Evohome + Opentherm v Evohome + Boiler Outside Weather Compensation

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  • bruce_miranda
    Automated Home Legend
    • Jul 2014
    • 2307

    #46
    Lets start with a standard S Plan evohome system.

    One BDR91 is bound as a Hot Water controller. This is triggered whenever the evohome needs HW. The BDR91 triggers the HW zone valve which in turn fires the boiler. The other BDR91 is bound as a System Device in Boiler Demand Relay. This is triggered whenever any radiator needs heat. The BDR91 triggers the CH zone valve which in turn fires the boiler.

    So far so good?

    Now when I add OpenTherm to this. How do things change?

    I didn't think I could use both an Opentherm bridge as well as a Boiler Relay for Boiler Demand?

    Comment

    • top brake
      Automated Home Legend
      • Feb 2015
      • 837

      #47
      Originally posted by bruce_miranda View Post
      Lets start with a standard S Plan evohome system.

      One BDR91 is bound as a Hot Water controller. This is triggered whenever the evohome needs HW. The BDR91 triggers the HW zone valve which in turn fires the boiler. The other BDR91 is bound as a System Device in Boiler Demand Relay. This is triggered whenever any radiator needs heat. The BDR91 triggers the CH zone valve which in turn fires the boiler.

      So far so good?

      Now when I add OpenTherm to this. How do things change?

      I didn't think I could use both an Opentherm bridge as well as a Boiler Relay for Boiler Demand?

      The OpenTherm bridge is used instead of the Boiler Relay

      The Hot water BDR opens the hot water zone valve at S Plan system layer, the heating BDR opens the S Plan heating valve
      The third BDR91 is for your UFH zone at zone layer
      I work for Resideo, posts are personal and my own views.

      Comment

      • bruce_miranda
        Automated Home Legend
        • Jul 2014
        • 2307

        #48
        I understand the HW and the UFH zone valve wiring and BDR91 binding because that is very simple. It both cases the BDR91 is bound as the actuator which in turn opens the relevant zone valve. The Opentherm bridge will now independently fire up the Boiler because it too knows there is heating demand.

        What I don't understand yet is the CH zone valve wiring and BDR91 binding. I thought that the whole point of a "System Device Boiler Relay" was so that if any radiator or HW needs heat it would trigger the boiler relay.

        Now if I replace the boiler relay with the Opentherm, the Boiler Demand is handled by the Opentherm, so the boiler will start up. But how will the CH zone valve open when there is CH demand? How do I bind the CH zone valve BDR91? I can't bind it as a Boiler Demand System Device because that is now the Opentherm bridge. So what options to I use to make sure that the CH zone valve opens whenever any of the TRV zones need heat.

        Comment

        • paulockenden
          Automated Home Legend
          • Apr 2015
          • 1719

          #49
          Is the confusion because in an S-Plan system you don't (normally) HAVE a boiler relay? So there's nothing to replace?

          There's an alternative method of wiring / configuration where you lock the CH 2 way valve open, and then you can use a BDR91 as a boiler relay. Of course this only works if you have HR92s on all of your rads.

          I'm assuming that this is the starting point when upgrading to OpenTherm?

          P.

          Comment

          • bruce_miranda
            Automated Home Legend
            • Jul 2014
            • 2307

            #50
            That has actually confused me even more!

            I thought in a S plan evohome system you would have 2 BDR91

            1. One BDR91 would work the HW zone valve. The HW zone valve would in turn fire the boiler via the Orange wire. This BDR91 is bound to the evohome controller as the HW kit's acuator.
            2. The second BDR91 would be bound as a "System Device" boiler relay. This would open the CH zone valve. The CH zone valve would in turn fire the boiler via its Orange wire. The idea behind binding the BDR91 as a 'System Device' for CH was so that ANY radiator demanding heat would be able to fire the boiler as the evohome controller would collate the multiple requests.

            Moving to Opentherm.

            I disconnect the second BDR91. I connect the Opentherm bridge to the boiler via the Opentherm connection. I replace the "System Device" binding from Boiler Relay to Opentherm bridge. All good so far. But because of the disconnected second BDR91, who opens the CH zone valve when there is radiator heating demand?

            Comment

            • paulockenden
              Automated Home Legend
              • Apr 2015
              • 1719

              #51
              'Conventional' S-Plan setup is 2 x BDR91s, one controls the HW valve, the other the CH valve. And then it's the output FROM THE VALVES that fire the boiler. There's no direct Evohome connection to the boiler. There is NO boiler relay.

              'Alternative' S-Plan setup (only if you have HR92s on all of your rads) is you lock the CH valve so that it is always open, and have one BRD91 for the HW (as above), and the other bound as a boiler relay.

              Does that helps?

              I'm assuming that for Opentherm you start from this 'alternative' setup, and replace the boiler relay with the OT Bridge.
              Last edited by paulockenden; 4 April 2016, 12:00 PM. Reason: typo

              Comment

              • bruce_miranda
                Automated Home Legend
                • Jul 2014
                • 2307

                #52
                So in the "Conventional" S-Plan setup. How do you bind the BDR91 for the CH valve?

                Comment

                • top brake
                  Automated Home Legend
                  • Feb 2015
                  • 837

                  #53
                  Originally posted by bruce_miranda View Post
                  I understand the HW and the UFH zone valve wiring and BDR91 binding because that is very simple. It both cases the BDR91 is bound as the actuator which in turn opens the relevant zone valve. The Opentherm bridge will now independently fire up the Boiler because it too knows there is heating demand.

