Opentherm + EvoHome + Viessmann 111-W overshoots

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  • StephenC
    Automated Home Guru
    • Feb 2017
    • 102

    #76
    Very interesting indeed....:

    I have just completed the re-binding steps and gone through some crude tests given limited time between work ;-)

    Observations:
    • Boiler reacts very very swiftly to changes made via the T87RF round thermostat (up or down) which in turn goes through the R8810 OT Bridge. No delays (obviously) due to HR92 comms and Evohome aggregation.
    • Different behavior to Evohome is noted when an increase of only 0.5 degrees above setpoint is made when the room is reporting to be at the original setpoint. (i.e. a 0.5 degree increase request in room temp). The T87RF requested around ~44 degrees (well that is what the LCD boiler temp was showing to be fair). Evohome seems to send through a max CH flow temp for even 0.5 degree room temp increases (via HR92 sending what I can only presume to be a 100% heat demand to Evohome even for 0.5 degrees)
    • Boiler temp was held at approx ~65 degrees for a 1.5 degree increase request in room temp and reduced as it approached the set point
    • Only when I pushed beyond 2.5 degree increase did the boiler start to really fire up at full pelt. I didn't have time to see it heat up to a max temp and then stop (whatever that was) unfortunately - i only saw it get to 72 degrees and it was still going before I re-binded it all back to how it was setup with Evohome, but appeared to be similar boiler firing to Evohome when any temp changes are requested
    • Bonus bullet: the T87RF round thermostat displayed boiler firing symbol when directly connected to R8810 OT Bridge and when heat was requested :-)



    I guess this is how I was expecting the R8810 OT Bridge to function with Evohome: only fire up at a high flow temp when there is a significant difference in room temp vs desired set point.

    What I am seeing with R8810 OT Bridge with Evohome is more like on/off, i.e. on=max CH flow temp, and off = off or very very low CH flow temp. This has somewhat surprised me. But maybe that is expected behavior, and the HR92 devices I have need time to learn to request lower than 100% heat demand? After all, mine have been messed up for the last week or so with intermittent boiler firing every 20-30mins.

    Does anyone else have an R8810 OT Bridge with a T87RF OT compatible Honeywell round stat that can try this as well?
    Last edited by StephenC; 30 March 2017, 03:54 PM.

    Comment

    • StephenC
      Automated Home Guru
      • Feb 2017
      • 102

      #77
      So the thread and specifically the post #36 linked to below seems strangely similar to the behavior I am seeing when comparing single zone (T87RF) and multi-zone (Evohome + HR92's)...:




      Other OT issues similar:
      I installed Evohome over 2 years ago. I am now looking to replace a 16 year old boiler with either a Viessmann, ATag or Intergas product using an Opentherm connection. I know that the Viessmann 100 needs a HW junction box for HW priority; the Atag needs an EBus to Opentherm converter and...


      So maybe there *is* an issue here with Evohome and the heat demand % it sends to the R8810 OT Bridge. (for clarity: not the "Viessmann" issue, but the issue I have observed and noted in the URLs above)
      Last edited by StephenC; 30 March 2017, 11:31 AM.

      Comment

      • bruce_miranda
        Automated Home Legend
        • Jul 2014
        • 2307

        #78
        This confirmed my observations where I think Evohome doesn't calculate the aggregated Heat Demand well. It almost always over compensates and that results in a higher than required CH Flow temperature. The end user is less likely to complain that their house is too warm! The T87RF doesn't need to aggregate anything and so it able to control the OT bridge a lot better. It however doesn't help you because it seems like your boiler is expecting the OT device to set it's max flow, and because neither the Evohome or T87RF have the flow temperature as a configurable parameter, you are left with the boiler going to max.

        Since you have moved into experimentation, here is another one : The BDR91 allows multiple devices to bind to it, so I wonder if the R8810 does too. What would happen if you paired both the Evohome and a device that allows Flow temperature configuration. What would be the end result!

        Comment

        • bruce_miranda
          Automated Home Legend
          • Jul 2014
          • 2307

          #79
          Originally posted by StephenC View Post

          So maybe there *is* an issue here with Evohome and the heat demand % it sends to the R8810 OT Bridge.
          I think you are at risk of confusing two issues here Evohome's Heat Demand calculation (agreed it may be buggy) and the fact that Evohome is not setting a boiler max flow temperature - only relevant to your boiler.

          Comment

          • StephenC
            Automated Home Guru
            • Feb 2017
            • 102

            #80
            Hi Bruce_miranda - no not confused, I was referring to the linked URLs as I have observed the same behaviour. ;-) EDIT: I have updated the original post #77 for clarity.


