Evohome & Opentherm

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  • PJB
    Automated Home Jr Member
    • Feb 2020
    • 16

    Evohome & Opentherm

    Hello

    My setup:

    ATAG iC Economiser Plus27 combi. (installed Sept 2018)
    Evohome & OpenTherm Bridge
    HR92 rad valves in 5 zones. Plenty of bypass rads.
    Nodo-Shop OpenTherrm Gateway
    Home-Assistant monitoring all of the above, running on RaspiPi

    All works pretty well, bar some fun with the DHW ECO mode - solved now & probably best saved for another thread.

    I have a question regarding the Evohome implementation of OpenTherm. The graph below shows OpenTherm Setpoint against time, as an output from the OpenTherm Gateway, placed between the Opentherm Bridge & boiler. Apologies, the picture looks rather small in the preview. I think you can click for a larger view. There is no DHW demand on the boiler at this time.

    evo.jpg

    I've noticed that at times of reducing/reduced CH demand Evohome steps the setpoint down to 10deg and then after ~1 mins steps it back up to the reduced setpoint. Purple arrows in the graph above. This looks more like TPI control than OpenTherm. Has anyone else noticed this & could you comment on whether this is as expected, as designed or otherwise? This is before the 02.00.19.31 Beta firmware update btw.

    Many thanks.
  • kevinsmart
    Automated Home Ninja
    • Sep 2018
    • 257

    #2
    Honeywell call this “low load control”.

    When an appliance is no longer able to modulate lower the control switches from modulating control to low/off control.

    Off in OpenTherm is 10C.

    Comment

    • PJB
      Automated Home Jr Member
      • Feb 2020
      • 16

      #3
      OK thanks. That sounds plausible around 17:30 - 17:45 in the graph. But the appliance is able to modulate down .. down to 24deg as you can see. I don't understand why Evohome thinks the boiler can't modulate from 57deg to 52deg (first purple arrow), then 52deg to 47deg without going all the way down to 10deg for a minute.

      Comment

      • kevinsmart
        Automated Home Ninja
        • Sep 2018
        • 257

        #4
        PJB, enable the flow temperature graph as well. I expect you’ll see your boiler overshooting the temperature demand and then anti-cycling.

        See my post here:

        Comment

        • PJB
          Automated Home Jr Member
          • Feb 2020
          • 16

          #5
          Happy New Year all.

          I'm afraid that Evohome's habit of sending CS=10 to the boiler for a short time is still bugging me.

          evo2.jpg

          Regards @kevinsmart's suggestion above, could anyone confirm that 'low load control' is implemented in Evohome? As far as I could read it's related to the T6 series thermostats. https://ensupport.getconnected.honey...language=en_US

          If so, can I switch 'low load control' off in Evohome?

          The implication is that flame on & CH return temp Opentherm messages from the boiler are monitored by Evohome. Could anyone confirm this?

          Thanks.
          Last edited by PJB; 2 January 2021, 04:22 PM. Reason: Additional question.

          Comment

          • kevinsmart
            Automated Home Ninja
            • Sep 2018
            • 257

            #6
            Originally posted by PJB View Post
            Happy New Year all.

            I'm afraid that Evohome's habit of sending CS=10 to the boiler for a short time is still bugging me.

            [ATTACH=CONFIG]1737[/ATTACH]

            Regards @kevinsmart's suggestion above, could anyone confirm that 'low load control' is implemented in Evohome? As far as I could read it's related to the T6 series thermostats. https://ensupport.getconnected.honey...language=en_US

            If so, can I switch 'low load control' off in Evohome?

            The implication is that flame on & CH return temp Opentherm messages from the boiler are monitored by Evohome. Could anyone confirm this?

            Thanks.
            Happy New Year! It would be helpful if you can share a graph which includes the boiler flow temperature to see whether it is overshooting and anti-cycling.

            Richard from the Evohome shop refers to low load control here:



            Unfortunately you can’t disable this, but with some custom firmware in your OTGW, you could probably alter it.
            Last edited by kevinsmart; 2 January 2021, 06:12 PM.

            Comment

            • PJB
              Automated Home Jr Member
              • Feb 2020
              • 16

              #7
              Originally posted by kevinsmart View Post
              Happy New Year! It would be helpful if you can share a graph which includes the boiler flow temperature to see whether it is overshooting and anti-cycling.

              Richard from the Evohome shop refers to low load control here:



              Unfortunately you can’t disable this, but with some custom firmware in your OTGW, you could probably alter it.
              OK, thanks. I see what's happening now. I must say that I'm not convinced that the 'low load control' is handing a reducing demand any better than the boiler does when left to it's own devices. Low load control doesn't kick in with every reducing demand and it sometimes kicks in when the demand is constant and relatively high (CS=50). Very odd.

              I'm intrigued by the thought of suppressing the short duration CS=10 command from Evohome controller with the OTGW. Is that what had you in mind?

