Diy Air Purifier, Box Fan + HEPA Filter

Dust, DUST! I can't stand dust especially with a glass top desk it collects in a matter of hours!

I made a home made air purifier based on this design: http://rapidnewsnetwork.com/make-your-own-...9s-design/1393/

Here is a video: http://youtu.be/kH5APw_SLUU

I started with a cheap fiberglass filter and when it fills up I will work my way up in filter quality. ANYWAY, I have read this is a bad idea because it's a fire hazard with the resistance on the fan motor? Obviously the higher the quality of the filter the greater the resistance will be, I have mine on the INTAKE/BACK side of the fan. What do you guys think? Is there a way to tweak the motor to make this a safer unit?


On a side note, I found a few neat products. This actually uses a plant, I have lots of house plants for this reasons but this is a bit of a turbo charged oxygen creator. I assume with the RIGHT PLANT you could pump oxygen at a good rate, I'm just not sure how much Co2 is being exchanged for oxygen in the split second it takes to push the air through the plant and out of the unit:


They even have air purifying CFL bulbs that clear smoke and odor, I have a goose neck CFL here on the desk that stays on as background lighting I might as well get one:

http://youtu.be/hjU9cmaBYPQ

http://sanibulb.com/

if the fan motor gets too warm ... then change the design .
however ... those box fan motors are "impedance protected" ... you can actually stall them and the temp will rise but it won't burst into flames .
plus ... most of them have a thermal protection device .

those purifiers with the plant in them ... they are cute and that's about it .
a brag/cool factor device for yuppies .
you would need a lot of plants with good illumination to do any amount of appreciable oxygen enrichment .

an experiment :
the ol' plant-in-the-test-tube ...
grab a sprig of a plant and place it in the test tube .
fill with water , invert it and place it in the water (an aquarium works well for this ( nutrients and dissolved CO2) .
expose to sunlight and see how long it takes to make a given amount of oxygen .
extrapolate the results (scale it up) to see how much surface area of plant you would need to make a dent in the level of oxygen in a room .

Alternatively, presume you took whatever plant matter was in the globe, and you burnt it thoroughly. That consumes O2 and converts all the plant matter © into CO2. Think about how little fumes and smoke it would make, and how quickly it would be over and done with (moments).

Then consider how long it would take from a seed to re-grow that plant to its original size (weeks/months). Divide the amount of smog you created when you burnt it by the amount of time it takes to regrow, and you'll have a rate of how fast it scrubs the air.

Which, however, makes me wonder, why when you're in a plant-rich environment the air seems fresher. Why is that? Perhaps that's just the wet-soil-smell you get after it rains, and nothing to do with the plant?

Edited to add: Did you know that if you put a capital C between parenthesis, ( C ), without the spaces, it creates a copyright symbol? I didn't. ©

@ Matt, the problem is you only need about one pound of carbon per square inch of the earth to consume all of the oxygen out of the air.
*4 pounds per square inch of land surface area.

there's a lot of plant matter on the earth...

@Pink Floyd

just get 5 filters, put them in a square box configuration, with the fan at one end.

just how effective are those units?

Everyone seems to be hung up on the plant filter, so I will say this. I think some of you may be off on your evaluation, just a few years ago (in high school) I was taught in biology class that most plants can use something like 20X or 2000X the amount of Co2 available in our atmosphere; in other words if you put a plant in a tank and filled it with something like 80% Co2 it STILL wouldn't be using it's full potential because it can eat so much more Co2 then it has available to it. If our planets Co2 level ever raised a good amount plants would thrive not dwell. SO if your continously keeping the air moving through the right plant it would be making a greater efficiency of their foliage surface area. If the unit was kept near or in a window illumination would not be required, and even IF I found some amazing plant to work in this I could always add a few high power LEDs to simulate sunrise and sunset (extend the daylight hours).

Back to the box fan, I did not realize they were that safe! The motor DOES get very hot to the touch but it never warms up the fan frame, however if the filter fragments got pulled into the motor that might be another story? (cheap fiberglass filters) Now I have seen these with the cutout around the motor, not sure how much it would really help then again it would run 24/7:


Instead of building a clunky box to hold 5 filters I think 2 would work better, one HEPA filter approximately MERV 11 with one cheap fiberglass filter over that to catch the large dust and extend the life of my HEPA filter. Anything more than that may reduce my airflow too much! The filters practically suck right to the back of the fan housing with no brackets or tape required:


Some filtration systems use a UV light as well to kill germs and mold, however I think that may bump the power consumption up quite a bit. If anyone checked out those sanitizing CFL's I was thinking one of those in FRONT of the fan may help but at that point I might as well compare the power consumption between a sanitizing CFL and a small UV light:


These shrouds are also on the market for $25 that accept a 16x16 furnace filter, would the air being pulled through a smaller filter reduce the fan resistance??

