Since 1986, Tower Engineering in Fort Worth, Texas, USA, has been designing and installing high-quality cooling towers for the large institutional market, including hospitals, universities and airports. The HVAC systems in these facilities rely on cooling towers to maintain a comfortable inside temperature. Cooling towers work by using water to extract heat from the system and release it into the atmosphere through evaporation. A fan on top of the cooling tower brings air from the bottom of the tower and moves it up and out in the opposite direction of the warm condenser water at the top of the unit. Cooling towers are capable of achieving a more cost-effective and energy-efficient cooling system than air-cooled systems; however, traditional system designs are not without their issues.
The most common method for driving the fan in modern cooling towers has been a right-angle gear reducer, drive shaft and disc coupling arrangement, along with a standard foot-mounted AC motor. Mechanical losses through gears, bearings, seals and auxiliary components reduce the system’s overall efficiency, and excessive vibration and noise are other inherent problems. With the high speeds, the gearboxes generate heath can lead to shortened seal and bearing life. In addition, maintenance requirements can be complex and time consuming, and failure to perform continuous preventative maintenance can lead to mechanical failures.
Tower Engineering President Rod Applegate had been looking for a solution to gearbox issues for more than 20 years, and in 2007, he began to discuss his ideas with ABB (then Dodge-Reliance Industrial) engineers. He explained that what he needed was a direct drive fan motor. In subsequent meetings, Rod shared his insights on the needs of the cooling tower industry. Once all the parameters were set, the engineers went to work.
The result of that research and development collaboration became ABB’s Baldor-Reliance RPM AC Cooling Tower Direct Drive Motor, a synchronous permanent magnet motor that uses laminated finned frame construction to provide a highly efficient, power-dense package with flange mounting dimensions that can replace the right-angle gearbox and jack shaft installation in many conventional cooling towers. This same technology is offered in conventional, yet power-dense, foot-mounted designs that can replace the belt and sheave application where more vertical mounting space is available. Derived from one of the toughest motor platforms used in the most demanding industrial applications, the RPM AC Cooling Tower Direct Drive motor is the right solution for operation inside a tower’s hot and humid environment.
The totally enclosed air over (TEAO) cooling tower motor is designed for minimal maintenance. Bearings require lubrication only once per year, and water ingress along the shaft is prevented with the use of an Inpro/Seal® bearing isolator and a slinger. The electrical insulation system is manufactured using a vacuum pressure impregnation (VPI) process that ensures long motor life even in the most extreme environmental conditions. Condensation drains relieve any moisture that may collect inside the motor. No more changing gear oil or belts or lubricating pillow block bearings.
The combination of these innovative technologies has allowed ABB to build a high-torque, low-profile motor, with the fan mounted directly on the motor shaft. It’s a synchronous machine that runs at precise speeds without slip in combination with an ABB ACS880 cooling tower variable frequency drive (VFD). The drive also provides custom features for HVAC applications including trickle current motor heating, locked motor rotor functionality to prevent windmilling when not enabled, de-ice mode, accelerometer feedback and RTD temperature feedback.
A greener technology
Eliminating gearbox maintenance issues with a simplified direct-drive motor is just the beginning. The permanent magnet motor and drive package provides high system efficiency. The variable speed control allows the cooling tower to operate at optimum performance, which results in a considerable amount of energy being saved.
The motors also run quieter, and the reduction in noise level is important, especially in towers that are located near “people-dense” buildings. In addition, by replacing the gearbox, the potential of environmental contamination is eliminated.
Designed for power - refined for performance
Like all Baldor-Reliance RPM AC motors, the Cooling Tower Direct Drive Motor represents high performance in a power dense, true variable speed package, and the product line continues to be enhanced and extended to represent one of the broadest variable speed AC motor offerings available. RPM AC was designed to handle the most difficult and demanding applications, and with the launch of Generation 3 in 2021, the power range has been extended, grounding provisions are now standard, setup and deployment are easier than ever, and ABB Ability™ smart sensor technology puts connectivity and data analytics at your fingertips.
Measuring performance and efficiency in real-world applications
Baldor-Reliance Cooling Tower Direct Drive motor and drive systems have been installed and field tested for extended periods of time in a variety of cooling tower applications. One system was run under a controlled environment on one of two identical cooling towers at Clemson University in South Carolina. During testing, both towers were instrumented, and the traditional geared system was evaluated against the ABB solution. Each tower had the same five-blade, 18-foot diameter fan, with pitch and tip clearance adjusted to identical settings. Performance results, which were verified by a third party, showed that the ABB solution reduced losses in the system by approximately 50 percent and provided a measured power savings of 11.8 percent when compared to the traditional geared system, with high-speed noise reduction from 82.3 dBA to 74.4 dBA. Vibration was also reduced.
Predicting the future
During an early interview, Applegate described the Baldor-Reliance Cooling Tower Direct Drive Motor as a revolutionary product and predicted the motor’s success – not only in new cooling tower construction, but as a retrofit for existing systems. With continued design and manufacturing improvements, the Cooling Tower Direct Drive Motor has become a feature-rich offering across the entire product family, providing not only the highest levels of performance, but also immense opportunity for power savings and greenhouse gas reductions.
