Options for new well pump

nickdearing88nickdearing88 Registered Users Posts: 86 ✭✭✭
Hi everyone.

I recently purchased my future off-grid property, but will remain grid-tied for the next few years, and need to plan for a replacement well pump. The current jet pump is an old Goulds 1/3 hp and running on it's last legs. It only seems to manage half of it's rated flow at water depth and looks like it's had a rough life. I drained the system down, corrected pressure tank setting to 2 psi below cut-in (38 psi), the system is currently set to 40/60 psi.

The well is a 4" casing and about 12 feet to static water level. Bottom of the well is about 25 feet. The current pressure tank is 25 gallons, but I'd surely replace it (at the same time as the new pump) with a larger one to avoid short cycles. Average water use is about 2000 gallons/month and I'm hoping to stick with a minimum flow rate of 8 GPM but could probably get along with slightly less.

As stated above, the system will be on grid power for awhile but my future plans are off-grid, so efficiency and startup surge are my main concerns. Price is also a factor but third on the list.

I was considering a solar direct submersible pump with a storage tank but I'm concerned about the storage tank and potential "code/permit" issues. This would also require a good-sized storage tank and second pump for pressurizing the home supply.

I also read about the Grundfos systems but they are very expensive and I worry parts/replacement would be difficult to locate during a sudden failure. The AC/DC and wide voltage range is a definite appeal though.

Finally, I wonder if my best option would be to simply replace with a new jet pump, since the well depth is so shallow. With the cost savings of a very affordable jet pump, I could buy a larger inverter to cover the startup surge. What about VFD/soft start options for jet pumps?

Just curious what others with more well system experience suggest. Thanks!
Current test system: 4-100w Renogy panels mono/poly, 1 string of 4 panels in series - 24v 100Ah AGM Battleborn LiFePO4 batteries - Morningstar MPPT40 CC - 1500W Samlex PSW inverter

Comments

  • Ralph DayRalph Day Solar Expert Posts: 871 ✭✭✭
    edited August 15 #2
    I once had a jet pump for my house system...couldn't get it primed because the water line was not all downhill .  Well system has always been on submersible pumps.  The first 2 worked fine off utility power, you wouldn't even notice the inrush/startup.  Off grid our colour tv would go black and white with 30% less screen for a second when the pump kicked on (over 40amps startup).

    Present pump is a Grundfos.  Starts at zero amps, ramps up to 9amps then shuts off when done.  Never notice lights flicker on startup.

    House also has a 3000gal cistern/tank using rainwater for 6-8 months of the year.  Went from a noisy inefficient jet pump to a Conergy booster pump.  Jet pumps are the most inefficient way to pressurize water by their design. Tank level is above pump level, so no lift required.  Only 2gpm,, but large pressure tank so lots of water pressure.  I even measured power consumption to compare between submersible and booster.  The booster won on daily use, but only by a few kwhrs per week.

    Ralph
  • EstragonEstragon Registered Users Posts: 1,416 ✭✭✭✭
    Might be pushing it a bit on the suction side for a jet pump. 12' might work, but I 'd be concerned it would lose prime or cavitate when/if the well is drawn down faster than it recharges. Seems to me they have about a 10' suction side max lift, but maybe some are designed for more?

    I have no trouble running my regular submersible off-grid. Unless you're planning a pretty small off-grid system, the extra cost for a high end pump probably isn't worth it.

    Bigger is usually better for the pressure tank, subject to well recharge and pump flow rates though.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • BB.BB. Super Moderators Posts: 26,758 admin
    Suction side lift can be a big issue.

    You have the simple laws of physics (x PSI of air pressure will push y feet of water up against a pure vaccum).

    Then you have the reality of "pressure" drops of a partially plugged input screen/filter. Higher than sea level. tiny air leaks in the suction line/joints. And momentum of the water (getting the water moving into the pump).

