Why Power Usage Effectiveness (PUE) is Important

August 20, 2015

PUE, or power usage effectiveness, is a term that’s been thrown around a lot in the data center industry, particularly in the last few years. But what exactly is PUE? What makes it important and how does it impact clients whose servers are colocated in a data center?

What is Power Usage Effectiveness (PUE)?


According to TechTarget’s Margaret Rouse, PUE can be defined as the measurement of energy efficiency in the data center. In other words, it is the metric that illustrates how efficiently data centers utilize their power resources.

“PUE is determined by dividing the amount of power entering a data center by the power used to run the computer infrastructure within it,” Rouse explained. “PUE is therefore expressed as a ratio, with overall efficiency improving as the quotient decreases toward 1.”

The scale ranges from 3.0 which is very inefficient to 1.2 which is very efficient. While many data centers may have achieved a PUE of 1.7 or 1.8 others like OVH have attained 1.09 across their datacenters in Europe and North America. That’s as close to perfect as possible.

Why PUE matters to data centers and customers?


Measurements of efficiency such as PUE helps data center owners/operators gauge their overall operations; as well identify opportunities to increase efficiency. But this metric isn’t just useful for an owner – it matters to customers as well.

Power costs can wreak havoc on customer IT budgets. Therefore, it’s important to understand how a data center charges customers for power. The majority of data center providers charge based on actual usage. Charges are measured in kW/hr and include customer equipment and overhead costs for the entire data center. Overhead can include items like running multiple utility feeds, multiple generators, and multiple UPS systems for each and every customer.

A lower PUE rating means a more efficient data center, which in turn means lower operating costs for both the owner/operator and customer. A data center that makes the best use of its power without wasting available resources costs less to maintain and manage, and these savings can be passed on to the customers.

The opposite is true for inefficient facilities – data centers that require more power likely have considerably higher operating costs. In order to support these processes, these providers must charge their customers more for their services.

How can data centers lower their PUE?


There are several strategies data center operators can leverage to lower their PUE rating, including raising the temperature inside the facility. Data Center Journal contributor Jeff Clark noted that many data centers managers maintain much lower temperatures than those recommended by ASHRAE. Raising the temperature to a slightly higher, yet still safe level will not damage machines and can help improve PUE.

In addition, hot/cold aisle containment is also beneficial. This arrangement ensures that the cold air pumped through the facility to cool down machines doesn’t mix with the hot air created by computing equipment. This not only makes cooling a more efficient process, but helps reduce power used by the system as well.

Cooling systems are some of the most energy-intensive systems within a data center and account for as much as 30% of power usage within a facility. For this reason, it’s important to reduce reliance on this system as much as possible with free air cooling. Depending on where the facility is located, the area may have a cooler climate, lending itself well to a free air cooling approach, where outside air is utilized for cooling. Think Alaska!

Clark also recommended examining the power distribution throughout the facility. “Using high-efficiency UPS systems and eliminating unnecessary voltage conversion stages reduces power loss,” Clark explained. “And since this power loss becomes heat, it also reduces the cooling load, meaning even more savings.”

Want more information about PUE?


There are numerous resources available to help data center operators calculate the PUE of their facility, including this white paper from The Green Grid.

Datacenters.com is also a valuable resource. We are the authority on the data center and cloud industry providing valuable insight into the latest technologies, providers and trends. We hope you enjoyed this article “Power Usage Effectiveness: What is PUE?” For more information about PUE or to find low PUE data centers, please contact one of our specialists at (877) 406-2248 or visit the contact us page.



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    PUE, or power usage effectiveness, is a term that’s been thrown around a lot in the data center industry, particularly in the last few years. But what exactly is PUE? What makes it important and how does it impact clients whose servers are colocated in a data center? What is ...