Help with Evohome / Opentherm / Intergas

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  • top brake
    Automated Home Legend
    • Feb 2015
    • 837

    Originally posted by StephenC View Post
    But boilers (slave) don’t have to set the max ch flow temp according to the OpenTherm spec either!!


    When both sides (master and slave) components of the control system are designed to set no value (which is possible and allowed within the specs - Honeywell/Viessmann) so the control system as a whole is not fit for purpose as has been shown. Finger pointing occurred in both directions in this case, and both were right unbelievably. (Honeywell vs Viessmann). That’s what led me to start assessing OpenTherm itself as a specification.

    OpenTherm specification is flawed as it stands (the version I assessed)

    What I’m saying is the OpenTherm specification must be updated to dictate that one or the other (master or slave) sets a value.

    It’s irrelevant at this point taking about Honeywell EvoHome, Nest or Intergas or Viessmann etc. Fundamentally it’s a spec problem that will manifest itself again and again. Because the spec allows for it.

    P.S. I still think EvoHome with BDR91 is great.

    ;-)

    Stephen
    Boilers have their own control systems that look after ignition, combustion and usually flow. The OpenTherm spec only covers communication between the master and slave.
    Most boilers have the ability to set CH Tmax and DHW Tmax on their control panel.

    Hope this helps
    I work for Resideo, posts are personal and my own views.

    Comment

    • The EVOHOME Shop
      Site Sponsor
      • Dec 2014
      • 483

      Originally posted by Dan_Robinson View Post
      I figured this out the other night buggered if I can remember exactly what it was.... Not fan speed though
      I think it is fan speed in the case of boilers where the fan governs the output of the appliance - I'm sure I have seen the fan speed (ID 15 graph) shown under ID 14 (max modulation value) on the OpenTherm monitor.

      Comment

      • blowlamp
        Automated Home Sr Member
        • Apr 2017
        • 98

        Originally posted by top brake View Post
        Not every boiler allows the ch Tmax to be set. So to avoid conflict Honeywell controls don't try to.

        Remember the best selling OpenTherm thermostat in NL has a Honeywell logo on it... Honeywell are experts in OpenTherm as they invented it...
        I thought I saw a flag in the protocol which communcates whether a device is a master or a slave.

        If the boiler won't allow the CH maximum to be set by the master controller, then it follows that it must be settable at the boiler.
        It would be quite bizarre for a boiler manufacturer to simultaneously deny access to this setting at the master whilst also disabling the setting at the slave.

        Wikipedia states that Honeywell sold the OpenTherm spec for £1 in 1996. That doesn't boost my confidence if it's true.
        Last edited by blowlamp; 13 August 2017, 11:24 AM.

        Comment

        • Dan_Robinson
          Automated Home Ninja
          • Jun 2012
          • 347

          It was sold to be openish source. Do you have faith in Unix? How about Python?

          The controller is supposed to be the master. The boiler is the slave. To be otherwise doesn't make much sense
          Kind Regards - Dan Robinson (Jennings Heating Ltd)

          Comment

          • blowlamp
            Automated Home Sr Member
            • Apr 2017
            • 98

            Originally posted by Dan_Robinson View Post
            It was sold to be openish source. Do you have faith in Unix? How about Python?

            The controller is supposed to be the master. The boiler is the slave. To be otherwise doesn't make much sense

            The only faith I have currently is in Bitcoin.

            Comment

            • mylesm
              Automated Home Guru
              • Nov 2015
              • 153

              Ok Intergas Boiler installed today working great with Evohome and BDR91 as Boiler Relay I have an opentherm bridge on order from Evohomeshop so I just want to check as installer has no idea re Controls and intergas boilers are very rare here I live in Dublin
              I will replace boiler relay with OT Bridge and change Evohome to be opentherm and wire bridge into 11&12 of X4 removing 6&7 and also no switched live into 1 on X2
              This means OT bridge is only control I just want to check Intergas parameters
              Parameter C Step modulation this is default set to 1=Step Mod during CH operation

              It can be set to 2=CH output controlled by OT Controller should I set it to this

              Also Parameter E Min Supply Temp during OT Demand is default 40c is this ok

              Anything Else I need to know before changing to OT Control

              Thanks
              Mylesm

              Comment

              • Dan_Robinson
                Automated Home Ninja
                • Jun 2012
                • 347

                Lower parameter E to 25
                Kind Regards - Dan Robinson (Jennings Heating Ltd)

                Comment

                • mylesm
                  Automated Home Guru
                  • Nov 2015
                  • 153

                  Originally posted by Dan_Robinson View Post
                  Lower parameter E to 25
                  Thanks Dan any idea on Parameter C

                  Comment

                  • Dan_Robinson
                    Automated Home Ninja
                    • Jun 2012
                    • 347

                    I haven't finished playing with it as it's summer. Mine is on 1 at the moment and works fine. Buts it's very hard to test these things in this heat when you're working the hours I am at the moment.
                    Kind Regards - Dan Robinson (Jennings Heating Ltd)

                    Comment

                    • blowlamp
                      Automated Home Sr Member
                      • Apr 2017
                      • 98

                      Originally posted by mylesm View Post
                      Ok Intergas Boiler installed today working great with Evohome and BDR91 as Boiler Relay I have an opentherm bridge on order from Evohomeshop so I just want to check as installer has no idea re Controls and intergas boilers are very rare here I live in Dublin
                      I will replace boiler relay with OT Bridge and change Evohome to be opentherm and wire bridge into 11&12 of X4 removing 6&7 and also no switched live into 1 on X2
                      This means OT bridge is only control I just want to check Intergas parameters
                      Parameter C Step modulation this is default set to 1=Step Mod during CH operation

                      It can be set to 2=CH output controlled by OT Controller
                      should I set it to this

                      Also Parameter E Min Supply Temp during OT Demand is default 40c is this ok

                      Anything Else I need to know before changing to OT Control

                      Thanks
                      Mylesm

                      My boiler manual only shows parameter C as 0 or 1 as options, so basically either off or on.