    All of this can cause "cavitation" in the pump:

    https://blog.craneengineering.net/what-is-pump-cavitation

    Which can cause excessive wear and damage to the wet parts of the pump (on the lift side).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jonrjonr Solar Expert Posts: 844 ✭✭✭✭
    edited August 16 #5
    25' is the usual limit for a shallow well jet pump. 12' will be fine, even if there is draw down (which can't  go lower than 25' because your well is only 25').
  • nickdearing88nickdearing88 Registered Users Posts: 86 ✭✭✭
    What about a piston pump for this application? I assume they're quite heavy-duty and a motor could be easily replaced/swapped. I don't know if anyone uses them for residential well applications.
    Current test system: 4-100w Renogy panels mono/poly, 1 string of 4 panels in series - 24v 100Ah AGM Battleborn LiFePO4 batteries - Morningstar MPPT40 CC - 1500W Samlex PSW inverter
  • mcgivormcgivor Registered Users Posts: 1,190 ✭✭✭✭
    Piston pumps are wonderfully simple, I used one for 10 years, pumped water for home and irritation, powered by a Kubota diesel engine, which was totally overkill but at that time I had no grid or solar, well has static water 2 to 6 meters depending on seasons, total depth 40 meters, 6 inch diameter. Had to replace the piston after  many thousands of hours, donated it to others who still use it for irrigation with a 1/3 hp electric motor, they sell them here with 24 V DC brushless motors for ~$400.
      1500W, 6× Schutten 250W Poly panels , Schneider 150 60 CC, Schneider SW 2524 inverter, 8×T105 GC 24V nominal 

  • MangasMangas Solar Expert Posts: 537 ✭✭✭✭
    edited August 16 #8
    We have our off grid water system set up on storage to on demand basis. Only way to go in my opinion to reduce well cycling and assure redundancy.

    8 gpm is plenty of water on solar hours, storing it for on demand use in a potable water tank.  Our two Norwesco 1,700 gallon underground water tanks are plumbed with Grundfos 1/2 hp pumps to pressurize a 500 gallon pressure tank but above ground potable water storage of similar size with a smaller pressure tank would work fine .  Norwesco builds above and below ground potable water storage tanks holding a hundred gallons to thousands of gallons.

    We like building headroom capacity in all our systems. Suggest a pressure tank larger that what you are using. We use a Square D 40/60 pressure switch which is easier on the unions and fittings.  Don't like wasting water either.

    Many people here gravity feed from water storage tanks either on a tank stand or using elevation without pressurizing.

    From your post not was not sure if you're planning an off grid system to handle something like the above but thought I'd share our set up for comparison.

    Many resourceful folks on this forum to weigh in.
    Ranch Off Grid System: 2 x pair stacked Schneider XW 5548+ Plus inverters (4), 2 x Schneider MPPT 80-600 Charge Controllers, 2 Xanbus AGS Generator Start and Air Extraction System Controllers, 64 Trojan L16 REB 6v 375 AH Flooded Cel Batteries w/Water Miser Caps, 44 x 185 Sharp Solar Panels, Cummins Onan RS20 KW Propane Water Cooled Genset, Rastra House Construction, 2 x High Efficiency Variable Speed three ton Central A/C 220v compressors, 2 x Variable Speed Air Handlers, 2 x HD WiFi HVAC Zoned System Controllers
  • jonrjonr Solar Expert Posts: 844 ✭✭✭✭
    edited August 16 #9
    I see a lot of tanks on small towers in hot climates.   But once you have batteries and an inverter (for other reasons), then I think that it's most cost effective to either "pump on demand" or pump to a ground level tank while the sun shines and pressurize on demand.

    On the other hand, if you happen to have a hill above you, why not do all your pumping while the sun shines?
  • nickdearing88nickdearing88 Registered Users Posts: 86 ✭✭✭
    jonr said:
    I see a lot of tanks on small towers in hot climates.   But once you have batteries and an inverter (for other reasons), then I think that it's most cost effective to either "pump on demand" or pump to a ground level tank while the sun shines and pressurize on demand.

    On the other hand, if you happen to have a hill above you, why not do all your pumping while the sun shines?
    Not much elevation difference on my land. My lot is on top of a large hill but the house is at the same level.

    @jonr you have extensive knowledge about wells and water pumping - What would you go with in my situation for on-demand: jet pump, Grundfos, other submersible, piston, etc?

    Do they make a jet pump with a "soft start/inverter" type motor?

    Thanks!
    Current test system: 4-100w Renogy panels mono/poly, 1 string of 4 panels in series - 24v 100Ah AGM Battleborn LiFePO4 batteries - Morningstar MPPT40 CC - 1500W Samlex PSW inverter
  • jonrjonr Solar Expert Posts: 844 ✭✭✭✭
    There are lots of variables to consider, but I'd probably continue on with the existing pump and if it dies, replace it with a similar one.  It's < 100Wh/day and not a huge startup surge - don't spend much to optimize it.
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