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What is Power Usage Effectiveness (PUE)?

Power Usage Effectiveness (PUE) is a calculation used to measure data centre energy efficiency. Introduced in 2007 and endorsed by The Green Grid, PUE has become a global standard for data centre energy management. Essentially, PUE helps data centres optimise their energy consumption by comparing the total facility energy to the IT equipment energy usage.

How to calculate PUE in data centres

To calculate PUE at your data centre, a company must determine two factors:

Their IT load: This includes the energy consumed by all IT equipment, typically measured at power distribution units (PDUs).
Total facility energy consumption: This encompasses all energy used at the facility, including cooling systems, lighting, and uninterruptible power supplies, usually measured from the utility metre.

The formula for PUE is: Total amount of Energy used / IT equipment energy usage = PUE data centre ratio.

For instance, if a data centre uses 50,000 kWh of total energy and 40,000 kWh of that energy is used by IT equipment, the PUE would be 1.25. A lower PUE indicates better power usage effectiveness, making it a critical metric for assessing how green and efficient a data centre is.

PUE and data centre energy usage

Modern data centers host the critical IT infrastructure that many industries demand. While this IT equipment uses energy, it also generates a lot of heat. As data centres grow and provide more and more processing power, they must also keep their equipment in top condition through effective heat management, cooling, and use of space.

Data centre management can then use PUE to monitor their energy usage. Put simply, if a data centre has a high PUE ratio, it should explore areas to optimize energy consumption. Not only does lowering PUE reduce unnecessary energy spending, but it also contributes to energy saving initiatives, reducing emissions, and providing the best possible customer experience.

What is a good PUE?

A good PUE is one that is close to 1.0. The closer the PUE value is to 1, the more efficient a data centre is in utilising its power solely for IT equipment, without wasting much on other infrastructures. According to the Uptime Institute, the average PUE was about 1.55 in 2022, showing a trend towards more efficient energy use in data centres over the years.

What is DCiE?

Data Centre Infrastructure Efficiency (DCiE) is another method of judging a data centre’s energy usage. It uses the same metrics as PUE but communicates results differently. While PUE is a ratio, DCiE shows the IT load as a percentage of total facility power usage.

How much energy does a data centre use?
Data centers use a lot of energy. This places a responsibility on data centre providers to use less energy where possible. The widespread adoption of real-time business processes, machine learning, and high-speed connectivity means existing energy consumption could increase in the future.

So, with data centers accounting for 1 per cent of the world’s energy consumption, it’s critical to make improvements wherever possible. Both PUE and DCiE are vital tools in tackling unnecessary energy consumption.

Why is DCiE important?

Data centres use a lot of energy. This places a responsibility on data centre providers to use less energy where possible. The widespread adoption of real-time business processes, machine learning, and high-speed connectivity means existing energy consumption could increase in the future.

So, with data centres accounting for 1 per cent of the world’s energy consumption, it’s critical to make improvements wherever possible. Both PUE and DCiE are vital tools in tackling unnecessary energy consumption.

How to calculate PUE and DCiE

To calculate DCiE, you reverse the formula used for PUE. Specifically, you divide the energy consumed by IT equipment by the total energy used by the facility (IT equipment energy / total facility usage = DCiE). For example, if a data centre uses 50,000 kWh of total energy and 40,000 kWh of that is consumed by IT equipment, the DCiE would be calculated as 40,000kWh/50,000kWh x 100 = 80% ). This percentage indicates the proportion of the total energy that is effectively used for IT operations, providing a clear metric to assess infrastructure efficiency.

Including DCiE alongside PUE provides a comprehensive view of a data centre's energy efficiency, offering different perspectives on how effectively energy is being used relative to IT equipment. This dual approach allows data centres to monitor and improve their energy usage more effectively.

How PUE and DCiE help you manage costs

Calculating these metrics is incredibly useful. The higher the PUE calculation, the less efficient a data centre’s energy usage is. Conversely, the closer the PUE is to 1, the more efficient is its usage of energy.

A data centre provider should use PUE to drive continual improvement in energy efficiency and, ultimately, make the data centre more cost-effective.

How to use PUE

Data centre management should regularly measure their PUE. Energy usage can vary with the time of day and season – taking regular measurements helps overcome these fluctuations. Over time, these results show how companies have improved and create future data centre benchmarks.

According to the Uptime Institute, the average PUE value was 1.57 in 2021, meaning data centers used around 60 per cent of their energy consumption on IT equipment. This is a slight improvement to 2020’s score of 1.59 – but a significant gain from the 2007 average score of 2.5. By collecting PUE over time, data centers can prove their efforts to reducing PUE.

How to reduce PUE

Reducing PUE makes a data centre more economical and provides an advantage over less efficient competitors. There are several ways to reduce PUE.

Cold Aisle Containment - Cold aisle containment counts as the largest contributor to the PUE improvement in combination with by pass air flow avoidance (blanking plates, by pass air etc)

Enhanced cooling technology - Much of a data centre’s energy is spent on cooling IT equipment. Whether it’s through enhanced airflow management, advanced cooling systems, or better layout, improving the cooling system can save a great deal of energy.

Make small improvements - Modest improvements add up. Using advanced power supplies, automatic lighting, and removing waste ensures that the whole facility contributes to a lower PUE.

Measure regularly - Above all, a data centre should measure its PUE regularly. Not only does this show when there is an issue, but it also provides a record of efforts and successes.

Why reducing PUE is important

PUE and DCiE demonstrate how efficiently a data centre uses energy. By understanding the amount of energy spent on different processes, companies can assess how to make improvements that save money, improve service, and reduce waste. Our colocation data centers are designed with efficiency in mind.