How much A/C Do I Need?

[New Holland]

I'm planning a 8Kw grow. How much AC would I need to cool that many lights in a 16x12x8' growroom?. Answers in Kw or Horsepower would be appreciated

 

[Guest]

I'm really just guessing because my grow is 3K in an 8 by 8 by 8 room but I'd say probably an 18000 BTU window unit and I'd have at least 1 9 or 12 BTU portable to be able to move around if needed.I use a 12000 BTU in the window and a 9K portable,its plenty

 

[Joe A. Grower]

I'm planning a 8Kw grow. How much AC would I need to cool that many lights in a 16x12x8' growroom?. Answers in Kw or Horsepower would be appreciated

Well, if you want the answer in KW, you already have it. You can figure that pretty much every Watt consumed by your lighting will be converted to heat. So if you have a perfectly insulated room (no heat from outside) with 8,000 W of light, then you need roughly 8,000 W of cooling power to remove that heat. Of course no room has 100% perfect insulation, so you have to add in more AC for the heat that is coming in from outside the room.

How much AC you need for the outside heat depends on a whole lot of things, including the outside temperature, the insulation value of your house, and whether the sun shines directly on the wall of the room. That being said, a room of your size could probably be cooled in the summer by as little as 750 W of cooling power. The heat from the lights will absolutely dominate the AC.

Now of course I'm assuming you are not using air-cooled lighting fixtures. If you are cooling your lights, you will need less AC. How much less is almost impossible to calculate without a whole lot of info and some pretty advanced heat transfer calculations.

For those of you living in North America and wondering what all this "Watt stuff" has to do with air conditioning, multiply the Watts above by 3.414 to get BTU/hr, which is what we use here to rate AC. A "ton" of AC is just 12,000 BTU/hr. So 8,000 W of AC is 27,312 BTU/hr, or 2.28 tons.

 

[MTF-Sandman]

Actually a 1k light puts off about 3500 btus of heat...so using simple math, you're looking at 28kbtu plus ~20btu's per square foot of floor space (with 8' ceiling) which brings you to a grand total of 31840btus. Air cooling the lights will take off some of the required cooling as well as your climate (if it's cooler than the desired grow room temp) as well as remoting the ballast or several other heat saving methods.

So a 32kbtu (or a 2.5-3 ton) should take care of you...

 

[Joe A. Grower]

So a 32kbtu (or a 2.5-3 ton) should take care of you...

Which is 9,370 W -- not too far from the 8,750 W I mentioned above.

He's Aussie, Sandman. Ya gotta talk to him in French Units, not God's Units.
:wink:

Frankly, the more AC, the better, IMO. The more the compressor runs, the more humidity the AC is going to pull out of the air. I've always had a bigger problem keeping humidity UP during veg than I've had keeping it DOWN during the last few months of flower. Big AC units run less and don't screw with the RH as much.

 

[Guest]

as it was mentioned earlier 1000w bulbs put out about 3500 Btu of heat so the rule of thumb with ac's is about 4000 btu of cooling power per light Dependinng On Your Environment. Some places are very hot outside and you'll need more btu per 1000w bulb. Another factor that you should take into consideration is whether or not the walls are insulated. Insulated walls are much better for keeping temps stable due to the fact that the outside heat and cold wont affect the room too much.

If you cant cool you room with 4000 btu per 1000 try air cooling the lights with a strong inline fan or 2. Also remember if you're growing ina sealed room with AC's, co2 injections are not only highly recommended but will more than likely be needed for your plants survival. Good luck

 

[New Holland]

Wow, this is some good info fellars. Alot more detailed then I was expecting. I was going down the air cooled light route with miximum ventilation in the room. I worked out that I need 250 litres/sec ventilation for the plants. I was going to try and cool the room with all out ventilation. Something like 1200 litres/sec.

But that brings problems such as noise, and cost. I discovered I can buy a 7Kw A/C unit for $800. Its gonna cost me $1600 dollors for 2x600 Litre/fans and filtres. Now I'll prob buy 1 fan and filter for $800 and 1, possiblly 2 A/C Units.

 

[Guest]

I'm still working on miximum ventilation is dat a little or a lot?

 

[MTF-Sandman]

Which is 9,370 W -- not too far from the 8,750 W I mentioned above.

Maybe I'm missing something here, but don't most ACs have about a 10.0 EER (on average)...That would mean a 32000btu AC would use ~3200w of juice right?

 

[Buzzsmirk!]