                      Like Dan, I have parameter E set in the low 20s to take advantage of low flow temperatures, as the days begin to cool off and the heating eases its way, seamlessly, back on.

                      Comment

                      • DBMandrake
                        Automated Home Legend
                        • Sep 2014
                        • 2361

                        Originally posted by blowlamp View Post
                        My boiler manual only shows parameter C as 0 or 1 as options, so basically either off or on.

                        Like Dan, I have parameter E set in the low 20s to take advantage of low flow temperatures, as the days begin to cool off and the heating eases its way, seamlessly, back on.
                        Surely setting the minimum flow temperature as low as 20 is wasteful for electricity use of the pump ?

                        It might be seamless in terms of temperature regulation, but circulating 20 degree water around your radiators in a 20 degree warm room is just pumping water around for the sake of it without actually putting heat into the room. Modern pumps don't use a lot of electricity, but it still adds up if its running all day long when it doesn't really need to.

                        I don't think I would set it any lower than about 30 maybe even 40, so that the pump would not come on until there was some actual demand to put heat into the room. (Consider this setting to be analogous to the "minimum on time" setting when using a boiler relay - it sets a minimum amount of heat required before boiler and pump come on)
                        Last edited by DBMandrake; 23 August 2017, 12:13 PM.

                        Comment

                        • blowlamp
                          Automated Home Sr Member
                          • Apr 2017
                          • 98

                          Originally posted by DBMandrake View Post
                          Surely setting the minimum flow temperature as low as 20 is wasteful for electricity use of the pump ?

                          It might be seamless in terms of temperature regulation, but circulating 20 degree water around your radiators in a 20 degree warm room is just pumping water around for the sake of it without actually putting heat into the room. Modern pumps don't use a lot of electricity, but it still adds up if its running all day long when it doesn't really need to.

                          I don't think I would set it any lower than about 30 maybe even 40, so that the pump would not come on until there was some actual demand to put heat into the room. (Consider this setting to be analogous to the "minimum on time" setting when using a boiler relay - it sets a minimum amount of heat required before boiler and pump come on)
                          Parameter E is the minimum CH supply temperature the boiler will give (settable between 10C - 60C) when there's an accepted call for heat from an OpenTherm control, so if there's no demand, the pump & boiler are off.
                          Whether the call for heat is accepted is determined by parameter E. (known as OpenTherm response) and refers back to parameter E as below.

                          0= ignore OT if < E
                          1= limit OT if < E
                          2= OT on-off

                          The only time I've known the pump to be running without the boiler being lit, is when the OpenTherm controller was asking for a lower flow temperature than the boiler was configured to give under these settings. Probably a small change to the weather compensation curve would eliminate the chances of it happening again.

                          Our radiators are much oversize and able to warm the room with quite modest increases in CH flow temperature above room temperature. Having the option of lower flow temperatures gives us an even environment which we find very comfortable.

                          Comment

                          • mylesm
                            Automated Home Guru
                            • Nov 2015
                            • 153

                            Originally posted by blowlamp View Post
                            Parameter E is the minimum CH supply temperature the boiler will give (settable between 10C - 60C) when there's an accepted call for heat from an OpenTherm control, so if there's no demand, the pump & boiler are off.
                            Whether the call for heat is accepted is determined by parameter E. (known as OpenTherm response) and refers back to parameter E as below.

                            0= ignore OT if < E
                            1= limit OT if < E
                            2= OT on-off

                            The only time I've known the pump to be running without the boiler being lit, is when the OpenTherm controller was asking for a lower flow temperature than the boiler was configured to give under these settings. Probably a small change to the weather compensation curve would eliminate the chances of it happening again.

                            Our radiators are much oversize and able to warm the room with quite modest increases in CH flow temperature above room temperature. Having the option of lower flow temperatures gives us an even environment which we find very comfortable.
                            This is all good stuff the OT response as above what do you have it set for ie 0,1,or 2

                            My Boiler has an option for Parameter C as
                            Parameter C Step modulation this is default set to 1=Step Mod during CH operation

                            It can be set to 2=CH output controlled by OT Controller

                            OT Bridge is on the way so should be interesting to see how it works out

                            mylesm

                            Comment

                            • blowlamp
                              Automated Home Sr Member
                              • Apr 2017
                              • 98

                              Originally posted by mylesm View Post
                              This is all good stuff the OT response as above what do you have it set for ie 0,1,or 2

                              My Boiler has an option for Parameter C as
                              Parameter C Step modulation this is default set to 1=Step Mod during CH operation

                              It can be set to 2=CH output controlled by OT Controller

                              OT Bridge is on the way so should be interesting to see how it works out

                              mylesm
                              I think mine is at its factory setting of 1.

                              Which boiler do you have?

                              Comment

                              • mylesm
                                Automated Home Guru
                                • Nov 2015
                                • 153

                                Originally posted by blowlamp View Post
                                I think mine is at its factory setting of 1.

                                Which boiler do you have?
                                I have Intergas Rapid 25 and it has a setting for parameter C It can be set to 2=CH output controlled by OT Controller

                                What about your Setting for E.
                                0= ignore OT if < E
                                1= limit OT if < E
                                2= OT on-off

                                What is it set for
                                Thanks
                                Mylesm

                                Comment

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