1) Ozone is bad for plants I hear 2) Ducting on intake is okay as long as its ground level relatively on other side of room than exhaust you should be good but don't run it where it will get in the way. Maybe a short run but not really needed.
Going to do it just to keep light proof as the incoming air will becoming from the outside. Ozone will be on time for 2 minute durations every 10 minutes to produce enough to keep air clean with be located near ventilation tubing. Any idea on the yield I can expect?
2000W first grow 40 plants.... if nothing goes bonkers fucked on you I think you could pull 1-2 lbs without too much trouble. At the very least 10oz 2nd grow probably double that. But I would say expect a lb.
I have a quick question about your formula for CFM and removal of air. I have a small cab, 3x3x2. I have two 3" holes drilled in each corner of the bottom with a 90 degree pvc elbow in it. For exhaust I have one of these: High Tech Garden Supply Theoretically, I should not have a problem. My exhaust goes from a carbon filter to a 4-6" adapter to fan, to a 4-6" adapter, to a small bend out the top of the box. For lighting I have CFLs, a pvc frame filled with 10 light sockets. I was planning on just using 5 of the sockets for veg, and I but the lights it, swithced it all on and my temps go over 100 degrees after about 30 minutes of being on. Did I do something wrong as far as my intake holes, or is the exhaust fan, just not strong enough?
The CFM formula is for air replacement via ventilation not thermal reduction. 5 sockets could be 13W each or 54W each. The fan should be plenty to replace the air, and I would think it should be able to cool 5 26w lights, maybe even 5 54W. But you are restriction a fan with not a lot of static pressure (power) down to 4" reducing its airflow by half probably. You can try creating an intake by cracking the door a half in. and see if that does it. If so you just need to cut some passive intake. If not you may need a stronger fan for cooling purposes. CFM replacement is purely for plants to breath. I went wrong here my first time too I thought I had plenty of ventilation and my room shot up to 90-100 degrees. Bought new fans and now I run 72-78 with lights on normally.
wow dude...im building a small 1-2 plant cabinet (1.5ft long x 1.5ft wide x 3ish feet tall) to grow some lowryders in and this clears up all my questions about vents. +rep on this shit for sure
Hey Bohbo, thanks for putting this together. Tho i think you should state clearly on the first page, as you just said, "The CFM formula is for air replacement via ventilation not thermal reduction. " about that, and my real reason for posting. I wish i could remember where i C&P this info from, but it should be useful. Perhaps more blades(ies) can chime in on its validity but, i think it should be a part of your faq. again my apologies for not knowing my source. ***Overheating is a common problem encountered by growers, especially in closet or 'box' setups. High temperatures cause whispy buds and is often a sign of inadequate ventilation, which brings a whole host of other problems. Whether at the design stage or struggling with an existing problem, the following formula can be useful in assessing your situation. Its pretty basic in terms of heat transfer but from experience has proved to be pretty accurate for our purposes. The formula is: Q = V x P x C x dT where: Q = Amount of lighting (kW) V = Volume of air being ventilated (m3/s) P = Density of air (assume 1.2 kg/m3) C = Specific heat capacity of air (assume 1.02 kJ/kgK) dT = Temperature difference between ambient and growspace air in degC You can use this to determine what the temperature rise in your space will be (dT), or given a desired temperature rise you can use it to work out how much ventilation you will require (V) To get from CFM to m3/s divide the CFM by 2119. Examples Here are some examples of how you could use the formula in three different ways, each using the same basic figures for clarity. What temperature am I likely to get in my growspace? Assume: Lighting = 400W (0.4kW), ventilation = 240m3/hr (0.067m3/s) and temperature of air entering room = 21degC Q = V x P x C x dT => dT = Q / (V x P x C) => dT = 0.4 / (0.067 x 1.2 x 1.02) => dT = 4.87, i.e. 21 + 5 = 26degC in growspace How much ventilation am I likely to need? Assume: Lighting = 400W (0.4kW), temperature of air entering room = 21degC and temperature of growspace to be no more that 26degC Q = V x P x C x dT => V = Q / (P x C x dT) => V = 0.4 / (1.2 x 1.02 x (26-21)) => V = 0.065 m3/s i.e. 240 m3/hr What is the most lighting I can put into my growspace? Assume: Ventilation = 240m3/hr (0.067m3/s), temperature of air entering room = 21degC, temperature of growspace to be no more that 26degC Q = V x P x C x dT Q = 0.067 x 1.2 x 1.02 x (26-21) Q = 0.41 kW i.e. 400 W So that's it, once you get used to using it its very simple really, Just stuff the formula and figures in a spreadsheet and let it do the work.**** again, not my work, but the figures do seem to work out in my case. Greens to You, Cyrate __________________
Thanks Cyrate, I added it to the formula FAQ and Permalinked to your post. Thanks for posting that! +Rep for sure mate.
WOW! Awesome thread! This helped me out so much, thanks for putting your time and all the info in here Bohbo! +rep sir i just have one question i hope someone can clear up: so, if i have a negative pressure inside a cab, odor leaking out shouldnt be a problem since the exhaust will be sucking so much air in and then through a carbon scrubber right? oh, and good find on the heat Calculation too Cyrate! I will have to go back and fix my ventilation for this, but i am glad i saw this before it starts getting hot this summer!
