Air/ac Circulation Help

Discussion in 'Grow Room Design/Setup' started by ThaLoner, Aug 19, 2014.

  1. This will officially be my second harvest if I can pull things together.
    I used black and white poly to create a 13x8x9' shell for my tent. Running two 600w HPS with non cooled reflectors (no tempered glass on one system and an umbrella reflector on the other). Intake fan is 4" 170cfm. Exhaust is 4" 170cfm. AC is a portable unit at 8,ooo BTU's and mounted directly under the intake. There is a 30 pint dehumidifier exhausting on the same side as the main exhaust. One 16" oscillating fan mound mid way in the tent. Also two 6" fans on the floor to help move the air aound.
    My temps are inconsistent throughout the tent (See sketched floor plan).
    I also have a window unit (4,000 BTU's) with 6" duct fan attached to vent inside the tent but it never does more good than harm.
    I've tried moving the AC to different areas of the tent, inside venting out as well as outside venting in. Initially I had the AC (8,000 BTU's) exhausting into the chimney with a 6" duct fan but it would never operate sufficiently.
    Can anyone pin point where I am going wrong? Spending money isn't the best option these days. Any help or suggestions would be madd appreciated.
    I attached some pics of parts of the set up and also a PDF of a layout I drew up. AC Intake Outside T1.JPG AC Intake Inside T1.JPG
    Ducted Window AC.JPG
    T1 Dehumidifier.JPG T1 Exhaust.JPG T1 Lighting.JPG T1 6Inch 1.JPG T1 6Inch 2.JPG View attachment T1 Layout.pdf

  2. #2 Julius Caesar, Aug 19, 2014
    Last edited by a moderator: Aug 19, 2014
    You don't need an intake fan. If you can't afford to buy a decent sized fan right now, turn around the intake fan and use it as a second exhaust. Just add a few passive intakes - the more the better as long as they are light tight.
    Your fans are undersized for two 600w HPS - way too small. Start saving up for a 400 to 600 cfm fan ASAP.
    I have 2 x 600w HPS with cool tubes. I use 2 x 240 cfm in-line duct fans on the cool tubes (isolated from the grow room air) and a 400 cfm vortex fan for the grow room ventilation. My air intake is 16" x 20" with air filter. Even with all of this air exchange and an isolated cool tube vent, my grow room sits around 86F during the summer.
  3. Yeah a 4" exhaust doesn't even cut it for my 3x3x6 tent. You're gonna need at least 6" maybe 8". Even using the 2 4" fans you'll only get like 2/3 maybe even 1/2 of the CFM of a 6"
  4. Ok. Sort of an update. A friend had an extra 10" 790 CFM inline fan. I intend to use it for intake in place of my 4" 170 CFM. This will enable me to re-setup the proper exhaust for the Portable AC to the chimney (using the 4" inline as a booster fan). That way I'll lower the temperature outside my grow tent (from which I am getting my air for intake) and increase the strength of the incoming air pressure and amount. Also I will be moving every air system (AC included) to provide better circular air flow.
    My concern is: This fan is huge. My plants aren't strong enough for the force of it's winds if it's mounted low to the ground. How should I direct the strong air coming in not to harm my plants?
  5. #5 CanadianOrganic, Aug 19, 2014
    Last edited by a moderator: Aug 19, 2014
    Why wouldn't you just use it as an exhaust and have a passive intake?
  6. #6 Julius Caesar, Aug 20, 2014
    Last edited by a moderator: Aug 20, 2014
    You don't need a fan on the intake - period. If you absolutely insist on having an intake just because you want to be special, make sure the intake fan is a lower cfm than the exhaust fan - otherwise you will have positive pressure which you do not want.
    Use the large fan on the exhaust and call it a day. Take our advice and save a headache. 
  7. Thanx for all the comments. I'm using the 10" for exhaust. Using the 4" for intake. Then using another 4" for my portable AC exhaust. Didn't really know much about passive intake (partly the purpose of this post), and I've probably always had positive pressure because it makes my tent bubble out. I'm still confused as to which is good and which is bad to have. But I guess things should take a couple days to adjust with the ventilation upgrades to get some cooler temps. I hope pockets hurt.
  8. #8 CanadianOrganic, Aug 20, 2014
    Last edited by a moderator: Aug 20, 2014
    Just make an open hole at the bottom on the opposite side of the exhaust that is 2x the size of your exhaust. Boom, passive intake.
    Your intake either way is supposed to be 2x the size of exhaust.
    Also, you want negative pressure, not positive. Positive means air is finding all the cracks on your room and leaking out there. Negative means air is being sucked in through those small cracks.
  9. #9 Julius Caesar, Aug 20, 2014
    Last edited by a moderator: Aug 20, 2014
    \nThe most important reasons for slight negative pressure is so that odor doesn't leak out without being filtered, and it creates a continuous flow of unobstructed airflow. A passive intake is just simply an opening so that air can be "sucked" into the tent. Air can only enter a room as fast as it is being removed. The room is not a balloon - it will only hold so much air under atmospheric pressure. This is why you want the large fan on the exhaust, so it can pull in the same amount of air it is pushing out. Opening extra passive intakes reduces the negative air pressure so the tent won't cave in on itself or so to speak, and will lighten the load on the fan which will increase overall air exchange. I would open two vents for intake - just be sure they are light tight.

  10. What are your plans for the 4in you have? 

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