Calculating The Size of a Air Conditioner

OK guys so this come's up as or in a thread just about every other day....
with this formula a room would be able to get in the 70-72 deg range even when it's 100+ but yet still maintain humidity at night time with proper air movement

Calculating Heat Load
Heat is measured in either BTU or Kilowatts. 1KW is equivalent to 3500BTUs.
The heat load depends on a number of factor's

1.The floor area of the room
2.The heat generated by equipment
3 the heat from lighting
4.The number of room occupants
5.The ambient temp ( your room's starting temp ) this will be added asap im still playing with the #'s

1.Floor Area of Room

Room Area BTU = L x W x 40 ( H = 8foot + 5btu per foot after that)

If you have a wall that is facing the sun add in for the extra heat

Sun facing wall BTU = L x H x 40

2.Equipment
This is trickier to calculate than you might think. The wattage on equipment is the maximum power consumption rating, the actual power consumed may be less. However it is safer to overestimate the wattage than underestimate it.

Equipment BTU = Total wattage for equipment x 3.5

Ballast in room BTU = ballast wattage/2 x 3.5

3.Lighting

Lighting BTU = Total wattage for all lighting x 4

Air cooled hood BTU = wattage x 4 / 2
@
400= 200-250 cfm
600= 250-300 cfm
1k = 300-350 cfm
^ is just a guide cfm per hood will be on your ducting/SP....

4.Occupants
even being that im only there for 2 or so of the 12 hrs i like it to be able to handle the extra sweat when i smoke one.

Total Occupant BTU = Number of occupants x 400

Total Cooling Required

Add all the BTUs together.

Total Heat Load = Room Area BTU + Total Occupant BTU + Equipment BTU + Lighting BTU

If your using a portable a/c

Total Heat Load BTU x 2

^this has been from threads on this site i dont have any real experince with portable a/c's other then one and it was not in a growroom but if you plan on getting one id think about one thats bigger then you thought about


sample

so if we have a 3 x 3 room with 1k and 200 watt's in fan's/pump's

for room we need 360 btu
for fan we need 700 btu
1k = 4000btu
ballast in the room = 1500 btu

we would need a/c that is 6560 btu i would round up to the next size 7kbtu


air exchange
aka intake/exhaust
complete air exchange every 4-5 minutes is average for a grow room/greenhouse (co2 control)....
for heat control (no a/c) i like to use 2.5 minutes {1M is best imo}
m=air exchange in min's

l x w x h = cf / m = cfm

lets use are room from above as a sample
3 x 3 x 8 = 72 /2.5 = 28.8 (30)
highend turn over = 72cfm
lowend turn over = 30cfm
now for the light 1k = 300-350cfm

exhaust system and air-cooled hood should be separated but most ppl cant/dont ( it's spendy) so add them together if your using 1 fan for both

the fan size we need is 330-422 remember you have duct loss (SP) in the sample room i would use a 440 cfm fan

SEER & EER ratings NO they are not the same.....

EER, or the Energy Efficient Ratio, is a measure of how efficiently a cooling system will operate when the outdoor temperature is at a specific level - usually 95°F. EER is calculated as a simple ratio of BTU's to the amount of power a unit consumes in watts. Here is an example using an air conditioner with 12,000 BTU's and consuming 1500 watts of power:

EER = BTU's / Watts

12,000 / 1500 = 8

EER = 8


While it is true that the higher the EER and BTU's, the more efficient the cooling system, many make the mistake of purchasing oversized air conditioners and ignoring EER ratings. The following is an example of an air conditioner with 12,000 BTU's and 1200 watts:

12,000 / 1200 = 10

EER =10

This would mean that this second unit can produce the same amount of cooling but more energy efficiently. Therefore, to save money on your monthly electric bill, choose a cooling system by getting an appropriately sized unit with a high EER.


SEER(seasonal energy efficiency ratio) measures how efficiently a residential central cooling system (air conditioner or heat pump) will operate over an entire cooling season, as opposed to a single outdoor temperature. As with EER, a higher SEER reflects a more efficient cooling system. SEER is calculated based on the total amount of cooling (in Btu) the system will provide over the entire season divided by the total number of watt-hours it will consume:

SEER = seasonal Btu of cooling / seasonal watt-hours used

Nice thread!

00420 said:

If your using a portable a/c

Total Heat Load BTU x 2

Click to expand...

Are you saying that portable units are roughly only half as efficient as others? A few others on another A/C-related thread seem to be saying this as well.

another vote for stickyifiying this

thanks 00420!

Just curious, where'd you get the numbers from?

I go with 5000 BTU's per 1W of light.

Thank for the info!

clowntown said:

Nice thread!
Are you saying that portable units are roughly only half as efficient as others? A few others on another A/C-related thread seem to be saying this as well.

