need fan advice for cab with co2

[Spuzzum]

I'm currently building an led panel, for an 18" x 30" x 3' high chamber space. Although 3' high, it's going to be in a "step style" set-up, so it's only 3' tall in the center, with 1' tall on the sides (or so, yet to be determined).

http://i851.invalid.com/albums/ab80/thereal_spuzzum/chamber.jpg


Now, since it's a step set-up, I wanted to utilize the sides of each step, by mounting 2 or 3 90mm intake fans per step (18" long). I've modified a 350w atx psu for the led's power source, using the 3.3v, 5v, and 12v lines. I plan on powering the 90mm pc fans off one of the the 5v lines. They'll be reduced in speed, but they'll be quiet. And since I'll be using multiples, that will make up for the reduced cfm flow. And of course, led's will be less heat to begin with, so fans are really only for air exchange. There's also intake fans on the floors of the side chambers, and exhaust fans in the roof of the chamber.. which will be carbon filtered first.

http://i851.invalid.com/albums/ab80/thereal_spuzzum/intake-exhaust.jpg


Now for the question I have for co2...

Since my chamber is roughly 7.5 cubic feet of actual space, the read-me's suggest I'll need less than 1 gram of co2 per day.

"In our sample room (8x8x8), we would need to create about 1 lb (8.5 cu ft) of CO2 over a 24 hour period.

To calculate the amount of Carbon Dioxide needed to enrich a room to 1500 ppm, first calculate the volume of the growing space. For instance, an 8x8 foot room with an 8 foot ceiling would contain 512 cubic feet of space. Determine the CO2 needed to enrich to 1500 ppm by multiplying the volume of space by .0015.

512 x .0015 = 0.768

Thus, 0.768 cubic feet (or rounded up to 0.8 cu ft ) of carbon dioxide will be needed to enrich this room at 1500 ppm. 1 lb of CO2 is equal to about 8.5 cubic feet at normal temperature and atmospheric pressure."

My cabinet...

18" x 30" x 2' = 7.5 cubic feet.

7.5 x 0.0015 = 0.01125

8.5 / 0.01125 = 755.55556 (756)

1 lb = 454 grams

454g / 756 = 600.5291mg (600mg)
--------------------------------------

18" x 30" x 2' high growth chamber would need 600mg of co2 every 24hrs.


So, with less than 1 gram a day required, I was thinking a 20oz paint ball co2 cannister should last quite a while.

http://i851.invalid.com/albums/ab80/thereal_spuzzum/20oz-co2-tank.jpg


But as for the fans.. since the temp will be low enough for a sealed environment, I was planning on just exhausting during the night cycle (if using co2).. unless specifically needed periodically during the day cycle. So, intake fans in the side chambers, and the exhaust fans at the top, will only run during the dark.

But.. I still wanted the fans on the steps to act as the circulating fans. As long as the main intake and exhaust fans are "off".. will the side fans still draw air in (not wanted), with no exhaust to allow the air replacement to begin with, or, will the fans act in reverse, creating some kind of vacuum.. therefore pulling the co2 "out" of the chamber rather than just circulate it?


Any ideas?


Spuzzum.....