What's new
  • Please note members who been with us for more than 10 years have been upgraded to "Veteran" status and will receive exclusive benefits. If you wish to find out more about this or support IcMag and get same benefits, check this thread here.
  • Important notice: ICMag's T.O.U. has been updated. Please review it here. For your convenience, it is also available in the main forum menu, under 'Quick Links"!

Calculating The Size of a Air Conditioner

Dab Strudel

Active member
with an 11'4"x9'4"x11" room, 4200w lights and 1231w of electricity fueling the room (fans, pumps, dehueys) I came up with just under 38k BTU with your formula... WTF did I do it wrong or is that about right? I was thinking 24k BTU would be enough.... FML
 

naxxan

New member
Anyone still here?

Anyone still here?

Hey I see the thread hasn't been used for a bit but I need to confirm a few things with someone that knows what's up
 

Biologist

Active member
What is a good calculation to use for how much heat you gain in a room with air cooled hoods used on a separate intake/exhaust system? If the air comes in, cools the lights and leaves again, what percent of the 1000W of heat from a SE HPS will still enter the room from the light?
 

UnHypothetical

New member
What is a good calculation to use for how much heat you gain in a room with air cooled hoods used on a separate intake/exhaust system? If the air comes in, cools the lights and leaves again, what percent of the 1000W of heat from a SE HPS will still enter the room from the light?

The number I used to use was 50%...

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. They get dirty and block light output, no matter how hard you try- it's just like mylar- technically it's superior to black and white poly, but often not in practice.

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.
In an aircooled setup 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 again, 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 CFM fans using 100 watts properly ducted and insulated on nice short straight runs. That's 1100 watts of fans, and it 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.
 
Pretty much everything is covered on the first post on the first page.


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....
 
Top