Official Luthiers Forum!

I can't be the first to think of this air filtration idea -- I am tired of paying about $50 every time my big honking Delta air cleaners need filters. I got to analyzing exactly what that piece of equipment was actually doing -- and that is sucking air through a couple of fabric or electrostatic filters which BTW are not HEPA grade. Top CFM is 1200. Plus the thing weighs a ton and at high speed I don't like the whiny noise it makes. So I look up the CFM specs of the $16 Lasko 20 x 20 box fan --- over 2500!!! And they are very quite -- to the design board -- here's what I came up with -- works great, I use MERV 12 furnace filters ($4.50 ea) which I understand do perform on a par with HEPA -- so effective that when I tested the flow with a smoldering piece of wood the smoke odor was gone. I made room for a pre-filter not sure its necessary. I wanted the unit to be very light so its made of CB and foam with wood framing. Works very well.

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Ken Cierp

http://www.kennethmichaelguitars.com/

Hmm...

Why are they angled like that? Could you not have had them stacked in line with each other and made it half as deep? I have a bunch of those fans sitting idle...

Stacking them up in front of each other means all the air has to go through the first filter then the next. . . Angling them like that makes for roughly 4 times the surface area filtering the air and 4 times the airflow. It is the same reason air cleaner filters in your car are pleated.

Ken, make sure you report back in time to tell us how this has performed for you!

Edit: I wonder if the box fan will have enough static pressure to actually pull enough CfM through the filters. The fan may just happily spin with out having to worry about the extra air resistance. I had an oscillating fan that was on constantly and never cleaned. It ended up completely caked with dust on the back screen and never actually blew much air out but it ran anyway. Once I cleaned the screen, it began blowing again.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

I really just copied the standard design -- like the Delta has a bag filter that has three sections, seems like common practice and what can be found in all the top brands. I don't think the "strainer" concept is as effective as increasing the filtering area -- my configuration matches the Delta unit in that regard.

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Ken Cierp

http://www.kennethmichaelguitars.com/

I have been using this one for a couple of weeks and it works great -- I am going to make a couple more to hang above our CNC machines -- those 3 1/4 HP Porter Cable routers have high velocity cooling fans and it difficult to contain the small particles.

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Ken Cierp

http://www.kennethmichaelguitars.com/

That makes sense...

Which direction is the airflow? Through the filters into the fan, or opposite?

The fan draws the air in through the filters. The filters are taped together to form the "W" shape. There is flow symbol so you have pay attention so they are facing thr correct direction. I was being careful and still screwed it up the first go round.

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Ken Cierp

http://www.kennethmichaelguitars.com/

I quickly eliminated paralysis through analysis by just Googling the concept -- like I said this is simply not a new idea, I wanted a lot of surface area so my configuration is a little different -- not enough air flow? Time to turn up the fan speed or change the filters.

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Ken Cierp

http://www.kennethmichaelguitars.com/

Ken,
What speed do you typically run it at? ...Low, Medium, or High? Great idea BTW.

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Steve Sollod (pronounced sorta like "Solid")
www.swiftcreekguitars.com

Low is working fine -- I see some of the Lasko 20" box fans are rated at 3500 cfm of course without the filters in the way. The Delta with clean filters is rated at 1200 cfm. I have not check the amperage ( I will) the thing I like as I mentioned is that even at the high speed its very quite. I figure that just one of these can turn over the air in our 2000 sq ft shop in about 12 minutes

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Ken Cierp

http://www.kennethmichaelguitars.com/

Nice. Where did you find MERV 12 rated filters for 4.50? What brand are they?

James

Sorry that is a typo -- they are Nordic Pure Merv 10 (package of 12 Duh!) ---- Amazon a while ago.

These are the same ones

http://www.amazon.com/gp/product/B006NW ... UTF8&psc=1

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Ken Cierp

http://www.kennethmichaelguitars.com/

I use a simpler version of this. Just a box fan with a 20"x20" filter taped to the back of it. I use it mostly for hand sanding and will put it as close as I can just behind the work and brush any sanding dust into the filter. Works great. I have had good luck with quality inexpensive filters at http://www.filtersfast.com.

