Electronically commutated permanent magnet (ECPM) motors always have higher efficiencies than conventional single-phase, fractional horsepower induction motors because they do not suffer resistance losses from current flow in aluminum rotor bars. As smaller motors have higher losses than larger motors, research in the 1990s focused on small ECPM motor design and optimization. This assessment focuses on programmable ECPM motors that are used for indoor blowers and outdoor fans driven by 1/15, 1/10, 1/5, 1/3, ½, ¾, and 1 horsepower motors. These ECPM motors have much higher full-load efficiencies than standard or conventional capacitor start/induction run and capacitor start/capacitor run (PSC) motors. They come with integral controllers or electronic inverters that can control both motor speed and torque, which can result in far greater energy savings in many applications compared with conventional constant-speed motors.
A review of manufacturer’s literature for fractional horsepower ECPM motors supplied by Marathon, Genteq, and QM Power indicates that full-load efficiencies fall in the range of 78% to 82%. The typical maximum efficiency of a multi-speed PSC motor is around 60% at rated full-load speed (Beloit, 2010). ECPM motors hold their high efficiency when lightly loaded, operating near 80% efficiency across the motor’s entire operating range (Beloit, 2010). At part-loads, the differences in efficiency between the variable-speed ECPM and standard motors grows in favor of the ECPM motor. As ECPM motors feature inherent variable speed capability, energy savings are substantial in applications with fluctuating load requirements.
ECPM motors are increasingly being recommended or required in city or state energy codes for some single-phase evaporator and condenser fan units, or fractional or integral horsepower series fan terminal units, swimming pool pumps, and circulating hot or chilled water pumps. With these systems, hot water, air, or refrigerant is circulated through a heat exchanger to condition a space. Energy savings of 20% to over 70% can occur when ECPM motors are used to replace conventional fractional hp single-phase PSC fan or blower drive motors.
ECPM motors could also be used in residential equipment, although the savings may be less because more residential fans are multi-speed and thus the addition of variable-speed motors wouldn’t be as much. Furthermore, this is less cost-effective due to the additional costs of programming the ECPM motor to duplicate the performance of a multi-speed baseline motor.
Electronically commutated permanent magnet (ECPM) motors always have higher efficiencies than conventional single-phase, fractional horsepower induction motors because they do not suffer resistance losses from current flow in aluminum rotor bars. Smaller motors have higher losses than larger motors, so research in the 1990s focused on small ECPM motor design. In partial load applications, the differences in efficiency between the variable speed ECPM and standard motors increases.
In commercial variable air volume (VAV) applications, ECPM motors may be equipped with voltage feedback control (0-10 VDC) from sensors so constant pressure or constant air flow operation can be provided. Good duct design and clean filters are important for ECPM operation. With a permanent split capacitor (PSC) motor-driven blower, an airflow restriction (such as a clogged filter) has much the same impact as a discharge damper: airflow and motor input power are reduced. With an ECPM motor, the motor speed increases to maintain a constant airflow, resulting in an input power requirement that may exceed that of the old PSC motor.
ECPM motors can also be employed to control fans used in package terminal air conditioners, room air conditioners, unitary condenser fans and blowers, and exhaust fan applications commonly found in commercial buildings. With these systems, hot water, air, or refrigerant is circulated through a heat exchanger to condition a space. Energy savings of 20% to 33% typically occur when ECPM motors are used to replace conventional fractional hp single-phase PSC fan or blower drive motors.