Chilled-Out Buildings Save Energy, Money

September 28, 2010

Christopher Joyce

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Mike Ruocco
Inside Veolia Energy's Plant Three in Baltimore, blue pipes carry chilled water that will be sent out to cool nearby buildings. The green pipes carry condensed water that removes heat from the chilling system, and orange pipes carry a refrigerant. The yellow pipes are for a future cooling system.

This year Congress tried and failed -- yet again -- to pass energy legislation to curb global warming. But the death of the climate bill hasn't stopped efforts to use energy more efficiently. In fact, it puts the spotlight back on some rather old-fashioned ways to cut emissions and electricity bills.

Downtown Baltimore is home to an unusual experiment that seems almost quaint -- cooling buildings with ice. It's a service provided by Veolia Energy, a small fry in the world of energy companies. Veolia doesn't run big coal or nuclear power plants -- instead, it tries to deliver "efficiency" -- basically getting more out of the electricity grid.

Veolia does this with a concept called "district cooling," which sends water chilled by ice at a central plant out to several nearby buildings. A nearly 10-mile circuit of cooling pipes connects the downtown buildings, including the convention center, government buildings and hotels, to a squat brick building with two domes about 30-feet high next to it. They're the kind of structures that never catch the eye.

"They fit back behind a little commercial strip in an alleyway, but are hardly noticeable from the street itself," says John Gibson, a vice president at Veolia Energy.

Inside the domes are tanks filled with water. A lot of tubes run through the water tank carrying chilled glycol, a fluid that freezes at a very low temperature -- far below that of regular water. This process runs at night, and ice forms around the tubes.

"During the day, when we are using the ice to produce cooling for customers, we run water over the outside of the ice and melt it and actually provide cool water out to the distribution system," Gibson says.

That's one of two ways they cool water. The other method runs room-temperature glycol through those same iced-over tubes. The glycol is cooled by the ice surrounding the tubes, and the now-cold glycol is used to chill a different water supply that gets piped to refrigeration units in city buildings.

Nighttime Electrical Efficiencies

Why ice? The ice essentially stores the cheaper energy that's available at night.

"It allows you to basically make ice at night, when electrical demand is lower and costs are lower, and then melt that ice during the day to supplement your mechanical refrigeration," Gibson says.

He says his customers don't need to buy their own refrigeration units, so they save about 10 percent on cooling costs by using Veolia's district setup.

Using nighttime electricity also takes the heat off the electricity grid, the national network of power lines and substations. By using ice, Veolia doesn't need to use as much electricity during the day.

Dan Delurey, who heads the Demand Response and Smart Grid Coalition, says the most inefficient time on the electricity system is the peak period during daytime hours.

"Normally during a hot summer afternoon, that's when you have the least efficient plants put into service," he says. "But also the physics of transmitting the electricity mean that it's less efficient to do it during that middle-of-the-day peak period."

In fact, if you put a lump of coal into a power plant, you normally only get one-third of its energy content at the socket in your home -- the rest is lost at switching stations and from overheated power lines. There is less loss at night.

Delurey also points out that electricity made at night is more likely to come from wind turbines because that's when the wind blows best. So ice cooling also functions as a way to store wind energy.

Gibson says it's not cheap to build all of the pipes and pumps for a district cooling system, but it saves money in the long run, especially if existing underground infrastructure can be used.

Efficiency advocates point out that with no immediate prospect for a tax or price on carbon in fossil fuels, off-the-shelf techniques like this -- that get more out of the existing grid -- are looking a lot more attractive. Copyright 2010 National Public Radio. To see more, visit http://www.npr.org/.