Iowa Discharge Line Hammering

Discussion in 'Maintenance and Troubleshooting' started by CommanderDave, Nov 20, 2019.

  1. CommanderDave

    CommanderDave New Member

    I recently had an HVAC company install a new Open Loop (Pump and Dump) Geothermal heat pump. It is a Bosch SM036, 2 stage, 3 ton unit. The system is serviced by a single deep well and discharges into a pond, the well services the geo and nothing else. Also, there is no pressure tank in the configuration. Unfortunately the installer did not follow the installation procedures recommended by the manufacturer.

    A day after installation I began to hear a hammer and the sound of rushing water that lasted about a minute immediately after the unit calls for water. I originally thought it was a problem with the inlet line but isolated it to the discharge line. After thoroughly researching the problem and studying the manufacturer's installation manual myself, I've found that the installer did not configure the inlet and discharge lines correctly (see attached photos). Also, for some reason he did not install a flow control valve that came with the unit and instead installed a ball valve where (he thought) the flow valve should be on the inlet line.

    I am going to correct these mistakes myself, with the help of my well driller who has extensive experience in geo systems and appears much more knowledgeable about their installation, especially when it comes to water flow issues. In the photos you will see two valves on the inlet line: a valve that has an internal filter screen with an adjustable knob for psi, and a ball valve. We want to remove the psi valve and replace it with a spin down visual (sand) filter. I have attached a proposed configuration schematic that I came across that looks correct (again no pressure tank). I have the following questions:

    - The hammering appears to be coming from too much water pressure/flow to the discharge line when the unit turns on and calls for water. The manufacturer requires a slow closing solenoid valve be installed in the discharge line and wired to the control panel. However, don't I need a slow opening valve instead...or does the one valve do both? Also, it's my understanding that on a 3 ton 2-stage system one solenoid valve should suffice. I have seen the valves made by Taco, but there are reports of them failing after a few years.

    - I see on the drawing that the flow regulator is downstream of the solenoid this correct, or can/should it be placed upstream of it? We have the option of installing the adjustable flow regulator that came with the unit (shown in the photo), or installing a standard 10psi constant flow regulator valve.
    (my unit requires 6gpm @ 20 psi minimum).

    Any suggestions recommendations on changes or additions to the configuration are appreciated. GeoConfig.jpg Picture1.jpg Picture2.jpg
  2. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Hi and welcome!
    Hopefully your driller can get you sorted out, your hvac contractor did not.
    1. open loops need to be valved on the outgoing side of the unit. This keeps the unit full of water, not air that can precipitate minerals and corrosion.
    2. how you regulate the flow is dealers choice. I prefer valves over flow orifices, both work.
    3. unless your driller deems it needed, I would not filter water going into the unit, it may plug and freeze the coil.
    4. I hate pex pipe.
    5. the need for unit adapters and pt ports on an open loop are over stated
    6. rubber hose on a open loop is bullshit
    7. open loops need flow not pressure. I advocate low pressure pumps or a pressure reducing valve prior to the unit to lessen noise and water hammer.

    hope this helps
  3. CommanderDave

    CommanderDave New Member

    Thanks for the reply and helpful info. Well water here tends to be rather sandy, in fact just as you mentioned that psi control valve did plug up once, so we want to replace with a filter that can be viewed and drained.
    Couple questions....should the flow control valve be installed before or after the solenoid valve on the discharge line? What type/model of pressure reducing valve would you recommend installed on the inlet line?
  4. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    No worries, glad to help.
    Flow control valve goes after solenoid valve on discharge line. This takes into account any flow restriction the valve may or may not provide.

    Bell and Gosset have been the gold standard for boiler control/ ie pressure reduction valves since the late 1800's. Most are adjustable in regard to pressure setting and have a remove able screen for cleaning out debris.

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