scope:

FOREWORD

Addendum g lowers the Mechanical Load Component (MLC) values required for compliance in Section 6. The MLC values published in the 2016 edition of Standard 90.4 exceeded the required limits found in ASHRAE/IES Standard 90.1-2010 and in the energy codes for California, Oregon, and Washington, which are more conservative than intended for data centers guided by this standard.

The goal of this addendum is to provide an updated list of MLC values that can be achieved with the use of readily available packaged cooling products, including (a) packaged computer- room air conditioners with indirect evaporative cooling (IEC) and (b) packaged air-cooled chillers with integrated dry coolers serving packaged computer-room air handlers without air-side economizers. Both technologies are readily available from most of the leading computer-room air-conditioner manufacturers. An IEC unit uses an air-to-air heat exchanger to cool return air from the data center by spraying water on the outside of the heat exchanger and drawing outdoor air (scavenger air) across the outside of the heat exchanger. The outdoor air does not mix with the recirculated data center air. No outdoor air or humidity is introduced into the data center, which eliminates any air quality or humidity control issues associated with an air-side economizer. A DX coil handles any load that cannot be handled by the indirect evaporative air cooler.

The MLC values proposed herein are still conservative. Our analysis has shown that they can be achieved with or without the use of an air-side economizer and in keeping with ASHRAE TC 9.9 recommended thermal guidelines.

This addendum also removes the Design MLC compliance path from Section 6 in favor of a more accurate Maximum Annualized MLC calculation. Design MLC was intended only as an interim provision to be used as the necessary tools and techniques for calculating Annualized MLC were being developed. The Annualized MLC technique is detailed in this addendum.

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.