Critical Power Supplies - Facebook-double Critical Power Supplies - Twitter-double Critical Power Supplies - Linkedin-double Critical Power Supplies - Google-plus-double Freephone 24 Hour: 0800 978 8988 Int: +44 (0)1844 340122

How to calculate your PUE to understand and improve your data centre

Published by Lee Kelly on 30 August 2019

Data centres rely on robust and affordable power to ensure best practice. Calculating the energy efficiency of your working environment is a necessary first step for any organisation that wants to reduce power consumption. From cooling and air conditioning through to computing itself, it's important to measure all factors that contribute to your energy costs.

Power Usage Effectiveness (PUE) is a common and widely accepted benchmark that can be used to calculate and align your energy demands with the infrastructure of your data centre. When you calculate PUE effectively, you will develop a better understanding of your energy requirements and be able to improve your energy efficiency.

What is PUE?

PUE is an energy measurement standard for the IT industry proposed by the Green Grid, a non-profit consortium of technology providers and policymakers. Designed alongside its reciprocal, Data Centre Infrastructure Efficiency (DCiE), this standard is applied across the IT sector to ensure accurate energy calculations and maximum energy efficiency.

PUE calculations present a unified efficiency score and repeatable testing framework based on a comparison of IT energy loads with existing energy and infrastructure demands. While PUE and DCiE calculations are nothing more than benchmarks, they can play a pro-active role in determining the overall efficiency and improving the operational capacity of your data centre.

Standards play an important role in this context, with data centres able to compare their raw energy usage with other facilities operating in similar environmental conditions. This reliable data can be highly useful when adopting new technologies, expanding operations, or making architectural decisions.

PUE and DCiE are not the only energy standards used in the IT sector, with The Uptime Institute also adopting and recommending a comprehensive benchmark known as Corporate Average Data Center Efficiency (CADE). Green Grid has also introduced additional benchmarks for data centres, with Data Center Productivity (DCP) and Data Center energy Productivity (DCeP) designed to measure factors of work rather than efficiency thresholds.

How to calculate PUE and DCiE

PUE is the ratio of the amount of energy used by the entire data centre relative to the amount of energy used by IT equipment:

Critical Power Supplies - Computer Control Unit Room

PUE = total energy into a data centre / energy used by IT equipment

DCiE is the ratio of the amount of energy used by IT equipment relative to the amount of energy used by the entire data centre:

DCiE = 1 / PUE

For example, a PUE of 3.0 is the same as a DCiE of 33%, which is deemed to be very inefficient. A PUE of 2.0 is equivalent to a DCiE of 50%, which is deemed to be average. A PUE of 1.2 is the same as a DCiE of 83%, which is deemed to be very efficient.

How to affirm and improve your PUE

1. Develop an efficiency plan and schedule

Critical Power Supplies - Person Writing on White Book

Like everything in life, an accurate PUE calculation demands a solid plan from the outset. You need to develop a realistic testing schedule, with the frequency of each measurement needing to align with the testing technology and overall program. Energy loads can change over time, with automated software measuring systems needing to work on multiple scales. It's important to understand the temporal nature of PUE testing, which is designed as a consistent standard to measure and enable improvements over time.

While you can capture incoming electricity directly from the meter or through the UPS, you need to be consistent in order to get accurate results. While leading technologies such as the Multipower UPS from Riello or the Eaton 93PM Modular UPS enable precise power management and measurements, the exact calculations you need to make will depend on the number of components you have, along with the goals and budget of your data centre.

2. Understand power components and requirements

Most data centres are large and complex beasts, with each facility having its own unique electrical requirements and distribution needs. In order to make sense of the data presented, you need to understand key power components and how they influence the overall power needs of your data centre. Accurate PUE measurements don't happen by accident, you need to understand how power flows through your facility and its assorted components.

Critical components include the transformer, the uninterruptible power supply (UPS), the power distribution unit (PDU), the automatic/static transfer switch (ATS/STS), and the building management software. While a total building management system will give you access to all incoming electricity and component loads, it may be necessary to track energy consumption at the component level with sensors and software products.

3. Measure your power loads

In order to obtain accurate PUE and DCiE measurements, you need to calculate both the total amount of energy used by the data centre and the amount of energy delivered to IT equipment. Dedicated building management software or transformer metering generally provides the most accurate results for the entire data centre, with the output of the ATS/STS also useful in some situations.

In order to track the load of your IT equipment, it's important to measure the output of your UPS or PDU. Leading technologies such as the Multipower UPS from Riello or the Eaton 93PM Modular UPS offer extremely accurate power measurements for modern data centres. If you're purchasing a new UPS, access to a readable front panel or web interface can be extremely valuable.

4. Take action to improve efficiency

Critical Power Supplies - Data center power distribution schematic

Accurate PUE and DCiE calculations are only useful if you take action to improve efficiency over time. There are lots of things you can do to manage your data centre more effectively, from upgrading power and cooling equipment through to changing airflow patterns and adapting building architecture. Generally speaking, newer IT equipment is able to handle greater workloads with reduced power consumption, with technology upgrades one of the simplest ways to improve your PUE score.

When you get it right, a low PUE reading has a number of positive implications. Along with reducing operating expenses and presenting a more efficient operational framework, a low PUE measurement also helps to indicate a cleaner and greener organisation that's ready to tackle the future of data and lead the industry forward with confidence