Which is better for open loop discharge...recharge well or drywell?

Discussion in 'Solar and Geothermal Water Heating Forum' started by Thumper, Aug 3, 2009.

  1. Thumper

    Thumper New Member

    Messages:
    8
    Situation and a need for quick assistance:

    I'm currenty installing a geo system with a well-water sourced open loop. I have a choice of a recharge (dump) well or a really big french drain/drywell (plenty of land either way). Cost to drill a well is estimated at $5000 for 200'+-. Cost for a 10' x 40' pit, 10' deep with a 4' deep bed of rock, fabric and 6' of soil replaced on top is $1200.

    The area's soil type is pure fine silt (almost no clay), very dry, with a percolation rate of 2.9 min. per inch at 10' down (identical soils from surface to about 150' down). The maximum amount of water to dispose of is about 12,000 gallons per 24 hours when system is operating at max. Groundwater is around 180'.

    The pit can be placed somewhat downhill narrowing the pump head recovery difference between the two disposal methods (recharge well has about 27' at this altitude and the drywell has about 13' (only a 14' difference).

    Will the drain work or is the drilled well the best option?

    Thanks to the forum,

    Thump
    Last edited: Aug 3, 2009
  2. valveman

    valveman Moderator Staff Member

    Messages:
    4,383
    Location:
    Lubbock, Texas
    Water quality is always the big concern when dumping water. If the water has high mineral content or something else, it can clog the perf in the recharge well or the dry well. Cooling or heating the water can cause the minerals to come out of solution and clog the perfs or sand.

    If your water quality is such that it will not clog the dump well, then either type set up will work. The deeper wet well would allow you to install a longer drop pipe and the siphon effect will reduce the head and power used by the supply pump. But a few feet of difference is not going to change much. Also if the well clogs and stops taking water, it would be easier to work on the wet well as the other one would be covered up.
  3. Thumper

    Thumper New Member

    Messages:
    8
    Valveman,

    Thanks for bringing in the maintenance perspective of things. So if either method stops accepting water then a recharge well should be easier to maintain (or replace) than a large drywell pit?

    The water in this area typically has little iron, sulpher, etc., however it does have a good amount of calcium (in Montana). I was under the impression that with heat-only geo that cooling the well water would not increase the precipitation rate of minerals nearly as much as heating it up.

    BTW: Does anyone have any thoughts on the size of the proposed pit? Do they think it is large enough to handle the job long term?

    Thanks,

    T
  4. Waterwelldude

    Waterwelldude Well driller,pump repair. and septic installer

    Messages:
    303
    Location:
    Texas
    Any well or pit you have drilled or dug, If it will not make water it will not take water.

    A "dry well or hole" A well/hole that does not produce water will not take any water.



    Travis
  5. valveman

    valveman Moderator Staff Member

    Messages:
    4,383
    Location:
    Lubbock, Texas
    I would also add, that if the soil won't take water or stops taking water because of mineral build up, then you can't make a big enough hole to get rid of 12,000 gallons per day.
  6. gator37

    gator37 Retired prof. engr.

    Messages:
    108
    Location:
    Alabama
    issues

    In some states open systems are not allowed anymore and some states allow it but the local building authroity (city etc) do not. You might want to check with you local building authority.

    In 3000 systems in (Ft Polk, La) and one system we had installed (HAAF, Ga.) as a test (all closed loop ground coupled systems, deep well type, CLGC) around 1993 we noticed there was what we called "creep" where the ground temperature slowly got warmer from all the heat dissipation over the years. The last time I was associated with it the units were still working fine but at a slightly higher return temperature.

    If you go with a closed loop system pay particular attention to how you grout the pipe loops. Seems like a minor issue but it is a very important in terms of conduction heat transfer of the loop. Also on closed loop systems, air in the lines needs to be addressed when you charge the lines with water (purging).
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