I wanted to start this thread to answer some basic questions about sizing cooling systems. Feel free to ask for help here for sizing your garden but first check out this interactive BTU calculator specifically for cooling gardens that I helped create. I personally tested everything 3x's and am very confident with my numbers. I did this by absorbing the heat in to water and then measuring the BTU's in the water. I put up some round numbers to make it easy, so these are not my exact findings.
http://www.hydroinnovations.com/faq/14032011-CoolingSystemChart R2.pdf
Basically this is how it breaks down...
Cooling BTU's needed before any equipment is added. This is for warm climates with 3 1/2" insulation, approx 40 BTU sq ft
1000 watt lamp inc radiant heat 4,000 BTU
1000 watt magnetic ballast 3,500 BTU
1000 watt digital ballast 2,500 BTU
600 watt lamp inc radiant heat 2,400 BTU
600 watt magnetic ballast 2,100 BTU
600 watt digital ballast 1,500 BTU
Co2
The amount of co2 varies on how well the room is sealed, the amount of plants consuming it, and the ppm setpoint. Typically generators have single burners inside that are rated at 3,000 BTU each. So a 4 burner gen produces approximately 12k BTU if ran for an entire hour. My best suggestion is to buy the gen before the cooling system and run it while monitoring the on and off cycle. Keep in mind that the initial run time will be longer than the maintenance run time. If you monitor for one hour and you know your generator size you can calculate your BTU's. Make sure that if you are ventilating your lights or your room that you do this while testing the BTU of the generator. You can run this test over 30 mins, just double your results. Keep in mind that plants consume it as well and this will raise your BTU's....how much depends on your plant size...I would figure at least 20% more than your BTU's test results to be safe. Just for an example I have a well sealed 12' x 24' flower room with 12 very large plants (3' wide 5-6' tall each) and my 12k BTU generator runs for about 15 mins an hour, so about 4k BTU per hour. Although not as accurate as a field test here is a co2 calculator that gives you an idea of initial run time for a particular room size. BTW 15 cubic feet of co2 equals 12k BTU.
Dehumidification
This is even trickier to calculate. BTU's created of course are based on run time. It's effected by outdoor humidity levels, how well the room is sealed, what growing system you are using (soil is highest IME), amount of plant material, and room temperature (the warmer the room the more the plants transpire), cooling system used, and humidity setpoint. Far to many variables for me to make a solid suggestion on BTU's. But to help size them I will tell you that a 70 pint dehu produces about 2k BTU per hour. If you think that you need a 70pint I would figure worst case scenario and add 2k BTU to your total. I use a 70 pint dehu for my garden (12' x 24') and it runs 50-70% of time depending on my plant cycle, but its my only form of dehumidification. With a standard a/c you will get some dehumidification out of it making the dehu run time less.
Ventilating lights
This varies depending on temp of the air being used and the amount of airflow (CFM). I've never cooled lights using outside air because in my location the air is too hot to use so I don't have any suggestions for sizing for this. I can tell you without a doubt if the air used to cool the lights is above the room temp is far less effective, in fact it can heat your room. Reflectors have about 8 sq ft of metal and 4 sq ft of glass and along with all the ducting they become heaters. Lets say your room is 80 degrees and the air you are using to cool the lights is 90 degrees. After the air flows through the reflector(s) its heated up well beyond this. All of the reflectors and ducting heats up to this temp and radiates heat in to the room. Something else to consider is that HID lighting produces radiation that even if using ice cold air radiation still passes out of the reflector. A great example is to hold your hand 1/4" away from the metal on the top of the reflector near the bulb and you can actually feel the radiant heat. This is approximately 500 BTU per hour per 1000 watt. A simple fix for this is to use Reflector Heat Shields.They will block 99% of the radiant heat on anything they cover and are a must for air cooling IMO. The radiant barrier fabric traps more heat in the reflectors allowing it to be removed with the forced air. For anyone using above room temp air to cool their lights I would insist they use these covers, I guarantee they will make a significant difference.
Lastly I always design my cooling systems 10-20% over the BTU's needed so that the cooling equipment can cycle on and off properly. These figures above have some cushion built in to them so 10% is probably fine.
If you need help sizing beyond this or have any other questions feel free to ask :)
