OpenTherm control behaviour

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  • kimber.kimber
    Automated Home Sr Member
    • Jan 2017
    • 89

    #61
    I sent an email to Ideal last night. Will be reasonably annoying if their selling it as open therm compatible and it's not really. I guess by running a BDR91 to control the boiler, I'd at least be able to limit the temperature flow.

    Already feel a little suckered with the boiler as the modulation is not what I expected. My fault as I should have dug into the specific specs of the boiler, rather than just go off the marketing material of "up to 7:1"! .

    Comment

    • HenGus
      Automated Home Legend
      • May 2014
      • 1001

      #62
      I confess that with Opentherm control I am not really sure what to expect. I have gone out to look at the boiler settings when there was little heat demand only to find the boiler running at 70/67C. I have also seen the boiler return temperature as low as 47C.

      I have asked Evohome Technical Support for more information about what the homeowner should expect with Opentherm control as I think that this level of detail would be helpful.

      What is clear though is that my daily heating costs are significantly down. I suspect that this is more to do with a new boiler rather than Opentherm.

      Edit: Thinking about it a bit more. The real question in my mind is 'how do boiler modulation and return temperature work? Is the boiler more efficient running with, say, a 24kW output, but at a low return temperature, or a 5kW output with a 67C return temperature? This must be part of the conversation that Evohome has with the boiler under Opentherm.
      Last edited by HenGus; 23 April 2017, 12:02 PM.

      Comment

      • bruce_miranda
        Automated Home Legend
        • Jul 2014
        • 2307

        #63
        How far does the flow temperature knob or setting go to? I.e. is 75C the max or can your boiler go higher than that?

        And what's the difference between setting by the knob or the menus?

        Comment

        • kimber.kimber
          Automated Home Sr Member
          • Jan 2017
          • 89

          #64
          Maximum temperature is 80, and I've not seen it get that high.

          Menu setting is there to limit what the knob can do i.e. If the menu is set to 60, it can never be adjusted higher than that with the knob in the front. However if the menu is set to 80, and the knob to 60, anyone could turn it up at any point. I'm guessing to limit how much fiddling kids etc could do.

          Comment

          • bruce_miranda
            Automated Home Legend
            • Jul 2014
            • 2307

            #65
            OK the Vaillant boilers are similar. They have an installer menu that determines how high the knob will go to.
            So what is set to 75C? Is either the knob or the installer set to 75C. Are you sure it stops at 75C and doesn't rise any more? The reason I ask this is if the knob is set to 60 and the temperature is rising to 75C then something is stopping the temperature at 75C, if indeed the physical max is 80C. It's important you understand because when you add HW, your boiler is going to run at max when there is HW demand. What is max in your instant is looking like a guessing game.

            Comment

            • kimber.kimber
              Automated Home Sr Member
              • Jan 2017
              • 89

              #66
              Nope, both are set to 60. I say I haven't seen it get to 80, but I must admit I haven't camped in the airing cupboard when the heating is just coming on. Perhaps I need to do this!

              Will feedback when Ideal come back to me.

              Comment

              • dty
                Automated Home Ninja
                • Aug 2016
                • 489

                #67
                Originally posted by kimber.kimber View Post
                I haven't camped in the airing cupboard when the heating is just coming on.
                You have Evohome and OpenTherm and you haven't done this?! Very odd...

                Comment

                • HenGus
                  Automated Home Legend
                  • May 2014
                  • 1001

                  #68
                  I 'camped out' next to the boiler this morning to monitor the boiler operating parameters. Interestingly, even though the boiler flow temperature is set to 70C (or so I thought - via the installer menu as the Atag has no mechanical controls), it rose and remained steady at 74C for about 10 minutes; HOWEVER, a boiler parameter called Calculated Flow Temperature (T-Set) remained steady and fixed on 70C until the raw boiler flow temperature started to fall away as the radiators got hot.


                  A0 Flow water temperature in °C

                  A1 Return water temperature in °C

                  A2 DHW temperature (only with 3 port diverter kit) in °C

                  A3 T-set temperature (calculated) in °C

                  A4 Flue gas temperature (only if a ue gas sensor is connected) in °C

                  A5 Outside temperature (only if an outside sensor is connected) in °C

                  A6 Water pressure in bar

                  A7 n.a.

                  A8 Ionisation current in mA.

