Commercial refrigerated display cases commonly use shaded-pole motors (SPMs), permanent split-capacitor motors (PSCMs), or electronically commutated motors (ECMs) to drive evaporator fans. For certain retrofit applications, synchronous motors are emerging as a cost-effective replacement for these motor types.
SPMs are used in roughly 65 percent of evaporator fan applications, and they dominate the market thanks to simple construction and low first cost, according to researchers at Oak Ridge National Laboratory (ORNL). However, SPMs have an average operational efficiency of only 20 percent.
PSCMs are more efficient than SPMs, in the range of 40 to 50 percent efficient, and they are still relatively inexpensive.
ECMs, while more expensive than SPMs and PSCMs, are gaining popularity because they offer an operational efficiency of 50 to 60 percent. These motors also run cooler and typically have a longer operating life, making them a cost-effective alternative to SPMs.
Synchronous motors, until recently, weren’t considered cost-effective because they require an expensive controls circuit to synchronize the shaft rotation with the frequency of the supplied current. But motor manufacturer QM Power introduced a permanent-magnet, synchronous alternating-current version called the Q-Sync motor—which offers efficiencies on the order of 70 to 80 percent.
Q-Sync and ECMs are similarly constructed: both use permanent magnets to generate a magnetic field. Where the two motors differ is in their electronic controls. For an ECM, the control circuit consumes power whenever the motor is running. In contrast, the Q-Sync control circuit adjusts control needs based on the motor speed: Once a steady-state motor speed is achieved, the control circuit disconnects itself from the motor’s power supply. With the control circuit de-energized during steady-state operation, the motor assembly consumes less energy overall—making it up to 20 percent more efficient than a standard ECM. In addition, the Q-Sync power factor is higher (0.94 compared to 0.61 in ECMs), so that the Q-Sync puts more electricity to use while wasting less internally in the circuit.
The report Q-Sync Motors in Commercial Refrigeration: Preliminary Test Results and Projected Benefits (PDF) documents how ORNL researchers measured Q-Sync energy consumption through field demonstrations. The researchers found that Q-Sync motors outperformed ECMs (Figure 1).
Figure 1: Evaporative fan motor annual energy consumption
In a field study, researchers found the annual energy consumption of Q-Sync motors to be 54 kilowatt-hours less than that of electronically commutated motors. With equipment and installation costs similar to other motor types, Q-Sync motors should be an ideal choice for motor replacement.
ORNL researchers estimate that in the US, replacing all evaporator fan motors in refrigerated display cases and beverage vending machines with Q-Sync motors would cut the total motor energy consumption by 68 percent—translating to about $516 million in annual savings. Q-Syncs can also be used for ice makers, heating, and ventilation and air handling applications. They are comparable in cost to ECMs and are manufactured with the same form factor as the stock motors found in the original refrigeration equipment. This facilitates drop-in installation, making these motors an ideal choice for equipment retrofits. Existing motors can be replaced with Q-sync motors for only around $100 more than replacing with the same model, as long as the fans are compatible.