Where Does The Power Go?

The biggest consumer of energy in the data center isn't the IT equipment
You'd think that most of the power consumed by data centers is by IT equipment. You'd think that, but you'd be wrong. The accompanying chart shows the typical breakdown.

One of the biggest power hogs is chillers, the outdoor systems that cool water and other refrigerants. For large-scale systems, chiller manufacturers are working on bearingless designs, as the bulk of chiller inefficiency comes in energy lost through friction in the bearings. For smaller systems, technology such as Liebert's Digital Scroll compressor offers substantial savings. The Digital Scroll rapidly turns the compressor on and off, letting it efficiently work from 10% to 100% of its capacity.

Another approach is IBM's Cool Battery, which uses a chemical reaction to "store cold." Substantial savings can come by running chillers at off-peak hours and using the stored energy during peak load times. A deal with the local utility for lower-cost off-peak power goes a long way toward ensuring a good total cost of ownership for the Cool Battery.

The efficiency of uninterruptible power supplies also has changed substantially over the past few years. The inverter circuitry that turns the DC power from batteries into the AC power required by IT equipment draws a base level of power regardless of its load. New designs substantially reduce that base level load as well as the proportional loss under load, moving efficiency from the 80% range to about 95%.

Some UPS systems also have an economy mode, which lets power from the grid feed IT gear directly. These systems also can monitor power consumption, which solves another data center challenge: knowing just how much power you're using.

Regardless of the technology deployed, all of these systems--from chillers to UPS systems to humidifiers to computer room air conditioning units--operate most efficiently when they're working at or very near their rated load. Modular data center designs that let systems either run at load or be turned off will be far more efficient than designs that load systems at some fraction of capacity.

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The Cold Green Facts

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