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Ventilation: what size of fan you need

Blitzen

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Hi all! long time lurker first time poster :)

I'm a novice grower but I design odor control systems for many industries like plastic extrusion vents where the odors and VOC's are pretty high. Working out your carbon filtration is really just a matter of doing some math. Hopefully some of you will find this useful.

For carbon to work properly the smelly air needs a certain amount of "dwell time" in the carbon. I see a lot of people use fan systems that are too poweful and the air gets pulled too quickly through the carbon. Get in touch with these guys http://www.generalcarbon.com/ and ask for a carbon pellet that is formulated for cannabis. potassium permanganate and coconut Shell are another odor absorption medias that work well. There are literally 100's of different carbon formulas for VOC and odor control.

To work out your cfm needed for 10 air changes per hour you multiply your fan systems cfm x 60 and divide by the volume of the space. For example...if a 4" cent' fan has a cfm rating of 187cfm - if your grow space is 6' x 8' x 8' then 187x60=11,200/384 = 29.1 ach.

So..a 4" fan that does 187 cfm running on full speed with an line carbon filter is pulling too fast and the air is not getting adequate "dwell time"...but that same fan running at 1/2 or 1/3 speed is going to be much more effective.

I hope this info is useful..
This is the stuff
 

Blitzen

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Awesome information, this is the stuff that saves lives!!!! THANKYOU!!!
 

Simplicio

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Hi all! long time lurker first time poster :)

I'm a novice grower but I design odor control systems for many industries like plastic extrusion vents where the odors and VOC's are pretty high. Working out your carbon filtration is really just a matter of doing some math. Hopefully some of you will find this useful.

For carbon to work properly the smelly air needs a certain amount of "dwell time" in the carbon. I see a lot of people use fan systems that are too poweful and the air gets pulled too quickly through the carbon. Get in touch with these guys http://www.generalcarbon.com/ and ask for a carbon pellet that is formulated for cannabis. potassium permanganate and coconut Shell are another odor absorption medias that work well. There are literally 100's of different carbon formulas for VOC and odor control.

To work out your cfm needed for 10 air changes per hour you multiply your fan systems cfm x 60 and divide by the volume of the space. For example...if a 4" cent' fan has a cfm rating of 187cfm - if your grow space is 6' x 8' x 8' then 187x60=11,200/384 = 29.1 ach.

So..a 4" fan that does 187 cfm running on full speed with an line carbon filter is pulling too fast and the air is not getting adequate "dwell time"...but that same fan running at 1/2 or 1/3 speed is going to be much more effective.

I hope this info is useful..
Very useful info.
The accepted range of values for number of air exchanges per hour is probably too high, and your 10 exchanges per hour sounds more realistic.
 
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