Supercomputing's latest challenge: Keeping cool

NEWPORT, R.I.'Organizations building and running supercomputers need to develop new ways of keeping those systems cool, said Eng Lim Goh, the chief technology officer for Silicon Graphics Inc. of Mountain View, Calif.

Goh spoke yesterday at the National High Performance Computing and Communications Conference, being held this week in Newport.

While supercomputers continue to make giant leaps in processing power, cooling technologies are not advancing as rapidly. As a result, system designers are seeing a disparity growing between the amount of heat generated by newer supercomputers and the ability of data centers to cool these processors.

Newer supercomputer facilities 'feel like wind tunnels now,' Goh said. As a result, 'People are starting to think about a different medium. Air can only carry so much heat.'

'This is a very serious problem' agreed Srinidhi Varadarajan, the architect of Virginia Tech's Terascale Computing Facility. 'Today's processors produce a phenomenal amount of heat.'

While a rack of servers can easily be cooled with an air conditioner, 'when you have a hundred racks, that is not a viable solution,' Varadarajan said.

Virginia Tech chose a hybrid liquid-air cooling system after finding that the traditional approach of cooling the system would not be sufficient, given the space restrictions of its data center. Varadarajan estimated that the 1,100 Apple G5 processors the system uses would produce 3.2 million British thermal units of heat in the 3,000-square-foot space.

In a traditional air-cooled approach, multiple fans would force air up through the perforated floor tiles, Varadarajan said. The computers would suck in the cold air and blow out the hot air, which would be carried away by ceiling exhaust fans.

Varadarajan's team calculated that air would have to blow through the facility at 60 mph in order to adequately cool the G5s.

In Virginia Tech's hybrid liquid-air approach, a liquid is cooled and then sent through pipes underneath the facility's raised floor. Fans blow the cooled air off these pipes, which carry 750 gallons of liquid a minute.

In addition to being less windy, the hybrid system also was less expensive, Varadarajan said. An all-air cooling system would cost around $5 million to build'far too expensive for the budget-conscious university. The hybrid system cost less than a million dollars.

Tetsuya Sato, director of the Earth Simulator Center in Japan, said the center's 5,100-processor supercomputer'the world's most powerful supercomputer'is kept cool with blasts of air that enter the facility at 16 degrees centigrade and are exhausted at 23 degrees centigrade. Each processor has its own individual cooling unit as well.

'It is very noisy,' Sato said of the system's air-conditioning units.

About the Author

Joab Jackson is the senior technology editor for Government Computer News.

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