Calculating The Size of a Air Conditioner

[Maripan]

WOW! What a thread, yet I am still a bit confused as to how to calculate my situation, which will be:

Running 8 1000w lights, under Adjust-A-Wing Reflectors (not air cooled), ballasts outside the 20' x 25' room, 2 8" Max Fans for intake and 1 14" Max Fan for exhaust (filtered by a Phresh Filter), as well as a total of six wall mounted fans and six stand fans (all 18"). No CO2 (that is, natural CO2 will come in through the two 8" intakes), and lights will be running at night 7:00pm-7:00am, at a CA elevation of about 3200 ft. Winter nights get down to 40-50 degrees outside, and I am not sure what Summers outside temps will be at night (maybe 60-70 degrees).

I want the AC unit to serve as a dehumidifier while the girls sleep and cool the room when lights are on. The intake and exhaust fans will likely run continually while the girls take in light...

I'm considering the Ideal Air Mini Split units...

How many BTUs do I need for the AC unit?

 

[RomulusUSA]

I have a question folks! Hopefully I can get some pro input.

Last summer, I ran 1000w 12/12 and 500w 24/0. I cooled it with a 5.6k window ac unit that was boxed up. According to the table provided in the first post of this thread, I needed 18.9kBTU last year to maintain temps, but I was able to hold low 80s with 5.6k. I assume this is somewhat due to my climate, etc. Or the table just over calculates, which I know is what about 50% of HVAC contractors do lol.

This summer, I will be running 2kW 12/12 and 1.5kW 18/6. The calculator says I need 28.5kBTU to maintain temps. I am having no luck finding a used 18-24kBTU unit at this time, and don't really want to spend $600ish on a new 24k unit. How do you guys suspect a 12k would do. I am worried it will be undersized and I'll run into issues... Input plz!

 

[Jnugg]

According to the main post,I need an 8000 to 10000 BTU a/c.

Room Dimensions = Roughly 12' x 12' x 8' high ceiling (This does not include the 2' x 8' closet).

Lighting = Bare bulb vertical 400w HPS

Fans and equipment = 1x 4" 170cfm inline centl exhaust fan,1x 12" fan on ground pointed up at bulb.170cfm fan is rated 65w,and the floor fan is rated 45w.

Room occupants = 1

So I did the calculations/math and this is what I came up with...

Room BTU's for 12' x 12' room = 5760 BTU's

Equipment BTU's = 385 BTU's

Lighting BTU's = 1600 BTU's

Room Occupant BTU's = 400 BTU's

Total BTU load = 8145 BTU's

If I include the closet in the room that makes the room roughly 12' x 14' and bumps Room BTU's up from 5760 BTU's to 6720 BTU's bumping the total BTU load from 8145 BTU's to 9105 BTU's.

Here's the thing.I'm growing in a 3' x 3' x 6' SJ DR90II placed in the 12x12 / 12x14 room,so basically using the room as a lung room so to speak,for the tent to draw it's fresh/cool intake from,and exhausting into the attic.

Does that seem about right for what I'm doing?

I'm wanting to bring the temp of the room down to 65°F/68°F as I already know my exhaust fan with bulb on in tent brings the tent to about 10° F aFbove ambient,so that I can keep tent temps during lights on at 75°F-78°F, and lights off temps 65°F/68°F.

So should I shoot for a 8000/9000 BTU unit or a 10000 BTU unit,or since I'm growing in a tent in the room,and the tent having active exhaust/passive intake should I be looking at something slightly smaller?

 

[Jnugg]

According to the main post,I need an 8000 to 10000 BTU a/c.

Room Dimensions = Roughly 12' x 12' x 8' high ceiling (This does not include the 2' x 8' closet).

Lighting = Bare bulb vertical 400w HPS

Fans and equipment = 1x 4" 170cfm inline centl exhaust fan,1x 12" fan on ground pointed up at bulb.170cfm fan is rated 65w,and the floor fan is rated 45w.

