Tony Robinson

Trinity College

Topic: 

A Data Centre Energy Crisis or a Rebirth of Cool

Synopsis:

Data centres are the fastest-growing energy consumer group worldwide. The total energy consumption by data centres was 416.2 terawatt-hours last year. It is not the Google and Facebook server farms that are the main source of the problem; it is the numerous small data centres scattered around the globe. These are typically very inefficient, especially when it comes to the cooling of the servers, which accounts for about half of the energy consumption. Focus on improved air handling is the first step towards mitigating the impending energy crisis. New concepts, like Open Bath Immersion, can cut energy consumption by half.

Takeaways:

  • Smaller data centres consume the lion’s share of the energy consumed by the data centre industry as a whole because they are so numerous and are generally run very inefficiently, mostly due to poor air handling, and this is leading towards an energy consumption crisis
  • Immediate steps must be taken to mitigate the escalation of small data centre energy consumption or extreme measures, like limiting internet use, may result
  • Simple fixes to the air handling can improve data centre cooling and have significant energy savings
  • Open Bath Immersion technology, where servers are immersed in a low boiling point dielectric fluid, has to potential to halve the energy consumption of data centres

Submission:

The Impending Crisis

Data centres are now the fastest-growing energy consumer group worldwide. Estimates put last year’s total world energy consumption by data centres at 416.2 terawatt-hours (that’s edging towards half a trillion kilowatt-hours). Here are some facts to put this into perspective;

-This is significantly higher than the UK’s total energy consumption (about 300 terawatt-hours)

-It translates to on average almost 50 gigawatts of power being consumed 24/7. This is over twice the peak power produced by the Three Gorges Dam in China. Alternatively, you would need over 100 combined-cycle power stations, like the Poolbeg Generating Station in Dublin (Ireland’s highest capacity power station) to meet this demand.

-U.S. data centres consume about 90 terawatt-hours annually, the equivalent energy use of about 6.5 million average American homes.

-Currently, data centres are consuming about 2-3% of the worlds global electricity supply and producing 2% of the world’s greenhouse gas emissions.

-Data centres now have higher carbon emissions than the aviation industry.

-In Ireland, a conservative estimate is that there is currently about 311 megawatts of data centre load on the Irish Grid on a 24/7 basis. This is equivalent to 7% of current winter peak load and 8.6% of summer load.

Problematically, the world’s total energy consumption by data centres is projected to triple in the next decade, despite innovations targeted at making them operate more efficiently. For Ireland, EirGrid expect an additional 1gigawatt of data-centre base load by 2020. That’s more than the output of Ireland’s two highest capacity power plants combined.

Interestingly, big web-scale data center operators like Microsoft, Facebook, Google, who tend to run very efficient data centers, only comprise a small fraction of the world’s total data centre energy footprint. The brunt of the consumption is by much smaller data centres; mid-size enterprise data center, local government IT facility, university IT department etc.

Analysts say that the rate of data centre growth with associated escalation in energy demand is simply not sustainable beyond the next 10 to 15 years. Clearly we have a big and growing problem and some suggest that the only long-term solution will have to involve major cuts to our internet use in the future. Either that or switch to a black & white internet. I do not think any of us want that, so the question is ‘what are we going to do about it’?

The Rebirth of Cool

Fact: About half of the energy consumed by data centres is used to cool the servers.

The smaller data centres consume the lion’s share of the energy consumed by the data centre industry as a whole. As it turns out, these data centres are the ones with the most inefficient cooling systems. The main culprit? –overcooling. Refrigerated air is the coolant fluid used to keep servers cool. Smaller data centres tend to lack control systems that can manage air temperature and airflows. Therefore, since reliability supersedes efficiency, the air cooling system is run at full capacity full time; this is termed redundancy. Flooding the entire data centre with cold air is also a brute force method used to deal with hot spots; servers that run hotter than others. Of course this is wasteful since the rest of the servers are running unnecessarily cold.

A necessary first step towards slowing the rate at which data centre electrical energy consumption is escalating is simple: improve the cooling system of the smaller data centres. Simple fixes such as ensuring proper air routing (about 40% of the air can bypass the servers), installing control systems and ensuring that the hot exhaust air doesn’t mix with the cold supply air are straight forward and incredibly effective. For example, Future Resource Engineering focused on improvements to the cooling system of 40 data centres and projected savings of 24 million kWh total.

Air is of course a terribly ineffective coolant fluid. Can we get rid of air and with it the power hungry CRACs, air handlers or hot/cold aisles?

The answer is yes.

Open Bath Immersion (OBI) technologies are now being researched whereby the servers are completely immersed in a low boiling point dielectric fluid. With a little bit of engineering on the integrated heat spreader (IHS) and surface morphology, boiling directly on the surface of the IHS can offer more than sufficient cooling of the server CPUs/GPUs etc. The vapour that is generated is simply condensed by room temperature water being pumped through tubes which sit above the liquid free surface. Thus, the only energy cost is for running a pump and a fan, which is almost negligible. This simple yet effective technology has the potential of cutting data centre electricity consumption in half. A prototype boiling OBI data centre is currently operating in Hong Kong. Allied Control, who are operating the system, claim it is 4000 times more efficient than an equivalent refrigerated air system and that their OBI data centre is likely the most energy efficient one on the planet.

About Tony Robinson:

Tony’s specific expertise is in experimental and computational thermal sciences. He has 15 years’ experience in heat transfer, fluid mechanics and applied energy research in Ireland, France, Canada and parts of Africa. He is the author of over 130 peer reviewed papers. Also author of 60 technical reports for industry, business and professional organizations and 7 patents. He is also the director of Confluent Research Ltd., a thermal consultancy focused on industrial product development and thermal trouble-shooting. In-line with national and global energy priorities, Tony and his team perform research that specifically targets the critical need for improved energy efficiency of thermal energy transport and conversion technologies as well as developing novel clean energy devices. The research underpins the rational use of energy with regard to the reduction of energy use as well as clean generation with their consequent reduction of greenhouse gas emissions. To achieve this, the research focuses on both the fundamental science of enhanced heat transfer as well as innovative systems level engineering of clean technologies for biomass, geothermal, solar thermal, energy storage and waste heat recovery applications.

About Trinity College Dublin

Trinity College  is the sole constituent college of the University of Dublin, a research university in Ireland. The college was founded in 1592 as the “mother” of a new university, modelled after the collegiate universities of Oxford and of Cambridge, but, unlike these, only one college was ever established; as such, the designations “Trinity College” and “University of Dublin” are usually synonymous for practical purposes. It is one of the seven ancient universities of Britain and Ireland, and is Ireland’s oldest and top ranked university.

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