Not all steps that improve the energy efficiency of your data center will boost performance in key metrics for measuring "green" data centers. An example: removing fans from servers, which actually has an adverse effect on Power Usage Effectiveness (PUE), the leading metric for data center efficiency.

This dilemma was discussed in a new video from Microsoft featuring Dr. Dileep Bhandarkar, Chief Architect for Microsoft Global Foundation Services, which designs and builds Microsoft's data centers. Bharkander discusses how Microsoft realized it was duplicating effort by using fans in both servers and air handlers in its data center environment. So it designed the latest version of its IT-PAC data center container module as a giant air handler, with airflow management that eliminated the need for fans in the servers.

This strategy reduced overall energy usage, but altered the load distribution within the data center operation. This move had implications for PUE, which compares a facility’s total power usage to the amount of power used by the IT equipment, revealing how much is lost in distribution and conversion.

"If you look at the PUE, the server power went down because I removed the fans," said Bhandarkar. "And the infrastructure power went up. So if I calculate my PUE, it got worse. But if I look at the overall energy efficiency, of how much work I'm getting done for the total power consumed, I end up ahead."

Here's the full video, which runs about 3 minutes.

Microsoft isn't the only data center operator looking at eliminating fans or reducing their energy use. Yahoo is working with vendors to develop custom racks and server trays that move fans to the back of the rack or cabinet, and provide sleeker trays to improve airflow through the equipment.

Facebook recently worked with its vendors to adjust the fan speed of its servers as part of a broader energy efficiency retrofit of one of its Silicon Valley data centers. "These fans are PWM fans – pulse width modulation," explained Jay Park, Facebook's Director of Datacenter Engineering. "They’re typically pre-set by the manufacturer to run at higher speeds. You modulate the fans to a lower speed and you bring less air through the servers."

At least one server vendor has developed racks that embrace this concept. In 2008 SGI (then known as Rackable) introduced CloudRack, which featured server trays with no covers and no fans, using larger fans in the rear door of the rack to cool the equipment. See our video demo of CloudRack for more.