COB heat

Gquebed · Dec 26, 2018

So Im going to hydro. I plan to put 1300w of COB light (cree 3590s) over two 4x4 flood tables, in a room that is 11X11, 7.5' high. So i did a test... just fired up the lights to see how fast the entire room (completely empty right now) would heat up. In 2.5 hours it hit 85f.

I was hoping to cool the room with a 6" 440 CFM fan, filter and a temp switch (perfectly straight shot out a window, total run about 5').

Think thatll be enough CFM?
11x11x7.5 = 900 cu ft. / (440× 80%) = full room air change in 2.5 mins???

NanoGadget · Dec 26, 2018

Should be fine. Honestly, 85 isn't even that far outside optimal for LED. Without the IR to heat up the surface of the leaves at canopy level like you would get with HPS, I have found that my plants like a slightly higher ambient temperature than they did when i ran HPS. 80 to 84 seems to be my sweet spot under LED.

coreywebster · Dec 26, 2018

Should see about a 6-7 degree rise from ambient with that cfm I think. So depends on what your ambient is.

Don't forget its not a test of much just switching on 1300w in a non vented room.

Boatguy · Dec 26, 2018

I have a 400 cfm fan, 6" duct with a 24x8 filter in my 2x2.5' tent.
With cobs at 200w it runs for about 3 min on, 15 min off,fan on low. I keep temps around 75.

Gquebed · Dec 26, 2018

NanoGadget said:
Should be fine. Honestly, 85 isn't even that far outside optimal for LED. Without the IR to heat up the surface of the leaves at canopy level like you would get with HPS, I have found that my plants like a slightly higher ambient temperature than they did when i ran HPS. 80 to 84 seems to be my sweet spot under LED.

Is that soil or hydro?
Im just concerned that higher ambient temps will raise the res temps enough to be troublesome...

Gquebed · Dec 26, 2018

coreywebster said:
Should see about a 6-7 degree rise from ambient with that cfm I think. So depends on what your ambient is.

Don't forget its not a test of much just switching on 1300w in a non vented room.

True. I just wanted to guage how warm it would get and how fast so i could guess better at what might be needed for cooling. I was surprised at how fast it went from 65f (which is the normal ambient in that room) to 85f.

NanoGadget · Dec 26, 2018

If your ambient is 65 you will probably looking at 72 to 75 with the exhaust you mentioned above. Good for your reservoir, possibly not optimal for your canopy temps. But better a lower than optimal canopy temp than catastrophic root rot. Do you not have a cooler for your res?

Gquebed · Dec 26, 2018

NanoGadget said:
If your ambient is 65 you will probably looking at 72 to 75 with the exhaust you mentioned above. Good for your reservoir, possibly not optimal for your canopy temps. But better a lower than optimal canopy temp than catastrophic root rot. Do you not have a cooler for your res?

Im just building out the room now so no. And im hoping to avoid it if possible. Lol
But... if i have no choice then i will...

NanoGadget · Dec 26, 2018

Overall i think the setup you have in the works will serve you well. You should have the flexibility to tweak the environment until you find the happy medium. I'd do everything you can to keep the lights on temps above 75 though, I've noticed a measurable loss in growth rates under my LEDs when i let the temps dip below that.

Madmungo · Dec 27, 2018

NanoGadget said:
Should be fine. Honestly, 85 isn't even that far outside optimal for LED. Without the IR to heat up the surface of the leaves at canopy level like you would get with HPS, I have found that my plants like a slightly higher ambient temperature than they did when i ran HPS. 80 to 84 seems to be my sweet spot under LED.

It’s not IR from the HPS, it’s radiant heat that warms the surface of the plants, 85 is optipmum for led grown weed.

Old Thcool · Dec 27, 2018

Gquebed said:
Im just building out the room now so no. And im hoping to avoid it if possible. Lol
But... if i have no choice then i will...

You can have the Rez outside the room. Not a big deal.

Old Thcool · Dec 27, 2018

Madmungo said:
It’s not IR from the HPS, it’s radiant heat that warms the surface of the plants, 85 is optipmum for led grown weed.

Much beyond that and they clamp down hard ! Leaves will droop and growth will stop so you mustn’t let it get into the 90s!

