Need help with Alternate Method of pumping in two-well "pump & dump" systems?

Discussion in 'Solar and Geothermal Water Heating Forum' started by Thumper, Apr 3, 2009.

  1. Thumper

    Thumper New Member

    Apr 3, 2009
    I have combined the following two posts from "Green Building Talk" into this thread in hopes of obtaining some expertise or direction. I am building in the coming months and am willing to experiment IF the science is solid. Proposed is a two well (source and recharge) geo setup.

    This is a proposed alternative to the traditional domestic well pump scenario with the associated head lift/high-pressure/energy consumption problem:

    Post #1:

    [ Since a [submergized] domestic well pump when being used for geo pressurizes the water to 35-50 psi and lifts it to the house with low efficency can the following method be used instead:

    1. install a second 3/4 or 1" geo water source pipe in the supply well placed alongside the normal pipe from the submergized water pump. Maybe use a "deep-well jet pump" pitless adaptor (a dual fitting for two pipes) for the casing connection to handle the two pipes...

    2. install a check-valve at the bottom of the geo source pipe and drill a smallish "bleed" hole above the valve (for priming purposes).

    3. run this second pipe to the house and connect via a "T" to 1) a valve that is connected to the cold domestic water supply (high pressure water) and 2) a small "jet-pump" or simply a normal circulator pump with decent head.

    4. this circulator pump (or small jet-pump) feeds the geo exchanger and then the dump side continues via pipe to a second [recharge] well. This return pipe continues via a pitless adaptor and pipe down to somewhere permanently below any static water level in the second well.

    5. the valve in the house would be used only to prime the supply pipe and small pump.

    The standing water levels in both wells would obviously vary depending on many reasons. However, wouldn't the small water pump only have to overcome the following flow resistances: total pipe length restrictions + geo exchanger head loss + any difference between the standing water levels in the two wells. If the standing water levels are roughly equal then the little pump only needs to overcome pipe and exchanger resistance and would not encounter much lift [gravity] resistance.

    If I understand correctly it's a combination of lifting the well water to the surface and pressurizing to a high-level is what uses so much energy. This seems to solve both problems. Would this work better than using a varible frequency motor well pump or a domestic use/pressure adjusting method?

    Also it seems this configuration would be free from a flow direction that otherwise would be dictated by the domestic water pump. In otherwords depending on well yields and the static levels maybe we could use one well to supply the geo and dump into the domestic source well. This way the water use load is split between the wells and not all coming from just one well. ]

    Post #2:

    [ Location is SW Montana; estimated 4 to 5 tons required (sorry, no precise heat calc performed yet for a well-insulated house). Proposed GSHP system type; WaterFurnace Synergy 3D or rough equal for radiant floor (gypcrete thin-slab), forced air AC (electric strip backup), & desuperheater.

    There is plenty of flat land to work with so any system type could be installed. My biggest horizontal closed-loop concern: very soft, powdery loamy+fine sandy soil (no rocks at all a good thing), soil will have low conductivity issues and is very dry even at at 8' down (only 10" annual precip)...probably have to use a soaker for a horizontal loop.

    A domestic water well will need to be punched anyway and may be upsized for light irrigation purposes and yield boost. Adjacent properties have both residential and some irrigation wells averaging 250' to 275' deep with standing water to 100' of surface. Yields are almost always high: between 25 to 35+ gpm. Precise water quality is unknown but adjacents don't have or need water softening systems (anedotal evidence only, no test data available yet). Bedrock depth is usually between 50 to 120'. Groundwater temp in the area is reported at 55 to 56 degrees.

    This is new construction and I am weighing all pros/cons/costs. The cost of the second well is mostly offset by not having to buy and bury a couple of 1000 gallon propane tanks so it would come down to the Geo equipment upgrade costs versus conventional high-eff. propane equipment. For cost estimating I'm also guessing the return well would be drilled down to the same depth and aquafer as the supply well. ]

    The last paragraph of post #1 has additional implications. I am considering light irrigation over part of the property. If the geo source well returns [dumps} into the domestic water source well, then in the summer months when both AC and irrigation are both needed then the two wells in essence share the load...thinking of it as a sortof parallel source well arrangement. Can the domestic source well also function as the geo recharge well?

