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  1. #1
    Join Date
    Sep 2012
    northern Ohio

    out of my "comfort zone"

    recently a long time customer of mine purchased a farm house that has a FHP geothermal HVAC system for the main house. It seems this system was installed about 8 years ago and was maintained by the owner. there are records of filter changes and humidifier repairs near the heat pump. one thing i noted was that at least once the "underground loop was flushed out" and that "glycol" was added (unknown amount) twice. It looks like they used PEC pipe underground but i am not sure of that. I did my first check-up of the system today and the system seems to be functioning OK. I have experience with water source heat pumps but this is my first with an underground loop. my temp. drop on the low side was 6/8deg. with a 44deg. water inlet temp. and 89# suction pressure (r-410a). I have been unable to get an answer as to what the static pressure in the undergroung glycol loop should be. the air handler is in the basement and my loop pressure is at 12# , there is also a nearly full gallon of glycol at site. This thing seams OK but I feel like a dentist doing eye surgery, i realy like these people and consider them freinds as well as good customers. I call for a "profressional, experienced, honest" second opinion. thanks in advance.

  2. #2
    Join Date
    Dec 2008
    South Jordan Utah
    10 to 40 PSI will work on the ground loop.
    Dewayne Dean

    See my live system data here:

    We Heat and Cool with Dirt

  3. #3
    Join Date
    Mar 2007
    Cedar Rapids, Iowa
    Leave your gauge set in the truck. Always do a Heat of Extraction/Rejection first. If those numbers indicate a problem then, and only then, hook up the gauge set.


  4. #4
    Join Date
    Apr 2012
    Georgetown Delaware
    Nothing to fear when loooking at the loop. As said the diagnosis should go to the gas last. The pressure in the loop will vary with operation, so really there is no set pressure for the loop. The single most important thing is the differential betweeen ewp and lwp. With the chart from the manufacturer that differential will give you the gpm flow through the coil. As long as the pressure differential is adequate for the given gpm, it really does not matter what pressures you are seeing in the loop.
    Eric Sackett
    Delta P= 8 ATA

  5. #5
    Join Date
    Feb 2009
    Portland OR
    If you do not know the equipment you should probably call in somebody that does, hooking up gauges is usually a no-no on a geo system unless tech support tells you too. As others said heat of rejection, and GPM calculations are good. You should also get a hydrometer and check the glycol content to see where your freeze protection is and the % of glycol will change some numbers. Typically a 20% glycol/methanol with 80% water will give a freeze protection to 15F.
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