Please critique my carbon scrubber design

[0p0rat0r]

Hi everyone. I'd like your opinions on my carbon scrubber design. Does it look like it would be effective to you? If not, why? Let me know of anything you'd change and why.

I'm not sure how many CFM I'll need to move to make it through 3" of carbon spread over a 12" area, and maintain an adequate air flow in my box which will be 2'x3'x4' approximately. I'm also unsure if 3" of activated carbon will be enough to effectively neutralize the odor.

I'm hoping some of you experienced with carbon scrubbers will chime in and help me out. Thanks.

 

[0p0rat0r]

I'm using activated carbon I got in an unmarked pale from the hydro store. I think he said it was for aquariums. I was thinking about pulling instead of pushing but I want to keep the fan deeper inside the grow box to help reduce the noise so I thought I'll try pushing.

I'm gonna go with as little carbon as I can get away with, guess I'll have to experiment.

 

[BlindDate]

Looks pretty simple. I would only question whether PC fans can produce enough pressure to push air through the carbon bed. CFM has nothing to do with it. It's pressure that you need. That is why all carbon scrubbers use Blowers not fans.

 

[Haps]

Folks who have tried both seem to agree, as do I, that you want to pull. not push, it is simply more effective, not that it wont work the other way. Three inches is way too thick for pc fans to pull through, I use a 750 cfm shop blower, and I don't try to pull through more than 1.5-2 inches, and it looses effectiveness close to 2 inches. If you want to use the small fans, think filter sandwich, half inch thick at most, which can still be effective.

Your design is cool, just tweek it to fit what you have to work with, a thinner filter just needs changing more often, not a big deal if you plan for it. Have fun building.
H

 

[MTF-Sandman]

I think he's referring to muffin fans (computer fans) lack of ability to deal with static pressure. They're fine for moving air around in an open space, but if you put much static pressure on them, they become worthless pretty quick.

0p0rat0r - I understand that you're trying to save some money by doing the DIY scrubber and all, but ultimately the security of your setup will be riding on how well this scrubber works, so you might want to consider a 4" Vortex or a squirrel cage fan to get the air through that scrubber. Odor control is definitely one of those areas where it's safe (and smart) to give it a little overkill...

 

[8bitNES]

computer style muffin fans are not very good at generating static pressure. when it comes to pressure yes, design is everything. as stated, "regular" type fans are great for air circulation within a room but not for pushing air down a tube/duct or thru a bed of carbon. for conventional scrubbing scenarios, centrifugal fans are the preferred fan type.

0porator, there are a few things i would change in your design. sandwiching the fans would produce higher pressure. so i would probably have 2 fan holes than 4. since the fans aren't that "efficient" i wouldn't make the carbon layer more than 1" at most. also since the carbon can settle it would be better if it was a vertical design than horizontal as in the picture above. if the carbon were to settle in a horizontal design unscrubbed air would just pass thru the gap leaving a stinky room.

find the fattest fan you can. conventional fans create more pressure the deeper the blades go so a 1" deep computer fan would produce higher pressure than a 1/2" fan even though they can have the same cfm rating.

8bit

 

[0p0rat0r]

I'm considering getting a centrifugal fan but I'm concerned about the noise they make. Do any of you know of any places that list the sound ratings of the various fans? Are there any particular brands that are considered superior?

I didn't think 1" of carbon would be suffecient to remove the odor, figured I'd need more.

Haps,

Thanks for your advice. I'll consider having the fan pull instead of push. It will complicate things a little bit though.

MTF-Sandman,

I agree with you. I'm considering a better fan, but I am trying to save money too, and also the noise of the stronger fans concerns me. I need to strike a balance between cost, noise and effeciency. PC fans are relatively cheap and quiet but not very effecient at moving air through resistance.

8bitNES,

I think I get what you mean about the carbon settling if I were to mount the scrubber so that the air is escaping from the side of my box rather than the top but I guess if I filled it up enough that shouldn't happen right. Point taken though. Also thanks for the tip on the fan depth, I didn't know that.

I'm going to revise my plans a little bit, based on your feedback, and see what I can come up with. Thanks everyone.

