Temperature

[La Grasserie]

My situation:

I am doing a sog-style indoor soil grow under 800w HPS at 30 days into flower. When the lights are 12" off the canopy, the temp is 87. Move them back to 24" and the temps fall to 81-83. The plants have stopped stretching and are showing great bud development. The main strain is Jock Horror.

Question:
Would the increase in light intensity at 12" merit upper 80s temps on the canopy? Should I stick with 24" and more ideal temps? Lights off temps are in mid 70s.thanks

 

[FreezerBoy]

I'm guessing that's a pair of 400s you're talking about? 24" is a long way away for a 400. What kind of ventilation/heat transfer you got?

 

[La Grasserie]

Correct, dual 400s. They are vented to the attic by a ~200cfm inline fan. Cooled by 73F air from adjacent room. I'm sure a stronger fan would lower ambient temps, but that's out of the question til after harvest.

I'm dropping these lights down to 10-12" and will monitor from there. I knew about the inverse square law, but that chart really pulled it together. Thanks Freezer

 

[CMoon]

your distances look good man and jock can take a bit of heat.......id get the osilator in soon as , helps to move the air dramatically on the high temp numbers imo

cmoon

 

[Quazi]

You should be able to bring the temps down on those 400s.

Every inch you move the lights away causes an exponential decrease in the amount of light that your girls will be exposed to.

It's called the inverse square law:


Some oscillating fans aimed at the canopy should help clear some of the heat that your girls are receiving.

-Q

 

[FreezerBoy]

They are vented to the attic by a ~200cfm inline fan. Cooled by 73F air from adjacent room. I'm sure a stronger fan would lower ambient temps

That sounds like maybe half of what you need. How's your intake?

fan-intake calculator

 

[La Grasserie]

Freezer, you are one numerical mofo. My calc lists 320cfm...upon checking, my fan is rated 160cfm and has to pull through a little curve to boot. So yeah, I could use an upgrade. But first...

My intakes are two 6" holes to the cooled room, one with a small desk fan pulling intake. They are partially covered with these air diffuser orb things, though. I am certain this restricts airflow and was bad design on my part. Thus I leave the grow room "door" open when lights are on for now. This completely compromises security as well as air tightness.

How's this sound: Removal of the 165cfm inline with subsequent placement on a 6" intake (its a 6" fan so it'll be snug) and the procurement of a 300+cfm venter for my lights? I'd like a little neg. pressure for odor control, and with winter coming, I'll be able to put that cool room down to 60F if duty calls ;p. Maybe also some nice ducting as the flex aluminum product definitely has its shortcomings.

 

[FreezerBoy]

You're operating a bit out of my league. A room may be a box but, it's a big box. I don't know how much of my cab info correlates. I don't know where the room is or where the air is coming from.

I can't help with powered intakes. I avoid them. I'd play with the fan-intake calculator to get an idea of how far off from optimum you are. Maybe enclose the hoods on a separate duct? Maybe AC?

 

[La Grasserie]

I'll figure it out soon enough, its all trial and error with me. Caught a dab of burn on one of my colas...lights have been backed off to 16-18" with temps at 85.