Why water-cooled systems are cool again

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Making a splash: There’s a strong case for water-cooled computers

Received wisdom has it that water and data centres don’t mix. Water-cooling was a necessary evil in the age of the mainframe, but these days our dear little servers are perfectly capable of being cooled by the merest draft – probably along with a whiff of air freshener at the same time – right?

Unfortunately, the boffins at Intel and AMD have been struggling a bit. I remember an Intel event where one very senior person said something along the lines of: “We do have one small problem… If we continue the way we are going, by 2015 the core temperature of a CPU will be greater than the surface of the sun.”

Okay, so this was a while ago and the silicon engineers have been beavering away to try and ensure that fateful day is postponed for a few more years yet. Even so, it’s true equipment densities have been increasing, and hot spots getting hotter, faster than we have been able to deal with them. Mass air cooling is becoming not only less effective, but a major energy cost – and if we end up with a high-cost, low-effective cooling system, surely something’s wrong.

So water is back in the running, so to speak. Rear-door heat exchangers (where the heat from air cooling is withdrawn through a water-cooled heat exchanger placed across the back of an equipment rack) can be pretty effective in many cases, but are probably just a stop-gap solution. IBM, though, has been working on something with the Swiss Federal Institute of Technology (ETH Zurich) that looks rather more promising.

Called Aquasar, the co-project has been launched in a blade-based supercomputer at ETH Zurich and the results seem impressive. The computer is a biggie (6 teraflops) and churns out a lot of heat. Some is still removed via air cooling, but Aquasar uses micro-channel copper heat exchangers that fit over the CPUs. These little blocks plug into a self-sealing water back distribution bus. Not only does this prevent any leakage, but it also makes it possible to swap out blades as necessary without any tricky plumbing work.

It’s a contained system – high purity water is used to ensure there are no deposits within the micro-channels and no reaction between impurities in the water and the copper. The inlet water temperature can be as high as 60

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