No, I didn't pull you up when you misinterpreted my last post, but this isn't applicable.
The aircon sizing based on area, makes a number of presumptions. Most around the structures heat gain. Things like number and size of windows. Outside walls, North or south, roof, floor. The air exchange likely. Number of occupants and there tasks. All is presumed when people don't care to do it properly.
In this space, there is a large heat source, and also extraction. Factors of greater importance than the usual presumed one's. If this grow was pushed in a room half the size, the requirement would barely change. You still must cool the same amount of air going in. Enough to account for the heat gain of the grow. It's 8000w of gain, or 27500btu to remove. Then you could start looking at the room size needing 9000 because of building gain. Which is nonsense, because it's not a sealed room.
This needs looking at from a commercial ahu plant prospective. Where a building needs a volume of air blowing in, at a certain temperature. This ahu is the garage. Though the plant is likely portable and pointing at the rooms intake duct, it's the same principle.
The 6252a amemometer is $20 and a typical wind speed measurement device. You can put it in a duct, and tell it the duct size. Allowing it to see the air speed, and calc duct flow. Most of us guess airflow, and tend to think the sticker on the fan is achieved. Which is far from the truth. This would be a reasonable way to find cooling requirements for the volume of air passing through. The size of the floor isn't a big concideration, as building gain isn't a big part of the problem.
