In most jurisdictions ASHRAE 90.1 is used as the building energy standard to be followed as part of their building codes. Data centers were often exempt from 90.1 until 2010 when they were specifically noted to be included. There was push back, as some provisions of 90.1 were deemed too prescriptive, so in 2012 there were changes made specifically for data center adherence. After further criticisms, review and deeper discussions, ASHRAE formed a separate committee dedicated to creating a new energy performance standard specific to data centers. This would eventually become standard 90.4.
ASHRAE released 90.4, the energy standard for data centers, in 2016 yet it seems few are aware that it exists and even fewer are familiar with its implications. Perhaps it will take a few years to catch on, but so far it hasn’t gone viral in the way PUE has, which used kW when initially released in 2007 then updated with annualized kWh in 2011. The purpose of PUE was to measure a data center’s energy performance over time, then aim to make improvements against its own baseline. Instead it has been used as a measuring stick to compare one data center against another, which led to PUE being ousted as easily manipulated mainly based on means of measurement and IT equipment use. However PUE was so widely accepted, no matter how it is used, that ISO made PUE a standard metric for the data center industry in 2016 (ISO/IEC30134).
It should be noted that 90.4 is a design standard while PUE is a performance metric. The use of 90.4 is aimed at the cooling performance calculations since the electrical power losses are removed from the energy analysis. While this is the case, it does go on to detail the maximum electrical losses through the entire electrical power path with differences based on the types of redundancy, N to 2(N+1), and at varying loads.
The mechanical load component (MLC) of 90.4 includes location using the defined 18 climate zones (per ASHRAE Standard 169) as a factor for energy compliance. The updated standard, to be released in 2020, is aiming to bolster the efficiency requirements for data centers even further. These updates include 3 addendums: ‘f’ to set a minimum UPS efficiency; ‘g’ decreases the MLC compliance factor for each climate zone; and ‘h’ focuses on efficiency factors for closets instead of a typical data center.
But this might not matter to the typical designer as 90.4 isn’t seen as the de facto data center design guide for new facilities. That guide has often been the TC9.9 handbooks that include updates on a regular basis. Also most data center owners have been motivated to improve energy efficiency, whether as a benefit to themselves (such as enterprise and hyperscale data centers) or to share savings with clients (colocation).