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7: The Need for Standard IT Energy-Use Metrics 123

♦ Compute, network, and storage nodes.
♦ Other miscellaneous component loads such as data center lighting.
The PUE and DCiE provide a way to determine opportunities to

■ Improve a data center’s operational efficiency.
■ Compare a data center with competitive data centers.
■ Assess data center operators’ design and process improvements over time.
■ Repurpose energy for additional IT equipment.

Although both of these metrics are essentially the same, you can use them
to illustrate the energy allocation in the data center differently. For example,
if a PUE is determined to be 3.0, this indicates that the data center demand
is three times greater than the energy necessary to power the IT equipment.
In addition, you can use the ratio as a multiplier for calculating the real
impact of the system’s power demands. For example, if a server demands 500
watts and the PUE for the data center is 3.0, then the power from the utility
grid needed to deliver 500 watts to the server is 1,500 watts. DCiE is quite
ptg
useful as well. A DCiE value of 33 percent (equivalent to a PUE of 3.0) sug-
gests that the IT equipment consumes 33 percent of the power in the data
center.
Total Facility Power is measured at or near the facility utility’s meters to
accurately reflect the power entering the data center. This reading should
represent the total power consumed in the data center. The data center-only
portion of a building utility meter should be measured because power not
intended for consumption in the data center can result in faulty PUE and
DCiE metrics. For example, if a data center is in an office building, total
power drawn from the utility is the sum of the Total Facility Power for the
data center, plus the total power consumed by the nondata center offices.
In such a case, the data center administrator needs to measure or estimate
the amount of power consumed by the nondata center offices. An estimate
will obviously introduce some error into the calculations. IT Equipment
Power will be measured after all power conversion, switching, and condition-
ing is completed and before the IT equipment itself. The most likely meas-
urement point would be at the output of the computer room power
distribution units (PDUs). This measurement should represent the total
power delivered to the computer equipment racks in the data center.
The PUE can range from 1.0 to infinity. Ideally, a PUE value approaching
1.0 would indicate 100 percent-efficiency (that is, all power used by IT