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White paperCitation2010

WP#29 - ERE: A Metric for Measuring the Benefit of Reuse Energy From a Data Center

The Green Grid · Mike Patterson, Bill Tschudi et al.

ERE credits sites that hand waste heat to district heating, offices or greenhouses, something PUE has no way to recognise.

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Overview

This 2010 white paper (no. 29) starts from a structural limit of PUE: it counts energy entering the facility and ignores the value of heat leaving it. A data centre that feeds a district heating network, offices or greenhouses can post the same PUE as one that dumps the same heat to the atmosphere. ERE (Energy Reuse Effectiveness) closes that gap by subtracting reused energy from total facility energy before dividing by IT energy.

The formula is ERE = (total facility energy - reused energy) / IT equipment energy. The paper also defines the Energy Reuse Factor (ERF), reused energy as a fraction of total facility energy, and the two are linked by ERE = (1 - ERF) x PUE. With an ERF of 0.2, for instance, ERE comes out at 80 percent of PUE. ERF was later standardised in ISO/IEC 30134-6.

Two boundary rules matter. First, reuse inside the data centre boundary does not count; heat warming an office floor in the same building is credited only if it crosses the boundary. Second, PUE cannot fall below 1.0 but ERE can, because the subtracted term may exceed the IT energy in the denominator. PUE itself stays unchanged: exporting heat does not improve it. The full text requires registration, so this page rests on the publicly summarised definition.

Key points

  1. ERE = (total facility energy - reused energy) / IT equipment energy.
  2. ERF = reused energy / total facility energy; ERE = (1 - ERF) x PUE.
  3. Reuse inside the data centre boundary does not count.
  4. PUE cannot go below 1.0, ERE can.
  5. ERF is standardised in ISO/IEC 30134-6; EN 50600-4-6 and the German EnEfG are related frameworks.

Using it in design

  • Take annual reused kWh from heat-recovery equipment (heat pumps, liquid-cooling return loops) and compute ERF and ERE.
  • Keep PUE separate; never lower PUE for exported heat.
  • Lead with ERF in reports for jurisdictions with heat-reuse mandates, such as the German EnEfG.
  • Where no heat offtaker exists, show explicitly that ERE equals PUE.

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Who should read it

Designers planning heat recovery and investors negotiating with district heating operators.

Related standards

  • ISO/IEC 30134-6
  • EN 50600-4-6
  • German Energy Efficiency Act (EnEfG)

Publication details

Authors
Mike Patterson; Bill Tschudi; Otto VanGeet; Jud Cooley; Dan Azevedo
Publisher
The Green Grid
Year
2010
Document number
WP 29
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

Mike Patterson; Bill Tschudi; Otto VanGeet; Jud Cooley; Dan Azevedo (2010). WP#29 - ERE: A Metric for Measuring the Benefit of Reuse Energy From a Data Center. The Green Grid. WP 29. https://www.thegreengrid.org/en/resources/library-and-tools/242-WP%23-29---ERE%3A-A-Metric-for-Measuring-the-Benefit-of-Reuse-Energy-From-a-Data-Center

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