            Has anyone raised a case with Honeywell with this specific issue (not the Viessmann issue, but the Evohome HR92/multiple zone R8810 OT Bridge issue)?

            As your previous posts suggests, this compounds the Viessmann issue - making it (max CH flow temp in use) appear more often, and therefore overshoots on multiple zones is occuring.
            Last edited by StephenC; 30 March 2017, 11:33 AM.

            Comment

            • bruce_miranda
              Automated Home Legend
              • Jul 2014
              • 2307

              #81
              It would be good to know what that DIY post means by Evohome not being able to handle multi zone Evohome. If they mean that Evohome can't represent the demand from multiple zones correctly via OT, then maybe. But I have seen that my boiler does modulate. I think I need to perform a controlled experiment myself to see what's really happening on the boiler.

              Comment

              • StephenC
                Automated Home Guru
                • Feb 2017
                • 102

                #83
                Just installed the Viessmann weather compensation unit and connected it up.

                It's looking like the boiler is ignoring this unit and just relying on Opentherm.

                It's not complicated - 2 wires either end, so nothing really to get "wrong" as far as I'm concerned.

                Just called up Viessmann technical support to ask what the troubleshooting steps are and got told:

                1. There are none (?)
                2. Viessmann don't recommend Opentherm & Weather Compensation (wtf?!! I asked this a few weeks ago and got told the opposite!)
                3. They don't recommend 3rd party Opentherm due to reported interoperability issues.


                Well, I'm feeling beaten at this point.

                Not sure now whether to:

                1. Go back to bdr91 + Weather compensation (assuming the unit is not faulty) and sell the R8810

                Or

                2. Stick it out with Opentherm only and hope that a) the HR92's learn quickly to deal with the high ch flow temps (and therefore close early or send a lower heat demand %), and b) maybe Honeywell will look at this further. I'm not hopeful of b) being possible to be honest. Sell the weather comp unit or give it to family member (most local Gas Safe installers seem to have gravitated around fitting Viessmann boilers over last 6-8 years, so all family members also have Viessmanns)

                Shall I flip a coin?! ;-)
                Last edited by StephenC; 31 March 2017, 05:06 PM.

                Comment

                • bruce_miranda
                  Automated Home Legend
                  • Jul 2014
                  • 2307

                  #84
                  TBH I couldn't see how weather compensation and OT were ever going to work together, unless the weather unit was OT too. My vote would be for weather + BDR91. Sell the OT bridge on.

                  Comment

                  • DBMandrake
                    Automated Home Legend
                    • Sep 2014
                    • 2361

                    #85
                    Originally posted by bruce_miranda View Post
                    TBH I couldn't see how weather compensation and OT were ever going to work together, unless the weather unit was OT too. My vote would be for weather + BDR91. Sell the OT bridge on.
                    If done properly weather compensation should dynamically set the maximum flow temperature limit based on outside temperature, (equivalent to turning the dial manually) and OpenTherm should then be able to modulate the flow temperature from a very low temperature to the current weather compensation maximum limit depending on demand from the HR92's.

                    However it doesn't seem like Viessmann do it right. Big surprise!
                    Originally posted by StephenC View Post
                    Just installed the Viessmann weather compensation unit and connected it up.
                    1. There are none (?)
                    2. Viessmann don't recommend Opentherm & Weather Compensation (wtf?!! I asked this a few weeks ago and got told the opposite!)
                    3. They don't recommend 3rd party Opentherm due to reported interoperability issues.


                    Well, I'm feeling beaten at this point.
                    This does seem like a pretty crap situation, and pretty crap service I have to say. It shouldn't be this difficult - you seem to be a fairly technically inclined person and you still can't get any results from them. I'd be pretty miffed in your situation.
                    Not sure now whether to:

                    1. Go back to bdr91 + Weather compensation (assuming the unit is not faulty) and sell the R8810

                    Or

                    2. Stick it out with Opentherm only and hope that a) the HR92's learn quickly to deal with the high ch flow temps (and therefore close early or send a lower heat demand %), and b) maybe Honeywell will look at this further. I'm not hopeful of b) being possible to be honest. Sell the weather comp unit or give it to family member (most local Gas Safe installers seem to have gravitated around fitting Viessmann boilers over last 6-8 years, so all family members also have Viessmanns)
                    It's my opinion that if you can't manually set a maximum flow temperature that is suitable for your radiators, and can't use weather compensation as a workaround, that the results will never be satisfactory. Overshoots are inevitable no matter how much learning the HR92's do with the current Evohome design, because it always calls for 100% heat demand when even a single zone is 1.5 degrees or more below the set point - which will always give a ridiculously high flow temperature on your system using OpenTherm.

