How Strong Of A Air Conditioner Would I Need For 84 Gavita's?

Rabbi · May 25, 2017

I recently bought a place with a 1500 sqft Quonset and was just wondering how big of a AC unit would I need to cool 64 1000watt Gavita's? Peak of the ceiling is probably around 18' or so but obviously that would just be the center of the Quonset.

Up until now I've only done the regular single ended bulbs with air cooled hoods but thinking about making the move to the double ended bulbs and sealed facility, however I've been hesitant due to heat issues that come with making that switch.

I also will be running co2 burners and dehumidifiers as well.

Thx for the help guys, this is my go to place for tough questions like this.

packerfan79 · May 25, 2017

I am thinking a buttload. Lol I think it's 4k per light plus additional for dehumidifier, and burners. There is a thread with a chart here in the equipment section I believe

brown_thumb · May 25, 2017

I can't help with A/C sizing but I have a question: Is the building wired for that much current?

PdxFarms · May 25, 2017

Is it insulated?
I would guess 7+ tons of cooling. Depends on what other means of heat management you'll be using.

brown_thumb · May 25, 2017

^^^ I'll bet it's much more than that, especially if the building is in full sun. If it was a storage building then it may not be insulted at all. If that's the case then I'd assume it's very impractical to attempt until excellent insulation is added.

vancityj · May 25, 2017

I think you'd cover about 12-14 (12 in summer?) X 1000W with a 5-ton unit, so maybe 25 X 1000W on at once, with a combined 10 ton (5-ton unit X2) AC running, burner and dehumidifier/s included. If you're on municipal non-metered water, maybe you can utilize swamp coolers in the off-cycle on both sides to avoid much additional power draw, otherwise you could maybe make due with a 3-ton unit on each side for off-time. I assume you'd be running only half the lamps at a time, and then flipping to a second area every twelve hours. 24 X 1000W @ 4.3-4.5-amps (@240) = 108-amps approximately. I think each 5-ton AC might draw about 45-48 amps on a 60-amp breaker (X2). Do you have 2, 200-amp circuits handy? I'd recommend Quest dehumidifiers for power efficiency. I bought the Dual 105 model and at under 5 amps (@120) it removes upwards of 3X what an off-the-shelf dehumidifier from Home Depot might truly realize operating at 7-9 amps.
If you were to run 64 1000's at once, I think about a combined 25 ton of cooling would suffice. Can you even cram 64 lights in there with any degree of elbow room/sanity? Maybe a 24-light flop would be adequate as each light would likely cover up to about 25-sqft (48 X 25-sqft = 1200-sqft, plus work/veg/dry/etc area). As has been mentioned, some spray insulation would likely be required if there isn't any.

Rabbi · May 25, 2017

brown_thumb said:
I can't help with A/C sizing but I have a question: Is the building wired for that much current?

In the process of having 800amp single phase, plus 3 phase installed.

PdxFarms said:
Is it insulated?
I would guess 7+ tons of cooling. Depends on what other means of heat management you'll be using.

Yes, it is in the process of being fully insulated. Gonna need way more than 7tons though, I'm pretty sure.

vancityj said:
I think you'd cover about 12-14 (12 in summer?) X 1000W with a 5-ton unit, so maybe 25 X 1000W on at once, with a combined 10 ton (5-ton unit X2) AC running, burner and dehumidifier/s included. If you're on municipal non-metered water, maybe you can utilize swamp coolers in the off-cycle on both sides to avoid much additional power draw, otherwise you could maybe make due with a 3-ton unit on each side for off-time. I assume you'd be running only half the lamps at a time, and then flipping to a second area every twelve hours. 24 X 1000W @ 4.3-4.5-amps (@240) = 108-amps approximately. I think each 5-ton AC might draw about 45-48 amps on a 60-amp breaker (X2). Do you have 2, 200-amp circuits handy? I'd recommend Quest dehumidifiers for power efficiency. I bought the Dual 105 model and at under 5 amps (@120) it removes upwards of 3X what an off-the-shelf dehumidifier from Home Depot might truly realize operating at 7-9 amps.
If you were to run 64 1000's at once, I think about a combined 25 ton of cooling would suffice. Can you even cram 64 lights in there with any degree of elbow room/sanity? Maybe a 24-light flop would be adequate as each light would likely cover up to about 25-sqft (48 X 25-sqft = 1200-sqft, plus work/veg/dry/etc area). As has been mentioned, some spray insulation would likely be required if there isn't any.

