Nova Scotia Desuperheater noise- comes and goes

Discussion in 'Maintenance and Troubleshooting' started by Marsman, Jan 18, 2019.

  1. Marsman

    Marsman New Member

    I have a 6 year old Nordic ground source heat pump. Has been working well. Over past 2 weeks I have heard some screeching noise and now banging noise coming from the desup system. I have it looped through a separate buffer tank before the pre-heated hot water goes into my powered tank. The noise goes away when I turn off the desup pump. If I wait it starts up and there is no more noise. I have audio file with the recorded sound. It is attached to this thread.

    This is the latest- It has been cold and the system has been running a lot. We have not used much HW in the house over the past 2 days. and now the desup system is having a pulsing banging noise every 2 seconds. The water in the buffer tank is 140F. SO this is what I did. I used about 5 gallons of hotwater and the cold well water went into the buffer tank and the noise went away. Now the system has been running for 90 min and still no more noise. Hmmmmmmm Thoughts?
     

    Attached Files:

    Last edited: Jan 18, 2019
  2. Marsman

    Marsman New Member

    Here is the audio recording of the pump prior to me turning it off
     

    Attached Files:

  3. arkie6

    arkie6 Member Forum Leader

    I didn't open any of your audio files.

    140F seems pretty hot for the buffer tank. Does your heat pump use the newer R410A refrigerant?

    If your heat pump is producing 140F output with R410A, your unit is making some pretty high head pressure (>525 psig) and this will reduce unit efficiency and challenge the longevity of the unit. How warm is the air coming out of your vents near the unit? Is there a setting on the unit that allows a lower buffer tank temperature, say 125F? If so, I would consider that setting if you have any concerns with the life of your heat pump compressor. Or maybe the temperature switch on the desuperheater isn't working properly?

    How is your geo unit and buffer tank plumbed? Can you get a picture of the water lines going from the geo unit to the buffer thank?

    What about an air bladder tank on the inlet line to the buffer tank? If no air pressure bladder tank is installed and there is a check valve or pressure regulator upstream, those 140F water temperatures could be causing the Pressure Temperature (P/T) valve on the tank to intermittently lift to relieve the high pressure created in the tank. Have you checked the P/T valve tailpipe to see if any water is coming out or if the line is warm/hot indicating it is relieving pressure/hot water?
     
  4. Eric Kurtz

    Eric Kurtz Member

    Could it be the water boiling in the de super heater?
     
  5. Eric Kurtz

    Eric Kurtz Member

    I would say it sounds a bit like a compressor rattle. And I confirm, what arkie just said. 140* is way too high. Which means your head pressure is probably beyond max design pressures.
     
  6. arkie6

    arkie6 Member Forum Leader

    I'm still having a hard time wrapping my head around the fact that you have 140F water in your buffer tank. Do you have the heating elements to this tank wired up as a backup? If so, did the circuit breaker inadvertently get closed and now the heating elements are powered on?
     
  7. Marsman

    Marsman New Member

     
  8. Marsman

    Marsman New Member

    No- it is a "dummy" tank ahead of the wired one. The system has been running for almost 3 day and we have not used much hot water. Once I used about 10 gallons the sound/noise went away
     
  9. Marsman

    Marsman New Member

    The sounds disappears 100% when I turn off the DSH pump. I just confirmed with Maritime GeoThermal their Nordics are set to 140F
     
  10. Marsman

    Marsman New Member

    I actually wondered that. Is that even possible? The sound did go away when I used about 10 gallons of my HW and cold water came in to the buffer. Has been running for 3 hours and the sound has not repeated itself. I know where there is a 5 year old Geo Unit (used) . I may cannibalize a pump and see if the problem comes back. I wonder if I need to check the hi temp cutoff switch or sensor
     
  11. arkie6

    arkie6 Member Forum Leader

    Maybe pump cavitation? At those higher temperatures but still well below boiling, the low pressure at the suction side of the pump impeller could be causing steam bubbles to form and then they collapse as they cross into the higher pressure region of the pump. Those collapsing steam bubbles can make a lot of noise. They also erode the pump impeller. What is your water pressure? This cavitation would be more likely to occur with low pressure. What about the pump suction source? Is there a valve on the pump suction between the geo unit and the buffer tank that is partially closed? That would restrict flow and possible cause cavitation at the pump suction. Where does your pump take a suction? Top of the water tank in the inlet line or at the bottom of the tank at the drain valve? If at the top of the tank, did you remove the check valve in the inlet dip tube? If at the bottom of the tank, is it possible sediment has partially blocked the line?

    Edit: I see from your reply above that your desuperheater pump takes a suction from the bottom of the tank. Do you have any kind of filter screen or Y-strainer on that line to keep sediment out of the pump suction? If so, when was the last time it was cleaned? When was the last time you drained the tank to flush the sediment out?
     
    Last edited: Jan 18, 2019
  12. Marsman

    Marsman New Member

    Yes I do take it from the bottom and I cleaned the tank a few weeks ago when this started. It is possible there could be more in there and I will fully drain and then pulse water to flush it. This morning the sound started up again. I put my hand on the pump and I could feel the sound in the pump. I just took the pump off and looked around the body for crap etc. just a bit of biofilm. I pulled ouut the magnetic vane and looked at it for a piece of contaminant. Seemed good. I put it all back and everything is working fine again. The temp is about 101 F right now and climibing. It was 125F when the sound started. A great project to work on in the dead of winter :) I appreciate all the suggestions and advice.....
     

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