'Double piped' well?

Discussion in 'Vertical and Horizontal Loops' started by Viper GTS, Sep 14, 2018 at 4:32 PM.

  1. Viper GTS

    Viper GTS New Member

    I'm in the process of having a new system installed in northern New Jersey. I got two quotes from the two biggest Waterfurnace dealers in the area and went with the one that could meet my timeline + more reasonable cost. I'm getting a 4 ton 7 Series, desuperheater, etc. Calculated heating load is around 3.5 ton.

    Well drilling started on Monday. Originally the main contractor told me I was going to get 2 x 375' x 1 1/4" wells. Drilling has not gone well at all, in 5 days they managed to get one ~300' well and have elected to 'double pipe it.' Essentially they pushed two separate U bends down it (I have four pipe ends above ground) and are claiming it's spacer separated + grouted between. I didn't see it go in the hole so I have no way to verify this.

    Before I let the crew leave I called my installer and verified that he had signed off on this design change. He swears that he has validated this design and I will still have ample loop but the math side of me is skeptical. If it were this simple it seems to me that every system would be designed this way to cut drilling cost in half.

    Is this a reasonable design choice? Anybody have the math to say how two vertical loops with normal 10-15' spacing would compare vs this?
     

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  2. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Hi and welcome!
    2 loops in one borehole is done quite frequently when planned for in advance. The math side of it I will leave to the designers, but two loops in one borehole does not equal the same load as 2 loops in two separate boreholes. Will the 2 loops in one borehole support your load is the question.
    Hope this helps
    Eric
     
  3. Viper GTS

    Viper GTS New Member

    That does help, thank you. The installer claims an install base of ~800 systems, I'll have to trust him (have little choice I suppose). It's just something I had not seen in my fairly lengthy research so I got a bit paranoid. I suppose I will know nearly immediately if I am going to have a problem as we'll be nearly into heating season by the time this is done.
     
  4. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    You gain about 15-20% by putting in a second pipe, not more....
     
  5. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    I have not seen a spacer for double pipe before. Doesn't mean they don't exist, but I have heard of them. Not that it would add to efficiency much.

    So, your 2 x 375' boreholes are now 1 double piped 300' borehole? The latter is about 1/2 the capacity of the former. Or are they doing 2 x 300' double piped boreholes?
     
  6. Viper GTS

    Viper GTS New Member

    That is kind of the range I would have expected.

    Maybe they just meant they did their best to keep them on opposite sides of the hole while it was grouted. Perhaps not a literal physical spacer. And yes, 2x375 became 1x300' double piped.

    Is this completely outside the realm of workable?
     
  7. arkie6

    arkie6 Member Forum Leader

    If the original design required 2 wells x 375' with one loop per well, and it seems reasonable, then 1 well x 300' with 2 loops in that well is nowhere near equivalent. As stated above, a single 300' well with double loop pipes will perform maybe 20% better than a single 300' well with a single loop in it. With the single well double loop 300' bore, you would get roughly 300 + 20% / (2 x 375) = ~48% performance of the 2 wells x 375' with a single loop in each well. Now if they are installing 2 wells x 300' with 2 loops in each well, then you are roughly equivalent to the original 2 x 375' with a single loop in each well.
     
  8. Viper GTS

    Viper GTS New Member

    Met with the installer today, it seems to have been a miscommunication from mixing terms (intermixing borehole depth vs loop length per U in the same sentence basically). Seems due to all the trouble they had getting to bedrock (at 165 feet) they opted to do it all in one borehole at 600'. So 600x1.2 = 720 which is basically where we were originally supposed to be. He agreed that a single 300' with two loops would not be nearly enough, so I think we are all on the same page.

    Life looks much better when the math and sources align. Thanks for the math assist everyone, the 1.2 multiplier was what I needed to make sense of it all.
     
  9. arkie6

    arkie6 Member Forum Leader

    No to be a doubter (I'm a believer in trust but verify, especially when a lot of $ is involved), but did the installer or well driller provide you with a copy of the drilling report that typically has to be filed with the state? If not, you should be able to get a copy from the state.

    https://www.state.nj.us/dep/watersupply/pw_permit.html
    "Once a well is constructed, the driller is required to submit a well record document which is the as-built description of the well."

