Opentherm + EvoHome + Viessmann 111-W overshoots

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  • DBMandrake
    Automated Home Legend
    • Sep 2014
    • 2361

    #31
    Originally posted by Stephen Crown View Post
    Running the radiators that were sized and installed for between 45/50(autumn/spring) to 60/65(winter)CH flow temps (i'd guess as that is what works for me with BDR91) at 81/82 degrees C is going to be a problem.

    Maintaining a set temp does not seem to cause an issue on the whole from what i can see, it is bringing rooms up to temp. I regularly see the boiler running - well mostly just the pump - at 26 or 31 or 35 or 41 degrees C whilst maintaining temps through the day/night, so it does appear to be dialing down when little heat demand is made.
    As I said earlier, the problem is that the peak temperature is not being limited to something reasonable that is appropriate for your radiator output and house heat loss. If its modulating down as low as 26 - 41 degrees when the zones are all in their proportional range (+/- 1.5 degrees from the set point) then the system has learnt what is required to maintain the rooms and is modulating the flow temperature, however when there is a "large" demand, like any room at least 1.5 degrees below the set point the system is designed to call for maximum allowed flow temperature to ensure that rooms can actually get up to temperature in extreme cold conditions.

    It's up to you to either manually set a sensible maximum flow temperature that is high enough but not too high (except your boiler won't let you in this instance) or use weather compensation to do that for you and adjust it automatically as the outside temperature (and thus heat loss through the walls) change. I would certainly try to pursue this problem to its logical conclusion if at all possible, and let us know your progress.

    It seems like something that should "just work", and even if it takes knocking Viessemann's and Honeywell's heads together to get a proper resolution it should be worth it. After all both companies have taken your money and provided you a fancy product that should perform as advertised and no matter whose fault it is both should be willing to work with each other to resolve it I would have thought, rather than just sending you, the customer back and forth between them like a ping pong ball.

    Comment

    • StephenC
      Automated Home Guru
      • Feb 2017
      • 102

      #32
      Originally posted by Rameses View Post
      (with your permission) support can see what your opentherm is trying to do (commands, etc). This might give you some insight.
      Hi Rameses,

      I'm happy for this to happen - I've nothing to hide and everything to gain from advice. There could of course be something wrong my end - I just haven't got access to the data to determine that.

      re: radiator sizing, some are old some are new (1880's building), but were appropriate for the rad temps in the seasons i mention above, and the BDR91 seemed to have much much better control.

      It's the red hot scalding temps in the radiators that is the cause of the overshoots, it doesn't seems to dial down the temps as it approaches the set point as you would expect. To make it worse, the R8810 allows the CH flow temp to stay high for far too long, well beyond (time-wise), reaching the setpoint from observing the boiler and the controller at the same time. And this is ignoring the safety issue of rads that hot

      Just to add, the CH Heat output (KW) has been reduced from full power to around 2/5ths (full = 35KW), this just takes longer to reach the max CH flow temp of 81/82 degrees C. It is a modulating boiler that can go down to 8KW I believe for info.

      Comment

      • Rameses
        Industry Expert
        • Nov 2014
        • 446

        #33
        Understood - the support team can get insight into what your opentherm is doing. We need to prove/see what commands are being sent to ensure things are behaving itself.
        getconnected.honeywell.com | I work for Honeywell. Any posts I make are purely to help if I can. Any personal views expressed are my own

        Comment

        • victorp1612
          Automated Home Jr Member
          • Jun 2016
          • 24

          #34
          As Viessmann told me ' not our problem', I've also got a case open with Honeywell (14568935 ) for the same issue . @Rameses , happy for you and support to check what opentherm is doing and what command gets issued when heat demand is high.

          Comment

          • StephenC
            Automated Home Guru
            • Feb 2017
            • 102

            #35
            Originally posted by DBMandrake View Post
            , however when there is a "large" demand, like any room at least 1.5 degrees below the set point the system is designed to call for maximum allowed flow temperature to ensure that rooms can actually get up to temperature in extreme cold conditions.
            Hi DBMandrake - Indeed - I'm posting here to help other people out and provide info on the experience rather than the logic and theory that I had before. I'm definitely seeing max CH flow temps being called for changes of 0.5 degrees upwards set point changes. Whether I'm missing something I can't say as i cannot determine what the Evohome controller thinks the heat demand is, nor the flow temp request from the OT.

            I'm looking at Weather comp seriously now, but i would like to understand why if Viessmann are telling me the CH flow temp dial *should* work with OT, then what is the R8810 doing different? That might save someone else the trouble/money on needing weather comp as well in the future. Or have i uncovered a bug? Let's see where the evidence and data goes.

            Comment

            • StephenC
              Automated Home Guru
              • Feb 2017
              • 102

              #36
              Originally posted by victorp1612 View Post
              As Viessmann told me ' not our problem', I've also got a case open with Honeywell (14568935 ) for the same issue . @Rameses , happy for you and support to check what opentherm is doing and what command gets issued when heat demand is high.
              Thanks for this - I'm hopeful with 2 systems that are similar, we'll get to understand whats going on.

              Comment

              • Rameses
                Industry Expert
                • Nov 2014
                • 446

                #37
                Our support team are reviewing your posts. We see Viessman have disabled the boiler temperature limit when a OT room unit is connected. (!)
                On the positive side, if the logic control learned the control parameters with a manual limit on the boiler flow temp in place then it will relearn now that has been removed.

                Anyway - I am told they will be in touch.
                getconnected.honeywell.com | I work for Honeywell. Any posts I make are purely to help if I can. Any personal views expressed are my own

                Comment

                • StephenC
                  Automated Home Guru
                  • Feb 2017
                  • 102

                  #38
                  Great - thank you. I'm happy to assist diagnosis (set point changes etc.) where required and am available.

