Running 5x600HPS open hood need a/c help

Mrkline006 · Feb 25, 2019

I know it’s close to 4000btu per 1000watts.. I read the a/c sticky and I’ll be pretty close to the thresh hold 5x600hps and 3x viparaspectra led 1200 (520 real draw). I have 2x12000btu window air conditioners and my room will be oversized (for possible later expansions) 24x12ftx8ft ceiling. With living in the Midwest and getting hot humid Summers can I possibly make this work?

I have 4 of the 5 are open winged hoods. Should I swap them out for air cooled? Can I possibly make this work still without swapping lights? I’m running 24 plants. Any advice be awesome. Once walls are up ima gonna run the room for a few days with no plants but won’t get real numbers till summer hits. Sealed room with co2 and fully Insulated.

Ibechillin · Feb 25, 2019

Ill try and help out, Im estimating with kansas city area (~90F degree summers and 90% humidity):

Its 3.41btu per watt of power used.

3000w HPS + 1560w LED = 4650 watts total x 3.41btu per watt = 15549.6btu roughly heat from all lights while running.

Cooling for a room is typically estimated based on the floor space sq ft when using standard 8 ft ceilings. Kansas city area recommends around ~18btu per sq ft from what I found searching and running the numbers.

24x12 room = 288 sq ft x 18btu per sq ft = 5184btu roughly needed with no lights on recommended.

15549.6btu cooling needed while lights on + 5184btu needed to cool room = 20733.6btu roughly cooling needed while lights on.

24000btu from your 2 12k window ac ÷ 20733btu needed while lights on = 1.15754138210441 or 15.75% more cooling than you would need while lights are on in hot and humid Kansas city area based on what I could find.

If your somewhere that deals with high humidity normally many of the AC articles I found advise against using too large or too much AC for a space as it is less efficient at dehumidifying the area by short cycling constantly, I think your Ac setup should be capable of the task.

Running Co2 you will want to maintain closer to 85f room temperatures as well to maximize it benefits helping even further with AC load.

Mrkline006 · Feb 25, 2019

Thanks man... I kept thinking it’s possible to do but read and seen a few things that made me kinda think twice... as a safe measure I may swap out open hoods for air cooled and pull glass off till or if needed to lower temps. Grow will be done by July so shouldn’t be crazy heat, and if I choose just skip hot muggy August lol

UnHypothetical · Feb 26, 2019

I'm a former overgrower, and I'm like 14 years removed from actual growing... I could be out of touch on this.

I've always just tried to avoid using full lighting from late May to mid September. Summer is for outdoor growing. Fighting heat, humidity, PM and pests every summer got real old, real quick.

dank.frank · Feb 26, 2019

32,000 BTU ductless for 3-4k if your summer temps ever get above 90 - unless you are in a basement, which can lower that demand significantly.

It'll never struggle to keep up and achieve a better efficiency rating and better cooling as a result. You don't want one of your key components to be "just enough". A bit of over kill is always nice in regards to A/C. Something that can still cycle on and off without running 24/7, like an A/C is supposed to do.

I've run 24 btu, 2 - 12k window bangers, with inline ducting on sealed hoods. 6k and temps struggled to stay below 88 with lights on. Had to drop to 4k to make it doable. This was in the northern midwest, during winter. Trying to bring in outside air for the hoods created a condensation issue like you wouldn't believe.

Found an OLD pic:

dank.Frank

Mrkline006 · Feb 26, 2019

We’re those 1 ks? I’ll be changing out the open hoods for vented so I can atleast deal with some heat. I’ll leave the glass out and if it starts getting hot, throw glass in and rock a closed air exhaust for 4 of the 600s.

dank.frank · Feb 26, 2019

Those were 1k. If you want another example, look at Phillthy's old thread.

He ran 4k turned down to 4 @ 750. I don't remember exact room specs, but he ran 32k btu. HIS example is what I learned from when it came to the statements I made above, ESPECIALLY, after the issues I ran into in the above example.

dank.Frank

chronic82 · Feb 26, 2019

What if you ran your lights at nighttime when it’s cooler outside? I doubt to many places in the world have 90 degree nights. Then when it’s 90+ during the day the only thing in your room running would be the ac and maybe a dehumidifier

dank.frank · Feb 26, 2019

If in the midwest, it's very likely to have different utility rates for off peak hours, which means, by default, growers run more at night already.

dank.Frank

UnHypothetical · Feb 26, 2019

I have a bunch of old air cooled reflectors, cool tubes and the like. I wouldn't bother with air cooled lights. If I was designing a room, I definitely wouldn't be planning for them.

Some quick math. Let's talk just about the lights, and the energy needed to cool them.

1000 watts is 3415.
A good air conditioner has a real EER of 10.
You need ~375 CFMs of unencumbered straight duct run to remove half the heat.
You lose right around 10% of light to the glass of air cooling. More if it gets dusty/smudgy, which will happen.
A 400 CFM fan uses 100 watts.

Let's say we've got a 10k light garden, and we want the same light output with both air cooled and air conditioned.

10k x 3415= 34,150 BTUs / 10 EER = 3415 A/C Watts + 10,0000= 13415 Watts.

