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Hitachi refrigerates rack rears

Nearly no fans? Cool

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Hitachi is mounting refrigerators on the rear doors of racks to suck out heat at a much lower cost.

The Hitachi Data Centre Solutions Group idea, announced at yesterday's Datacenter Dynamics conference in London, is to treat a rack as a quasi-refrigerated cabinet and have its heat turn refrigerator liquid into a gas.

Air is pulled through the rack by fans set into the rear door and heats the dual coil air-refrigerant-heat exchangers fixed to it. Continuing evaporation pushes the gas along pipes to a heat-exchanger where it loses its heat, turns back to liquid and is then gravity fed back to the rear door refrigerator unit.

Colocation operator Telehouse West is using this NC (Natural Circulation) system and likes the idea of a natural circulation with no pumps and compressors needed. In its London Docklands facility the gas is piped to a riser shaft in the building and passes through a chilled water heat exchanger, giving up its heat as it returns to a liquid state, and then flows back to the rack it started out from.

Bob Harris, Technical Services Director for Telehouse, said: "This system uses only a very small amount of fan power to move the air. So the coefficient of performance (COP) of the system is 43.5. For every kilowatt of power you put in it produces 43.5 kilowatts of cooling capacity. Normally for a data centre you get 5 to 6 kilowatts out for every kilowatt in. The Hitachi scheme is extremely more efficient."

Hitachi also has an in-row unit that uses the same principle to cool a row of racks. Its COP is 29.5. Harris said: "The door unit cools ten kilowatts and the in- row unit cools 23 kilowatts. At the 2.3 normal rack level there is a marginal differential. Beyond that the in-row unit is more effective."

There are other rack-level cooling technologies but they all use use pumps or compressors, Hitachi being unique in its approach. Harris said the rear door unit can be deployed to a number of different vendor's racks, which Telehouse West has already done. It can attach to a 600mm wide unit or an 800mm one or other rack widths.

He said: "It's very easy to install [and] connect to existing chilled water networks that were there. You need no more skills than those needed for a water-cooled rack. The benefit is that there is no water associated with it at the rack position. It's a refrigerant gas. As a data centre operator we don't like water and customer equipment to mix."

Hitachi can supply the technology as a complete system or as components, and there is built-in redundancy at the component level. ®

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