McStrats
Well-Known Member
I posted something similar to this in a thread a while back that was about odor and ventilation control...but I still see new threads asking the same questions..and I also see a lot of bad information. I am reposting this as it is based on math and science and decades of proven results.
I'm actually a novice grower myself but I design odor control systems for many industrial applications like plastic extrusion vents (much smellier than cannabis) 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 powerful and the air gets pulled too quickly through the carbon. Potassium permanganate is another odor absortion media works well. There are literally 100's of different carbon formulas for VOC and odor control. Building your own carbon scrubber is actually quite easy and it will be better than the ones on amazon. There are several vids on youtube for DIY carbon scrubbers.
To work out your cfm needed for 10 air changes per hour you multiply your fan systems cfm x 60 (mins to hrs) and divide by the volume of the space. For example...if a 4" cent' fan has a cfm rating of 187cfm and your space is 6' x 8' x 8' then 187x60=11,200/384 = 29.1 ach. Unless you are building a wind tunnel, 30 ach is way too much air.
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. For a space that size you need "make up air" but definitely not an intake fan. A passive inlet is all you really need for most small grow spaces.
I hope this is useful to some..
I'm actually a novice grower myself but I design odor control systems for many industrial applications like plastic extrusion vents (much smellier than cannabis) 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 powerful and the air gets pulled too quickly through the carbon. Potassium permanganate is another odor absortion media works well. There are literally 100's of different carbon formulas for VOC and odor control. Building your own carbon scrubber is actually quite easy and it will be better than the ones on amazon. There are several vids on youtube for DIY carbon scrubbers.
To work out your cfm needed for 10 air changes per hour you multiply your fan systems cfm x 60 (mins to hrs) and divide by the volume of the space. For example...if a 4" cent' fan has a cfm rating of 187cfm and your space is 6' x 8' x 8' then 187x60=11,200/384 = 29.1 ach. Unless you are building a wind tunnel, 30 ach is way too much air.
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. For a space that size you need "make up air" but definitely not an intake fan. A passive inlet is all you really need for most small grow spaces.
I hope this is useful to some..
