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256 P P a r t V : a r t V : T h e G r e e n i n g P r o c e s sh e G r e e n i n g P r o c e s s

whereas DCE is defined as

DCE = IT equipment power/total facility power
Total facility power is the power as it is measured at the meter for the datacenter. IT
equipment power is defined as the power needed to manage, process, store, or route data
within the datacenter.

NOTE Total facility power means just the power to the datacenter, not your whole building. Using
the power to the whole building will give you false numbers.
IT equipment power includes the load associated with all the IT equipment, including
the following:
• Computers
• Storage
• Network equipment
• KVM switches
• Monitors
Total facility power means everything that is used to support that equipment, including
the following:
• Uninterrupted power supplies
• PDUs
• Batteries
• Cooling system
These metrics can tell you various information:

• When you can improve your datacenter’s operational efficiency
• How the datacenter compares with competitors
• If datacenter processes are improving with your changes
• Opportunities to repurpose energy for extra IT equipment

These metrics can be used to illustrate how energy is being used in the datacenter. For
example, if the PUE is 4.0, you know that the datacenter demand is three times greater than
the energy needed to power the IT equipment.
You can also use these numbers to calculate how much power a new piece of equipment
will need from the power grid. For instance, if you add a new server that demands 250 watts
of power to run, and that multiplier is 4.0, you know that the utility grid will need to deliver
2000 watts.
DCE is probably even more useful. Using the same example of a 4.0 PUE, the DCE
equivalent is .25. Therefore, we know that IT equipment consumes 25 percent of the power
in the datacenter.