It has been almost three years since the ASHRAE 90.4 Energy Standard for Data Centers was finalized and went into effect in 2016, yet even today, many in the data center industry are not fully aware of its existence or its implications. Far more people are familiar with The Green Grid power usage effectiveness (PUE) metric, first introduced in 2007, which started the data center industry thinking about the energy efficiency of the physical facility. While originally PUE was based on power measurements (kW) which were snapshots, it was updated in 2011, and based on annualized energy usage (kWh), which reflected a more meaningful efficiency picture under various operating conditions. This snapshot power measurement was one of the loopholes of the original version of PUE metric. Subsequently in 2011, TGG updated the PUE metric to Version 2 (https://bit.ly/2usqKPj).
Its purpose was to help data center operators to baseline and improve their own facility. PUE has been criticized by some since it only covers the energy efficiency of the facility (not the IT systems), however, that was clearly its stated purpose. Nonetheless, its underlying simplicity allowed managers to easily calculate (or guess) a facility’s PUE which drove its widespread adaption. In addition, the PUE metric helped prompt the U.S. EPA to create the Energy Star program for Data Centers which became effective in 2010. This program continues to be a voluntary award program and currently there are 152 Energy Star Certified Data Centers listed at https://bit.ly/1V5Vafa.