Conversations with an Engineer: ECM Motors in Pumping Applications

What’s the difference between electronically commutated motors (ECM) and traditional electric motors?

According to Jim Swetye, a pump system expert with Swetye Services LLC, the primary difference is that ECMs are synchronous DC type motors that include permanent magnets built into the rotor. Compared to traditional motors that are asynchronous AC induction type, ECMs achieve about a 15% energy use reduction, on average.

The permanent magnet motors that are used in the pump industry today run from fractional horsepower sizes up to 15 horsepower. There are larger sizes coming.

The primary advantage of ECMs is efficiency. The process of inducing a magnetic field in the rotor by way of the stator’s magnetic field consumes about 15% of the energy that’s wasted. Another advantage is that ECMs enable pump manufacturers to produce combinations of pumps and motors that meet the stringent new U.S. Department of Energy efficiency requirements for pumps.

One of the primary applications for ECMs is in hydronic circulation, for both hot water heating and air conditioning systems. They are also found in pressure boosting applications in industry, municipalities and commercial buildings. They’re found in hot water recirculation, and in irrigation systems as well.

There are downsides to using ECM motors. The primary disadvantage is that they require a variable frequency drive to take advantage of those permanent magnets, making them a bit more expensive. A complete cost analysis will reveal that in most cases the additional expense of the ECM is more than offset by power cost reductions.

ECMs offer tremendous energy savings and other benefits when they’re applied to the right application.