Over the past eight years, Duke University in Durham, N.C., has been modernizing its campus-wide HVAC systems for better comfort, more efficiency and reduced maintenance costs.

In 1999, Duke University had no central chilled water plant. Each building had its own chiller plant or other types of air conditioning systems. As more buildings were added, the need for more equipment and maintenance staff grew.

SOLUTION

To ease the strain on staff and budget, Duke’s Facilities Management Division built a central chilled water plant to serve the campus. Working with Trane, construction of a 10,500-ton capacity central chilled water plant began in 2000. Connections to several university buildings and the hospital loop were added in 2004. This more efficient chiller plant resulted in energy savings and additional cost-avoidance savings as Duke no longer needed to replace aging chillers around the campus and hospital.

In March 2006, Duke completed a second central chilled water plant. This chiller plant features three 3,500-ton Trane Duplex centrifugal chillers and serves the university and hospital campus. Final combined capacity of Chiller Plants #1 and #2 is 45,000 tons.

Chiller Plant #2 uses Trane’s EarthWise™ design concept to boost overall chiller plant efficiency. The plant uses a variable primary flow pumping system with low chilled water flow rate (1.5 GPM/ton) and delivering 40°F chilled water temperature at 2.3 GPM per ton flow rate on the condenser, along with variable-frequency drives on condenser water pumps and cooling towers. The plant delivers chilled water annually at a system efficiency of .70 to .95 kW per ton of cooling capacity, compared to traditional chiller plants that consume .80 to 1.2 kW per ton.

The design also saves construction material costs due to reduced chilled and condenser water piping and pump size, and downsized electrical service needs.

The system in Chiller Plant #2 proved so successful that Duke retrofitted Chiller Plant #1 to a variable primary flow pumping system. That resulted in the following specifics:

Chiller Plant #1

• Two 2,000-ton Duplex chillers

• Two 2,700-ton Duplex chillers

• One 1,100-ton chiller with variable-frequency drive.

Chiller Plant #2

• Three Duplex chillers with 10,000 tons cooling capacity presently, with seven additional chillers yet to be installed;

• Rainwater captured from the roof for use as cooling tower makeup water;

• Daylight provided over the west wall to incorporate LEED concepts and save energy.

Chiller Plants #1 and #2 are interconnected and operate as a single plant. Buck Young of Brady Trane, Trane’s independent office in Greensboro, N.C., said, “Duke University is a great example of an owner involved in decisions regarding their total HVAC systems, working in partnership with Trane’s applications engineering expertise throughout the project’s design, construction and operational phases.”

For more information, visit www.trane.com.

Publication date: 05/07/2007