Kansas Lets throw together a horizontal loop plan!

Discussion in 'General Discussions' started by fastline, Jul 24, 2020.

  1. fastline

    fastline Member

    We are finally breaking ground on the shop. LOTS of delays. I don't want to get too hung up on "required btus" because I already own a 2 stage ClimateMaster 5T T27 unit, and target temps can sometimes be "better than what is going on outside"..... There will also be supplemental heating so this is not the only means of heat and the heat strips will be disabled.

    What we have is is a septic system that will be placed about 300ft from the building. I am installing my geo tubing directly under the septic lines. Some might offer concerns here but I did a lot of work in this area and there is no way one will cause issue with the other. I was originally going to go deep on this but right now, I need to target a more reasonable depth and design. Thinking 4ft but I need to run more numbers. I am in the middle of KS.

    What I need to do is run tubing out to the field, then return. The lateral runs will probably be 4x 125ft or so. I will probably make them 3ft wide. I want to make a straight run out there, run coils in each trench, then return, possibly in a separate trench. I would like to figure out a design for this, optimally without connections in the field and only using continuous pipe.

    Thermal conductivity of this area should be well optimized by the continuous wetting of the sewer, and the 5T unit will likely operate at the low setting of 3.25T most of the time, so if 5T is demanded, it would not need to be continuous because the shop is perfectly fine at 78F and reduced humidity, which is what running on low will provide.

    I am mostly trying to figure out how to move fluid between the EWT and LWT lines in the ground. How much separation?

    Also, these lines will have to be in the middle of my rock driveway. I am totally conflicted if I want to bed them with concrete, flowable fill, sand, nothing, etc. Concrete should eliminate potential breaks, but if an issue occurs, repair becomes a nightmare.
  2. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Hi and welcome. The " poop loop " has been discussed here before. The major concern is the potential freezing of the ground during heating. You may be over estimating the amount of wet rejection in your septic field vs. btu rejection. Just a thought.
  3. SShaw

    SShaw Active Member Forum Leader

    The supply and return lines normally will not exchange much heat with each other. A trench 3' wide might be adequate, but see what the pros say.
    To keep the pressure drop low you will need to use a large diameter pipe for the supply and return lines between the field and your house. You'll want a header to divide the flow between your loops.
    My loop field is 160 feet from the house and I used 2" diameter pipe for the supply and return. I think you should be able to model the pressure drop using the online tools at geo-flo.
  4. fastline

    fastline Member

    Yeah, I am coming around that I might need a header here. My intention was to use multiple pipes, one for each circuit, bundle them, then build a header indoors, but that may not be optimal use of pipe unless I dig deep and keep them separated so I can take full advantage of the extra surface area.

    I ran some calcs and will probably be in the 1" area for flows if I plan to keep this laminar and in separate circuits. I think pushing to turbulent flow is more ideal here but seems most guys don't really chase that.

    I have plenty of land here so if I need to add another circuit later, it would not be a a life ender, but would be nice to get this dialed on the first run.

    As far as freezing the septic, that has come up many times, but I dove pretty deep in this years ago the reality is due to my climate, separation of geoloops vs laterals, and other thermal mass factors, it should be a non-issue. I do design for septics and know them well. It should work.

    This is sort of multi use deal where I am doing geoloops, septic, and solar field all in the same ground.
  5. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Well,.... I do design for geo, and if you put the geo right underneath, it is an issue. Just make sure you don't blame geo when your septic system freezes.
    Specifically you are only at 4ft.

    If you are running 300ft out, and then 300ft back, and you separate the loops you would likely need to be close the 1000-1200 total length.

    My understanding is that you don't want fusions outdoor. What antifreeze do you want to use? Methanol would be preferable.

    Sand is best to embed pipe in, but unless it is saturated, you don't get much heat transfer out of this portion of the pipe.

    So how can we help?
  6. fastline

    fastline Member

    Seems like I might need to do a quick drawing just for a visual but the building is 300ft from where the lateral field is. I would need to jog out there with pipe, then lay horizontal loops in each lateral trench. The sand bedding would only be over about 50ft of the 300ft straight where the driveway will be. It seems like Methanol is much preferred over PG so I will probably run that. I have not yet compared the density or viscosity.

    As to the septic, have you seen one freeze up? If so, where? My geo tubes will be at least 3ft below the laterals.

    I am mainly wondering about my jogs out that 300ft. Run separate runs for each loop? Run a larger pipe as a header and branch off after the 300ft run? I am not a fan of fittings for this in the field, but I realize it is done daily. I probably need to get over it.

    Are you specifying 1000-1200' per ton? I think my calcs were at 800' per ton but also trying to buy off some for the moisture conditions.
  7. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    I have seen freeze up when the loops were under the leach field, but only 1-2 ft below. Keep in mind, during freezing conditions, your frost line is maybe 2ft. The reason why it is at 2 ft is that that the ground continues to supply heat to the upper layers, and at 2 ft is the balance point where it reached 32F compared to the 0 degrees F of ambient air.

    However, now you are putting in a heat exchanger below so heat cannot rise up anymore, you might freeze that ground to below the geo loop field. I have seen ground being frozen 7ft down to the coils, 6ft above the coils and 1 ft below. It depends on your design and operating temperatures.

    Now, if you run your trenches, and separate your trenches wide enough (2ft apart), you might be able to use the 300ft going out as your loop field. Not sure what your soil is, you can run 8 circuits at 5-6ft down, 600-700 ft each, and bring them in the house individually.

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