Evohome + Opentherm v Evohome + Boiler Outside Weather Compensation

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  • paulockenden
    Automated Home Legend
    • Apr 2015
    • 1719

    #61
    Bruce_miranda,

    One thing to note is that in the diagrams you posted, and I've seen this in a lot of the official schematics, the pump APPEARS to be controlled from the heating valves. It's not obvious that the connection between the junction box and the boiler is two way, and that the pump signal comes from the boiler, up to the junction box, and then back down to the pump.

    In my versions I made it explicitly clear that the pump is controlled by the boiler. However, that control might (in fact, probably would) still be via the junction box.

    I was just trying to make it more obvious how things actually work.

    P.

    Comment

    • paulockenden
      Automated Home Legend
      • Apr 2015
      • 1719

      #62
      Originally posted by HenGus View Post
      Am I missing something?
      What happens when your heating is off, and your hot water comes on? I bet your heating valve opens...

      You may even have it double bound.

      P.

      Comment

      • top brake
        Automated Home Legend
        • Feb 2015
        • 837

        #63
        Originally posted by bruce_miranda View Post

        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.
        yes that is correct
        I work for Resideo, posts are personal and my own views.

        Comment

        • bruce_miranda
          Automated Home Legend
          • Jul 2014
          • 2307

          #64
          Now that I understand, the CH motorised zone valve is actually redundant in a system with HR92s. In fact until you introduce OpenTherm into the equation, it doesn't matter if you control the Boiler Directly via the Boiler Demand relay or control the zone valve (which in turn calls the boiler) via the Boiler Demand relay.

          Infact in an S Plan system with HR92s @HenGus would have wired the Boiler Demand relay to the CH zone valve, so that whenever there is Boiler demand, it's the CH valve that opens and fires the boiler.

          I now need confirmation if by adding Opentherm as my Boiler Demand device will it also handle Boiler Demand for Hot Water too? Because now none of the zone valves will be able to fire up the boiler.
          Last edited by bruce_miranda; 4 April 2016, 03:44 PM.

          Comment

          • HenGus
            Automated Home Legend
            • May 2014
            • 1001

            #65
            Originally posted by paulockenden View Post
            What happens when your heating is off, and your hot water comes on? I bet your heating valve opens...

            You may even have it double bound.

            P.
            It doesn't. Heating is off at the moment and has been most evenings this week. Water heats up to the set temperature and everything shuts down.

            Comment

            • paulockenden
              Automated Home Legend
              • Apr 2015
              • 1719

              #66
              It matters inasmuch as there's a delay between the BDR91 switching and the boiler firing, because the latter doesn't happen until the valve has fully opened. So it messes with the fancy minimum on time settings etc.

              Comment

              • top brake
                Automated Home Legend
                • Feb 2015
                • 837

                #67
                Originally posted by bruce_miranda View Post
                Now that I understand, the CH motorised zone valve is actually redundant in a system with HR92s. In fact until you introduce OpenTherm into the equation, it doesn't matter if you control the Boiler Directly via the Boiler Demand relay or control the zone valve (which in turn calls the boiler) via the Boiler Demand relay.

                Infact in an S Plan system with HR92s I would actually wire the Boiler Demand relay to the CH zone valve, so that whenever there is Boiler demand, it's the CH valve that opens and fires the boiler.

                I now need confirmation if by adding Opentherm as my Boiler Demand device will it also handle Boiler Demand for Hot Water too? Because now none of the zone valves will be able to fire up the boiler.

                yes it will handle heating and hot water demands concurrently

                it will fire the boiler to the maximum heat demand

                if you want to configure hot water priority you can connect the A terminal on the CH BDR to the C terminal on the DHW BDR

                make sense?

                this will give the advantage of ensuring that the heating flow temperature is at it's lowest possible (heating will be effectvely isolated when DHW cylinder is charging).
                I work for Resideo, posts are personal and my own views.

                Comment

                • bruce_miranda
                  Automated Home Legend
                  • Jul 2014
                  • 2307

                  #68
                  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).
                  How would you bind a single BDR91 to multiple zones calling for heat. I thought you couldn't hence why the separate Boiler Demand function in the System Devices. Are you saying there is a way to have the BDR91 bound for heat only demand to control a zone valve and not be bound as a Boiler Demand device?

                  Comment

                  • paulockenden
                    Automated Home Legend
                    • Apr 2015
                    • 1719

                    #69
                    Originally posted by bruce_miranda View Post
                    Are you saying there is a way to have the BDR91 bound for heat only demand to control a zone valve and not be bound as a Boiler Demand device?
                    Yes, exactly that. If you go through guided configuration for 'Sundial' systems it gives you the option to bind both DHW and CH relays.

                    P.

                    Comment

                    • bruce_miranda
                      Automated Home Legend
                      • Jul 2014
                      • 2307

                      #70
                      Ok stay with me for a little longer because I am again confused.

                      Firstly the Sundials - System Devices have been removed from the new Wifi evohome controllers.

                      Lets assume you had two radiators and one HW cylinder. These were previously connected via an S Plan system.

                      The HW motorised valve opened when the HW was needed. The CH motor valve was opened when the radiators were needed. These were generally controlled from a 2 channel time clock.

                      Now you were upgrading to evohome.

                      You put two HR92s on the radiators. You put the HW kit in.

