My guess is that someone will come up with an inexpensive, reliable way to put a heat collector, which will basically look like a car radiator the size of a rear rack door, directly behind the hot air coming from the systems in the rack.
b) air is a lousy way to transfer heat away from where you want it to be compared to other materials.
So how did you propose to get the heat from the equipment to the car-radiator door? The idea of making the entire room into a refrigerator by bringing coolant to the racks is a good one, but I think that for this to be successful, more attention needs to be paid to physical placement of things, and the chillers need to be broken open. By that I mean that chillers cease to be a big box at the edge of the room because they are now part of the room itself. Think of a flat chiller attached to the ceiling with spaces for racks to be inserted into it. --Michael Dillon