[RE-wrenches] Off-Grid Whole House RO

[Jason Szumlanski]

Water pump is not my strong suit. I usually leave that up to the experts
around here. Unfortunately, the experts are clueless when it comes to
off-grid living. I have a client with a setup that is pretty unworkable.
I'm trying to give him some general guidance.

The setup uses a brackish water (might as well be salt water) very shallow
well. It is about 3 ft underground for the water table. The RO system
installer has a 1 HP 1.25 SF Century centrifugal surface pump drawing water
from the well and pressurizing the inlet of a StaRite 1.25 HP booster pump
designed for about 10 GPM at 150 PSI to run water through the RO system.

Both of the pumps run simultaneously and continuously when producing water,
and the water production is ridiculously low. I understand that RO
production is going to be slow, but the amount of power these pumps are
using is pure insanity. I have advised the client that, at a minimum, this
system needs to be on a smart load circuit to run only when there is
adequate battery capacity. The startup surgery is not a concern, but it
does flicker the lights and it makes quite the racket.

My thoughts are that the well pump is drastically oversized. The booster
pump only needs 10 gallons per minute, and it has a suction head of 15 ft.
I don't even know if the well pump pressurizing the booster pump inlet is
required. I'm thinking we should be slow pumping water into an interim
holding tank at least at the height of the booster pump. At a minimum, the
well pump should be on a pressure switch with pressure tank so it can
cycle.

Can anyone give me some general guidance, and perhaps a VFD pump that does
not have the startup surge and is maybe more efficient? During times of
heavy use, the RO system can easily eat up half of the PV produced during a
day at this site.


Jason Szumlanski
Florida Solar Design Group
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