                      How would you connect the two BDR91s in a way that when the HW was needed, it would open the HW zone valve and fire the boiler. And when either of the two HR92s needed heat, it would open the CH zone valve and fire the boiler?

                      I thought the only way to do this was to wire the HW BDR91 to the HW zone valve and bind it as the HW acuator.
                      Wire the CH BDR91 to the CH zone valve and bind it as the Boiler Demand relay. The reason being, there is was no single acuator for all heating demands coming from the various HR92s except for using the Boiler Demand Relay function.

                      Comment

                      • HenGus
                        Automated Home Legend
                        • May 2014
                        • 1001

                        #71
                        Originally posted by bruce_miranda View Post
                        Ok stay with me for a little longer because I am again confused.

                        Firstly the Sundials - System Devices have been removed from the new Wifi evohome controllers.

                        Lets assume you had two radiators and one HW cylinder. These were previously connected via an S Plan system.

                        The HW motorised valve opened when the HW was needed. The CH motor valve was opened when the radiators were needed. These were generally controlled from a 2 channel time clock.

                        Now you were upgrading to evohome.

                        You put two HR92s on the radiators. You put the HW kit in.

                        How would you connect the two BDR91s in a way that when the HW was needed, it would open the HW zone valve and fire the boiler. And when either of the two HR92s needed heat, it would open the CH zone valve and fire the boiler?

                        I thought the only way to do this was to wire the HW BDR91 to the HW zone valve and bind it as the HW acuator.
                        Wire the CH BDR91 to the CH zone valve and bind it as the Boiler Demand relay. The reason being, there is was no single acuator for all heating demands coming from the various HR92s except for using the Boiler Demand Relay function.
                        I am waiting with interest for the answer as well. If I go into the new Device Settings, there are 3 options: Boiler Relay, Opentherm and None. None does nothing, and I do not have Opentherm. With Boiler Relay configured, the motorised valve opens when I turn up the target temperature, and the motorised valve closes when I turn the target temperature down. With HW set to On, the motorised valve for the HW opens and CH valve stays closed.

                        Comment

                        • bruce_miranda
                          Automated Home Legend
                          • Jul 2014
                          • 2307

                          #72
                          Originally posted by HenGus View Post
                          I am waiting with interest for the answer as well. If I go into the new Device Settings, there are 3 options: Boiler Relay, Opentherm and None. None does nothing, and I do not have Opentherm. With Boiler Relay configured, the motorised valve opens when I turn up the target temperature, and the motorised valve closes when I turn the target temperature down. With HW set to On, the motorised valve for the HW opens and CH valve stays closed.
                          And this is how I thought it was supposed to work. That was until people said there is a way to configure the BDR91 to open the CH zone valve for ANY heat demand from the various HR92s, WITHOUT using the System Devices->Boiler Demand->Boiler Relay option.

                          Comment

                          • HenGus
                            Automated Home Legend
                            • May 2014
                            • 1001

                            #73
                            Originally posted by bruce_miranda View Post
                            And this is how I thought it was supposed to work. That was until people said there is a way to configure the BDR91 to open the CH zone valve for ANY heat demand from the various HR92s, WITHOUT using the System Devices->Boiler Demand->Boiler Relay option.
                            I recall having this discussion with my Honeywell-trained installer. There were two options: one, was to de-activate the CH zone valve, remove it or disable it in the OPEN position. Two, was to use the existing CH zone valve controlled via the BDR. I think that he went for Option 2 because it was easier to do. I recall as he flashed through the settings he mentioned boiler on times and cycle rates. No mention was made of a third way and I can find no reference to it in the installation guide. Heating and HW have been working fine for 5 days now.

                            Comment

                            • bruce_miranda
                              Automated Home Legend
                              • Jul 2014
                              • 2307

                              #74
                              @HenGus Can you please confirm how your system is wired and bound.

                              As I understand your HW BDR is bound as the HW acuator and that switches on the HW zone valve, which in turn fires the boiler via the wired junction box.

                              Your CH BDR is bound as a System Device->Boiler Demand->Wireless Boiler Relay. That switches on the CH zone valve, which in turn fires the boiler via the wired junction box.

                              But as if you are sure that the CH zone valve doesn't open when your HW only is requesting heat then surely there is a difference between using a Wireless Boiler Relay as opposed to an OpenTherm Bridge. @top brake is sure that the OpenTherm bridge fires the boiler for ANY heat demand rather than what you are seeing where HW and CH are being opened independently.

                              Comment

                              • HenGus
                                Automated Home Legend
                                • May 2014
                                • 1001

                                #75
                                My system is as you describe. Two motorised valves and 2 BDRs. The HW BDR was part of the HW kit connected to an unvented system. When Paul suggested that something was amiss, I went up stairs with controller in hand and turned on the HW. The BDR light illuminated and the valve opened. The HW valve remained shut. I repeated the exercise with the Htg BDR and the valve motored and the HW valve remained shut. At this point, it got tricky as both outlet pipes were hot.

                                I have just been up again. The HW is ON on the Evohome timer and the BDR green light is ON. The Htg BDR green valve is OFF and the CH motorised valve is closed. As I type, the Hot water has just reached temperature, the BDR green light has gone OFF and the motorised valve has closed. The pump and boiler have shut down.

                                Comment

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