Evohome & Opentherm - flow temps UFH and radiator zones

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts
  • jdp80
    Automated Home Jr Member
    • Mar 2016
    • 38

    Evohome & Opentherm - flow temps UFH and radiator zones

    Just wondering how this works.
    Say I have Evohome controlling radiators, UFH zones and hot water, how does it decide the flow temperature to demand from the boiler?

    I'd imagine that UFH would need 35-50c (say)
    Radiators would be 35-70c
    DHW would need to be 70c to heat the cylinder to 65c
    I can imagine the rads getting up to temp while the UFH is still heating so would want UFH to be full strength while rads could be controlled using TPI.

    Is all this stuff calculated automatically?
  • top brake
    Automated Home Legend
    • Feb 2015
    • 837

    #2
    Originally posted by jdp80 View Post
    Just wondering how this works.
    Say I have Evohome controlling radiators, UFH zones and hot water, how does it decide the flow temperature to demand from the boiler?

    I'd imagine that UFH would need 35-50c (say)
    Radiators would be 35-70c
    DHW would need to be 70c to heat the cylinder to 65c
    I can imagine the rads getting up to temp while the UFH is still heating so would want UFH to be full strength while rads could be controlled using TPI.

    Is all this stuff calculated automatically?
    TPI doesn't control flow temperature, for that you need OpenTherm
    I work for Resideo, posts are personal and my own views.

    Comment

    • jdp80
      Automated Home Jr Member
      • Mar 2016
      • 38

      #3
      Originally posted by top brake View Post
      TPI doesn't control flow temperature, for that you need OpenTherm
      So would Evohome decide on different flow temperatures depending on the type of zone calling for heat?

      Comment

      • top brake
        Automated Home Legend
        • Feb 2015
        • 837

        #4
        Originally posted by jdp80 View Post
        So would Evohome decide on different flow temperatures depending on the type of zone calling for heat?
        Yes indeed it does. It modulates flow temperature according to the heat demand, ramping up to suit hot water for example
        I work for Resideo, posts are personal and my own views.

        Comment

        • bruce_miranda
          Automated Home Legend
          • Jul 2014
          • 2307

          #5
          I know that the opentherm does change heat demand between hw and ch.

          But i'm not sure if it can distinguish between radiators and ufh. Maybe it can if you pair the devices as UFH. However in my case the ufh is just another motorised zone valve that is controlled by evohome as a zone valve as part of the CH. I'll see if the opentherm provides a lower flow temperature when only the ufh is calling for heat.

          It does however vary the flow temperature based on how many CH demands are there.

          Comment

          • paulockenden
            Automated Home Legend
            • Apr 2015
            • 1719

            #6
            Isn't the temp of UFH usually controlled by a separate manifold mixer valve? To reduce the temp of the heating loop down to a sensible level?

            Comment

            • jdp80
              Automated Home Jr Member
              • Mar 2016
              • 38

              #7
              Yes, dependent on the floor type etc. Ours is set to about 50 degC

              I wonder what will happen if there's a period when radiator zones are in a low demand situation, but the UFH is high demand - could the boiler modulation cause flow temperature to drop below what is required to run the UFH circuit?

              Comment

              • bruce_miranda
                Automated Home Legend
                • Jul 2014
                • 2307

                #8
                Originally posted by paulockenden View Post
                Isn't the temp of UFH usually controlled by a separate manifold mixer valve? To reduce the temp of the heating loop down to a sensible level?
                Yes that is true. But it's such a waste for the boiler to heat the water to 50+ only for the manifold to cool it down to 30+ before sending it down the loops.

                Hence I was just keen to find out if evohome was intelligent enough to know and set a reduced target flow for UFH demand only?

                Comment

                • top brake
                  Automated Home Legend
                  • Feb 2015
                  • 837

                  #9
                  Originally posted by bruce_miranda View Post
                  Yes that is true. But it's such a waste for the boiler to heat the water to 50+ only for the manifold to cool it down to 30+ before sending it down the loops.

                  Hence I was just keen to find out if evohome was intelligent enough to know and set a reduced target flow for UFH demand only?
                  a regular fixed flow temperature UFH manifold doesn't cool it down, it simply bleeds in hot water as required
                  I work for Resideo, posts are personal and my own views.

                  Comment

                  • paulockenden
                    Automated Home Legend
                    • Apr 2015
                    • 1719

                    #10
                    It doesn't 'cool it down', more 'ekes it out' - no heat is wasted (other than losses in the system). It's no different from a rad valve being turned down.

                    Comment

                    • bruce_miranda
                      Automated Home Legend
                      • Jul 2014
                      • 2307

                      #11
                      True, but even so the flow temperature doesn't need to be as high for ufh demand only as opposed to radiators. But then again, i think the evohome does see the number of heat demands and varies the target accordingly via Opentherm.

                      I personally haven't seen a 40+ heat demand but I'm not looking at the boiler, which is in the loft. Others here claim they have seen 46C.

                      Comment

                      Working...
                      X