Horizontal Slinky(s) in 21' Deep Excavation!

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

  1. Danny313

    Danny313 Member

    As I'm utilizing the excavation for deep foundation, I wanted to place loop inside the cut and backfill.
    At lowest elevation at base of footing and a five foot construction path then four feet of vertical soldier pile then sloped cut at 65 degree to top...I figured another coil....
    I am currently working with loop link program...thanks for that.
    Last edited: Feb 8, 2020
  2. SShaw

    SShaw Active Member Forum Leader

    LoopLink includes analysis for a dual-layer slinky, which is two slinkies in one trench with 3' vertical separation between them. I think you might find that a 3-ton Waterfurnace 7 Series will work for your 3.5/2.5 ton load. You would need something like 400' - 450' of trench with a dual-layer slinky. You'd need to break it up into three or four runs off a common header to keep the pumping power down.
    Danny313 likes this.
  3. arkie6

    arkie6 Active Member Forum Leader

    And you don't want to put the loops under your foundation if there is any possibility of the loop fluid dropping below 32F; otherwise, freezing moisture in the soil external to the loop pipes could lift your foundation.
    Danny313 likes this.
  4. Danny313

    Danny313 Member

    Yes! Thanks for that. I put that to the tech yesterday and they confirmed. I have appt Monday to figure this. I think I may have that kind of trench run, including the foundation cut and area on the west and south sides.
    If that happens it's a winner.
  5. Danny313

    Danny313 Member

    In your experience is the 5' distance ( IGSHPA guideline) from any structure reliable? And no way would I install under foundation!
  6. Danny313

    Danny313 Member

    I signed onto the program and getting familiar with it. Have an appt on Monday with a tech to assist in figuring the loop configuration. Thanks for your help! Greatly appreciate!
  7. Danny313

    Danny313 Member

    I consulted with a local "pro"...who knows the area well. As part of what he tells me, I am happy to hear that after I install my plan for horizontal slinky around foundation and rear of planned house (distant 10' code requirement), and after startup of system, I can run a test to determine capacity of installed loop measuring water temps differential over time. This will then tell me how much more capacity I will need to match winter load requirement of 3.5 ton.
    Then a decision for a vertical 300 foot bore or maybe even two. I will have the room for this as I will make sure the slinky install is properly distant.
    Add to this the idea that LOOPLINK indicates I can STACK the slinky, using proper distancing/ spacing! WOW!
    The bottom line here is that i can achieve 100 percent from the ground and do so in cost effective way as i will install slinky myself, also avoiding trenching costs!
    I'm motivated as I am heading into a hearing with the local school board where I will be seeking to get their approval for the 10 year property tax relief if i achieve the leeds or green building certifications which the State requires.
    School taxes take the biggest bite and the State allows them to "opt in" unlike local govts which are mandated to go along with it. The benefit would be over 100,000.00 in relief! I think it's worth it!
    This stuff is exciting!
  8. Danny313

    Danny313 Member

    I'm wondering why you didn't size the loop field to account for those lower temps of extended mid teens or lower?
    And I find interesting your 4 200' bores requires the aux kicking in for those lower temps, which our area does get during winter.
    Your response tells me the info I'm getting from drillers is....questionable?
    Latest estimate from an experienced driller is...3 175'-200' bores satisfying the 3.5 ton heating load. No question!
    I'm wondering if it's pipe diameter or maybe type of grout that makes difference. I think I understand there is variety of grout with varying thermal conductivity.
    They quoted 1.0" pipe.
    I'll ask what the design temp their system proposal is modeled on.
    Can you provide the pipe size used, the bore diameter and the grout details? It would be helpful to figure this out. Thanks
  9. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    To all here. If your aux kicks in when your loop field is in the 30s, that means that your heat pump capacity is not large enough, not that your loop field capacity is not large enough.
    There is a reason why heat pump capacity is rated at 32F entering water temp (EWT).
    The amount of heat delivered to your house is solely determined by the capacity of your heat pump. Nothing else. To a minor amount that capacity is determined by EWT,
    The loop field capacity determines the amount of heat which can be delivered over the season, the heat pump capacity determines the peak capacity the system can deliver.
    To give you real world examples, a lets say 4 ton dual stage heat pump has a 37.2 Kbtu/h heating capacity (HC) at 30F EWT, and 43 KBTU/H at 40F, about 15% more. A 5-ton unit would have a HC of 45.8 kbtu/h at 30F and 53.8F at 40F, a 17% increase. However, a 5 ton would have 23 % more HC at the same EWT than the 4 ton.
    The same loop field would remain the same and deliver similar EWT to either a 4 or a 5 ton, since it determines the annual capacity, not the peak capacity.
    Lets say a 4 ton loop field delivers 80 million BTUs per year, and the 5 ton would extract 10,000 more BTUs out of the loop field during the 2% of the time when your aux heat is running with a 4 ton on an annual basis, which is about 40 hours/year. Meaning a 5 ton covering the peak extracts about 400,000 more BTUs from the ground than the 4 ton. Or 0.5 % of the total annual load the loop field delivers. In other words the loop field does not even notice that, and the loop field temp does not change noticeable.

