Electric motors are a critical component in modern pumping applications. They are the core driver for pumps to move fluids across many applications, from municipal water systems and industrial processes to heating, ventilation and air conditioning (HVAC) systems and irrigation systems. Within these different applications, two main types of electric motors are used: single-speed motors and variable-speed motors.
This article will discuss the advantages of variable-speed motors and why they are becoming more common in commercial and industrial pumping applications.
Understanding the Basics
A variable-speed electric motor is often used with a variable frequency drive (VFD) or some other type of electronic controller. This type of motor can adjust its speed based on the frequency and voltage supplied by the VFD. This type of speed adjustability allows the pump to supply more or less flow pressure, depending on the system requirements. This allows for a significant advantage in energy consumption, responsiveness to the system demands and the longevity of the equipment.
Core Advantages
Variable-speed motors, when connected to a VFD, allow for rotations per minute (rpm) modulation. A system may not demand full speed when running, allowing for more energy efficiency. Variable-speed motors can run at 40% of full power, as the system is only demanding a certain point of flow. The variable-speed motor can also meet different points of the pump curve rather than being at a single point on the pump curve.
In a pumping system, the flow demands may vary. In water distribution networks, HVAC systems or process cooling systems, variable-speed motors can offer more efficient performance and flexibility to not overpressure a system when the demand for full speed is not required. In a circulation pump system, water may not need to be running, or only light demand may be needed, due to all valves being closed. The variable-speed motor will run very slowly to move the liquid at a slower pace. When the demand increases, the motor will ramp up based on demand from the VFD. Once the demand is not needed, the motor will then slow down due to the VFD signal. Small changes in motor speed can lead to energy savings over time.
System Wear & Maintenance
There may be less system wear and maintenance when using a variable-speed motor. Variable-speed motors utilize a soft start/stop approach. The motor gradually ramps up or down to speed, and pressure surges are less likely to occur with this starting option. Typically, this reduces the mechanical failures on the motor, prolongs the system components and, overall, reduces the maintenance needed.
Process Control & Readiness
A variable-speed motor, when connected to a VFD, allows systems to minimize the use of extra pressure controlling mechanisms and adjust for demand accordingly in a pumping system. At times, when correct sensors are used, variable-speed motors can automate pressure control based on the feedback the sensors are sending to the VFD.
Motor Cost
Variable-speed motors can be expensive up front. There is an added cost for a VFD. Because these systems are more complex, they can take some time to program.
However, the long-term savings of a variable-speed motor and system may decrease the total cost from installation and usage due to energy savings over a set period. There have been cases where, within one year, the energy savings from a variable-speed motor make up for the extra costs of investing in it. The maintenance costs for a variable-speed pumping system are also a factor in lifetime savings.
Variable-speed motors, when connected to a VFD, have many advantages. The cost savings, maintenance wear and longevity are key reasons to choose this type of motor for a pumping system. With the rising costs of energy in the world today, better efficiency is key to saving money in the long term.
