Google and Open Compute Project: What’s behind the energy efficency of it’s 48V rack power distribution

Google recently announced that it is joining the Open Compute Project (OCP), a five-year-old project founded by Facebook and a number of other companies that aims to drive IT infrastructure development forward through open source hardware.

As part of this initiative Google has signed on to work with Facebook and others on the OCP Open Rack project. This project aims to bring 48 volt power distribution to data center racks. Google says it has been working on 48V rack power distribution since 2010 and, in the process, it found that it had increased its energy efficiency by 30 percent by eliminating the multiple transformers usually deployed in a data center.

This sounds very good, but it is also worthwhile to analyze the figures in more detail. Ian Bitterlin does this in a highly insightful article at „DatacenterDynamics“:

„To avoid misleading the general reader from running away with the idea that Google have saved 30 percent of their energy demand, we should translate the ‘30 percent improvement’ into something more like ‘reduced electrical distribution losses from 9 percent to 6 percent’ but the rest of the sentence is absolutely key to our understanding of the arguments in favour (or against) DC power in the data centre.“

He argues:

„The point is that we (in 4-wire, 50Hz, Europe) don’t use ‚the multiple transformers usually deployed in a data center’ that Google refers to. I can’t remember the last time I saw a European UPS with an output transformer (>8 years?) and we have never needed PDU transformers. Our electrical distribution system can already achieve <3 percent losses between utility transformer and load, even with a VI UPS not using eco-mode.“

His conclusion:

  • If you are in North America „then changing to DC will save you energy as long as you remove all transformers (and that is more resisted than accepted in many situations). They could alternatively choose the European 400V 4-wire and achieve the same goal.“
  • If you are in Europe „then changing to DC will save you nothing as you will have no transformers to remove.“

Source: Open Compute power distribution doesn’t travel well?, by Ian Bitterlin

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