Seeking guidance, reassurance. Horizontal ground loop install

Discussion in 'Geothermal Loops' started by Jerome Scarpati, Jul 7, 2017.

  1. Jerome Scarpati

    Jerome Scarpati New Member

    Hello forum,

    I am a new member and this is my first post. I have been reading this site for two years and finally ready to start my project. I will do my best to provide as much info as I can at this time.

    My wife and I are building our dream home on a farm we have owned for a few years. For reasons of cost, but more importantly our desire to be as self sufficient as possible, we are doing as much of the construction process ourselves. I have been an advocate and student of geothermal for a long time, reading as much as I can. I am committed to using it in my new home. After much reading and conversation, I am hopefully I can install the majority of the system myself ( and with some guidance by those here, hopefully)

    Our farm is located in central eastern Pennsylvania, Lehigh valley area if anyone is familiar. I have a backhoe on site. Ground temps at 52degrees. We are building a 4200 sqft home, with great focus on energy efficiency (quality insulation, windows, etc). Home will have wood burner backup, but system not accounting for its usage at all. My goal is all electric as I am considering other renewable sources (home hydro, solar) in the future to augment my electric bill. My soil is relatively dry and full of shale. Farm is on a hilltop area and ground is almost all shale.

    We are planning on a 5 ton two stage unit, based on analysis from a private company, with an auxiliary variable heat strip to supplement. I am planning on a horizontal loop system. It is now the beginning July and I am hoping to install my loops in August, as I will have the time and equipment to do so at that time. House construction will begin in the spring (April 2018). My goal is to have the loops done now, allow for settling etc and be ready to hook into come the spring/ summer next year.

    Loop Design:
    Based on my size system, rocky and relatively dry soil, my proposed loop design is 6 individual 800ft slinky loops of 3/4in HDPE. All six loops will start and end inside the basement and connnect to the manifold there. I am not overlapping my slinks. 3 ft wide trench, 6feet deep, one slinky loop of pipe (10 linear ft of pipe) per 3 linear ft of trench.

    That is the general overall idea. I hope that is enough info. So, to my questions. Basically, I am just nervous about actually pulling the trigger. I was hoping to get the opinions of the experts here before doing anything and getting into trouble.

    As this time, I am mostly interested in opinions/ thoughts on my loop as that is what is happening now.
    1: am I in good shape with my design?
    2: should I consider 1 inch pipe rather than 3/4?
    3: I am considering a drip/ soaker tube/ pipe in each trench to increase my thermal conductivity. This would be gravity fed from grey water system from the house with additional rainwater collection system as well. Is this worth the time/ expense?

    Thank you to any and all who would be so kind to offer any advice. It is greatly appreciated.
  2. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Initial thought is that 800' of 3/4 pipe is going to give you one heck of a lot of friction loss. Friction loss drives up pump size and power consumption. I would increase pipe size and number of circuits, at a shorter length each to yield the same amount of pipe in the ground. Ending the loops in the basement would make this easy to do. I would also recommend a non pressurized flow center.
  3. Jerome Scarpati

    Jerome Scarpati New Member

    Eric, thank you very much for the reply. I have read on here something to the effect of "anything over 200ft one should use 1inch pipe over 3/4". You recommend larger pipe due to friction loss. Is it safe to assume you mean 1 in? Any larger I may have a hard time with my loops I was thinking? With 1 in, will I still have good exchange and turbulent flow? Is the increased cost of 1in pipe over 3/4 worth it in terms of efficiency gained/less energy consumed?

    Concerning your suggestion on the smaller length loops, but still same amount of pipe, what would be your suggestion as to how? Assuming I want to have all my connections in the basement, would you suggest maybe 8, 600 ft loops? Or, by increasing by pipe size from 3/4 to 1in would I be ok with original design?

