As Heather Clancy wrote yesterday in her "Thinking micro about PUE" piece, a vendor of energy management systems has proposed a much more low-level energy metric tied directly to power and cooling devices that it refers to as Micro PUE. The vendor describes Micro PUE as "the actual amount of energy used to cool 1 kW of IT load through a given cooling unit."
There is a fair amount of interesting commentary in the white paper, but I'm of the opinion that the whole issue simply begs the question. PUE is becoming an accepted metric, because at the macro level, it does actually provide a broadly accepted measurement that, when the appropriate steps are taken to improve a datacenter's energy efficiency, does provide a good starting point for the processes. The problem with starting at the micro level is that you run into "the forest for the trees" problem.
The concept of micro PUE seems to be more of a fine-tuning process. When you've taken a data center through all of the macro level changes that can be made to have a positive impact on PUE you then have the opportunity to take a look at the more micro changes that will have an impact. At that point you can more practically weigh the value of the potential changes at the micro level.
Starting at the micro level and working up rarely works well. And at its worst, the potential for individual PUE ratings on equipment will lead to all sorts of true but eventually valueless ratings. I have to admit my immediate thought was the analogy to performance car parts. Multiple-vendors making verifiable claims of power gains for their particular part, and customers expecting to be able to aggregate those performance gains by purchasing a bevy of performance parts, whose sum is far less than the total of its whole.
While I've oft discussed my concerns about the value of the basic PUE metric, I'm not of the opinion that a narrowly focused metric is the right way to go for the organization looking to make their datacenter more efficient.