 

[8bitNES]

umm... what i meant to explain is that in a horizontal box, if the carbon would settle you'd have a little open gap at the top of the carbon filter. air travels at the path of least resistance so all your air would pass thru that little gap in the upper part of the carbon filter. a little tricky to explain without pictures...

if it were vertical, there would be no settling effect ensuring even scrubbing. the "original" box scrubber from OG was a vertical box. there was a squirrel fan pushing thru 2 or 3 layers of carbon on the bottom of the box. same thing as yours but top to bottom rather than side to side.

what are the dimensions of your box? did you sift the soot out before filling the filter? what cfm are the fans? most 4" computer fans only put out about 35-40cfms but i have some 1" thick fans that boast +/-115cfms and silent too. 12vDC .9A though there are .6A available. never put together my box scrubber (same as yours... shit they're all the same if you think about it) so i'm eager to see how well yours turns out.

good luck and keep us updated!
8bit

 

[0p0rat0r]

8bitNES,

Yeah I know what you mean about the air escaping and the carbon settling. Actually I haven't made my box or my carbon scrubber yet. I'm thinking about if I should get a cheap premade dresser or maybe build something from scratch. At most it will be 2' x 3' x 4'. That's 24 cubic feet and I'd like to exchange the air 3 to 5 times per minute that means I'll need about 125 CFM total, but then I have to compensate for the carbon layer. So if I estimate the carbon layer will reduce the airflow of the fan by 1/2 that drops me down to about 62 CFM, so I'd require an additional 62 CFM to reach my target again. So I'd guess I'd need a fan or fans that could output around 200 CFM.

Does that seem like a logical approach?

I haven't got fans picked out yet either. I'm considering my options between an expensive centrifugal fan or a couple cheaper PC fans. Since it's a relatively small area I'm thinking I might be able to get by with PC fans.

I'll post back with pictures when I've got something happening here. Thanks again.

 

[MTF-Sandman]

I'm considering getting a centrifugal fan but I'm concerned about the noise they make. Do any of you know of any places that list the sound ratings of the various fans? Are there any particular brands that are considered superior?

I didn't think 1" of carbon would be suffecient to remove the odor, figured I'd need more.

MTF-Sandman,

I agree with you. I'm considering a better fan, but I am trying to save money too, and also the noise of the stronger fans concerns me. I need to strike a balance between cost, noise and effeciency. PC fans are relatively cheap and quiet but not very effecient at moving air through resistance.

Here's a few db ratings for some fans and common noises...

Size dBA
4" Vortex 49
6" Vortex 49
8" Vortex 54
10" Vortex 57
12" Vortex 67

60cfm Muffin 45

Soft Whisper 30
Rainfall 50
Library 40

In all honesty, with an inline like a Vortex, Elicent, etc the only real noise that you'll hear is the air moving through the ducting.

The effectiveness of a scrubber is basically determined by the amount of time that the air contacts the carbon...so a 1" thick layer will work fine if there's enough surface area. Here's a couple of pics of a scrubber I made (6"IDx8"ODx36"L) that works great with a 6" inline pulling through it...

 

[BlindDate]

Regarding Blowing vs Sucking:

My setups are all made to pull the air, but thats only because it accomodates my situation. After all, these fans are rated for their static PRESSURE, NOT their Vacuum power.

My point is that I'm sure pushing is just fine.

 

[0p0rat0r]

MTF-Sandman,

That's a nice looking scrubber you got there. Was it difficult to make? What kind of parts did you use and how much did it cost? Does that whole thing sit outside your grow area? Thanks for the inspiring pictures.

BlindDate,

I've seen a few people mention pulling being more effecient than pushing yet you do make a good point.

Anyone else care to post pictures of their carbon scrubber designs so I can get some other ideas?

 

[MTF-Sandman]

It's really not that tough...just took a few hours of time. I took an bunch of pics for an article I was writing for a site when it went down. I think it was about $75 total.

Here's a rundown of the parts list...

5' of 3'x5'x1/2" steel mesh (aka hardware cloth) - $5
83"x32" aluminum window screen - $4
2 - 8" duct caps - $8
2 - 6" tabbed duct starters - $7
1 package of self tapping sheet metal screws - $2
1 roll of 3M 322 foil tape $5
25lbs activated carbon $45

You'll need a pair of tin snips, a drill/cordless screwdriver, needlenose pliers and some light weight gloves.

I'll see if I can't UL some of the pics to my gally...

 

[NiteTiger]

Well, one thing I've found in experimenting with various carbon scrubber designs is that the larger the surface area of the carbon, the less air pressure it requires. I might not be saying that well, so let me explain.

I tried a design that involved a 5 gallon bucket that had been thoroghly swiss cheesed around the sides, and a 2 gallon bucket that had been swissed through the bottom. covered the holes in the bottom of the two gallon bucket with window screening, and added a layer of about two inches of carbon. Inserted the two gallon into a cutout in the lid of the five gallon, and placed my fan into the mouth of the two gallon. Still with me?

