Loop depth!

Discussion in 'Geothermal Loops' started by Wiley HVAC, Nov 29, 2011.

  1. Wiley HVAC

    Wiley HVAC New Member

    My question is more about how deep when one has vertical loops, should the runs of pipe be from the surface! Reason I ask is I usually dont see the loop being done, we dont do the drilling or loops, I did however see them on the last job I did and they were fuseing thr pipes and laying them in a trench that couldnt be more than 2 maybe 2 1/2 foot deep! I cant picture that retaining heat well!
     
  2. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    I presume you mean the header pipes in which case, we generally put them same depth as a horizontal loop (~6ft). However, many things can impact that such as point of entry into home, proximity of utilities etc. In more than one occasion we have had to enter a building above ground.
    It is not the header's job to collect or discharge heat, rather it needs to get the brine from here to there.
     
  3. Wiley HVAC

    Wiley HVAC New Member

    Thanks Joe!

    Yes sir I do mean the headers! My fear is that at 2 foot deep I'm just barely below frost line and I would think that 40 feet of header at two feet from the surface that I will be losing a great deal of energy to the lack of depth! This particular installation is in a basement and they could have come in at least two feet deeper! I'm not educated enough yet in the loop design end! And upon start-up, (realizing that it is a new loop) my incoming line temperature was the same temp as the outdoor ambient!!! I'm scared that when the temps drop, I'm really gonna have an issue!!! Or am I jumping the gun!
     
  4. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Just to reinforce what Joe said, the headers and transmision lines job is not to transfer heat. In fact they are very poor at it given the flow rates through them on the way to loops. What is the freeze depth where you are? Is that depth the hard freeze line every year?
    I can make a pretty good argument for not runnng the lines through a 40 foot ice cube for part of the winter, but again I do not think the loss or gain would be significant.
    Have you had other jobs done that have not had issues?
    Eric
     
  5. Wiley HVAC

    Wiley HVAC New Member

    One other job I have some issues with! Not sure how the headers were done there, as I said, I do not generaly get to see the loop being installed! I understand that the hr/he is done in the vertical portion of the loop, just a little concerned about the incoming brine temp being the same as the outdoor ambient! With that being said, if the headers are horizontial, what big gain is there to a vertical loop, horizontial loop or directional boring!? I have an individual that claims horizontial loops dont do as good a job as a vertical loop! Personally, I would think that if the loop is designed correctly, one shouldn't be any different than the other!
     
  6. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    You are 100% correct sir about designing. The only differance between all the types of exchanges you could or can do is the economics to install them.
    Eric
     
  7. Wiley HVAC

    Wiley HVAC New Member

    Am I worried over nothing, with the incoming brine temperature being the same as the outdoor ambient???

    What if anything has anyone heard of ground shift, and how would it play on a horizontal or vertical loop? What I'm referring to as ground shift, is like earth quakes, fault lines, and such!
     
  8. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    Faults and earthquakes

    Yeh, generally you got more serious things to worry about than your geothermal loop field in those cases.:eek:
     
  9. Wiley HVAC

    Wiley HVAC New Member

    I understand that, I meant more like minor ground movements not major, things we wouldnt necessarily notice right away! Reason I ask, I was out to a 2nd opinion the other day, several contractors over the last few years had been out to this clients home, constantly having to put brine into the loop, I already knew it was leaking, so I had decided to go out where the loop entere:pd the home and dig. To my surprise I find that right where the loop entered the home, the ground had a major drop off under the loop, the pipes were just about completely sheared off!!! I am still shocked that this had gone on for 11 years!!!
     
  10. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    That sounds to me like poor backfill practices and not paying attention to detail than a "ground shift issue". I have heard from other people that because the transmision lines will not freeze that good practices do not apply?????:confused:. I disagree
    Eric
     
  11. Wiley HVAC

    Wiley HVAC New Member

    I agree about poor back fill! I just had a friend in California asking me about geo, he hasnt ever heard of anyone doing geo work out there thinking maybe due to earthquakes due to ground movement! Told him I had no idea and would ask! The issues I was referring to about horizontal, vertical, or directional bores was for my reference, I have a self proclaimed I've experienced it all individual that lays claim that a horizontal loop in Kentucky just wont work as well as a vertical loop! I say balderdash, but again, not very learned about the loop side of geothermal, would love to get more hands on training!!! Oh ya this individual hasnt spent a day in the field!!! SUPER TECH from behind a desk!
     
