Words to go: 6 key data center sustainability metrics

When organizations go green in their data center, they will have to measure the facility's efficiency and environmental impact. Use sustainability metrics to get started.

As organizations look to improve sustainability in their data centers, they may have to quantify how a data center uses its resources. Many standards exist to provide data center management and key stakeholders guidance as they roll out their green initiatives, such as LEED, Green Globes and others. But organizations may find themselves overwhelmed with unfamiliar metrics as they look to measure and quantify their environmental impact.

Data center sustainability metrics help managers understand their data centers' energy use and measure ways to become more energy efficient as they design data centers. While there are scores of metrics to consider, become familiar with some of the basics to better understand how to quantify data center sustainability.

Resource effectiveness metrics

Of all the metrics data center managers can use to determine how efficiently they use resources, effectiveness metrics are some of the easiest to understand and quantify. There are metrics to measure the use of resources such as carbon, power and water. Many of these metrics were developed by The Green Grid, an organization that focuses on data center sustainability best practices and measurements.

Power usage effectiveness

The most prominent of all metrics, power usage effectiveness (PUE), is a measure of the energy efficiency of a data center and how well it uses input power. The metric is calculated by dividing the total facility power use by the power used by IT equipment.

The total facility power is the amount the facility uses as a whole, including all assets, cooling systems and lighting. Total power used by IT equipment refers to the power used for storage, networking, controlling and monitoring equipment as well as workstations.

PUE = Total facility power ÷ total power used by IT equipment

Anything not used for computing is attributed to the total facility power category.

Diagram of power usage effectiveness

PUE is expressed as ratio, where a ratio of 1.0 represents a "perfect" PUE. The more the PUE increases from 1.0, the less efficient data center energy efficiency is.

As of 2022 the average PUE was 1.55, according to the Uptime Institute.

Carbon usage effectiveness

Carbon usage effectiveness (CUE) is a metric that determines how well a data center uses carbon resources. The metric is calculated by dividing carbon dioxide emission equivalents (CO2eq) by total IT equipment energy use, usually in kilowatt-hours (kWh).

To calculate CUE, the equation is the following.

CUE = Carbon dioxide emission equivalents caused by data center energy use (CO2eq) ÷ IT equipment energy usage (kWh)

A lower CUE ratio represents more optimal use of carbon.

Water usage effectiveness

Many data centers use water to cool data center infrastructure. Water usage effectiveness (WUE) measures how effective the use of water is in a data center in relation to its energy consumption. It is calculated by dividing data center water consumption in liters (L) by IT equipment energy usage in kWh.

To calculate WUE, the equation is the following.

WUE = Data center water consumption (L) ÷ IT equipment energy usage (kWh)

A lower WUE represents more efficient use of water resources in a data center.

Green energy data center metrics

Data center infrastructure efficiency

Data center infrastructure efficiency (DCiE) is another metric to measure data center energy efficiency, and it is the reciprocal of PUE. The metric is calculated by dividing the power used by IT equipment by the total facility power use. While PUE helps organizations gain an understanding how efficiently a data center uses input power, DCiE measures how much of that input power IT equipment uses compared to all power available to other parts of the facility. A low DCiE could suggest other assets in the data center use too much power, such as lighting and cooling systems.

To calculate DCiE, the equation is the following.

DCiE = Total power used by IT equipment ÷ total facility power × 100% (or 1 ÷ PUE)

Whereas total power used by IT equipment and total facility power is categorized by the same characteristics as the PUE metric.

DCiE is usually represented as a percentage. For example, a PUE of 3.0 would mean a DCiE of one third, or 33%.

The higher the DCiE of a data center, the more energy efficient the data center is, and vice-versa.

Green energy coefficient

The green energy coefficient (GEC) measures how much of a facility's energy comes from green energy sources. The metric is calculated by dividing the amount of green energy consumed by the total energy consumed by data center resources.

To calculate GEC, the equation is the following.

GEC = Green energy used ÷ total energy used

The closer the GEC ratio is to 1.0, the more renewable energy a data center uses.

Energy reuse factor

Energy reuse factor (ERF) is a metric to determine how much a facility reuses compared to the total data center energy. For example, organizations can use the waste heat servers create to generate electricity or use it to heat other parts of the facility.

To calculate ERF, the equation is the following.

ERF = Reused energy ÷ total energy

The closer a data center's ERF ratio is to 1.0, the more effectively it reuses energy.

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