New Chillers, Controls Make the Grade
Marty Metcalf, director of operational services for the district, said, "Many of the units were flat worn out. They no longer provided ventilation at all." The district also needed to achieve and document classroom ventilation levels as specified by ASHRAE Standard 62-89.
SOLUTIONMetcalf and other school officials worked with Trane's Des Moines sales office to develop a plan to upgrade the two oldest schools in the district.
Ron Engelhardt, Trane sales engineer, said, "Older unit ventilators just don't have the capabilities for metered ventilation or for accurate control. Usually the best solution is to replace them with new equipment and to overlay the system with a modern digital control system."
The two schools were equipped with new Trane unit ventilators tied into the district's existing Trane Tracer Summitâ„¢ control system.
CENTRIFUGALSIn addition, old centrifugal chillers at several schools were replaced with Trane Model RTAA air-cooled chillers. The latter is a hermetic rotary refrigeration system that provides chilled water for either comfort or industrial or water-cooling systems.
The model - which comes in sizes from 70 to 125 tons - uses what the company calls a Helirotorâ„¢ compressor which is direct drive and low speed (3,600 rpm). The rotors and load/unload mechanism are the only moving parts. The model comes with two independent refrigerant circuits and single evaporator water connections.
The Adaptive Controlâ„¢ microprocessor controls "provide all unit control and safety functions in a proactive control strategy," according to the manufacturer.
Said Metcalf, "Not only are the new chillers more reliable and efficient, but the need for frequent cooling tower maintenance is eliminated."
Regarding the Tracer control system upgrade, Metcalf said, "When we have questions about conditions in any of the classrooms with the new unit ventilators and controls, we can check them on the Tracer Summit system instantly. That saves a lot of time and travel. Now we have complete documentation of temperatures and ventilation rates for each classroom."
For more information, visit www.trane.com.
Publication date: 05/01/2006