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Congress tried and failed again this year to pass energy legislation changing the country's energy policies. But that has not stopped efforts to use energy more efficiently.

NPR's Christopher Joyce traveled to Baltimore to report on an effort to cool buildings with ice.

CHRISTOPHER JOYCE: Veolia Energy is a small fry in the world of energy companies. They don't run big coal or nuclear power plants. Instead, they try to deliver efficiency, basically getting more out of our electricity grid. In downtown Baltimore, they do that with District Cooling. They cool several big buildings from a central plant that cools water with giant tanks of ice.

To see how that works, I took a ride with John Gibson, an engineer with Veolia through downtown Baltimore.

(Soundbite of machinery)

JOYCE: The pipes with the cold water, we're driving over them, right?

Mr. JOHN GIBSON (Regional Vice President, Veolia Energy): We are. There are actually both steam and chilled water pipes along the streets of the city.

JOYCE: The pipes run under the streets, a 10 mile long circuit that connects several buildings. We pull into an alley and park beside a squat brick building. Two domes about 30 feet high sit next to it.

Mr. GIBSON: They fit back behind a little commercial strip in an alleyway, but hardly noticeable from the street itself.

JOYCE: Inside the domes are tanks filled with water. Lots of tubes run through the water carrying a fluid. At night, that fluid is chilled and ice forms around the tubes.

Mr. GIBSON: During the day when we're using the ice to produce cooling for our customers, we run the water over the outside of the ice and melt it, and provide cool water out to the distribution system.

(Soundbite of machinery)

JOYCE: Big pumps push that cold water through pipes and under the streets to hotels, the city convention center, and several government buildings for their air conditioning systems.

Why ice? Well, what ice does is store the cheaper energy that's available at nighttime.

GIBSON: It allows you to make ice at night when electric demand is lower and costs are lower, and then melt that ice during the day to supplement your mechanical refrigeration.

JOYCE: Gibson says his customers don't need to buy their own refrigeration units, and 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 that moves electrons around. By using ice they don't need to use as much electricity during the day.

Dan Delurey heads the Demand Response Smart Grid Coalition.

Mr. DAN DELUREY (President, Demand Response Smart Grid Coalition): The most inefficient time on the electricity system is the peak period. Normally, during a hot summer afternoon, that's when you have the least efficient plants put into service. But also in the physics of transmitting the electricity mean that it's less efficient to do it during that middle of the day peak period.

JOYCE: 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. That loss is less at night.

Delurey also points out that electricity made at night is more likely to come from wind turbines; that's when the wind blows best. This is a way to store wind energy.

Gibson notes that it's not cheap to build all the pipes and pumps for a district cooling system, but it saves money in the long run, especially if you can use existing underground pipes.

Efficiency advocates point out that with no immediate prospect for a tax or a 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.

Christopher Joyce, NPR News.

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