Although they sound similar, choosing VFD or VSD will influence your energy consumption and bottom line

Whether you know it or not, your business likely uses electric motors in various ways. There’s no getting away from them, as they’re in nearly every building. For example, these motors are present in HVAC systems, elevators, central vacuums, and automatic doors, helping convert electricity into usable energy for the desired function.

When operating an office building, heating and cooling use a significant amount of energy from both natural gas and electrical sources. Your system already has an electric motor controlling its pumps, fans, and blowers, but there are ways to make them more efficient.

According to the U.S. Department of Energy, commercial and residential buildings use over 38% of the country’s energy and 76% of electricity. There could be financial incentives for reducing your business’s energy consumption, as the federal Energy Policy Act allows for tax deductions of up to $1.80 per square foot when a company meets certain energy reduction thresholds.

One method of lowering your energy use is installing a variable speed drive or variable frequency drive to regulate how hard your electric motors are working. The result is a more efficient system. Although these terms are used interchangeably, there are some differences in the drives themselves.

Here’s a look at how these drives work, so you can decide which is best for your commercial property.

Key takeaways

  • Variable speed drives and variable frequency drives work differently
  • Both can reduce your energy bills and create tax incentives
  • Learning how they operate can help you choose the right one

What is a variable speed drive?

As its name suggests, a variable speed drive (VSD) influences the amount of energy an electric motor consumes by adjusting its speed. The gist is that it works with the amperage and voltage of the current, increasing and decreasing the motor’s velocity whenever necessary. 

The result is the motor receives specific voltage and amperage based on its needs, rather than running at full capacity all the time. So, when using a variable speed drive to control the electrical components of a commercial HVAC system, the drive would supply the motor with less input voltage when the system doesn’t need to run at full capacity. 

Variable speed drives are also a bit different because they can be used with both AC and DC motors. 

If you have an AC motor, it works by sending alternating electric currents through a distributed winding. This reaction creates a rotating magnetic field that moves the driveshaft. This driveshaft controls components like pumps, compressors, and fans. 

However, the electricity’s frequency and supply control the speed and torque of the motor. Since electricity is a constant, there’s no inherent way to change an AC motor’s speed. A variable speed drive solves this problem by allowing you to control electricity distribution. It does this job by using a rectifier circuit to convert the AC to DC and then altering the voltage the motor receives.

Variable speed drives are also far more straightforward when controlling a DC motor because no conversion is necessary. The drive can directly alter the voltage the motor receives, saving energy in the process. 

Variable speed drives work well in most commercial settings, but you should evaluate your system before selecting this method.

What is a variable frequency drive?

A variable frequency drive (VFD) also changes the speed of an electric motor but accomplishes the job in a different way. 

First of all, variable frequency drives are limited compared to variable speed drives because they only work with AC motors.

Also, rather than changing the input voltage and amperage like a variable speed drive, a variable frequency drive changes the voltage and frequency. Altering the voltage changes the motor’s torque while adjusting the frequency changes the motor’s speed.

Therefore, a variable frequency drive is most effective at controlling the speed of a motor as it slows down and speeds up, helping prevent damage to the motor. They can also improve efficiency by limiting the rate at which the motor runs.

Companies with oversized HVAC systems might benefit most from a variable frequency drive because the speed control minimizes energy waste by preventing the unit from running at full capacity when it isn’t needed.

Which is better for your site?

Variable frequency drives and variable speed drives have a lot of similarities, so you might be confused about which option is best for your commercial building. Both devices can make your electric motors more efficient by limiting unnecessary power consumption and saving you money in the process.

A variable speed drive works best at above 82% capacity. As a result, it’s recommended in situations where your motor will be turning on, running at a high level, and then turning off. It can limit energy use while turned on but needs to operate at a relatively high level to maintain its efficiency.

On the other hand, a variable frequency drive is best if your motor runs continuously. You can run your motor at below 80% capacity and retain its efficiency with a variable frequency drive, so it will save you money under those circumstances.

Upgrading your electrical systems

Your commercial building has electric motors powering all types of components, including your HVAC, computer room, and data center cooling system. There’s a good chance these motors are running inefficiently but upgrading them with a variable speed drive or variable frequency drive is possible.

Once you complete your upgrade, these systems won’t run at full capacity around the clock, reducing your energy bills and potentially putting you in line for government tax benefits as you lower your consumption.

Universal Electrical Services is a full-service residential and commercial electrical contractor in South Florida that can assist as you make your business more energy efficient. Our attention to detail ensures that your job is done right the first time without any hassle. 

Contact Universal Electrical Services today for more information or a free quote.