Accredited Tier Designer Technical Paper Series: Engine-Generator Ratings

Overview

This technical paper belongs to Uptime Institute's Accredited Tier Designer (ATD) Technical Paper Series. It addresses topics that arose in the 2009 ATD sessions and in questions from industry. Its subject is the Tier consequences of engine-generator ratings. The paper sits behind a registration form, and the information recorded here rests only on the public landing page, so it does not reproduce detailed technical tables.

The paper starts from the core premise of the Tier Standard: the only reliable source of power for a data centre is the engine-generator plant. The utility supply is not treated as reliable in this sense. Which rating a generator is selected at therefore bears directly on the Tier class of the design. The paper restates this premise to clear up interpretation errors that designers commonly make.

The main conclusion concerns which ratings are accepted. For Tier III or IV, only continuous ratings, derated prime ratings or standby ratings with no runtime limitations qualify. Ratings that carry a runtime limit fall outside this scope. This distinction determines whether a generator model in a catalogue can be used for a Tier objective even when it shows the same kVA figure as a qualifying one.

Other topics in the series include the makeup water source, and the topics were shaped by questions from attendees from over 13 countries. The paper's limit is that it focuses on a single subject and is not a comprehensive generator selection guide. It cites ISO 8528-1 and the Uptime Tier Standard: Topology as related references, and a designer needs to read the two together.

Key points

1. Core premise: the only reliable source of power for a data centre is the engine-generator plant.
2. Only continuous ratings, derated prime ratings or standby ratings with no runtime limitations qualify for Tier III or IV.
3. The paper was prompted by interactions at the 2009 Accredited Tier Designer sessions and by industry queries.
4. It is part of the ATD Technical Paper Series, which also covers the makeup water source.
5. Series topics were raised by attendees from over 13 countries.
6. Related references are ISO 8528-1 and the Uptime Tier Standard: Topology.
7. The paper sits behind a registration form; the facts here come from the public page.

Using it in design

• In the generator catalogue, store the ISO 8528 rating type (COP/PRP/LTP/DCC) and runtime limits.
• Add a rule check for a Tier III/IV objective: reject standby (LTP) ratings with runtime limits unless derated.
• Size the generator on the rating that qualifies for the Tier objective.
• Treat the generator as the only reliable source and make fuel and commissioning decisions on that basis.

Who should read it

Electrical engineers designing for Tier III/IV and consultants evaluating generator selection.

Related standards

• ISO 8528-1
• Uptime Tier Standard: Topology

Publication details

Authors

Uptime Institute

Publisher

Uptime Institute

Year

2009

Document number

ATD Technical Paper

Document language

English

Source type

Industry body

Access

Citation only

Licence

Copyright retained; citation only — the publisher’s terms apply to the original document

Citation