Click to expand...

not really half as efficient but they take twice as much as a window unit atlest with the one i seen used, in a 12 x 20 no light 10,000 btu portable the lowest we could get the room was 75 max but after shorting the duct to less then a foot we where able to get 70 it took 3 hrs and never shut off the rest of the day, the next day we got a 10,000 window unit we reached the lowest setting 60 with in a hr this was not a growroom just a open room


being that you brought up efficiency im going to add how EER ratings are calculated

evlme2 said:

Just curious, where'd you get the numbers from?

Click to expand...

10 yr's experience with indoor growing
10 yr's researching indoor growing on google


potparty,FirstTracks glad you like it

Thats what i like to hear, "experience".
Somebody sticky this already!!

G33k Speak said:

I go with 5000 BTU's per 1W of light.

Click to expand...

I've heard similar (actually 4k BTU), but for non-air-cooled lights.

I realize the BTU's put out by air-cooled lights can vary widely depending on how it's ducted, how fast the air is flowing, whether the ducting is insulated, how well the reflector is designed, and so on... but anyone have a ballpark figure / rough guesstimate on how it compares to non-air-cooled? Or perhaps a "BTU rule of thumb" for air-cooled lights?

G33k Speak said:

I go with 5000 BTU's per 1W of light.

Click to expand...

i used to do the same.... but it is simply wrong

and all show you why twice

i run 3 flowering rooms....... 2 are 8 k each

8 x 5000btu = 40,000 btu

in my 2 growroom i use 1 25,000 btu a/c eachroom witch is 50,000 btu for 16,000k

40k btu is no where near what i need, 25kbtu is plenty they run 24/7 when lights are on, then about 6hrs at night ( it keeps hum down ) and on hot days ( 110+) i have to shut a lamp or 2 off. but its better the running a dehu


now in my 2 k flowering room
2 x 5kbtu =10,000btu

i run aircooled hood but the size of the room is 7.5x8x9 & one wall is in the sun 2/3rds of the day and i need 12,000 btu i had a 10,000 in there at first and it did not keep it under 80 if i was not running aircooled hoods i would need a 15/18kbtu unit

so as you can see my bigger rooms need less then 5000 btu per light but my 2k room needs more...

clowntown said:

I've heard similar (actually 4k BTU), but for non-air-cooled lights.

I realize the BTU's put out by air-cooled lights can vary widely depending on how it's ducted, how fast the air is flowing, whether the ducting is insulated, how well the reflector is designed, and so on... but anyone have a ballpark figure / rough guesstimate on how it compares to non-air-cooled? Or perhaps a "BTU rule of thumb" for air-cooled lights?

Click to expand...

i say 50% but i allways have had stright shot of duct work in & out and have never played with more then 2 aircooled and a 8" canfanHO 750 cfm my room is small but has a sunfacing wall.... if my math/numbers are wrong for air cooled hoods and someone can prove it i will be glad to change the top post to there experience i am getting ready to change my 2 8k grow rooms to coolhood's and drop the size of my a/c from 25,000 btu window units to 18,000btu mini splits im all so buying a 12,000 btu mini for my livingroom and 9kbtu for my bedrooms so i will be able to play with sizes

00420 said:

i used to do the same.... but it is simply wrong

and all show you why twice

i run 3 flowering rooms....... 2 are 8 k each

8 x 5000btu = 40,000 btu

in my 2 growroom i use 1 25,000 btu a/c's each witch is 50,000 btu

...

Click to expand...

I think there's a typo in that last line of the equation, but I take a SWAG and go ith you have 50,000 BTU's in an 8000W room.

I'd have to agree with you, that if you have 8-1000W ballasts inside your room, you probably need more then the base 5K.

But if you'd move the ballasts(AKA heaters:smile out of the room like a normal persontongue , switch to 18 hour cycles to save some energy, and put a big res in that room, you'd be fine.

(hope your sarcasm meter is on too)

G33k Speak said:

I think there's a typo in that last line of the equation, but I take a SWAG and go ith you have 50,000 BTU's in an 8000W room.

I'd have to agree with you, that if you have 8-1000W ballasts inside your room, you probably need more then the base 5K.

But if you'd move the ballasts(AKA heaters:smile out of the room like a normal persontongue , switch to 18 hour cycles to save some energy, and put a big res in that room, you'd be fine.

(hope your sarcasm meter is on too)

Click to expand...

hes saying he needs less then 5K not more.. what are you reading??
8x5000 =40,000 but hes getting by with ONLY 25,000 BTU?? sure the room is a bit warm, but cool enough.

now why would you degrade the ballasts by letting them get hot? that also makes them use more energy because there less efficiant. .5amps of 240 x 8 is alot of extra elec. thats almost enough wasted amps to run an extra 1K....

what the fuck is an 18 hour day? how do you flower with that shit.
do you even grow? what planet are you getting your info from?

16K btu for hoods/lights another 12k BTU for ballasts, and i can see why his room is a tad warm.

40K btu....

G33k Speak said:

I think there's a typo in that last line of the equation, but I take a SWAG and go ith you have 50,000 BTU's in an 8000W room.

I'd have to agree with you, that if you have 8-1000W ballasts inside your room, you probably need more then the base 5K.

