Evohome + Opentherm v Evohome + Boiler Outside Weather Compensation

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  • MadeTomatoHue
    Automated Home Jr Member
    • Nov 2022
    • 47

    Originally posted by bruce_miranda View Post
    The Evohome V3 contllers use the Internet weather services for outdoor temperature, which it uses for smart weather compensation...
    Is there any way to disable Evohome's weather compensation? If it is used to adjust TPI ratios then I suspect that will fight with the boiler flow temperature weather compensation that I'm doing via EMS. Disabling any change to boiler firing cycles might help keep loger, steadier burns.

    Having said that I've been very pleased with overall performance the last couple of days with flow temperatures dynamically nudged down to ~50C still keeping rooms at the targeted temperature despite anything Evohome might also be doing . Probably took a little longer to heat them up this morning, but as I shift more towards using load compensation to select flow temperature that might go away.

    Comment

    • bruce_miranda
      Automated Home Legend
      • Jul 2014
      • 2307

      You can turn off the smart weather features you don't want. And to be fair, smart weather isn't messing with the TPI directly, it is adjusting the Setpoints. And in doing that the Heat demand is adjusted accordingly.
      TPI is built into the firmware of the BDR91, it cannot be turned off. It can simply be adjusted to the levels allowed via the UI on the controller. Hence the workaround that I published to keep the BDR91 open using an HGI80 paired directly to the BDR91.

      Comment

      • G4RHL
        Automated Home Legend
        • Jan 2015
        • 1580

        I assume there is no way to link your own outside sensor to Evohome? No point my using the inbuilt setting as it is often 2 degrees out.

        Comment

        • bruce_miranda
          Automated Home Legend
          • Jul 2014
          • 2307

          Originally posted by G4RHL View Post
          I assume there is no way to link your own outside sensor to Evohome? No point my using the inbuilt setting as it is often 2 degrees out.
          No and it is one of thr things I miss from the old V2 controller days

          Comment

          • MadeTomatoHue
            Automated Home Jr Member
            • Nov 2022
            • 47

            Originally posted by bruce_miranda View Post
            You can turn off the smart weather features you don't want. And to be fair, smart weather isn't messing with the TPI directly, it is adjusting the Setpoints. And in doing that the Heat demand is adjusted accordingly.
            I can't see an option to disable it or that adjustment of setpoints so maybe it isn't doing anything on the 17.xx firmware, which might also explain why using external weather compensation seems to be working OK. Is there a list of what features came with that version?

            Comment

            • bruce_miranda
              Automated Home Legend
              • Jul 2014
              • 2307

              Smart weather features were introduced in 19.xx

              Comment

              • MadeTomatoHue
                Automated Home Jr Member
                • Nov 2022
                • 47

                I wrote a small bit of code to reflect some of the main relay and DHW demand Evohome messages into simple text fies. A shell script (with a bit of help ftom awk) then reviews these every few minutes to select a flow temperature based on highest of DHW (15C higher than current water temp) or CH (weather compensated) need. Seems to be working quite well. Next task is to move to load compensation by using system demand to select a CH flow temp.

                Comment

                • MadeTomatoHue
                  Automated Home Jr Member
                  • Nov 2022
                  • 47

                  Latest evolution is to use a layered approach to selecting a flow temperature:
                  • Start with a weather compensated 40C-70C flow temperature (for 15C-0C outside)
                  • Adjust that by -25% to +25% based on Evohome load inferred from CH relay %age (to encourage faster warm up but lower when rooms are warmed through)
                  • If DHW heating is active then use current cylinder temp +20C if it is higher
                  • Cap at 70C in all cases


                  I think the ongoing problem is that the boiler modulates down, but not enough to ensure long, low burns when only a couple of zones need heating. I'm planning to take a look at explicit adjustment of burner power via EMS. If my initial tests are correct it turns the boiler off when that goes below 30%. That may be OK in that it is a way to turn off the boiler until Evohome thinks more heat is needed. That probably means spaces have got a bit colder but I'm starting to understand that the constant temperature levels that Evohome seeks seem to inevitably lead to short burn cycles (in my case).

                  Comment

                  • MadeTomatoHue
                    Automated Home Jr Member
                    • Nov 2022
                    • 47

                    I added a bit more code to drop the burner level to 40% / 60% / 80% / 90% depending on the target flow temperature. Not sure it will make much difference, and I may look at turning Evohome system demand into burner % instead, and see what temperatires the flow reaches.

                    Comment

                    • bruce_miranda
                      Automated Home Legend
                      • Jul 2014
                      • 2307

                      Originally posted by MadeTomatoHue View Post
                      I added a bit more code to drop the burner level to 40% / 60% / 80% / 90% depending on the target flow temperature. Not sure it will make much difference, and I may look at turning Evohome system demand into burner % instead, and see what temperatires the flow reaches.
                      The Evohome Load Scaling feature might mess your calculations up, if you rely on the Summary Heat Demand from the controller.

