Horizontal Slinky(s) in 21' Deep Excavation!

Discussion in 'Vertical and Horizontal Loops' started by Danny313, Jan 18, 2020.

  1. Danny313

    Danny313 Member

    Just received permit for this 30'x 30' residence (5 level) which will be constructed using insulating concrete forms for walls/decks.
    With high elevation off of street below (60 degree slope), leveling off flat at the top (rear of property), I will be excavating down 21' and planting a two level foundation in the hole. One side (east) will be garage access via a tunnel.
    The other 3 sides, (north, west, south) will be available for the planned ground loop.
    With a 4' wide construction path at footing elevation and a 4' high soldier pile wall holding base of sloped grade, then sloping angle of repose grading at 60 degree to top grade elevation.
    As grade slopes upward, more area in width becomes available.
    With all this, I want to install multiple slinky loops at various elevations starting at lowest elevation around foundation base but not sure how this may be configured.
    Back filling as I go up and out.
    I have the manuals from years ago at IGSHPA and I'm confident of building the loop and installation.
    I was hoping to hear from the group here as to what you see with the layout, pitch, loop diameter, pipe size and production.
    I am designing backwards here and will conform the mechanical to fit the loop production.
    My primary purpose is to fully utilize the cut and fill it with loop according to rulebook.
    I'm interested in knowing what production in tons may look like with design.
    I will figure supplemental if needed later.
    I'm attaching 2 plan views for reference. Please refer to shaded area on site plan depicting outward grade slope from foundation.
    I plan the headers at the northeast corner of foundation.
    Location is Long Island, New York. Ground soil is clayey sand.
     

    Attached Files:

    Last edited: Jan 18, 2020
  2. arkie6

    arkie6 Active Member Forum Leader

    Be aware that ground water around your loop pipes can freeze during winter time operation, so consider this when placing loops under or adjacent to foundations.
     
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  3. Danny313

    Danny313 Member

    I forgot to post the grade elevation change from street to top rear of property where proposed foundation excavation will take place.
    Approximately 50'. So this is no issue.
    That being said, is there any other issue with proximity to foundation footing?
     
  4. gsmith22

    gsmith22 Member

    you are misunderstand what arkie6 is saying. During winter operation, the temperature of the loop fluid (inside the pipes) will likely go below 32degrees at some point. this isn't a problem for the heat pumps as they are rated for heat extraction at that water temperature. But it is a problem for any soil (or foundation) adjacent to the loops that will almost certainly freeze as its temperature drops below 32 degrees due to the proximity to the loop piping. Yes, you wouldn't expect soil to freeze at 50' below grade, but it will if you put something colder than 32degrees there.

    I looked at your drawings, I honestly don't understand why you wouldn't use vertical wells and size per the house's heat loss. The site is so tight to begin with, you won't be able to put a shovel in the ground and not hit something. I shudder to think how you coordinate the foundation construction, backfill, and loop installation all in one sequence to take advantage of the cut and fill operation to install the piping.
     
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  5. Danny313

    Danny313 Member

    So this is the plan...excavate the 40x40 hole for foundation. Accounting for natural grade collapse at perimeter which will cause an approximate 60 degree slope to top grade.
    My original idea is to install slinky at bottom of cut (lowest stated elevation- sbf) and wrap around 3 sides of foundation. Then backfill up to next slinky level (verical distant 6') where possibly two slinky coils can be installed next to each other because of slope?
    Then backfill over the two coils.
    Can I get a third layer? I will have a total of 21' excavation.
    Getting a drill rig will be impossible on this property, especially because of the deep cut. Couldn't get the rig anywhere near the edge of cut.
    Once the excavator digs down he then busts out of the hole onto the waiting driveway below.
    Average year round ground temp here are 55 degrees. The soil is found to be "clayey sand" for the entire cut.
    The construction will be using insulated concrete forms 2.5" on each side of wall with a 6" above Grade core and 12" below grade foundation wall core.
    How do you get 32 degree ground temps?
    You talk about shovel in ground hitting something....how is that? The coils will be deep!
     
