Plants are growing fine but trying to reduce the ambient 90F...

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bluegill

Well-Known Member
Update: ambient temps are sitting consistently between 80-82F range and my reso temps are a consistent 72F. I removed the carbon filter to get better airflow, but it does not help cooling the tent. One plant is still heat stressed but has not worsened. It's really just the corners on leaf edges pointing slightly upward.
 
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bluegill

Well-Known Member
Another thought... for the summer when I am running AC - I could remove the register box on the nearby vent and duct it down to the tent! For the winter, I could get a dual laundry exhaust vent and duct cool air in from outside. It gets very cold here, though...
 
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1212ham

Well-Known Member
bluegill said:
Setup:
2ftx4ft tent @ 5ft tall on a 2ft stand. RDWC with 5gal reservoir underneath and 5gal buckets - the buckets are black; 3.5 inch net pots, large airstones. I have a Phantom Pheno 440w LED on an 18/6 hour cycle. Vivosun 4" duct exhaust fan.

Plants:
2 indicas (black cherry OG) growing in a 2x4ft tent a la RDWC 5gal buckets. I'm seeing insanely fast growth. They were just seedlings a week ago and already have 5 nodes of growth; the largest leaves are >2 inches. They have been on GH nutes on mild/medium strength for about a week, and I have my LED set about 32" above the top of the netpots because of how young these are.

Heat Problem:
The tent was running at ~82F when I was running the light @ 80% power, but since I'm seeing such nice growth, I decided to run it full power. The problem is that in such a small tent, this increased the ambient temp at plant level to 86F, and the temp above the light to 100F. I put a large box fan in front of the intake, thinking that might help, but it only normalized the ambient temp to 90F. I read around online for a quick solution - I hung a damp towel behind the fan, and that has since dropped the temp to 88F. Just checked water temps. They are a 82F with the light on.

Potential Solutions? :weed: :bigjoint:
-I found a chart that seems to imply the ideal RH for this temp would be about 80% and that would further reduce the issues?
-With my next water change, I am going to swap the 5gal reservoir for a 20gal tote I originally intended to use - hopefully the water temp will go down, and that may also reduce the temp in the tent?
-I'm also planning on covering the black lids with a white plate to further reduce water temps. Worth it?
-I'm considering just dimming the light down to 60-80% and just lowering it. I just haven't found the sweet spot yet, as it's a new light. I stressed the seedlings out a bit with it at first.
-My last resort is to either add an immersion or external water chiller.

Is there anything else you would suggest to help reduce the heat?
Click to expand...
Easy, turn down the light. You can't force them to grow, you can only provide good conditions. 80% is still 44 watts/square foot in veg when most recommend 30-40 in flower. I'm flowering at 26w/ft on a 16/8 schedule with autos.

82F is fine, but I think it's still too much light. What's the distance above the canopy? Do the girls get droopy before the end of the day?
 
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bluegill

Well-Known Member
Right now the light is 25" above. No drooping at all. The plants have been thriving apart from a little heat stress on the one. I definitely want to run 50w/ft when I get to flower so I probably will throw in the 440 CFM in there. Indica likes it windy anyway right? :D
 
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bluegill

Well-Known Member
Still throwing ideas at it :D I decided to take my 6 inch intake fan (which overpowers the 4" exhaust fan) and use it as a supplemental exhaust until I get to flower. It's angled toward the heat sinks on the light. That's further reduced the ambient temp to 78F. The best part, however is that the LED is no longer hot with a total 430 CFM exhaust output. It's actually quite cool to the touch now. I can probably run it hotter with a negligible difference. That means I could rely on my Ventech 6" exhaust exclusively.

If I was giving someone advice on sizing an exhaust fan for a tent - I would say for a 2x4x5 ft, go with 6" minimum with an output of at least 300 CFM - adjustable as needed. The 4" @ 190 CFM is not adequate with decent lighting. You can get away with less if you intend on only vegging in the tent. I have used a couple different LEDs, both actively and passively cooled. Just my experience. That said, I absolutely have an overpowered light for my tent - it could comfortable do a tent double the size. Air flow is absolutely crucial - do not overlook it.
 
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bluegill

Well-Known Member
Thanks for all the tips guys. I ultimately decided to run the light @ 80% power, lowered it to 20", fan exhaust @ 440 CFM, and the plant are enjoying an ambient temp of 76-78 (higher later in the day for some reason), and consistent 72F in the reso. The secondary exhaust fan is temp controlled and turns off at 72F.

Today I noticed the start of some mag deficiency, so I moved up to aggressive growth for nutes - since my light is so strong. My pH was up to 7.5, so I added some pH down and now it's 6.5.
 
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