Ganging
together multiple fans can also increase efficiency. For instance,
Soler & Palau’s OEM Products Division of Montville, N.J., offers
backward-curved, motorized impellers that can be grouped for greater
efficiency. A backward-curved impeller is a centrifugal air-moving
wheel with blades inclined in the direction opposite to the
direction of rotation. The motorized impeller features an external
rotor motor. The fan blade assembly is press fit onto the external
rotor, which spins on the outside of the stator, and the rotor
revolves around it. The fins are curved against the direction of
flow, which pushes the air, says Carl A. Giordano, P.E., senior vice
president and general manager, Soler & Palau North America, OEM
Products Division, Montville, N.J.
Because the
impellers only produce, at maximum, about 2 in. of static pressure,
they can grouped together to increase airflow. In a typical
configuration, the fans are installed in a tray and situated along
the same plane, and they pull the air in the same direction and
exhaust it in the same direction. “So, if you want to filter air,”
says Giordano, “the fans would be placed behind the filter or behind
the heat exchanger, and the impellers will pull air through that
medium and then into the throat and exhaust it in the back of the
unit.”
The impeller
does not require a housing to work, which gives the designer an
“elegant solution” to a number of different applications. The
impellers have permanently sealed ball bearings and can operate in
any orientation. “They can be mounted upside down, sideways on a
vertical plane, or horizontal plane,” says Giordano.
The
permanent-split-capacitor motors come in about a dozen sizes ranging
from 5 in. to about 14 in., 115 V and 230 V, and are single phase,
speed controllable. “That has the benefit of allowing the designers
to change the RPM, which directly changes the air flow and static
pressure to meet the application,” he says.
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