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Easy, isn't it?
In the counter we find the total energy consumption in kWh, which is
multiplied by the CO
2
emissions per kilowatt hour. The denominator, which
comes from the energy that actually reaches the IT equipment is now
eliminated, the kWh are taken out of the equation, and the result is a CO
2
result to which the PUE factor is added (as we know, this must always be
greater than 1). As the inclined mathematician among the readers can easily
see, the energy supply consists entirely of renewable energies and thus 0
grams of CO
2
,
the CUE value is also 0. This is rather unlikely as the equation
also considers the datacentres diesel‐powered emergency generators, or
the petrol‐powered lawn tractor driven by the gardener, who takes care of
the greenspace around the datacentre and maintains the access routes.
CUE is a "sources‐based" factor; in contrast to a "site‐based" factor it takes
the sources of energy into consideration. For example, gas‐fired absorption
cooling is part of the equation, but equally a solar park on the roof of the
datacentre.
CUE is designed to provide a short term metric for measuring CO
2
emissions
at the datacentre; in the long‐term, the aim is to add more detail to the
computation methods. Just as many countries now have mandatory
certification for apartments and houses, the CUE factor should be included
with each Cloud offering in future.
Also, we should take some time to consider how many grams of CO
2
storing
our files on Dropbox, or on Google's Skydrive is causing, to name just a few.
What options to datacentre builders/operators have to optimise their
CUE?
We have already mentioned some things: location, choice of energy
supplier, proactive management of the deployed systems. In the last ten
years, UPS systems or refrigeration units have made enormous progress so
replacing the systems makes sense.
A further possibility for reducing the CUE factor, if renewable energy cannot
be obtained on‐site, is to at least promote the production of renewable
energy elsewhere; this is the approach that, for example, Google has taken.
Trading RECs (Renewable Energy Credits) is another alternative; if there is