Room occupants = 1

So I did the calculations/math and this is what I came up with...

Room BTU's for 12' x 12' room = 5760 BTU's

Equipment BTU's = 385 BTU's

Lighting BTU's = 1600 BTU's

Room Occupant BTU's = 400 BTU's

Total BTU load = 8145 BTU's

If I include the closet in the room that makes the room roughly 12' x 14' and bumps Room BTU's up from 5760 BTU's to 6720 BTU's bumping the total BTU load from 8145 BTU's to 9105 BTU's.

Here's the thing.I'm growing in a 3' x 3' x 6' SJ DR90II placed in the 12x12 / 12x14 room,so basically using the room as a lung room so to speak,for the tent to draw it's fresh/cool intake from,and exhausting into the attic.

Does that seem about right for what I'm doing?

I'm wanting to bring the temp of the room down to 65°F/68°F as I already know my exhaust fan with bulb on in tent brings the tent to about 10° F aFbove ambient,so that I can keep tent temps during lights on at 75°F-78°F, and lights off temps 65°F/68°F.

So should I shoot for a 8000/9000 BTU unit or a 10000 BTU unit,or since I'm growing in a tent in the room,and the tent having active exhaust/passive intake should I be looking at something slightly smaller?

Anyone?

 

[Rolldaddy]

Jnug

A 10000 btu ac should be fine for you. Maybe a bit larger could be better incase you ever want to add more light. If an ac is oversized it just means the compressor will cycle on less often

 

[Jnugg]

I would like to use more light....someday but no time too soon (maybe the next rental).

Too my understanding,if one has too large a unit that it will cool the room fine,but may just as well not dehumidify the room properly.

 

[Rolldaddy]

The more time your compressor is running the more your ac will dehumidify. Bigger is better, specially if you plan to use more light in the future but its up to you

If you want your ac to dehumidify more buy an undersized ac

 

[Jnugg]

Right and I live in Fla which is hot damn near 10 months out of the year,and humidity jesus it is swampland afterall.So if I get too big a unit,I'll be cooling just fine,but humidity could stay high making it feel clamy/balmy in the room.I'd hate to have to buy and run a dehumidifier as well because I only have a 20 amp circuit to use (it controlls the entire rear of apt) and to stay within the 80% safe load I can't use more than 1840w and light,fans,with 10000 BTU unit will put me damn close.

 

[Jhhnn]

Right and I live in Fla which is hot damn near 10 months out of the year,and humidity jesus it is swampland afterall.So if I get too big a unit,I'll be cooling just fine,but humidity could stay high making it feel clamy/balmy in the room.I'd hate to have to buy and run a dehumidifier as well because I only have a 20 amp circuit to use (it controlls the entire rear of apt) and to stay within the 80% safe load I can't use more than 1840w and light,fans,with 10000 BTU unit will put me damn close.

I think that in some situations, growers would do well to have 2 units. One that's definitely too small, set to a temp it can't maintain. It'll run all the time, both cooling & dehumidifying. Then a second unit set to a higher temp to pick up the load when the light is on, which will both cool & dehumidify as it cycles on & off.

Some of the newer window units use the inverter tech to achieve much the same effect.

Here in Denver, high humidity isn't a big problem. If anything, the opposite is true. Winter humidity is often quite low, and when the air is heated to the human comfort range, it'll plunge to nearly nothing. W/O a humidifier, the plants need large amounts of water.

 

[2nd_nature]

Super informative. Awesome.

 

[fandango]

Choice is mini split heat pump
1 ton
or 2 ton
20,000kw hps lights need 3-2ton systems
IMO
how much are you growers paying for heat pumps on line?

 

[michaelswines]

Here is a super easy way to calculate how much tonnage one needs to cool their room. Please note, the room is sealed and well insulated r-19 or better. In a NON air cooled light system (I prefer non air cooled hoods) the math is a half ton of AC per 1000 watt light fixture. This will give you ample amount of cooling power during those hot days when even insulation does not seem to help. Make sure to purchase a heating option, for example a mini-split system with heating capability.

