Opentherm to EMS gateway

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  • zxdavb
    Automated Home Guru
    • Jan 2018
    • 106

    Opentherm to EMS gateway

    Hello,

    I have a evohome system that works quite well with a BDR91 to a Worcester Greenstar 30si combi boiler. Unfortunately, the Worcester uses the EMS protocol for modulation rather than OpenTherm.

    I wonder if there is such a thing as an EMS to OpenTherm gateway, and (upon Googling), I have found this: https://en.robbshop.nl/ems-ot-opentherm-converter-nefit

    It is described as: The Nefit / BOSCH EMS IP Converter is capable of converting OpenTherm communication Nefit / BOSCH communication protocols. This allows you to OpenTherm thermostat connected without any problems to your Nefit or BOSCH HR boiler.

    Any ideas if it will work?
  • HenGus
    Automated Home Legend
    • May 2014
    • 1001

    #2
    I haven’t a clue but I am not sure what you are trying to achieve? My reading of the supporting information is that the converter is designed to convert Opentherm information into Worcester Ebus speak. I cannot see how this will give you the benefits of Opentherm. Surely, it would be less risky to stick with the BDR and see if external weather compensation is possible.

    Comment

    • zxdavb
      Automated Home Guru
      • Jan 2018
      • 106

      #3
      Hey thanks for the response.

      My understanding of OpenTherm is that it will call for modulated heat from the boiler (warm, a little hot, very hot, etc), as demand from the smart TRVs fluctuates. I also understand that, in the absence of OpenTherm (or EMS), the boiler is either 100% on, or 100% off. I understand that the boiler compensates for this by waiting for demand to exceed some threshold before the boiler kicks in (i.e. it cycles on/off)...

      I understand also that evohome can send a modulated request using the OpenTherm protocol, but that the combi boiler can only accept modulated requests via EMS.

      I thought that I could stick an OpenTherm to EMS 'gateway' between evohome, and the Worcester combi boiler and I would get a modulated call for heat.

      Of course, I am only new to this, and it is very likely I have misunderstood the material I have read (such as: http://www.honeywelluk.com/Documents..._FINAL_WEB.pdf). Are you saying that a combi boiler can modulate without OpenTherm/EMS (but would have to start at 100% on, I guess)? I guess it would do so on the basis of the temperature of the return water, then? In this case, what is OpenTherm/EMS useful for?

      If you suggest external weather compensation offers an easy win, then I'm all for that!

      Comment

      • HenGus
        Automated Home Legend
        • May 2014
        • 1001

        #4
        My first thoughts were that this was simply a device to connect an Opentherm thermostat to your boiler. In otherwords, it translates/converts Opentherm demands into instructions that your boiler can understand. It doesn’t necessarily follow that your boiler will then react as if it were under full Opentherm control. I could well be wrong.

        Comment

        • zxdavb
          Automated Home Guru
          • Jan 2018
          • 106

          #5
          Isn't it simply the case that each zone's thermostat sends a signal to the evohome hub, which resolves those against a schedule, and tells the TRVs to open, and the boiler to provide hot water?

          All I wanted was for the conversation from the evohome hub to the boiler be modulated rather than cycled, as per:
          evohome hub ----> R8810 --(OT protocol)--> OT/EMS gateway --(EMS protocol)--> Boiler.

          Comment

          • StephenC
            Automated Home Guru
            • Feb 2017
            • 102

            #6
            This was also brought up in a new post a few weeks back:



            I looked through the links and it does seem viable, however you’re taking a risk really for minimal gain.

            Stick to the TPI based BDR91 on/off control if you’re risk averse. It does a great job simulating variable flow temps with the constraint of the max CH flow temp the boiler is set at (just not as quick to react as OpenTherm).

            That said if you’re willing to take the risk with ordering the part (don’t take a risk with gas or electrics...) and have it fitted, then please feed back and let us know how it goes.

