Green Grid Starts To Measure Data Centre Carbon Use

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Alongside PUE to measure power efficiency, the Green Grid now has CUE to measure carbon use

A new measurement, CUE, defined by industry alliance The Green Grid, rates the carbon emissions produced by data centres. The Grid, whose PUE metric is widely adopted, also plans to measure water use.

CUE, or carbon usage effectiveness, is closely related to the successful PUE (power usage effectiveness) measure, but allows data centre owners to give a figure to the amount of greehouse gas emissions produced by the energy they use, whether that is produced on-site or by utility companies.

CUE for a cut in carbon emssions…

The Green Grid’s PUE, which has become the standard way to measure how efficiently a data centre uses energy, is a simple ratio which divides the energy the centre uses, by the amount that reaches the IT equipment.

The new measure, CUE, multiplies PUE by the amount of CO2 emitted per unit of energy used, according to a white paper on the Green Grid’s site. CUE can thus go to zero if the data centre is entirely powered by sustainable energy.

“You could argue that CUE is forward looking,” said Larry Vertal, executive director of the Green Grid. While reducing PUE has a direct effect on energy costs and therefore saves money, cutting CUE will not directly save a great deal of money, though this may change as carbon tax laws such as the UK’s CRC Energy Efficiency Scheme start to take effect.

It could also potentially bring some sense to debates about data centres that use dirty power, such as Greenpeace’s recent campaign  asking Facebook to “unfriend” coal. Greenpeace slated Facebook when it emerged that its data centre in Oregon will use coal-fired electricity, even though Facebook pointed out it is one of the most efficient data centres around.

“It was shocking, that [Facebook and Greenpeace] would get so confrontational so quickly,” said Vertal. “I don’t think that Greenpeace is an ignorant organisation.”

Water measure could prove complex

The Green Grid’s measure of water efficiency (WUE), which should be published around Febuary 2011, could prove more complex as water is not actually consumed in industrial processes, but made dirty to a greater or lesser extent.

The measure is likely to focus on water used in the data centre’s cooling systems as well as the water used in generating the power used by the centre. It will also have to take account of the quality of the water when it is returned to the environment – an issue which makers of cooling systems are increasingly aware of.

CUE does not take into account the lifecycle carbon footprint, ie. the carbon used in making the servers and cooling plant used by data centres, just as PUE does not include the energy used in the manufacture and disposal of servers.

All indications are that WUE is likely to leave lifecycle water use to one side, also.

The Green Grid is also working on ways to measure how effectively the computing power of a data centre is used once it has been powered, said Vertal. Heowever,  this would mean comparing how many of the servers’ CPU cycles are actually used on useful work, instead of on peripheral tasks or “overheads” such as scanning for viruses.

The difficulty here is that defining “useful” work will be a subjective decision, said Vertal.

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