The pump in pump and dump

Discussion in 'Open Loop' started by waterpirate, Jan 9, 2011.

  1. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    While at first blush the open loop geothermal solution seems to be more efficient, cheaper to operate, and diy new guy freindly. The pump aspect of this statement could not be further from the truth.
    Being and educator and a proffesional, I can tell you the sad fact that the quickest way to clear a room full of pump and well contractors is by saying three things.

    1. Pump curve
    2. Feet of head
    3. shut off pressure

    When we look at pumping water through a heat pump, we find out very quickly that heat pumps require for the sake of discussion.

    1. 1.5 to 3 gallons per minute per ton of load
    2. an operating presure of as low as 10 to 15 psi on the inlet side of the exchanger.

    If these two factors were the only parameters we have to meet with water supply it would require a pump with very low hp and depending on the tonage load a very small gpm flow rate. The problem occurs when we have multiple water usages at varying pressure demands.
    By far and away the best way to address the needs of a heatpump would be through a dedicated water system to support the system, however that takes away from the inexpensive aspect of the design by adding more wells.pumps, and systems.
    When we first look at upsizing pumping equipment to meet the demand of the heatpump is to simply add the needed gallons to the existing pumps capacity and we have a winner. Unfortunately that leads to the most common complaints involved with owners of these systems.

    1. Pump cycling
    2. Excessive electric consumption

    Pump cycling is a function of any operating system. Unfortunately everytime you turn an electric motor on and off, you are reducing its life expectancy. Water pump manufacturers have recomended run times for their products to maximise the life of the pump, however they all die a little bit each day like running up mileage on your vehicle.
    Excessive electric consumption occurs because the pump is now sized to meet the maximum demand placed on it by the distribution system. If you are only using a portion of your pumps capacity, and it is cycling on and off, you are paying for electric consumption to meet a demand that does not exist.

    A common complaint is that my water pump runs non stop. This should not be a complaint but a blessing as to the life of your pumping equipment. Todays submersible pumps were designed for continuous duty= non stop operation. If your pump can run non stop to support your geo and you suffer no defficiencys in regard to the rest of the system when the geo is running you have harpooned the white whale.

    The correct sizing of a systems size is paramount to its longgevity and cost effective operation. If you have any of the afore mentioned malladies be advised that there is no magic solution, nor is a solution inexpensive or quick to come. It is our demmand that makes this such an interesting puzzle.
    We demand low cost, multiple usages at differing pressures, and instant gratification with the unwillingness to put up with life style choices. The addition of more tanks, valves, pressure reducing devices, or variable speed pumps will never meet all of our goals.

    The summary reads as follows
    While we can take steps to address one or more of the maladies it all comes at a cost. There is no solution that meets all our expectations, just a combination of the ones we are willing to pay for and accept in terms of shortfalls in other areas. I hope this sheds some light on a reoccuring hot button of issues surrounding the pumping requirements of an open loop system.
  2. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    Thanks Eric for the well presented info. This should be a sticky that can be referred to often.

    only a true pirate would use this :D:D:D
  3. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader


    Well said.

    Historically I'd say folks have pushed towards open loop also has to do with not having to design a ground loop system. It looks like a DIY when you just need 9gpm, but you've pointed out the issues quite well. Might have to steal from this in the future.
  4. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Well-written, though I'd argue that required pressures entering a geo are more on the order of 5-10, and on the low side of that range. That accentuates the harsh difference between house water and geo water pressure requirements.

    Though my my own open loop (no pump needed) is a whale in a class of its own, I don't think I'd implement open loop absent a pumping system separated from the domestic water system, though I fully understand the dual attractions of low cost and simplicity.

    Some of the pumping power horror stories I read here lead me to believe that air source would be a better deal than geo in some of the described circumstances.
  5. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Thanx for the kind words, and feel free to share or disseminate as wanted or needed.

    Dwayne, did you expect a refrance from anywhere else? lol

    Curt, I really had to control my urge to hold up your system as the "holy grail" as I thought it would only add to the confusion factor. Agree that the pressure could be lower to operate.
  6. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    When I moved down here in 1995, I was checking out houses and someone showed me an artesian well I assumed they were rooking a Yankee. I searched high and low for the pump. The power was off to the house being shown me, but I still didn't believe it.

    Most well heads have a hose bibb to draw off unpumped water. Some folks irrigate solely with it.

    Right now my system's water output all passes through a 7/32" nozzle so I don't take too much off the aquifer. 71 in 53 out. I pinch it down to 5/32 or 1/8 when I need especially chilly water for the snow gun or hot water for the kiddie pool. In dry weather I drag a hose around the property to irrigate different areas with the discharge.

    Back to the subject at hand - Throttling 50 psig house water by 10x down to 5 for a geo is a huge waste especially when one considers that the pump that boosted the water to 50 is likely less than 30% efficient. The effect is to render all the geo efficiency savings moot as well as add the hassle of frequent pump failures.

    My reinjection project looms. Two wells with 4" casings are 80' apart. I peered down the cases and see the static water about 15' down in each. I need to find a pump to efficiently bring up about 10 GPM of that water, push it through a geo at 3-5psid and let it fall down the other well. I wonder if I ran a line down the dump well about 25' it would stay wet / primed and give me the benefit of the falling water...I'd get back the lift power from the first well. It will be interesting.
  7. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    I drank a lot of beer 11 years ago with a guy who went down this road, using the energy of the discharge water. He only got as far as putting a small wheel in side the well casing that powered a small external bulb that showed when the discharge well was accepting water. It helped identify a leaky selonoid valve early on.
  8. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Open loop systems have been pumping in MI for 60 years and doing well.
    I think the drift towards closed loop in my AO has as much due to the maintenance concerns as any other.
    The end point is that all systems have trade-offs. The only time I object excitedly is when someone tells me that system X is best.
  9. hardchines

    hardchines Member Forum Leader

    I read with interest all of your opinions and was only surprised by one, Curt you said to me several years ago that the cost to operate my well pump for my open loop system would be quite reasonable, I have found that statement to be true, so I am surprised to see you say the pressurization to 50 psi would negate the GEO savings, this is not true at least at my house, maybe true at others. I have tracked my pump power usage as well as my two GEO systems power usage, I do use alot of power and I do pay more for my power then 99% of the posters on this forum but it still cheaper then using OIL!

    The true-est statement about GEO is.........

    AMI "The end point is that all systems have trade-offs."

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