– W. Pitt Turner, Executive Director of the Uptime Institute (www.uptimeinstitute.org), says:

The PUE (power usage effectiveness), which is the ratio of total data center energy consumption divided by IT energy consumption, demonstrates the portion of energy at a data center required to support power, cooling, and other non-IT loads at the site. This is a measure of the ‘overhead’ required to support IT.

PUE is useful when the total energy for the data center can be easily identified. It becomes more complicated when a data center is in an office building or when the meters necessary to identify the energy consumption are not available.

The number of racks receiving cooling air outside of the ASHRAE (www.ashrae.org) temperature range for maximum reliable cooling is an easy and powerful metric that establishes the need to take action to resolve cooling issues. This data can be gathered with a hand held infrared temperature meter, with wired or wireless thermometers, or even taken from the IT device data stream. The energy used in cooling data centers is the largest component in a typical data center after the IT energy consumption. Research has found that the cooling energy can be dramatically reduced by properly managing the cooling air flow.

The primary opportunity to reduce energy consumption in a data center lies in the area of IT utilization. Some management teams measure this, most do not. If a company is serious about reducing energy consumption at a data center, looking into IT consumption is essential. Utilizations of 5-10% are common. Often the energy consumption at a data center can be reduced by 15% just be removing IT devices that were replaced in a technology refresh, but were never unplugged.