Off grid well

[jsmitman82]

I had a well drilled, specs are:
380' deep
200' depth water first encountered @ 1gpm
240' depth water @ 3gpm
300' depth water @ 5gpm
340' depth water @ 8gpm
380' depth water @ 15gpm
30' static water level

I have a contractor lined up to build a house next spring.  I currently have no power at the property, but plan to incorporate a large off grid power solution (inverter, batteries, solar, generator, etc).  There are no buildings currently on the property with which to locate the components for a power or water system.  I would like to have water functioning before the house build starts, which also means before I have an off grid power solution.  My well driller is trying to sell me an expensive $8k VFD system (goulds 10gs30, 3as30, 3hp 3 phase motor, 4.25gal in well pressure tank) and saying that it is what he recommends for off grid people, with a plug for a generator at the pedestal that also contains the vfd drive.  After tons of research I am not convinced that this is in my best interest economically.  I am concerned not just for the longevity of the components in my water system, but also the total power requirements of it - not just power required to pump the water we will use but also the idle power draw of the VFD drive.  I am not sure a CSV is going to be the best path either (in terms of efficiency), but I do like the simplicity of it and what it offers.  If I want to go for maximum efficiency then any constant pressure solution is probably not the answer, but I'm not sure that I need to optimize that heavily - I just worry about low solar production in the winters in Northern Idaho, and reducing my need for running a generator during those months.  I'm not sure what to do, but I am concerned that I will regret moving forward with this expensive VFD system; however, I'm not sure what my alternatives are for my situation of needing water before I have a building where I could locate water system components like a pressure tank.  My water needs before the house is completed will be much different (no toilets flushing with no house), so I could add things like a pressure tank and CSV at that time... but I'm not sure if I could/should run a submersible pump off a generator with no pressure tank before the house is built.  I'm also wondering if it's possible to install 2 pumps of different sizes in the well (each on its own CSV), one for small flow and one for larger flow, where the small one would run most often and be more energy efficient due to being closer to its BEP.

Apologies if I've left out important details, my brain is fried after reading about wells for several hours.

[jsmitman82]

Could you install a CSV after a large pressure tank?  I am wondering if you could achieve both constant pressure and maximize power efficiency (off grid concern), by combining a CSV and a large pressure tank, where the pump would run at BEP to fill the large tank, and then when water is drawn from the tank the CSV would keep the pressure down near the low end of the tanks pressure.  If not, is there another way to achieve this?

[Cary Austin]

Sorry for the delay.  Don't get much done when I am keeping the granddaughter over the weekend.  Lol.  First off a 3HP, 10GS30 is designed to work in wells from 600-800 feet deep.  All you need to get 10 GPM at 50 PSI from 380' is a 1.5, 10GS15.  Using a normal 240V single phase motor if you attack it to 480' of "10 wire, the long length of small wire works like a soft starter.  Using the longest length of the smallest wire possible for the HP pump being used causes a reduction in torque of 36%.  No need for any VFD or soft starter.

With a 30' static level the 1.5HP pump will build 225 PSI back pressure on the pipe prior to the CSV.  This is a little more back pressure than we like on the CSV1A but will work fine as long as your pipe is rated for 225 PSI or more.  All you need to control this pump is a PK1A control kit with a 10 gallon size tank.  The higher the pressure you want the better for the differential pressure.  So if you would like 60 or even 70 PSI constant, just get the PK1A kit with the heavy duty pressure switch that can be turned up to 60/80 as needed.  This size pump with the small wire will start easily on a generator of a 230V inverter.  The three wire version with a capacitor start box will start even easier, and is recommended.

Putting a CSV or a pressure reducing valve after the pressure tank will give you a constant pressure.  However, it will be low constant pressure and the pump will still be cycling itself to death while you are getting low constant pressure.

Call us ig you want to discuss.  Thanks.  Cary

[jsmitman82]

The performance chart here shows the 10GS15 as doing 7.4gpm at 50psi, so it seems like I would need a 2hp to break 10gpm and/or 50psi (at 380 feet).
https://www.aquascience.net/media/catalog/product/G/o/Goulds_10gs15_7.gif

What do you think about the 250psi rated HDPE pipe vs PVC (schedule 80 or 120?) for this well, in the context of me maintaining it myself?  Sch120 PVC has much better pressure rating, but it seems like it would be a lot more opportunities for leaks between sticks, and I'm not sure which would be easier for me to install and remove when the day comes that I need to replace the pump.

So if I have a CSV/PRV after the pressure tank set to 40psi, and a pressure switch at the tank set for 40/60psi, I wouldn't have a constant 40psi after the CSV/PRV, while the pump only cycles once the tank drops from 60psi down to 40psi?

[Cary Austin]

It really depends on your water needs?  For just a house you only need 5 GPM max and a total of 300 gallons per day.  Your well stores about 1.5 gallons per foot.  So, you really only need to set the pump at like 230' to have 300 gallons stored.  Set at 380' you would have 525 gallons stored in the well, and I doubt you will ever pull the water level down lower than 230' or so.  At that depth, even a 1HP, can give you 10 GPM at 50 PSI.

If you want to irrigate or something everything changes.  But we would still need to know how much water you need as it takes a much smaller pump set at a more shallow depth to give 5 GPM to sprinklers than if you want to run 15 GPM sprinklers.

The smaller the pump the lower the power requirements for solar or a generator.  For just house use I think you would be happy with a 7 GPM, 3/4HP set at 230' deep.

[jsmitman82]

I haven't tested how fast the water level replenishes up to the current static level, which I assume would be different rates depending on how far it draws down, given the GPM measurement increased the deeper it went.  Given I lack that information, I'm a bit worried about setting it too shallow.  I'm also not sure if I intend to use it for irrigation and gardening in the future.  So I'm leaning towards setting it at probably 360', just a small buffer from the bottom.  Can/should I use 250psi HDPE pipe at that depth?

[Cary Austin]

Just the depth of 360' will cause 155 PSI pressure on the pipe.  Add to that the 60 PSI needed up top and you are at 215 PSI.  You can still get 10 GPM at 50 PSI from 360' using a 10GS15, and the CSV will cause the pipe to see 242 PSI.  So, yes the 250# pipe is recommended.