I assume you're talking about centralized cooling for server farms? The solution I like for that is to turn the entire rear door of each cabinet into a water-fed heat exchanger, with no change to the servers. Then your piping is orders of magnitude simpler and safer.
Probably even better. Water has a nice heat capacity (I think about 10x as much as copper), but maybe that isn't that important for such a solution as long as the heat gets used. Even if we would just get 10% of the invested energy back, it would be a huge boon already.
Heat capacity doesn't really matter, unless you'll be using the device less time than it takes to reach that capacity. If you have two materials with equal thermal conductivity, but different heat capacity, their cooling properties will be the same once both reach their heat capacity.
