Keeping downtown Phoenix cool: A look inside the underground water-chilling plant

Did you know a lot of buildings in downtown Phoenix don't have a typical air conditioning unit? Instead, several buildings get their cold air from a network of pipes connected to a trio of water-chilling plants.

Through this non-descript, secure door is a staircase that leads you beneath downtown Phoenix to an underground cooling district. At first glance, it looks like a top secret nuclear weapons lab, but it's not.

"It's basically a big air conditioning system that provides cooling to about 40 buildings in downtown Phoenix," said Jim Lodge of NRG Energy Center.

The plant uses chillers, which are kind of like big refrigerators to create cold water. At night, the system goes into ice-making mode.

"We can convert to ice storage to melt that ice to take the water out to all the individual customers," said Lodge.

Take a look at the video -- a thermal water tank holds hundreds of thousands of gallons of water. It's not bubbling because it's boiling. This water is actually nearly freezing cold.

"We actually make cold water and that cold water is generated by building ice in the evening hours when electricity prices are lower and we melt that ice during the day," explained Lodge. "And that water is pumped through pipes underneath the ground in downtown Phoenix that goes to individual buildings in Phoenix."

The chilled water is delivered to individual buildings through the underground system, providing air conditioning for Chase Field, Talking Stick Resort, the Phoenix Convention Center, along with several hotels, homes and offices in downtown Phoenix, totaling about 12 million square feet.