Desuperheater Performance

Discussion in 'Maintenance and Troubleshooting' started by Jamesck, Feb 17, 2012.

  1. Jamesck

    Jamesck Member

    I have a set up with a buffer tank but am not sure I am getting the performance that I should. The output of the desuperheater seems very warm a lot of the time, but the discharge of the buffer tank (feeding the energized tank) never gets warm. Could it be the dip tube is missing on the buffer tank. :confused:
  2. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Are you certain the water pump is running?

    Are you certain the water pump is not vaporlocked?

    Depending on operating conditions, buffer tank capacity, system tonnage and operating stage. a desuper can be expected to reduce refrigerant temperature by as much as 40-50*F but will increase water temperature typically by no more than 5-10 degrees.

    Over several hours, water in the buffer tank will make several passes through desuper, picking up 5-ish degrees each time
  3. Jamesck

    Jamesck Member


    I am pretty sure it is working. The domestic water line going into the geo unit is very cold and the leaving line going to the storage tank gets very hot. What puzzles me is that the discharge line from the un-powered tank to the water heater always feels cold. It never seems to get warm and I am not sure if that is right. Thanks for an advise on this.
  4. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Is there any chance the line from the preheat tank to the finishing tank is connected to the "C" connection instead of the "H"?
  5. Jamesck

    Jamesck Member

    Yes the storage tank feeds the energized tank into the Cold inlet. There is 7-8 degree warmer water, entering the energized tank than what is supplying the house. So it does seem to be working. It has been a warm day here and there has not been much run time. I think I am expecting too much and forgetting that I am heating a 50-gallon tank.
  6. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    There should be a temp difference of 5-10F between the water entering the DSH and the leaving water going from the DSH back to the tank. What you describe sounds like thermal siphoning from the DSH with very low flow, I would suspect the pump not running, or being air locked.
  7. Jamesck

    Jamesck Member

    We had cooler temperatures last night and the 1/2" water line going into the desuperheater is coming in at 71 degrees and leaving at 90 degrees. I am reading these with an infrared thermometer. How could I test for vapor lock? We released the air thru the pop-off on the tanks when filling them before we turned it on.

    Thanks for the feed back on this!
  8. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    infrared thermometers are not very reliable depending on surface. Shiny things (i.e. sheet metal or copper) offer especially poor results.
    try a conventional thermometer taped to entering, leaving DSH and supply to finish tank.
  9. Jamesck

    Jamesck Member

    I turned the tstat up a degree to keep it running and got out the other style of thermometer, this is what it shows. At the geo unit the line going into DSH is at 61 degrees, out at 127 degrees. The water coming from the storage tank to the energized heater is at 66 degrees and the supply feeding the system is at 55 degrees.
  10. jrh

    jrh Member

    It sounds like it might be air locked.

    There should be a valve that can be closed in order to send all the flow through the desup coil.

    If you have that valve, close it.

    Then open up a couple of hot water faucets. Full domestic water flow through the desup. should purge it in a hurry.
  11. Jamesck

    Jamesck Member

    Yes I have several valves and closed the one that would send all water flow into the geo unit. I ran hot water in two locations for while and then opened the valve back. I hope this makes it work better! Thanks for the tip.
  12. mtrentw

    mtrentw Active Member Industry Professional Forum Leader

    Piping Diagram

    If you attach a picture or one line piping diagram to identify where Inlet, Pump, DSH, etc are, you will get much better input and advice.
  13. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Those temperatures may indicate natural rather than forced convection
  14. Jamesck

    Jamesck Member

    Is there anything that I can do to confirm that? I thought about pulling the leads from the pump and then rechecking.
  15. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader


    Send us a photo of the piping.

  16. Jamesck

    Jamesck Member

    I had a problem getting the pictures from my phone, but can we assume that lt is identical to the dual tank set up on pg. 26. I have gone over this more than once and am sure it is installed correctly. Yesterday I found that I had a 55* supply coming into the house, but a 66* leaving the storage tank to the energized tank. From what I have read I am not sure what to expect. Is it unusual to have a 60* rise across the DSH?
    Thanks for your replies.
  17. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    If pipes are bled, then circulator is not running.
    While I think it would get you closer than a 60* Delta T I'll reiterate that an infrared thermometer is not the best tool here.
  18. jrh

    jrh Member

    The newer models of this unit have a dip switch to start the Desuperheater pump.

    It should be in off position to operate the HWG. It is shipped in the on position.
  19. Jamesck

    Jamesck Member

    JRH you pegged the problem, but if it had not been for engineer I would not have been so curious. The dip switch was in the wrong position and the pump was not running. The DSH lines are now much closer in temp and the water leaving he storage tank is getting warmer. Thanks to all for your help!
  20. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader


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