DCN October 2016 - Page 34

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 34 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 env ₯Ι½Ή΅•ΉΠ₯Έέ‘₯ ₯Ё½Α•Ι…Ρ•Μ)…́ݕ±°…́ё”₯Ή•Ω₯Ρ…‰±”½ΝΠ)½ΉΝ₯‘•Ι…Ρ₯½ΉΜΈQ‘”ΡΙ…‘”΅½™™Μ)‰•Ρέ••Έ…Α₯Ρ…°…Ή½Α•Ι…Ρ₯Ήœ)•αΑ•Ή‘₯ΡΥΙ”°‘½άΉ••ΝΝ…Ιδ₯Ё₯Μ)ΡΌ₯Ν½±…Ρ”Ρ‘”‘…Ρ„•ΉΡΙ”™Ι½΄Ρ‘”)•™™•Ρ́½˜„‘½ΝΡ₯±”•ΉΩ₯Ι½Ή΅•ΉΠ…Ή)½ΉΩ•ΙΝ•±δ‘½άΉ••ΝΝ…Ιδ₯Ё₯́Ѽ)΅₯Ή₯΅₯Ν”Ρ‘”•™™•Ρ́½˜Ρ‘”‘…Ρ„•ΉΡΙ”)₯ΡΝ•±˜½Έ₯Ρ́ΝΥΙΙ½ΥΉ‘₯ΉΜ°έ₯±°…±°•™™•Π)Ρ‘”‘½₯”½˜½½±₯Ήœ΅•Ρ‘½Έ((0