    So again, loop field capacity determines the annual load, heat pump capacity determines the peak load.
    Danny313 likes this.
  10. Danny313

    Danny313 Member

    This is very helpful....I get it. What component of HP allows for the increase in capacity? Larger compressor? Coil? Also, I've heard that over-sizing of HP is not a good idea? I like the idea of getting 100% from the earth for all projected temps...is a "two-stage" the answer?
    Second question....is there variety of grout with various thermal conductivity characteristics? If so, I would want the best? Any suggestions?
    Pipe size....1"- 1.5"?
    I'm settled on vertical borehole application.
  11. gsmith22

    gsmith22 Active Member Forum Leader

    oversizing a heat pump may or may not be a good idea- it depends (like so many things). you are in a heating dominated climate so if you size the heat pump to cover the heating load, it will be oversized for a/c load. Oversizing for a/c and using a single stage unit will result in higher humidity due to short cycling. Short cycling is when a unit turns on and off a lot because it can cool so quickly due to being oversized for house load. This causes not alot of air to be moved acorss the cold coil for a long duration - the air in the house will keep humidity). If you are oversized for a/c and use a two stage (or better yet a variable speed unit), then the unit will run at lower stages for a/c and not really be oversized. It essentially impossible to have an oversized variable speed heat pump. I would recommend making a two stage unit your base choice and strongly recommend you consider a variable speed unit. If you were in a cooling dominated climate (southeast), and you are sized for a/c with a single stage unit, you would then get short cycling for heating but that tends to be less of an issue since dehumidifying during heating seasons isn't critical

    You would only need grout if you do vertical bores. You can make the bentonite based grout have a range of thermal conductivity (from 0.45 to 1.6 BTU/hr-ft-deg F) depending on how much graphite (or silica sand) gets added to the grout. look to geopro for well known manufacturer of grout with thermal enhancement. In general, there isn't much sense in making the grout have better thermal conductivity than the ground (matching it would be ideal). What you mainly want to do is not have the grout be an insulator (0.45 value; prevent heat from moving between pipe and ground) and be more like a conductor (1.0 and above). I personally designed using 0.8 and had contractor strive for 1.0. I had the grout tested by geopro (they will do it for free if you send them samples) and got values between 1 and 1.6 on three wells.

    Pipe size in vertical bores should be done so as to maintain flow in the transition to turbulent range (Reynolds numbers >2500? can't remember what is recommended) and not laminar flow at full load. So you want pipe small enough to promote high flow but large enough so that friction loss from flow isn't too big so pumping power skyrockets. If you have the IGSHP design manual (I think you said you did), there is a whole chapter on this aspect. Once you size the wells, then it is a pumping/friction loss design problem to minimize friction loss in the piping between the vertical wells and heat pump. That pipe should be as big as necessary to keep friction loss low - you want high flow (so high friction loss) where heat is exchanged - in wells and in heat pump. you want lower flow (lower friction loss) in piping between wells, circulator pump, and heat pump.
    Danny313 likes this.
  12. Danny313

    Danny313 Member

    You guys are the best! Thank you!

    There's no question I would opt for the variable speed HP and it should be sized for the dominant load, in my case the 3.5 ton heating load. But let's say that the analysis finding for load is somewhat "off" for some reason, or maybe there's been some deviation in house construction that ADDS to the load somewhat.
    That VSHP will not be reaching "beyond" its design capacity to let's say....4.0 or 4.5 ton (is there a built-in margin). In that case I could still get caught short.
    Should I play it safe and go with a slightly larger capacity HP and then with variable speed to address issue of short-cycling, to insure no use of aux? It would seem to me to be money well spent?
    I'm looking closely at this as there will be two accessory apartments plus one so I want to squeeze as much out of the system as I can, to plan for unknowns such as a tenant leaving a window open in winter!!! Even though I'll have an ERV for fresh air intake.

    There's bentonite used for the drilling mud (to stabilize the sand borehole) and also the grout. These are two separate components never together in combination? What happens when the bore goes into water table? Seems to me that both would be impossible to use.

