Who cares about carbon emissions?

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Why I don’t think the new sustainability metrics from The Green Grid will be widely used.

I like to say that I care about carbon emissions. I’ve replaced all my traditional light bulbs with energy saving bulbs, my fridge has the best energy efficiency rating available, I never leave my TV set on standby during the night, and reducing my carbon emissions makes me feel good.

To be honest, though, what I really like about reducing my energy consumption is reducing my energy cost.  Each time I replace an old device with a new efficient one, I know that I can expect my next energy bill to be lower.

I doubt that the people running the world’s data centers think much differently. In recent years, the energy efficiency metric PUE has attracted a lot of attention as data center managers have strived to improve their efficiency and lower their energy cost.

The misuse of PUE

As PUE is readily available in most data center software solutions and does measure the efficiency, it is often used to promote the greenness and sustainability of a company. That is, however, not a task that the PUE metric is well suited for.

Due to the way PUE is calculated, there are actually ways of improving your PUE score and consuming more energy at the same time. Also, the PUE does not take the source of the power into account. Running your equipment on renewable power does not give you a better PUE than spending energy from coal powered plants.

To address this issue The Green Grid, the organization behind PUE, decided to create a new set of metrics, focusing on the sustainability of data centers.

The core of these metrics is the CUE, Carbon Usage Effectiveness. CUE is calculated as the carbon emissions caused by the total data center energy divided by the energy consumed by the IT equipment in the data centers.

CUE formula

You can improve your CUE in several ways. If you reduce your power consumption by making the data center more efficient, the carbon emissions will be lowered and the CUE improved. In this scenario, the CUE metric adds nothing new to the PUE.

Focus on carbon emission

Another way of improving the CUE is to change the source of energy consumed. If you replace energy from a carbon emitting source renewable power you will improve your CUE as your carbon emissions are lowered.

You are, however, still using the same amount of power, and as the power company charges you for the power used, you will see no cost reduction. On the contrary, power from renewable sources is often more expensive than old-style power.

This leads to the big challenge of CUE and shows why the sustainability metrics are not naturally taking over the popularity of PUE. Where PUE improvements usually are good business, there’s simply no ROI on buying your power at a higher price than needed.

In the current economic climate, investments with no return are scarce, and – just like the rest of us – data center managers think about saving money before saving the world.


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