Founded in 1837 and named after the only physician to sign the U.S. Constitution – Benjamin Rush – Rush University Medical Center (RUMC) is now Chicago's second-largest hospital with multi-story buildings that dominate the city's medical district. But that prestigious location posed problems when RUMC's 11-story Professional Building 2 needed to replace two aging centrifugal chillers. It appeared the only alternative was to move a crane down a crowded street to lower new chillers through the roof. But some simple surgery made it possible for Smardt split-shell chillers with Danfoss Turbocor® compressors to simply take an elevator up to the penthouse mechanical room, a solution that cut installation costs while boosting energy savings.
“The professional building was using two fixed-speed 300-ton water-cooled centrifugal chillers,” said Mike Scalleta, Mechanical Systems Manager at RUMC. “They were installed when the building was built in the 1970s. Consequently, the old centrifugal chillers were using twice the energy compared to today's more efficient variable-speed chillers. It was time for them to go. The problem was we'd have to cut open the mechanical room and use a crane to drop in conventional replacement chillers. Fortunately, we learned Smardt had a solution. Their split-shell Smardt chiller design with compact Danfoss Turbocor centrifugal compressors could be taken apart to fit into our freight elevator. Using the elevator would minimize building disruption and reduce installation costs, and the efficiency of a variable-speed Smardt chiller would dramatically cut our energy costs."
RUMC replaced two aging fixed-speed 300-ton water-cooled centrifugal chillers (shown here) with energy-efficient Smardt split-shell chillers with Danfoss Turbocor compressors, reducing installation costs and saving $75,000 in annual operating costs.
As the worldwide leader in oil-free magnetic bearing chiller technology, Smardt sought to significantly reduce installation costs and boost efficiency – helping the overall bottom line.
Split-shell Chiller Fits Big Efficiency in a Tight Space
The energy efficiency of the Smardt chiller turned out to be a big plus that fit into a small space. According to Bullock, Logan and Associates’ Curt Bullock, Jr., a Chicago representative for Smardt, the difference between the Smardt chiller and the old centrifugal chiller was night and day. Bullock calculates that when the old chiller was new, its integrated part-load value (IPLV) was 0.716 kW/ton but used oil-lubricated bearings. Because oil fouls heat exchanger tubes over time, actual efficiency was worse.
“In comparison, the IPLV of the Smardt chiller is 0.315 kW/ton – 57% more efficient," said Bullock. "That's partly because there are no oil-related heat transfer losses and no mechanical-bearing friction losses. Another energy-saving feature is the compressor's ability to adjust automatically to off-design conditions. The Danfoss Turbocor TT400 compressor can turn down capacity to 10% of its total capacity. By automatically matching capacity to the load, the compressor reduces its speed, which also reduces energy consumption.”
The upgraded installation at RUMC includes a new 300-ton chiller with two 150-ton compressors.
But all that efficiency wouldn't do any good if the chiller didn't fit into the mechanical room.
“Professional Building 2 is sandwiched between Harrison Street, other professional buildings and rail lines in the Medical District,” said Carl Wigginton, Vice president of Service for Murphy & Miller, Inc., the Chicago-based HVAC contracting firm who handled the installation. “There is no easy access. The front of the building is a little cul-de-sac where they turn cars around, and that's where the crane would have to go. It's a big reach – the crane would have to come in about 100 feet, then travel another 100 feet to the mechanical room doorway. But, there is a freight elevator that goes right to the penthouse mechanical room. It's so much easier that way – if a chiller can fit into the elevator.”
The building's large freight elevator was rated to hold up to 7,000 pounds. A conventional 300-ton centrifugal chiller would weigh around 12,000 pounds empty. Consequently, the weight and size dimensions prohibit using the elevator. In contrast, the empty weight of a 300-ton WA0962HG4 Smardt chiller is about 8,500 pounds – and designed to be taken apart and easily reassembled.
“This Smardt chiller has a split-able shell design," said Wigginton. "That made it possible to disassemble the evaporator and condenser shells. Disassembly took about half a day. We transported the parts by elevator to the penthouse. It took six trips. The first two trips transported the evaporator, and two more trips for the condenser. Then, the control panel and miscellaneous components took one trip, and the compressors took one trip.
"Compare that with getting permits to shut down streets, disrupt traffic and block the building entrance with a crane. Plus, we would have to cut through the penthouse to give the crane access to the chiller site. You can see the advantages of this particular Smardt chiller configuration that uses two 150-ton Danfoss Turbocor TT400 compressors. The compressors weigh only about 300 pounds each, so we easily fit all four compressors into the elevator.”
Inside the mechanical room, it took two technicians five days to reassemble the shells, compressors and control panel and level the chiller. The next week, control and electric wiring were connected along with piping and valves.
