Use
Variable-Speed Motor Controllers for
Fans & Pumps with Modulating Flows
Where air
or liquid flows must be controlled to vary by 30% or more, they
are good candidates for variable-speed control instead of 2-way
control valves or dampers. These increase static pressure of the
fluid loop to reduce flow, wasting pump or fan energy. The larger
and more varied the flow, the greater the energy savings available.
It is now
economic to use variable-speed motor controllers for most fans,
pumps and compressors of 10 horsepower or more with variable flow
and high operating hours.
For many HVAC
applications, variable frequency drive (VFD) speed controllers
are a good choice. They offer precise flow control, quick response,
soft-start capabilities and high power factors, and are efficient
over a wide range of speeds. VFDs can be retrofitted to existing
motors, though motors are best selected specifically for use with
VFDs.
Be sure to
select a controller suited to the load; constant torque loads,
such as constant pressure and positive displacement pumps, and
some compressors may require oversized drives and motors to ensure
sufficient cooling under low speeds.
Cautions:
- Pumps operated
in parallel should all run at the same speed.
- Ensure
current rating of controller exceeds the total current rating
of controlled motors under overload conditions.
- Ensure
that VFD presents low harmonic distortion to the electrical
distribution system.