In my thinking, no, it will increase it.

Extrapolate, you put a cone on it and narrow the opening down to a pinhead. Easier or harder on the fan? Smaller is harder.

for 25$ i'd grab a roll of duct tape...


i made the suggestion that you tape 5 filters together, because the filters you're using appear square, and about the same size as the fan.
btw -the filters go in a cube, the air goes though all of them in parallel.
The idea is to get the air to move through the filter as slowly as possible.

If you want to save money and put the crappier filter in front of the HEPA filter then you've got the right idea, just tape them together. I'm not sure how clean you want that place but i would speculate that the standard filter will need to be replaced 2-3 times as often as the HEPA filter.

oh, and put the UV lightbulb inside the box of filters, in front of the fan, that way the light will strike the inside surface of the filters and keep them from growing anything.

In my thinking, no, it will increase it.

Extrapolate, you put a cone on it and narrow the opening down to a pinhead. Easier or harder on the fan? Smaller is harder.

That's what I was thinking too.

So more filters to slow down the air flow down is the concept?? I use bungee cords instead of duck tape it's cleaner, as far as the fiberglass pre-filters go you can blow those out somewhat with an air compressor but I would change it every month or so. The UV in front as in where it blows the fresh air out right? I would have to mount it in between the back of the fan blades and the HEPA, in front of the blades I don't think it would reach the filter that well. On a side note the room is 10ft x 11ft so the fan is on low (slow air draw) I'm afraid if I put it on high it would suck any loose dust caught in the fiberglass filter through.


Ironically the hardest part (even online) is finding a GOOD, solid, quiet, 20x20 box fan!

4 filters and a piece of cardboard/plywood would probably do just fine, consider it's a box fan that sits on the floor. Left, Right, Top, Back.

Slower air is probably superiorly filtered as the particles won't be slamming into the filter as hard.

Also, with 4 filters, the air resistance into the fan is cut to 1/4 of what is was with 1 filter because there's that much more surface area to pull air through. (maybe?).

Well no, if you read, "put the UV lightbulb inside the box of filters". Inside the box. Next to the fan.

But if you're only going with 1 fan, then, it doesn't matter too much, it'll be in the way either way. Jo seems to think the fresh-air side is the side that should be demoulded moreso than the intake.

Slower air is probably superiorly filtered as the particles won't be slamming into the filter as hard.

Also, with 4 filters, the air resistance into the fan is cut to 1/4 of what is was with 1 filter because there's that much more surface area to pull air through. (maybe?).

Again though, we are making the motor work harder = hotter

I'm going to see what 2 high quality filters do, 4 could get pricey and bulky it's only a 10x11 room.

If you have 4 or 5 filters in parallel, compared to one filter, then you'll have probably twice as much air flowing through the fan, and the air will be moving though the filter half as fast.

Actually, these pleated furnace filters are meant to be used at a much higher air flow rate than a box fan on low. I may actually buy one of those plastic shrouds because a 16x16 MERV 13 filter is much more common and cheaper than a 20x20, there are really good deals on bundle packs too so 16x16 must be a common furnace size.

No, you're not. Let's go back to the cone that ends in a pinhead. Now go the other way. Think about if you made a cube with solid walls and only 1 filter at the back. Think about how hard that would be for the fan (exactly the same as if there was no cube and the filter was stuck right on the back of the fan). Then, remove one of the walls and replace it with a filter, would that make it more, or less difficult for the fan to pull air than a solid wall? Then remove another wall and replace it with a filter, and another and another.

You will get higher airflow, and less load on the motor both.

I thought you were doing this because you are cheap.

Do you not have access to cardboard and tape/screws?

Order a large Hawaiian pizza. It will be about $18. Throw away the pizza because warm pineapple is disgusting and that was a poor choice on your part. Then cut an 18x18" hole out of the lid. Make 4 little diagonal cuts at the corners (in an X) so that you can bend out 1" tabs all the way around a 16" hole. Mount the filter to that hole. Mount the cardboard to the fan. Ta da. $18 shroud, cheaper than the $25 shroud you were going to purchase.