    You can also search for your well drilling permit here:
    https://www13.state.nj.us/DataMiner...ategory=y&catName=Water+Supply+and+Geoscience

    I assume the permit had to be amended if it changed from 2 x 375' to 1 x 600' ?
     
  10. Viper GTS

    Viper GTS New Member

    At one point the crew doing the drilling were talking about going to 600 in one borehole. Given that, my inclination is to believe them, but with the link I'll definitely check on it. Currently there are two permits for 300' each.

    I'll ask for a copy of the final well record document both from the drilling company and from the state once it's fully registered.
     
  11. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    So you have 1 borehole, 600' deep, with one single 1.25" flow circuit installed?
    You pressure drop now is pretty high, with Methanol it would be 45ft/hd just for the borehole (versus 7.9 ft/hd with 2x375 boreholes), plus about 15 ft/hd for the rest of the system.

    If that is the case, what circulation pump are they planning to use, and who is paying for the significantly higher pumping energy needed for the life of the system?
    You picture shows 4 pipes going into the hole. Are they at 300' borehole depth, or is the borehole 600' deep, with (2) x 1200' pipe in there?
    You need to figure out precisely what they are trying to do. How much pipe in how many holes, how many circuits and what pipe diameter....
     
    Last edited: Sep 16, 2018 at 9:45 AM
  12. Viper GTS

    Viper GTS New Member

    My current understanding subject to verification of borehole depth is:

    600 foot borehole
    2x1200 ft loop
    1x32-140 pump
    1 1/4" IPS loop (I photographed the spools on the truck)
    Ethanol with environal additive (I believe methanol is not allowed here)

    I have been following (or at least trying to follow) your best practices carefully. I was pleased with the pipe diameter, pump choice, and coolant selection originally as they tracked your summarized efficient system list as closely.as possible assuming methanol is indeed not allowed. I clearly need to read up on pressure issues as I don't have a good grasp on that currently.

    (furious google research)

    OK here's what I've come up with. It seems logical to me, but I'm sure I've made mistakes. Please do correct me as I want to understand.

    Base assumptions (from your post history mostly):

    3 gpm/ton, in this case with 4 ton I'll assume I need all of it so 12 gpm total system flow
    Methanol/ethanol are more efficient to pump than water so I'll use water to get worst case numbers and since I don't know the specific mix they will be using.
    15 feet of head outside the well itself
    0 elevation to worry about since it's a loop starting and ending at the same height
    12 gpm should get split in two for a parallel loop (which appears to be standard), we'll assume equal length and materials so each gets 6 gpm

    Web calculators vary quite a bit the worst case one I found using 6 gpm, 1200 feet of 1.25" poly pipe resulted in about 12.4 feet of head loss. So double that and round it to 25. Add your 15 and I'm looking at ~40 feet of loss total.

    The pump appears to be capable of only ~11 gpm at 40 feet of head but that number dropping would change the head pressure yes? With pumping efficiency gain from ethanol it looks like I'll be right at the edge of the pump's performance envelope.

    There's a lot of worst case/rounding up in this math so I think if anything I have erred on the side of caution unless I am just hopelessly misusing the tiny bit of knowledge I've gained today.
     
    Last edited: Sep 16, 2018 at 5:14 PM
  13. arkie6

    arkie6 Member Forum Leader

    With two (2) parallel loops, why would you double the head loss from 12.4 ft-hd to 25 ft-hd? Normally, with equal length/size loops, you only need to use the head loss for a single loop in your total head loss calculation when you have parallel loops.

    https://www.engineeringtoolbox.com/pipes-series-parallel-d_1787.html

    What size header pipe to connect those 2 x 1200' loops? How long will the header pipe be from the well loops to the unit?
     
    Last edited: Sep 16, 2018 at 10:55 PM
  14. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    WITH Ethanol I get about 14 ft/hd for the loop field, and 9 ft go hd for the unit. As Arkie mentioned, it now depends a bit on the pipe length side and outside to the loop field what your final system pressure drop will be.

    Ethanol has higher pressure drop than water, not the other way around, and is LESS efficient to pump.

    However, even if you only have 11 gpm during the rare occasion when the heat pump runs at stage 12 for full heating capacity you'll be fine.

    If that is what your design is, nothing strikes me as a concern.
     

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