Northstar Center

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Summary

Northstar Center is a three-building complex consisting of two high-rise office buildings and the seventeen-story, twenty-four-hour Crown Plaza Hotel, built atop a six-floor parking garage. Building tenants are extremely diverse, consisting of lawyers, banks, shoe stores and a variety of other businesses.

Challenge

Beginning with only a few tenants per floor, Northstar Center’s tenant list grew larger and more diverse. Along with the different tenants, came a variety of work hours, with some businesses working standard weekday hours and others requiring weekend personnel. The two aging chillers in the building did not have enough capacity to keep up with the increasing heat load, and building owners were challenged to keep different parts of the building cool to accommodate work schedules. In addition, Northstar Center was faced with new Department of Natural Resources (DNR) environmental regulations, which required the center to remove itself from its current well water system. Northstar Center sought to increase its chiller capacity and to accommodate the individual needs of its tenants, while helping to improve the environment for the surrounding community.

Solution

Investigating chiller options, the Northstar operations manager met with Trane engineers to discuss the capacity challenges of cooling its two office buildings. Taking into account the differences of the buildings and the varying ages of the equipment, Trane developed solutions to answer Northstar’s capacity and zone cooling needs.

Increasing chiller capacity
Northstar’s aging chiller was replaced with two Trane 800-ton CenTraVac™ centrifugal chillers. With only one moving part--a single rotating shaft supported by two aircraftturbine-rated bearings--the CenTraVac chillers are reliable and efficient. “We replaced our 1 kW/ton chiller with one that is .50 kW/ton. It’s amazing what it can do,” said Mark Erickson, Northstar Center operations manager. “One 800-ton Trane CenTraVac chiller, in the morning, running two towers, can do 1200 tons.”

Trane centrifugal chillers are also among the quietest in the industry. “You go down to our chiller room now, the only thing you hear are the pumps. With the old chillers, you couldn’t even talk,” Erickson added.

Meeting individual tenant needs
A plan was developed to address individual tenant needs. Rather than cooling the entire building for occupants on one floor, the low pressure CenTraVac chiller can be turned down to about 10 percent to run for partial capacity. “We have a core loop where we cool air for things that run 24-hours a day. Because of that, we had to keep our water a little cooler. Trane worked hand-in-hand with our engineering company to develop a solution that was the most efficient,” said Erickson.

“It’s nice that I can run just one floor,” Erickson added. “In the past I had to run the whole building just to keep the load even to keep the chiller from surging."

Improving the environment
The new chiller replaces Northstar’s old well water pump, which required chemicals to treat the water before it was run through the chiller. “There were a lot of things going in the water and down the drain,” said Erickson. “The new chiller is way more environmentally friendly.”

The CenTraVac centrifugal chiller also has the lowest total refrigerant emissions rate in the industry, and comes with a five-year leak tight warranty. Ensuring tenant comfort Controls with easy-to-navigate touch screens and displays allow Northstar engineers to monitor the equipment and make adjustments as necessary. “You can go down there and look at the pressures, scroll through it, everything. We do a daily log, but we don’t even have to do that log, because it logs itself,” commented Erickson.

Results

Replacing its aging chiller with two Trane CenTraVac centrifugal chillers has reduced Northstar Center’s electrical consumption nearly 50 percent, while significantly increasing cooling capacity. “Today is a very warm day and we’re running one chiller,” said Erickson. “Two cooling towers, but one chiller, and we’re doing just fine.”

The new chiller has also increased tenant satisfaction. “When I would get the complaints in the past, there was nothing I could do," stated Erickson. "Now, if for some reason we didn’t start up right away, I could actually catch up. I have enough capacity that I could turn on both chillers and cool the building down fast.”

The reliability of the new chillers also provides peace-of-mind for facility managers. “It’s one less thing to have to worry about," said Erickson. "And there are plenty of other things to worry about.”

About Northstar Center

As its tenants became more diverse and work hours varied, Northstar Center sought to accommodate the individual comfort needs of its building occupants.

Two 800-ton Trane CenTraVac centrifugal chillers have substantially increased capacity and tenant satisfaction.

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