sawyl | Cray's new cooling technology

Cray's announcement of their new cooling technology, ECOphlex, provoked a certain amount of wry amusement in some quarters. Here's the relevant snippet:

"Other systems use chilled water coils embedded in each computer cabinet and sometimes even embedded invasively into the compute blades. With ECOphlex technology, you still use chilled water, but much less of it. And because of our unique engineering, you don't need to worry about water condensation or leakage that could harm electronic components." [said Cray Chief Technology Officer Steve Scott.]

While it's true that the volume of chilled water used by the Cray is going to be less than that of a completely water cooled system, this point is essentially irrelevant. What matters is the amount of heat transported away by the working fluid. In an ECOphlex system, the working fluid is a haloalkane as far as the heat exchangers, at which point the energy is dumped back to the chilled water supply. The fact that the HFC uses two phases to increase the amount of heat transferred simply means that the chilled water needs to cycle through at a faster rate to keep up with the HEUs. So as far as I can see, the argument, while technically correct, isn't relevant to the point being made.

The point about condensation doesn't make much sense either. Condensation occurs when the temperature drops below the dew point. This in turn depends, not on the cooling method used, but on the humidity of the air in the computer room. So, regardless of whether you use a dual phase HFC or chilled water to transport heat away from the cold plates, if the temperature of the plates drops below the dew point, you're going to get water in your machine.

For all that I've complained about their press release, the actually technology sounds really interesting. Not that that's much of a surprise — they've always been good at the plumbing side of things. And while it's true that their machines are greener than most of the opposition, apparently their eco-friendliness comes more from being able to make better use of natural heat sinks than from clever in-cabinet cooling technologies. But I guess that's not exciting or sexy or new enough for a PR piece...