                  Viessmann stated their own OT controller/unit *doesn't* disable the CH flow temp dial....I don't have one of those, so I have to take their word for it!

                  Comment

                  • StephenC
                    Automated Home Guru
                    • Feb 2017
                    • 102

                    #39
                    Just thought I'd add a photo of the boiler display showing the temperature this morning when 4 of the 11 zones were only 0.5 degrees C under the set point, and all others were well above the set point as they were still "set back":

                    IMG_3133.jpg

                    Note the CH flow temp dial is set to minimum - showing how with R8810 OT connected, this dial is disabled, but still a boiler temp of 81 degrees C is being reached. As noted previously, Viessmann stated that this is a Honeywell R8810 OT implementation issue as their own OT bridge/interface allows the dial to still let the end user set a max ch flow temp.

                    R8810 OT telling the boiler to run at that temperature with rooms so close to the set point doesn't seem sensible. A couple of minutes later the set point was breached, and the boiler dialled down to 77 degrees, and only when beyond 1.5 degrees did the boiler shut off completely.

                    I'm sure Honeywell may have more accurate data to show this in greater detail, but all I can do is observe the boiler temp display and TCC App/EvoHome controller and I can honestly say the common sense and logical assumptions of dialing down the temps as set points are approached (to avoid overshoot) does not seem to be occurring here. Yet.

                    It's been 8-9 days now, so a few more to go until we could say learning has been completed.

                    Edit: boiler has been off for 20 mins and the following screenshots from the TCC app shows the issue:

                    IMG_3134.jpg

                    IMG_3135.jpg
                    Last edited by StephenC; 15 March 2017, 09:40 AM.

                    Comment

                    • paulockenden
                      Automated Home Legend
                      • Apr 2015
                      • 1719

                      #40
                      I'd love to see the output of an opentherm monitor sitting between the R8810 and your boiler.

                      Comment

                      • StephenC
                        Automated Home Guru
                        • Feb 2017
                        • 102

                        #41
                        Originally posted by paulockenden View Post
                        I'd love to see the output of an opentherm monitor sitting between the R8810 and your boiler.
                        You and me both!

                        Latest sample set point vs actual graphs for last 24 hours:

                        IMG_3136.jpgIMG_3137.jpgIMG_3138.jpgIMG_3139.jpg

                        Comment

                        • paulockenden
                          Automated Home Legend
                          • Apr 2015
                          • 1719

                          #42
                          I've got zones that do stuff like that though, without OpenTherm.

                          The problem is rooms that heat/cool quickly (poorly insulated and/or rads that are too big - or, I guess, too hot) combined with the reporting frequency of the HR92.

                          chart (3).jpg

                          P.

                          Comment

                          • DBMandrake
                            Automated Home Legend
                            • Sep 2014
                            • 2361

                            #43
                            Originally posted by paulockenden View Post
                            I've got zones that do stuff like that though, without OpenTherm.
                            Me too. Our kitchen is particularly bad like this as the radiator is somewhat boxed in.
                            The problem is rooms that heat/cool quickly (poorly insulated and/or rads that are too big - or, I guess, too hot) combined with the reporting frequency of the HR92.
                            Yep. Temperature measurements are only taken about every 4 minutes.

                            Radiators heat up very fast (if the rest of the system is already hot) and cool down very slowly. If you let them heat up to a very high temperature then even if the HR92 closed the valve completely as soon as it detected a rise in temperature the latent heat in the radiator would push the room well past the set point after the valve was closed, and cause an overshoot. No amount of learning can help when the problem happens within a single sample period.

                            The minimum "unit" of heat that the can be put out by the radiator with a high flow temperature is too great because within a single sample period the radiator can be fully up to temperature and then remain hot for 20-30 minutes putting a lot of heat into the room. This results in an uncontrollable unstable feedback loop, hence the temperature oscillates.

                            Setting the maximum flow temperature to be sufficient but no higher than necessary is the best way to avoid this, however this assumes that all your radiators are well matched (size/type) for each room so that the system as a whole is fairly well balanced. (Heat output vs heat loss per room)

                            If you have some rooms with undersized radiators and some with oversized radiators (particularly common if you have a mix of old radiators and modern convectors as we do, or if the install was done by rule of thumb to fit radiators under windows rather than based on actual calculations) then the undersized radiators force you to set the flow temperature higher than is optimal for the rest of the radiators, so the oversized radiators will overshoot.

                            It also assumes that you optimise your flow temperature as the outdoor conditions (and thus heat loss through walls) changes, otherwise nice steady temperature control in winter can revert to overshoots and oscillation in warm weather due to the flow temperature being too high for the conditions. This is where in theory good weather compensation can automate this process for you so you're not having to tweak the flow temperature manually.
                            Last edited by DBMandrake; 15 March 2017, 02:38 PM.

                            Comment

                            • StephenC
                              Automated Home Guru
                              • Feb 2017
                              • 102

                              #44
                              Interestingly, the US Viessmann manual for a 1xx combi boiler states the CH flow temp dial is disabled upon Opentherm device connection and control, exactly as we are seeing, and disputed by Viessmann UK Technical support:

                              Page 10:


                              IMG_3140.jpg

                              Comment

                              • paulockenden
                                Automated Home Legend
                                • Apr 2015
                                • 1719

                                #45
                                For many companies, outside of their home territory the national distributors are essentially just franchises. Companies that buy the rights to sell the product in that country. They don't have the design, r&d, etc. experience necessary to offer good quality technical support. And they are often reticent to pass cases back up the line to the 'real' company because they don't want 'the mothership' to think they aren't up to the job.

                                I've seen that SSSSOOOOOOOOO many times now.

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