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We have been in the Variable Frequency Drive business for many years and can offer you a number of options for commercial pools. You may also recognize our name for the work we have been doing in VGB arena with our Automatic Pump Shut Off Device (PSP20).
To answer your questions (in no particular order); the energy savings are considerable and are based on the Affinity Laws associated with variable torque loads. The energy will come down by the 'cube of the speed'; in other words, if you reduce the speed of the pump to say 66% of its original speed (by dropping the frequency to 40 Hz as opposed to 60 Hz), the 'new' energy consumption will be 0.66 x 0.66 x 0.66 = 0.287 (or 28.7% of the energy taken at 60 Hz). As you can see Brian, the savings are very attractive. However, a word of caution, some manufacturers (who shall remain nameless), are touting that you can run centrifugal pumps at 10% speed and still get the flow required to achieve the desired 1 to 2 times turnover per day. We question the fluid dynamics of this argument as we don't believe the centrifugal forces within the pump at such a low speed would overcome the head. Another factor here is if the VFD has been successful in reducing the energy to say 28%, so what that it could be bought down by say another 5 to 10% or even 15% - assuming the flow could even be achieved - especially if it requires the replacement of the entire pump / motor combo. Why not achieve the result using the existing pump / motor?
In terms of reliability, VFD's are extremely robust these days and are frequently used in harsh 'industrial environments'.
Set up for a pool pump would be very straight forward as the demands of this application are really quite simple.
Please get back to me with any questions.
Sincerely,
Paul Hackett
Emotron Inc.