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For some years now there have been people claiming DC power distribution systems in data centers were (“would be”?) more efficient than using AC power. Efficiency gains of 25% and more have been claimed. Unfortunately these misleading claims have been based on comparisons to old AC distribution system designs that included hugely inefficient transformers and UPSs. There’s no doubt that such ancient systems still exist out there somewhere. And, for sure, many data centers out there are still horribly inefficient. From our experience, the main reasons for poor data center energy efficiency have been primarily due to inefficient IT power supplies, lack of IT power management policy use, operation at loads well below the design of the system, and, yes, also from the use of inefficient transformer-based PDUs and inefficient UPSs too. But, for many of us, this comparison to old technologies and systems is irrelevant. When researching new car choices, do you compare them to a 1980’s Chrysler Lebaron? The question for project teams designing a new data center today should be how DC compares to today’s modern AC power distribution systems. A quantitative analysis of a 380Vdc distribution system to the most efficient forms of AC distribution (i.e., 415Vac in North America or 400Vac in Europe and Asia) shows that there is, in fact, very little difference between the two. The difference is typically on the order of 1% or less. In fact, if UPSs are operating in “eco-mode”, then the data center’s infrastructure using AC power distribution is actually MORE efficient by about 1%. You can read about this analysis here.
The bottom line from this analysis is that efficiency is not a basis upon which to choose one or the other. There are also other considerations that people think about when making this decision. Which is more reliable? Which costs more? Or which uses less copper? Are there any safety differences? Schneider Electric Chief Innovation Officer, Neil Rasmussen, speaks on many of these topics in this clip