A PUE from the data sheet is not a measurement

Machine room is our new Thursday series: power, cooling, cabling, emergency power and access, each checked against the source. Part 1 starts with the metric that gets a statutory limit next summer.

Section 11(1) of the German Energy Efficiency Act (EnEfG) requires data centres that started operating before 1 July 2026 to achieve a power usage effectiveness of no more than 1.5 from 1 July 2027, "permanently as an annual average" (our translation). From 1 July 2030 the figure is 1.3. New data centres must reach 1.2.

Ask for the PUE and you almost always get a number. Less often do you get an answer to where it comes from.

What the Act means by PUE

The definition in Section 3 No. 15 is more precise than the way the metric is treated day to day. Power usage effectiveness describes (our translation)

"the ratio of the annual energy demand of the entire data centre to the energy demand of the information technology"

within the meaning of EN 50600-4-2. Three words in it carry all the weight: annual, meaning twelve months with summer and winter. Energy, meaning kilowatt hours over time, not kilowatts at one moment. And entire, meaning everything the data centre consumes, including the chiller on the roof.

Four ways to a nice number

None of them is fraud. All of them arise because a number was needed before the measurement existed.

• Rated power instead of consumption. A PUE can be calculated from the nameplates of cooling, UPS and servers. It describes the design, not the operation.
• One day instead of one year. A reading in February, when free cooling does almost all the work, is a snapshot. The annual average includes August.
• The facility side is incomplete. If cooling hangs off the building's main meter instead of the data centre's distribution board, it is missing from the numerator. The PUE drops without anything having become more efficient. In the extreme case it falls below 1, which is physically impossible and means only one thing: a meter is missing.
• The gap is estimated. Where a meter is missing, rated power is inserted. Afterwards the number looks measured, but it is only partly so.

Measurement is already in the Act

Anyone planning to start measuring now is late. Under Section 12(1), data centre operators had to set up an energy or environmental management system by 1 July 2025. Paragraph 2 No. 1 requires within it (our translation)

"continuous measurements of the electrical power and energy demand of the essential components of the data centre"

On top of that comes the annual report under Section 13: by 31 March, for the previous calendar year, with the PUE under EN 50600-4-2 as a mandatory item in Annex 3. The figure for 2026, due by 31 March 2027, is therefore being measured right now, or not.

1.5 or 1.6

The federal government adopted an amendment to the Act on 24 June 2026, and the Bundestag debated it in first reading on 24 September. According to analyses by law firms, the draft provides for 1.6 instead of 1.5 for existing data centres and 1.4 instead of 1.3 from 2030, while new data centres get four years instead of two to reach 1.2. Until promulgation, the 2023 version applies.

For the question of this part, that is secondary. The limit moves by a tenth. Whether the number held against it is measured, no amendment moves.

How isidaten forms the PUE

In the DCIM module, the PUE is built from measured energy: feeds and distribution boards in the numerator, PDU outlets and devices in the denominator. If either side is missing, there is no result but a reason. A value below 1 is not output but reported as an incomplete measurement, and a manually entered value is never overwritten on recalculation. Data centre compliance takes this value into the metrics year and accepts only measured or partly measured values for the report, explicitly not estimated or derived ones. The limits are held as a rulebook by commissioning date and reference date, with law in force and government draft kept separate and labelled. If the actual value is missing, the verdict is "not assessable", never "not affected".

The check question

Which meters is your PUE calculated from, and which cooling consumer is connected to none of them?

If the answer starts with "according to the data sheet", you have a design figure. It is not yet the metric the Act means.

Sources

Energy Efficiency Act (EnEfG), Section 3 No. 15, Section 11(1) and (2), Section 12(1) and (2), Section 13(1), Annex 3 No. 2 f (German). German Bundestag, first reading on 24.09.2026, printed paper 21/8027 (German). Draft values according to CMS (01.07.2026, German). EN 50600-4-2 (in substance, text of the standard protected by copyright).

In the next part: not every server room is a data centre, and what applies below the threshold anyway.