25 tons sounds a little more to what I was thinking but can't help but wondering if maybe more? Having too much cooling is the last thing I'm worried about but not enough is always a problem.

Maybe 30 tons to be safe? Maybe even more perhaps?

Yes I think I can fit in the all 84 but nice to hear from someone who knows better to ask that question. We're building a second level just for veg(so only a bit of the building)so it will be 20 veg on top and 64 flower on bottom. Obviously will be a full house but I think do-able. We're also building a work station/entrance/trim/dry spot which is gonna take up some space as well. Not sure how much yet though. Do you think that's not enough as far as needed space? Close, I know, but was hoping to make it work.

I really don't wanna do the flip cycle so looking for more of a straight up answer without the flip.

MJINC · May 25, 2017

If you asked Gavita they would recommend about 256000 BTU's(about 22 tons) but they're based in Europe and it tends to have lower temps. I would be looking at around 320,000 to 380,000 BTU's(26 to 32 tons). You would also want to divide that up into multiple units in case of a breakdown or some other mishap

queequeg152 · May 25, 2017

86kw * 3.412btuh/kwh = 293.5kbtuh/12k tonn/kbtuh = 24.5 tonns internal heat gain.

24.5tons + other equipment heat gain + external heat gain = total heat gain.

if you have the capital to invest in this equipment you most certainly can afford a manual J. they cost something like 500 bucks.
many equipment installers will do them for free if you are buying their services.

make sure they actually do the manual J though... not bullshit with google maps calculating the perimeter of the building etc. thats a worthless manual J.

they need to actually measure the building, measure the insulation, verify insulation uniformity and verify roofing and siding qualities at a bare minimum.

queequeg152 · May 25, 2017

oh and btw, you need to go off of the nameplate ampacity. dont just assume the balallast is drawing a perfect 1,000w. it might be drawing 1050 or maby even 1100 watts. use the highest figure for conservative calcualtion.

also at 25 tonns you might consider staging your equipment based on the bare minimum heat gain at design loads( how ever you set up your lights to run... 12/12 or flip flopping or what ever).

what i mean is ... say you live in virginia or something... and you have roughly equal cooling and heating days.

stage 1 would be the maximum heat gain based on the average cool weather heat gain.

stage 2 would be both units running and would = the maximum based on your 1% maximum heat gain during hot weather.

this would mean that stage 1 would be running like 75... maby 90% of the time, and your second stage would be running probably 50% of the time mostly during your hot season.

of coarse this would all depend on how good your insulation is... the better the insulation the less variability you have in the external heat gain... so the less need for staging equipment.

keep in mind your external heat gain will be SMALL with respect to your internal heat gain... so the second stage would be very small compared to the first.

Lester Beans · May 25, 2017

Damn, solid info there, learned a lot! Thank for taking the time to post!

Speed of green · May 25, 2017

Queequeg152 i would consider to be the guru on this subject, OP would be wise to take his advice.

Calculating the internal heat load from the lamps and other fixtures is the easy part, The Quonset steel building with unknown insulation and unknown geographical location leave this question open ended and difficult to answer accurately.

FWIW i had planned a similar size operation for a warehouse in LA, it had a flat roof with poor insulation in a hot climate, building rooms inside the warehouse cuts the external heat gain wayyyy down, I had originally planned for 35 tons in the form of 5 ton residential units.

good luck!

Rabbi · May 25, 2017

Interesting stuff, thx guys.

I don't plan on filling the place up immediately with all 84 lights, that was sort of the end goal. Plan to start off with half or quarter(depending on the license situation) of that and work my way up. Maybe I'll just start off with 2 10 ton units and add more as needed.

Rabbi · May 25, 2017

I actually already have a 5 ton split unit. Maybe the split unit for veg and a 10 ton for the remaining. That would just be for half of 84 lights(42 lights obviously lol).

