How much lighting can I realistically run?

[Zarezhu]

Hey guys, I'm not having much luck in the ventilation part of the forum, so I figured I'd try here

I have a 12 x 12 x 8 shed (1152 sq feet) shed out back, its insulated with 1/2" rigid foam.

I have one 12" inline fan (1050 cfm) that I'm going to mount on the top of one of the walls, and on the opposite wall I'm going to have passive intakes(just regular 24" filters).

The lights will be "on" from 8PM to 8AM. The average night time weather for the next 3 months should be roughly 45-65.

Will I be able to run 4600-5000w with just the one exhaust fan, or should I only try to run 4000w on dimmers in case the room has a hard time staying cool?

If I need to, I can run as many of my lights air cooled as I need. If I need to, I have another fan (1599cfm) that I could use, but this would make a hugeee wind tunnel and stunt the plants. I realistically can only handle a 15 degree F increase in temp.

 

[doneit]

Easy fix... air conditioner with digital thermostat

 

[Zarezhu]

I will only use the air conditioner during the plants night cycle. The Exhaust fan will be turned off during this time, and the AC will keep the room at 65-70 during the heat of the day, when all the plants are sleeping. It's just an 8k btu window ac.

Running the air conditioner while the exhaust fan is running would be very inefficient, as there's complete air exchange once a minute. I feel like I should be able to keep the room temperature from rising any more than 15 degrees above ambient with enough air exchance? Am I crazy?

 

[Jhhnn]

I will only use the air conditioner during the plants night cycle. The Exhaust fan will be turned off during this time, and the AC will keep the room at 65-70 during the heat of the day, when all the plants are sleeping. It's just an 8k btu window ac.

Running the air conditioner while the exhaust fan is running would be very inefficient, as there's complete air exchange once a minute. I feel like I should be able to keep the room temperature from rising any more than 15 degrees above ambient with enough air exchance? Am I crazy?

I don't think you're crazy. I do think that you face complex issues with a lot of unknowns. If it were my project, I'd approach it like this-

1. Create a small foyer w/ inner door for light control purposes.

2. Figure on three or four 1000w lights, each covering a 4x4 area or slightly larger.

3. Create an attic space tall enough to accept vent hoods for each light. Seal & insulate it from the grow space, mount the hoods & ballasts in the attic along with the vent fan & air intake opposite the fan. The glass on the hoods should be flush or nearly so w/ the ceiling. Provide an access panel. Baffle the intake for light control purposes. You may need to baffle the exhaust as well. No ducting. Run that fan continuously or on a thermostat.

The vent hoods & attic space keep much (most?) of the heat from the lights out of the grow area, and most of the thermal gain from the sun out during daylight hours. It unloads the AC, makes temp control in the grow space easier.

4. Use another fan, light baffle & carbon filter to vent the grow space when the light is on. That can be a two speed arrangement w/ either a two speed fan or speed controller(s) & a flipflop relay on a thermostat. You may need to vent the grow space intermittently during the dark cycle to keep the air fresh. Light pollution control is critical when the dark cycle occurs during daylight.

5. Install a standard 30A 240V sub panel, breakers & receptacles. Run the lights on 240V with a timer controlled contactor & receptacles. Best practice is to run 120V equipment on a separate circuit & contactor or relay controlled by the same timer. You don't have to create a low voltage control circuit for all of this, but it's probably a good idea. Sketch out a diagram of the whole electrical system for clarity & future reference.

6. Set the plants on folding tables when small to get them closer to the lights if you're using soil or other pot methods. Ingenuity can provide intermediate heights. For some kinds of hydro, guess the best compromise height for the tables.

7. Incorporate an overtemp shutdown/ lockout control circuit.

Those are just ideas, in no particular order. I've never done what you describe, so take it all with a grain of salt.