The Green Grid released the definition and measurement of Power Utilization Effectiveness (“PUE”) in 2006 and its popularity has picked up with increased focus by all stakeholders on resource utilization efficiency. It is essentially an efficiency measurement, basically taking the total facility power usage divide by the total IT equipment power utilization over a period of 12 months, meant for use by a facility’s operator/owner to measure the energy efficiency of that particular facility which then can devise plan to improve its energy efficiency.
With the ease of understanding of PUE and its adoption came many different ways of measurement including using instantaneous and non 12 months measurement period and measurement points for the energy consumption on the IT side. The use by facility operators and large data center users have also promoted the use of low PUE to make non data center industry people to use PUE beyond its intended purpose of energy efficiency tool and more as a comparison metric.
Fortunately, The Green Grid has responded with a series of articles and whitepapers and continued to push for use of PUE in a proper and responsible manner.
The International Standards Organization has organized a standards committee comprising of more than a dozen countries under the name ISO/IEC JTC 1/SC 39, and The Green Grid has contributed its PUE work to it.
In April 2016, ISO has published three parts of data centers energy efficiency KPI series.
- ISO/IEC 30134-1 Part 1 of the series which is overview of the entire ISO/IEC 30134 series
- ISO/IEC 30134-2 Part 2, Power Usage Effectiveness (“PUE”)
- ISO/IEC 30134-3. Part 3, Renewable Energy Factor (“REF”)
You can get a copy of the above standards via ISO shop.
There are additional standard under the same series such as the IT Equipment Energy Efficiency for Servers (ITEE), and IT Equipment for Utilization of Servers (ITEU_SV).
The right ways of using PUE and its requisite measurement points are as close to the IT equipment as possible. Most of the quoted PUE figures on industry press and marketing material never stated the PUE category, whereby PUE category 2 is measured at the room level PDU while PUE category 3 is measured in the rack at the in-rack PDU. In addition, for PUE factor that is reported to be under 1.2, it has to be a PUE category 3 type of measurement point. The different categories of PUE are described in ISO/IEC 30134-2.
Furthermore, most of the PUE figures being thrown around are in fact designed PUE or should be denoted as dPUE. The various PUE derivatives including partial PUE (pPUE) and interim PUE (iPUE) are also described in the standard.
Another important factor to consider is that different design and redundancy design and implementation affects the PUE. There is an important note in the ISO/IEC 30134-1 Annex A under the A.2 Data Centre Availability Objectives that discussed this point.
Let me give an example, if there are two data center facilities close to one another, while DC-A reports a PUE category 2 figure of 1.4 and DC-B reports a PUE category 2 figure of 1.5 do not mean DC-A is more superior than DC-B in terms of energy efficiency measures. Besides the factor of actual IT equipment installed in each site and their power consumption, we need to look into the design and redundancy put in by each facility as each may be meant for a different type of client with different redundancy and operations requirements. DC-A may put all the standby chillers on purely standby while DC-B put one of the standby chiller on-line in order to overcome any duty chiller problem, which meant DC-B’s cooling infrastructure will use up more energy. Or DC-A uses 2N UPS with both on economy mode while DC-B uses 2N UPS with both on normal mode under client demand.
PUE as a tool
PUE is a tool and in times to come just one of the tool in a wider tool set to improve the resource usage efficiency of data center facility.
From site selection to design, to selection of equipment, to operational adjustments, to selection and operations of IT equipment; there are multiple ways to effect meaningful resource usage effectiveness.
With the ISO/IEC 30134-2 PUE standard, we should focus on using this and other relevant tools, to correctly measure and then devise plan for energy reduction in a continuous manner.
The ISO/IEC 30134 series will have other relevant data center resource utilization KPIs and so is the rest of the data center community including the Green Grid and other regional/international bodies, we should use it right, we could experiment and suggest improvement to the tools and we should be aware of its limitations such as using it to compare one facility to another without full understanding of the circumstances towards the PUE figures.