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  1. #1
    Join Date
    Jun 2008
    Posts
    47

    SE Pa: Sanity check on GSHP Vertical Loop Length

    Folks,

    Would anyone be able to share with me some information related to vertical loop lengths for Ground source in Pa (We are near Quakertown).

    Our GSHP vendor seems to be a little generic in terms of suggestion and has put us in a situation where we need to get our own drilling company and work in-between the teams to get our system installed. We are putting in one 5-ton and two 2.5 ton ClimateMaster units. Our GSHP vendor seems to have gone with 150ft/ton, and we are just wanting to be absolutely sure that this is correct for our area, with the goal that these things run all winter with as little emergency oil used as possible (we have existing hydro-coil backup).

    1. I think in a previous thread 150/ton was the ballpark number for each loop. there will be three separate loops. For Pa, is that OK?

    2. Is there merit to increasing the loop length or number of bores some percent / length that would hedge our bet (or assure that we don't end up with too little heat exchange capacity in the winter?

    3. How would depth figure into this calculation? Would deep(er) bore holes with less length be better or worse than more holes and less length?

    4. The tough one> Does anyone in this geographic region have representative sample numbers (temperatures) for Entering/Leaving water on: (5-ton, 2.5 ton units) that they can compare to their loop length/bore hole size for me?

    Any data? or thoughts? links to other threads anywhere?

    thanks

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,808
    Can't help you on the well depths.

    But, if your responsible for them. Then if the geos ever have troubles. Your HVAC "vender" can always fault the wells, and it becomes your liability.

    Use a HVAC contractor, and then its his responsibility.
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  3. #3
    Join Date
    Aug 2006
    Location
    Dallas (Plano), TX
    Posts
    168
    There are commercially available software programs that are used to design the water portion of a GSHP system. Many HVAC contractors that specialize in GSHP system installation become well skilled at using one (including purchasing it), or, they outsource the water design to someone who is.

    The design is dependent on many factors local to your conditions and/or equipment proposal - heating/cooling load for your residence (i.e., Man. J), amount of heat to be rejected to / absorbed from the ground, type/size of pipe to be used, volume/speed of water flow, ambient air conditions, type of soil, amount of rainfall, soil temperature conditions, type of thermal conductor to surround the pipe, etc.

    For example, for my vertical loop design and 8 tons of capacity, some of the many design factors were: pipe is HDPE, soil is a loam clay, high avg temp for the year is 89F, avg earth temp is 68, swing from high to low earth temp is 21, coldest earth temp occurs on the 34th day of year on avg (1st week of Feb.), hottest earth temp occurs on 216th day (1st week of July), 'normal' grout, etc.

    The end result of the design was 8 vertical wells each at 300' deep, with 1" pipe, with 21 gpm flowing for the 5 ton unit, 14 gpm flowing for the 3 ton unit, and some number greater than 21 when both units are running.

    And here's a chart showing the end result from an entering water temperature perspective, for my resulting water loop design (feeding in my case WaterFurnace units):




    I would think it would be pretty tough to just use a 150ft/ton rule of thumb for your area and simultaneously be confident you've got a well performing water loop design.

    There is performance benefit to having more wells, deeper wells, longer loop lengths etc., than that from which a good design would call for. But, that's an awfully expensive alternative to getting it right in the first place with a good HVAC contractor that understands GSHP systems. You're already going to pay a lot of money for a GSHP system that has the right capacity.

    Best regards,

    Bill

  4. #4
    Join Date
    Apr 2005
    Location
    NE PA
    Posts
    698
    For your area 150'/ton is a good estimate. It will vary somewhat as afunction of soil/rock. A wet hole (water) helps a lot.

    Going deeper can improve efficiency, but it is not a big increase.

    There are a number of well drillers in the area that are certified for geo drilling. You could contract them directly, or let the installer/contractor find out for you.

    paul

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