New sealed room help help

I'm in the works of building a 20x12x12tall room
In my pole barn shop , barn is not insulated , has concrete and electric , my new room is gonna be insulated well r49 roof and r29 walls , I'm using 4x5 Veg tent , 4x8 flower tent haven't decided if imma just make a room and do away with tents or what yet , my veg is 600w and my flower tent has 2x 1000w hps , air cooled raptor hoods , I have 3 430cfm inline fans , plenty of oscillating fans , gonna purchase a ductless mini split , I have a humidifier and dehumidifier, my question is what is a good way to control the air coming in like winter time it's cold summer it's hot , so the air being brought in will be cold or hot then having to cool that or heat it at whatever rate and then extract , ways of being efficient as possible ,
Also will I have to run co2 if I go this route by pulling outside air in and pulling it out since that will be the only air ways .

My thoughts was to air cool the hoods threw the interior of the barn threw the room lights and out so brutal heat and cold wouldn't affect the lights , and just run mini split and co2 , but I no there is some great rooms and better ideas and I wanna no the best way possible without killen the bank , I ain't on a tight budget but I also ain't a millionaire, my barn and house is away from
Everyone so this ain't gotta be a secret thing
So I ain't limited there ...

If you are circulating some fresh air through you shouldn't need CO2 supplementation.

Unless your grow is legal, I wouldn't make it too obvious, even in a barn out int he middle of nowhere. It's easier to design stealth in up front then try to do it due to some unexpected visitors.

My only concern with intaking the air is even
Though the room 12x20 is gonna be insulated well the barn being not insulated when Intaking air into the room weather be summer or winter that air gonna have to be heated or
Cooled , a ductless mini is pretty damn efficient but pullin in 0 to 45 winter air and 80 to 105 summer heat would in turn require the mini to work a lot more , which I guess if ur outtake was pulling lil faster then intake would it not allow to warm or cool to fast for the mini to keep up and also allow for plenty of co2 ..

I have been exactly where you are! First off, split that area up into at least TWO rooms, while adding a clone/germ area/ cabinet. Three rooms wouldn't be a bad idea either! I.E.-Entry/clean room/nutes/clone cabinet, etc., into veg, then flower. Veg in center will somewhat help temps if using flourescent, or other light source which will not emit much heat (during cooler months). Create small room or use entry area to install mini split and divert most of the cool air into other rooms as you need it using ducting, fans, electric dampers w/therm controls. If done correctly, depending on Co2 supplement method (generator or tank, gen will create plenty of heat/tank will not) as well as oscillating fans/ventilation helping cool and keeping from staling the air, with C02 though, you can keep your rooms much warmer (78-88F). Will definitely need to kick up the Dehumidifier to keep mold/mildew down. Keep in mind on AC position in whatever room you decide, AC also dehumidifies at same time, not on same level as an individual Dehum unit, but you get the idea. SIDE NOTE run continuous drain hose from Dehum.! Works great! Also, when using C02, don't forget Co2 is heavier than air! I am babbling at this point, but hope you kinda get the picture! haha

Dont skimp on the drywall and vapor barrier!

I got what ur sAyin , what I came up with thou was tiny bit different might have to drawl it out to make sense cause I dnt explain shit worth a hoot ... as far as drywal vapor barrier . I'm doin 6or 8ml plastic all the walls and roof , then blown in sound and moisture insulation , the ceirling is open above so gonna blow in 16 inching then the walls are gonna be 6inchs on the walls makking the top r49 and the walls r29 so the chart says , and 1/4in osb painted ... that's my intentions ,