[convolvatron]

for large machines the air setup is really less efficient and takes up alot of space. you end up building a big room with a pressurized floor which is completely ringed by large ac units. you have to move alot of air through the floor bringing it up through the cabinets and back through to the acs. its also a big control systems problem, you need to get the air through the cabinets evenly, so you need variable speed fans or controlled ducts..and those need to be adaptive but not oscillate.

with a water cooled setup you can move alot more heat through your pipes just be increasing flow rate. so you need pumps instead of fans. and now your machine room isn't a mini-hurricane, and you can more flexibly deal with the waste heat.