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Is a VFD (Variable Frequency Drive) Right for me?


For this blog, I am specifically writing about residential submersible well pump systems that use variable speed drives to achieve constant pressure.

The short answer to the opening question, Maybe. But most likely Not.

Are VFD’s more efficient? No, not even close. A pump is much less efficient at slower speeds and also when it is operating outside the recommended range. Most in home applications require less than 2 to 3 gpm and thus would be very inefficient. A conventional pump system runs 1 to 2 minutes generally at its most efficient point to refill the pressure tank. In most low flows using a standard size tank, you can use 20 to 25 gallons between pump cycles.

So what about cost of installation? Installation is generally a little higher than conventional.

Constant water pressure is one of the major reasons that people get excited about VFD’s, however, this can easily be accomplished by inexpensive mechanical means. Cycle guards, cycle stop valves, even pressure regulating valves can be used. It is worth pointing out that a VFD will provide constant pressure at greater efficiency than a mechanical option.

So after all that, what does a VFD really do that’s good?

  • The main benefit is cycle protection at the expense of efficiency.
  • They provide constant pressure, however, mechanical valves can do this also.
  • They protect the motor from a variety of situations that could damage it, however, motor protection devices are inexpensive compared to VFD’s.
  • There is a potential for longer motor life due to soft start capabilities and the overall higher reliability generally found in 3 phase motors.
  • They are compact.

So when is it a good time to consider a VFD?

  • Wide range of flow (Small agriculture, small community systems)
  • Exceptionally deep wells or great distance from electrical source (wire size, but wire doesn’t wear out like electronics). Make sure you consult the manufacturers limits on wire length per drive.
  • Situations where space for sufficient pressure tanks for standard system with non-VFD is not available. VFDs require a much smaller pressure tank.