[RE-wrenches] Off-Grid Whole House RO

[Jay]

Hi Jason

What’s the actual water output from
The RO? We had one at our house before I took it out and replaced the house water with rainwater catchment. 3 yrs and counting in the high desert. 
I couldn’t live with the 2-3 to 1 loss ratio. 

A few options as I suspect the actual RO output is closer to 1-2 gpm. 
1. Use a 1/3hp well pump into a large pressure tank with relatively low pressure switch.  You might even get away with a small sump pump. The RO should t need but minimal input pressure 

2. Assuming the RO system doesn’t need rhe 1.25hp pump ( i  am assuming the RO goes into a tank and much then has a pressure pump to supply the house. If it doesn’t I would recommend installing said design) I’d install a smaller motor and pump head to better match the RO flow rate. 
You could look at getting a high efficiency DC pump or 3 phase with vfd. 
Sun pumps has such things. 

Jay



> On May 8, 2025, at 12:38 PM, Jason Szumlanski via RE-wrenches <re-wrenches at lists.re-wrenches.org> wrote:
> 
> 
> 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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