DIY: Pro grade 400cfm Air filter

Discussion in 'Do It Yourself' started by jamesreed, Nov 17, 2010.

  1. Sort of. The usefulness of carbon for air purification is all about the microns.

    Activated carbon is simply carbon that has been processed from a solid object to a porous one by burning out the impurities. The air actually passes through the carbon like a screen, and any molecules which are to large to pass through are trapped or diverted. Water is a larger molecule than air but their fluid dynamics are similar. The usefulness of carbon for filtering either depends on how large the pores in the "screen" are. Generally, purer carbon will "activate" with a smaller pore size and is more suitable to trap the smaller contaminates typically found in air versus water. Aquarium carbon has a bigger ratio of larger pores and as such, air penetrates further into the pellet before contaminates are trapped. This means that (gram for gram) water grade carbon has fewer pores of a sufficiently small size to capture things like odor particles. It will still work, but not as long.

    The purpose of crushing larger air grade carbon pellets down for reuse is this: a carbon pellet is like a screen on top of a screen on top of a screen etc. as air passes through the first screen it will deposit the larger contaminate molecules and block off that passage. once all the outer screen holes are blocked, the path of least resistance is to just go around the pellet. When you break the pellet up, you expose fresh screens to the air and allow it to continue working. Gram for Gram, the most effective and longest lasting carbon pellets are going to have the smallest grit size as well as the finest pore size. Unfortunately we are limited by our ability to contain small pellets by the size of screen we use to hold them in place. In addition, to small a pellet greatly restricts air flow and many fans cannot overcome the pressure.
     
  2. Thanks so much for a clearer explanation. So, if the aquarium stuff doesn't last as long as the air-quality stuff (gram for gram), does the air-quality last 3-times longer? From what I have found, I can get 5 pounds of air for $38 to my door, or 15 pounds of water for the same price......
     
  3. Depends on your environment and the carbon grade. If you don't mind changing your carbon more often, give it a shot. Could work for you. I run a perpetual grow and always have 4 plants in the final stage of flower, so I prefer to have the filter work longer between cycles and always change it before it stops working. The smell is unbelievably strong when I shut the filter down for repair. I wouldn't want to risk the smell reaching my neighbor because the filter stopped working when I didn't expect it.
     
  4. Well, my setup is under constant construction. Eventually, I am going to have four rooms and this one filter is (hopefully) going to take care of the smell from all four rooms. I am also shooting for the perpetual grow, harvesting one room each month...I also am very close to my neighbors and also don't want to go outside a get a nose-full. I know you only recently made this post, but how much 'time' have you gotten out of 5 pounds of the air stuff (assuming you have been using DIY carbon scrubbers for a while...)?
     
  5. Well, I ordered the 5 pounds of the air-quality carbon. If nothing else, I will get at least two filter's worth...going to HD this weekend to get the stuff for the filter build, as well as my new bulbs. Says the carbon should be here 2nd or 3rd of December...
     
  6. I think you made the better choice. I actually just started using this filter on Nov 8th in a new room I am running with all DIY wherever possible (blower, hood, filter, cloner etc). It currently has 4 ladies with about a week to go and 4 ladies with about a month and a week to go and all you can smell is the sweet scent of filtered air. I installed this filter in that room and a new 400cfm phresh filter in another with identical plant setups but all factory equipment. My plan is to track the effectiveness of both rooms over the next year and see what items are best bought and which are best to build. The very day my DIY filter lets out even the faintest odor I'll post it here. I can tell you right now that my filter is considerably lighter than the phresh filter as well as more compact and less restrictive per inch. We'll see how it goes, but I figure that the phresh is supposed to work for 2 years and costs $160; so even if I have to change the carbon in my filter every 3 months, I still break even for the first two years. Every year after that I save $60 a year. If I get 6 months out of a charge, it pays for itself the first year. If I get 1 year out of a charge, the cost of one factory filter would run mine for 10 years.
     
  7. ........solid explanation!
     
  8. I got the filter housing built today...just waiting on the carbon...I went with a 4" inside tube, and an 8" outside tube (giving me a 2" thick layer of carbon) at about 12" long. I ended up making my own 4" to 8" adapter while still allowing me to use my current 6" fan.
     
  9. Here's a couple pics of mine...
     

    Attached Files:

  10. Interesting. What did you use for the grate, Aluminum screen? Let us know how well the air flows through the extra inch of carbon.
     
  11. Yeah, I used aluminum screen. I am actually hoping that my fan will have a bit harder time with the 2" thick layer....Average temp outside here is in the high 30's to the low 40's, and my room doesn't get above 65....I also am making an adapter to be able to use my 4.5" axial in place of my 6".
     
  12. keep us posted... im really interested to see how the extra inch of carbon holds up... nice build

    and james.. if i could give you more rep i would..
     
  13. This may be a stupid question, but how do you go about rinsing the carbon??? A strainer in the sink??? Also, do I need to let it dry before putting it to use??
     
  14. i have a metal strainer i use.... like a champ...

    and i didn't let it dry... i shook the water out and turned on the fan outside my grow to air dry the carbon.... it worked in about half an hour...
     

  15. I suggest using a spare piece of the screen you used in the build. That way, only the pieces that would otherwise have blown out of the filter, get lost as waste. Tihspeed has the right idea about drying.
     
  16. Hoping to be able to make 2 shorter ones out of the 24" sections.
     
  17. Update: one month in, three 6' girls in full flower (purple diesel, black pearl, super haze), about 1 week till harvest, Zero smell.
     
  18. Got mine installed this morning. Turns out 5 pounds (was not able to weigh to verify I actually got 5 pounds off eBay) was only enough to fill my filter about 2/3 full. Filled the empty space with a couple of t-shirts until I can order more carbon. BTW: 5 ladies 21 days into flower. Got my 6" 250cfm axial sitting on top of it. MUCH quieter that my DIY ozonator.

    Lesson learned: WHEN FOLLOWING SOMEONE ELSE'S DIY...FOLLOW IT TO A 'T' THE FIRST TIME!!!
     
  19. hmmm. The math doesn't add up. Following your specs, it should have only taken 170% (4.25LB) of the carbon amount the specs called for. Either your carbon is denser than mine (not good, it means it wasn't "activated" enough), or they cheated you on the amount. Who did you buy from and what kind of carbon? If it's in pressed pellet form, try crushing it up a bit and see how the volume work for you then.
     
  20. #40 MindBender01, Dec 16, 2010
    Last edited by a moderator: Dec 16, 2010
    Here's the stuff I got:
    5 lbs Activated Carbon LARGE AIR PHASE pellets coarse - eBay (item 300387518196 end time Dec-26-10 01:00:10 PST)

    This may sound geeky, but I made somewhat of an excel spreadsheet to help me calc how much carbon to get, but thinking about that now, it was based on numbers freakin gave me over the phone from his memory of when he built his. I am now tweaking it based on what you used....

    Shoulda...woulda...coulda....

    Since mine is the pellet-style, if I crushed it, wouldn't that make it take up less space and pack more densely?
     

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