Desuperheater hot water getting into cold water faucets

Discussion in 'Maintenance and Troubleshooting' started by GeoAppyMtn, Mar 31, 2013.

  1. GeoAppyMtn

    GeoAppyMtn New Member

    Contracter recently installed 4 ton Trane (WaterFurnace) geothermal residential heat pump with desuperheater in my home. Have been getting hot water through the cold water fixtures since installation. Contractor utilized my existing Marathon 60 gallon water heater and plumbed according to manufacturer specifications with Geo hot feed line at bottom of tank. Contractor came back and installed beck flow preventer on the cold water in line at top of the tank, hoping to resolve, but still getting hot water through the cold faucets. When the desuperheater is not running cold water flows normally. When the desuperheater is running hot water flows through the cold water lines initially and finally turns cold after about 45 to 60 seconds of flow. The contractor called WaterFurnace and said this was probably due to residual heat transfer where the hot and cold water come in contact and could not be resolved. Does this typically happen with all desuperheater installations? Is there a way to separate the hot water from the cold water? I asked the contractor if adding a second holding tank would improve the problem as I had seen some installations done this way on the Internet. The contractor said WaterFurnace told them it may help a little but would not completely eliminate my problem. I am really getting concerned with Summer temperatures soon approaching thinking I will have no cold water once the heat pump switches to cooling mode. All comments/recommendations are greatly appreciated.
     
  2. Bergy

    Bergy Member Industry Professional Forum Leader

    Single tank set ups are, for the most part, worthless. The electric elements ability to heat the water out paces the desuperheater's ability to so. Having said that... Can you post a drawing of the piping, including ball valves, for us?

    Bergy
     
  3. GeoAppyMtn

    GeoAppyMtn New Member

    Pictures attached. More to follow in next post. There is a back flow preventer in the hot line from the DSH shown in pic. There is now a back flow preventer in the cold line into the water heater (installed after the pic) above the T. There is a ball valve (clean out) in the cold line in to the DSW beside the T. There is a ball valve (clean out) at the DSW hot in to the water heater. There are ball valves at the heat pump located on both the DSW hot out and cold in lines.
     

    Attached Files:

  4. GeoAppyMtn

    GeoAppyMtn New Member

    More pictures attached.
     

    Attached Files:

  5. ACES-Energy

    ACES-Energy Member Industry Professional Forum Leader

    This is a really dumb question, but is this a new problem after the geothermal had been installed? Is it one faucet or all in the house?

    My tech was at a house last week for a similar issue, turned out to be a combination of a faulty facet and the homeowner running water pressure in the house at 90psi....
     
  6. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    A back-flow preventer installed without a expansion tank is as ill advised as a DSH without a buffer tank.
     
  7. GeoAppyMtn

    GeoAppyMtn New Member

    Yes, this a new problem after the geothermal was installed. It affects all the faucets in the house. My contractor sent someone yesterday and they think the shower faucet on the second floor may be letting the hot mix with the cold. The sink faucets have separate hot and cold lines and the shower has scald protection so they think the shower must be faulty by process of elimination. They can't think of anything else to check. I only have the problem when the DSH is running.
     
  8. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Wellll- we already agree that the DSH is plumbed wrong. Get in the installation manual and see if the pipe schematic your installer used is one of the methods if not ask him to change it. Tell him you want a buffer tank and will be glad to pay for it, or replumb yourself.
     
  9. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    I wonder if the DSH is plumbed backward - injecting its warmed water into the cold line. I also wonder if they remembered to remove the heat trap at the CW inlet to the tank.

    I additionally 3rd the motion that a single tank DSH is well nigh worthless.
     
  10. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    One wonders how these guys stay in business?
     
  11. GeoAppyMtn

    GeoAppyMtn New Member

  12. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Do add the buffering tank. I would not change the shower until the system is re-piped. Bergy has a GREAT drawing of how the piping should go.

    Mark
     
  13. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    I concur, and very much doubt the shower plumbing is to blame...it wasn't a problem before, right?
     
  14. Bergy

    Bergy Member Industry Professional Forum Leader

    I keep it on my Desktop now... Twin Electric Piping for Geothermal Desuperheater.jpg
     
  15. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    I had a similar problem, that I lost BTUs from my buffer tank and my final tank to the cold water circuit, only when the DSH pump was running. I also suspected the shower mixing valve. I put a check valve between the 2 tanks, and a check valve on the T for the cold water inlet, and the problem was solved. I never bothered to investigate why that happend.
    So we put a check valve on the T to the DSH from the cold water inlet line as a standard, I call it the "bergy" modified version.

    See sample at
    Temperature and Energy logging by: Web Energy Logger
     
  16. GeoAppyMtn

    GeoAppyMtn New Member

    Yes, your are correct the shower plumbing was not a problem before the DSH.
     
  17. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    What am I missing? Put a checkvalve in the coldwater supply before it enters any part of the buffer/DSH loop. That stops the thermal siphoning.
     
  18. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Rememeber any check valve is best accompanied by an expansion tank.
     
  19. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    expansion tank in the hot water circuit is required by code by our municipalities anyway
     
  20. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Hmmm doc, not a bad rule. Unfortunately thats not true everywhere so I figured I'd mention it. We have an entire village in our AO that had back flow preventers installed on water mains and they wrecked a few T/Ps and many water heaters. We have many clients on wells whos bladder tanks handle the expansion but new variable pumps are changing that.
     

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