NanoGadget · Dec 27, 2018

Madmungo said:
It’s not IR from the HPS, it’s radiant heat that warms the surface of the plants, 85 is optipmum for led grown weed.

I'm not sure you know what IR is...

"Light sources produce infra-red radiation, perceived as heat. Its amount depends on the type of lamp used. Any object under direct light is therefore subject to constant thermal stress, which can change its properties. In food stores, clothes shops, pharmaceutical labs the production of IR radiation is usually not desirable.

A classic source of IR radiation is incandescent lamp, a notably inefficient light source where only 5 percent of energy is turned into light. High pressure sodium lamps, although more efficient, still turn as much as 70 percent of energy into heat, the rest is visible light."

Madmungo · Dec 27, 2018

NanoGadget said:
I'm not sure you know what IR is...

"Light sources produce infra-red radiation, perceived as heat. Its amount depends on the type of lamp used. Any object under direct light is therefore subject to constant thermal stress, which can change its properties. In food stores, clothes shops, pharmaceutical labs the production of IR radiation is usually not desirable.

A classic source of IR radiation is incandescent lamp, a notably inefficient light source where only 5 percent of energy is turned into light. High pressure sodium lamps, although more efficient, still turn as much as 70 percent of energy into heat, the rest is visible light."

I know what it is, the reason LEDs need a warmer grow room temp is due to radiant heat (or lack of)
Knowing more than that is not a requirement for growing big healthy high yielding cannabis plants,
Some people seem to forget what we’re here for.

Gquebed · Dec 27, 2018

NanoGadget said:
Overall i think the setup you have in the works will serve you well. You should have the flexibility to tweak the environment until you find the happy medium. I'd do everything you can to keep the lights on temps above 75 though, I've noticed a measurable loss in growth rates under my LEDs when i let the temps dip below that.

Thanks
Say...what leds are you running?

Gquebed · Dec 27, 2018

Old Thcool said:
You can have the Rez outside the room. Not a big deal.

I did think of that. But it would be a long run...lol

Randomblame · Dec 27, 2018

Temps will also go down if you have a few plants inside cuz the light isn't all reflected and converted into heat anymore. Plants use up to 10% of the light and als take up some of the heat.
Expect 2 or 3° less at least...
You really don't need AC I would rather invest in a small humidifier because air tends to dry out under strong LED light and at 80-85° you need at least 60-70% RH to keep your plants happy. Its not as easy to keep the VPD in a healthy range with LED light. A too high VPD would cause serious issues with Ca and Mg uptake and you are forced to lower the nutrient strength. For this reason you'll find CalMag in almost every growers nutrient box.

NanoGadget · Dec 27, 2018

Gquebed said:
Thanks
Say...what leds are you running?

Currently i am running HLG Quantum Boards. Efficiency is as good or better than COB and it works better for me now as i have more height restrictions than i used to. I'll eventually get more space and at that point I'll be putting the cobs back into the mix as I've seen stellar results from QB/COB combos.

OneHitDone · Dec 27, 2018

Randomblame said:
.
You really don't need AC I would rather invest in a small humidifier because air tends to dry out under strong LED light and at 80-85° you need at least 60-70% RH to keep your plants happy..

What say you about the weed grown outdoors in the "cannabis producing" areas of the world - Say the hills of Northern California? Is that not the exact opposite of the climate you are describing?

Gquebed · Dec 27, 2018

Randomblame said:
Temps will also go down if you have a few plants inside cuz the light isn't all reflected and converted into heat anymore. Plants use up to 10% of the light and als take up some of the heat.
Expect 2 or 3° less at least...
You really don't need AC I would rather invest in a small humidifier because air tends to dry out under strong LED light and at 80-85° you need at least 60-70% RH to keep your plants happy. Its not as easy to keep the VPD in a healthy range with LED light. A too high VPD would cause serious issues with Ca and Mg uptake and you are forced to lower the nutrient strength. For this reason you'll find CalMag in almost every growers nutrient box.

A/C is exactly what im trying to avoid....lol

I have a vague understanding of VPD... so when you say too hugh VPD youre meaning not enough humidity for light/heat, which would mean too low VPD would be the opposite?

Also... wouldnt 70ish RH be a little high in bloom, risking mold?

COB heat

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