"It's extremely energy efficient," says Credit Suisse engineer William Beck.
At the heart of the system: 64 tanks holding 5,000 gallons of water. The water is frozen in these tanks overnight when energy demands are low and electricity is at its cheapest. The ice melts during the day and helps make cold air that eventually circulates throughout the building.
Although traditional air conditioning supplements the system during peak demand, the ice still shaves $1 million a year off Credit Suisse's electricity bill.
"We had almost like a three dimensional win on this," says Beck. "One was the energy cost savings, the other was energy savings and the third was operational efficiency."
What's old is new again. A doctor in Apalachicola, Fla., built an ice making machine in the 1830s. It basically blew air over a bucket of ice, cooling hospital rooms full of patients suffering from malaria. Thousands of ice-based systems are still used around the world.
"The applications range anywhere from small school systems to large commercial buildings," says Todd Coulard, general manager of Trane Energy.
But Credit Suisse's is one of the biggest.
Within a year, a similar system may be available for your own home. A $10,000 residential version is being tried out in Colorado, Arizona and California. It could end up being one of the coolest ways to beat the heat.