Looking for information on direct exchange geo

Discussion in 'Geothermal Loops' started by gte, Jul 31, 2011.

  1. Looby

    Looby Member Forum Leader

    That means very little. HDPE wall thickness is typically about 0.1 inch,
    so the pipe wall presents less thermal resistance than the first 1/2 inch
    of soil surrounding the bore.

    That alleged "efficiency" has little/nothing to do with the piping material.
    The fact that DX can (sometimes) get by with a shorter loop field is almost
    entirely due to the much larger delta-T available with DX. Copper pipe is
    used only because plastic pipe isn't suitable as a refrigerant container.
    Last edited: Aug 4, 2011
  2. gte

    gte New Member

    Ok, thank you Looby!

  3. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Your interest in copper and diagonal drilling suggests that a DX web site or salesman have done a good job selling you on their design. Fact is DX gets very high initial efficiencies (as advertised) then has to wait for the ground to catch up. A local distributor mentioned radial cuts can ocur from ground freeze if system is not sized for down time.

    To answer your question about converting air source to DX the problem early DXers had and you might without precise design or uncanny luck is running the compressor dry. DX loops come from the factory in specific sizes to ensure proper ref. oil recovery.

    Where you are located matters in design. Your 4.9 ton load, if heating does not indicate a 5 ton heat pump to a geo designer/installer. Depending on cooling load, cost of electricity, size of ducts, desired set points, you would likely pick a 4 ton and maybe a 3. Running a larger compressor all the time to avoid modest auxiliary heat occasionally often costs more to operate and always costs more to install.

    RE loop design, it's all about foot print. When you discuss more efficient transfer of heat, all that means is the loop can be shorter. It has no impact on operating cost.
    Picking diagonal loops over horizontal (if you have the room) will elevate your installation cost not your efficiency.

    You are well researched but have missed a few pcs of the puzzle. Hope I helped.

  4. gte

    gte New Member

    Hi Joe,

    Thanks for the reply, you have helped. I thought diagonal drilling would be less destruction in my yard, so that's what really attracted me to it, vertical would be fine too. I do not want horizontal trenches and although I have over 2 acres, my trees would probably make that quite difficult.

    I was planning on measuring the linear feet of coil in my pump and starting with that as an overall copper length, to try and avoid running the compressor dry. Is that the wrong way to go about it?

    I thought having a single pump, instead of a freon pump and water pump would allow for greater cost efficiency? Even if I needed a somewhat larger single pump, the kW usage could still be less than 2 pumps. Are you saying that thought is a misconception of mine?

  5. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    1) You really sound like a DX commercial. Diagonal or any drilling is going to tear up your yard. Pits and header trenches are not zero impact either. Horizontal is way more DIY friendly. Depending on the soil you could have as little as a 110'X36" trench/ton.

    2) This approach shows an acute lack of understanding of what you are getting into. Refrigerant has to be metered, loop design has to accomodate state change, existing feet of tube may not be adequate with out fan assist etc.

    3) Again the DX poster quotes. DX systems are often sized larger than water source to offer down time between cycles. DX systems (save one) are single stage while water to air are available in 2 stage. A heavier one stage compressor will not use less amps than a 2 stage compressor on a smaller unit with a flow center.

    I'm not bashing DX, if installed by an able company it can be very efficient. Higher AVERAGE efficiency than a 2 stage water source, I'm not convinced.

    But is efficiency really the question here? You want a DIY frankenstein heat pump made out of your old ASHP. Okay, if you want to do that I would submit to you that your odds will be better if you purchase a coax heat exchanger and go water source.

    Finally, was my comment on your size/design missed? Your job does not call for 4.9 tons.

    This job needs a re-boot.
  6. gte

    gte New Member

    I'm definitely not a commercial and there is no job yet, just someone humbly asking some questions. If the interpretation was that this was in the final stages and I was starting next week, that is not correct. I have theorized and am now looking for the holes in my theory. I also did not miss your comment, as it was a comment and not a question.

    I understand that the yard will be impacted no matter what, but there is no way I'll be raking rocks out of and seeding 330ft2 (x3 or 4) worth of dirt, with vertical or diagonal and that was the reason it appealed to me. Horizontal bore might be of interest as well.

    As for # 2) ... I agree and the only way to figure it out is to test or to get a system designed by someone else who has tested.

    Here is where I got my hvac tonnage


    Free Air Conditioning Calculator

  7. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    that calculator is not a good one. it doesn't seem to ask for zip code, it might be accurate for FL. you are probably in the 3 ton range.

    I'm not suggesting that you are a champion of DX, Im suggesting you are sold on their advertising bullets without understanding the distinctions......i.e. most efficient loops does not mean lower operating cost, it means less pipe in the ground etc.

    In my AO 3 vertical wells with grout might be $4,500 (no loops, header, excavation or flow center) while an excavator for the day might be $500. You could probably get a landscape company and sod to fix your lawn for less than $4,000.

    Further rebuilding your existing heat pump might run $500-$1,000. You could purchase a 3 ton 2 stage tax credit worthy warrantied unit for about $4,500. Now if you go vertical, driller, grout, and your loops with flow center will be ~$6,000ish minimum, what about electric? DIY or electrician? permits?
    Lets say you have $13,000 into this (I'm again assuming a terrific amount of work done by you). Less 30% tax credit you save $3,900 for a new warrantied heat pump. Or you can pay up to $4,000 less to build your own.
    Are warranties and high efficiency worth $100 to you?

    Since you are in fledgling stages of research, start with an accurate heat loss calc.

  8. gte

    gte New Member

    Hi Joe,

    I will definitely defer to your experience over a generic calculator. Do you favor any calculators online, I thought I had used a calculator that the EPA put out, that calculated a "J-[something]" but I cannot find it now.

    I see your point with the well/vs excavator pricing comparison, I think it would cost me about $500 to rent a machine for a few days, maybe $700 for the week so I have time to put the dirt back in the hole.

    To answer your question, no it is not worth it. Is the $13,000 figure a vertical system or horizontal system?

  9. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    13,000 can be anything you want it to be if you do enough of the work yourself.
  10. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    We packed

    5 500' loops in Shawn's back yard in 60 foot lengths. When the pool guys are done I will go hook them up.

    If you rent a track hoe get the biggest you can find. If you do not run one every day double the rental time estimate. I dig way to slow.

    I have my heat loss program on my laptop.

    We use an RV park just inside the beltway when we visit.
  11. teshj

    teshj New Member

    Last edited: May 7, 2013
  12. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

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