                  What I don't understand yet is the CH zone valve wiring and BDR91 binding. I thought that the whole point of a "System Device Boiler Relay" was so that if any radiator or HW needs heat it would trigger the boiler relay.

                  Now if I replace the boiler relay with the Opentherm, the Boiler Demand is handled by the Opentherm, so the boiler will start up. But how will the CH zone valve open when there is CH demand? How do I bind the CH zone valve BDR91? I can't bind it as a Boiler Demand System Device because that is now the Opentherm bridge. So what options to I use to make sure that the CH zone valve opens whenever any of the TRV zones need heat.
                  the S Plan heating valve BDR91 is bound during guided configuration on the hot water path
                  the CH zone vale than automatically opens whenever there is a heat zone demand

                  have you taken the www.youlearn.honeywell.uk.com online training, this should help your understanding
                  I work for Resideo, posts are personal and my own views.

                  Comment

                  • bruce_miranda
                    Automated Home Legend
                    • Jul 2014
                    • 2307

                    #54
                    Yes I have been through the online training.

                    Like I said I understand the HW part fine. It's the CH part that I don't understand.

                    How is the CH BDR91 bound to the evohome in a normal S plan? Is it bound via the System Devices Boiler Demand Boiler Relay or some other way?

                    Comment

                    • top brake
                      Automated Home Legend
                      • Feb 2015
                      • 837

                      #55
                      Originally posted by bruce_miranda View Post
                      Yes I have been through the online training.

                      Like I said I understand the HW part fine. It's the CH part that I don't understand.

                      How is the CH BDR91 bound to the evohome in a normal S plan? Is it bound via the System Devices Boiler Demand Boiler Relay or some other way?
                      the S Plan heating valve BDR91 is bound during guided configuration on the hot water path
                      the CH zone vale than automatically opens whenever there is a heat zone demand
                      I work for Resideo, posts are personal and my own views.

                      Comment

                      • bruce_miranda
                        Automated Home Legend
                        • Jul 2014
                        • 2307

                        #56
                        I re-looked at the training demos again. I think that when you use the radiator TRV valves you are not supposed to use a CH zone valve as well but instead control the boiler directly via the Boiler demand. And if you have a CH zone valve you need to have it open all the time.

                        115438_4xGraphics5.jpg

                        The only time you would have both HW and CH zone valves is only if you had only 2 zones i.e. HW and CH (whole house). i.e. a bog standard S Plan (or Y plan).

                        115438_4xGraphics2.jpg

                        Ok back to the Opentherm question then. Will the Opentherm bridge operate the Boiler for any demand? Be it Hot Water, Radiator or (in my case) the UFH zone valve? The reason I ask is because I will now fully relying on the Opentherm to start the boiler. The BDR91s will only be operating the motorised zone valves, which will have their Orange wires disconnected from the boiler.
                        Last edited by bruce_miranda; 4 April 2016, 02:12 PM.

                        Comment

                        • HenGus
                          Automated Home Legend
                          • May 2014
                          • 1001

                          #57
                          Originally posted by bruce_miranda View Post
                          So in the "Conventional" S-Plan setup. How do you bind the BDR91 for the CH valve?
                          Read the advice at The Evohome Shop - Help. I have a 2 valve system with 2 BDR91s. All radiators have HR92s. CH is turned on by a Zone calling for heat which, in turn, activates the BDR91 to open the CH zone valve. Knowing very little about CH, I consider the BDR91 to work in the same way as my old Hall thermostat. It clicks, the zone valve opens and the boiler comes on.

                          The confusion - as explained by Richard - is Honeywell's choice of terminology. The BDR91 that controls the CH has to be configured in the controller as a Boiler Relay.

                          The alternative is to leave the CH zone valve open and the use the BDR91 to control the boiler whenever a zone demands heat.

                          Comment

                          • paulockenden
                            Automated Home Legend
                            • Apr 2015
                            • 1719

                            #58
                            Originally posted by HenGus View Post
                            The BDR91 that controls the CH has to be configured in the controller as a Boiler Relay.
                            I think that's wrong.

                            In the setup you've described ("CH is turned on by a Zone calling for heat which, in turn, activates the BDR91 to open the CH zone valve") it's important that the CH BDR91 *isn't* configured as a boiler relay. (In an S-Plan setup).
                            Last edited by paulockenden; 4 April 2016, 02:44 PM. Reason: Clarity

                            Comment

                            • paulockenden
                              Automated Home Legend
                              • Apr 2015
                              • 1719

                              #59
                              I think I've got these right:

                              evo-s-conventional.jpg

                              evo-s-alternative.jpg

                              (I've never seen an official version of the second one).

                              Note that in the alternative version the boiler is controlled by the boiler relay, not the valve outputs.

                              P.
                              Last edited by paulockenden; 4 April 2016, 03:19 PM.

                              Comment

                              • HenGus
                                Automated Home Legend
                                • May 2014
                                • 1001

                                #60
                                Originally posted by paulockenden View Post
                                I think that's wrong.

                                In the setup you've described ("CH is turned on by a Zone calling for heat which, in turn, activates the BDR91 to open the CH zone valve") it's important that the CH BDR91 *isn't* configured as a boiler relay. (In an S-Plan setup).
                                Now - I am confused. when I changed the controller I just copied what my Honeywell Specialist Installer did when he set up the system, and when he replaced the controller a year ago. If I look in System Devices - it shows that the Boiler is controlled via a 'Wireless Relay Box'. When heating is demanded, I can hear the Zone valve open followed by the boiler coming on. When heating is no longer need, the BDR clicks and the zone valve closes. My system has been working like this now for nearly two years. Am I missing something?

                                Comment

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