 

[coldcanna]

Your choice also depends on your climate zone, I found this calculator on the fed website that I'm using, many of us need both AC and heat functions especially if one chooses to use an out building like a barn, shed, garage, or something else thats not lived in.

 

[coldcanna]

Your choice also depends on your climate zone, I found this calculator on the fed website that I'm using, many of us need both AC and heat functions especially if one chooses to use an out building like a barn, shed, garage, or something else thats not lived in.

http://energycode.pnl.gov/EnergyCodeReqs/

 

[thunderbunny]

Trying to find out how a thru wall AC unit works:

Is my co2 enriched inside room air just recirculated constantly over the cooling plates, and moved back into the room?

Or does the thru wall unit suck the co2 enriched warm air to the outside, and then blow air from the outside over the cooling plates, and pump that now cooled outside air back into my room, thus defeating my CO2 injection completely?

Just came back from Menards, and I am now more confused than when I left. I was told by one of the floor workers that the thru walls suck in outside air, cool it, and pump it into your room, while pulling the hot, CO2 enriched air to the outside which is a complete waste of CO2......seems to me that AC thru wall units used to have an option for cooling only the room air (recirculate setting I believe), and blowing same cooled air back into the same area?

Stood there reading instruction manuals for half an hour and am now more confused than ever! none of then mentioned a thing about recirculating the same air over and over?

If I am just repeating a question that has been asked over and over again, please just direct me to the thread where they discuss the operation of these units........HELPPPP!

Thank you in advance for your info!

 

[paper thorn]

hey thunderbunny, through the wall units work just like window units. Outside air is pulled through the condenser coils on the outside(back) part of the unit and expelled outside.

The air handler part on the inside(front) of it pull from inside and blow back inside. No mixing of outside air to the inside.

Really the only difference between a through the wall a/c and a window a/c is the wall unit is longer so the outside intake vents on the side of the unit are actually on the outside of the house. If you used a window unit the side vents would be partially inside the wall.

 

[Asslover]

Right and I live in Fla which is hot damn near 10 months out of the year,and humidity jesus it is swampland afterall.So if I get too big a unit,I'll be cooling just fine,but humidity could stay high making it feel clamy/balmy in the room.I'd hate to have to buy and run a dehumidifier as well because I only have a 20 amp circuit to use (it controlls the entire rear of apt) and to stay within the 80% safe load I can't use more than 1840w and light,fans,with 10000 BTU unit will put me damn close.

Jung, you're going to need a dehuey for when the lights are off. No heat signal from the bulbs means the AC won't run much and thus not dehumidify. Trust me, during lights off your humidity WILL skyrocket

 

[DemonTrich]

awesome thread. didn't feel the need to start a new thread as this one and your guys help should be spot on.

I have a new built room (8x12x7 sealed, no co2). currently I have 3x600hps in big kahuna hoods (fully sealed, no air leaks). both hoods have 2x6" 440cfm fans on a push/pull setup. I also have a MONSTER carbon scrubber matted to an 8" 720cfm fan. 8" 400cfm intake fan and an LG 8000btu portable ac with a custom hose that feeds into my intake fan (intake fan sucks cold air in, not forced by the ac). I also have 2x 18" oscillating fans on HIGH blowing under the hoods to remove hot pocket. current under hood temps are 77* (temp taken directly under the bulb.

im wondering if I step up to a 10000btu a/c if I can drop my temps a bit more? I grow underground so temps are mild atm. once summer hits, (imo) ill be running 5* hotter, even tho im underground. ambient underground temps are 72-74*. OR if I upgrade my hood fans to 2x8" 720cfm fans and put them on speed controllers, and leave the ac alone?

 

[DemonTrich]

bump to the a/c guru's

 

[whadeezlrg]

any differences in lighting btu calculations for gavitas?