Keeping the waters clean for PUE

The Power Usage Effectivness (PUE) metric is an excellent metric for overall data center efficiency. As a result of standardization and clairifcation of hte metric by The Green Grid, it has become the defacto metric for data center efficiency.


A recent whitepaper, TrendPoint Systems advocates breaking the TotalFacility Power consumption into smaller sub-components and proposes a “Micro PUE” metric.

While the intent (improving overall data center efficiency by focusing on subsystem efficiency) is a good one, creating the term “Micro PUE,” in my opinion, just muddies the waters by giving a new name to something that has already been standardized into the industry lexicon.

As Michael K. Patterson pointed out to me, the original whitepaper by The Green Grid on Power Usage Effectiveness (PUE) has already defined sub-system indicators.

The Cooling Loading Factor (CLF) and Power Loading Factor (PLF) are defined as:

  • Cooling Load Factor (CLF) is the total power consumed by colling equipment (including chillers, cooling towers, computer room air conditioners (CRACs), pumps, etc. divided by the IT Load.

  • Power Load Factor (PLF) is the total power dissipated by the Power Distribution System, including switch gear, uninterruptible power supplies (UPSs), etc. divided by the IT Load.


Expanded PUE.bmp

So with




you get the relationship

Simplified PUE.bmp

Obviously, understanding CLF and PLF are requisite for any improvment plan. And as TrendPoint indicates, tools are available to do this.

While sub-system efficiency is the right engineering approach to improving data center PUE, inventing the new term “micro PUE" just muddies the waters in terms getting to an agreed industry lexicon for discussing key factors affecting data center efficiency.

As a disclaimer, I am the Intel alternate member of the Board of Directors of The Green Grid. These comments reflect my own opinion, and may not reflect those of The Green Grid or Intel.