I use the more expensive filters because MERV 10's capture invisible particles less than a micro -- and its my understand that the stuff that can kill us.

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Ken Cierp

http://www.kennethmichaelguitars.com/

Good stuff! I've had building something similar on my To Do list for quite a while. This is just what I needed to get me going!

One question: Your third photo is a top view of the "M", meaning the back filter is not yet in place and we are seeing through the open frame and down to the floor, yes?

Just want to make sure my eyes aren't playing tricks on me!

Thanks,

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George :-)

Correct -- I think I am going to add the pre-filter perhaps a lower MERV (cheaper) to catch the big chunks. Our Delta's have those so I guess its a good idea. I just use some scrap to make the filter locators, foam rubber would have been better to form a seal -- but it move and filters so much air so fast I doubt that would be necessary.

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Ken Cierp

http://www.kennethmichaelguitars.com/

Ken,

http://www.alpinehomeair.com/viewproduc ... =453066897

This is a replacement filter that is similar to the one in my Aprilaire 2200 filter in my home central heating/air unit.
You could use your same design with just 1 of these filters, and shorten the box by several inches and DECREASING the amount of air flow area by 900 SI. Similar filters are in stock at Lowes and Walmart in my area. The one shown is a 16 X 25 X 6, but they are available in 20 X 20 as well. They are also available with a higher MERV rating if you want it. They just want more money.

The way I estimate, your 4 inner filters have a total surface area of 4000 SI. This 6" deep filter has a total surface area of approximately 3100 SI. The MERV rating is 11. You can still do a pre-filter, to catch the chunks, and your total box length will only be approximately 13". The cost is not much more than the 4 filters in your unit.

I just sit my $12 Lasko box fan up against the front of the filter, and let it run at night. I originally laid a sheet of paper on the input side of the filter, to make sure that I was getting air flow through the filter. It will suck the sheet of paper up against the filter and hold it there.

I plan to build an enclosure similar to yours, but it is handy the way it is, since I can hang the filter and the fan on the wall separately, when not in use.

James

Great suggestion! I agree the depth is cumbersome for most applications.

Where did you find the surface area spec? I calculated about 1800 square inches, but that is still more than the (4) 20x20 = 400 X 4 = 1600

Thanks

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Ken Cierp

http://www.kennethmichaelguitars.com/

Ken's filters (the way they are arranged) have considerably more than 400 square inches of surface area. One 20 x 20 filter will have 400 square inches of surface area (if you ignore the pleats). Four arranges in this way offer 1,600 si. Each of those 4 are pleated filters which at least doubles the surface area. Think of stretching out the pleats into a flat sheet, that is the real surface area of each filter. Then multiply by 4 filters (since they are in parallel not series). He is probably looking at more than 3,200 si. The filter you picture certainly makes more efficient use of space though.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

Men, I just saw your last post. How did you get your 1,800 number? Do the filters list their surface area? It seems like they should have much more than 450 each.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

Typo. I corrected my post to 4000, not 400

25 folds X 2" per fold give a width of 50" x 20" height = 1000 SI per filter, x 4 filters = 4000 SI

James

The 1800 was my estimate on the 6" deep filter X number of pleats times 6x20 but I see now that should be doubled to take into account both sides of the pleat. And you are correct the math for the "M" filter is just 20x20 so if the pleats are used for the calculation for each filter would be closer to 800 square inches. In that regard these simple DIY devices crush the commercial units no I could not find the manufacture specs

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Ken Cierp

http://www.kennethmichaelguitars.com/

I agree. Look at my correction/edit.

James

Yes, it will shorten the box, but you sacrifice about 1/4 of surface area. I still think it will do a good job.

I assumed the one in the link was 6" deep, but I can't find that in the specs on that page. They also come in 4" and 5"

James