Horizontal closed loop depth obsolete after 33 years?

Discussion in 'Vertical and Horizontal Loops' started by FredH, Aug 31, 2018.

  1. FredH

    FredH New Member

    I am a homeowner, not an expert. In 1985 when my south-central Pennsylvania house was newly-built, a 4.5 ton CanTherm unit was installed and connected to a 1,500-foot closed loop buried 3-feet in limestone soil, which I suppose was cutting edge at the time. In 2005, a 4.5 ton FloridaHeatPump replacement unit was connected to the same loop.

    The house is efficient for natural cooling from breezes, so the heat pump isn't turned on unless it's hitting 83F outside. keep the thermostat set at 78F. This year, there are more days hitting 90F and up, and the heat pump was blowing air only slightly cooler than room temperature. Fluid was coming in from the loop at 80-85F.

    After these 33 years, I've never had a problem with either of the two heat pumps keeping pace with cooling. The installer of both units is well-experienced in residential, commercial and government geothermal installations across the mid-Atlantic states. After two visits in July and August, the FloridaHeatPump checked out okay and the conclusion is my loop is too shallow at 3-feet, and will have to be abandoned and replaced with a new loop. I was informed that horizontal closed loops are now placed 5-6 feet underground, or I could opt for a vertical closed loop with approximately 4.5 x 150 feet of well depth.

    I'm finding it hard to accept that a loop with 33 years of proper function at its 3-foot depth is now failing with these 90-degree days. Is it possible that the glycol solution in the loop could be at fault, like automotive anti-freeze that needs to be replaced? Has global warming pushed its impact down past the 3-foot depth?
  2. arkie6

    arkie6 Active Member Forum Leader

    There is nothing wrong with 80-85F entering water temperature from your loop in summer. That is quite common down here in the south. You need to have a heat rejection calculation done to determine the cause of your units poor performance. This measures the heat rejected to the loop (requires entering and exiting water temperature and loop flow which can often be determined by the pressure drop across your unit heat exchanger coil) and compares it to the heat removed by the refrigerant coil (supply and return air temperature and air flow rate across the coil) and compare this to the units rating at various water temperatures.

    We're not seeing any adverse effects of global warming or climate change in my area. If anything, the summers are cooler now than in the 1980's. I'm not sure about average summer temperatures in your area, but the last two summers in my area (Arkansas) have had lower peak temperatures than the past 28 years that I have lived in this area. We used to see multiple days top 100F here in the summer and the past two summers have not had a single 100F day. I went back and looked up some weather history for our area. In August 1985, we had three days top 100F with 8/31/1985 reaching 102F. Today, 8/31/2018, it is 87F with a forecast high of 89F and as I stated previously, no days at all this summer or last summer above 100F. In August 2017, we only had 1 day top 95F.

    2012 was a hot summer here. We had 40+ days top 100F with a high of 109F.
    Last edited: Aug 31, 2018
    FredH likes this.
  3. FredH

    FredH New Member


    Thank you for your recommendation.
    Just to be sure I am clear, the glycol exiting my heat pump and heading to my ground loop is in the mid-90s F. The glycol on return from the loop is 80-85F, and I was told it should be about 65F this time of the year.
  4. arkie6

    arkie6 Active Member Forum Leader

    Yes, that is fine. You will lose a little bit of efficiency and capacity at 85F entering water temperature vs. 65F entering water temperature in cooling mode, but it still should be able to drop your air supply temperature ~20F from the return air temperature unless our unit is undersized for cooling or there is something else robbing efficiency. You being up north, I would assume your unit is sized more for the heating load and it should have excess cooling capacity.

    Our deep earth temperature here is in the mid 60's to start with. Mid 80F or higher entering water temperature is normal here and units continue to function normally.

    Did the unit work fine 5 years ago? If so, what changed? Not the loop depth. The soil temperature likely didn't change more than a degree or two.

    Is it extremely dry in the area of your loop field? Lack of moisture can adversely affect loop-to-soil heat transfer. If you are in a drought, you might consider watering the area where the loop is located.

    Where is your supply and return air duct located? Is any of it in the attic? Have you inspected it recently to verify no missing insulation, holes, or disconnected pipes?

    If you have any remote air return ducts, what is the return air temperature right at the inlet to the air coil? Is it warmer than room temperature? If so, that could indicate a break or leak that is pulling in unconditioned air into the return.
    FredH likes this.
  5. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Your BS meter should be blinking.

    While your overall capacity might be affected by slightly higher EWT (water temps coming back from the loop field), units are rated at 78F, and yours running at 83-85F does not affect performance much. There is something wrong with your units(s), first thing to check is the amount of heat it rejects into the water. Should be an easy task for a technician. Takes a couple minutes.
    FredH likes this.
  6. FredH

    FredH New Member

    Thank you, docjenser and arkie6. I am asking my technician to do a heat rejection calculation to determine the amount of heat the unit rejects into the water (in my case, into the closed loop's coolant, a glycol solution).

    My unit is a little oversized to accommodate a house addition that was never built.

    Ground moisture is way up this summer, with record-breaking rain, most of which soaks into the soil of my limestone field that contains my horizontal loop.

    Ground temperature was interesting to find out about. The National Weather Service and the USDA maintain soil temperature gauges in some locations around the USA (especially the north central states), most reading 2 and 4 inches deep for farmers, but a few have sensors at 20 and 40 inches deep reporting daily over the internet. The closest one is run by the USDA, about 40 miles away, and indicates 79F at 20 inches and 76F at 40 inches, the latter about the depth of my loop.
  7. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Do not have your loop abandon. Have your units checked out.

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