Number of wells

Discussion in 'Geothermal Loops' started by jmeitz, Dec 9, 2010.

  1. jmeitz

    jmeitz New Member

    Going to have a geo system put in and had one installer tell me that i needed 750ft of well for a 4 ton system vs. the 600 the others have been telling me. His reason was in his heat calcs that my water temp would be 89 degrees with a 5 ton design vs. 98 with a 4 ton design in the summer and that if it was hot out(over 100) my unit would shut off and i would not have any air conditioning until the outside temps dropped. is this true? the unit was a geo comfort gxt048.
     
  2. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    It is true that cooling efficiency and capacity fall dramatically with rising loop temperatures. Design EWT for cooling should be less than 90.

    In general loops should provide for an EWT +/- 20 or so above or below deep undisturbed ground temperature. That is, if St Louis has a deep ground temp of 60 (I'm not near my map of this, so just guessing) then winter EWT ought to be able to be 35-40 and summer EWT 80-85 under design load conditions. During record cold snaps / heat waves, some excursion from these values will occur and is OK, to a point.
     
  3. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    I would add the question,
    How deep are the proposed boreholes?
    You have a 4 ton machine.
    Different areas use different bore depths to achieve differant results. The point being you can not buy a 1/2 of a bore. We drill 200' for every ton, meaning for a 4 ton unit we would drill 4 200' bores, 800' total.
    If your area uses 150' per ton you would need 600' of bore. I would bet the guy proposing 750' of bore is telling you the truth about anticipated operating temps he is familiar with and thus adding footage to cover a larger design temp swing.
    hope this helps
    Eric
     
  4. jmeitz

    jmeitz New Member

    my issue is all the other 5 drillers are using 600 ft, 4 bores 150 ft. the one suggestion 750 is using one of the driller of the 5 that own both the boring machines and geo systems. They all say 5 would be better but not cost efficient. Also, i am having it bored underground to my house approx 75ft ontop of the 600ft. they guy who is telling me 750 ft is also 12000 more than the other 5 who have done over 300 installs each.
     
  5. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    The question of footage and who you beleive is a choice. It allways goes back to the quality of the installer and their design. You must choose the one you trust. In regard to the drilling, the gshx is a part of the design for your whole project. Your perspective installers can provide you with projections for what the operating conditions for their design entails, including: balance point,loop temp,effecincy,operating cost per year. With that data in hand you will be able to compare te proposals and "see" any or no benefit of cost vs. performance.
    Eric
     
  6. Reiner

    Reiner New Member

    No doubt that 750 ft of bore will produce better results than 600' of bore. Your auxiliary heat will probably be called into action a little less often. Is it worth spending an extra $12,000 for (not sure if the $12,000 was only for the additional bore)? I would have my doubts. Ask the potential installers what their designs will produce as Eric suggests and do the math ( or have them do it for you).


    Just about any system can be made more efficient, but there comes a point where the cost to get that efficiency is not cost effective. Spending a dollar to save a dime is only valuable to a very small part of our population.
     
  7. jmeitz

    jmeitz New Member

    the additional bore was 1650, sorry for the confusion. My point was the guy pointing out the 5th well was 12k more that the others who had more experience. If i qualify for the MO state 10k rebate i am going to get the extra well cause it will be really 800 bucks or so for the extra well since i am under the 20k threshold. thanks for all your guys responses, it has really helped.
     
  8. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    I didn't quite follow the economics of that choice, but it is gratifying that a newbie in the field wants to err on the side of caution.
     

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