Continuous Metering and Monitoring of PUE in Data Centers

Overview

The paper explains how to plan permanent PUE metering rather than rely on models or one-off audits, which miss weather and load variation. The steps are choosing a Green Grid reporting level, tracing circuits so every IT and non-IT load is identified, deciding where embedded meters suffice and where new ones are needed, installing meters in a live facility, and aggregating data in a DCIM/EPMS. Levels differ by IT-load meter location: Level 1 at UPS output, Level 2 at PDU output, Level 3 at IT equipment input, for example metered rack PDUs.

Data frequency depends on the level: Level 1 requires monthly measurement while Level 3 requires 15 minutes or less, and 15 minutes is the recommended minimum frequency. Non-IT loads such as air handlers on the UPS output inflate the measured IT load at Level 1 and artificially improve PUE. IT-load metering cost ranges from free with embedded meters to $300 per kW of IT load. Generators are suggested for estimation rather than metering because they are often shared and are not a big PUE driver.

Shared-building cases get detailed treatment. In the panel examples a mostly-data-center panel needs 3 meters (input minus two office breakers) while a mostly-office panel needs 4 (the sum of four CRAH breakers). A shared chiller is apportioned with supply/return temperature sensors and a flow meter on both the main and data center loops, multiplying chiller electrical power by the ratio of data center to chiller heat rejection. Split-core current sensors are less accurate than solid-core but suit live installs; ultrasonic flow meters avoid draining piping but cost far more. The dashboard should show PUE, percent IT load and a subsystem energy breakdown so poor PUE from light loading is not mistaken for poor design.

Key points

1. Level 1 meters IT at UPS output, Level 2 at PDU output, Level 3 at IT equipment input.
2. Level 1 needs monthly data, Level 3 every 15 minutes or less; 15 minutes is the recommended minimum frequency.
3. Non-IT loads on UPS output inflate IT load at Level 1 and flatter PUE.
4. IT-load metering costs from free to $300 per kW of IT load.
5. Panel example: 3 meters for a mostly-data-center panel, 4 for a mostly-office panel.
6. Shared chiller: sensors and flow meters on both loops; chiller power times heat-rejection ratio.
7. Estimate generators rather than metering them.
8. Split-core CTs are less accurate but suit live installs; ultrasonic flow meters are much more expensive.

Using it in design

• In the single-line editor let users place meter nodes tagged by role (utility input, UPS output, PDU output, rack input, mechanical) and derive the achievable Green Grid level automatically.
• Warn when non-IT loads are fed from UPS output while PUE is metered at Level 1; detect double counting when a metered panel feeds another metered panel.
• Flag shared chillers or generators with no apportioning method (ratio, subtract, thermal metering, model).
• Default to 15-minute logging; the dashboard spec includes PUE, % IT load and subsystem breakdown.

Who should read it

Design and operations engineers planning PUE monitoring and meter layouts.

Related standards

• ISO/IEC 30134-2
• EN 50600-4-2
• ASHRAE Datacom Series Book 11

Publication details

Authors

Wendy Torell

Publisher

Schneider Electric

Year

2016

Document number

WP 204

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