    Any and all constructive thoughts or directions to existing bodies of work on this subject are greatly appricated. Again, I am willing to to pony the $$ to "experiment" with this but I will need to see the science and pitfalls first.

    Last edited: Apr 3, 2009
  2. Bill Arden

    Bill Arden Computer Programmer

    Sep 30, 2006
    computer programmer
    MN, USA
    1. The bottom pump would still have to pressurize the water up to a small amount in order to prevent a vacuum at the surface.

    15PSI = ~30 feet. This means that for each 30 feet that the water has to be lifted the pump has to create an extra 15PSI.

    pumping the water back down the well does not help more than 30 feet since if the water table is lower than 30 feet you would be pulling a vacuum at the surface.

    2. Check your local codes. Pumping water back down a well is not allowed in some areas. (here in MN for example does not allow it)

    I feel that open loop is a good stepping stone, however it's not a destination. The goal should be to plan for closed loop.

    Personally I'm going to try and drill a 3/4 well down 60 feet this summer and the thought is that I can cap the bottom end and slide a pipe inside the pipe to create a closed loop well. I'll need 12 of them in parallel, however the idea is to reduce the drilling costs by eliminating the need for a large rig or drilling mud.
    Last edited: Apr 5, 2009
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  4. Master Plumber Mark

    Master Plumber Mark Master Plumber

    Feb 6, 2005
    Sensitivity trainer.. plumber of mens souls
    indianapolis indiana - land of the free, home of
    Geo thermal works great here...

    Geo-thermal works great here in our state and from what I have seen , most all of the bugs have been worked out of most systems for years..

    From what I am reading you are trying to re-invent the wheel to save just a little energy over a normal conventianial geo thermal system that would work great.. and be trouble free for decades...

    would the cost saveings be worth all the risk of troubles??




  5. Bill Arden

    Bill Arden Computer Programmer

    Sep 30, 2006
    computer programmer
    MN, USA
    I would calculate the theoretical energy needed and then compare that to other possible changes.

    1. Water can only be sucked up a set distance. This also tells us the weight of the water column.
    14.7 pounds per square inch = 33.9 feet
    ratio = 33.9 / 14.7 = 2.3 feet per pound

    2. Figuring a 10GPM rate for easier comparisons figure the energy needed to lift/pressurize the water to 45PSI.

    Convert PSI to height 45PSI = 45 * 2.3 = 103.5 feet
    Convert GPM to Weight 10GPM = 10 * 8 = 80 pounds per minute

    So the ideal horsepower needed can be calculated by thinking of how much energy is needed to lift 80 pounds 103.5 feet every minute.
    hp = (103.5 * 80) / 33,000 = .25 HP ?
    1 hp = 33,000 ft·lbf·min

    3. Figuring a 100 foot deep water table calculate the energy needed to lift 10GPM.
    Convert GPM to Weight 10GPM = 10 * 8 = 80 pounds per minute

    So the ideal horsepower needed can be calculated by thinking of how much energy is needed to lift 80 pounds 100 feet every minute.
    hp = (100 * 80) / 33,000 = .25 HP ?

    4. Now calculate how much energy an "IDEAL" pump would use.
    .5HP = 745.7 watts * .5 = 373 watts

    373 watts * 24 hrs * 32 days= 286Khw

    286Khw * .1 = $ 28.6 per month with an ideal pump

    Since most pumps are far from ideal we have to multiply the above value by 2

    Now since we can't prevent having to lift the water out of the well, we would only be able to save half the energy.
  6. Thumper

    Thumper New Member

    Apr 3, 2009
    Hi Guys, thanks for the responses.

    Bill I was under the impression that the weight of the water column in the supply well pipe would be mostly offset by the suction created by the pipe dropping/returning the water to the recharge well as long as the return pipe was long enough to always be below the standing water level.

    Mark, the reason I was thinking supply/recharge wells instead of horizontal or vertical closed loops is the poor conductivity of the soil, extreme surface dryness but a nearly unlimited water supply 100'+ down.

    How is this for a different model?:

    Place a submergized pump (maybe 1/4hp or so) in the geo supply well, set it for 5 to 10psi at the house (just enough for geo exchanger flow rate & pipe resistances) and return the water to the domestic supply well (that has it's own VFD pump for normal water uses). The return pipe would go down alongside the normal pump pipe near to the pump to recover some lift energy from the geo pump.

