Sizing the ground loop (Ground loop oversized??!)

Discussion in 'Geothermal Loops' started by Skogen, Feb 27, 2013.

  1. Skogen

    Skogen New Member

    Hey guys, I've visiting this site for a while now learning all about ground source heat pumps and would really like to use one on our new home we are building. I've had a manual J and D completed, and now the ground loop design in coming back and I just don't understand how these folks are coming up with their numbers. Here are the details:

    House size: ~5170 sqft. (I know this really doesn't matter, but thought you would like to know)
    Location: Mountain area just East of Albuquerque NM (Very similar to Santa Fe, NM)
    Elevation: 6890'
    Ground temp: 66-68° (according to all the charts that I have seen)
    Ground material: Limestone (we had a soils report done)
    Heat loss: 90,510 Btu/h

    Loop design will be vertical, we have 2 acres, but there is limestone just under the surface and trenching would be difficult.

    Some folks (I don't know who came up with these numbers exactly) believe we need the following:

    Bore holes: 9
    Depth: 300'
    Pipe size: not listed

    What do you guys think? I know some of you have access to the computer software that can size these loops, would you care to run my numbers? I think that the size should be more like 8 bore holes at 250' each, and that may be over doing it still.

    Please help, over sizing this loop will put this system out of reach financially!!
  2. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    This is a pay to play world.

    Like the giant boat, if you need to ask the maintenance costs, do not apply.

    I find that one is into geo or one is not into geo.

    What numbers are you looking for?

    If it is not affordable then what, buy propane? Go "All Electric" and get the discounts just taken away by First Energy?

    I am a comfort guy. My job is to make you and Mrs. You not get divorced about a thermostat. Once I do a job that lets you do a 50 years party, I look at fuel costs.

    If you can not afford geo then go propane, electric or LNG. In some areas you can get natural gas piped into your home. I do these systems very well.

    I have never had a divorce about a thermostat.

    I have never lost a customer to over or under comfort.

    I have never had a customer declair bankruptcy over fuel bills.

    I think you need to fine tune what you want. When you are done with looking at your wants and needs then decide.

    This can become a money is no object sport.

    I have been at this for a while. I just said no to a near net zero house because the GC would not pay my design fee. He said, "Why should I pay for a design my customer can not afford.". I looked at that statement two ways.

    The first look for me said the customer who found me could really not afford me or the house he wished to build.

    The second look said the GC would not afford me, as I would take away from granite, tile and such. It did not matter that I could have paid for myself and my design fee in 5 to 7 years of energy savings. I feel bad for my NOT customer.

  3. Skogen

    Skogen New Member

    Mark, Thanks for your reply.

    Maybe you misread my post. I have been researching this HVAC system for the last 6+ years. I have a good idea of the costs, so your 'big boat' analogy does not apply. Let me get straight to the point, I believe that the folks who computed the needed loop size have miscalculated. I am asking the experienced members of this forum for their honest opinion of what the proper loop size should be. I also have my own calculations, which I also included in my original post.

    Let me ask you this, why would I buy something that is more than what is required (over-sized loop), would you? I am asking for a second opinion, not soliciting a lecture about luxury items.

    So, my question remains...can anyone offer a second opinion or direct me to someone who may be able to offer one?

  4. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    I did not mean to lecture or offend. I can tell you that in Northern Ohio your reported load is between 7.5 and 10 tons. We do a loop per ton at between 150 and 175 feet deep so twice the pipe per hole.

    I would think, not being a driller, that limestone would make a good heat transfer, especially with grout.

    Hope that helps.


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