What is PUE?

Power Usage Efficiency (PUE) is a metric used to calculate a data centre's energy efficiency. Data centres require a lot of energy to run, so ensuring your data centre's PUE score is low is crucial. The Green Grid created PUE in 2007, which has since become a global standard for measuring energy efficiency for data centres.

The idea is simple: PUE shows how much incoming power reaches the IT equipment, versus how much is eaten by cooling, power distribution and lighting.

How to calculate PUE

PUE is calculated by dividing the total amount of power entering the power system by the power used to run the I.T. equipment in the data system.

Total power entering / Power used to run I.T. equipment = PUE

For example, if a data centre draws 50,000 kWh in total and the IT equipment uses 40,000 kWh, the PUE is 1.25. The remaining 10,000 kWh is going on overheads such as cooling. A theoretically perfect facility would score exactly 1.0, meaning every watt entering the building reaches the servers. In practice that's unattainable, since cooling and distribution always take a share.

What is DCIE?

DCiE (Data Centre Infrastructure Efficiency) is the reciprocal of PUE, but expressed as a percentage rather than a ratio. The formula for DCIE is 1/PUE X 100. The higher the DCIE the more efficient the data centre. E.g. A PUE of 1.2 would mean a DCIE of 83% which is very efficient.

What is classed as a 'good' PUE score?

The closer to 1.0, the better. Industry surveys have put the global average PUE around 1.55 to 1.6 in recent years, a figure that has improved only slowly since the mid-2010s. Hyperscale operators such as the big cloud providers report fleet averages nearer 1.1, which shows what modern design can achieve. If your facility sits above the average, there's usually meaningful money on the table.

Regulation is moving too. The EU's revised Energy Efficiency Directive has introduced mandatory energy reporting for data centres. Some European countries have gone further and set PUE ceilings for new facilities. Germany, for instance, requires new builds to meet stringent PUE limits. UK requirements differ, but the direction of travel is clear. Efficiency reporting is becoming a condition of operating, not a nice-to-have. UK operators serving EU customers may also find the standards reach them through contracts, whatever domestic rules say.

How to reduce PUE / DCIE

Reducing a data centre can be difficult. However, reducing your PUE score can reduce costs and improve the company's carbon footprint. You can reduce your PUE score by:

  • Improving cooling systems—Data centres require cooling systems to prevent overheating. However, refrigerant-based cooling systems use a large amount of energy. Improving cooling systems or reducing your reliance on them can help decrease PUE.
  • Virtualise Servers - Having virtualised servers means they can run their own workloads, which saves space and reduces energy consumption.
  • Replace inefficient equipment - The quality of I.T. equipment deteriorates over time. Checking for inefficient equipment and replacing it with more energy-efficient equipment can help decrease your PUE.
  • Use an energy-efficient UPS (Uninterruptible Power Supply) - Using a UPS will reduce the power supply's run time, decreasing PUE scores.

Advantages of PUE / DCIE

  • Allows for repeat calculations - You can calculate the data centre's PUE / DCIE before and after making changes to your energy consumption and see how the changes affect your PUE / DCIE scores.
  • PUE can pair up with DCIM software - DCIM software can automatically calculate your PUE / DCIE scores in real-time and then transfer this data into reports for you to analyse.
  • Using PUE for marketing - By having a good PUE score you can look more desirable to customers. Tackling climate change and keeping your carbon footprint low has become a priority for many businesses.

Disadvantages of PUE / DCIE

  • Calculating the accurate total amount of power - The total power running through the data centre significantly affects your PUE. Therefore, if your total power measurements are even slightly off, this can affect your PUE score and give inaccurate results.
  • PUE does not include consumption at the rack level - Since PUE cannot measure the data centre's usage at the rack level, the overall PUE score will be slightly inaccurate without this usage.
  • Not always effective for marketing - PUE does not account for idle software, or take the efficiency of how the IT equipment is used into account.

If you have any queries about PUE or would like help lowering your energy costs, contact us on 0161 521 3400 or email us at Info@purelyenergy.co.uk. Alternatively, get a quote.

If there are any suggestions or questions - Please get in touch with us.