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  • Dual Well Geo Thermal Heat Pump

    Here my grid tied solar PV system has done well, in part because a modern air to air heat pump efficiently
    converts my KWH reserve into house heat/cooling. Not much invested in the pump, but the trade off is
    switching to resistance or propane for the most sever cold periods. A trenched in geo thermal heat pump
    can handle more extreme temps, at least until it freezes its heat sink dirt.

    One method mentioned has been a dual well system; bring water up one, send it back down the other. This
    sounds like a big expense, and what are the implications if drinking water is coming from this system? The
    thought I just had, was run a water line to my neighbors, and we share our 2 existing wells. When flow is
    needed either could turn on a pump, and we could reverse the system periodically to keep things evened
    out. Maybe the very first issue is a one way valve at the pump, but perhaps a return pipe could be added
    at the top. thoughts? Bruce Roe

  • #2
    The standard install in my area are deep wells with HDPE lines grouted into the well. The grout is supposed to improve the conductivity between the surrounding rock and the glycol. SInce the loop is sealed, the pump only has to overcome friction loss in the pipe versus elevation head. Wouldn't your proposed "open" method require a lot more horsepower as the pump has to overcome the lift? Of course if the water table is high the lift may not be that much. I have heard of smaller systems that have the HDPE loop piggybacked onto the well string with the pump hanging below the loop. This would work but given the estimate of 300 feet per ton of heating it wouldn't cover a normal house.

    I do have spare surface well with two lines going to it. I have considered attached a loop in the bottom of the well to the well lines and circulating water to my home and then to heat exchanger on a mini split return line to see if I could use ground water in place of air when the air temps are lower. I also think it would help in the summer when the air temps are high. Just curious why some company hasn't come up with it.

    Comment


    • #3
      Bruce,
      I have the "trenched in" geothermal system you mention. I have never had it freeze, not even close. If sized right that is just not a problem. I am not a big fan of the pump and dump option using wells but everyone has their favorites. I don't like the idea of messing with my aquifer at all.

      I'll give you my 2c, take it or leave it. If I were to go back in history, I would probably skip the ground source heat pump. It has been efficient when it is working correctly, but even with a good installer and my knowledge of the system, it has been far from worry free. I have had the compressor lock up (replaced under warranty, but still costed $$ for service above the "allowed" amount from the vendor). I have also had to have the loop purged several times now as the pumps get bubbles in them and make noise. This could be due to air that was still in the huge multi-pathed loop field or just a microscopic leak. Anyways... with an open loop system you would have different issues, like water quality corroding or clogging parts of your system, etc. To me, even with the system working relatively well over 7 years, it is just over complicated. I have several backup systems, so I could honestly just rip that out and be fine, but now that I have it, I might as well use it. I like the fact that it heats the domestic water and provides nice heat for the in-floor system. Nothing that couldn't be done with a propane boiler though.

      Feel free to ask questions, i'm happy to provide what experience I can to the group. Dave

      Comment


      • #4
        Move further south where the ground never freezes so you never need dual fuel sources. .
        MSEE, PE

        Comment


        • bcroe
          bcroe commented
          Editing a comment
          True, but I'm enjoying the challenge here. Bruce

      • #5
        Originally posted by cabindave View Post
        Bruce,
        I have the "trenched in" geothermal system you mention. I have never had it freeze, not even close. If sized right that is just not a problem. I am not a big fan of the pump and dump option using wells but everyone has their favorites. I don't like the idea of messing with my aquifer at all.

        I'll give you my 2c, take it or leave it. If I were to go back in history, I would probably skip the ground source heat pump. It has been efficient when it is working correctly, but even with a good installer and my knowledge of the system, it has been far from worry free. I have had the compressor lock up (replaced under warranty, but still costed $$ for service above the "allowed" amount from the vendor). I have also had to have the loop purged several times now as the pumps get bubbles in them and make noise. This could be due to air that was still in the huge multi-pathed loop field or just a microscopic leak. Anyways... with an open loop system you would have different issues, like water quality corroding or clogging parts of your system, etc. To me, even with the system working relatively well over 7 years, it is just over complicated. I have several backup systems, so I could honestly just rip that out and be fine, but now that I have it, I might as well use it. I like the fact that it heats the domestic water and provides nice heat for the in-floor system. Nothing that couldn't be done with a propane boiler though.

