Loop field design HORIZONTAL

Discussion in 'Quotes and Proposals' started by JC115, Jan 20, 2013.

  1. JC115

    JC115 Member

    We are getting ready to start construction of our new home. We are installing a 3 ton Tranquility 30 digital. I am digging the trenches and laying pipe, I was originally going to do slinkys, but the simplicity of just putting straight pipe in a trench has me wanting to do just that. The HVAC company suggest 400' of trench (2' wide) with 6 pipe (3/4'') in the trench (3 loops). Which seems like a lot of pipe in a small trench to me. So I am suggesting 800 feet of trench with 3 pipe (3/4'').
    My question is does either one of these sound limited or excessive? How would you install loops if it was your house?
    This is in Cincinnati Ohio See attached pdf for site plan, it will be running in a low area that stays moist most of the time.
    Thanks in advance
     

    Attached Files:

  2. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    I'm not sure if you're talking about 1 trench totaling 800' or 800' of trench(es)?

    Point being that will be a long (too long) length of 3/4" pipe if you're talking 1 trench.
     
  3. JC115

    JC115 Member

    I am talking about one 800 foot trench that has 3 800' long pipe. It would be 3 loops 800' all in the same trench. The trench would go in a circle with reverse return manifolds
     
  4. JC115

    JC115 Member

    not sure if it would be considered a "racetrack" or not, not sure what exactly it is, but with loop link as a "racetrack" it comes out to around 700' of trench.
    How much pipe is too much? I understand that the loops have to be under a certain size to keep the antifreeze moving a certain speed.
     
  5. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    There is no such thing as too much fun or too much loop as long as it is piped correctly.

    If pumping is free then run a loop to my house and back. It is not so that is out.

    When using a manifold in a loop field one may reduce the size of the pump to the length of the transportation pipe and a single loop. The less pumping required The less fuel used. If you do not take this into consideration you may use more power going geo than using an air to air heat pump in the Queen City area.

    Mark
     
  6. JC115

    JC115 Member

    the tranquility 30 has variable speed pump... either way 3 800ft loops of 3/4 inch doesn't seem like that much to me, pipe and digging are cheap so what say you?
     
  7. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    I say, "we have talked before about this job".

    I would have you look up the new Caleffi loop field manifolds and their flow meters.

    If you want the loop field down in the swampy front yard by all means put the field there. Wet is good for heat transfer.

    I get away with 300' and sometimes 500' loops per ton in Cleveland, so I think 800' ton is over kill. I dig at least 12" below frost line or footer depth which ever is deeper.

    The trick is making the piping between the field and the house large enough to move the BTUH required by the design.

    I will not get into the sizing of the equipment but lets look at what a 3 ton unit needs. It needs 3 gpm per ton or more. Those numbers can be found on their wed site buried in the I/O manuals.

    A ton is 12,000 BTUH. Three equals 36,000 BTUH. To move 39,000 BTUH you only need 3/4" pipe at 4.2' of friction head per 100' of pipe. This is at a 20* delta T and your pump works it's ass off but can only do 3.9 gpm. Your heat pump will not like that and will lock out and turn on toaster heat.

    To get your heat pump the at least 9 gpm it wants, you need the transportation piping to be at least 1 1/4".

    So put the loop field in the swamp. Install a manifold in the yard. Run back and forth to the house with 1 1/4" pipe and buy the smallest pump that will give you 9 gpm at 4.2 per hundred of friction on the 3/4" loops.

    Sounds easy.

    Mark
     
    Last edited: Jan 22, 2013
  8. JC115

    JC115 Member

    The 30 has a built in flow center... I will look into callefi manifolds...
    As for the single 1.25 pipe that sounds crazy, there is a velocity that has to reached for best heat transfer. Wouldn't it be reached much faster with smaller pipe?
    Also there is much more earth in contact with the loop with smaller pipe.
    Haven't heard of anyone using this large diameter pipe, doesn't make sense to me
    I do understand how it requires less to pump the 9gpm, but surely there are other factors than x amount of gpm
     
  9. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    I do not know how Climate Master knows what I installed for a loop system and therefore provides, "a pump to move fluid through the system". I know how to design these systems and how to pick a pump size to match the flow requirements. I spec only enough pump to do the job, as any more is wasting pump and energy. I have found that the increased cost of the pre-pumped equipment far exceeds what it costs to buy and install just enough pump.

    There are several factors at work when sizing pipe. One can only get a certain amount of fluid through a given pipe. Period. There are published tables that document proven capacities, including Bell & Gosett's System Syzer, Burnham Hydronic Helper, and the Grundfos Handbook. All three are always open on my desk and never make their way to the book shelf. All three are close enough to each other as to be in my mind interchangeable.

