Desuperheater water getting too hot. . ..

Discussion in 'General Discussions' started by mx125, Feb 27, 2009.

  1. mx125

    mx125 Member

    I just had my new system reconected properly and they put the desuperheater into use. They said I should expect a slow climb to 80-90F domestic water. I expected better and certainly got it.

    I have a unit that heats air and water for infloor, which also has separate desuperheater coil. After a few hours of the compressor running to heat my infloor side . . .my 60 (imperial) gallon domestic storage tank was circulating at 150F. There is a temp sensor which is designed to shut my compressor down if if passes 130F . . but is doesn't seat properly on the copper so likely wasn't sensing full temp. I opened my hot water faucet which injected cold in order to lower the tank temp and then turned down the infloor thermostats so the compressor would shut down sooner.

    What is the solution for getting very high water temp in the closed passive desuperheater loop if the forced air or infloor are calling for heat (or cool) for very long periods of time?

    If I'd tried to push the infloor thermostats to higher temps and let the floor run for several hours . . i don't know where (or if!) the desuperheater would have levelled off!!??
     
  2. ShoeShineBoy

    ShoeShineBoy New Member

    Repair/replace the thermostat that is malfunctioning
     
  3. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    You have a control or piping error.

    If the DHW tank is show 130 to the sensor it is plumbed wrong.

    Send an image.
     
  4. mx125

    mx125 Member

    Sorry . .I don't have an image (and not at the property) but can describe the plumbing. It's simply desuperheater "OUT" to 1 amp circulator pump (which runs when compressor is running) into bottom of storage tank. Return to desuperheater "IN" comes off a tee from cold water "in" on storage tank. The hot out runs to cold in on my domestic electric tank. I'm using a small temp gauge resting on copper line to monitor temp. The cut off shows no temp . .it is simply a thermostat switch wired to compressor.

    So are you saying the desuperheater can not heat to 130+ regardless of run time of compressor?
     
  5. Bergy

    Bergy Member Industry Professional Forum Leader

    temperature sensor

    There should be a temperature strapped to the copper output line of the desuperheater. The sensor should also be insulated. If your tank is getting hotter than 120~130* you should have your service tech look at it. 150* can pose a GRAVE DANGER to you and your family!!

    Bergy
     
  6. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    MX125

    I like you. I even turned on the light since I never got typing without looking at the keyboard down.

    You are going to teach me, since I have not looked at or worked on these magic does some of everything three way units. You will tell me what the salesman said faster than I can visit the web site.

    Is your concern the DHW temp in the preheat tank too high? do you scald yourself at the sink faucet? Or is the system shutting down because it is seeing 130* water?

    I have an issue with low water temps for DHW in storage tanks, I am very anti-Legionella. I tend to pipe stuff to keep the finishing temps for DHW high enough to be healthy and there add a three way mixing valve to prevent scalding.

    I am not against grabbing BTUH where one can, lets just stay healthy.

    Your turn.
     
  7. mx125

    mx125 Member

    The temp guage is strapped to the copper but looks to be sized for 1/2 inch pipe while my pipe is 3/4 . . so not a good contact. So what is the preffered scenario? If the pump stops running then I will simply have the static water resting in the DSH coil rocketing up in temp while the compressor runs. Is that not a problem? Or are the high temps in the coil not a problem . . . it's really the issue of the water tanik getting too hot? In other words . . the DSH internals are desinged to cope with very high temps . . and shutting the circ pump is all I need to worry about??
     
  8. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Everything

    I install has the desupperheater pump controlled by the board.
     
  9. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    Yes .
     
  10. mx125

    mx125 Member

    Ahhh . . . I better get onto the tech and get a proper fitting thermostat strap! Thanks!
     
  11. amxtra

    amxtra New Member

    Wish I had your problem. My hot water never gets over 80 with the air on?
     
  12. Desuperheater too hot

    I'm not sure about other brands, but Waterfurnace has a thermister limit to cut off desuperheater at 130 inlet temp. I had one fail, and melt cpvc threaded fittings, leak etc. on a brand new unit.
     
  13. Tdog

    Tdog New Member

    We recently had a meltdown of the PEX pipe going from the desuperheater on our geo unit to our electric domestic hot water heater. It flooded our basement! Has anyone experienced a meltdown like this before? Is this a malfunction of the desuperheater, the PEX, or installation, or something else? The geo unit is 1 yr old and has been working well until now.

    Any feedback or ideas would be appreciated.
     
  14. Most manufacturers recommend copper pipe connection instead of pex to avoid this. There is a failure of the temp control on your unit that needs repair. To avoid this in future, use 10-12" of hard copper or brass after the unit connections. Ive seen "runaway" desuperheaters heat water in excess of 200 degrees.
     
  15. Kogashuko

    Kogashuko Member

    That would be great with a mixing valve and radiant floor heat.

    With those kind of temps do you ever have to run your residential water heater? Also how many tons is your unit?
     
  16. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Web Energy Logger:

    LWT from the DSH was 205 F with the circulation pump shut off and thermal siphoning yesterday...My one is 6 ton, residential water does not run for 4 months in the winter. All DSH.
     
  17. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Could something be wrong, perhaps a charge or expansion device issue, driving compressor discharge refrigerant superheat too high?

    Mine is running 157*F (compressor discharge tube temperature), having been on for several hours; however that's low stage, not high stage
     
  18.  
  19. I have a customer with propane heat in South Texas. He literally shuts off his gas heater except for December thru about March, when it doesn't run enough.
     
  20. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    In the interest of adding more data to this thread I operated my system in Y2 for 20 minutes. AT the end of that I had 2500 Watts (up from 1700 in Y1) LWT = 55*F (down from 60 in Y1), and refrigerant discharge temp of 160*F (up from 157 mentioned above) when I dropped it to Y1 for a couple minutes refrigerant dischg temp dropped to 147*F. All of that in heating mode.

    That further supports my opinion that systems (R410a) experiencing compressor discharge temps of 200+ have a charge or metering / expansion problem. I'm certainly open to hearing from folks with more data on this
     

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