Comments needed on ventilation design...

[blueberryfarmer]

I am building a cabinet style grow with a 400w MH for lighting. I have no air-cooled reflectors or anything like that, and am therefore planning to divide the grow chamber with a pane of glass. I have purchased a 130cfm squirrel cage fan for ventilation. This is my plan: the 130cfm fan will pull air through a passive intake in the bottom grow chamber, into a home-made can-style carbon filter, through the filter into the upper light chamber, then from the light chamber into the fan itself and out the top of the cabinet. The size of both the lighting and grow chambers is about 30 cubic feet. Will a 130cfm squirrel cage fan have the power required to move so much air through the carbon filter and both chambers? THere won't be much use of ducting or anything except to connect the fan to the lighting chamber and the carbon filter to the lighting chamber. As long as there is enough suction and everything is sealed properly it seems like it should work.... but i'm not certain... i'm not confident about it. Any ideas people? thanks.

 

[Mackawber]

I dont think you will have enough cooling air coming in from the bottom. Put a smaller fan down on the lower part of the cab to suck in lots of cool air. Have it discharge at or slightly below plant canopy level. Use a thermostatic controller to turn that intake fan on and off to maintain the temperature inside your cab.

 

[Guest]

I respectfully disagree with the part of Mackawber's repsonse that says

Put a smaller fan down on the lower part of the cab to suck in lots of cool air. Have it discharge at or slightly below plant canopy level. Use a thermostatic controller to turn that intake fan on and off to maintain the temperature inside your cab.[\QUOTE]

Mackawber is probably right in that you don't have enough cooling. However, the flaw is that you will not be drawing more air through the cab by using a fan on the intake. You will merely be raising the pressure in the cab and/or possibly addingresistance for air coming through the intake being sucked by your 130cfm fan.

What you want to do is either get a second fan or a bigger fan. The one you have could possibly work, but most likely temps will be too high. Make sure you have at least 2X the intake size as the exhaust, and a little extra probably won't hurt as long as there's still suction at the intake holes.

It would be good to have another fan (possibly ocsillating) inside your cab just to increase air movement within the cab.

 

[blueberryfarmer]

Thanks for your input. I hope this fan is sufficient to ventilate my cabinet. Thanks for the point about having the intake be at least twice the size of my exhaust, i was not aware of that. I will attempt to get an oscilating fan to help encourage airflow within the grow chamber. Does anyone have any other opinions? Remember this is designed to pull air not only through both chambers but also through a can-style home made carbon filter... Thanks for the help everyone!

 

[blueberryfarmer]

Another question: Adding extra fans in-line with the current ventilation setup... for example... adding a computer fan to help pull air through the carbon filter.. will that help my overall airflow? Or merely restrict it? Any thoughts? Thanks

 

[mrgrowmez]

i would put the filter in the top part of your box, attach directly to the fan so its sucking through there. that and get a bigger fan if you havent already bought the 130cfm´r.
MRG

 

[blueberryfarmer]

Yes, i already purchased my fan. I wanted to limit it to the 130cfm fan for the sake of noise concerns... i would very much like this cabinet to be as stealth as possible. The filter i'm thinking of building is the DIY Carbon Scrubber shown here: http://www.icmag.com/ic/showthread.php?t=31679
Would that not have to be inside the grow chamber to suck air in through the sides? It does not flow through, due to the cap on the end. Is there a way to make it work by putting it with the fan in a separate compartment? Thanks for your help