DATA CENTRES
Liquid cooling keeps data moving
Steve Lorimer, associate director at Keysource looks at the role of liquid cooling in the world of data centres.
D
epending on your sources, the data centre sector accounts for between 1-2% of all global electricity usage and there is continued pressure for operators to be more effi cient. Energy and carbon are high on political agendas and we are likely to see more policy measures particularly if the UK is to reach our legally binding zero carbon target in the UK by 2050. The European Commission, meanwhile, is rolling out a hugely ambitious package of environmental measures and data centres are fi rmly in the fi ring line; the sector must be climate neutral by 2030, for instance. IT aside, the vast majority of this power usage is due to cooling within the datacentre and the need to relocate heat away from the CPU. Traditionally, air cooling is the go-to solution and makes up for the vast majority of cooling solutions in the data centre world. Existing air-cooling systems are usually fi rmly embedded into the physical infrastructure of a data centre and are largely eff ective and still the best option for 60-70% of set ups. However, where IT densities require some
organisations are looking at the option of liquid cooling solutions either as an alternative or as a complementary element. The reason is simple – liquid cooling is much more eff ective at removing heat than air cooling. To put this into context, currently air cooling has 60kW/rack limitation, direct liquid cooling 70kW/rack limitation and full immersion/fanless liquid cooling 120kW/rack limitations. This is important as we are seeing rack densities continue to increase driven by consumer demands for faster and more complex services in certain applications. However, it is also fair to say that alternative cooling methods doesn’t need to exclusively sit with high performance compute and presents a great opportunity. Although both air and liquid solutions meet the
36 July 2021 •
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objective of absorbing heat from a CPU, the process for both is worlds apart. Most air-cooling systems take in cold air via the front of the unit and then exhausts hot air from the back. In the hot aisle/ cold aisle arrangement, the rows of server racks are oriented so that the server 'fronts' face each other in one row and the server “backs” face each other in another row. Cold supply air is then delivered directly to each cold aisle and can be matched to the server airfl ow requirements for maximum effi ciency. A direct liquid cooling system, circulates a liquid through a heat sink attached to the processor. As the liquid passes through the heat sink, heat is transferred from the hot processor to the cooler liquid. The high specifi c heat capacity of the cooling liquid/water means it is much more eff ective than air at removing the heat enabling higher densities to be achieved. Finally, immersion cooling involves complete
servers being submerged into a thermally conductive dielectric liquid or coolant. Heat is removed from the system by circulating liquid into direct contact with hot components, then through cool heat exchangers. Fluids suitable for immersion cooling have very good insulating properties to ensure that they can safely come into contact with energised electronic components. In simple terms a liquid-cooled system can reduce a data centre facility’s overall power consumption and improve its power usage eff ectiveness (PUE) resulting in environmental benefi ts, including Improved power usage, reduced emission and overall less waste. The higher grade of heat rejected (70°C+) compared to air systems (<40°C) also opens the doors to heat reuse/recovery opportunities; through symbiotic relationships with industries that require continuous hot water for their industrial processes and produces less noise than air cooling. The increase coolant supply and return temepratures mean that full cooling is possible without the need for chillers and in most UK cases without adiabatic cooling – this can mean a lower cost to deploy and maintain cooling infrastructure. In addition, the stranded electrical capacity reserved normally for chiller use could be re-purposed into additional IT capacity.
The physical space requirements and layout of a facility that is liquid cooled, can require a diff erent
type of datacentre design than an air-cooled facility. This means that for many legacy datacentres the addition of liquid cooling may not be a realistic option. In addition currently not everyone needs the IT that systems that require direct liquid cooling, air cooled servers can be more than adequate and may represent a lower total cost of ownership, now. For many facilities it may not always be possible to implement wholesale changes in a live environment with inherent space, power and environmental constraints.
However, many hyperscale cloud operators, such as Alibaba, Google, Amazon, Apple, Baidu, Microsoft and Oracle are reportedly already investing in this technology since they need to address their high-performance computing (HPC) applications along with their AI customer demands. Colocation operators that are also competing in this HPC sector and attracting hyperscale cloud clients, are allocating raised-fl oor areas dedicated to liquid cooling racks. The Keysource 2020 State of the Industry Report, which surveyed over 100 senior IT professionals, highlighted the continuing importance of the green agenda with over three quarters of respondents stating that sustainability will have a medium or high infl uence on IT decisions. Liquid cooling could play a much bigger role in helping companies meet their targets and reducing the carbon and energy footprint of an operation and reusing hot water to help unrelated industries meet their green initiatives are just two of the obvious benefi ts of a liquid cooling solution. And though the scale of changing from air cooling to liquid cooling might be too off -putting for leaders within the date centre world today, it might well become more of a pressing issue as the task of saving energy on a signifi cant scale starts to become more apparent during the next few years. At Keysource we are seeing a growing uptake of liquid cooling solutions in specialist institutions and universities In many cases existing users are asking us to assist to adapt existing air cooled rooms with chilled water infrastructure to address small scale deployments. This can provide a good opportunity to re-use or supplement existing free cooling chlller capability and then to further optimise existing air cooled systems and infrastructure. Larger scale deployments in specialist facilities are more often scalable and optimised deployments (row and room based), modular and packaged solutions. So, whilst uptake is steady and we do not expect a widespread commercial shift from an air-cooled system to liquid cooling in the near future, it is becoming increasingly relevant.
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