The hot-aisle containment allowed Oracle to reduce the fan speed in its cooling system by 75 per cent, which reduced the fan's power consumption by 40 per cent, Khattar said. It installed a variable frequency drive to control the fan and got payback for the investment in nine months, he said.

Yahoo tested cold-aisle containment, and then installed a wireless sensor network to monitor temperature and humidity around the room. The sensor network allowed Yahoo to gradually increase the temperature in its data center without creating heat spots that could damage equipment. The set-up can reduce cooling energy costs by 25 per cent, said Christina Page, head of Yahoo's energy and climate strategy.

There are up-front capital costs to consider. Sensor networks cost US$6 to $8 per square foot to implement, said Troy Mitchell, sales director with SynapSense, which sells the sensor equipment. Doing hot-aisle containment in a big, 43,000-square foot data center like Yahoo's would cost US$250,000 to $300,000, he said.

The containment systems must not interfere with sprinkler systems. Yahoo used flame-retardant PVC connected to the racks with "fusible links" that would collapse at 130 degrees Fahrenheit in the event of a fire, allowing the sprinklers to operate, Mitchell said.

Another case study looked at air-side economizing, which is "basically just a fancy name for opening the windows" and using outside air for cooling, Bapat said. The air must be filtered and de-humidified, but in cooler climates like San Francisco it can be used for most of the year, he said.

Dean Nelson of Sun said data centers should consider raising their overall temperatures. Sun tested modular cooling systems on five-year-old servers and they operated without any problems even when aisle temperatures reached 85 degrees Fahrenheit.

"It makes me wonder," he said, "why are we running our cold aisles at 65 degrees?"

Accenture is publishing the results from the case studies on its Web site, along with an overview that compares their effectiveness.