        Feel free to ask questions, i'm happy to provide what experience I can to the group. Dave
        Thanks for the info. It sounds like the size of the ground system can easily be underdone and freeze. How would you rate
        the size of yours against the heat load; are you as cold as northern IL? I don't like the idea of an open loop system.

        If water was dumped back into a second well there certainly would be energy required to run the pump against the depth. I
        don't see that as a serious problem. Bruce

        Comment


        • cabindave
          cabindave commented
          Editing a comment
          Hi Bruce, The ground source heat pump is in my northern Minnesota house, so I would say quite a bit colder than northern IL. I have 3600 ft of pipe not counting headers, at about 9ft deep. That heats approx 2500 sq. ft. of concrete floor with hydronics. Quite the undertaking. I put some antifreeze in the loop, but it turns out I don't even need it. I went deep enough and large enough for it not to be an issue. Even with good design though, I just wanted to warn you that these are not maintenance free systems. They are kind of like solar in the fact that you take the good with the bad, and you can't just set it up and never think about it again for 20 years.

          I have a solar system at a cabin that works well too. Solar only, no grid tie and it works fine. Contrary to what you often hear at this forum and others it can be done, just requires a lot of planning and refinement. That and about 3x the panels you would normally use on a certain size battery bank to make the winter months work! I should add this is a small system, not one that we use microwaves, and all that other junk on. Lights, fans, and music mainly.

          Dave
          Last edited by cabindave; 11-14-2016, 04:34 PM.

      • #6
        Originally posted by bcroe View Post
        If water was dumped back into a second well there certainly would be energy required to run the pump against the depth. I
        don't see that as a serious problem. Bruce
        Bruce depth does not produce pressure in a loop. You are not lifting water like water well. You are using a column of water like a Manometer in a loop cancels the pressure. You are correct it takes more power, not to over come higher pressure, but to overcome the added resistance of the length of extra pipe you added. Yes it takes more power, but not much. Just like electricity, make the resistance lower to combat the extra loss, use larger pipes.

        Ever use a water level or did experiment in science class with Manometer, a U-Tube open at one end filled with water and the other end under vacuum or pressure. .
        Last edited by Sunking; 11-12-2016, 12:24 AM.
        MSEE, PE

        Comment


        • #7
          Originally posted by bcroe View Post
          True, but I'm enjoying the challenge here. Bruce
          Pay your money, take your choice. I said that about the challenge of Buffalo winters until I figured out that I prefer to pick my own challenges. Winters there were like an annual million dollar education in cold weather survival that you got up your ass a nickel at a time.

          One local saying was "I like winter because it helps me appreciate the nice weather in the spring." I always thought that was B.S. and made about as much sense as saying: "I like punching myself in the face because it feels so good when I stop." If winter is so great, why do so many folks work all their life and save like demons to be able to retire and be Sun eagle's winter snowbird neighbors ? Truth to tell, I wouldn't be at all surprised if he and I have a common acquaintance or two.
          Last edited by J.P.M.; 11-12-2016, 12:50 AM.

          Comment


          • #8
            Originally posted by J.P.M. View Post
            If winter is so great, why do so many folks work all their life and save like demons to be able to retire and be Sun eagle's winter snowbird neighbors ? Truth to tell, I wouldn't be at all surprised if he and I have a common acquaintance or two.
            I took it one step further, not only do I hate the cold, TX, OK, and NV heat I hate as much. Cannot do a dang thing outside after 10:00 AM in summer. So I moved where it is Spring all year round. A weather forecasters job here is easy. Every forecast is daytime highs mid 70/80's, night lows mid 50/60's with a chance of afternoon showers.
            MSEE, PE

            Comment


            • #9
              Originally posted by Sunking View Post
              Bruce depth does not produce pressure in a loop. You are not lifting water like water well. You are using a column of water like a Manometer in a loop cancels the pressure. You are correct it takes more power, not to over come higher pressure, but to overcome the added resistance of the length of extra pipe you added. Yes it takes more power, but not much. Just like electricity, make the resistance lower to combat the extra loss, use larger pipes.

