Veritical Questions - (1) 450' bore or (2) 225' bores?

Discussion in 'Vertical and Horizontal Loops' started by tywebb3, Jul 3, 2011.

  1. tywebb3

    tywebb3 New Member

    Does the depth of the bore make a difference in the operation of the system? I have (1) contractor quote (1) 450' bore (1.25" pipe) and another is quoting (2) 240' bores (1" pipe)? My uneducated assumption is that the deeper bore would be harder on the pump than splitting that up into (2) shallower bores? Is there any chance I am on to something here? By the way....this is on a 3-ton system.
  2. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Open can of worms here.
    The short answer is that the increase in pipe diameter to1.25 for one loop vs. two bores at 1" shallower would prolly be a wash after we get done measuring the friction loss numbers with a micrometer.
    When deciding on the construction of the GSHX it is all about the price per foot to drill. If there is no differance in the drilling costs between the two proposals the two proposals should be treated as "drillers preferance". The function of the GSHX is about feet of pipe in the ground not diameter of the pipe or how many pipes you can stuff in the same bore.
    If there is a price differance between the drilling costs, all other things being equal I would choose the cheaper drilling option of the two.
    Hope this helps
  3. tywebb3

    tywebb3 New Member

    Thanks for the response waterpirate.

    The contractor that has quoted (1) 450' bore of 1.25" pipe said he could do (2) 225' bores with 1.25" pipe for the same price. Is there any benefit to going with multiple shallower bores or should I stick with their original recommendation of (1) bore? I have read of some designs where people are getting (4) 150' bores and it made me think multiple shallow bores are better?
  4. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    The primary reason for paralell runs is to less pumping energy. How much this matters depends on cost/kw. Higher earth temperature at greater depths can easily be cancelled out by higher pumping cost.
    Like Eric, I think "driller's choice" is a good way to look at this.
    Depending on drilling equipment and nature of the soil, it might be easier for a driller to do multiple shorter vs one deeper bore.
    4 verticle loop system you read about is likely for a 4 ton system.
  5. tywebb3

    tywebb3 New Member

    Are there any advantages in regards to the geo system by going with multiple shallow bores vs. on deeper bore or is everything a wash and it really doesn't matter? I guess one advantage of the single bore would be less mess?
  6. SoundGT

    SoundGT New Member

    Borehole lengths

    Assuming borefield cost is similar...
    I can't address the loop length calculations because we don't have enough information. Therefore, I will have to assume that both contractors know what they are doing. That said, it becomes a hydraulic issue and a surface disturbance issue. As to the latter, two boreholes and a connecting trench disturb more ground.
    Ask the contractors what the pressure drop of their respective systems calculate to be, including any antifreeze. The lower of the two will be the least energy path.
    A three ton system requires (about) 9 gpm flow rate. For water, the pressure drop through one 450', 1.25" loop is ~6.5 feet of head (~2.8 psi) and the pressure drop through two 1", 225' boreholes is ~3.24 FOH (~1.4 psi). Not a lot of difference unless the run to the house, cold weather antifreeze viscosity, and heat pump connections drive the pressure drop up to force greater pumping horsepower.
    Eric's and AMI's comments are dead on.
  7. tywebb3

    tywebb3 New Member

    Ok...thanks for the quick feedback. Sounds like if I decide to pull the trigger and go with a geo system I will just go with the contractor's recommended single 450' well to keep the disturbance to a minimum. I just wanted to make sure that isn't too deep.

    I am really on the fence right now and can't seem to pull the trigger on a geo system. My current propane system is only 11 years old but the federal, state, county, and utility incentives to go geothermal would pay for more than half of a new system. Replace it now while the incentives are great or wait till it shows signs of dying? Decisions.....decisions.
  8. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    An 11 year old propane furnace is in the twilight of its life. Depending on your cost of electricity, the few years left in your furnace's life may be enough to spend a significant part of your geo's cost on propane. Paybacks in my neighborhood are often less than 5 years.
  9. tywebb3

    tywebb3 New Member

    Based on what I have received from contractors and figuring conservatively at today's current propane price and electric rates it looks to be an 8-10 year payback for me. Could be better....probably wouldn't be any worse.
  10. Bergy

    Bergy Member Industry Professional Forum Leader

    Remember, the tax credits are a GOVERNMENT program subject to the whims of Washington. I would not absolutely count on the tax credit being there through 2016, It can be taken off the table at any time.

  11. tywebb3

    tywebb3 New Member

    At any time? that's a twist I wasn't planning on. So if I had the system installed today they could decide tomorrow they are not going to offer the credit anymore and I would be hosed? That is one of my larger fears....have the system installed in the next month and then for some reason or another find out that something changed shortly after install and I can no longer get the federal, state, and/or county grants I was counting on. If the system is installed before any changes, would I be safe, i.e. grandfathered in?
  12. Bergy

    Bergy Member Industry Professional Forum Leader

    Also remember, the government moves slowly... Contractors would get plenty of warning were there to be a change. If you install something a the law changes the next hour, you are covered.

  13. Sound Geothermal

    Sound Geothermal New Member

    Loop Lengths

    I'd be more worried that the price of propane will go through the roof again. I converted the ranch from propane in 2002 and saved about $3k/yr. It didn't take long to pay out...

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