It's not a space shuttle or a bridge. There is no mission critical structural integrity. It needs to, somewhat, block air and give you something to mount the filter to. That's it. The fan is sucking the entire assembly into it, you probably won't even need any adhesive (ever stuck a paper to the back of a fan?).

Pricey isn't relevant unless you're short on cash immediately. Filters don't fill up passively. They fill up as a function of how much air has been drawn through them. 4 filters will need replacing 1/4 as often as one filter. No costs savings.

Why would you use 2 filters? You'd still eat up all that extra depth.

I get your point, I'm cheap, but not THAT cheap. I think a piece of cardboard on a box fan is an eye sore, looks like a piece of garbage. For an extra $5 it can actually look like it was made to come that way, I'm still a little bit confused about this multiple filter theory. Most MERV 13 filters are 5" think to begin with! Or I could put 4 of those on and add 20" in filters and several hundred dollars because a 5" think MERV 13 is NOT cheap.

With fans, motor load depends on the weight of the air moved. Block airflow & motor load goes down, not up. The same holds true for pump types that are not positive displacement.

As for filtration, the efficiency of cheap filters can be greatly improved by spraying them with oil, or with a special sticky spray made for the purpose. Oil isn't recommended for home use though, as it tends to evaporate & leave a film on everything nearby.

$25, unless you're actually buying a disposable pizza for the cardboard.

MERV 13 eh?

not cheap.

ok then, looking at the EPA tables, I would think you would want to remove 90% of the 3-10um particles before they get to the expensive filter and clog it up. That means you need a MERV 9 or 10 in front of that MERV 13.

I suppose the art to this arrangement is figuring out how much of each particle size there is.. and how do you know when to replace the MERV 13 filter.

anyway, i'm not sure how you're still confused on the filter arrangement.
No one suggested stacking the filters on top of each other and pulling the air through 20 inches of media. Put them in a cube, such that the filters are the faces of the cube, with the fan being the 6th face, so the air goes through all of them in parallel.. not series like a stack.

I was thinking about spraying them with Endust, I think that would work well.

Yeah a MERV 13 with ONE over it was my intention, even just a cheap fiberglass filter sprayed with Endust I replace once every other week. I would say when the MERV 13 appears to be dirty I would replace it, the 16x16 MERV 13's are MUCH cheaper than the 20x20 and being designed to work at a much higher air flow (furnace) then a low speed box fan a smaller filter may be a better choice AKA 16x16.

Oh I get what your saying now, something along the lines of this concept:


So maybe if I found some smaller filters and made something like a 20x20x6 or something. Two 20x20 on the back and a 20x6 on the sides and top, I get it now!

endust ?
mix a little detergent with water and spray the filters .

Yeah Endust is a spray in an aerosol can that you dust things in your house with, spray it on a rag and then wipe it collect dust and ensure it STICKS to the cloth you are wiping with. Some types leave a slight glossy wax coating

Wiki: Endust

Home grown electrostatic precipitators are not difficult to build, if a bit tedious. They get most everything out, if they're designed right. The secret is making the cell large enough so that airspeed is low enough to give the electric field time to make all the dust clump & settle out.
Done right, this is the best way to remove suspended solids from the air. Precipitators have little to no air resistance, depending on the design. If a bit of ozone generation is included, they also remove volatiles & odors. They are also permenent, never needing replacement. A properly built electrostatic unit & a simple washable foam prefilter is enough to give HEPA levels of performance.

lol I'm not going to go that far, I will eventually just be purchasing an "Alive Air" unit for $299 that has the following:

An ionizer

UV bulb COMBINED with a TiO2 washable filter (Titanium Dioxide)

Large HEPA COMBINED with an activated charcoal filter

A washable PHO grid (Photo-Catalytic Oxidation)

Large washable pre-filter

Tons of sensors for different allergens, molds, and pollutants along with when to service each filter

All this for $299 BUILT lol It covers a room up to 861 square feet (mine is 110sq ft) the HEPA/Charcoal filter would need replacing once a year for $35 and the UV bulb once a year as well for $20 so it costs a grand total of $55 a year to maintain you can't beat that!

aren't those the same guys selling that bridge in Brooklyn?