But if you'd move the ballasts(AKA heaters:smile out of the room like a normal persontongue , switch to 18 hour cycles to save some energy, and put a big res in that room, you'd be fine.

(hope your sarcasm meter is on too)

Click to expand...

yes there was a typo..... sry it was late and after working a 12 hr day + tending to my grow room's on top of sum grape ape.... i fixed the typo's in my post sry about this guy's

the reason i dont put my ballasts out of the room ( btw i run 8 ballast on flip flop's 4 in each room) is theres no other place to put them i have a huge room with 4 rooms built in that.... any place i put them there in a growroom...

the reason i get away with under 5000 in the 2 rooms is i have a unit that runs the building it self to a 78 deg start point witch is like someone who starts a room in a empty bedroom and has central air in there house it's called ambient temp and it plays a role in picking a a/c as well but i have not came up with a good "base" to go by for this so its not posted but will be soon

18/6 is only good for my mom/veg rooms if you look back at my post is says the a/c's run 24/7 when lights are ON...... witch is what you want or you will run into hummity prob's..... if you run a 40,000 btu the thing will kick on/off so much not only will you have spikes and lights trying to relight when you run power like me but you will have white powder mold to start growing on your bud's from the high hum....

......................................

my sarcasm meter is allways on..... i dont take shit but if im wrong im the first to man up..... 5000btu is wrong on all levels of growing from 2k to 8k even with 1k in a 3x3 room 5kbtu would not cool with out air cooled hoods or intake/outake

DIGITALHIPPY said:

now why would you degrade the ballasts by letting them get hot? that also makes them use more energy because there less efficiant. .5amps of 240 x 8 is alot of extra elec. thats almost enough wasted amps to run an extra 1K....

Click to expand...

big up's on this bro......

i have seen 100's of ballast returned & or need a new cap my first ? to them everytime is was this in a room that was cooled answer: NO

i have ran the same USED ballast for 5 yr's now it was used atlest 3 yr's befor me and i have yet to change a cap o ya did i say i run them 24/7 i might pay a lil more to cool it but save on not having to change caps or buy new transformers..

28,000btu frigidair cools 9 digital 600s and a burner just fine. Same goes for 24,000btu kenmore on 12 600s w/burner

great thread

some questions

do elec ballasts count the same as standard ballasts

what is the assumption regarding air cooled hoods? .. how many cfm/watts of light cooling are you assuming to be the standard here?

ty in advance

Not many people are mentioning whether:

1) Light is air-cooled or not
2) Insulation of any type is used (ducting, walls, room, etc)
3) Whether ballasts sit in or outside the room
4) EER of the A/C unit
5) Ambient temperature

Seems to me like they're very important variables, and a change to any one of them could produce a much different result than the next setup.

clowntown said:

Not many people are mentioning whether:

1) Light is air-cooled or not
2) Insulation of any type is used (ducting, walls, room, etc)
3) Whether ballasts sit in or outside the room
4) EER of the A/C unit
5) Ambient temperature

Seems to me like they're very important variables, and a change to any one of them could produce a much different result than the next setup.

Click to expand...

and this is why i made this thread...............

im not saying my 1st post is how it has to be... just giving a good guide line & pointing out 4 or 5 btu per 1k is not really a "base" that should be used with the variables that there are.... i have got away with 2-3kbtu but have used as much as 7-8kbtu per 1k

do elec ballasts count the same as standard ballasts

Click to expand...

i would say yes.....as they use the same amount of power (ie 1000,600,400).....
the reason they run "cooler" is they have a fan built in
but im not sure 100% mine are standard

what is the assumption regarding air cooled hoods? .. how many cfm/watts of light cooling are you assuming to be the standard here?

Click to expand...

again im no guru on this but 375cfm per 1000 work wonders on mine i run a straight duct line so this could be why, with 750cfm on 2k proper ducting 50% btu on a/c is used for me

DIGITALHIPPY said:

hes saying he needs less then 5K not more.. what are you reading??
8x5000 =40,000 but hes getting by with ONLY 25,000 BTU?? sure the room is a bit warm, but cool enough.

now why would you degrade the ballasts by letting them get hot? that also makes them use more energy because there less efficiant. .5amps of 240 x 8 is alot of extra elec. thats almost enough wasted amps to run an extra 1K....

what the fuck is an 18 hour day? how do you flower with that shit.
do you even grow? what planet are you getting your info from?

16K btu for hoods/lights another 12k BTU for ballasts, and i can see why his room is a tad warm.

40K btu....

Click to expand...

oops- I misread his original post.. I read it as his lights were running on a 24 hour on cycle.

My bad.

But we seem to agree that the ballasts should go utside the room.

Ambient temp makes a HUUUGE difference... in winter, If the house got to around 65Fish , the (10K BTU portable) would do just fine, but that same set up with the house in the 80's and the AC would struggle.
I'd rather have too much AC, then not enough. But I guess it makes a difference wether you live in minnesota, or in arizona.

An undersized AC unit is teh suxxor.