Case Study: Wells Fargo's Free Data Center Cooling System

Computerworld - Bob Culver generated $150,000 in free cooling last year by using water-side economizer technology in the air conditioning system serving Wells Fargo & Co.'s Minneapolis data center. Culver, vice president of technology information group facilities, expects to save double that amount this year and up to $450,000 annually as the bank continues to expand operations in the new, 80,000-square-foot facility. That's a 15% overall savings on energy use  not bad for an investment that added $1million (about 1%) to total construction costs when the facility was built two years ago. "It's one of the better decisions we made," Culver says.

The water-side economizer uses a combination of a cooling tower outside the building and a "shell and tube" heat exchanger inside. For about four months each year, the system can provide water that's sufficiently chilled by outside air to allow the heat exchanger to directly feed Wells Fargo's data center with cold air, bypassing the chiller. Savings this year will come from shutting off two chillers that currently feed the data center. Culver expects to add a third chiller in the next few years as the data center expands to full capacity.

Climate Matters

Free cooling starts to kick in when outside temperatures hit about 55 degrees, and it can bypass the chillers when temperatures drop to about 35 degrees, says John Smith, vice president at Michaud Cooley Erickson, a Minneapolis engineering consulting firm that worked on the Wells Fargo project.

Water-side economizers are less appealing in warmer climates, however, and may not fit neatly into existing data centers. "It's somewhat expensive to retrofit," says Culver, who has looked into using the technology at Wells Fargo's other facilities.

Adds Smith: "While it can be done, it does require more mechanical space to contain the equipment, which would probably be difficult to incorporate into an existing facility."

But Wells Fargo does use what's called an air-side economizer in its Roseville, Calif., facility. "An air-side economizer works well in temperatures that wouldn't be low enough to provide free cooling in a chilled-water design," Culver says. But the systems, which directly use outside air to cool a facility, aren't effective in most data centers because it takes more energy to control the humidity level of incoming air than the system saves. It's a good fit in Roseville, Culver says, because humidity control isn't an issue thanks to the moderate climate. The economizer saves energy by reducing chiller loads, and it occasionally allows one of the site's two chillers to be shut down.

In facilities north of the Mason-Dixon Line, economizer technology can save up to two-thirds of cooling system energy costs while extending the life of existing chillers, says Mark Bramfitt, principal program manager at Pacific Gas & Electric Co. Although economizers are fairly common in commercial building designs, they haven't been used much in data centers until recently.