When Enterprise Rent-A-Car completes a move from PCs to thin clients this season, as part of the rollout of a new rental transaction system, it expects to cut internal energy consumption by 5 million kilowatt-hours.

That will save about US$500,000 annually while reducing the company's carbon dioxide emissions by 6.5 million pounds each year, according to Enterprise officials. Energy costs and consumption were considerations when planning for the new system began earlier in the decade. But they have grown in importance for Enterprise -- so much so that the company issued a press release in April to let the public know how its shift to thin clients would help the environment.

That Enterprise would trumpet the environmental benefits of an IT upgrade says something about how going green is now viewed as a potential competitive advantage for companies. And the increasing focus on green computing as a marketing tool is giving new muscle to IT managers looking to make the case for steps such as upgrading to more efficient technologies, virtualizing servers and consolidating systems.

For instance, environmental concerns are reshaping Enterprise's approach to IT well beyond its installation of Hewlett-Packard thin clients. Six months ago, the US-based company set up a committee specifically to evaluate the environmental and energy-usage ramifications of IT purchases.

It also has measured the amount of power consumed by the servers, networking devices and other IT equipment in its main data center. Using a metric developed by The Green Grid, a vendor consortium that focuses on IT energy efficiency, Enterprise found that only 40 per cent of the energy consumed within the data center was being used by IT equipment, as opposed to air handlers, cooling systems and uninterruptible power supplies.

By turning off unused equipment and better managing its cooling processes, the company increased that percentage to 44 per cent. "Just by doing a few small things, we were able to move our energy efficiency up significantly," said Jim Miller, assistant vice president of IT. Now Enterprise is evaluating more extensive, and more expensive, efforts to improve the cooling systems in the data center, he added.

The municipal government in San Francisco is taking an approach similar to the one at Enterprise, as part of an effort to meet an IT energy-efficiency mandate issued by Mayor Gavin Newsom in February.

At this point, San Francisco officials don't even know exactly how much the city spends to power its IT and communications equipment. But that didn't stop Newsom from promising that the government would reduce its IT-related emissions of greenhouse gases by 24 per cent within four years.

Chris Vein, the city's CIO, is currently overseeing a project in which IT staffers are measuring the energy-usage levels of everything with a plug in some municipal buildings, in an effort to develop estimates that could be applied citywide.

Newsom's mandate also calls for Vein to develop a framework for considering the environmental impact of new technologies. One result is that desktop printers are out and network printers are in. The idea, Vein said, is that if workers have to walk down the hall to a printer instead of using one at their desks, they will likely do less printing.

In addition, San Francisco is moving from a three-year refresh cycle on its laptops to a four-year cycle in order to keep them out of landfills for a longer period of time. And Newsom ordered that as of April 1 this year, all new PCs and monitors must have at least a silver rating under the Electronic Product Environmental Assessment Tool standard, with a gold rating being preferred. EPEAT, which was developed by the Green Electronics Council, is used to rate systems on the basis of their energy efficiency and use of environmentally friendly materials.