    Sorry for barrage of questions... quite excited about this project! Thank you again for your time and consideration.
    - Jerome
  4. ChrisJ

    ChrisJ Active Member Forum Leader

    I have a PVC pipe watering loop system in the 5 trenches of my horizontal loops. I have a hose connection at the foundation. Once a year I send water into the pipes for about 4-5 hours. Honestly don't know if it helps, my dirt was pretty good and I have had very little settling. I have a feeling shale will not make good contact to the pipes in the ground. Maybe you could save the top soil from the foundation area to put around the loops then fill the rest of the trench with what came out of the trench.

    My straight pipe 1", 200' out and 200' back X 5 has worked fine supporting the original 4 ton combination heat pump. I have a single loop pump so I doubt I have very turbulent flow.

    One thing I learned, we built the house mostly our selves, was the heat load calculations were quite high compared to what we have, after 7 years in the house. It's a 1920 sq. ft. ranch with walk out basement and drive under(heated) garage. So we heat 3800 sq.ft. The 4 ton has been replaced with a 3 ton and stage 2 almost never kicks in.

    With good air sealing and better then code insulation, you should not need 5 tons of heat pump. If I were starting over I would use a variable speed unit like the Series 7 from WF.
  5. Jerome Scarpati

    Jerome Scarpati New Member

    First, thank you for your reply. It is greatly appreciated to have insight from those who have done it. Concerning your watering system, how did you construct your pvc pipe? Just drill holes in the bottom? How do you prevent the pipes from clogging with dirt? Or roots? Are roots a problem that deep? I have looked at "soaker drip tubes" but most say not to bury them... thoughts? What are your opinions on 3/4 vs 1 in? What do you think about my lengths and the rocky soil? I agree shale not the best soil type, so trying to compensate with longer length loops... ?? Thank you kindly!
  6. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    OK. I have to admit I'm swamped these days and not going to take on a re-design of this, but I'd better speak up. Installing in dry shale being the red flag for me.

    We don't have a design here to really answer these questions. Sounds good is the best you may get.

    Give us your heat loss/heat gain to start.
    Last edited: Jul 8, 2017
  7. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    As far as soil types and length of pipe, I do not have any info on dry shale install. As for loop length and pipe size for optimal pumping and flow. Eight circuits 1 inch at 600' each is far better than 6 circuits of 3/4 at 800' each. You really need to troll up Dewayne Dean, formerly of Pallace geothermal. He was our resident poor soil, slinky guru. He can be found on linkidin as well as messaged hear. His involvement here has decreased as of late.
  8. arkie6

    arkie6 Active Member Forum Leader

  9. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Everything he said! ^^^^^^^
  10. Jerome Scarpati

    Jerome Scarpati New Member

    To better clarify, my soil at 6-8 feet is definitely full of shale, but certainly not solid shale. A bucket of earth from that depth in my opinion would be 40-50 percent shale/rock, the remaining dirt and smaller pebbles. I just don't want to imply I am installing in a solid shale bank.

    I will defiantly change my design to 1 inch pipe rather than 3/4 based on all of your recommendations. Thank you very very much to everyone.
  11. Jerome Scarpati

    Jerome Scarpati New Member

  12. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    What kind of antifreeze would you use? Would you be comfortable with Methanol, and handling methanol? Glycol would drop your Reynolds number significantly, and is more expansive.
    If in doubt, you would always benefit from a larger loop field. Not sure how good the soaker lines will work, or what they change.

    What pump do you plan to use? If you go with a 5 ton heatpump, your goal should still be to use only one pump.

    Nothing wrong with 3/4" pipe. We played around with 1" pipe, but went back to 3/4 and shorter ones.

    Some examples: If you go with 6 loops of 1", 800' and glycol, your pressure drop in the loop field is only 6.9ft/hd, but your reynolds number is also only 1000 at 16 gpm total. So 1" pipe does not work too well with glycol. With Methanol it is more like Reynolds of 2195, much better, PD is 5.9.

