High density data centers can improve their power usage efficiency with judicious audits that quantify power usage effectiveness (PUE). Knowledge of PEU will help facility managers reduce costs, says James McEnteggart of Primary Integration Solutions.
The computing function, or useful work of the data center, is measured in kilowatts for point-in-time readings, and in kilowatt-hours for readings done over time; those same measures also apply to energy consumed by the facility infrastructure. Useful work divided by the power needed to produce it is defined as “efficiency.” By measuring the components of power needed for computing, facility managers gain important information on efficiency.
A power audit should focus on electricity used for the following: (1) information technology (IT); (2) removal of heat from the space (HVAC); and (3) electronic losses at transformers and uninterruptible power supply (UPS) systems. First, make a list of equipment used for IT, HVAC, and UPS. Next, trace the path from the utility power source to the computer racks. Then trace the heat transfer path from inside to outside the data center, noting every piece of equipment along that path as well.
Now categorize equipment according to load profile: some equipment consumes energy at a steady rate, whenever it is energized, and regardless of the amount of work performed, while other equipment consumes power according to the amount of work performed. Steady loads may be accurately measured at any point in time. To get an accurate measurement of a variable load, measure it over time in the context of system parameters.
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