How Variable Frequency Drives Save Energy

Variable Frequency Drives (VFDs), also known as variable speed drives, adjustable frequency drives, adjustable speed drives, AC drives, or inverter drives, are powerful tools for managing electric motors. These devices can slash your motor’s energy usage by up to 90%, significantly prolong motor life, and often offer a return on investment in as little as six months. Plus, installing VFDs can make you eligible for various financial incentives aimed at promoting energy efficiency.

What are VFDs?

A Variable Frequency Drive (VFD) controls how fast an electric motor spins by adjusting the electricity's frequency and voltage. Think of a VFD like the gas pedal in your car. Just as you press the pedal to make the car go faster, a VFD can speed up or slow down a motor smoothly and precisely. VFDs are used in many industries, including HVAC systems, water and wastewater treatment, manufacturing, and agriculture.

There are three main types of VFDs, each suited for different jobs: Voltage-Source Inverters (VSI) are the most common type and allow for flexible and precise motor control. Then there are Current-Source Inverters (CSI), which are ideal for applications that need precise current control, like solar power systems. Finally, there are Pulse Width Modulation Inverters (PWM). These are used in many power electronics applications because they also provide precise control over motor speed and performance.

How VFDs Save Energy

VFDs save energy by adjusting motor speeds to match the actual need rather than running motors at full speed all the time. By following the Laws of Affinity, they cut energy use dramatically, making them a smart choice for any operation looking to improve efficiency and reduce costs.

Understanding the Laws of Affinity

• Flow Rate Proportional to Speed: Reducing motor speed by 50% cuts the flow rate by 50%.

• Pressure Proportional to Speed Squared: Cutting speed by 50% drops pressure to 25% of the original.

• Power Proportional to Speed Cubed: Reducing speed by 50% reduces power use to 12.5% of the original.

Real-World Example

Imagine you have a large fan running at full speed all day. Without a VFD, the motor operates at its maximum speed, using a lot of energy. With a VFD, you can slow down the fan when full speed isn’t needed (like during cooler parts of the day). By reducing the speed, you significantly cut energy use, and since most fans and pumps don’t need to run at full speed all the time, this adds up to substantial savings. Let’s break it down:

Reducing Speed by 25%:

• If you slow down a fan or pump to three-quarters of its full speed:

• It blows out 25% less air.

• The force of the air drops to a bit more than half.

• It uses less than half the energy, saving around 60%.

Reducing Speed by 50%:

• If you slow down a fan or pump to half its full speed:

• It blows out half as much air.

• The force of the air drops to one-quarter.

• It uses only about one-eighth of the energy, saving almost 90%.

Even though VFDs themselves consume a small amount of energy (around 2% to 3%), the overall energy savings are still substantial. For example, if reducing speed by 50% saves you 90% of the motor’s energy, factoring in the VFD’s energy use still leaves you with a net savings of about 87%.

Why You Should Install VFDs

If your facility is looking to save energy and reduce costs, Variable Frequency Drives (VFDs) are a smart solution. By managing the speed of electric motors, VFDs can offer significant energy savings and other benefits. Let's explore how VFDs can help your facility become more efficient:

Energy Savings

By allowing motors to run at slower speeds when full power isn't needed, VFDs can cut energy consumption by up to 90%. That’s a big win for your energy bills!

Reducing Wear and Tear

VFDs start motors slowly by ramping up the voltage gradually. This smooth start reduces wear and tear and prevents overheating.

Offsetting Oversizing

In many HVAC systems, centrifugal fans and pumps are oversized to handle uncertainties. VFDs help control the speed of these oversized motors, preventing wasted energy.

Reducing Demand Charges

Commercial and industrial facilities often face utility demand charges based on peak energy usage. VFDs can help reduce these charges by limiting the high inrush currents that occur when motors start up.

Financial Incentives

Many utilities and government agencies offer credits, rebates, and tax deductions to encourage the installation of energy-saving VFDs.

The Main Takeaway

Installing a VFD isn’t a magic bullet for energy savings. To get the most out of your VFDs, you need to understand your HVAC systems and how VFDs can be best applied. That’s where experts come in.

At ACI Controls, we take a holistic approach to saving you energy and money. Our team of engineers and technicians has the experience and know-how to optimize your VFD applications. We offer smart building controls, distributed energy solutions, and process control tailored to your specific needs. Ready to learn more about how VFDs can benefit your business? Reach out to ACI Controls today.