Design/facilities
While the Green Grid has provided very specific and helpful
guidance, some organisations are still debating the finer details, such as whether to include lighting in PUE calculations.
problematic however is a “mine is better than yours” scenario. Such comparisons will necessarily be misleading if you’re not using a common frame of reference. In addition to the time frame in which PUE is measured, there are also variations in terms of the components which are factored into the calculations. While the Green Grid has provided very specific and helpful guidance, some organisations are still debating the finer details, such as whether to include lighting in PUE calculations. Some will say ‘no’, on the basis that lighting isn’t important to the electrical or IT load. Others will say ‘yes’, because in reality the lights need to be on in facility in order for its typical operation. The point is, the resultant figure has more value as a metric to the individual organisation than it does to the company’s peers.
Some of the most impressive PUE scores in the industry are being quoted by large-scale internet players like Google, Microsoft and Yahoo. However, organisations such as these can drive such low PUEs because they have the scale, the uniformity of applications, and also the integration built into their applications. In short, the entire facility and its applications are built for a single purpose. But for most other businesses aspiring to reduce their PUE, the reality is that their infrastructure will not accommodate the level of uniformity and integration required to record a score as low as 1.2. What’s more, factors such as the geographical location of a facility will have a direct
February/March 2011
impact on the PUE. A site in a region with hotter average temperatures will suffer from greater solar loading than one in a temperate climate, for example.
The difference in cooling requirements could be enough to ‘win or lose’ that PUE competition, before you’ve had the chance to explore the efficiencies in place within a data centre. All organisations also need to recognise that at a certain point, the law of diminishing returns determines that their investment into the infrastructure will not net out as a benefit in reduced operating costs.
Put simply, PUE ‘contests’ are typically a distraction from the real business in hand.
With regulations such as the Carbon Reduction Commitment (CRC) in the UK becoming an increasingly important consideration for the data centre manager, the process of making efficiency improvements is an essential one. Here, PUE should play its most important role.
If a business measures its PUE in a consistent way, it has a level against which to judge itself – a critical part of the improvement process.
The need for accurate reporting is growing within the marketplace – so much so that Digital Realty Trust has developed its own measurement tool, which our customers are already using to monitor their PUE. The ready availability of such data will help spur
on energy efficiency initiatives, as the outcomes become more tangible. Recently an end-user offered a real proof point as to the value of PUE in meeting efficiency aspirations. He mentioned to us that he was planning to clean his facility’s roof, as part of a campaign to reduce the data centre’s PUE. He explained that in the years that his facility had been running, the roof had accumulated a large amount of dirt which reduced the reflectivity of the surface. Cleaning the roof increased the reflectivity, which in turn reduced the solar loading of the building and hence the facility had a reduced requirement for cooling.
A couple of months later, he was able to report a demonstrable reduction in PUE - not a major change, but nonetheless noticeable. It goes to show that apparently insignificant actions can make a real difference in reducing energy wastage.
When it comes to reporting PUE, therefore, there’s nothing wrong per se about advertising an efficient data centre. In fact, if that makes the marketplace a vibrant one, with companies working hard to achieve greater efficiencies – all the better. But what we must not leave behind is the core principle that the PUE is a metric which enables individual organisations to gauge their power efficiency and to strive to make improvements. So next time you visit a data centre conference and hear the PUE competitors lining up, step away, and try to remember when you last cleaned the roof at your facility.
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