The number and average size of IT data centres has increased significantly worldwide with a trend towards super large, modular centres with power requirements in excess of 5MW and some as great as 25MW. Because of this rapid growth, data centres are consuming a considerable and growing proportion of the world’s total electricity supply and are set to overtake aviation as a global source of CO2e emissions.

Concern over this relentlessly increasing demand for power, combined with a desire to reduce both environmental impact and cost, has lead to an industry-wide drive to increase efficiency and to reduce energy costs and CO2 emissions. The industry is doing this by improving its power usage effectiveness (PUE).

Between 2007 and 2009, the modal PUE rating for a large sample of data centres moved from more than 2.00 to within the 1.85 -1.90 range. A growing number of data centre operators in temperate climates are driving PUE below 1.5, with Microsoft claiming a PUE of 1.06 for its modular facility in Chicago.

In addition, regions with hot climates, such as the Middle East, with ambient temperatures in excess of 27 degrees centigrade, represent a major PUE challenge typically requiring 3 times the energy for cooling as is needed to run the IT servers/processors. Finally, there are many legacy data centres and even some new ones that still have PUE ratios greater than 1.5.

PUE Boundary Efficiency

The percentage of energy converted into power at a typical coal fired power plant can be as low as 33%, while even the latest combined cycle gas turbine (CCGT) can only achieve an efficiency of 55%. The effect of this inefficiency is best illustrated by the diagram above which shows the impact of centrally generated electricity, with a 50% electrical efficiency, combined with transmission losses of 4%, on a data centre PUE of 2.  If you take into account the losses incurred in both generation and transmission, then what 2OC would call the True PUE is 4.35 (note that true PUE is in effect the total energy utilisation efficiency, not just the electrical power efficiency).

However, a distributed, efficient power generation plant such as 2OC’s iQuadgen®, located adjacent to a data centre, (also shown above) can provide low carbon energy at very high efficiency, with the potential for a much lower True PUE (1.45).