Indoor Options to reduce temp with exhaust system: more CFMs or double the duct?

[Simplicio]

I'm getting ramped up with my first grow and trying to dial in the environment temps to get me thru the summer.

Indoor grow in a detached garage with an 8x8 tent. I have two 600 watt lights in cool tubes and a charcoal filter all inline as the exhaust system. The exhaust fan is 8 inch, the ducting and tubes are all 6 inch. I also have a 4 inch centrifugal bringing in fresh air to the tent from the garage floor.

At first I was exhausting directly in to the garage right outside the tent and passive air intake. Then I added the 4 inch fan on the input. But since I was exhausting in to the garage and basically pulling in that warm air back in to the tent, the tent temp was too hot in my summer conditions.

The garage is insulated. And it has a storage loft/attic above the floor. And the roofing has 2 passive square vents.

I added more ducting for the exhaust, making the length longer, and now have the exhaust system going directly out of the garage roof instead of inside the garage. This is 6 inch ducting connected directly to the a vent in the roof. The vent is a square thing (not sure what to call it). It is not one of the round spinning whirly vents.

Right now, even on a moderate summer day, I'm getting tent temps of 30C even with all the active air movement. I don't have any temp data from our peak hot days yet, but it will be even hotter. I would like to be able to reduce the temp by a good 5 degrees C.

There is another vent in the roof. One option is to put a Y splitter in the ducting and exhaust to the second roof vent. I'm assuming if I can double the volume or capacity of the exhaust output vents with the Y I'll reduce the tent temps. The ducting would still be all 6 inch, but I'd exhaust to 2 exits instead of 1.

Or would I get better results using the same setup with one exit point but adding more CFM to the line?

My gut says having 2 outside external exhaust exit points will be the most effective option. Those square vents in the roof have to be restricting airflow compared to the spinners. And if I kept things the same and added another inline fan and additional CFM's as is, I would not see any improvement because of the vent size bottleneck.

Or would adding another booster inline fan to the existing exhaust be a better approach?

Or would adding an AC cooler to the garage itself be better?

I'm curious how all these things factor in reducing tent temps. Where do you get the most efficiency? Input or output CFMs? Size of ducting? Size of exit points? Air conditioning?

I should mention I just realized the temp test I did today were not done with any tent circulation fans. I have a couple of fans in the tent that I'll use during the grow, but are off right now. Would that make a 5 degree difference?

Another strategy would be to embrace the heat, and create high humidity to compensate. The Vapor Pressure Deficit chart claims to give humidity values that maximize growth for a give temp, and my experience is that it actually does. I've run my plants with humidities in the 70s during flower without bud rot in a hydro system.

 

[stepside]

Mine run hit all summer long as well.. that chart up above is accurate.. you could also add co2 and use the heat to your advantage

 

[bartlancertp]

BTW, my 5 month cycle goes like this - plant 4 autos and 2 photos. 18/6 light cycle until autos are done, then 12/12 for the 2 photos. We discovered this by accident, but it sure has worked out nicely.

then how long to finish the photos?

 

[Phil Dunphy]

The photos are in veg while the autos are going. Once they're done I put the photos into 12/12, which usually takes 2 months. 3 months auto/veg, 2 months flower.