by Alexandra Ferretti


Introduced February 8, 2008, the RPMAC PM Direct Drive Cooling Tower Motor and VS1CTD Drive for wet cooling towers replaces an existing motor, jack shaft and gearbox with a more efficient and environmentally responsible variable speed motor and drive with the motor mounted directly under the fan.

The RPM AC product is a power dense industrial motor with proven reliability in industrial applications including steel mill, paper mill and drill rig applications. The Cooling Tower version of this motor uses interior permanent magnet rotor technology and is designed to be mechanically interchangeable with many existing cooling tower gearbox designs. Mounting the fan directly to the motor eliminates the entire gearbox and driveshaft torque transmission components.

Permanent Magnet Rotor (PMR) construction using high flux strength Neodymium Iron Boron (NdFeB) magnets allows the motor to be manufactured in a compact form. The same basic motor design requirements for a hybrid vehicle-high torque, efficient, low weight, reliable, quiet and highly compact-also apply to the cooling tower application.

The motor is designed to be in the air stream with shaft sealing protection to keep out water and contamination. The special bottom end brackets and overall length profile are designed to be directly interchangeable with many existing gearbox designs. This same direct drive motor and drive package can be used to replace belt driven configurations as well.


End User Testimony

A test site with twin instrumented side-by-side cooling towers at Clemson University including third party independent verification was used to verify cooling tower performance between conventional and new direct drive PM technology.

According to testimony from Clemson University, "Baldor Electric presented a new cooling tower permanent magnet motor and variable speed electronic control system that would reduce energy consumption, increase system reliability, reduce noise and be more environmentally friendly by eliminating the traditional oil filled gearbox that is prone to leak oil into both the air and chilled water system. Clemson offered the use of twin identical cooling towers.

"One tower was retrofitted with the new Baldor direct drive technology and the second was kept unchanged and used as a baseline control tower for performance comparison.

"This evaluation program combined with third party certified independent testing, confirmed the overall benefits of this technology. In addition to reduced maintenance costs and the environmental benefits, Clemson University will realize a system efficiency improvement from 81.2 percent to 92 percent, resulting in a 4.5 kW energy consumption cost savings for every hour of operation. Additional energy savings will be gained anytime the system is run at lower operating speeds to maximize system efficiency."

Pumps & Systems, December 2009