Now, due to the 10% light loss, this same garden, aircooled is going to require an 11th bulb to get the same amount of light on the canopy.

11k x 3415 = 37,565 BTUs. Half that heat to be evacuated needs 11 400 watt fans properly ducted and insulated on nice short straight runs. 1100 watts of fans. Leaves you with 18,782 BTUs of heat... which is still 1878 Watts to air condition. 11k+1.1K+1878= 13,978 watts.

You can get by with a little less fan wattage, for sure, but this illustrates why air cooling might not be something you would want to plan on, when designing a room.

Mrkline006 · Feb 27, 2019

chronic82 said:
What if you ran your lights at nighttime when it’s cooler outside? I doubt to many places in the world have 90 degree nights. Then when it’s 90+ during the day the only thing in your room running would be the ac and maybe a dehumidifier

Yeah I 100% plan to have lights on only at night. I may be over compensating having 2 x 12ks... but I’d rather have them both and only need 1 than needing 2 and only having 1. My main issue is the summer heat in the garage even with my sealed and insulted grow room. Maybe I should have a inline fan in wall encase lights off period gets too hot to help remove some heat while running the a/c don’t want room to get overly humid either. Read with using co2 when lights go off room humidity or co2 rises insanely ( can’t remember which off top of my head) so to have an extractor fan to run for 15min to help I wonder would be okay?

Ibechillin · Feb 27, 2019

After lights off plants continue transpiring, even when not running co2. Its good to have an exhaust fan/dehumidifier to mitigate the issue. Stomata are mostly closed at night so co2 isnt really needed in abundance.

Asslover · Feb 28, 2019

I live in Florida and run 4x1k in uncooled Adjust-A-wings. The room is within a garage, and it’s 10 x 10. I run my lights during the day. For cooling I use a 30k btu Mitsubishi
mini split AC. I have no problem keeping temps where I set them, which is 80. At night the temps go down to 75. During the day, the AC keeps the humidity in check, during lights off I have 2 70pt dehumidifiers set to 50%.
I’m sure I’m forgetting some details but you get the idea :biggrin:

Edit-The room is fully sealed, no air in or out. Co2 is supplemented with co2 gas.

UnHypothetical · Feb 28, 2019

Ibechillin said:
After lights off plants release all the excess moisture they havent used, even when not running co2. Its good to have an exhaust fan to mitigate the issue. Stomata are mostly closed at night so co2 isnt really needed in abundance.

CO2 is indeed functionless at lights out, but I think the drop in temperature of lights off is what generally causes RH to spike, rather than the plants spitting it out.

https://www.lenntech.com/calculators/humidity/relative-humidity.htm

28*C at 50% RH is 12.04g of water / kg of air.
lights go out, and temp drops to 20.
20*C at 82% RH is 11.99g of water/kg of air.

Ibechillin · Feb 28, 2019

Makes sense, it was something DunHav`nFun said that stuck with me over the years. Could be a combination of both since indoors plants are at their max rate of transpiration when the lights turn off abruptly.

UnHypothetical · Feb 28, 2019

I love watching the videos of plants sped up for the first hour... it's really quite cool.

It really almost looks like they're stretching their leaves(arms) up and out while at the same time they open their stomata to gulp in their first breaths after they wake up. I wouldn't be surprised to find out that plants breathe out deeply just like we do as they fall asleep.

The rules of climate control are like so:
Oversize your AirCon.
Oversize your Dehumidifier.
Oversize your Fans.
Oversize your Pumps.
Oversize your Chillers.
And even have a few of those ultrasonic foggers on standby, just in case.

popta · Feb 28, 2019

Mrkline006 said:
Yeah I 100% plan to have lights on only at night.

Alternatively you could split it in half, use only three 600hps at a time, and get a higher yield with lower peak air conditioning power demand.

Mrkline006 · Feb 28, 2019

UnHypothetical said:
CO2 is indeed functionless at lights out, but I think the drop in temperature of lights off is what generally causes RH to spike, rather than the plants spitting it out.

https://www.lenntech.com/calculators/humidity/relative-humidity.htm

28*C at 50% RH is 12.04g of water / kg of air.
lights go out, and temp drops to 20.
20*C at 82% RH is 11.99g of water/kg of air.

Yeah the lights off was my possible issue. Read when lights off co2 can raise crazy as well as humidity. I’ll have 1x 70 pint dehumidifier and 2x pints so hopefully it’ll help

dank.frank · Feb 28, 2019

I run my dehumidifier in the lung / veg area. Exhaust runs 24/7 and re-circulates. The veg needs the moist air. The dehumidifier helps balance it out, while getting mixed with fresh air and cycled back into the flowering room.

I stack 5 gallon buckets, with a piece of 1/2" PVC run through the center as an overflow. 4.5 gallons fills the top bucket, then reaches the top of the pipe, and beings to drain into the bottom bucket. Dehumidifier has a hose run to the top bucket. This is the best way for me to ensure I never have a shut off or an overflow.

I used to pull about 3.5 gallons a day of water per 1k out of a 5 x 5 with 9 5 gallon plants in mid-flower. Temps 76-78. Humidity 40-45%.

dank.Frank

Running 5x600HPS open hood need a/c help

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