Florida Pool Pro
sm
• November 2014
15
at a similar price to VFD-on-pump models. These offer advanced features like
Modbus internet-ready communications, 4-20mA control circuit connections
to flow meters and chemical controllers, and monitoring and documentation
of electrical supply power mishaps.
Commercial Applications: Many commercial renovation and service
contractors have complained of limited success with VFD applications, including
premature failure of the VFD’s and of the pumps. At the same time, some other
companies have experienced great success with many hundreds of highly
successful installations. What is the difference? One big difference has been
the “completeness” of the commercial VFD package. Historically, “VFD-only”
installations have experienced more issues while more complete packages
have prospered.
Limitations: While the VFD power conversion sequence offers a bit of inherent
power conditioning, it has not proven to be robust enough to protect the VFD or
the motor in an alarming number of (dirty) pump room power systems, leading
to failures. Also, connection of starters, interlocks, line reactors, etc. call for
in-field design of both high and low voltage circuits and (field) UL approval in
many municipalities.
Options: Once you get to larger and more expensive pumps, it seems fitting
to add more protection features to the VFD package. These have included
phase protection, incoming power conditioning, output isolation relays, etc.,
thus protecting the VFD’s on both incoming and outgoing power circuits.
These can be added to the initial VFD package at a reasonable price, while
providing a more complete UL-listed package. Finally, in the event of a mishap,
it is advantageous to have an installed “bypass loop” to allow direct operation
through an integral starter at the flip of a button. If not so equipped, it would
be necessary to (have an electrician) rewire the pump directly in the event of
a VFD issue, meaning the pool would be “down” until that was accomplished.
Conclusion: VFD savings can be extremely significant. How much?Apump
with a clean basket strainer and filter can operate as low as 30-40 Hz instead
of 60 Hz. At 40 Hz, the power consumption (based on proven affinity laws)
would be around 29 percent of normal power. Yikes!