    In my post of 1.22.2013 I quoted Burnham, it was on top of the pile. Would one try to flush a toilet through a 1 1/2" drain? Think about the different sized drain pipes in your home, 1 1/2" for a sink, 2" for a tub or shower and 3" for a toilet. Each fixture has its own requirements for volume and flow.

    Velocity, volume and flow rate, given that we are using water, which is not compressible, are easy to measure and hence the tables. Why experiment with your hard earned cash setting up geo loops in your front yard when we can look at the tables and predict a result?

    The 1 1/4" transportation piping between the loop field manifolds and your heat pump are not really a part of designing for the heat transfer. We rely on the three 3/4" loops in the swamp to transfer heat and the 1 1/4" is the interstate getting the BTUH in and out of the house.

    Yes you are correct there is a lot more to this than gpm.

    Mark
     
  10. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    You have small pipe in the loops for heat transfer and large pipe between the house and the loop field.
     
  11. JC115

    JC115 Member

    Sorry Mark I read your post wrong, yes 1.25 to and from the loop field is what I had in mind as well.
    What are your opinions on having the loop min temp designed to be 34? The default is 30, my HVAC guy said 34 would be safer. I know the antifreeze will keep the loops from freezing, is this 4 degrees going to make a difference?
     
  12. JC115

    JC115 Member

    "I get away with 300' and sometimes 500' loops per ton in Cleveland, so I think 800' ton is over kill. I dig at least 12" below frost line or footer depth which ever is deeper."

    Can you describe these loops more, are they in the same trench ussually, or do you put each loop in a separate trench? How far apart should lines be inside a trench?

    I will most likely be using a 2 foot bucket on either a backhoe or trackhoe, other sizes could be available up to 4' if it were a significant difference in heat exchange

    I am just curious what others are having success with, I have looked through all the different loop designs on both geo designer and loop link. I know it doesn't make any sense to me to layer pipe in a ditch, when I could probably dig another trench just as fast.
     
  13. JC115

    JC115 Member

     
  14. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    I tend to use the pipe in the lengths it comes in like 300' and 500'. More than 500' of 3/4" and you start getting into pumping issues. To figure your head pressure you need to account for the transportation piping, one loop, the CV of the manifold and the near heat pump piping, (but Climate Master is doing that for you).

    I am not sure I understand how to project an EWT at 30* or 34*, much less design to those numbers. Too many variables.

    I like glycol and install enough to prevent growing things. If that machine still uses the CMX control board you can clip a jumper and take your EWT way down.

    A two foot trench is OK for an out and back loop. I try to get at least 10 feet of separation and like 15 better. Since I use the pipe as it comes, I dig 4 foot holes for slinkies. Four foot holes take a bigger machine. We intended to slinkie MtrentW's field but we had the room and our excavating contractor dug faster than we could re-roll pipe.

    On an out and back keep the pipe at the edge of the trench. Slinkies go in flat in the 4 foot trench. I do not layer loops.

    I understand ECM drive pumps and have used them since I learned about them. They still are manufactured in different sizes with different pump curves.

    My wholesale price on pre-pumped equipment is around 140% of non-pumped equipment. I can buy all kinds of pumps for that kind of money. Plus I get the value added of knowing the pump is sized correctly.

    Mark
     
  15. JC115

    JC115 Member

    Maybe you can tell me where I am off on my numbers in the attachment. Seems like I am missing something this is 1300ft of pipe per ton
     

    Attached Files:

  16. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Jesse:

    Nice report. I get it all but the digging. That is a LOT​ of dirt to move to build that race track. I think the loops are too close at the edge of the trench and again lots of dirt to move to get the ten feet of separation between the out going and inbound loops.

    I have seen lots of holes and they never come out nice and neat like the picture. I am a keep it simple kind of guy. Why not do this: trent 003.jpg trent 007.jpg trent6-27-12 017.jpg
     
  17. JC115

    JC115 Member

    in between the out going and incoming loops would be unexcavated, they must put that in there to show the distance between the two ditches... is that too much pipe?
     
  18. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    I agree with Mark, there is no sense to dig all of that dirt out of the middle just to put it back.

    Switch to a different layout and save a lot of digging. Lower your min EWT to 30° and save even more digging. See the attached for explanation





    30.JPG 34.JPG
     
  19. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    The reason it is 1300' per ton is the trench depth is 4', make it 6' and then you are closer to 800' per ton
     
  20. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    The other question is why a TC of .50? Is there no moisture in your soil? If the TC is .80 and the depth is 6' then the amount of pipe needed is cut in half.
     

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