scope:

FOREWORD

Uninterruptable power supplies (UPSs) have become more efficient since the 2016 publication of this standard and their efficiency curves have become flatter over the full load range. SSPC 90.4 believes it is the responsibility of any standard to encourage the use of equipment meeting the improved performance standards available from manufacturers today. This has resulted in increased efficiency requirements for the UPS segment of the electrical loss component (ELC).

Transformers have also become more efficient as a result of the 2016 publication of transformer efficiency standards by the U.S. Department of Energy (DOE). These standards require compliance only at 35% loading, which is below the design levels of most data center power distribution units (PDUs). PDU manufacturers have recognized this and provide transformers in their equipment that not only meet or exceed the DOE 35% load efficiency minimums but are also more efficient than standard building transformers at higher load levels. The committee believes it is our responsibility to encourage the use of equipment that not only meets legal mandates but also performs well under relevant conditions beyond those that federal authorities prescribe. We have, therefore, adjusted the minimum efficiency (maximum loss) requirements for the information technology equipment (ITE) distribution segment of the ELC to correspond to the loading levels more common to data centers (80% for nonredundant systems and 40% to 45% for redundant systems). The result is increased ITE distribution segment efficiency requirements at load levels above and below the federally prescribed 35% level, as well as adherence to the maximum loss values prescribed in electrical codes for feeders and branch circuit conductors.

The mechanical load component (MLC) has always required calculation of mechanical loads at 25%, 50%, 75%, and 100% of the ITE design load. The ELC required calculations at only 25%, 50%, and 100%, which related to fully redundant, nonredundant, or minimally redundant UPS designs. In order to parallel the MLC, the ELC has now been adjusted to require compliance at all four load levels. This also eliminates the need for distinctions among UPS redundancy configurations. The ELC maximum loss (minimum efficiency) tables have been revised to reflect these changes.

Section 8.2.2 has been removed because of more stringent electrical distribution efficiency requirements in data centers. As a result, the alternative method is no longer available in Standard 90.4.

Lastly, the incoming service segment of the ELC has been eliminated from the ELC calculation. A thorough examination of multiple incoming service designs has revealed that too many combinations of utility transformers (utility or privately owned), voltages, and feeder designs are now being used in data centers for tables to realistically cover all possibilities. Further, the two major elements of the incoming service segment (transformers and feeders) are all covered by federal transformer regulations and electrical code dictums. Therefore, the standard now simply requires adherence to those standards and regulations and restricts the ELC calculation to the UPS and distribution segments where the standard can realistically require designs meeting efficiency levels that can be reasonably achieved with technologies available today.

Note: In this addendum, changes to the current standard are indicated in the text by underlining (for additions) and (for deletions) unless the instructions specifically mention some other means of indicating the changes.