Energy savings with VFDs in pump applications

Variable frequency drives (VFDs) are widely used in pump applications to regulate the speed of the motor and reduce energy consumption. By varying the frequency of the electrical power supplied to the motor, VFDs allow pumps to operate at different speeds, optimizing their performance and efficiency. This article will discuss the potential energy savings of VFDs in pump applications and how to calculate them.

Traditional pump systems operate at a constant speed, regardless of the actual demand for water or other fluids. This means that the motor is running at full speed even when only a small amount of fluid is required, leading to wasted energy and increased costs. In contrast, VFDs can adjust the speed of the motor to match the demand for fluid, reducing the energy consumption of the pump system.

The energy savings achieved with VFDs in pump applications depend on several factors, including the flow rate, the pressure, and the speed of the motor. As a general rule, reducing the speed of the motor by 20% can result in energy savings of up to 50%. This means that VFDs can potentially reduce the energy consumption of pump systems by half or more.

To calculate the potential energy savings of a pump system with a VFD, you need to know the following parameters:

• Flow rate

The amount of fluid that the pump system is expected to deliver, typically measured in gallons per minute (GPM) or liters per second (L/s).

• Pressure

The pressure required to deliver the desired flow rate, typically measured in pounds per square inch (PSI) or bars.

• Efficiency

The efficiency of the pump system, which is the ratio of the output power to the input power.

• Power consumption

The power consumed by the motor at full speed, typically measured in kilowatts (kW).

Once you have these parameters, you can use the following formula to calculate the potential energy savings with a VFD:

Energy savings (%) = (1 – (P2/P1)^3) x 100

Where P1 is the power consumption of the motor at full speed, and P2 is the power consumption of the motor with the VFD at the desired speed.

For example, let’s say that you have a pump system with a flow rate of 200 GPM, a pressure of 50 PSI, an efficiency of 70%, and a motor power consumption of 20 kW. By installing a VFD that reduces the motor speed by 20%, you can calculate the potential energy savings as follows:

Flow rate: 200 GPM
Pressure: 50 PSI
Efficiency: 70%
Power consumption: 20 kW
Desired motor speed: 80% of full speed
Power consumption with VFD: 9.1 kW

Energy savings (%) = (1 – (9.1/20)^3) x 100 = 59.3%

In this example, installing a VFD in the pump system can potentially reduce energy consumption by 59.3%.

VFDs offer significant energy savings in pump applications by reducing the speed of the motor, which in turn reduces the energy consumption of the system. The actual energy savings depend on several factors, including the flow rate, the pressure, and the speed of the motor, but can potentially reach 50% or more. By calculating the potential energy savings and considering the cost of the VFD, it is possible to determine whether installing a VFD in a pump system is a cost-effective solution for reducing energy consumption and improving efficiency.