Power Usage Effectiveness (PUE)

What is PUE?

Energy efficiency is rapidly becoming a key data centre issue. The more energy efficient the data centre, the lower the on-going operating costs for facilities’ users. In order to aid potential customers to compare the energy efficiency of a Digital Realty Trust data centre to those of other firms that may be considered we have begun to publish the PUE number as a data centre benchmark for each facility that we are building in 2008 going forward.

Power Usage Effectiveness (PUE)

Power Usage Effectiveness (PUE) is a standard developed by The Green Grid™ consortium to provide a clear answer to the primary issue surrounding energy efficiency within the data centre which is how much power is devoted to driving the actual computing/IT components (servers, for example) versus the ancillary support elements such as cooling and lighting. With the rise of computing demands and high density computational environments, the power distribution expressed by either metric is extremely important. The components of the PUE calculation look at the relationship between "Total Facility Power" (TFP) and "IT Equipment Power" (IEP). TFP is measured at the utility meter for the data centre space and includes all of the components required to support the IT load including:

• Power components including UPS systems and PDUs
• Cooling elements such as CRACs and chillers
• Other infrastructure components such as lighting

As might be expected, IEP, or more simply, IT Load, is the sum total of the power used by the facility’s computing components including servers, storage devices and networking equipment. The main difference between these two standards is the placement of each of these elements in their equations and their resulting output.

Calculating PUE

To calculate a facility’s PUE simply divide the Total Facility Power by its IT Equipment Power. Your answer will be a whole number. For example, a PUE score of 3 indicates that the data centre demand is three times greater than the energy necessary to power the IT equipment.

Interpreting PUE

The PUE can range from 1 to infinity. In the case of the PUE, data centre energy efficiency increases the closer the number comes to one which indicates that a greater portion of the power required by the facility is used to drive the IT equipment. Digital Realty Trust's PowerVU is a standard component of the Turn-Key-Datacentre^® and provides graphical displays of your PUE

More on Data Centre Efficiency

Visit the Digital Realty Trust Knowledge Library to view various archived resources including a one-hour recording of a webinar where, our CTO, Jim Smith, discusses the nuances of efficient data centre design.