# Power Usage Effectiveness (PUE) and Data Centre Infrastructure Efficiency (DCiE)

Power Usage Effectiveness (PUE) and Data Centre Infrastructure Efficiency are measures of the energy efficiency of a data centre.

Although they are essentially the same, they are used to illustrate efficiency differently.

They compare the amount of energy used to power I.T Equipment (which makes a data centre money) with the energy powering supporting devices such as switches, UPS, A/C etc (operational costs). Therefore PUE is expressed as a ratio while DCiE is expressed as a percentage.

I.T Equipment Power includes profit making aspects such as: Servers, Storage and Comms Equipment.

While other operational costs include supporting requirements such as: routing and switching, UPS, Cooling, Fire suppressant etc.

How to Calculate the PUE
Equation:
PUE = Total Facility Power/I.T Equipment Power

Steps:
1. Take a baseline measurement at the data centre’s utility meter. This will provide the total amount of energy being used by the data centre.

2. Take a reading of the power used by I.T equipment after power conversion, switching and other processing. Ideally this will be a measurement of the power going to the server racks. In many cases this can be read from the Power Distribution Units (PDUs) in the suites.

3. Divide the total power input (1) with the I.T Equipment Power (2). As the resulting figure approaches 1.0, the data centre becomes more efficient.

How to Calculate DCiE
Once PUE is calculated, DCiE is easily found using the equation below.

Equation:
DCiE = (1/PUE)*100