Data Center Continuous (DCC) Ratings: A comparison of DCC ratings, ISO definitions and Uptime requirements

Overview

Under Uptime Tier III/IV the generators are the primary source: they must carry the entire data-centre load and have no limit on run hours. The ISO 8528-1 run-time limits are: COP unlimited at 100 % for a constant load, PRP unlimited only at 70 % average or less, and ESP limited to 200 h/year with 70 % average or less over 24 h. Uptime accepts a manufacturer's certified unlimited-duration capacity, including site-specific ratings via a manufacturer letter (Tier Standard: Topology sec. 3.3).

The ISO Data Centre Power (DCP) rating added in 2018 is stated as not appropriate for Tier III/IV because it references utility availability and prohibits prolonged utility-parallel operation. In the example, four 2,500 kW DCC-rated sets meet a demand that would need five 2,500 kW ISO Prime-rated sets with no run-time limit.

Low load is the second argument: diesel engines should run above 30 % of maximum horsepower to avoid wet-stacking, valve wear and turbo degradation. In an example of five 1.6 MW sets at 36-39 % system load, COP-rated sets run below 30 % of max hp while DCC-rated sets run above it. QSK95-based sets offer ratings up to 3.5 MW (ISO 8528-1). The paper is a manufacturer defending its own rating, so the comparisons rest on Cummins product classes.

Key points

1. Under Uptime Tier III/IV generators are the primary source: they carry the whole load with no run-hour limit.
2. ISO 8528-1: COP unlimited at 100 % constant load; PRP unlimited only at <= 70 % average; ESP 200 h/year with <= 70 % average over 24 h.
3. The 2018 ISO DCP rating is not appropriate for Tier III/IV: it references utility availability and prohibits prolonged parallel operation.
4. Uptime accepts a manufacturer-certified unlimited-duration capacity, including site-specific letters (Tier Standard: Topology sec. 3.3).
5. Four 2,500 kW DCC sets meet demand that would need five 2,500 kW ISO Prime sets.
6. Run above 30 % of maximum hp to avoid wet-stacking, valve wear and turbo degradation.
7. At 36-39 % system load with five 1.6 MW sets, COP-rated sets fall below 30 % while DCC-rated sets stay above.
8. QSK95-based sets offer ratings up to 3.5 MW (ISO 8528-1).

Using it in design

• Give generator catalogue entries a rating table keyed by class {ESP, PRP, COP, DCP, DCC/manufacturer-unlimited} rather than a single kW value.
• For Tier III/IV targets, size N on a rating with unlimited run hours at design load (COP, DCC or a site-specific letter), reject ESP and DCP, and allow PRP only at 70 % average or less.
• Warn when the expected normal load per set is below 30 % of the selected rating, and suggest load-bank provisions or fewer, larger sets.

Who should read it

Electrical engineers selecting the generator rating class and set count for Tier III/IV targeted data centres.

Related standards

• ISO 8528-1
• Uptime Institute Tier Standard: Topology

Publication details

Authors

David Matuseski

Publisher

Cummins

Year

2025

Document number

Bulletin 5600406

Document language

English

Source type

Manufacturer

Access

Free to read

Licence

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

Citation