sizing loop fields to building load?

Discussion in 'Vertical and Horizontal Loops' started by TowPro, May 28, 2013.

  1. TowPro

    TowPro Member

    I understand that you size the whole system (Loop and HP) for your requirements.

    But what if you have 24K BTU heating requirements (2 ton) and a loop field designed for that load, only you find a deal on a 3 Ton system?
    The 3 ton unit has the potential to move more BTU, but you still only have 2 ton BTU load, thus the bigger heater will still require the same load of the loop field (since all your really doing is moving BTU and the heat sink is the earth).

    I figure since the loop is undersized for a 3 ton HP, it would draw down the EWT faster, but it will run less thus the EWT catches up between cycles?

    I know the side affects are poor humidity removal when summer loads are just starting, and more cycles = shorter life span, but just was wondering.

    No, I am not planning on doing this, but just had the question.
     
    Last edited: May 28, 2013
  2. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader


    You are pretty much right
     
  3. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Lets go outside of the box, and this time the box is duct work. If we use water to move the heat on both sides of the heat pump we gain some advantages.

    The first advantage that comes to mind is the reduced number of cubic feet of the building dedicated to moving the BTUs. Size does not matter as far as building load, we always use less volume of space to move the heat. In either direction. With controls like the Tekmar 406 house control, (They gave me a free hat at the class) we are able to monitor the dew point and instruct the heat pump to keep the chilled water temperature above it. It will work with radiant floors, chilled beams, radiant panels and low temperature panel radiators. So their goes the sensible heat out of the building.

    We still need to remove the latent heat and water out of the space, so we need some box, (duct work) to get that done, however since we need to jump back into the duct work box to get that done, our requirements for duct work are greatly reduced. Saving cubic feet of space, materials, and installation labor. I use high velocity systems to do that job. I can train a person with a cordless drill motor and a tape measure to install the stuff in under one working day.

    Towpro, lets go back to back to your math question. Water to water geo-units do not care about load. I think they do care about loop fields. All the BS on all the threads about all the loop fields are a SWAG on what works. We have very hard data on what does not work. Design and installation of a loop field to building load is almost impossible until the digger is on the track hoe or driller is bringing up mud. A good designer/contractor will make changes in the field, to accommodate the thermal dynamic transfer available. I do not know of anyone not installing what they spec'ed, the tough pitch is adding more.

    So my guess is we all over size slightly if we know what we are doing and this job is not our first Rodeo.

    Water to water equipment, delivery systems and control could make your theory work. I would install what I thought was a 3 ton loop, but is could work with a "two-ton loop" by using a buffering tank.

    Mark
     
    Last edited: May 28, 2013

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