Open Loop Blocked Discharge Line

Discussion in 'Open Loop' started by CommanderDave, Dec 29, 2020.

  1. CommanderDave

    CommanderDave New Member

    I have a Bosch SM036 water geothermal HVAC system. The configuration is open loop with incoming well water that discharges downhill into a pond. This past week the weather was very windy and sub-zero and the discharge line apparently froze. The back pressure in the line caused a compression fitting in the discharge line located above the basement ceiling to fail and the unit kept running and flooded my basement. My question is does the unit have an automatic feature that will shut it down when it reaches a certain threshold of back pressure in the discharge line? If so, could it be that the compression fitting blew out before the unit reached that threshold? I will direct my HVAC guy to run a new line that has no compression fittings at all in the ceiling, but I'm concerned that it could happen again.
  2. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Hi and welcome!
    The unit itself does not have a failsafe AFAIK. Your water pump could be retrofitted to have one, or at a minimum the unit could have a water pan shut off installed that would shut the solenoid in the future.
    Just curious, was it a " shark bite " fitting ?
    A local library had a million dollar loss due to a bad fitting and no safe gaurds.
  3. CommanderDave

    CommanderDave New Member

    Thanks for the response. It was a 1" PVC coupling/compression fitting rated for 150psi, which we thought was more than enough for the non-pressurized discharge line. If I understand correctly, the geo unit has no auto shutdown for over-pressurization, so if the discharge line gets blocked the unit will continue to run and build up pressure. If the water lines/fittings hold then the pressure will continue to build inside the unit until it explodes?
  4. bpsmicro

    bpsmicro New Member

    I'd have thought that the max pressure you'd get is the cut-off pressure for your water pump (typically around 60 PSI), then your well pump would just shut off (same as if all taps were off). Then I'd expect the furnace to notice a lack of water flow and then switch to Aux heat (or just shut down).
    But then I'd expect your entire discharge line to remain pressurized at that 60'ish PSI for some period of time, and eventually find your weak point (in this case, the compression fitting). Once that happens, the pressure drops, your well pump kicks on again, and the furnace restarts and dutifully does it's thing, not particularly caring *where* all the discharge flow is going.
    You need something like this:
    (that's my Canadian supplier for stuff like this, but you'll find alternatives easily enough). They notice water where it's not supposed to be and shut a valve just after your well's pressure switch. You can get additional sensors if required. This is a good backup for any potential rupture-related problem, not just specific to geothermal.

  5. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Yes. The problem is when the discharge gets blocked, the unit and all fittings in front of the blockage see full pump pressure from the supply side.
  6. Valveman

    Valveman New Member

    Anything with pressure doesn't need to be using a compression coupling unless it is thrust blocked or chained down. Without something holding it, the pipe will just squirt out of a compression coupling with very little pressure.

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