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GSHP with Buffer Tank - Advice Needed

I've recently bought a new house with a Danfoss GSHP connected to a buffer tank.  The reason a buffer tank was included was because of lots of zone control on the UFH.  Unfortunately, the inclusion of the buffer tank is causing problems and is preventing the system working as well as it should.

The main problem is that the temperature of the supply from the heat pump to the buffer tank is never matched at the UFH manifolds.  To get the UFH supply to 40 degrees, I'm having to set the heat pump supply temperature to 50 degrees.  This can't be right?  The buffer tank is plumbed with the heat pump supply going in at the top side of the tank, the system supply coming out of the top of the tank, and the two returns going in at the bottom.

What do I need to do to get the system properly, and actually deliver the temperature generated by the heat pump to the actual heating system?  I'm assumign that the problem lies with the way its all been connected to the buffer tank?


  • meplumber
    meplumber Member Posts: 678
    A little hard to follow.

    Your post is a little hard to follow.

    Can you post pictures? It is normal to see a drop in temperature between the output temperature of the water to water heat pump and the actual temperature delivered at the point of radiation. But 10 deg F is a little excessive. I am assuming that the temp numbers are in Celsius? Which would be 18 deg F.

    Post some pictures and maybe we can help you out a little.
  • zacmobile
    zacmobile Member Posts: 211

    What kind of tank is it? A purpose built buffer or an electric water heater? If the latter you might be pretty limited for repiping options. Ideally the heat pump supply would be 1/3 to 1/2 way up from the bottom for good stratification action. But by your description this may not be the problem, what is controlling the heat pump and where is the sensor located?
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    it's not the tank

    but if you have very high radiant side flow rates you might blend it down with your return water.

    In any other circumstance if you hot in and out at the top, water to the radiant would be about the same as water out of the geo unit after a short period of time... unless you're using a tank with dip tubes in it or something. in a case like that then you'd have to bring up the tank temperature over time and it will always lag behind geothermal load out temperature.

    a more important question though is why are you messing with the water temp in the first place? was it not working?
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
This discussion has been closed.