Adding more exhaust capacity to get that hot air out is very important. 90F is not too hot for the hardware to be safe running 24/7 as long as you can exhaust that hot air out of there and keep the GPU temperatures safe. How hot are your GPUs running when it's 90 F in the room?
AC is a waste of electricity unless you have free power, your exhuast fans need to be ABOVE your rigs not in at the same level and you also need to make sure your room is somewhat presurerized
you can tell this by when you open the doors you feel the suction of the exhaust fans pulling heat up.
I have 30 rigs in my garage with only 1 of six exhasut fans going and my temps are like 30 degreees in winter, fall with three fans going like 60
How big size is the exhaust fans? I wonder what type is the most useful for venting.