how do you calculate how much water Open Loop uses?

Discussion in 'Open Loop' started by rollandelliott, Jun 29, 2011.

  1. rollandelliott

    rollandelliott New Member

    Can someone check my calculations below:
    Proposed 2 ton system
    I read for an open system that the Average water use is 2.5gpm per ton x 2tons =5gpm

    Lets say I run the system for 10 hours a day
    10hrsx60min/hr x 5gpm = 3,000 gallons per day

    Im trying to figgure out whether a ground closed loop system or an open based system would be more economical.

    Obviously open loop requires a LOT less labor, but where to put the water becomes an issue, dumping 3000 gallons a day anywhere on my property will cause lots of errosion unless I use some kind of drip system I have not though of.

    I could dig a pond, but there goes the costs savings of not having to excavate.

    I live right outside of charlotte, nc, anybody care to tell me which system is going to be more economical short term and long term? thanks!
  2. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader


    Depends on how deep you drill. On the height of your water table. On whether or not you plan to return the water to the aquifer you took it from. On what % run time you've designed your system for - hint, you will need to design for the max not average. On the horizontal loop layout.


    Just too much behinds the scenes stuff to write the design geo book on here.
  3. rollandelliott

    rollandelliott New Member

    don't need to be spoon fed.

    Looking at my well pump the casing (of 6.25") depth is 37 feet and the depth is 445 feet.
    yield is 40gpm, but actual flow rate is 15gpm

    if there is more information i need to know, just ask.

    or even better just post a link of where I need to go to educate myself. I'm not asking people to spoon feed me information.

    Just trying to get a basic idea of closed loop vs open loop economics.

    Obviously Open loop is cheaper to install. just dig a trench from the pump to the geothermal unit.

    I would think most closed loop systems would use less pump electricty because they are pushing it around in circles and not having to pump it hundreds of feet out of the earth, but I have no idea what the friction losses are in pipe that long.

    So the general question is if you plot expenses over time for both systems given identical locations, when does it become more economical to do closed loop as a guesstimate, obviously every place is different.
  4. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Open loop allways trumps anything closed short term, especially if you have an adequate water supply to start with. You have identified one of the drawbacks allready in where to put the water. If you do any kind of irrigation you could store the water and then pump it again to irrigate? This drives up the cost of electric consumption. Plus the container cost. Check your local regs, about where you can dump the water. Some states like mine give credits/rebates for digging ponds to create duck habitat.
  5. rollandelliott

    rollandelliott New Member

    according to this web site:
    ASWM: State Wetland Programs

    south carolina does not have any wet lands conservation policy.

    thanks for the ideas.
  6. Designer_Mike

    Designer_Mike Member

    How much electricity does your well pump draw?
    If it's 450 feet deep, you have a pretty significant well pump.
    If you don't have a decent sized storage tank to let the pump cycle on and off it will be running almost constant.
    Let's say it's a 2 hp well pump and it runs any time the heat pump is running. The pump will easily draw more electricity than the heat pump:eek: so you just doubled your operating cost. It will still take quite a while to cost you more than a closed loop but you will also wear out that well pump much sooner so you need to add the cost of well pump replacement. You say you get 15 gpm out of it so with a good sized storage tank the well pump only runs 33% of the time the heat pump runs (best case) but you are still running it a LOT.
    Normally you would probably use 3-4K gallons a month of are considering using 90K gallons a month and increasing the workload of that well pump 30x or more.
    Can your aquifer provide that much additional water?
    A small loop pump may draw 200-300 watt depending on the loop design compared to the well pump that is possibly going to draw 2000 watt or more.

    You might be better off with an air-source heat pump if you don't want the install expense of the closed loop. You wouldn't have to deal with 90K gallons of water every month, well pump wear and tear, and if you add in the well pump electricity, the air-source unit would most likely draw less power. Install costs have to be much less too.
  7. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    If you figure the cost of the drain and or injection well, plus pumping, plus wear and tear on the well (heat loss determines water use, but I'd guess 3+ hundred thousand gallons a year), plus two solenoids, two flow raters, a sediment filter, a flow gauge, ball valves and additional plumbing.........
    closed loop may be less than a thousand dollars more (or just hundreds after tax credit).

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