A group of organizations led by The Green Grid has recommended a standard way for data centers to measure their Power Usage Effectiveness, aiming to bring consistency to the metric and make it easier for different facilities to compare their results.Slideshow: Secrets of Successful Data CentersSlideshow: 5 Tools to Prevent Energy Waste in the Data CenterPUE was developed by The Green Grid as a way for operators to measure the efficiency of their data centers. It compares the total energy consumed by a data center to the amount of energy that actually reaches the IT equipment, showing how much is lost to other equipment such as cooling systems.While PUE has won support, there has not been a standard way to measure it, making it difficult for data centers to compare their efficiency. Earlier this year, The Green Grid got together with the U.S. Department of Energy, the Environmental Protection Agency's Energy Star Program, the Uptime Institute, the U.S. Building Council and others to define a common way for calculating PUE.On Thursday they released their recommendations for dedicated data center facilities. They plan to release a second version in the future for data centers that are part of a mixed-use facility such as an office building. "This guidance is meant to help the industry have a common understanding of energy efficiency metrics that can generate dialogue to improve data center efficiencies and reduce energy consumption," the group said in a white paper. They defined four ways of measuring PUE in an effort to encompass a wide range of data centers, including those that don't yet have the capability to accurately measure all their energy consumption. PUE Category 0 is the lowest level, measuring demand based on peak loads during a 12-month period. The measurement is taken at the utility meter. While the metric offers only a snapshot, omitting the potential impact of fluctuating loads, taking consistent Category 0 measurements can still help operators track their energy efficiency, the group said. The most accurate level, PUE Category 3, measures energy consumption using a 12-month total reading taken at the point of connection of the IT devices to the electrical system. It's the most accurate method, the group says, because it removes any impact from losses related to electrical distribution components and non-IT equipment. "The goal is to recommend a consistent and repeatable measurement strategy that allows data center operators to monitor and improve the energy efficiency of their facility," according to the white paper. "A consistent measurement approach will also facilitate communication of PUE among data center owners and operators."