cooling
computing , the benefits it offers in terms of greater efficiency and more environmental flexibility now make it worthy of consideration .
Liquid-to-server cooling can take one of two general approaches : direct liquid cooling ( DLC ) or total liquid cooling ( TLC ).
The former approach involves placing a small , fully sealed heat sink on top of the server board or chip that needs cooling . As the board generates heat , the heat is transferred into the heat sink , which is basically a metal plate full of cool liquid . As the liquid inside heats up , tubes connected to the plate transfer the liquid outside to a cooler that rejects the heat outdoors and routes the cooled fluid back to the heat sink . Between 40 and 60 per cent of the heat generated by a server can be absorbed using this approach , so it does not remove the need for air conditioning or chillers in the data centre , but it does help to reduce the burden on such systems and reduce energy costs as a result .
The TLC approach involves no air cooled components . Instead , the server is completely immersed in a dielectric fluid or mineral oil solution that absorbs heat . In practice , it typically involves placing an entire IT rack of servers on its back in a tub full of fluid with network and power cabling hanging from rails above . All the heat generated by the servers is absorbed into the fluid and , once again , the fluid is continually pumped away to be cooled and returned .
The trade-off for removing the need for any sort of air cooling is serviceability , which is inherently more complicated in liquid cooled systems . Replacing any server components requires a board to be removed from the fluid and allowed to dry before performing the replacement and submersing the board back in the fluid – a time consuming process .
Another form of total liquid cooling involves placing each server board or blade inside a housing that ’ s sealed and full of a dielectric fluid . The exterior of that housing is a heat transfer plate with a secondary cooling liquid running through it to reject the heat from the fluid surrounding the server board . Each housing fits into a larger chassis . The secondary cooling liquid from the exterior of each housing flows to the chassis , from there it rejects the heat to the outside environment .
Among the advantages of TLC systems are a much greater resilience to fluctuations in humidity and air quality , such as dust and particles , making them particularly suitable for ruggedised applications in industrial , military or mining environments .
The lack of fans and air cooling also allows TCO systems better to withstand power outages . Even without replenishing the liquid supply , servers could expel heat for up to an hour or so before the liquid would become too hot to cool the load . That is typically plenty of time to restore main power , shift to back up power or gracefully shut down the IT equipment .
Liquid cooling , particularly TLC , is also far quieter than traditional data centre cooling systems because it requires fewer fans , or none at all , to move air . This also makes them inherently more energy efficient . As a further benefit , the heated liquid that immersion systems generate can be used to supply heat to radiators in offices or other buildings . They also allow for greater flexibility in data centre design , because there ’ s no longer a need for hot aisle / cold aisle configurations . Operators can put liquid cooled racks wherever they like .
Conclusion The cooling options from which data centre operators can choose are many and varied and continue to evolve in response to technology developments . The correct options to deploy depend on the particular requirements of the data centre , in particular the environment in which it operates as well as the inevitable cost considerations . The trade-offs between capital and operating expenditure , how necessary it is to isolate the data centre from the effects of a hostile environment and conversely how necessary it is to minimise the effects of the data centre itself on its surroundings , will all effect the choice of cooling method .
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