  12. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    The only differance between a super desk tech and experianced field personell is generally just their choice in foot wear when preparing for work in the morning.
    Eric
     
  13. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    I agree with Joe and Eric

    on the job of the header. In most applications the velocity of fluid in the header is enough that cross contamination from proximity of the incoming and out going piping is not an issue.

    How deep to keep the header is another issue. I spec the loops and headers be at least 18" below the frost line depth required by the LAJ for footer depth. Deeper is better, IMHO.

    Shallow headers can be fixed with bales of wheat straw, but why bother.

    Mark
     
  14. Wiley HVAC

    Wiley HVAC New Member


    my fear is, was, that at 2 foot deep the header is not far enough below frost line and that the header is going to pick up or loose temperature through the header. As it sits we only have 20" from the top of the header to the surface.
     
  15. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    situations require headers above the frostline from time to time and its okay. With hundreds vs thousands of feet exposed the loopfield will do the bulk of the extraction or rejection.
    j
     
  16. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    If the header pipe is below the frost line, which means the temp of the ground around the header pipe usually is 32F or above, which is normally the temperature coming back from the loopfield at the peak of the heating season. 32F water in the pipes is not going to loose any heat to 32F ground temp around the header pipe.
     
  17. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    For a multitude of reasons we often have to daylight the transmission lines and penetrate the structure above grade. This penetration is then enclosed and insulated with something nominal.

    We have recorded no significant differance in these systems from ones that the lines continued below the frost line into conditioned space.

    So yes there is prolly a loss there, but it would be measured with a micrometer.

    Eric
     
  18. Wiley HVAC

    Wiley HVAC New Member

    Well that is good to know, that its that small of a differential! I have a question I have about the loop in general! I have had the impression that the purpose of geothermal was that we are conditioning based upon the ground being a constant temperature and that it is what is extracting or rejecting the heat from the home! Now I have another tech that is telling me that the loops are running into the ground and that were the loops are is now like an energy vault per say, and that is how it is heating and cooling the home! His outlook on it makes absolutely no sense to meI I would think that if it was a storage vault that the earth temperature would disappate the loop temperature! If his theory is correct would the ground not just continue to heat up? I would think you woould see the ground and trees and such especially in like a pond loop situation start to kill things off!
     
  19. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    It is all the same, just different descriptions and terminology. There are no free btu's. A closed loop system as I explain it, works like a heat sink for electronics equipment. This is passive geothermal, not direct.

    From the top the earth has a constant temp that varies by geography. The closed loop is the exchanger or radiator if you will.

    As we operate the exchanger in heating mode, the heat pump is rejecting cold into the earth and cooling the surrounding dirt, if you will.

    As we operate in cooling mode the exchanger is rejecting heat and warming up the dirt.

    The design of any given system will have a range of temp. swing for the exchanger that is all normal, as we go from one season through to the next, year after year.

    This is commonly refered to as the "pendulum effect".

    Help any?
    Eric
     
  20. GCI

    GCI Member

    Loop Temps

    As Eric mentioned, the water temperatures entering the heat pump will swing between some minimum value in heating and some maximum value in cooling in a closed loop section. When you design a loopfield, you actually specify the min/max temperatures that are allowed. Min/max values of 30/90 are common.

    Attached is an (old) illustration that shows measured temps from a 4-ton system on a slinky loop here in Elkton, SD. As you can see, during the course of the year the loop temps swing from a minimum value of around 30F (entering the unit) in heating to a maximum value of around 70F (again, entering the unit) in cooling. The deep earth temp in this area is 47-48F.

    When the unit is working properly, you should see a 4-6F temperature drop through the coil in heating and an 8-10F temperature rise through the coil in cooling. This assumes a system flow rate of 3 gpm/ton.

    Sidenote: This 4-ton system serves a 3800 ft2 home (1900 ft2 above grade and 1900 ft2 below - standard construction R-19 walls, R-38 ceiling) and has never used supplemental resistance, even when outdoor air temps reach -30F.
     

    Attached Files:

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