Even on an evaporative cooling system you need to get the “evaporativaded” parts/particles out, so i would say: give the fans - sugessted from svennand - a try. Cool Air in, hot air out of the room should be enough for normal rigs. Your 6 - 8 GPUs are making muuuuuch hot air so… 1200m3/h could be not enough, but test it… maybe you will need 4 or even 6 of the fans…
Otherwise you could build a watercooled rig with a room centralized radiator :) There are so much possiblities :D (aircooling is the cheapest and less efficient)
-Plopsi