Ventilation advice needed

[SauronBlue]

I'm going to start up a grow with the flower space in a 39x39x72" tent after a few years away from growing. I have an enclosed 600w hps that I had a fan sucking over the light from the main grow area to vent outside and circulate air(along with a couple small clip fans blowing on the plants). My question is; if I'm not using co2, is this an ideal way to setup my tent, or should I think of venting the light from outside straight thru, keeping the air inside the tent separate?
My thought has always been that it's good to get the people air in there, since we're breathing out co2, and the outside temp (in the house, outside of the grow tent) is generally a comfortable temp. I also used one port on the side to connect to an a/c unit in the summer, and right out the window in winter, allowing the negative pressure to pull in frosty air. I'm thinking to try and work out some kind of slider to control how much of the intake hose is sucking from inside vs. outside, in case I want to limit some of the winter air for temp reasons.
Thanks for any feedback!

 

[TorturedSoul]

Carbon filter? Odor concerns?

With "enclosed, air-cooled" light fixtures, I've always liked one ventilation run for the lighting - bringing cool air in from elsewhere, passing it through the light(s), and sending it away without said air ever mixing with the grow space. And a second, separate, ventilation run for the actual grow space environment.

As the lighting "run" is sealed, it shouldn't pick up any odor from the plants. Ergo, this run doesn't need a carbon filter, just a fan. Not having to push air through a restriction (carbon filter), this fan need not be particularly strong in a "pressurized" environment (although it still needs to move an adequate amount of air, of course). The actual grow tent/space - and odor-control - ventilation run, which does have a carbon filter, need not move so much air, because that air isn't overly warm. Because the air moving through the carbon filter in a "two-run setup" isn't heated - and because you move a lot less of it - your carbon filter should last significantly longer. You might be able to turn the fan down to a lower speed, use a somewhat smaller-capacity fan, or even set up that one on a timer during the lights-on period instead of having to run it constantly. This is very much a YMMV ("your mileage may vary") situation, of course. . . .

 

[SauronBlue]

That's a good point, regarding fan speed. Lowering your fans from the max setting also gives a good noise reduction. I hadn't considered that having 2 systems, while needing an extra fan, would give me more control of temp by cooling the light without necessarily having much circulation over the plants, but then able to amp up the tent fan if I want more air over the plants. More control is generally a good thing. Also, in my case, I have really cold air at night in winter, and I like pumping that in to cool off the heat from the 600w HPS, but it can be TOO cold sometimes, but by keeping that in my light, it would super-cool the light, while allowing much more temperate air to come in from the room the tent is in.
I think you helped me talk myself into a dual system LOL