Carbon Usage Effectiveness (CUE) is a measuring method developed by The Green Grid to measure data centre sustainability through carbon emissions. CUE is the ratio of total carbon emissions caused by the data centre’s total energy consumption and the power consumption of IT equipment.
CUE = carbon emissions caused by data centre’s total energy/IT equipment energy.
An alternative way to calculate CUE is to multiply the annual data centre PUE by the region's Carbon Emissions Factor as determined by the EPA. The units of CUE are kilograms of carbon dioxide per kilowatt-hour.
CUE = CEF * PUE
The CUE has a value of '0' when the power for the data centre is derived exclusively from sustainable sources. It is therefore particularly useful to know which energy sources are used by data centres. The CUE is determined by the manner in which the data centre procures power and from which source it is derived. STULZ can make the most of the purchased cooling energy by using its efficient chillers at a data centre.
When making use of the electricity grid the CUE can be based on published public data of carbon emissions for the region. When making use of locally produced electricity, in an ideal scenario the actual emissions data from local meters are used, although calculations can also be made using data from a manufacturer or partner.