Temperature control issues

[spyro]

I have scoured the internet for this topic, but it seems it doesn't get discussed. I am currently using DWC buckets to flower in a sealed closet, 4 ft×10 ft (40 square feet) in size, and supplementing with bottled CO2. I keep the CO2 concentration at around 1500ppm as long as the lights are on. I have 10 buckets in there at all times, 5 on each side of the closet, and the room is equipped with four 600w air cooled HPS lamps. Naturally with all those lights, along with two 951gph air pumps all being in a sealed grow room together, I am having problems controlling the temperature. I do my best to keep the temperatures between 75 and 85°F, but it has been quite difficult. All the plants I've had in there after sealing the space have suffered significantly from heat stress. I don't feel like venting the room is an option due to fear of wasting CO2. I am considering the idea of dedicated cooling with a mini split AC system. With the closet space being so small, I am afraid that, even with the smallest system with the smallest BTU, which is 5000 BTU, it may cause the AC to repeatedly freeze up due to the lack of airflow in the space. A portable AC is out of the question, mostly because of the lack of space I have, not only inside the closet, but also in the room where the closet is. I live in the southeastern region of the US, so the humidity here is high, especially during the warmer months, or else I would have tried a swamp cooler. I kind of feel like, at this point, a dedicated mini split AC system is my final option. Does anyone have any experience with this? Do I have more options than I realize? I am totally open to suggestions. I cannot find one article on the internet about a sealed grow closet relatively close to the size of mine using a mini split.

 

[Old Salt]

What about a sealed ventilation run, separate from the room ventilation, to cool the lights?

 

[spyro]

Yes, actually that's exactly how I have it. I have a beast of a 6 inch exhaust fan, mounted right beside a 12000 BTU window unit. The duct goes from the fan into the wall where it connects to each light one by one and then exhausts out of the opposite wall. When I began supplementing with CO2, I thought that keeping cold air in the exhaust system would cut back on the heat drastically. Since then, I found that it does help a little, but then with the air inside the duct being colder than it is in the room, it caused condensation to develop on the ducts, and 12 hours of that will certainly leave a puddle in the floor. I have even tried insulated flex duct. That was a lot of trouble. The original walls of the closet that I use were torn out, and I insulated all of the walls with R-13. Every crack was caulked, and I even used insulated vapor barrier/infrared blocker on the ceiling. I even have two 16 inch oscillating wall fans going in there all the time just to keep the air circulating. And the temp still climbs into the 90s.