HVAC Upgrade: Replacing Permanent Split Capacitors With EC Motors

New governmental standards and the desire to save money are responsible for a large shift in the HVAC industry. Consumers are switching to electronically commutated motors (ECM), to power residential and commercial HVAC units.

ECM technology has been around for more than 30 years. Consumers are choosing ECMs over legacy permanent split capacitor (PSC) motors for many reasons. ECMs are more cost and energy efficient, provide greater levels of comfort and indoor air quality, and they meet recently-enacted government standards.

Let's take a look at the difference between ECMs and PSCs, as well as uses for ECMs, and why the company that introduced ECM technology is still leading the field today.

About Electronically Commutated Motors

Electronically commutated motors first hit the market in 1987. At the time, the predominant motor was the permanent split capacitor motor. PSC motors had a high market share until recently. The technology behind PSC motors is more than 100 years old. A PSC is a single-phase AC motor. When PSC motors run, they operate within a very small speed range or not at all.

ECMs, which are permanent magnet motors, have an onboard control converting AC line voltage to a DC bus voltage and then back into a simulated AC signal to drive the motor. ECMs contain a computer that controls the simulated AC signal to the motor, allowing it to regulate speed, torque, or airflow depending on application need. One ECM can operate across various speeds and/or torques, adapting to meet specific outputs and load demands while maintaining a high-level energy efficiency. But often most important to the homeowner or end user is ECMs can provide constant airflow; improving the comfort levels of indoor spaces.

PSC vs. ECM

Electronically commutated motors have many advantages over permanent split capacitor motors. Here are some of the larger differences consumers might see, feel or hear:

• Comfort - With constant airflow and the ability to manage humidity, ECMs create more comfort for users in indoor spaces.
• Energy Efficiency - PSC motors use more power. PSCs need more wattage at similar running points. For example, a typical induction motor operating at 1,000 RPM needs 130 watts more than an equivalent ECM running at the same speed. Additionally, when a heat or cooling cycle ends, the PSC motor deactivates. Any energy within the unit will stay there. A continuously-running ECM will distribute that air throughout the system.
• Speed Range - PSCs use 100 percent of their power when activated. ECMs are more energy efficient when running at the same speed as a PSC motor and have an added advantage of having a full range of running speeds without sacrificing efficiency. When the cycle completes, PSCs turn off. Compare that to an ECM, which can run efficiently at a much lower speed during the off cycle so that air continues to circulate in the indoor space; keeping an evenly distributed temperature throughout the indoor space without consuming large amounts of electricity.
• Indoor Air Quality - Because an ECM operates efficiently over a large speed range, an energy efficient, low speed continuous fan operation is possible; allowing air to continuously be circulated through the system filters for better air quality. This feature can be advantageous regardless if the system is cycled to condition the indoor space or if the home owner has window or vents open to bring in fresh air. Additionally, because the ECM constant fan speed is lower than a PSC, condensation is not blown off the system evaporator coils and back into the dehumidified indoor space at the end of a cooling cycle.
• Dealing With Static Pressure Changes - ECMs can handle factors impacting the airflow of the HVAC system. For instance, if a filter needs replacement, an ECM will try and put out the same amount of air, regardless of the range of static pressure. An ECM will adjust and continue making changes until the airflow gets back to where it's supposed to be. Certain ECM models can even provide a signal back to the system an alert to check the filter. Additionally, with constant airflow, ECMs can overcome the limitations of ductwork designs. Airflow changes with a variation of pressure and installations. PSC motors cannot overcome that. But an ECM will optimize system performance by matching the system and providing the right airflow.

It’s easy to see why customers are choosing ECMs for PSC replacement. Beyond changes for end users, ECMs have other advantages in the manufacturing and installation stages. For each application or piece of equipment a PSC powers, manufacturers have to design a new motor. Compare that to ECMs, where you can have one motor power thousands of applications.

Additionally, service technicians replacing PSC motors must use a motor with similar specifications. Technicians can use one ECM in the field to replace many PSC motors.

ECM Applications

Electronically commutated motors are flexible and efficient across a wide operating range. The most common places you'll find ECMs are powering indoor and outdoor HVAC systems. ECMs are in furnaces, condenser units and rooftop units. Beyond sustainable building solutions, ECMs are also used in:

• Kitchen Ventilation (fume hoods)
• Commercial Refrigeration (Cooling and freezing cabinets at retail grocers, walk-in refrigerators and freezers)
• Pool Pumps

Standards

At first, the HVAC industry saw electronically commutated motors as a comfort feature. Even though they hit the market in 1987, until recently, permanent split capacitor motors powered most new systems. Yet, consumers who adopted ECMs saw significant cost and energy savings. Over the years, in the United States, both state and federal energy standards started requiring ECMs for HVAC and refrigeration use.

In 2019 the new Fan Efficiency Rating (FER) adopted by the U.S. Department of Energy went into effect. The FER standards required furnace manufacturers to cut fan electrical consumption by 40 percent. Since then, most new residential HVAC systems have been equipped with ECMs. The Department of Energy estimates consumers could save more than $9 billion in energy costs through the year 2030.

Regal Rexnord has also paired ECMs with other technology to improve indoor air quality and efficiency. UVantage ™ indoor air quality technology integrates a UVC LED into an ECM blower to reduce airborne pathogens, leaving them unable to replicate and potentially cause disease. Applying the light at the blower is an ideal location for cleaning the air. As a bonus, the light will also clean the blower wheel and adjacent filter.

Not only is Regal Rexnord a pioneer in the ECM field, but we're continually driving evolution of the technology. To find out how a Genteq ECM motor can power your HVAC application, contact an expert today.