You will eliminate a lot of odor loss, but without vapor barriers and such depending on how smelly it can leak out and permeate through the wood or other porous material. But for all intensive purposes yes maintaining neg pressure with a carbon scrubber should reduce the majority of odor leakage.
One more quick question to you all. Since I have the heating issues with the cfls, I have decided I either need an inline high velocity fan, or an LED setup. I have a friend who will sell me a UFO for 185. Should I invest in the UFO or just keep the CFLs with a better fan. I know it doesnt match HPS/MH/HID, but for my first setup this is fine with me. I also plan on eventually building something bigger and using this as my cloning cab, with a mother in it.
Depends on the UFO if it is a 90W I might pass if its the 180W I would get it. If its a genuine 90W it could have its uses. If you spent $250 UFO+Inline Fan you should be rocking. It really depends on the UFO though... think about it this way. If he is selling it there is probably a reason. Buddy or not he probably doesn't want / need it. Food for thought. If you think its a good deal I say go for it, it can't hurt augmenting your CFL setup with it.
It's a 90 Watt UFO, but I will only be growing 2-3plants so it should suffice. He's getting rid of it becuase he's decided on an HID setup and T5 for veg/cloning
Well if you have the cash and can still buy a fan I would. 90W is still 90W and will create some heat. So adding more light will increase heat. If you get the UFO I would buy an inline fan as well.
I was thinking grow solely with the LED lamp for now and after I get a little more cash, get a better fan and then beef up the setup with some supplimental CFLs
Thanks for the great guide Bohbo! Im trying to set up a low cost stelthy grow cabinet here but i am unsure about what type of fans/air control to use. I want to do this low-cost so im thinking of just using 2 pc fans (have one already) but idk if that is enough power to pull through the carbon scrubbers enough air to cool my cab and replenish the air. The one i have is 120mm and they sell 360mm online for $30. unfortunately idk what a mm is. millimeters? Will this be enough power for my cab or do i need to get an inline fan? Also, how do i know when there is negative pressure in my cabinet? Stealth and odor are concern for me so will an inline fan create more negative pressure? or will it just be more noise? Oh and btw, using the formula on the first page i should need 3cfm (2.5ft x 1.5ft x 4ft / 5) to replinsh the air. but as for cooling the cab im not sure what i need, but i plan to pack 10 cfl into the space.
MM = Millimeter For 208W+ of CFL I would go with an inline myself, however Mechanibus' guide to modifying a stanley blower might do it for you. Neg air pressure: Put a small piece of paper over a hole or crack and it should suck the paper to the outside of the cab. (Or at least hold it in place temporarily) My Clone cab is 4x13W and it is cooled (barely) by a 120MM PC fan blowing out back of cab and another blowing down on lights. (Intakes are just cracks in door.) A PC fan doesn't have the static pressure to create any real observable neg pressure. My flower room though it can click the door shut with all the fans running.
Good thread man. I have my setup in a dedicated bathroom 9 feet H x 6ft W x 3ft D. The existing exhaust fan doesn't draw enough of the heat. I live in a very hot climate. I sometimes have to leave the door open to let the temperatures drop below the 90's. Usual temperature is around 82 but thats because I open the door a few times a day. Was wondering 1st does opening the door to cool the room a few times a day stress the plant. 2nd would removing the door and adding white vinyl to replace the door w/ velcro leaving small area open @ the bottom during lighting, closing the bottom during darkness cause any issues? What would you do about the heat? Remove the existing bathroom exhaust fan and just get a squirrel ? Replace the existing fan with a higher rated bathroom fan (do they make those?) from home depot ? I was hoping to kill 2 birds by using the bathroom because of the existing fan. Open to whatever works. Thanks in advance
Hmm... well you have options and sounds like you are open to them. Opening the door during lights on won't stress the plants in fact it would give them more fresh air so thats good. Here is a cheap solution that might work for you. ASSUMING STEALTH IS NOT AN ISSUE: Replace door with panda film or some sort of foam board (check out garage door insulation foam boards) you might be able to get one to fit. I would then cut a hole in the new barrier and attach ducting to this hole. Inside the room run the ducting to a new inline, Vortex, S&P, Eco Green whatever. Hell even a 6"-8" Booster duct fan might work, but I would get a real inline. Vent that into the house (carbon scrubbed = inline fan not duct booster). Granted this is blowing air into your house. Stealth. remove the bathroom fan (set aside so you can reinstall later) and use the in place ducting to attach a 4" inline fan or squirrel cage. I would think upgrading the fan using current ducting would do well for you. Cutting a hole in the door / new barrier and light proofing a passive intake 4-6" would help too.
After reading this thread and posting my own comments my hampster wheel started turning in my head. I removed the outer cover of my bathroom exhaust fan and the light assembly to "open" her up more. Also if I just crack the door open just a hair I get really good negative whatever you called it (good suction). I'll post my findings but thinking the vinyl Velcro might be the way to go. Suggestions