Tifton Aluminum's Variable Frequency Drive Experience

Condenser water control, in commercial chilled water systems, is key to operational efficiency and life expectancy of cooling equipment.

There are different control schemes used to maintain condenser water temperature for water chillers. Condenser water bypass and tower fan cycling are commonly used methods.

Tifton Aluminum in Delhi Louisiana used condenser water bypass and tower fan cycling to control the condenser water for their Trane process chiller. The system worked well under most conditions, however, they were experiencing rapid fan cycling to maintain the designed temperature during low ambient conditions.

Tifton's Maintenance Superintendent, Sammy Bland, was concerned about rapid cycling and failure of the fan motor. Storer Technician, Bobby Howard, suggested using a Variable Frequency Drive (VFD) to control the tower fan motor. The VFD would allow the motor to ramp up slowly and vary the motor speed to maintain water temperature. This control would eliminate the torque induced stress of the motor cycling on and off at full load.

Terry Colegate, Storer's Service Representative, evaluated the application of a VFD to control the tower fan. He concluded that the VFD could be used to start and modulate the motor, providing consistent condenser water to the Trane process chiller. Below the minimum set point the tower bypass would be used to control the condenser water temperature.

Working with Sammy Bland, we determined that the VFD would resolve Sammy's concern of premature motor failure. Two additional benefits as a result of this application were: the VFD would actually pay for itself through energy savings and the smoother operation to the Trane process chiller.

We estimate the energy savings will provide a simple payback in just over two years. Projected energy savings over the next five years are expected to exceed $38,000. The Internal Rate of Return on the investment is projected to be greater than 35%.

We have successfully utilized Variable Frequency Drives to solve low ambient operating problems on cooling towers and air cooled condenser applications. Please contact your Storer representative for solutions to your operating problems.