Unfortunately, this created massive back pressure that defeated the negative pressure in my growroom that could only be solved by cranking my 747 CFM fan up to the max. This, of course, caused quite a bit of noise. So while noone would have asked about the smell, they certainly would have commented on the jet taking off behind the locked door. Obviously, not a solution.

What I finally settled on was using the same 5 gallon bucket from above wrapped in window screening, with a cyllinder of window screening covered hardware cloth inside of it, with approx. a two inch gap between the holey walls of the bucket and the hardware cloth. Filled the gap with 5 9oz carbon containers from the aquarium section of walmart (probably the most expensive way to do it, incidentally).

More carbon, and same thickness, but didn't have to adjust the fan speed off the lowest setting, and the only thing that changed was that my house no longer smelled like 4 battalions of skunks played WW3 in the walls. Only difference was the surface area the air had available to move through.

Since cylinders have the most surface area bang for your buck, you'll always have more luck with a cylindrical design than a single plane design like yours. Perhaps for a cab like yours, you could use a scaled down cylindrical design, like Sandman's suggested design (and mine too, for that matter, both are the same principle, just different executions and size).

I'm thinking a good cab size could be made with holed coffee cans of different diameters? Also, the cylindrical designs will help reduce the static pressure, possibly (emphasis on possible, not probable) allowing the use of PC fans.

If you need a pic to help visualize my muddied words, just say the word and I'll grab a pic, or layout a diagram.

 

[Curly]

MTF,

Your design looks like an excellent copy of a commercial scrubber and simple to.

What was the dimensions of the scrubber you posted?

And, what wattage grow did it effectively vent?

I've been looking for a suitable design for some time, I think yours is what I'm after.

Thanks mate

 

[MTF-Sandman]

MTF,

Your design looks like an excellent copy of a commercial scrubber and simple to.

What was the dimensions of the scrubber you posted?

6"IDx8"ODx36"Long...

And, what wattage grow did it effectively vent?

I've only tried it with a 2K SOG and it worked fine for it.

 

[0p0rat0r]

I just went out and bought a 4" Elicent Aeroflow centrifugal fan that's supposed to move about 140 CFM. It's very powerful, and unfortunately, also very loud! I do have a speed controller for it, but it doesn't slow the fan down enough. Even on the lowest setting it's still very loud. I think it's rated at like 54 db. In contrast I've got PC fans that claim to move 30 CFMs @ only 20 db. Of course the problem with the PC fans are their lack of power when facing static pressure.

I tried resting the Elicent on a towel inside my cabinet to keep it from vibrating. Then I covered the exhaust with another towel to help muffle the noise some more. I also turned the speed down to minimum using my speed controller and closing the cabinet doors. After all that my cabinet still sounded like a fridge, and that's not stealthy at all.

I'm probably going to try to come up with something using PC fans, and if that fails I'll try a bathroom fan.

MTF-Sandman,

Thanks for uploading some more pictures of your carbon scrubber design. I'm going to take a closer look at them.

NiteTiger,

Thanks for the info. A diagram or picture of your scrubber design would be much appreciated.

Here's a picture of my new cabinet I'm working on. I've got about 7.5" height from the shelf to the top of the cabinet and 28.5" in width by 14.5" depth. I am thinking about putting the ballast, power bar and timer in the upper right hand corner of the top shelf, taking up about 12" of width. That leaves me with 16" of width remaining on the shelf. I was going to use this space to mount some PC fans or a bathroom fan on the underside of the shelf. A few inches above the shelf I was thinking about installing a carbon tray, similar to my diagram in my first post. The tray would then be 16" x 14" approximately, and filled with a layer of carbon 1/4" thick. I'm not sure if PC fans would be capable of pushing the air through though.

 

[BlindDate]

I've never purchased a carbon scrubber since making them is so simple, but I would not rule it out since even the store bought units can be refilled. After your third or fourth refill the original price has been justified and you do have a nice strong sheet metal unit vs. home made chicken wire.

One bit of advice for the do-it-yourselfer is to pay attention to details and make sure flanges overlap carbon and such so that there aren't any unfiltered paths.


Operator:

If you can't quiet it to your liking then I would consider masking the noise. A table top fountain, small desktop refigerator or just a little clock radio playing when your not around. If that is not good enough, then I would seriously rethink your dubious location and the foot traffic that worries you.

Also, I don't think that 1/4" is sufficient to scrub anything.

Also, The best way to muffle noise is with mass. Glue some 5/8" drywall panels to the inside of your cab and doors.