That should work for 42 lights shouldn't it? Start off with 42 lights and work my way up 84 when needed. It would be the 5 ton split unit cooling off 10 veg lights and a 10 ton unit cooling off 32 lights in flower.

queequeg152 · May 25, 2017

you are asking all the wrong questions, and in the wrong order man.

just layout your proposed final building FIRST, then come up with a phase in plan... then do the manual J in block load for each phased room SECOND.

its actually alot easier to do a manual J for new construction than it is for old construction. just make sure you insulate properly... if you call for r15 walls in your load calc, then do a shit job insulating with r15 batts you will not arrive at your calculated external heat gain.

you probably have 3 phase service so you probably wont be able to use the 5 ton unit you have... unless you want to swap in a new compressor and some electronics ( assuming its not a minisplit).

just do the manual J first. i promise you its not hard to do. there is even software out now that will walk you through it.

if you wan to do the spread sheet, you need the book.

https://www.amazon.com/Residential-...coding=UTF8&psc=1&refRID=26NJYYC94HT3RTCTYRB2

the spread sheet is free, and available here.

http://www.acca.org/communities/com...umentKey=0bc73e80-6c3c-43cb-bdb2-43316a380fa4

you need the book to explain the spread sheet and to look up tables and correction factors for partition walls, exterior walls, slabs etc.

Rabbi · May 25, 2017

queequeg152 said:
you are asking all the wrong questions, and in the wrong order man.

just layout your proposed final building FIRST, then come up with a phase in plan... then do the manual J in block load for each phased room SECOND.

its actually alot easier to do a manual J for new construction than it is for old construction. just make sure you insulate properly... if you call for r15 walls in your load calc, then do a shit job insulating with r15 batts you will not arrive at your calculated external heat gain.

you probably have 3 phase service so you probably wont be able to use the 5 ton unit you have... unless you want to swap in a new compressor and some electronics ( assuming its not a minisplit).

just do the manual J first. i promise you its not hard to do. there is even software out now that will walk you through it.

if you wan to do the spread sheet, you need the book.

https://www.amazon.com/Residential-...coding=UTF8&psc=1&refRID=26NJYYC94HT3RTCTYRB2

the spread sheet is free, and available here.

http://www.acca.org/communities/com...umentKey=0bc73e80-6c3c-43cb-bdb2-43316a380fa4

you need the book to explain the spread sheet and to look up tables and correction factors for partition walls, exterior walls, slabs etc.

Thx again for your help, I really appreciate it.

It's for sure going to have 800amp single phase. We're discussing with the power company right now about the 3 phase so that's really just a solid maybe atm lol.

The 5ton ac that I currently have is indeed a minisplit, single phase.

I'll check into the manual J you suggested, thx.

stoney917 · May 26, 2017

Split into 2 rooms u could get by with half the tonnage... Also being up north in Canada u can pull air from outside most of the year and reduce u load... I assume u got a nice budget n there's many ways to skin a cat ... They scream every time... Id check out Dj thread on coco trees he was running multiple 24 lighters with minimal ac. vpd perfected n it should work for your local.... Everything will be fixated on ya design, with some creative air movement u could possibly pull it off with minimal a.c. like 7.5 if u split the room up n bpd style but Id have at least 2 on hand for summer or you could need 30plus all depending on plans n ingenuity...

Rabbi · May 26, 2017

Not looking to make rooms(other than veg) and do a flip. Yes I know I would be able to use half the load and a way smaller a/c unit but would rather get a bigger one and not do the flip flop. It's just way easier on my schedule that way.

Although I do live in Canada I don't really want to be pulling in outside air, hoping to keep things sealed. This quonset is located on a farm and I could only imagine all the bugs I'd pulling in along with the fresh air. Plus it dilutes the co2 levels.

Maybe perhaps I should give up on the Gavitas and just get regular single ended ones and use air cooled hoods. So many tough decisions when putting together a set up like this lol.

packerfan79 · May 26, 2017

Rabbi said:
Not looking to make rooms(other than veg) and do a flip. Yes I know I would be able to use a way smaller a/c unit but would rather get a bigger one and not do the flip flop. It's just way easier on my schedule that way.

Although I do live in Canada I don't really want to be pulling in outside air, hoping to keep things sealed. This quonset is located on a farm and I could only imagine all the bugs I'd pulling in along with the fresh air. Plus it dilutes the co2 levels.

Maybe perhaps I should give up on the Gavitas and just get regular single ended ones and use air cooled hoods. So many tough decisions when putting together a set up like this lol.

The new 945 cmh would be a good choice, less heat and a better spectrum

Rabbi · May 29, 2017

Fuck it, think I'm just going to try starting off with the 32 gavitas for flower, 10 regular single ended mh with air cooled hoods for veg , get a 10 ton ac(or two 5's) for the flower/gavitas and use my 5 ton mini split for the veg. I'll just make adjustments as needed, this isn't my first rodeo lol...although it is my biggest

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How Strong Of A Air Conditioner Would I Need For 84 Gavita's?

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