Carbon Usage Effectiveness (CUE) – a new sustainability metric

Article by Jayabalan Subramanian



The biggest challenge organizations face while implementing energy-efficient and eco-friendly technologies is the difficulty in measuring the energy saved and associated costs. This inherent difficulty in measuring energy efficiency leaves organizations confused as how their solution worked, and how well, if it did?

The Green Grid, a global consortium of organizations working towards going green through technology had come up with a metric for energy efficiency a few years ago that is now a global standard by which data centers measure their energy efficiency. This is called Power Usage Effectiveness (PUE). While organizations are using PUE to better understand the energy efficiency of their data centers, The Green Grid has now come up with a new metric – Carbon Usage Effectiveness (CUE). PUE compares the total amount of energy a data center consumes with the IT equipment inside it, but unlike CUE it does not take into consideration the carbon footprint of a data center’s power source (coal, natural gas, renewable energy). This is important because data centers with an excellent PUE ratio may have high carbon emission levels.

Carbon Usage Effectiveness or CUE takes things further than PUE: it straightaway measures the carbon intensity of an IT deployment, going beyond measuring the energy effectiveness. This is great news, because even data centers in India can now clearly compute the amount of polluting emissions produced by the data center.
The formula for CUE as given out by The Green Grid is as below:

CUE = Total CO2 Emissions caused by the Total Data Center Energy / IT Equipment Energy

The ‘Total CO2 Emissions’ are measured in kilograms of carbon dioxide (kgCO2eq) per kilowatt-hour (kWh) and ‘Total Data Center Energy’ is the amount of power used as measured at the utility meter. If your data center is running completely on power-grid electricity, the region-wise government data will give you the numbers. To get the IT Equipment Energy quantity, add up the entire load associated with the IT equipment such as storage, network equipment, switches, monitors, workstations used to control the data center. Exclude the cooling and lighting equipment. The answer from this basic division is a number that you can compare with the numbers of other data centers and see how you compare.

With Carbon Usage Effectiveness (CUE) and Power Usage Effectiveness (PUE), it is a big thrust in the arm for IT organizations to better understand and improve the sustainability and energy efficiency of their existing data centers. This will help organizations to make smarter decisions on new data center deployments.

To conclude, while I think CUE is a step in the right direction, its limitations must be kept in mind. It only measures the carbon emissions produced by the operations of a data-center, not the environmental footprint for the whole life-cycle of all the equipment (manufacturing, usage, and disposal). That would make the metric even more revealing, but it would also make it extremely difficult to use and would certainly slow down its adoption. What are your views on the adoption of Carbon Usage Effectiveness (CUE)? I would definitely want to know.