By ROBERT P. MADER of CONTRACTOR’s staff
NASHVILLE, TENN. — Back in 1973, Nashville Machine Co. built the Nashville district energy plant. It was the first job for young Assistant Project Manager John B. Coben. Today that plant is dying from old age.
This year Coben, now vice president of Nashville Machine, is finishing up the new district energy plant — seven months ahead of schedule — a block away from the old one. The new plant will provide 23,000 tons of cooling and 260,000 lb. per hour of steam generation to heat and cool 39 downtown buildings. Nashville Machine’s portion of the $48 million project is $38 million, so the firm acted as the construction manager and general contractor as well as the mechanical contractor.
Nashville Machine won the contract from Constellation Energy in Baltimore, which entered into a contract with the Metropolitan Government of Nashville and Davidson County to build and operate the plant. Constellation Energy will operate the plant for 15 years with options for three additional five-year extensions. Metro Nashville will retain ownership of the plant.
The old plant burned garbage to produce steam and chilled water. It caught fire several years ago and, while it was damaged, the plant was still operational. The fire galvanized everybody in authority in Nashville to get the plant replaced. Metro Nashville spent a year interviewing energy service firms before picking Constellation Energy.
“This new district energy plant will replace the aging waste-to-energy facility, which originally went into operation in 1973,” Mayor Bill Purcell said in 2002. “When done years ago, our community leaders had vision. Now we are creating a new vision for district energy downtown that will be able to work alongside exciting redevelopment plans underway for downtown.”
The new plant will save Nashville about $66.9 million by 2014, lower heating and cooling costs for downtown customers, and cost taxpayers nothing since it will be financed by revenue bonds and supported only by revenues from the sale of chilled water and steam, said David Manning, Nashville’s finance director.
“They were spending huge sums to keep the old plant going,” Coben said.
The energy plant serves the Tennessee State Capitol; Metro’s Courthouse; Adelphia Stadium, home of NFL’s Tennessee Titans; the Gaylord Entertainment Center, home of NHL’s Nashville Predators; hotels; privately owned office buildings; and other government offices.
Nashville Machine partnered with consulting engineers Smith Seckman Reid Inc., which has experience in infrastructure and water supply work. Nashville Machine is well known, Coben said, for being the big contractor for big projects, and it negotiated the contract with Constellation Energy.
“It was a very good project for us,” Coben said.
Nashville Machine started construction at the end of 2002 and started firing the plant up after this past Christmas.
The new all-electric plant contains nine 2,600-ton Trane chillers cooled by 18 Baltimore Air Coil 1,300-ton capacity cooling towers. Steam is provided by four gas-fired 67,000 lb. per hour boilers from English Boiler & Tube. The loads were fairly well known, Coben said, and Constellation Energy performed that engineering.
Six 500-hp chilled water pumps move 7,500 gpm each, and five 350-hp condenser water pumps at 10,000 gpm each move water through the cooling towers.
“We hooked this plant up to the existing system with three-quarters of a mile of 42-in. pipe,” Coben noted.
The ductile iron pipe was joined using the Megalug mechanical joint system produced by EBAA Iron Inc. Nashville Machine built the plant by putting the building around the pipe, rather than the pipe inside the building.
“We were able to design-build the project utilizing Smith Seckman Reid as the engineer, but we were able to design the building where we put all of the pipe up as the steel in the building was going up,” Coben said. “So when the building was topped out, all the pipe was in place.”
While Nashville Machine acted as the general contractor, general construction work was performed by R.C. Matthews Co., Nashville. The electrical contractor was Travis Electric.
The job peaked last summer with about 50 workers on site. Nashville Machine has done business with both firms for years, Coben said, and the project was a true partnering with them. The company also enjoyed great cooperation from the city in terms of getting the drawings reviewed and released, plus the weather was good.
The 42-in. pipe extends to the downtown loop and then reduces to smaller diameters to serve the various buildings, Coben explained. The system has proved so popular that it has maxed out, not because of chiller or boiler capacity but because the 42-in. pipe is carrying all the energy it can move. If new buildings wanted to hook up, the city would have to contemplate building a satellite plant, Coben said.