    If you go with 8 loops of 600' and 3/4" pipe, your PD in the loop field is 7.5, with a Reynolds of 2062. So 1" pipe is not necessarily better.

    A single 26-99 would give you 14 gpm. Good enough for a 5 ton.

    Keep in mind that your loop should be designed to fit the smallest possible pump. Yes, you should go with a non-pressurized flow center.

    Not knowing you ground conductivity, I would throw in a few extra loops to cover myself. Yes, knowing your load numbers would help.
  13. Jerome Scarpati

    Jerome Scarpati New Member

    Doc! So happy to hear from you! I have read many many many of your posts. One of which was from a while back when you commented on 3/4 vs 1 inch... you mentioned that the larger pipe creates a "thermal reservoir" or something, which cannot be calculated but is beneficial. I understand that was a while ago, but does that still hold true now? Or should I stay with then 3/4 pipe? Thank you!
  14. mtrentw

    mtrentw Active Member Industry Professional Forum Leader

    Reservoir is beneficial, but rapidly dissipated. Ballpark difference between 4800' of 1" vs 3/4" pipe is 195 gallon fill vs. 110 gallon fill. that 85 gallons or about 700 pounds of water can hold an additional 1 btu per pound per degree F. With a few degree swing each day, you may be able to pull out an extra quarter ton hours of cooling from the reservoir.
  15. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    There are many things which are not accounted for in the simulation software, such as reservoir, the effect of pulsing (on and off cycling) and variable speed capacity including variable speed pumping.

    Again, not knowing your local conditions, load numbers and antifreeze, in general I would go with 3/4" pipe and use (8) 600' loops instead of (6) 800'. Much better pumping scenario.
  16. arkie6

    arkie6 Active Member Forum Leader

    Plus, if you are building slinkies for a 3' wide trench, I would think that 3/4" pipe would be a lot easier to work with than 1" pipe. I have vertical wells and don't have an experience with slinkies, but I sure some of the guys here that do install slinkies can chime in with their experience.
  17. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    3/4" is much easier. 1" slinky we did in 4" width.
  18. Jerome Scarpati

    Jerome Scarpati New Member

    End of the Season UPDATE:

    Hello forum, new member Jerome here. One thing I did not want to be was that guy that gets his questions answered and then never returns. I am back after a few months and wanted to relay what I have accomplished so far, much because of all your great recommendations.

    I have installed 6 individual loops, 6 feet down, 3/4 Hdpe, and each loop is 800ft in length. I went with the 800 ft lengths because of a slight variability in final home site location. As mentioned previously, this system is installed now and the house is not coming until next year. So, to guarantee I would not be short either entering or exiting the house, I left myself 50 feet extra on each end. So, at minimum I’ll have 700ft per loop. Also, as suggested by another member, I used the top soil and very nice top two feet of dirt to sandwich my coils. I put 8-12 inches of nice non rocky soil both above and below my coils. I then back filled the remaining trench with my rocky shale. In addition, 10 inches above the coils in each trench I laid 4in perforated pvc drain pipe that is connected to non perforated drain pipe that will eventually be connected to my rain gutters. I built in an overflow compensation as well. I got the perforated pipe very cheap and for a few hundred bucks, it seemed like a good way to increase my soil
    Conductivity. Also, it makes me happy to think I’m repurposing my rain water a bit.

    All of my trenches are back filled and I got s nice bed of grass on top already. I have my 6 supply pipes in a trench ready to go and the same for the returns. Once foundation is ready, my plan is to run all 12 pipes through the foundation and to a manifold, no outside connections.

    I have included some pics! Very excited and wanted to express my thanks and gratitude to you all. I’m sure I’ll have some more questions when it comes to pumps and antifreeze mixture, but for now thank you all very very much.

    Attached Files:

  19. Jerome Scarpati

    Jerome Scarpati New Member

  20. Jerome Scarpati

    Jerome Scarpati New Member

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