An FAQ About Green Data Centers

How can I get more out of my data center's cooling and mechanical systems?

Getting back to basics is key, says Dave Kelley, manager of application engineering at Columbus, Ohio-based Liebert Precision Cooling, a division of Emerson Network Power Co. "You have to go back and look at a lot of the things that you didn't worry about 10 years ago."

The biggest potential savings come from airflow optimization. For every kilowatt of load, each rack in a data center requires 100 to 125 cubic feet of cool air per minute. Airflow blockages under the floor or air leaks in the racks can cause substantial losses, says Kelley. The typical response to such problems has been to increase the air conditioning temperature - and that's a big energy-waster.

Simple steps such as implementing hot-aisle/cold-aisle designs, sealing off cable cutouts, inserting blanking plates and clearing underfloor obstructions make a big difference. With greater airflow efficiency, air conditioning output temperatures can be raised.

After performing a computerized airflow analysis of its data centers, San Francisco-based Wells Fargo & Co. did exactly that. "In many data centers, you can hang meat in there, they're so cold. With computerized control and better humidification systems, we've raised the set point of our data centers so we're not overcooling them," says Bob Culver, senior vice president and manager of facilities for Wells Fargo's technology information group.

At Pacific Gas and Electric Co. (PG&E), cable races under the floor were blocking 80% of the airflow. The utility expects to save 15% to 20% in energy costs by rewiring under the floor, redesigning the return-air plenum and carefully choosing and placing perforated tiles in the cold aisles. Choosing the right perforated tile - a seemingly small consideration - can actually make a big difference. "There are better tiles out there that will give you more efficient distribution of cool air," says Jose Argenal, PG&E's data center manager. The changes also allowed PG&E to avoid adding chillers, pumps and piping - and piping is a potential problem in its older, basement-level data center.

Data center managers can also optimize air conditioning systems by using variable-speed fans, says Ken Baker, data center infrastructure technologist at Hewlett-Packard Co. "AC runs at 100% duty cycle all the time, and the fans have one speed: on," he says. HP's Dynamic Smart Cooling initiative uses rack-mounted temperature sensors, and variable-speed fans allow the power consumption of air conditioning units to vary with the IT equipment load. Intelligent control circuitry manages both fan speed and temperature settings on air conditoners.

It's relatively easy to retrofit existing fans, Baker says, and the approach has two major benefits. One is that cutting fan speed dramatically reduces energy use. A 10-horsepower fan uses 7,500 watts of power at full speed but just 1,000 watts at half speed, he says. The increased efficiency also allows the temperature of the cool air supply to be automatically raised from the typical 55 degrees Fahrenheit to between 68 and 70 degrees, he says.

"The biggest low-hanging fruit is just turning the thermo­stat up," Baker says. People keep the temperature set too low because they fear that the equipment will overheat after a power interruption before the air conditioning system can get the room temperature back under control. "The truth is that the temperature won't rise that rapidly," Baker says.

Managers of data centers located in colder locales can also save money by designing air conditioning systems that use economizers that take advantage of outside air to cool their facilities during the winter. Wells Fargo implemented such a system in its Minneapolis data center. That technology makes the most sense when designing new data centers.