Horizontal loop in hot / humid environment

Discussion in 'Vertical and Horizontal Loops' started by Steven, Jul 28, 2017.

  1. Steven

    Steven New Member

    I have been helping people do solar on the cheap for years. I originally planned to just do conventional cooling (Texas 95% of the time I need A/C) and using solar power as I can create it cheap.

    I am however going to have to have equipment here to dig in my septic, so I could dig some other trenches for GEO at the same time, and wanted to take a look at it. I saw a 5Ton system on ingrams for 8k and it got me thinking.

    In the country, no permits needed, nothing underground to hit utilities etc, power on poles, water on edge
    Black Dirt Clay class 4 soil for at least 5 ft. everywhere around 6ft I hit caliche
    My house will need (I am framing it by hand now ugggh) two A/C's with a conventional system.
    4k sq ft, 1800 bonus area up.

    So the questions:
    Is there a field loop length recommendation calculator / or formula ?
    Is there anything one should do different in a GEO system that is almost exclusively for cooling ?
    I am guessing not, as 50 deg cool, what more can you ask for.
    Slinky versus large closed loop what would you recommend ?
    For a large house, I was thinking multiple loops joined together, and maybe two units connected to the same distribution ?
    I have 10 acres, so I could do slinky, I could probably even easier make some very long runs with a trencher. But could do either.

    Sorry for all the questions, I am more than happy to share solar knowledge if you need it, I am just a newbie in GEO
  2. Steven

    Steven New Member

    Forgot to mention, I am on 10 acres, lots of room to play
  3. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Hi and welcome!
    Everything in geo starts with a load calculation for your home. Swagging it is not recommended. After you have a load calc for your cooling dominated home expressed in tons of load, there is some nifty low cost share ware and other trial offerings to design your loops. As to the race track slinky war? Its your dirt and time, do what feels right to you. hope this helps.
  4. arkie6

    arkie6 Active Member Forum Leader

    What did you mean by the above statement? If you mean't ground temperature, you are a bit off the mark for Texas. Deep ground temperature in most parts of Texas (where exactly in Texas are you?) will be approaching or exceeding 70 deg. F. And with a cooling dominated climate plus most likely dry clayey soil, you will likely need double the amount of pipe in the ground as more northerly installations to keep your loops from overheating in the summer.
  5. Steven

    Steven New Member

    Thanks for the reply, just north of Austin. And yes nothing but clay. From Jan to April the clay is extremely wet. from Jun-Aug it can be quite dry near the surface, still damp lower down. I haven't lived here long, so not sure if historically it is the same. As you state, cooling is about all we care about, very little heat used around here. And your correct I was way off on the ground temp
  6. Steven

    Steven New Member

    I understand. The problem I am having is getting any idea. My so called professional A/C bids have been all over, and seem to have no science behind them. The guy here yesterday wanted to put in two 5 ton units. That seemed excessive, as I have 4000 sq on ground level (ranch style) open floor plan, and there are 3 rooms that are 1000sq ft that are usually closed off and rarely used. The bonus area upstairs is around 1700 sq ft, It will be used occasionally, say 4 days a month. So 5700 sq ft worst case.

    The other thing that made it seem excessive to me is the fact that this is a closed cell spray foam insulation envelope. I know we will need some serious air, I am thinking 6 tons would do it, but 10 tons seems excessive in my opinion.
  7. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Your guess is a slippery slope. To plan on 1 ton to cover 1,000 square feet of house does not pass the sniff test anywhere. Contractors do not care what you tell them about usages in rooms. They can not take your word for it cause their reputation is at stake. What if your usages change? Then what? Without a true load calc, we are all guessing.
  8. Steven

    Steven New Member

    I agree that a contractor not only can't take my word on useage, but have to think towards the future if the house was sold etc. HOWEVER,

    A quick google of tons per sq ft, spray foam will yield results such as
    A typical house gets about 500 square feet of living space per ton of AC equipment. When you use foam insulation, you can get between 900 and 1,400 square feet per ton of AC equipment.

    There are countless articles, studies, etc. Texas A&M being the local unbiased source that I believe the most. 1,000 per ton is considered conservative in a spray foamed house.
    Note, that is even with open cell, closed cell (what I am using) is even better on the envelope.

    10 tons, in 5700 sq feet, would not only be overkill, but in high humidity would be irresponsible in my opinion, it will never run long enough to get out any of the humidity. That is not counting zoning or any other efficiencies. Just my opinion ofcourse
  9. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Well, make you loop big enough, then it will work. Sure you can out 5 tons in your house, but if you do the rues of thumb design, you might have to live with the fact that you might get a bit warmer on the hottest days of the year. Not a problem to see how far 1000 qf/ton would get you. But remember, you cannot complain to anyone but yourself if it is not good.

    Horizontal loop in Texas? make sure you make it at least twice as big....
  10. Steven

    Steven New Member

    Thank you so much for the reply. I have talked to several people about sizing the system, and they are all over the place. The closest I can get to a consensus is 8Tons. I have the advantage that my house does allow for a lot of flexibility after the fact, so I thought I would put in a 6 Ton System, see where I am at, and then size the remaining accordingly.

    You made a comment that texas loops need to be twice as big. Interesting. Logically that makes perfect sense, as it is quite warm here. So my question is how to hit that right balance. If I undersize my loops then I can over heat them. Loops that are too big, to my understanding require more pump than needed etc, so then your system uses more power, losing some of the advantage. I really appreciate the advice, as I am very novice to geo thermal.

    I did talk to a local Geothermal place, but aside from sizing me at 8 Ton, they only did vertical systems, so talking 20k in drilling cost before a system is even started.
  11. arkie6

    arkie6 Active Member Forum Leader

    I'm in Arkansas. I had a geothermal well driller out of Oklahoma drill my geo wells a couple years ago at $7/ft. I bought the loop pipes myself at that price, but it was ~$165 per well for 3/4" x 510' U-bend loops. We installed one 220' deep well per ton of HVAC. I had three wells total. I have ~2.5 tons of peak load with a 3 ton 2 stage unit. Typical geothermal well depth in my area is 200' per ton. I went 10% over that for additional margin. In your area, I would estimate needed geothermal well depth of 250'to 300' per ton. If you go over 250'deep, I would increase loop pipe size from 3/4" to 1" to reduce pumping losses. If your load is 6 tons, that is approximately 6 wells x 250' x $7/ft = $10,500 for well drilling, pipe installation, and grouting + 6 x $165 for pipe = ~$11,000. I'm not sure if that driller in OK would travel that far, but it might be worth a call. If interested in his name and number, send me a PM and I will provide the info.
  12. Horizontal loops work well even here, although a lot of installers refuse to do them. Part of the trick to to parallel as many loops as possible to keep pipe friction lower, and yes, total 850-1100' of pipe per ton depending on soil. I typically dig 5-6', lay two pipes, backfill to 3' and lay two more. Slinky loops tend to build up more ground heat than horizontal pipe.

    The loop should be sized to the load of the home, not the unit size. And all the manufactures offer good loop design software, but it takes a little experience to use it correctly.

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