              Ever use a water level or did experiment in science class with Manometer, a U-Tube open at one end filled with water and the other end under vacuum or pressure. .
              Depth does produce different pressure in different elevations in a loop - more at the bottom than the top. That's static or head pressure.

              In a closed loop, for the same fluid, at the same temp. and the same flow rate, the flow induced pressure drop, inlet to outlet, through 2 x 100 ft. straight sections of pipe connected by a 180 deg. elbow will be the same regardless of orientation.

              If the sections are vertical with the connecting elbow at the bottom, the static pressure will be greatest at the bottom.

              Confusion in terms: Static or head pressure usually caused by gravity, and flow induced pressure drop caused by friction, either internal to the fluid (viscosity) or external between the fluid and containment wall.

              Comment


              • #10
                Originally posted by J.P.M. View Post

                Pay your money, take your choice. I said that about the challenge of Buffalo winters until I figured out that I prefer to pick my own challenges. Winters there were like an annual million dollar education in cold weather survival that you got up your ass a nickel at a time.

                One local saying was "I like winter because it helps me appreciate the nice weather in the spring." I always thought that was B.S. and made about as much sense as saying: "I like punching myself in the face because it feels so good when I stop." If winter is so great, why do so many folks work all their life and save like demons to be able to retire and be Sun eagle's winter snowbird neighbors ? Truth to tell, I wouldn't be at all surprised if he and I have a common acquaintance or two.
                On my Jan trips to the coast (in my 79 Olds) the snow was usually worst around Niagara Falls. I finally learned to take a more
                southernly route through PA. The temps here don't bother me so much, as the snow and humidity. We pretty much handle the
                snow, unlike so many places I read about. A friend winters to warmer GA, and has been rewarded with terrible ice storms.
                And the traffic across Atlanta is so terrible he has to plan trips across in the middle of the night; mountains preclude easy detours.

                At my Moms church in FL I first saw a sign pointing to the OXYGEN facility room. People and regulations EVERYWHERE, prices
                hard to believe. I could go west to places with terrible water issues, not to mention earthquakes, brush fires, more traffic issues,
                regulations, astounding prices, houses with more square feet than the lot they sit on, HOAs, and much more. Instead I sit on a few
                acres where I can't see my neighbors houses, and the nearest towns don't have a traffic light. It cost less than an apartment in
                the city, 6 cars all park inside, build big stuff in the back with no permit and out of sight. The 4WD tractor deals with snow in
                short order, and now I have plenty of PV energy coming in to run the place. The on site maintenance facility makes it easy and
                very economical to greatly prolong vehicle life; hers and mine currently total 570,000 miles and counting. 79onLift.jpg

                If I add a return pipe to a well, it will be higher than the water level I pump from, so there will be some lifting energy required.
                Bruce Roe

                Comment


                • #11
                  Originally posted by bcroe View Post
                  If I add a return pipe to a well, it will be higher than the water level I pump from, so there will be some lifting energy required.
                  Bruce Roe
                  Actually, as you describe it, in an open, pumped system, with the return to the well higher than the discharge, you'll get a slight boost that will show up as something called velocity head = V^2/2g = height difference between return and discharge. In an open system, unless you figure out how to defy gravity, you'll always have that, working either for or against you. In a closed system such as one that uses the earth as a heat sink, it won't matter.

                  BTW, a good portion of the area around Niagara Falls - about 20-30 miles north of Buffalo is generally much less snow bound than Buffalo, with the Falls getting about half as much snow or thereabouts over an average winter although the two are only about 20 - 30 miles apart. Google "Lake Effect" for reasons why.

                  As for the rest of the weather/climate/conditions, particularly around the U.S., there ain't no perfect place. San Diego has about the best weather going, but Buffalo has some of the best folks in the world, almost - but not quite enough to make up for the winters. Pay your money, take your choice.

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