More than half of the energy consumed by buildings in the U.S. is used by electric motors. Refrigeration systems are dependent on motors to operate fans in both condensing and evaporator units. The evaporator fans found inside a walk-in cooler or freezer are especially good candidates for energy-saving motor technology for several reasons. First, a typical walk-in cooler in a convenience store may have 8 or more evaporator fans, so a more efficient motor design can have multiple applications within the same space. Second, those fans usually run 24/7/365 in a cooler and almost as much in a freezer, so there is almost never a moment when a more efficient motor would not be saving energy. Third, because all the electrical energy used by an evaporator fan is converted into heat that must be removed by additional operation of the compressor and condensing unit, there is a multiplier effect called the “compressor bonus” (perhaps an extra 40% in a cooler and 60% in a freezer) that applies to any reduction in energy used by the fan motors in the refrigerated space.
For the vast majority of time that commercial refrigeration has been around simple, cheap shaded pole motors were all that were available, and though invented way back in 1888, are still in use for almost 2/3 of the evaporator fans operating today. Shaded pole motors use electricity to induce the magnetic fields they need to operate and are only about 20% efficient. The electricity they consume over their 15-year lifetimes costs about 50 times as much as they cost to produce.
When the ever-rising cost of electricity and concerns about global warming began to spur interest in energy efficiency a couple of decades ago, the first widely adopted advance in motor technology was the permanent split capacitor (PSC) motor. A PSC motor uses a capacitor and windings to effectively provide a 2-phase motor that runs at about 29% efficiency.
A giant leap in efficiency came to the market for evaporator fans about a decade ago with the introduction of the electronically commutated motor (ECM). ECMs use permanent magnets to induce the needed magnetic fields and a sophisticated electronic circuit board that rectifies the current from AC to DC to bring the efficiency up to 60 to 66%. Today, after a mandate from the federal government for ECM technology to be installed in all new equipment, about 1/3 of the evaporator fan motors in the country have been upgraded to ECMs.
Just when it seemed that we may have reached the apex of efficient motor technology, something called a permanent magnet synchronous AC motor (PMSM) has appeared on the horizon. A simpler, non-rectified motor that may deliver up to 75% efficiency has performed well in tests done by the Oak Ridge National Laboratory. PMSM motors represent an improvement of 27% less energy use compared to ECMs. Significantly, the current draw is 53% less than with an ECM, because the Power Factor is a healthy .936, versus an ECM with only a .601 power factor. This is a big improvement for the electric utility, which can provide a smaller amount of power to a customer who often does not pay any penalty for a poor power factor.
It will take a while for new, more efficient motor technologies to become fully accepted in the commercial refrigeration marketplace. In addition to evaporator fans for walk-ins, both larger evaporator fan motors for refrigerated warehouses and smaller motors for reach-in coolers and vending machine, as well as condenser fan motors can potentially benefit from these rapidly changing developments.