I guess it depends on how hot it is. 80 outside but what's the temp in the house? If you already manage the temp of your home adding another ac just for the grow room shouldn't have to be that big. If you don't have any form of ac on your house then you may need a larger unit.
I run 2 K HID lamps in my flower area. I actually sometimes just end up shutting one of them down when it gets extra hot. J
AC is the only way to go, mine is fine until 5pm until sundown when the inside temps closely match outside temps, one issue i have with daytime dark periods is light leaks unless you can keep the room the tents in completely dark as well
I've been told by my old school hps growing buddies that when you dim an hps ballast it screws up the spectrum and it should only be done at the hot part of the day to get past it then turned back up. HPS bulbs by design have to run hot to put out their best light and spectrum. It's fine for a temp solution but running a 1000 watt hps fixture at 750 watts long term will reduce growth from the less optimal spectrum as well as the reduced wattage.
I had a very similar issue running LED's so I just added a 5,000 BTU AC in the grow room and my temps stay between 71-78 all day and night....grow room is about the same size as yours ....I run a 4" exhaust, 1 small clip on fan, and a 8" desk fan inside the tent ...keep my exhaust set on medium and works like a charm
I changed out my old ac for a new more power efficient, I purposly bought a model with knobs an no led programming so i can hook it to a temp controlled outlet so it shuts off completely on cooler days, nights with no programming/loss of power issues... units with a energy efficiency rating above 11 are going to savr you money on power although mine only uses $40 worth for the entire 3 months well worth the piece of mind
If you're really having heat issues, you might want to switch to LED lights. If running the lights at night doesn't work.
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