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Operating Efficiency and Energy Saving

6In data centres as stated above a considerable amount of power is used to provide mechanical services and air-conditioning. This power compared to the actual power used by the IT load is used to measure the operating efficiency of a data centre and is called “power usage effectiveness” PUE. The PUE is an industry accepted ratio for the measurement of the effective usage of electrical power in a Data Centre Facility and is represented by the quotient:
      PUE = Total Facility Power Load /  IT Equipment Power Load
The reciprocal of PUE expressed as a percentage is known as the Data Centre infrastructure Efficiency – DCiE and is represented by the quotient:
                                          DCiE = 1/PUE %
The nearer the PUE is to unity and more efficient data centre is. The table below gives a typical range of PUE values and indicates the considered efficiency level

PUE

DCiE

Level of Efficiency

3.0

33%

Very inefficient

2.5

40%

Inefficient

2.0

50%

Average

1.5

67%

Efficient

1.2

83%

Very efficient


Clearly for large data centres with megawatts of IT load then even very small improvements in PUE can give large reductions in the total power consumed by the data centre. This results in reduced operating costs, energy saving, and a better carbon footprint.
The use of a specialist adviser in this field can often produce cost savings far in excess of the consultancy fee.