Dr. Srinidhi Varadarajan, the head of Virginia Tech‘s recent construction of a 1,100-node Power Mac G5-based supercomputer (currently tentatively ranked as the 3rd fastest supercomputer in the word) gave a presentation at the O’Reilly Mac OS X conference this week. Lots of interesting little technical tidbits in the article, detailing just how they were able to get the project up and running.
If you’ve ever sat with a TiBook in your lap, you understand that there is a further significant issue. As hot as a G4 runs, a G5 runs hotter. With a traditional air-conditioning setup, the calculations showed that instead of emptying out the air three times an hour as would be typical, they would need to empty the air three times per minute. Computers tend to each cool front to back. So the plan was to arrange the computers in rows back to back and pull the hot air out of the hot aisle. This would have required wind velocity under the floor of more than 60 miles per hour and still would have resulted in some hot spots. They decided instead to use a refrigerator-like system. Chillers cool water to 40 degrees to 50 degrees, which is then used to chill refrigerant, which is piped into a matrix of copper pipes. Effectively, you have a distributed refrigerator.