filters filter primarily PM2.5 but the wildfires also produce hazardous gases like NOx, VOCs which you would need carbon filters to remove.
With my company AirGradient (we offer open source air quality monitors [1]), we monitor thousands of indoor spaces and the only technology that we found consistently working -no matter of the level of air pollution- are positive pressure systems.
A positive pressure fresh air system takes air from outside, filters it through HEPA/Carbon filters and pumps it into the room. Thereby pressurizing the room and thus preventing dirty air from entering the room.
With this system you just need to achieve a slightly higher pressure then outdoors and then you can consistently achieve zero PM levels inside -even when hazardous outdoors. As a result the system, often runs at low fan speeds and does not create much noise.
Additionally, due to the fact that it uses fresh air, the CO2 levels remain low and you can often add carbon filters to the system.
I made a comparison test of this type of system [2] and a detailed description how it works [3].
[1] https://www.airgradient.com/open-airgradient/kits/
[2] https://www.airgradient.com/open-airgradient/blog/air-purifi...
[3] https://www.airgradient.com/open-airgradient/blog/positive-p...
To get a remotely apples-to-apples comparison, look at commercial air purification systems -- think devices intended for areas that allows indoor smoking, such as bars/casinos/smoking rooms/etc.
My experience was that a relatively modest 20x20 (x12' high) room requires a massive amount of air movement, and products actually designed for spaces of that size generally run $3-6k or more.
A Corsi-Rosenthal box can delivery very good PM2.5/PM10 numbers, even with challenging environments & when "stretched" to provide purification for an entire home.
PurpleAir or a similar quality AQ monitor provides some very objective data to guide you; I trashed my Levoit purifiers rapidly after realizing just how ineffective (and expensive) they were versus a CR box.
The Levoit moves a lot of air on its highest setting. The filter is $23 and lasts for 6-8 months. It works amazingly and effectively in a bedroom or living room or office. I know, I use them and measure my indoor air quality with an Awair.
The CR box is probably far more powerful, yes, but it's also gigantic. You'd never put it in a bedroom or living room. I'm honestly not sure where you'd put it.
If it were a quarter the price then I appreciate a DIY thing, but this is already in the same ballpark price-wise as the best-selling air purifier on Amazon. I don't get it.
The Levoit uses 1 filter "unit", and filters are $55 for a 2-pack on Amazon ($27.5/ea), or half that if you trust the third-party ones.
Levoit recommends to replace the filters every 6-8 months, so you could get 12-16 months of filtration for $55. I can't find any calculation in the article for how long the author estimates their filters would last.
Levoit filters are advertised as lasting 6–8 months and cost $23 each.
Meanwhile a set of four filters like the one in the tutorial cost $70 and looking up comparables online at that price point indicates they're good for 3 months.
So even if using 4 at a time extends to 12 months, that's still more expensive than the up-to-2 Levoit filters you'd use in that time.
I see zero cost benefit here over Levoit -- it seems to be more expensive actually?
The CR box is tremendous overkill for something like an apartment. It's gigantic and I don't even know where most people would put one even in a house.
But it's also not what the original post was talking about. The original post is a device akin to a Levoit in terms of size and power.
I see that in the test he compares four filters being used completely in the cube setup to three being used incompletely on a box fan. But that doesn't seem like it can be the entire explanation -- particularly given the reduced airflow of the duct fan.
In order to meaningfully clean the room's air? Not on one PC, with any reasonable number of fans.