On June 14, 2010, the U.S. Environmental Protection Agency (EPA) announced that stand-alone data centers and buildings that house large data centers can earn the Energy Star label if they are in the top 25 percent of their peers in energy efficiency as measured by power usage effectiveness (PUE).
The EPA designed the Energy Star label to identify and promote energy efficiency. The program supports the underlying policy of optimizing energy use and reducing environmental impacts created by various types of electric use applications. Therefore, the inquiry that leads to Energy Star status should center on the relative improvement achieved in electricity production emissions due to the particular electric application being considered.
Data centers account for more than 1.5 percent of total U.S. electricity consumption at a cost of $4.5 billion annually, according to the EPA, an amount that is expected to double by 2012. It is appropriate that this concentrated energy demand be targeted for efficiency improvements, and the Energy Star label could provide a simple way for data center developers and tenants to distinguish good facilities from bad.
An important opportunity was missed, however, because PUE simply is the wrong metric to use in this application. To understand why, it is necessary to understand how electric energy is generated and distributed and how the PUE calculation works in practice.
Electric distribution is a hub-and-spoke system. Energy is generated at power plants and distributed to end-users via a complex network referred to as the "grid." There is an electric distribution substation at each power plant where energy is transmitted between the power plant and the grid. Electricity can travel down a wire in either direction, so a power plant substation is the confluence of energy from that particular power plant as well as all the other power plants connected to the grid. In fact, power plant substations are the only places where onsite generation and the grid come together.