Just when you thought you had PUE mastered (or had taken some basic power measurements and perhaps done a rough estimate of your data center's efficiency), along come more new metrics. The Green Grid announced the creation of CUE and WUE as part of the 'xUE' family of sustainable metrics.
Carbon Usage Effectiveness, or CUE, was the subject of The Green Grid's white paper #32, which was just released.
So what exactly is CUE, how is it calculated and how will it affect data centers? The CUE calculation is based on annualizing energy use in the underlying PUE formula (Total Data Center Power / Total IT Power), and then multiplying it by the 'Total CO2 Emissions.' In other words, the 'New Green' for the Data Center is CUE=PUE x CEF (Carbon Emissions Factor).
So how is CEF calculated and what does it mean? CEF is based on the 'source' energy, which is based on where your electricity comes from and how it was generated.
According to The Green Grid's CUE White Paper:
'CEF is the carbon emission factor2 (kgCO2eq/kWh) of the site, based on the government's published data3 for the region of operation for that year.'
But wait, there is more. In case you are not confused enough by CUE and CEF, there is WUE. The use of water for cooling has long been ignored in evaluating the efficiency of a data center under the PUE formula. To address this factor, The Green Grid has also announced the Water Usage Effectiveness (WUE) metric which is still 'under construction' and is expected in 2011.
What does this mean for the data center designer, operator and customer? Well, while these new metrics are just released and are still works in progress, the possible implications and effects are wide ranging. Clearly, the long-term intent is to not just directly improve the energy efficiency of the data center infrastructure itself, but to try to influence where the data center is located and which fuels the utility is using to provide power to the data centers. Next year, it'll be how much water is used and perhaps its source as well.
This can be seen in the Long Term Goals section of the CUE document:
'One can envision a future scenario where data center location, design, architecture, and infrastructure decisions include PUE, CUE, and other potential metrics as well as the full source energy of delivered, locally produced energy, stored energy, and natural resources.'
Moreover, the white paper ends with the following statement:
'The Green Grid feels that CUE and future xUE metrics will have the same positive impact on the industry as did PUE and sees this as a huge opportunity for the industry to rally around. The Green Grid encourages other industry stakeholders to participate in further developing measurement and reporting guidelines for CUE and other xUE metrics that The Green Grid creates, adopts, and shares with the industry. Moving forward, The Green Grid recommends the use of CUE even though refinement is needed for this metric.'
The Bottom Line
Energy Efficiency and now Sustainability will be part of the growing set of Green Data Center metrics, as the xUE acronym library expands (also adding to marketing buzzwords and boasting rights). Moreover, the inclusion of 'source' energy in this new metric seems to mirror the language of the EPA's Energy Star for Data Center program, which was finalized in June of this year. The Green Grid worked with the EPA, which adopted and modified the original PUE metric to reflect annualized energy in BTUs (instead of power in kilowatts), as part of the Energy Star program's method of efficiency calculation using source energy. While it is impossible to predict if this is an early harbinger of government regulations of the data center industry, it is definitely something to bear watching.
In the meantime, download the white paper and get ready to watch for your CUE.