Maybe I'm missing something here, but don't most ACs have about a 10.0 EER (on average)...That would mean a 32000btu AC would use ~3200w of juice right?

10 seer is tyhe new minimum standard for window A/C, though at HD ive seen some offerings in the high 9s

most split units have to be like 12 or maybe 13 or higher to be offerd on the market today. ( the govt fucks with the A/C industry almost yearly w/ new standards and such)

i run 6-400 watt HPs in bloom , i cool my lights, my ballasts are "remoted" i run a single burner propane CO2 unit. i run a one ton or 12K BTU unit and it seems to be just enough to handle it all. if i did it over i would have gone with the 18K BTU or 1an1/2 ton unit.

the seer rating on the unit has to do with efficiency not BTU performance in the context we are usin it in.

BUZZ!

 

[New Holland]

Oh hardy ha ha Skel,.....everyone wants to be a comedian! It's not easy typing on a laptop sitting on your lap while your flying a Boeing 737!

 

[Guest]

Id say 4K btu per 1K fixture is about perfect.I have a 12K window unit and it handles 3 1K vertizontals well.I used to have a 9K portable but realized even though it was a dual hose,it still was blowing my co2 up into the attic somehow.

 

[Joe A. Grower]

Maybe I'm missing something here, but don't most ACs have about a 10.0 EER (on average)...That would mean a 32000btu AC would use ~3200w of juice right?

Probably, but New Holland is still talking about cooling capacity not power draw. In Europe and Australia (and most of the rest of the civilized universe) they don't use BTU's/hr like we do. They use Watts (or kilowatts). Since a BTU is a measure of energy, a BTU/hr is a measure of power -- just like Watts. If you go into a store oversees looking for a 32,000 BTU/hr air conditioner, you won't find it. You might find a 9,373 W air conditioner, which would be exactly the same thing.

The power draw for either air conditioner would probably be around 3,200 W, just as you pointed out, and would probably be labled in Watts both here and abroad. However, you could just as easily express the power draw in BTU's/hr or horsepower or any other unit of power you like. Its all the same thing.

In North America we have a weird, mixed up system where we use US Customary Units for cooling capacity, and SI units for power draw. Overseas they are alot more consistent and just use SI for everything.

 

[Joe A. Grower]

Wow, this is some good info fellars. Alot more detailed then I was expecting. I was going down the air cooled light route with miximum ventilation in the room. I worked out that I need 250 litres/sec ventilation for the plants. I was going to try and cool the room with all out ventilation. Something like 1200 litres/sec.

But that brings problems such as noise, and cost. I discovered I can buy a 7Kw A/C unit for $800. Its gonna cost me $1600 dollors for 2x600 Litre/fans and filtres. Now I'll prob buy 1 fan and filter for $800 and 1, possiblly 2 A/C Units.

My personal opinion is that it is always best to go with an air-conditioned sealed room if at all possible. Venting is a good cheap way to keep temp, CO2 and humidity in check, but as you pointed out, it has its downsides. Venting means noise and possible smell leaks. It is also hard to get maximal benefit from CO2 enrichment if you rely on venting for temp control.

If nobody is going to be checking up on your power consumption, I'd say screw the fans and filters and air-cooled lights. Buy those two 7Kw AC units (that's 47,796 BTU/hrs total cooling capacity for all you metrically challenged North Americans) and a CO2 enrichment system. Seal that room up tighter than a drum and never vent. Just AC and enrich the CO2. If you need to rais humidity, buy a greenhouse fogger. If you need to lower it, get a dehumidifier.

Sealed rooms are just plain more secure. They can also be more productive because you can keep your CO2 levels consistently high.

 

[MTF-Sandman]

Probably, but New Holland is still talking about cooling capacity not power draw. In Europe and Australia (and most of the rest of the civilized universe) they don't use BTU's/hr like we do. They use Watts (or kilowatts). Since a BTU is a measure of energy, a BTU/hr is a measure of power -- just like Watts. If you go into a store oversees looking for a 32,000 BTU/hr air conditioner, you won't find it. You might find a 9,373 W air conditioner, which would be exactly the same thing.

The power draw for either air conditioner would probably be around 3,200 W, just as you pointed out, and would probably be labled in Watts both here and abroad. However, you could just as easily express the power draw in BTU's/hr or horsepower or any other unit of power you like. Its all the same thing.

In North America we have a weird, mixed up system where we use US Customary Units for cooling capacity, and SI units for power draw. Overseas they are alot more consistent and just use SI for everything.

K...that makes sense now. Thanks for clearing that up