            Comment

            • zxdavb
              Automated Home Guru
              • Jan 2018
              • 106

              #7
              Originally posted by StephenC View Post
              ... if you’re willing to take the risk ...
              The main problem is I'd have to pay a man to connect it.

              Still, I'd be tempted if the economy benefits were to be had? Or is there not much in it?

              Comment

              • HenGus
                Automated Home Legend
                • May 2014
                • 1001

                #8
                I would say that there is not much in it in terms of usage savings. Long term benefits re boiler life etc are an unknown. I should add that once all zones are up to their set temperatures there is very little variation UNLESS a zone set temperature is changed or, in my case, the system switches over to hot water priority.
                Last edited by HenGus; 31 January 2018, 05:52 PM.

                Comment

                • Wlife
                  Automated Home Lurker
                  • Jan 2020
                  • 8

                  #9
                  Originally posted by HenGus View Post
                  I would say that there is not much in it in terms of usage savings. Long term benefits re boiler life etc are an unknown. I should add that once all zones are up to their set temperatures there is very little variation UNLESS a zone set temperature is changed or, in my case, the system switches over to hot water priority.
                  hi I tried this cant get to work correctly though tried many wiring configs Opentherm cant fire the boiler

                  Comment

                  • zxdavb
                    Automated Home Guru
                    • Jan 2018
                    • 106

                    #10
                    I have connected this device to my Worcester GreenStar, just plugged it into the EMS bus, and a two-wire to the Honeywell R8810A (I unbound the BDR91A, but left it place). Worked first go.
                    Last edited by zxdavb; 22 October 2021, 09:34 PM.

                    Comment

                    • bruce_miranda
                      Automated Home Legend
                      • Jul 2014
                      • 2307

                      #11
                      From my experience of these "man in middle" devices (I too use a VR33 on my Vaillant) is that you are completely dependent on the OT translation implementation within that device.
                      e.g. I have noticed a strange behaviour when I query the outdoor temperature via my OT gateway. Whereas that same data point is fine on the native eBUS side. This can only mean the VR33 is screwing things up in the middle.

                      Having said that, when it works, it works brilliantly.

                      Comment

                      • Wlife
                        Automated Home Lurker
                        • Jan 2020
                        • 8

                        #12
                        hi @zxdavb any chance you could share some photos or wiring diagram please. I think someone said I may not have set it up correctly on the evohome controller rather than wired it wrong. Did you treat it as a fresh install on the controller and start from scratch?

                        Comment

                        • Securitybyte
                          Automated Home Jr Member
                          • Jan 2016
                          • 19

                          #13
                          I saw this thread when it started and have just come across it again. Pleased to see it has some updates.

                          @zxdavb, I'd love to know if you noticed any benefits or got the improvements you hoped for?

                          Comment

                          • MadeTomatoHue
                            Automated Home Jr Member
                            • Nov 2022
                            • 47

                            #14
                            Just joined, so not sure I've found the best thread to mention this yet...

                            I've been looking for a way to manage our Worcester Greenstar boiler's flow temperature in line with heat demand. I've got started on using ramses_rf to understand what is available, and reimplementing relevant bits in a little utility program to run on my broadband router under OpenWRT. General concept is that it will keep track via the HGI80 I have plugged in of messages saying whether DHW or CH load is needed, and then use a BBQKees EMS gateway to control the boiler flow temp.

                            I'd expect that some automaters might want to use an opensource OpenTherm device rather than EMS, so bearing that in mind and to hint at the general functionality I'm calling it EvoTherm for now.

                            Comments on how this could be done already to save me the trouble, what I might be missing, better places to discuss the concept, etc would be welcomed.

                            Comment

                            • bruce_miranda
                              Automated Home Legend
                              • Jul 2014
                              • 2307

                              #15
                              Why not just use the already built OT to EMS interface with the Honeywell OT Bridge?
                              Opentherm Convertor✅ Maak Je Verwarming Slim✅ Vandaag Besteld Morgen In Huis✅

                              Comment

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