DC refrigeration fan motor.
Fan sizes of 12 in (300 mm) and smaller are traditionally operated with
a.c. shaded-pole fractional-hp motors (SP motors) in the refrigeration
According to ebm, even though the manufacturing cost of SP
motors is very low, their uneconomical energy transfer is a growing
problem for equipment manufacturers. More than 70 percent of electricity
by SP motors is said to be lost to motor winding temperature rise.
condenser fan motors heat the air coming off the coil before it is discharged
into an oftentimes air-conditioned ambient such as a
convenience store, supermarket building, or residential home. "While
that might be acceptable in the heating season, unnecessarily high amperage
and power ratings on the equipment nameplate can affect the purchasing
decision," explains Armin Hauer, product manager at ebm. "In
the cooling season, the building operators suffer from additional heat
loads, resulting in high electricity bills. Architectural design and
construction engineers are sizing air-conditioners larger, offsetting
savings from buying so-called 'low-cost' fan motors."
problems are amplified in evaporator applications, according to Mr.
Hauer. The self-heating of the motors increases the pull-down
time, extends the on-cycle of the fans and compressors, and affects
sizing of components.
Along with a very aggressive cost target, Mr. Hauer says
the design criteria for ebm's electricity-saving motors (ESM) included
simplicity and drop-in
replacement for shaded-pole motors. The result is an a.c.-line operated
brushless d.c. motor. The entire drive and control electronics (including
EMI/RFI filters) are hidden in the motor enclosure, where they are
sealed and protected from moisture, citric acids, and cleaning solvents.
motor system's overload protection is accomplished electronically. "Since
the ESM operates with internally rectified d.c., there will be no performance
change if equipment originally designed for 60 Hz will be used at 50
Hz and vice versa," says Mr. Hauer. "Within limits, a reduction
from nominal 127 V a.c. in Mexico, to nominal 110-120 V a.c. in the U.S.
or Canada, results in unchanged motor output," he adds. The ESM
ambient temperature range of -22°F to 122°F (-30°C to +50°C)
allows for both evaporator and condenser applications.
Mr. Hauer explains
that the ESM development was based on an external rotor motor. "Instead
of providing a shaft extension to apply a component impeller, fan blades
can attach directly to the hub of the
external rotor," he tells APPLIANCE. "Sickle-shaped blades
and a plastic fan housing were optimized for the ESM performance characteristics.
Five curved struts have a guide-vane effect. The combination of the high-speed
ESM with the newly engineered fan provide interesting solutions to the
problems of modern refrigeration equipment."
The motor's mounting
details include an optional shaft extension that adapts to a wide variety
of component impellers, typically made of plastic
or sheet-metal. A durable ball bearing system, suitable for any shaft
orientation, is also used. According to Mr. Hauer, permanent magnets,
which are inherent to brushless d.c. motors, can generate a disturbing
mechanical ripple, especially in vibration-prone, thin-gauge sheet-metal
assemblies common in the refrigeration industry. Therefore, he says,
an effective vibration isolation system has been built into the motor