Built in 1983, One Logan Square is a 32-story office tower in Center City Philadelphia. The building was recently renovated, and the last remaining need was replacement of the original cooling tower.
“We elected to replace the three-cell cooling tower to improve efficiency and optimize the building’s systems, and while it presented engineering and logistical challenges, we knew it would be worth the investment and that our expert partners would execute the intricate project well,” said Tom Holden, Brandywine Realty Trust’s chief operating engineer at One Logan.
Limbach Co. LLC serviced the building’s entire chiller/boiler system for years. The team quickly realized that the scope and unique challenges of replacing the 2,400-ton cooling tower made the ambitious project a true collaborative process.
“Avoiding downtime on this project was quickly identified as the first concern,” said Christine Batchelor, account manager at Limbach. “But the fact that neither a crane nor helicopter could be used to exchange the cooling towers greatly complicated things.”
“Our team of Joe Carango and Tom Sherwood knew we needed to tap the expertise of Eric Calvitti, director of field operations at our tower subcontractor, Calvitti Co., to have a successful project,” she added.
The restrictive layout of the mechanical space required a six-month design process. Limbach worked with Calvitti to replace the original crossflow cooling tower for a new, CTI-certified Evapco AT Series counterflow tower.
Tim Schmidt, with rep firm Energy Transfer Solutions (ETS), and Adam Radford, global products manager, Evapco, also focused on the need to deliver an unassembled cooling tower with previously selected Cooling Tower Institute (CTI) certification.
“CTI certification was the key on this job because the existing tower was underperforming despite being sized for the full cooling load,” said Radford. “Some of that was due to its age, but tower certification didn’t exist 35 years ago either. Brandywine needed proven and tested technology that would provide 100 percent capacity while also fitting the available space.”
The AT Series towers are available with a 20-by-18-foot box size, which allowed installation of three cooling cells in the penthouse space without requiring any steel rework.
Once the system was on paper, a plan to execute the work needed to be determined. Limbach technicians handled all piping, electrical, and control work, while Calvitti would be in charge of tower construction.
Calvitti’s plan maintained partial cooling capacity throughout the whole process by phasing replacement of the cooling tower cells. Beginning the project in early November 2017, a deadline was set for the following April. It was imperative to have an operational cooling tower during the entire process. As one unit was installed, another unit was always up and running.
Two of the existing three cells were temporarily piped and controlled to maintain operation while one cell was demolished. Within two weeks, the first cell of the new Evapco tower was erected.
The remaining towers were taken apart in early January. While winter weather meant frigid rooftop working conditions, it also ensured that the first cell of the new tower could easily handle the building’s entire cooling load on its own.
“The final two cells were removed and replaced simultaneously,” said Calvitti. “Our crew worked side-by-side with Limbach’s welders during demo and construction, and everything went smoothly. All told, there was only one scheduled 12-hour period of downtime over the weekend.”
The challenge of keeping the system operational throughout the project was upstaged by one logistical element — physically removing the old towers and getting the new ones to the 32nd story.
“Considering the size of the cooling tower cells and the building’s 400-foot height, using a crane was out of the question,” said Calvitti.
The open-air portion of the penthouse features diagonal concrete bracing in two corners, providing mere inches of clearance from the original tower, and only several feet from the new, smaller unit. With the full weight of a cooling tower suspended from a cargo helicopter, the margin of error was too small to complete safely.
The only remaining option was to use the building’s cargo elevator to transport the old cooling tower down, and the new one up — piece by piece.
“We used demolition saws to cut the old tower into manageable pieces and palletized them before sending them down the elevator,” said Calvitti.
The more complicated job was bringing the new equipment up. All material was delivered on a single day. Some components, like a 600-pound, 20-inch inlet water tee, provided a weight challenge, while others were limited by the dimensions of the elevator.
The AT Series towers aren’t designed for delivery in an 8-by-10-foot elevator. Radford and Tim Schmidt at ETS modified the tower design to fit the dimensions of the elevator. Ultimately, the new cooling tower went up in 400 pieces, sized to fit.
The floor and casing panels, along with framework, required the most modification. Once upstairs, panel segments were bolted together with gaskets in between. Calvitti explained that the increased labor was negligible compared to the cost of a crane or helicopter.
Thanks to improved fan design, tower design, and fill material, each of the new cooling tower cells uses a 40-hp fan motor, replacing the 50-hp models that served the original tower. A few years ago, Limbach retrofitted the existing fan motors with Yaskawa VFDs. Those drives were still serviceable and were reused on the fan motors supplied with the new tower.
Brandywine expects to see a decrease in energy costs and a life cycle cost improvement over the previous cooling towers.