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The Greening of IT
122 How Companies Can Make a Difference for the Environment

will publish future white papers that provide detailed guidance on using these
metrics. The Green Grid will also continue to collaborate with organizations
such as the EPA, DOE, GIPC, ASHRAE, and SNIA to further its mission of
advancing data center energy efficiency worldwide.

Short-Term Green Grid Approach

The Green Grid recognizes the importance of establishing metrics for data
center efficiency and offers guidance on technologies that claim to improve
performance per watt. Ideally, these metrics and processes can help determine
if the existing data center can be optimized before a new data center is
needed. The two metrics currently in use are PUE and DCiE.
The PUE is defined as follows:
PUE = Total Facility Power / IT Equipment Power
and its reciprocal, the DCiE, is defined as follows:
DCiE = 1/PUE = (IT Equipment Power/Total Facility Power)
× 100%
For these two equations, the Total Facility Power is defined as the power
measured at the utility meter—the power dedicated solely to the data center. ptg
(This is important in mixed-use buildings that house data centers among
other consumers of power.) The IT Equipment Power is defined as the equip-
ment that manages, processes, stores, or routes data within the data center. It
is important to understand the components for the loads in the metrics,
which can be described as follows:

1. IT Equipment Power: This includes the load associated with all
the IT equipment, such as compute, storage, and network equip-
ment, along with supplemental equipment such as KVM switches,
monitors, and workstations or laptops used to monitor or otherwise
control the data center.
2. Total Facility Power: This includes everything that supports the
IT equipment load such as the following:
♦ Power delivery components such as UPS, switch gear, generators,
PDUs, batteries, and distribution losses external to the IT
equipment.
♦ Cooling system components such as chillers, computer room air-
conditioning units (CRACs), direct expansion air handler (DX)
units, pumps, and cooling towers.