    All for now....thanks again.
  13. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    The questions are what is oversizing, and what is right sizing.
    Dual stages were a game changer, variable speed heat pumps are a quantum leap.
    I look at this also from a 30,000 ft view. With no disadvantages for, I call it, right sizing heat pumps when you use variable speed. In the very near future, the heating sector will be electrified with heat pumps, and it will simply collapse the grid when all the heat pumps use supplemental heat at the coldest hour of the year.
    If you have 2 apartment with tenants, you cannot share the air with them. Imagine one has a dog, the other one is allergic to dogs.
    Now you would need 3 heat pumps.
    You need some professional help from a HVAC planning perspective. You are adding more and more information here of what you want to achieve, difficult to predict all this.
    No issue here with the water table. Our water table is around 18ft, and we go down 500ft. talk to your driller.
  14. gsmith22

    gsmith22 Active Member Forum Leader

    only thing I would add to what doc says is that most variable speed units aren't infinitely variable. Using WF7 as an example, it has 12 compressor stages ramping them up and down as needed to maintain set point of thermostat. Making up some numbers for example purposes, if you have a 3 ton load (peak) and put in a 4 ton unit (ie its oversized), then that unit will probably never have to run in the upper stages (say 9 to 12). So in effect what you did was take a 12 stage unit and make it an 8 stage unit. Not terrible, but not best bang for buck. Taking this to its logical extreme, put a 5 ton unit on a 2 ton load, and you have a unit that probably runs in stage 3 on the peak load day, runs in stage 1 almost all the time and may even short cycle because stage 1 in a 5 ton unit is probably 1 ton which would be half of your 2 ton load. Congratulations, you just made a variable speed unit essentially a 2 stage unit. So oversizing when you use a variable speed unit isn't nearly the concern it is with single or two stage units, but don't get carried away with the oversizing because the more oversized it is, the less and less benefit you will see from the variable speed aspect.

    I mention this because with your future planning, there might be an incentive to upsize the unit (maybe alot) now (because it is sized for future load) only to have the interim period before those plans are developed not work out so well (ie 5 ton unit on 2 ton load).

    I don't see any issue with upsizing the ground loop for the future plans and it makes sense to do that while the driller is on site and excavation is going on running the header pipes so you don't tear up the landscaping later. Worst case, you water temps are more moderate and the heat pump has higher capacities in heating/cooling in the interim. But to echo doc, you really do need some professional help with all this. There is only so much that can be disseminated over an internet chat board especially when the information provided is constantly changing.
  15. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Just to be clear, no one suggests putting in a 5 ton unit with a 2 ton load.

    Yes, instead of putting in a 2 ton unit needing supplement heat we are today putting in a 3 ton units covering the entire load including the peak, especially with a variable speed. Ground loops are the same size, thus the only difference is a 1 ton larger unit, usually about $1,000 more.
    But the unit runs more efficient, since it operates at a lower stage, thus saving some operating costs, and also saving the supplement electric heat.
    Units simply run much smoother.

    Utilities are happy, including regulators and Grid operators. essentially it is a win-win for everyone.
  16. gsmith22

    gsmith22 Active Member Forum Leader

    doc, I'm not saying you were suggesting putting a 5ton unit on a 2ton load or a critique of you. I was using a somewhat extreme example to prove a point - while it is hard to "oversize" a variable speed unit, the fact is they have discrete stages and are not infinitely variable. And if one gets carried away with the idea that it doesn't matter what size unit I use for the load (and just get the biggest unit made), you could effectively neuter all of the benefits that the multiple stages provides. It certainly happens with oversized two stage units - you end up with a only using the first stage. And if you do that, you are right back to a "short cycling single stage unit" using a dual or variable speed unit.

    Its important to point out that you still have to determine the load to get a right sized unit. Using variable speed units, being exact (which was always a crap shoot) with verifying that load has gone away because of the ability to change compressor speed and more closely match output with load. I brought it up because all of a sudden, future load is showing up in Danny313's design and there might be a temptation to put in the biggest unit possible to plan for the future which has consequences on the current (or if the future never materializes).
  17. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Danny cannot use the same unit for tenant apartments. Thus oversizing the heat pump to cover the additional load does not make sense.

    But to put it in perspective, if now a 3.5 ton load would be served by the largest residential unit, at (5) ton 7 series Waterfurnace, it would probably run up to stage 7 or 8 on the coldest days, and still a world of a difference compared to a dual stage, which would run only in 1st stage, or a single stage, which would cycle more.
  18. mtrentw

    mtrentw Active Member Industry Professional Forum Leader

    One addendum to Docs comment. It may be neither. It seems that often times aux kicking in is due to thermostat settings. If people get too carried away on temperature setbacks and/or the differential threshold is set too low in stat program, you could be setting up for unnecessary aux use when you have both adequate loop and heat pump capacity.

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