DuPage County Governmental Complex
POPULATION GROWTH REQUIRES COUNTY GOVERNMENTAL COMPLEX TO POWER UP
Hybrid Technology and Chiller Storage Tank give DuPage County Governmental Complex Ulitmate Flexibility
DuPage County in Illinois has been enjoying prosperous growth over the last three decades, caused by sprawl from Chicago, which is located 20 miles east. But with the increase in people came extra demand for services. This fell on the shoulders of the DuPage County Governmental Complex, which has grown itself to meet the needs of the area. Today, the complex encompasses 12 buildings with 1.5 million square feet. The chillers that serve the facility are located in the power plant building that dates back to 1970.
Because of concern for the machines’ age and the refrigerants used, as well as a desire for greater efficiency, the complex’s management went in search of an alternate cooling solution. They evaluated chiller plant options, considering both electric centrifugal and hot water absorption options. Colin Oakley, Facilities Manager with DuPage County, became instrumental in driving the design to maximize efficiency and to take advantage of off-peak electric and gas rates. His concept was to install a sophisticated hybrid system with both absorption and electric centrifugal capacity. The project involved replacing three single-stage centrifugal chillers ranging in age from 18 to 30 years and totaling 3,300 tons of capacity. A chilled water storage tank was also being installed under an earlier contract.
An integral part of the hybrid system was left to Trane products. The electric chillers chosen were a 1,000-ton TRANE CenTraVac™ centrifugal chiller and a 2,000-ton TRANE duplex CenTraVac machine. The absorption machine is a 1,150-ton TRANE Horizon™ two-stage absorption chiller.
In normal summer operations, the absorption chiller is base-loaded during the day with the electric chillers operated to meet additional cooling needs. However, with both electric and gas-fired absorption capabilities, the county can choose which unit to base-load, depending on fuel costs, energy charges and demand charges.
As a part of the system upgrade, the chilled water distribution system was converted from a conventional primary–secondary system to a variable volume primary system. According to Oakley, this change, along with the greater capabilities of the new chillers,allows the system to deliver chilled water in the range of 39°F (4°C). Lower-temperature chilled water offers several advantages over the earlier system, including significantly reduced pumping cost and superior dehumidification.
Another important improvement was installation of a Tracer Summit™ control system. This system allows optimization of the chiller plant and distribution system, and provides an opportunity to observe system conditions from the chiller plant control room or from remote locations.
With the new technology in place, the Trane chillers went to work and provided the DuPage County Governmental Complex with some really cool results. They now have a comfortable surplus of cooling capacity and the option to use either steam absorption or electric chillers directly or to use stored cooling capacity. This flexibility allows them to respond quickly to changing energy prices or supply conditions. With the experience gained from two years of operations, Dan Baran, facilities supervisor of power plant operations at the complex raved, "The system performs like a champ."
1,000-ton TRANE CenTraVac™ centrifugal chiller
2,000-ton TRANE duplex CenTraVac centrifugal chiller
1,150-ton TRANE Horizon™ two-stage absorption chiller
Tracer Summit control system
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