Desuperheater Performance

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

  1. Jamesck

    Jamesck Member

    Things have improved and I now have warm water entering my energized tank. The temp rise across the DSH does not appear to be normal and I think it might be because the unit sits directly beside of the hot water tanks. My question is if I should throttle down the flow going to DSH or just let it run wide open. I have a valve coming from the storage tank and could restrict flow to DSH to increase temp rise. I just wondered if it really matters as long as it keeps increasing the storage temps?

    While the unit is running I am only getting about 2* rise across DSH and that is with a stick them on input and a meter on the output. I calibrated them before the test was made for accuracy.

    Thanks for your input!
     
  2. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    The lower the temp rise, the more heat is transferred.

    The only disadvantage to overpumping the DSH may be too high flow operating to de-stratify the preheat tank
     
  3. Jamesck

    Jamesck Member

    I have a ball valve in line that is feeding DSH. Would you throttle it back if it was yours in order to prevent this?
     
  4. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Maybe, but probably not. I don't think the itty bitty DSH pump flows enough to break up the thermocline in a typical unfired storage electric water heater acting as a preheat tank (you have one, right?)

    If I absolutely, positively couldn't resist the urge to scratch the itch, I'd get some data first: I'd install digital thermometers on the inner tank wall at the upper and lower element ports on my preheat storage tank (you have one of those, yes?)

    I'd keep an eye on those thermometers, particularly after moderate hot water draws, such as a single shower, load of wash or dishes and look for lower temp to markedly fall while upper temp is maintained. As long as that holds true, no need to fool with it...
     
  5. Jamesck

    Jamesck Member

    Yes I have a preheat storage tank, but I agree on leaving it the way it is for now. Thanks for giving the feedback
    !
     
  6. Jamesck

    Jamesck Member

    I have noticed that I am not getting any hot water now that I am getting into cooling mode. Is there anything that could have changed or could a sensor have moved? I am not sure I understand how this unit generates heat for the DSH. I would have thought it would have been easier, when you were rejecting heat from the system in air conditioning.
     
  7. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    heat is a product of a refrigeration system that is running. if you are saying you don't have as much heat in the buffer tank it is likely because unit isn't running a lot.

    we do not throttle down our circulators.....besides the suggestion by manufacturers that you don;t have to have a buffer tank, the rationale side of me says reducing flow to improve performance is silly in this context (more GPM with less DeltaT ~= less GPM with more DeltaT) further the inspector in me cringes every time I see their diagrams with isolation valves on both sides of a source of heat (aka closed vessel).....
     
  8. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    A geo operating in a heating dominated climate won't make much warm water early in the cooling season, especially a two stage unit staying in low stage during mild weather.

    Compressor discharge refrigerant temperature is relatively low and cycle times are short so that preheat tank may only show a 5-10 degree temperature rise
     
  9. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Source water is too cold, the is not enough desuperheat. Electronics do not allow the DSH pump to turn on under those conditions. This is for cooling mode, not an issue in heating mode.
     
  10. Jamesck

    Jamesck Member

    The pop off valve on the storage tank developed a drip, and I finally decided to replace it. In the process I decided to also change the ball valve at the bottom of the tank. It had also developed a minor leak over the years too. Both of the water heaters are 50 gallon Whirlpool and I am trying to plan on their replacements before they finally go. I would like to upgrade to a Marathon style water heater and some sort of similar storage tank when the time comes. Do they sell just a storage tank, or do you have to buy two water heaters?
     
  11. James F

    James F New Member

    I came across the thread and found it helpful since I have been asking the same questions as you initially posed about inlet/outlet temps. First, my take on your tank replacement questions: I view the Marathon brand tank as best for its insulating properties. So that would make a great, new "finishing" tank. For the "storage" tank, I found that purpose-built storage tanks were considerably more expensive than a standard electric hot water heater. I would have done that for my storage tank except I went the total cheapskate route and found an unused hot water heater (75 gal) on craiglist and bought that for ~$500.

    Second, which brand/model did you have which required moving the dip switch?
     
  12. Jamesck

    Jamesck Member

    Climatemaster is what I have and it shipped with the desuperheater pump in the off position. I need to check loop pressure and add some fresh water but am hoping to get more advice on the best way to go about this. The water heaters sit directly beside of the unit and I am thinking about just getting water from one of them. How old is your system? This one has been in since 2010 and so far has worked flawlessly.
     
  13. James F

    James F New Member

    Our system is brand new as July 2018 and is a WaterFurnace 7 series. To activate the DSH, you must both ensure the switch on the outside of cabinet is turned on as well as ensure the function is enabled via AID tool diagnosis. Only dealers have the AID tool as most know. I had hooked up the DSH , flipped the physical switch and experienced a very hot DSH outlet temp and cold DSH inlet temp suggesting the pump wasn't activated. Sure enough, our dealer went into the AID tool and enabled the feature. We have it set to 125 degrees target.
     

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