More efficient servers help too. Last spring, Tisdale discovered that his data centres had reached their air-conditioning limit. While he had always imagined that a lack of physical space would be his biggest constraint, he discovered that if he ever lost power, his main problem would be keeping the air-conditioning going. Tisdale had replaced all 22 of his company's Intel servers in its Houston data centre with two dual-core Sun Fire X4200 servers, part of Sun's new Galaxy line. The new servers are more energy-efficient, according to Tisdale. And so when he proposed installing the servers in Atlanta, he justified the purchase by arguing that he could avoid having to buy a bigger air-conditioner, which would have used even more power. Tisdale said that according to company projections, the move will save electricity and reduce heat output by 70 percent to 84 percent.

What's more, there are better ways to use traditional air-conditioning. Neil Rasmussen, CTO and co-founder of American Power Conversion (APC), a vendor of cooling and power management systems for data centres, says CIOs should consider redesigning their air-conditioning systems, particularly as they deploy newer, high-density equipment. "Instead of cooling 100 square feet (9 square metres), it makes sense to look for the hot spots," concurs Vernon Turner, group vice president and general manager of enterprise computing at IDC.

Traditional cooling units "sit off in the corner and try to blow air in the direction of the servers", Rasmussen says. "That's vastly inefficient and a huge waste of power." Rasmussen argues that the most efficient way to cool servers is with a modular approach that brings cooling units closer to each heat source. Meanwhile, he adds, CIOs who manage data centres in colder climates should use air conditioners that have "economizer" modes, which can reduce the power consumption in the dead of winter. Newer air conditioners have compressors, fans and pumps that can slow down or speed up depending on the outside temperature.

A More Efficient Data Centre

Just as ageing cars are not as fuel-efficient as newer models, the majority of the country's data centres are using a lot more energy than they should. A survey of 19 data centres by the consultancy Uptime Institute found that 1.4 kilowatts of power are wasted for every kilowatt of power consumed in computing activities, more than double the expected energy loss.

However, like many people who aren't going to junk their older cars right away, many companies aren't ready to tear out their data centres to build new ones with a more efficient layout. "We haven't reached the point yet where it makes financial sense to rebuild most data centres from scratch," says Rackspace's Froutan. And so for most companies, the journey toward an energy-efficient data centre will be a gradual one.

For NewEnergy Associate's Tisdale, that means retiring ageing servers in one data centre seven at a time and replacing them with more energy-efficient equipment. But redesigning your data centre also means making the most of what you have through server consolidation and, more specifically, the use of virtualization software.

Virtualization is a technology that allows several operating systems to reside on the same server. Froutan says that virtualization will help his data centres make do with fewer servers by allowing them to perform more tasks on one machine. In addition, he says, energy can be saved by deferring lower-priority tasks and performing them at night, when the cost of power can be three times less expensive. IDC's Turner agrees that CIOs need to improve server utilization in order to cut both power and cooling costs. Instead of building one server farm for Web hosting and another for application development, for example, they should use virtualization to share servers for different types of workloads.

Finally, advises APC's Rasmussen, if you are building a new data centre, it's better to design it to accommodate the equipment that you need right now, rather than building facilities designed for what you might eventually need as you grow, as many companies have done. By using a more modular architecture for servers and storage - so capacity can be added when needed - a company can avoid such waste and still be prepared for growth.

How to Start Saving

As CIOs search for more energy-efficient data centre equipment and design, they need to educate themselves about which solutions will work best for them. As part of the information-gathering process, CIOs should establish metrics for power consumption in their data centres and measure how much electricity they consume.

There aren't many generally accepted metrics for keeping tabs on power consumption. But according to Turner, such metrics could include wattage used per square foot, calculated by multiplying the number of servers by the wattage each uses and dividing by the data centre's total square footage. Sun has come up with a method called SWaP, which stands for Space, Wattage and Performance. The company says this method, which lets users calculate the energy consumption and performance of their servers, can be used to measure data centre efficiency. John Fowler, executive VP of the network systems group at Sun, says sophisticated customers are installing power meters at their data centres to get more precise measurements.

It also pays to be an energy-aware buyer. When looking at how much energy a new server might use, "don't just take the vendor's word for it", Fowler says. He suggests having a method for testing the server and its energy use before buying. However, the industry is still working on methods for comparing servers from different vendors in a live environment.

Ultimately, vendors' "eco-friendly" messages may resonate only slightly. NewEnergy's Tisdale, for example, still cares most about maintaining server performance. But he is impressed that new equipment will help him add more computing capability while maintaining current power usage levels. "Like a lot of people," he says, "I'm not interested in turning off the servers."

SIDEBAR: Assess Your Energy Use

The US Department of Energy is developing ways for companies to evaluate how much energy their data centres consume. Go to www.hightech.lbl.gov/IDCTraining/top.html