advice on airintake and exhaust

[shannonball]

hi everyone, new to this site. came over from Rollitup.

We just finished fixing up our shed to grow (legal state of MA). We have a timber lighting 900 watt Vero 29c's LEDs in an 7x4'5" room 8' high.

We are going to install a fresh air intake (from outside) using a Hepa filter (to keep outside mold etc from coming room) in a yet to be designed filter box on a hurricane 735 cfm 8" inline fan. We will have an exhaust fan in the gable for outtake, no filter required as the smell is not going to be noticed due to no neighbors. We will fans blowing both plants and the heat sinks on the leds. What size exhaust would you recommend and does our setup sound alright and what should we change? Are we setting this up correctly?

thanks shannon

 

[jocat]

Air is key, unless you want to run a dehumidy/AC/CO2. I installed a couple windows & modified them to fit 16" X 20" hepa grade furnace filters, made it so i can change filters monthly or whatever's required for full flow, I use passive intake with a 12" inline on a titan 702895 day/night temp controller with idle/low temp settings. I have killed a few inline fans over the years, go with a metal fan/bearing like the 12" huricane/amazon these things last & last, Congrats on the freedom, I'm in Oregon & get to grow stinky Cheese & enjoy that smell around the place....freedom rocks!

 

[humble1]

7'x4.5'x8'=252'
An unrestricted 735 cfm fan will provide more than enough air exchange to provide plants with fresh air at ambient CO2 levels.
Whether it will adequately cool your grow, or maintain a desired rH, are totally separate issues.
First, how big is the opening for your exhaust? Is it roughly 8"x8" or more? Is there a grill or obstruction on it?
I would design the largest possible passive intake (common rule of thumb is 2x area of exhaust opening), with easily replaceable filters, and then match my exhaust fan to my exhaust opening. With that done, check the ambient temps/rH in your shed with the exhaust running full during lights on and running to achieve a minimum exchange of the air volume 1x per 3 minutes with lights off. If your temps or rH are not in an acceptable range, then make modifications as necessary.
A good place to start re: temps, especially with sheds, is with insulation.
For rH, if it's too high you may need a dehuey (especially if the ambient rH is high). More airflow will only bring in more of whatever the ambient rH is outside.
Make sense?

 

[shannonball]

Hi everyone, thanks for the quick responses. Will check out the titan controller.

When you say "passive intake" are you referring to no intake fan; having the exhaust fan pull air through the room via the filter box sort of like a vacuum sucking air in? Our thoughts were to use the 8 inch hurricane to suck in clean filtered air via the filter box,using the a/c if needed, and the exhaust fan pulling out any heat and to keep the air exchanging.

We've grown for many years but not in this organized, legal fashion. Typically 1-3 plants in our bsmt. Now we're trying to go bigger etc.

Our gable vent is exactly 8x8". We have a hurricane 6 inch 435 cfm fan we could use for the exhaust gable vent to pull the air out. We also have a small A/C unit (BLACK+DECKER BPACT08WT 8,000 BTU Portable) to help with any humidity n cooling.

We plan to not run the 20/4 for four-six weeks for a good veg period, using scrog, then lights out 8am-8PM during flowering hoping this helps with heat, etc.

Sorry if i'm asking too many basic questions here. I'm in charge of the setup and hubby is in charge of the growing/plant care etc. Splitting up the efforts.

thanks much everyone for your time n advice.

shann

 

[jocat]

Ya I don't use a fan on intake but like a huge exhaust fan placed up high and in a spot to get the air moving on it's way through the room, circulation fans to stir, and the titan to slow or speed up the exhaust as required by increasing/decreasing temps, I don't like to work graveyard shift but with the summer temps I have more control/success going this way. Just don't get lazy & put off required chores....Iv'e done that too.

 

[humble1]

Passive intake = no intake fan.
The way I think about rooms is by their limiting factors.
With an 8" intake fan and 6" exhaust fan, you either generate balanced pressure (because of flow restrictions) or more likely a positive pressure on the room and the exhaust is limited to the max capacity of the 6" exhaust fan.
Reversing those fans, with 6" intake and 8" exhaust, there is negative pressure in the room and the exhaust is still (mostly) limited by the 6" intake fan's capacity for air exchange.
Instead, with a passive intake and an 8" exhaust fan, you are limited by the external opening of the filter and the restriction of the filter itself (which would be the same regardless of airflow layout). Also, that portable A/C needs an output for its hose and I would suggest placing the output at least a few feet away from the intake opening (so that it does not cycle back into the room).

 

[shannonball]

Humble!, thanks, that makes sense. thought passive meant no fan but wanted to make sure. We are going to start with a passive intake filter box, the 8 inch hurricane for exhaust to start and see how things go. The portable A/C will have a four inch vent to the outside, think dryer vent style. Thank you very much for helping me out. have a great morning. It's only 6:45 pm here. shannon