I've been looking at pumps for our DIY build. An energy efficient pump is especially important since we have a battery backup system (power cuts up to 3-4 days) and will be installing a larger, totally off-grid system in the near future. (Unreliable power at $0.25/KwH the main reason). Without getting into the specifics of the pool and required pump, I have some general thoughts and questions to run by forum members.
I've had very little success finding 12-24 volt DC pumps suitable for a pool installation (suggestions welcome). Variable speed pool pumps may be an option as a last resort. They are more attractive to me than 2 speed pumps since they seem to operate at much lower power levels(eg. 160 watts - 230Vx0.7A for the Intelliflo). My hesitation at the moment are reports of the controller failing (especially the Intelliflo), no warranty service in Nicaragua, the addition (and inefficiencies) of a step-up transformer (from 115 to 230V) to our system, and a cost of over $2000 to get one here.
Given the energy efficiencies and cost savings reported for these pumps I began searching for "variable speed pump" alternatives. I came up with an item called "AC Drives" (variable frequency drives, variable speed drives). These are the controllers that allow one to control the speed (rpm) of an AC motor. They have been around for decades and are not quite the newest, greatest thing that the pool industry would have you believe (well, maybe for pool pumps, but not by a long shot for other pump applications). For .5 to 1 HP pump motors they cost $100-$200, have very sophisticated control features, and wire easily between an AC source and the pump.
Questions for forum members:
1. Could the appropriate AC Drive be paired with a (less expensive) single speed pool pump to make a "workable" variable speed pump (probably at half the cost or less than current VS pumps; and the AC drives being a considerably more mature product with a better warranty and more easily fixed/replaced)?
2.The AC Drive literature references the pros and cons of such controllers--such as moving pumps off their best efficiency operating point by changing their RPMs and unexpected electrical issues (harmonics?) and vibrations due to currents and RPMs not in original engineering specs--but generally concludes that the energy savings far outweigh the downside of such issues particularly for low voltage and low HP pumps (i.e. the 115-230 volt, .5 to 3HP pumps found in most pools). Do Pentair, Hayward, Jandy and StaRite VS pumps also face these issues? Have they engineered their pumps in any special way to mitigate/minimize these issues? (thus, perhaps, justifying a higher cost?)
3.Related to the point above about a pumps best efficiency, I believe that a pump's motor is closely matched with the wet-end impeller (correct me if I wrong). As above, the literature mentions that there will be inefficiencies due to an impeller operating at an RPM it wasn't designed for. I couldn't find anything in layman's language about such inefficiencies or if they are show stoppers. Is this also a problem though, for the current crop of pool VS pumps and, for that matter, 2 speed pumps? Are the impellers designed differently? If so, could (should?) a VS or 2 speed impeller be swapped into the wet end of a single speed pump with an AC Drive? Or, are the inefficiencies simply not "big enough" to worry about in relation to energy cost savings?
Thanks in advance for your thoughts and comments.