                    In theory Honeywell could add a user configurable upper cap on the heat demand sent to the OpenTherm bridge which in effect would let you limit the maximum flow temperature, (except done at the Evohome instead of the boiler) however it doesn't currently have this feature and I would not be holding my breath for it to be added.

                    So sadly I think your only solution for the time being is to go back to using the BDR91 either with or without weather compensation. Maybe still hang onto the OpenTherm bridge for a bit longer instead of selling it immediately, just in case the situation changes.

                    Poor showing Viessmann.
                    Last edited by DBMandrake; 31 March 2017, 05:27 PM.

                    Comment

                    • paulockenden
                      Automated Home Legend
                      • Apr 2015
                      • 1719

                      #86
                      There's a third option. Out there on the Internet there are plans for devices that monitor/control opentherm connections.

                      I can't see it would be beyond the abilities of a clever person (there are several on this website) to modify one of these to allow it to set a limit on the max temp requested by the R8810 when there's radiator demand.

                      Comment

                      • Rameses
                        Industry Expert
                        • Nov 2014
                        • 446

                        #87
                        Or you could do like the German market does and let evohome operate independently of the boiler + weather control (this is how evohome is used in Germany, no BDR boiler control, just active control of the rads, the boiler is controls by weather comp). But I suspect your home isn't built to German spec insulation standards. In the rest of Europe we have seen a decline in weather comp with better internal sensing. We have seen that the HR92 are able to 'learn' and I am bias so I would say stick with what you have.
                        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

                        • bruce_miranda
                          Automated Home Legend
                          • Jul 2014
                          • 2307

                          #88
                          Originally posted by paulockenden View Post
                          There's a third option. Out there on the Internet there are plans for devices that monitor/control opentherm connections.

                          I can't see it would be beyond the abilities of a clever person (there are several on this website) to modify one of these to allow it to set a limit on the max temp requested by the R8810 when there's radiator demand.
                          I had linked to several OT projects for precisely this. Also if the boiler max is a set-once setting, until power down. Then OT monitor could be used for boiler stats etc.

                          Comment

                          • StephenC
                            Automated Home Guru
                            • Feb 2017
                            • 102

                            #89
                            Thanks all for the suggestions. There are more options there than I had considered in my post.

                            I'm not against, but at the same time not keen on the Opentherm Max ch flow temp value configuration via a different device.

                            I have to bear in mind:

                            1. My wife needs to be able to understand this
                            2. My Gas Safe heating engineer or A N Other if he is not available in the future for some reason also needs to be able to troubleshoot the system

                            I (or my wife/heating engineer) would need to be able to isolate this OT device if I do decide to pursue this route - maybe via a physical switch connected in line with one of the two wires. Does that sound possible? If there is no electrical path, there is no power. With no power, the device cannot send an override max ch boiler temp command as it is off.



                            Another option that the responses you've given has made me think of is:

                            Have both the BDR91 Relay (in theory with WC working) and also the R8810 OT bridge connected to the boiler at the same time......however, leaving the option of which to use via EvoHome binding configuration (which lets face it would take less than a minute to switch)

                            I could carry on trialling OT and letting the HR92s have significant time to learn (albeit little heat demand in the summer - just towel drying after showers etc.).


                            A point I have just remembered from speaking to a very knowledgeable chap @ Honeywell who dealt with my case personally, is that at this time of the year with relatively low and particularly short heat demands, the HR92 learning process will take a lot longer as they don't have enough "experience" to alter the logic being applied. Both this chap and Rameses have both stated now they are confident that the HR92's will learn to cope and that this is not an impossible situation

                            I therefore assume that my HR92's needed longer to learn than the 14-15 days since I switched to R8810 OT Bridge before I saw boiler errors and this had clearly not figured things out yet (at which point the boiler error issue would have messed up any HR92 learning as I had a week of leaving rooms at 21 to "capture" heat whenever the boiler kicked in for a few mins at a time", so they were waiting for heat to come through a lot of the time whilst demanding a fair bit).


                            I would have the option to switch to BDR91 if needed - such as the rads being much too hot for gentle warming needed. Overly hot radiators I'm finding is not that comfortable when it's not that cold at this time of the year, so maybe BDR91 from April 1st to October 1st, and R8810 Opentherm the rest of the time. This would still give HR92's a fair amount of learning time.
                            Last edited by StephenC; 2 April 2017, 08:51 AM.

                            Comment

                            • paulockenden
                              Automated Home Legend
                              • Apr 2015
                              • 1719

                              #90
                              Even if the HR92s do learn, you still have the possibility of dangerously hot radiators. I can't believe they'd never open fully.

                              It's that safety aspect that would worry me most.

                              Comment

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