    Last edited: Jan 20, 2020
  6. arkie6

    arkie6 Active Member Forum Leader

    Because the water/anti-freeze mixture inside the loop pipes can and often does drop below 32F in winter in northern climates. That is why you have anti-freeze in the loops. Once the water in the loop pipes hits the freezing point, water in the soil external to the pipe starts freezing and expanding.
     
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  7. gsmith22

    gsmith22 Member

    in short, loop fluid doesn't freeze because of anti-freeze mixture in pipes but soil (with only water) around the pipes freezes. That frozen soil seems like it will be right next to your foundation because there is no room on the site.

    On the vertical layering configuration you are describing I don't see how any of the "upper" loops will be able to exchange heat with the soil (or at least exchange it effectively). The lowest loop has access to relatively deep ground temp but middle and top loop won't - they will see variable soil temps influenced by the lower loop(s) and can't pull heat sideways due to the extreme slope (on one side) and house foundation on the other. I've never heard of anyone vertically layering horizontal loops likely because the upper loops won't perform - they will effectively have ground temp of the lower loop.

    You are taking me literately regarding shovel in ground. What I mean is the entire site will have slinky pipes buried in it. How do you run utilties to house with all those loops buried during the foundation work? Have you called a driller to see what is possible? If you are willing to bench the foundation excavation backfill, you might be able to create a flat enough area to get one or two wells in. Run them deep (400 to 600ft). Otherwise I don't think you have a workable plan. But I could be wrong. - advice is as good as the amount of money you paid for it :) Hope others weigh in
     
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  8. Danny313

    Danny313 Member

    So this is to say that the "return" water from house going back to ground is....32F, which is lowering the temp of surrounding soil? Or....the surrounding ground formation at that elevation of 21' and 15' below top grade has changed from the annual 55F average year round (below 6') to 32F in winter, on its own?
    So what I'm trying to understand is HOW or WHY has it changed? There can only be the two reasons above.
    One reason for my confusion is that the local state code for install of domestic water line from street to house must be buried below the 3' depth to get below the frost line to avoid freezing.
    You state "once water in loop pipe hits the freezing point".....soil external to pipe starts freezing.....so this tells me that ABSENT the freezing water in loop pipe, surrounding water/moisture in soil will NOT freeze and expand.
    So this leaves only one reason for this issue, and that is water in loop pipe hits 32F. Which, by extension tells me that the return water coming from house is causing this, as it's not being caused by the ground.
    Am I missing something here?
     
  9. Danny313

    Danny313 Member

     
  10. arkie6

    arkie6 Active Member Forum Leader

    That is it. The geothermal heat pump lowers the water loop temperature while in heating mode. In general, the longer it runs in heating mode, the colder it gets. It can and often does go below freezing in the loop water leaving the geothermal unit, especially in northern climates with a long heating season. That's why you have anti-freeze in the loop pipe. But the anti-freeze inside the loop pipe doesn't prevent water outside of the pipe from freezing.
     
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  11. Danny313

    Danny313 Member

    OK so the layering of the loops won't perform as well as they should because of multiple limiting factors such as foundation, the slope on one side and the lower loop below pulling available heat.
    The option then starts looking like verticle borehole.
     
  12. Danny313

    Danny313 Member

    Wow! I never imagined return water could go that low because of HP!
    I'm now clear on this important issue and it's relation to proper loop field design.
    Thanks to all for this.
    I am considering slinky for couple of reasons mainly costs. And fact that I can build it and install properly.
    I suppose I could backfill foundation and bring in drill rig and do multiple boreholes around West and south sides.
    But costs on this special house are big enough and if I can avoid them ...
    With all you guys have provided here my thoughts now going to one last alternative.....
    Lay in 100' slinky at bottom elevation (sbf-122') around foundation base 3 sides.
    Then backfill to some point.
    Then possibly install coil around West and south sides where there is no slope?
    I'm thinking about running some loop program where I can project some " what ifs".
    As to ground/foundation freeze issues remember I will be using icf construction top/bottom including flat roof deck.
    Forms are 2.5" thick each side of wall.
    As to utility lines interfering with loop field, they will run from street to NE corner of foundation entry via a below grade tunnel, and Pierce wall at one local area only.
    No interfere.
    With 2 West and south side coil installs (no slope) (at elev. 130.0) I can travel to east side property line providing a run of approx. 75'x2 or 150'.
    Add 100' from coil at bottom base of foundation, (9' below)....250'.
    And I'm thinking I can install another coil at South side next to the 2 coils, for another....70'. total 320'.
     
