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Addendum sets ASHRAE 90.4 as energy-efficiency standard

The publication of ASHRAE 90.4 in 2016 brought a new set of energy guidelines, but the industry still used Standard 90.1. A new addendum has changed protocol and best practices.

Robert McFarlane
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Published: 07 Oct 2019

In June, ASHRAE approved Addendum "bv" to its Standard 90.1 for 2019 publishing, officially recognizing Standard 90.4 as the energy-efficiency standard for most data centers. Critical data center industry now has a standard for energy-efficient design that recognizes the important issues of reliability and the realities that often exist in specific data center designs.

Standard 90.1 is the Energy Standard for Buildings Except Low-Rise Residential Buildings. It covers virtually every building and is adopted almost everywhere, including locations abroad. Every design professional is familiar with 90.1 because it's not just an Advisory Standard; organizations and data center design engineers must abide by it to gain approval of designs by Code Officials.

This approved Addendum came from the need to streamline standards and make compliance easier. Standards are updated and republished every three years. When the 2010 version of Standard 90.1 removed a data center exemption, it placed potentially onerous requirements on data center designs that could have serious reliability issues. Industry pushback led to the development of ASHRAE Standard 90.4, which was concurrently published in July 2016 along with 90.1-2016. Technical committees specifically wrote ASHRAE 90.4 as a "sister standard" to 90.1. This meant 90.1-2016 did not yet recognize or account for Standard 90.4, resulting in conflicting standards, which did not please Code Officials.

Aligning standards with ASHRAE 90.4

With Addendum "bv," Standard 90.4 is now recognized as the alternate to Standard 90.1 for data centers. Therefore, when jurisdictions adopt 90.1, they also adopt ASHRAE 90.4, relieving the dilemma for Code Officials and allaying the concerns of many data center developers and operators.

It takes most jurisdictions one to three years or more to adopt new standards, but when they do, they will also adopt 90.4-2019, which includes three main updates:

  1. ASHRAE renumbered many parts of 90.4 and revised wording to align it even more closely with 90.1 language. This ensures that 90.4 is now fully compliant with code language and addresses guidelines with concise, prescriptive wording.
  2. Mechanical efficiency requirements are now based entirely on yearly energy calculations and no longer include a power calculation option. The included table values are also aligned with the newest ASHRAE Climate Zones. This ensures that efficiencies are truly based on energy, not on instantaneous design power, which could be set at almost any convenient number.
  3. There are significant improvements to uninterruptible power supply (UPS) technology since the publication of 90.4-2016. This version of the standard addressed both mechanical and electrical infrastructure elements and had mechanical calculations yield the mechanical load component and electrical calculations yield the electric loss component (ELC).

The ELC has three segments: Incoming Electrical Service Segment, the UPS Segment and the ITE Distribution Segment, which, added together, become the ELC. With higher efficiency UPS designs and transformerless operation common in data centers, organizations can achieve UPS efficiencies as high as 98%, even without resorting to economy mode operation.

Further, UPS performance curves have flattened to deliver lower losses and higher efficiencies at the partial load end of the scale, where most redundant systems operate. ASHRAE 90.4 includes updated UPS Segment tables that reflect available hardware and average outputs.

There's not much reason to buy an inefficient UPS anymore, but if admins must use them -- or still have ones installed -- Standard 90.4 helps counteract it with lower loss Incoming and Distribution segments, or to even offset performance with a highly efficient mechanical design.

ASHRAE 90.4 will officially be the applicable standard for data center efficiency within a few years, unless individual states adopt it sooner. Being a performance-based rather than a prescriptive-based standard, it enables designers to utilize the latest and most effective equipment and techniques to achieve energy efficiency in data centers, while also avoiding potential reliability issues. It also gives Code Officials an easy way to verify compliance.

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