    I guess it would be the difference in power consumption between a 1/4 hp pump @ 5 psi, with some lift recovery, and running more or less continuously versus a 2 or 3 hp VFD pump @ 40-50 psi, cycling, and no lift recovery?

  7. nhmaster

    nhmaster Master Plumber

    Jul 30, 2008
    Tech. Instructor
    S. Maine
    Ok, (nice job on the math Bill) since were in a mathmatical frame of mind here. Has anyone calculated the cost of materials and installation (including excavation and drilling costs) along with the operating cost and finally the pay back period for their ground water heat pump?

    When you all get it figured out let me know what you come up with because the figure I come up with says to save my money or at least apply it to something with a better cost \ payback ratio.

    Truth is, these systems are toys for rich boys. Impractical for most folks. Pricey and prone to mechanical problems. The cost of electricity used to run the pumps and electronics if often erroniously left out of the figures along with maintainance issues.

    Heard today that GM is putting a bunch of money and research into development of yet another electric car. No hybrid here, straight up electric. Just for around the city they say. Wonder how a few thousand extension cords hanging out 3rd story windows are gonna look on the streets of NY :D
  8. Thumper

    Thumper New Member

    Apr 3, 2009

    I'm not sure what your saying here. Are geo systems as a class not economical to install or operate? Too difficult to implement and frought with excessive maintenance issues? Rich boy I'm definnately not...we have to get it right the first time!

    I agree that the efficency ratings on these geo systems leave out the pumping power required to operate. That is why I'm exploring these alternative pumping methods.

    As to installation costs I'm comparing the following scenarios:

    Conventional System:

    Good modulating/condensing boiler
    In-floor radiant floor tubling for lower operating temperature
    Indirect hot-water tank for DHW
    Completely seperate ducted AC system
    2000-3000 gallons of buried propane tanks (for stockpiling during off-peak prices)
    A normal well system with VFD pump
    Dependancy on future oil prices for ROI calculations

    3-in-1 Geo system:

    Geo water & air exchange system w/ducted AC
    In-floor radiant floor tubling for lower operating temperature
    A standard electric water heater for top-off
    A normal well system with VFD pump (also works as geo recharge well)
    A second well system with smaller standard pump (works as geo supply well)
    Dependancy on electricity prices for ROI calculations (BTW southwest Montana is almost entirely powered by hydro).

    After getting some actual quotes it turns out the large buried propane tanks are almost a wash with the second well and standard pump.

    Bill, can you recalculate the power consumption of the dedicated geo pump taking into account the drop effect of the geo return pipe into the recharge well and flow/pressure levels required? I would like to add that to the manufacturer's COP/EER to get a truer effeciency picture.


  9. Bill Arden

    Bill Arden Computer Programmer

    Sep 30, 2006
    computer programmer
    MN, USA
    I don't have all of the figures handy, however here are my cost estimates for my closed loop system.

    1. Used ground source heat pump from auction $90 (was some sort of research unit)
    2. Repair of heat pump $100 (it was nitrogen filled before removal and need to be re-filled with R22)
    3. Bronze Circulation pump $200 (~90 watts)
    4. PEX $300
    5. 3/4 inch Drill pipe for 12 wells 60 feet deep. $864
    6. home made drilling rig $300 in parts + lots of time
    7. Everything else $1000
    total $2854 + my time

    Cost savings over current baseboard electric
    Currently spending $3000 per year in off-peak electric.
    ($0.066 for 6 hr interruption per day)
    I am adding insulation and sealing things up to get my heat load down to where the small heat pump will be enough. This is expected to lower my heating needs to ~$2200 per year.

    Factoring a COP of 3 reduces my energy needs by 3 + 90watt pump + blower fan.
    90 watt pump 24/7 on off-peak = 788Kw * .066 = $52
    Blower fan ?, guess maybe as much as $10 per month
    ($2200 / 3) + 90 watts = $733 + $52 + 120 = $905
    Savings from heat pump = $2200 - $905 = $1295 per year
    ROI = $2854 / $1295 = 2.2 years

    I know that it takes a lot of time, however for me it's both an excersize program and a hobby.

    ... Possibly starting a geo well drilling business... priceless.
  10. Bill Arden

    Bill Arden Computer Programmer

    Sep 30, 2006
    computer programmer
    MN, USA
    What I am trying to say is that you can only recover 33 feet of lift using suction since the water will change into the gaseous phase due to the low vacuum pressure.

