Baldor has launched a direct-drive technology for controlling cooling tower fans in commercial buildings that is said to improve reliability by eliminating moving parts while also saving energy and running quietly.
The technology is based on a permanent magnet motor that packs the high torque required into a compact space so that it can easily be retrofitted into cooling towers – sitting underneath the fan in the space currently required for the gearbox element of conventional power transmission systems.
Air cooling towers are commonly used as part of the heating, ventilating and air conditioning systems of offices and industrial buildings. Large fans pull air over water-soaked media to cool it before it is returned to the chiller unit.
The most common technique for driving such fans has been a standard AC induction motor, connected to the fan via a driveshaft and disc coupling arrangement into a right-angle gearbox, which reduces the motor’s speed to the range required for fan circulation.
Such arrangements have several drawbacks: the gearbox runs at high speed and requires regular inspection and maintenance of the lubrication and seals; misalignments in the power transmission system can cause vibration, wear and noise; and the complex power transmission system introduces significant energy losses.
Baldor’s solution, the VS1 Cooling Tower Drive, provides a direct slow-speed drive for the fans combined with variable-speed control that is optimised for the building cooling application. By eliminating the driveshaft and gearbox, the system minimises moving parts, improving reliability and power efficiency.
Baldor said the permanent magnet synchronous motor design uses energy-efficient technology that, with the elimination of the gearbox and drivetrain transmission losses, results in a more efficient system than conventional fixed-speed designs.
Additional energy savings can be gained by operating the fan at reduced speeds during non-peak load conditions. The direct drive also greatly reduces noise and eliminates the issue of cooling tower water becoming contaminated from leaky gearboxes.
Baldor’s technology was trialled and compared with a conventional cooling tower fan drive system, at a university building with identical twin cooling towers with 5.5m fans.
One tower was left as constructed. The other was retrofitted with the permanent magnet motor and variable-speed drive. Measurements showed a decrease in input power of 13% for the direct-drive arrangement when running at full load.
© PE Publishing, 9 September 2009