                  A9 rpm of fan (x100)


                  The above would seem to be confirmed in this set up table:

                  1. CH Tmax: 80°C; Gradient: 5; Heating line 24

                  2. CH Tmax: 70°C; Gradient: 5; Heating line 19 (My present set up)

                  3. CH Tmax: 60°C; Gradient: 4; Heating line 15

                  4. CH Tmax: 50°C; Gradient: 3; Heating line 11

                  Conclusion, my boiler is being controlled by Opentherm to a T-Set (Max) temperature not the raw flow temperature. Might this be the same for other boilers? Hence, the 'overshoots' might in fact be part of the normal operation of the boiler.

                  Comment

                  • bruce_miranda
                    Automated Home Legend
                    • Jul 2014
                    • 2307

                    #69
                    Your ATAG seems fine. And the OT bridge is atleast respecting a max value. Be it called Tmax etc which are boiler specifics. Overshoots of a few degrees are perfectly normal and to be expected. Anything over 5C is suspicious and 10C is an issue.

                    Comment

                    • HenGus
                      Automated Home Legend
                      • May 2014
                      • 1001

                      #70
                      Originally posted by bruce_miranda View Post
                      Your ATAG seems fine. And the OT bridge is atleast respecting a max value. Be it called Tmax etc which are boiler specifics. Overshoots of a few degrees are perfectly normal and to be expected. Anything over 5C is suspicious and 10C is an issue.
                      fair enough. I just thought that I would add my experience to the mix.

                      Comment

                      • kimber.kimber
                        Automated Home Sr Member
                        • Jan 2017
                        • 89

                        #71
                        Originally posted by HenGus View Post
                        Conclusion, my boiler is being controlled by Opentherm to a T-Set (Max) temperature not the raw flow temperature. Might this be the same for other boilers? Hence, the 'overshoots' might in fact be part of the normal operation of the boiler.
                        Cheers for the information. Very informative.

                        Are these all things you can read from the boiler display, or are they read through a PC?

                        Interestingly I've reset the max temps to 60 degrees on the installer menu and 50 on the knob and I'm seeing steady temps of 54 degrees or so. Also when I reported temps of 75 degrees the other night, the temperature did drop back after the rad was warm.

                        I'm going to try and keep an eye on it over the next week or so and see what happens - heating comes on early, so I'm going to try and watch it when I'm off on Friday afternoon. Hopefully Ideal will also come back with some information.
                        Last edited by kimber.kimber; 24 April 2017, 09:35 AM.

                        Comment

                        • DBMandrake
                          Automated Home Legend
                          • Sep 2014
                          • 2361

                          #72
                          Originally posted by dty View Post
                          You have Evohome and OpenTherm and you haven't done this?! Very odd...
                          I don't even have OpenTherm and I have camped out in the boiler cupboard multiple times to check and confirm various aspects of system functioning...

                          Comment

                          • HenGus
                            Automated Home Legend
                            • May 2014
                            • 1001

                            #73
                            Originally posted by kimber.kimber View Post
                            Cheers for the information. Very informative.

                            Are these all things you can read from the boiler display, or are they read through a PC?

                            Interestingly I've reset the max temps to 60 degrees on the installer menu and 50 on the knob and I'm seeing steady temps of 54 degrees or so. Also when I reported temps of 75 degrees the other night, the temperature did drop back after the rad was warm.

                            I'm going to try and keep an eye on it over the next week or so and see what happens - heating comes on early, so I'm going to try and watch it when I'm off on Friday afternoon. Hopefully Ideal will also come back with some information.
                            LCD on the boiler. I understand that if an Atag One controller is fitted, the boiler can be monitored on a remote device.

                            Comment

                            • kimber.kimber
                              Automated Home Sr Member
                              • Jan 2017
                              • 89

                              #74
                              Originally posted by DBMandrake View Post
                              I don't even have OpenTherm and I have camped out in the boiler cupboard multiple times to check and confirm various aspects of system functioning...


                              Oh don't get me wrong, the missus is starting to go be me funny looks for the amount of time I'm spending looking at the boiler. I've just not been there on start up!
                              Last edited by kimber.kimber; 24 April 2017, 09:15 PM.

                              Comment

                              • bruce_miranda
                                Automated Home Legend
                                • Jul 2014
                                • 2307

                                #75
                                Another way check is to run the Custom Quick Action with all zones set to 30C. See what the boiler gets to then. It shouldn't go past what you have set as max, but will run at that max set forever.

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