              Thanks

              Comment

              • kevinsmart
                Automated Home Ninja
                • Sep 2018
                • 257

                #8
                Originally posted by PJB View Post
                I'm intrigued by the thought of suppressing the short duration CS=10 command from Evohome controller with the OTGW. Is that what had you in mind?

                Thanks
                Yes, you could suppress the CS=10 and start a timer. Stop the timer if CS>10 sent, otherwise issue CS=10 after timeout.

                I recall max modulation settings also change, so you might need to workaround those too.

                Still waiting for the installation in my new house to be completed. Can probably provide further insight when I’m in the guts of the OTGW firmware again.

                Comment

                • bruce_miranda
                  Automated Home Legend
                  • Jul 2014
                  • 2307

                  #9
                  I too see this on the eBUS side on my Vaillant boiler and it often doesn't make any sense to me at all. I too have toyed with the idea of manually altering the Target Flow temperature requested on these short bursts, both 10 and 90 actually. The boiler handles the modulation levels.
                  chart (1).jpg
                  See the above chart, why did it bother requesting a 10C, when the next moment it jumped back up to 90C, when all the while it could have stayed at the 45C mark.
                  Last edited by bruce_miranda; 14 January 2021, 10:04 AM.

                  Comment

                  • oxygen
                    Automated Home Jr Member
                    • Sep 2018
                    • 40

                    #10
                    Somewhat unrelated to the Boillers listed in this thread, I have a feeling that something is going wrong with OT in my setup.
                    Or more exactly that OT is creating some side issues.
                    I'm running a Perfinox 4100/LMU64 boiler, controlled with OT (not via a BDR91).
                    Seems to run fine, but it generates from time to time some errors on the Boiler:
                    - LMU64 error (basically the OT is asking things to the LMU64 that are not expected, generating a defect).
                    - Temperature Sensor error
                    Sometimes, it also has trouble firing up the boiler, turning into a strange loud noise.
                    This usually happens under very low loads.

                    Last year, I had to replace the electrodes. They were 8 years old from my understanding, so nothing too worrysome.

                    However, 3 days ago, the Boiler again started to show some issues on the electrodes, but they failed totally today.

                    I suspect that the the OT controll may be pushing the OT to the limits.
                    My boiler is 10 years old, and was already a condensing boiler.

                    I'm wondering if an "old" boiler may be less receptive to low loads requests, or if the low load requests may push the electrodes to degrade themsleves more quickly ?
                    I've the feeling that they get oxidize with the condensing, but I'm not 100% sure of that.

                    Am I the only one having to do "more" proactive maintenance on the boiler with a full OT controll ?

                    (manual of the Perfinox is visibile here: https://www.jeanpaulguy.fr/notice/no...4100_bvi_r.pdf )

                    Comment

                    • bruce_miranda
                      Automated Home Legend
                      • Jul 2014
                      • 2307

                      #11
                      I have not seen these issues. But then again, I have an OT to eBUS converter between the OTB and my Vaillant Boiler. But low modulation of a boiler becomes quite important with OT. You boiler just seems to be causing self harm in doing that.

                      Comment

                      • mtmcgavock
                        Automated Home Legend
                        • Mar 2017
                        • 507

                        #12
                        Originally posted by bruce_miranda View Post
                        I have not seen these issues. But then again, I have an OT to eBUS converter between the OTB and my Vaillant Boiler. But low modulation of a boiler becomes quite important with OT. You boiler just seems to be causing self harm in doing that.
                        What you using to do that out of interest? a VR33?

                        Comment

                        • bruce_miranda
                          Automated Home Legend
                          • Jul 2014
                          • 2307

                          #13
                          Yes a VR33

                          Comment

                          • mtmcgavock
                            Automated Home Legend
                            • Mar 2017
                            • 507

                            #14
                            Originally posted by bruce_miranda View Post
                            Yes a VR33
                            Does it work OK?

                            At some point i'll probably be replacing my boiler with a Vaillant and wondered if it's worth the extra hassle.

                            Did you manage to get it to differentiate between CH and HW like it would with the Vaillant controls?

                            Comment

                            • bruce_miranda
                              Automated Home Legend
                              • Jul 2014
                              • 2307

                              #15
                              On the eBUS side there doesn't appear to be any indication of a difference between the two Heat Demands.
                              Hence why I was surprised when @kevinsmart reported in another thread that the OT messages did infact differ. So I will check again.
                              However I have implemented different temperatures for CH and HW in a roundabout way. I am monitoring the eBUS side and when I detect that Evohome is calling for HW, I vary the max on the Heating dial scale, that in turn raises or lowers the flow as required. It works extremely well. I can have CH flow set to 55C and then when there is HW demand, I set the flow to 70C.
                              Vaillant by default only allows dual temperatures if you use their proprietary eBUS controls. But if you add that in, it overrides the VR33 because there is a eBUS hierarchy and the VR33 is lower than Vaillants own thermostat, that you need in order to use their HW kit.

                              Comment

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