They waited for the hottest months of the season (that is, on the northern hemisphere), but a taskforce led by The Green Grid has finally laid out plans to come to a standard way to measure PUE. They have published their proposal in this white paper. As things stand, this is the proposal for stand alone data centers, not computer rooms integrated into other buildings (ie. offices).

Now you might be confused. Is PUE not a fairly easy metric? And isn't it not widely used already? Yes and yes. However, the problem lies in the details. As you know, PUE is the total energy consumption divided by the energy consumption by IT. The problem is: what is energy consumption anyway? Is it the peak total energy demand, or the peak annual energy? Where do you measure IT consumption? Isn't a processor fan technically part of the cooling infrastructure instead of IT?

Even with these discussions going on, PUE is still a very useful metric. for example, it is great if you use it to compare the performance of your data center this year, compared to the year before. You can immediately determine what the gains are from new equipment or that new lay out you chose. As long as you are consistent in determining your PUE in the same way over and over, nothing really can go wrong.

Where things start to go awry is when you want to compare different data centers with each other. PUE in its current form is just adequate for that. Sure, for PR reasons many companies pride themselves on data centers with PUE's in the 1.2's, but that's just on the surface. Right now, those claims do not mean anything.

And so, here it is: a standard. Actually, four different ways of measuring PUE are proposed, depending on the situation. As a result, you can only compare a PUE1 facility with another PUE1 facility, and not with a PUE0 or PUE3 facility. The reason for this is that some managers prefer to take a snapshot, while others want a very comprehensive measurement over a long period of time, which includes IT workload peaks.

Not only does the taskforce propose to standardise measurement, they also aim at sophisticating the metric itself. For example, PUE as it is now does not discriminate between different power sources. You could start a dedicated wind park the size of Greenland, but your PUE would remain as bad as it was before. Not anymore: they are going to introduce weighing factors.

Later on, the taskforce is planning a version for computer rooms.