I received a few inquiries regarding the carbon usage effectiveness (CUE), water usage effectiveness (WUE), and energy reuse effectiveness (ERE) metrics in my last blog. In case you didn’t recognize these metrics, they aren’t something HP thought up, they were developed by the the green grid organization that developed the original PUE metric back in 2007. Don’t feel bad, however, if you never heard of CUE, WUE, or ERE before. The CUE metric was only released in December 2010 and the WUE metric was just recently released last month.
The ERE metric was developed, among other reasons, to measure excess energy reuse separate from PUE. One common misconception is that you can have a PUE < 1.0 by subtracting the reuse of waste heat from your energy usage in PUE. While reusing waste heat is a good thing to do, you are not allowed to count that in the PUE metric. This allows PUE to remain strictly focused on power usage effectiveness by your data center equipment. It makes sense, if you think about it, to introduce a different metric for ERE.
In Australia, the Australian National University (ANU) has had a long standing policy of requiring a large percentage of it’s energy to come from renewable energy sources, even though the local utility in Canberra charges a high premium for renewable energy. This certainly improves the CUE of the ANU supercomputer. Some states, including California, do have regulations which set targets for renewable energy usage by utilities, with the costs being amortized across all consumers. It would be a long public policy debate to discuss which model is more effective in promoting renewable energy usage, so I’ll leave it as kudos to both for doing something.
If you are interested in data center sustainability, besides the green grid website, another highly recommended source of information is the GreenMonk Blog. You can also read more about what HP is doing for global citizenship and the environment, like our purchase of 131 million kw/hours of renewable energy in 2009.