The Green Grid, the industry organisation focussed on resource efficiency in data centres, and the global taskforce created to harmonise metrics and measurement protocols for energy efficiency metrics, have announced agreement on measurement guidelines and next steps for three new efficiency metrics; the Green Energy Coefficient (GEC), Energy Reuse Factor (ERF) and Carbon Usage Effectiveness (CUE).
The Data Centre Metrics Coordination Taskforce was set up in 2010 to ensure clarity and consistency in data centre metrics. The Green Grid joined with the US Department of Energy’s Advanced Manufacturing Office and Federal Energy Management Programs, the US EPA Energy Star Program, the EU’s Data Centre Code of Conduct, Japan’s Ministry of Economy, Trade and Industry’s (METI) and Japan’s Green IT Promotion Council (GIPC). In 2011 they published a report entitled “Recommendations for Measuring and Reporting Overall Data Center Efficiency: Version 2 – Measuring PUE at Data Centers”, which completed the guidelines for applying the Power Usage Effectiveness (PUE) metric
The three new metrics were selected by discussion, exercise and trial among the taskforce participants. Joyce Dickerson, Board Member of The Green Grid said “Although there is more work to do, we think this will bring us one step closer to a universally adopted set of metrics, indices and measurement protocols that will have a positive impact on the industry.”
The new metrics are as follows:
Green Energy Coefficient – GEC quantifies the portion of a facility’s energy that comes from green sources:
Carbon Usage Effectiveness – CUE enables an assessment of the total GHG emissions of a data centre relative to its IT energy consumption. CUE is computed as the total carbon dioxide emission equivalents (CO2e) from the energy consumption of the facility divided by the total IT energy consumption.
Full details of the metrics are in Harmonizing Global Metrics for Data Center Energy Efficiency.
Review: The new metrics go a long way in addressing the limitations of the original PUE metric, which only really measures how efficiently the energy consumed is being used. It doesn’t look at the inputs to and outputs from the PUE, nor at the implications in terms of carbon emissions.
The new metrics address the issues, with the CUE focussing directly on emissions, rather than power use. The other metrics go further by looking at the extent of renewable energy input to the equation (GEC) and also whether the ‘wasted’ energy is being employed elsewhere, for instance as a heat source for other facilities (ERF).
The group still has some work to do, including agreeing on an energy efficiency metric that measures the actual IT work output of a data centre compared to energy consumption. That’s not going to be easy. And the ultimate aim must be to pull all these metrics together into one overall absolute calculation of carbon efficiency to work done, if that’s even possible. But every step is improving the tools to assess and compare an important aspect of green IT.