Battle of the UPSs

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A quantitative showdown between DRUPs and Static UPSs


Diesel rotary UPS (DRUPS) systems have found a niche in the data center industry as a backup power source for critical IT and cooling loads.  This technology of combining flywheel (or battery) energy storage with a diesel generator in one unit has been around for a long time.  The basic idea is that when utility power is lost, the flywheel or battery powers the load just long enough (seconds) for the diesel generator to come online to ensure continuous operation of the load.  This is positioned by some as a superior alternative to stand alone Static UPSs (paired with standby generators) more commonly used in data centers today.  Claims are often made that DRUPS is more efficient, uses “40-60% less space”, and is equally scalable as any other modular UPS.  But is this really true?

The answer lies in the assumptions of the analysis, of course.  In this case, these misleading comparisons are apparently based on older UPSs with poor efficiency curves, Static UPSs being saddled with excessive battery runtime, and individual components being compared while ignoring the performance of the larger overall system.  So our “Center of Excellence” engineering team in Singapore responded with their own analysis; an analysis that is quantitative and based on real world conditions with published assumptions for all to see.  This analysis is now available for free in our new White Paper 222, “Diesel Rotary UPS (DRUPS) vs. Static UPS: A Quantitative Comparison for Cooling and IT Applications”.

Don’t have time to read the paper? Like with all of our white papers, you can always just read the exec summary and scan through the tables, figures, and end with the conclusion.  It’s a quick way to get the gist.  For this comparison, however, I can say right here that a Static UPS system (includes gensets, all the switchgear, batteries, thermal buffer tank, etc) in a common “2N” architecture is cheaper, more efficient, and has a lower 10 year TCO (about 7% less) than a comparable DRUPs system.  The Static UPS does, however, take up a bit more space…but is nowhere near the 40% savings claimed by some.  See the paper for all the details.  And we also analyzed the systems in a tri-redundant architecture as well in the Appendix.


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