Ventilation vs. CO2

Okay, I'm preparing long in advance for a grow room setup.

Based on what I've read (in the Overgrow FAQ on ventilation) on the ventilation front, ideally the output fan should replace the volume of the grow room 2-3 times per minute.

As for CO2, supposedly the goal concentration of the air should be 2000ppm CO2, or .2%. This I got from one of the growing books I purchased, Marijuana Grower's Handbook by Ed Rosenthal. I should note, though, that in his book, he doesn't mention anything about exchanging the air. It seems assumed that the air in the grow room will be stagnant.

So here's some mathematical formulas I came up with while figuring out how to maintain a 2000ppm CO2 level while simultaneously replacing the air in the room 2-3 times per minute.

<o =""></o>To supply the CO2 to the room, I plan on using a CO2 tank with a flow meter/regulator.

For the purposes of these equations, I'll use these variables:

v - Volume of the grow room (cubic feet)
C - CFM of the output fan(s)
x - Number of times that the air in the room is exchanged completely each minute
F1 - Total hourly airflow out of the room (cubic feet)
F2 - Hourly CO2 flow out of the room (and therefore the necessary flow out of the CO2 tank to replace the gas that left the room)



So, although I'm yet to choose a grow room, I'll say that the maximum size available will be 10x10x10.

<o =""></o>http://www.purennatural.com/prod_desc.php?prod_id=597

That's the output fan I've chosen (for the ozone odor control, largely). Assuming I need to change the air in the room 2 times/minute, I would buy 5. I know, expensive, but this is an investment for me and the first harvest will hopefully be worth it.

<o =""></o>So now I have enough given information to solve for F2, the amount of CO2 I need flowing out of my tank to give the plants what they want.

v=1000
C=2000



Someone let me know if my math is flawed somewhere, but according to those calculations, a 10 ft. x 10 ft. x ft. grow room with 2000 CFM total would need 240 cubic feet of CO2 per hour to maintain the .2% recommended.<o =""></o>

Although I haven't looked at any CO2 tanks/regulators, Rosenthal's book says they usually can release up to 50 cubic feet per hour. I'd need 5 tanks all pumping out CO2 at full blast simultaneously to get the amount of CO2 I'm after.

Did I read something wrong? Was I misinformed? It seems to me that replacing the air in the grow room 2x per minute is a lot of airflow, and to try to constantly replace all that CO2 is going to be difficult.

Basically I'm just looking for someone to either help me out with ventilation and CO2, or to tell me I fucked up with my math.

Edit: My bad, I meant to put this in Grow Room Design/Setup. Sorry!<o =""></o>

 

So, as far as ventilation goes, was the Overgrow FAQ right? Exchange the full volume of air in the room 2-3 times every minute? That seems excessive to me, but I have no growing experience at all.

 

Yeah, so far I haven't decided how I'm going to control the temperature at night (night for the plants). I've thought about a small space heater as far from the plants as possible, but I wouldn't want to run it very long. As long as I can keep the room at a fairly steady 70F somehow, I'll be happy.

Yeah, I looked into CO2 generators. $500 for one that puts out only 36 cubic feet per minute, and that's the most efficient one I saw. The tanks would be cheaper and faster.

So it looks like either I need 5 CO2 tanks running full blast while the fans are on, or I'm gonna have to go with an imperfect timer setup, where I let the plants soak up some CO2 for a while, and then clear out the air, etc. etc. in a repeating cycle.

Would it be possible to supplement a smaller amount of ventilation with an overhead ceiling fan that just pushes the plants around with a constant, gentle breeze?

 

Cool cool, that CO2 generator would help. Plus, it runs off natural gas, much cheaper than refilling propane/CO2 tanks.

Anyway, as far as I know the size of the CO2 tank doesn't matter, it's all in the valving. While I haven't actually gone tank-shopping, from what I read most regulators allow 10-50 cubic feet/hour.