On a sweltering day in Baltimore during some summer in the future, you may find your wastebasket cooling your office.
Not literally, of course. But a local company is exploring the feasibility of installing massive air conditioners to cool clusters of downtown buildings with the energy produced by burning trash.
Some of the city's electricity, and thus air conditioning, is already provided by a waste-burning generator. But Baltimore Thermal Energy Corp., the company that now provides steam to hundreds of downtown buildings for heating and other uses, is talking with potential customers about a "district cooling system" that would be powered mostly by burning garbage.
Such a system -- which would bring new meaning to the term "central air conditioning" -- allows building owners to scrap individual air conditioners mounted on their buildings and plug into a series of big coolers.
The machines -- monstrous devices with their own, 20-foot cooling towers -- work by chilling water to 35 degrees. The water is then pumped through underground pipes into buildings, and then through a series of smaller pipes across which air can be blown. The chilled air is circulated though existing air ducts to cool offices.
The Baltimore plan is in its early stages. But a $50,000, federally funded study performed by Baltimore Thermal last year concludes that a small version of the system could save money for a handful of users and pay for itself within a few years. Eventually the company would like to hook up a big network of downtown buildings.
"We're out there talking to customers and looking for a location," said G. Michael Larkin Jr., vice president of marketing for Baltimore Thermal. If customers and financing can be lined up, a system could be built in three to five years, Larkin said.
Baltimore Thermal has looked at several possibilities, including one that would put the chillers on the garage of the Baltimore Arena. From it would run pipes of cold water and return lines to the G.H. Fallon and Garmatz federal buildings and some nearby commercial office and medical buildings.
A district cooling system was recommended in the long-term development plan for downtown released in June by Mayor Kurt L. Schmoke. But Bruno Rudaitis, an official with the city planning office, said he is skeptical that financing could be put together until the economy and the banking industry both improve. Also, Baltimore Thermal is already busy expanding its steam operations, he said.
"I don't think it would fly right now," Rudaitis said of a district cooling system, adding, "It would be a good idea, especially environmentally."
Larkin said he does not view financing as a problem, because there is private and public money available for such projects.
The company has not gotten to the point of seeking either city or state approval.
"I would say we have a better than 50 percent chance of making something happen in Baltimore," company president Morris O. Hill said.
The plan would be very expensive. A system to cool a few large buildings would cost $20 million, but could be expanded as customers are added to the network.
Half of the cost is in laying the pipe through city streets, Larkin said. The investment would have to be recovered by users of the system.
Most of the power would come from the downtown BRESCO trash-to-energy plant, where Baltimore Thermal gets almost three-quarters of its power, Larkin said.
Several cities already use district cooling systems, including Nashville, Tenn., San Antonio, Texas, Hartford, Conn., and Minneapolis, Minn. Supporters say the systems, when compared with conventional air-conditioning systems, use energy more efficiently, offer better control of environmentally damaging refrigerant emissions, and save users space and money.
"When you have one plant operating at maximum capacity, it's more efficient than having 10 systems going," Larkin said.
Anthony Jacobi, assistant professor of mechanical engineering at Johns Hopkins University, said district cooling systems can be very efficient -- if they are designed and operated correctly.
"The idea is very good. It depends a lot on how you do it," he said.
The systems add an additional step in the air-conditioning process -- cooling a refrigerant and then using it to chill water -- which consumes energy by itself. So does pumping the water through long pipes, Jacobi said.
The systems are also expensive to build and install. And although they may be managed to reduce the release of 'D ozone-eating refrigerants, an accidental spill could be very large, Jacobi said.
And there is the obvious danger of an equipment failure that would leave thousands of downtown workers sweltering in their offices.
Nashville has had only a few brief outages since its system was installed in 1974, said Roger Beckham, plant engineer with Nashville Thermal Transfer Corp., operator of a steam and district cooling system that is powered by burning municipal waste.
The company cools about 35 buildings -- most of the city's major downtown structures -- from a central bank of four air conditioners, each about 40 feet wide, 50 feet long and 25 feet tall, Beckham said. Customers include some private buildings and all municipal, county and state office buildings in the city, which is Tennessee capital.
Outages are prevented by back-up air conditioners and gas and oil boilers that can be switched on quickly, he said.
Rob Skipper, assistant director of general services for the Metropolitan-Davidson County government in Nashville, said the system is far more reliable than the self-contained air conditioners still in some of Nashville's city schools.
"From a mechanical point of view, it's probably one of the best systems. It saves you a lot of maintenance. But I wish they would bring the costs down," Skipper said.
A self-contained system is much cheaper in the first few years of operation, but over time the district-wide plan is probably cheaper because of low maintenance costs, he said.
Carolyn Millunzi, assistant director of the Washington-based International District Heating and Cooling Association, said, "District cooling has seen a lot of growth in the last several years."
Cities that have the systems are expanding them, and others, like Baltimore, are considering installing them, Millunzi said. The big cost, experts say, is finding vacant real estate downtown for the coolers and digging around utility lines and pipes when burying the pipes.
Baltimore Thermal is still comparing various ways of building a system, including the use of chemical air conditioners known as "absorption" coolers, Larkin said. Absorption units are now in place on several buildings downtown, powered by Baltimore Thermal steam.
Larkin said a district cooling system could also use turbine-driven, conventional chillers that would resemble air conditioners powered by the company's steam.
Baltimore Thermal, a regulated utility owned by United Thermal Corp. of New York, now does better than 85 percent of its business in the winter, piping steam to 400 customers for heating.
Expanding its summer cooling business would improve its profitability during the slack months. And it could ease the strain on Baltimore Gas and Electric Co. during its peak months, Larkin said.
A spokesman for BG&E; declined to comment, saying Baltimore Thermal is a "competitor."