This piece was originally published in the January 2018 issue of electroindustry.
Keith Waters, PE, CEM, Manager of Industry Standards, Schneider Electric
Increasing the use of electronics to control mechanical systems allows for a more efficient operation of these mechanical systems. One of the most common applications is to utilize variable-frequency drives (VFDs) in lieu of traditional motor starters to control pump and fan motors. This application provides several positive impacts for the end user. The most advantageous are:
- Energy efficiency
- Operational efficiency
- Building analysis improvement
- Maintenance cost reductions
Energy efficiency is achieved by taking advantage of the affinity laws. These physical laws provide the basis for saving energy for pump and fan applications by maintaining the necessary speed while reducing the mechanical energy needed to do so. The application is achieved by varying the frequency of the motor to slow down the motor to the actual speed needed to maintain the proper output. There have been online calculators developed to provide details on the actual energy savings and the costs associated.
Operational efficiency is another area that can be improved with the expansion of electrical controls. The processing capabilities within VFDs allow for increased laminar flow and the alarming of items such as high currents caused by blockages or other issues associated with setpoints. Better flow control reduces the effect for water hammer during pump starting vs. mechanical methods.
Building analytics provide an opportunity to maximize efficiency. These improvements are created by the integration of more electronic controls and their ability to provide an enhanced level of information to building management systems. VFDs can provide more information via communications instead of adding more sensors or other measurement devices.
Mechanical systems used to control pumps and fans require belts, mechanical flow controls systems such as dampers in HVAC applications, and other mechanical devices. These systems require extended maintenance to provide a continuous level of operation needed by users. The number of these components increases as the systems get larger, thereby increasing the maintenance costs. Reducing the number of these mechanical components provides an opportunity to lower maintenance costs.
The installation of VFDs can increase energy, operational, and overall building efficiency as well as reduce the maintenance needed in mechanical systems using pumps and fans. These cost savings opportunities show the reason we see more electrical systems becoming integrated with mechanical systems.