The Power Usage Effectiveness (PUE) metric, which measures how efficiently a data centre uses its power, is set to become an ISO standard within the next year, according to The Green Grid. 

Speaking at The Green Grid EMEA Forum in Brussels, Andr Rouyer, Industry and Government Alliances at Schneider Electric and EMEA Liaison Work Group Chair for The Green Grid, said that standardisation is key to the future success of the metric. 

"It takes time to do this, there is a process to follow. But PUE will be standardised in a few months," he said.

PUE compares the total energy consumed by a data centre to the amount of energy that actually reaches the IT equipment, showing how much is lost to other equipment such as cooling systems. 

While PUE has won support within the IT industry, there has not been a standard way to measure it, meaning that operators can fiddle the figures in their favour if they choose to do so. 

This makes it difficult to compare the energy efficiency of one data centre to another, and also means that the metric cannot be used as a point of reference in any official or legal situation.

Efforts to define a common way of measuring and publishing values for PUE, and get it recognised as a formal standard, have been carried out by a taskforce of global leaders from government, industry and the non-profit sector since 2009.

The taskforce includes The Green Grid, the US Department of Energy, the Environmental Protection Agency's Energy Star Program, the Uptime Institute and the US Building Council, among others.

The most recent version of the taskforce's recommendations was published in May 2011 and is availablehere, and the first plenary session with the ISO (International Standards Organisation) took place last November. 
Now it seems that the efforts of the task force have finally paid off. Once PUE becomes a standard, data centre operators will have to follow a very strict set of rules on how energy consumption is measured. This should, in theory, make data centre PUE ratings stand up to scrutiny.

Rouyer warned that standardisation is not the same as certification. Once the standard is in place, it will be up to an external body like KPMG to set up a certification scheme, whereby data centres are audited and PUE ratings verified. However, standardisation is an important first step.

"In future, rather than referring to our metrics, we can measure PUE according to the ISO standard," said Paolo Bertoldi, Directorate-General of the European Commission's Joint Research Center (JRC).

The news could have significant implications in the UK, where the government's CRC Energy Efficiency Scheme forces large organisations to monitor their emissions and purchase allowances for each tonne of CO2 produced by the energy they use.

Intellect, the UK tech industry's trade association, has been campaigning on behalf of the data centre industry for the government to grant the sector a exemption from the CRC, due to the contribution that it makes to reducing power consumption in other industries. 

The data centre industry hopes to secure a Climate Change Agreement (CCA) that acts as a carrot rather than a stick, offering a £22 rebate for every tonne of carbon saved. However, in order to secure a CCA, the industry needs to provide evidence of the energy intensity of data centre operations.

According to Andrew Donoghue, analyst at 451 Research, the standardisation of PUE could help.

"There isn't an overall way of assessing the energy efficiency of data centres, so if the data centre industry is given a special exemption under a CCA, how would they prove that they were being efficient if there aren't any recognised standards for doing that?" he said.

"At the moment everyone uses PUE all over the shop, so you couldn't form any kind of regulatory mechanism around that. Having a standard would make it more structured."

Donoghue added that CRC is on its last legs anyway, and is likely to be amended or thrown out entirely before long, but said that a PUE standard could help the industry defend itself against any future carbon tax that comes down the pipeline.

"This is all about the industry trying to come up with its own metrics and ways of measuring itself, basically to avoid a top-down approach," said Donoghue. "The last thing they want is a bunch of civil servants to draw up a standard independently and impose it on them."

David Snelling, assistant division manager of Fujitsu's Information Systems Division and vice chair of The Green Grid's EMEA Technical Work Group, added that PUE will probably be the first in a series of metrics to be standardised as a way of dealing with the question of energy and data centre usage. 

"I think the industry has done very well with PUE, but it doesn't address that end carbon use or the total energy use issue," said Snelling.

"PUE is the right metric for the right time, but there is also a wider sustainability issue that we're looking at, and the metrics about carbon usage (CUE) and water usage (WUE) start to capture that forward-looking attitude."

Last week, The Green Grid announced three new energy efficiency metrics designed to help data centre owners and operators improve the performance of their facilities. 
The Green Energy Coefficient quantifies the portion of a facility's energy that comes from green sources, the Energy Reuse Factor identifies the portion of energy that is exported for reuse outside of the data centre, and the Carbon Usage Effectiveness metric enables an assessment of the total greenhouse gas emissions of a data centre relative to its IT energy consumption.

The Green Grid said the new metrics bring the industry one step closer to a universally adopted set of metrics, indices, and measurement protocols.