By using water-side economizer technology in the air conditioning system serving Wells Fargo & Co.’s Minneapolis data centre, Bob Culver generated US$150,000 in free cooling last year.
Culver, vice-president of technology information group facilities, expects to save double that amount this year and up to US$450,000 annually as the bank continues to expand operations in the new, 80,000-square-foot facility.
That’s a 15 per cent overall savings on energy use — not bad for an investment that added $1million (about 1 per cent) 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 centre with cold air, bypassing the chiller. Savings this year will come from shutting off two chillers that currently feed the data centre. Culver expects to add a third chiller in the next few years as the data centre 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 centres 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.
A hard sell
Bramfitt says he meets a lot of resistance from data center managers even though PG&E will reimburse California businesses for up to half the incremental cost, allowing them to recover their costs within one year.
One company that made the move is Hewlett-Packard Co., which recently completed a 50,000-square-foot data centre in Palo Alto, Calif., that includes an economizer.
“They’re saving $1 million a year in power costs, and we presented them with a check for $400,000,” Bramfitt says.
But despite such success stories, “I’m having a hard time convincing the industry to make it happen,” he says. That’s because of IT worries about availability.
“Data centres managers say, ‘Let’s not make this too complicated,'” says Dean Rafferty, president of Michaud Cooley Erickson.
Even Culver wasn’t sold on the idea at first. “We were doubting Thomases. But the engineers did a mock-up, we reviewed it and made a decision to go with it,” he says.
