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The Green Grid looks at how organisations can demonstrate data centre energy efficiency
 An increasing number of organisations and government departments are using The Green Grid’s PUE and DCiE metrics to promote the efficiency of their data centres. In general, this is a very positive trend as it demonstrates that the industry is willing to put forth a level of effort to improve on energy efficiency and challenge others to do the same.
However, interpreting results from individual data centres can be confusing and at times misleading, and comparing different data centres has become challenging. Creating and promoting PUE or DCiE measurement information, while a great first step, actually falls short of what data centre managers need, because there are various ways to calculate results, and too much weight can be put on one-off circumstances. For example, the number doesn’t address when measurements were taken, where they were taken, or how often they were taken.
Know the score
Considering each data centre is different, and because the ability to take ongoing accurate measurements inside each data centres varies so dramatically, The Green Grid has published guidelines and a required process for government departments and organisations alike to follow when determining the PUE or DCiE score for their data centres. This includes a standard nomenclature that will enable organisations to communicate more specific and relevant information about their scores. As a result, the “absolute” reported PUE or DCiE numbers will change, but the granularity will result in a more accurate “apples-to-apples” comparison across different facilities.
To provide a meaningful report of PUE or DCiE, the reporting organisation should provide additional information about the data collection process. The Green Grid has outlined four specific types of information: the ‘manner’ in which the data was collected, the ‘type of equipment’ from which the data was collected, the ‘timeframe’ covered by the reported value, and the ‘frequency’ with which individual data points were collected. This data falls into three levels:
- Level 1 (Basic): The IT equipment is measured at the UPS, total facility power measured at the data centre input, and minimum measurement interval is monthly or weekly
- Level 2 (Intermediate): The IT equipment is measured at the PDU, total facility power measured at the data centre input except for the HVAC, and minimal measurement interval is daily
- Level 3 (Advanced): The IT equipment is measured at the device (server, switch, etc), total facility power is measured at the Data Centre input less shared HVAC plus building lighting, security, etc, and measurements are taken continuously.
This additional information can be provided by adding a subscript to the name of the metric being reported. For example, PUE would be reported and formatted as PUEa,b ,where ‘a’ describes the metering placement level and ‘b’ describes the measurement frequency and averaging period. Similarly, DCiE would be reported as DCiEa,b. For example:
- 0.51 DCiEL1,YM would mean: yearly average DCiE score of 0.51, using data points gathered monthly with a Level 1 meter placement
- 1.8 PUEL2,WC would mean: weekly average PUE score of 1.8, using data points gathered continuously with a Level 2 meter placement.
Results
Once end-users start to use these guidelines, The Green Grid plans to review results that end-users want to communicate to the public by categorising these results into four groups:
1. Unrecognised: This category appears when the reporting organisation does not provide any additional detail as to the means or manner through which the data was collected, the timeframe covered by the result, or the granularity with which individual data points in the result were collected. While The Green Grid applauds any attempt to measure or calculate results, it will not comment on unrecognised, publicly reported figures. Accordingly, The Green Grid places no requirements on, nor has any specific recommendations for, unrecognised results.
2. Reported: The second class of results appears when the reporting organisation has submitted data using the proper nomenclature from The Green Grid and has self-certified using the measurement methodology defined for PUE and DCiE. The Green Grid will not recognise these results and will not provide any additional comment, and reported results that are not ‘Registered’ (see below) will also not be specifically referenced within The Green Grid’s website.
3. Registered: The third class of results falls under the category of “Registered.” To register a result with The Green Grid, the reporting organisation must provide additional data about the result and provide contextual data from The Green Grid’s database. This helps by providing key additional data that The Green Grid will use in commenting on and analysing overall industry performance and data centre energy efficiency trends. One key benefit in registering results is that the government body will receive a registration number if they meet the requirements, and this registration number may be used in any public document to verify that the organisation has met The Green Grid’s requirements. The Green Grid is working to provide a way for reporting bodies to record this data with The Green Grid – most likely a page on The Green Grid’s website. In the meantime, The Green Grid’s site will have the most up-to-date information on specific data elements, which will be refined over time.
4. Certified: The fourth class of results, ‘Certified’, has the most stringent data reporting requirements. In addition to those items required for a result to be ‘Registered’, the reporting organisation will provide contextual data, and any additional data, for third-party validation or certification of results. This additional data will allow organisations to qualify for inclusion in future award or recognition programmes created by The Green Grid. The Green Grid will accept any original source materials or publications necessary to validate the claim.
It’s also important to note that due to the limits of physics, any reports to The Green Grid with PUE measurements less than 1.0 or DCiE measurements greater than 100 per cent will automatically be rejected. It’s impossible for an organisation to be more than 100 per cent efficient using today’s metrics.
Whether a government department wants to report their PUE or DCiE results to The Green Grid according to the Reported, Registered or Certified classifications, this is a step forward for the industry. It provides consistent, apples-to-apples reporting, allows the industry to identify and promote exceptional results, and provides a level of quality assurance for all data centre managers. We hope The Green Grid’s PUE and DCiE reporting guidelines will lead to greater industry adoption of these metrics. |