Reducing Centrifugal Compressor Complexity with Oil-free Magnetic Bearings
The installation was also simplified because Danfoss Turbocor compressors don't require an oil management system. “The Danfoss Turbocor compressor uses oil-free magnetic bearings,” said Ken Koehler, Key Account Manager for Danfoss. “In a conventional hermetic compressor, the shaft rides on a thin layer of oil on mechanical bearings. Because the rotational speed of the shaft may exceed 35,000 RPM, oil is needed to minimize friction and heat buildup. The bearings also keep the shaft properly aligned with the stationary elements.
“In a hermetic compressor, oil circulates within the refrigerant gas. To maintain oil at proper levels, the oil management system uses elaborate piping, traps and risers. But Smardt chillers avoid all that complexity. Because the Danfoss Turbocor centrifugal shaft levitates within a magnetic field, the need for oil is eliminated.”
Koehler explains the Danfoss Turbocor shaft doesn't physically contact bearings in normal operation. Instead, the shaft rotates within ten separately controlled electro-magnetic cushions that continually change strength, slightly pushing or pulling the shaft to maintain its position.
“Danfoss Turbocor magnetic bearings use a digital controller that processes signals from 10 sensor coils,” said Rob Silecchia, Director of Healthcare and Pharma Applications at Smardt Chiller Group. “Shaft movements of less than 0.00002-inch are detected, and the magnetic field is adjusted to maintain the shaft orbit. Backup carbon or roller bearings are used only to hold the shaft when the compressor powers down.”
The Danfoss Turbocor compressor's digital intelligence also incorporates a powerful but user-friendly control system that interfaces with the Smardt chiller controller. The full-color control interface simplifies system configuration and commissioning through the chiller controller.
The The new compressor’s user-friendly control system interfaces with the chiller controller, helping simplify system configuration and commissioning.
“Danfoss’ monitoring software presents all the compressor operational data we need,” said Wigginton. “The software is pulling in data from multiple sensor readouts. Temperatures, pressures, heat transfer across bundles, load demand, maximum and minimum RPM, compression ratio and mass flow, amp draw – it's all there through the Smardt controller. It really simplifies setup and startup. We appreciated the support the Smardt rep – Bullock, Logan and Associates – provided. And our techs took advantage of the training Danfoss provided. The compressors are so easy to work with, we had no problem finishing the job ourselves.”
Smardt Benefits for a Hospital Application
What's more, RUMC's utility – Commonwealth Edison – gave the hospital a $24,000 rebate for using a variable-speed chiller. According to Bullock, the efficiency of the Smardt chiller beat out several competitive conventional variable-speed chillers.
"The size of the rebate is $10,000 more than they would have gotten with a competitive variable-speed chiller," Bullock emphasizes. "The Smardt chiller minimizes the number of amps used at startup and during peak electric periods. The calculated difference in efficiency meant that over the eight-month cooling season, the new chiller saved about $12,000 more in utility costs than the proposed replacement chiller. In comparison with the old chiller, however, the new Smardt chiller saved approximately $75,000.00 in annual operating costs. When you add in the installation savings, the cost difference between the split-shell Smardt chiller and the competing chiller paid for itself in the first year of operation."
All the problems with oil are a thing of the past, because there is no oil. There's very little maintenance with these units. Smardt and Danfoss have created a clean, compact chiller design that fits perfectly into our operation.
Another benefit is the Smardt chiller's quietness. “Sound transmission is always a concern with a chiller — especially in a hospital setting,” said Scalleta. “With a Smardt chiller, the magnetic bearings position the shaft so precisely, there's hardly any noise or vibration. The chiller does not have vibration-damping springs or sound-attenuating blankets. In fact, when we first visited the mechanical room to see the Smardt chiller in operation, we weren't sure it was running—it's that quiet compared to our old fixed-speed centrifugal chiller.”
Combining the installation, efficiency and acoustic advantages, it was not a difficult decision when RUMC accelerated the replacement of its second old centrifugal chiller with another split-shell Smardt chiller just three months after the first was installed.
"The Smardt chiller runs smoothly and quietly," said Scalleta. "That's important to us, and so are the energy and maintenance benefits. All the problems with oil are a thing of the past, because there is no oil. There's very little maintenance with these units. Smardt and Danfoss have created a clean, compact chiller design that fits perfectly into our operation."
About the Author
Ken Koehler serves as a Senior Key Account Manager for Danfoss, the world’s leading manufacturer of high-efficiency, oil-free magnetic bearing centrifugal compressors. He has 30 years of experience in both global HVAC and aerospace/defense, including sales, project management, quality, and sustaining engineering. Koehler can be reached at email@example.com, or 850-504-4821.
All photos courtesy of Danfoss. For more information, visit www.danfoss.com.
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