    This means that at best you can only recover 1/3 of the energy that was used to lift the water using suction.

    Worse yet most heat pumps have narrow water passages and need at least +1 to +2 PSI of pressure. They would most likely have major vapor lock issues at -15PSI.

    I think you would be better off just drilling one well and making a pond to collect the water. Then get a regular well pump with lower head pressure and using a CSV(Cycle stop valve) valve and skip the whole VFD(Variable frequency drive) pump.

    Then use two pressurized holding tanks with a pump in between to boost the ~10PSI water to the 45PSI house pressure.

    Then get a gas or electric pump to pump the pond water to where you need irrigation.

    Also keep in mind that you will probably want some other heat source so that you can take advantage of cheaper electric rates and have a backup when the power goes out.
  11. Thumper

    Thumper New Member

    Apr 3, 2009
    Bill, thanks for the constructive input.

    After reviewing more about the water-to-gas state Bill mentioned and outgassing issues of water at low *negative* pressures (in this case 27+- ft. @ 5000' elevation) it seems that returning the water at a low elevation to recover pump energy is simply not possible.

    Since I don't want to do a surface discharge (pond or otherwise) maybe the recharge well idea can still be used. My two big remaining concerns with this setup are:

    1) "releasing" the water near the top of the recharge well can be messy from an oxidation perspective. Does it clog the recharge well in any way or cause other problems?

    2) Equip the supply well with a regular submersible pump + low pressure tank for geo plus a booster pump + tank for domestic water (i.e. in series as Bill recommends) or just "KISS" and use a VFD pump and a oversize pressure tank to reduce cycling.

    Does anyone have any additional input on this problem?

    As to additional heat the 1st thing was to add resistive heating elements to the air duct side of the geo unit. We may also use a gas fireplace with a smallish propane tank for 2nd backup.

    Last edited: Apr 9, 2009
  12. Bill Arden

    Bill Arden Computer Programmer

    Sep 30, 2006
    computer programmer
    MN, USA
    >1) oxidation perspective.

    All you need to do is prevent air from leaving the well and you will over time get oxygen depleted air in the well. That will then prevent corrosion and aerobic bacteria.

    >2) "KISS" and use a VFD pump and a oversize pressure tank to reduce cycling.

    I was thinking of a CSV(cycle stop valve) instead of a VFD(Variable frequency drive)

    There is a third possibility if you really want to have some fun...

    You could use two VFD's with the DC buss connected together. The down well pump would spin backwards and the spinning would generate electricity...

    Unfortunately you would probably only recover about 25% of the energy since the standard pumps aren't designed to be very efficient as a turbine/generator.
  13. Chessiec

    Chessiec New Member

    Jan 8, 2009
    durham, nc
    I developed a 22-home subdivision with each home on its own geothermal heat pump. Finished in early 2000, with the build out of homes taking about a year and a half. These homes cost at or less than the average home price here in Durham, NC when sold, use less than 30% of the energy of other homes built in the same years, and in a recent study, still rank as the most energy efficient homes in NC.

    I disagree heartily with NH Master's posts. First off, I'm a woman, so these can't be rich boys' toys!

    The technology is so mature, and most of these units now use computer boards for most controls: there are very few moving parts. A little pump for the closed loop anti-freeze solution, a compressor and fan that live inside the home's thermal envelope, so it is protected from the weather and temperature extremes. The loops have very long warranties because they hold up so well with modern materials. And with no outdoor equipment except what is sunk in the ground, there is none of the air conditioner noise in summer that you get with conventional units. Great comfort, quiet, extremely low maintenance in my experience with this neighborhood.

    My advice is go with the most experienced and financially stabile contractor who does geothermal/ground source heat pumps in your area. Don't reinvent the wheel: with either a vertical or horizontal ground loop, the energy spent on circulating the fluid is minimal. I would definitely do closed loop, which avoids all kinds of contamination and other problems. If your native soil has poor conductivity, the tubing will get packed with material that will do the job.

    If you can fold the cost of the initial install into a refinancing, your energy savings will generate net savings from Day 1 of operation. I lived in one of these geothermal homes that I developed for 5 years, and loved the system. FWIW, ours were from WaterFurnace.
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