    Last edited: Jan 21, 2020
  13. Stickman

    Stickman Member Forum Leader

    Danny - if it helps: I am on Long Island also. I've got four 200' deep vertical bores = 1600 feet of loop on a 4 ton HP. My EWT dips down to mid to high 30s during weather like we have today (low in the teens, high around 35F). When we have extended hours of mid teens or lower outside temps, my aux engages. 320' of horizontal loop even for a 2 ton (guessing at what your load might be) may require a lot of aux.
     
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  14. ChrisJ

    ChrisJ Active Member Forum Leader

    Should figure out your approx heat loss/gain for your structure before you put way too much pipe in the ground.

    He is talking trench length with slinkies not straight pipe.
     
  15. Stickman

    Stickman Member Forum Leader

    Apologies - my thinking was off.
     
  16. Danny313

    Danny313 Member

     
  17. Danny313

    Danny313 Member

    I have to admit to having possession of the Energy Analysis produced by the company that figures these things. This document has a 10 page Wrightsoft load short form analysis rider attached, along with the rest of the report. Expensive but required by the local Town code. And I haven't reviewed it yet but initially it looks like i will have to consult with company to understand it.
    But if anyone here is familiar with it maybe you can guide me on what to look for that's relevant to what were talking about here?
    Steve, does this latest revelation by Chris J. possibly put me back in the slinky spotlight? If so then I need to provide the "load" found somewhere in this document to maybe arrive at a possibility for closed loop slinky?
    A quick review of report reveals company provided a "quick analysis" for purpose of building dept submission, to get me to permit. There are mistakes/omissions.
    Of course, upon completion and prior to C of O the final report and payment is due, reflecting the actual.
     
  18. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    @Danny313

    This is getting a bit chaotic here.....

    First, what are the loads of the house. How many BTUs do you need to extract from the ground?

    ICF are good, very efficient. Building into the ground is normally good, since surrounded by warm ground during cold temps. Now you are installing a stacked slinky next to the house wall. It will drive the ground temperatures down, and increase the BTU requirements of the house.

    Also heat travels through the ground from all side. The house wall now blocks some heat traveling to the pipes in the ground, so heat does not replenished.

    Also stacked pipes steal heat from each other. Heat from the ground cannot travel to the upper pipes since the lowest pipe is already extracting it.

    Your safest bet might be to drill a single 6 inch borehole down to the needed length. Usually you find room for 6 inches.

    @ Stickman
    Colder loop does not necessarily result in much more aux heat (only to a small fraction), which is usually driven by lower heat pump capacity (undersizing).
     
  19. Danny313

    Danny313 Member

    The design calls for a 3.5 ton heating load and 2.5 ton cooling load.
    I get that the true vertical "stacked" slinky design (one on top of the other) is not good....but what if I had a "lateral" separation such as 12' with a depth of 14'....basically providing an offset.
    Lowest loop at 24' then next loop at 14' with lateral separation of 12'? Any rules for this scenario?
    I'm pushing this issue to the limit as it could mean the difference of thousands of dollars cost for borehole mud drilling/loop installation in a clayey/sand environment.
    Further, and as I'm interested in utilizing a deep foundation excavation for loop installation and one that I can install without cost, I have to at least explore this possibility.
     
  20. gsmith22

    gsmith22 Member

    did you run the LoopLink RLC that I told you about in your other thread? Can you obtain a design that works with 12' of horizontal separation between slinkys? If you have enough room to laterally separate the slinkys 12', why even bother with the vertical separation? Put them all at the deepest depth.
     
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