I like the cold side/hot side approach with the larger vent fans. If you were the build another wall in the middle of that room (well, closer to the exhaust wall by a bit) you could put a couple of larger vent fans on the exterior wall to pull the air across all the miners. The small fans and capacity of flex hose is probably somewhat difficult for them to get their air up and out. You could loose the hoses, have a couple of large exhaust holes with vent covers. I'd try to get the exhaust from the PSU taken care of as well - as they are, they are putting their hot air into the intake space of the miners - making your AC have to work harder. The larger exhaust fans would be cheaper to operate than the AC unit as well.
Using that method, you could get many more miners in your space. You incoming power source would surely become the bottlneck.
Here is my setup I just finished (well, a few minor details left, but functioning):
200amp service, 200amp breaker panel, whole panel surge suppression, 2 20amp breakers of 120v to feed switches, fans, etc..., 8 - 20amp 220/240v breakers feeding 2 outlets each across 12guage wire. This will allow 16amp continuous draw - which is enough for 2 S9 miners per breaker. The fans are 3200cfm each. The 4 filters are each 1"x16"x20" central AC filters. My outside temp right now is 64f - but these miner temps have stayed pretty close when at 80f as well. This is the bottom floor - kind-of a basement, but not really - hard to explain, but the temps down there with no AC stays around 70f - even with these fans running.
I'm going to tie/anchor the power lines better, same with the power cords to the PSU's. I'm also going to put dimmer switches on the fans as I think I can slow them down some and keep the temps at the same level or very similar. 1 fan was almost enough - so I turned on the other one, but now probably overkill.
The smaller holes above the top shelf are to take out any extra heat the makes it up into the miner area.