                      Comment

                      • MadeTomatoHue
                        Automated Home Jr Member
                        • Nov 2022
                        • 47

                        Originally posted by bruce_miranda View Post
                        The Evohome Load Scaling feature might mess your calculations up, if you rely on the Summary Heat Demand from the controller.
                        I may be a bit out of sync with some features I'm still on 17.xx. But I think the problem that I am trying to amplitude-modulate energy input at the same time that Evohome is trying to time-modulate it may remain no matter which approach is being used.

                        I'm not sure where Summary Heat Demand appears. I'm using the eavesdropped CH relay demand, which looked to have the most granular demand range. There are also % demand for "system zone" and "system relay" that I could use. I may need to plot them to see how they inter-relate and adjust.

                        Overall system comfort seems to be similar, although given that we're running the house cooler rather than warmer that is somewhat subjective.

                        Comment

                        • megakid
                          Automated Home Lurker
                          • Oct 2021
                          • 3

                          Thanks to all in this thread, I have finally got around to installing a VR33 + evohome OT bridge today, it is way simpler than I thought. I have a Vaillant boiler which needed the VR33, which slotted it into the boiler nicely, plugged into X32 port - my VR33 had X32 *and* X31 terminals that I could connect to - the loose ribbon cable came out the box plugged onto X32 (with X31 empty). There was a corresponding X32 port on my boiler PCB so I connected that ribbon cable there. I figure if my boiler had X31 (as some seem to), I'd have done X31 <-> X31 instead. Then I disconnected my switched 240v live (from original BDR91 boiler relay) and bridged the 24v connection (to reenable low voltage control of my boiler) then connected up the Opentherm terminals to the evohome bridge - photos attached. It all seemed to work straightaway, then I swapped my UFH to a zone valve rather than electric zone as bruce suggested from my earlier posts in this thread.

                          I capped my flow temp to 65C (D71) at the boiler (this was my pre-OT fixed flow rate anyway) as evohome requests up to 95C for DHW etc so I wanted to dial it down a little, but I checked an hour later and it was requesting a flow temp of 46C so looked to be working fine.

                          Time will tell if it's more efficient / comfortable but I'm glad it's all setup and working (finally).

                          IMG_4545.jpgIMG_4548.jpg

                          Comment

                          • G4RHL
                            Automated Home Legend
                            • Jan 2015
                            • 1580

                            Originally posted by megakid View Post
                            Thanks to all in this thread, I have finally got around to installing a VR33 + evohome OT bridge today, it is way simpler than I thought. I have a Vaillant boiler which needed the VR33, which slotted it into the boiler nicely, plugged into X32 port - my VR33 had X32 *and* X31 terminals that I could connect to - the loose ribbon cable came out the box plugged onto X32 (with X31 empty). There was a corresponding X32 port on my boiler PCB so I connected that ribbon cable there. I figure if my boiler had X31 (as some seem to), I'd have done X31 <-> X31 instead. Then I disconnected my switched 240v live (from original BDR91 boiler relay) and bridged the 24v connection (to reenable low voltage control of my boiler) then connected up the Opentherm terminals to the evohome bridge - photos attached. It all seemed to work straightaway, then I swapped my UFH to a zone valve rather than electric zone as bruce suggested from my earlier posts in this thread.

                            I capped my flow temp to 65C (D71) at the boiler (this was my pre-OT fixed flow rate anyway) as evohome requests up to 95C for DHW etc so I wanted to dial it down a little, but I checked an hour later and it was requesting a flow temp of 46C so looked to be working fine.

                            Time will tell if it's more efficient / comfortable but I'm glad it's all setup and working (finally).

                            [ATTACH=CONFIG]2016[/ATTACH][ATTACH=CONFIG]2017[/ATTACH]
                            Just checked, my OT has my boiler running at a flow temperature of 31C at present.

                            Comment

                            • bruce_miranda
                              Automated Home Legend
                              • Jul 2014
                              • 2307

                              Originally posted by megakid View Post
                              Thanks to all in this thread, I have finally got around to installing a VR33 + evohome OT bridge today, it is way simpler than I thought. I have a Vaillant boiler which needed the VR33, which slotted it into the boiler nicely, plugged into X32 port - my VR33 had X32 *and* X31 terminals that I could connect to - the loose ribbon cable came out the box plugged onto X32 (with X31 empty). There was a corresponding X32 port on my boiler PCB so I connected that ribbon cable there. I figure if my boiler had X31 (as some seem to), I'd have done X31 <-> X31 instead. Then I disconnected my switched 240v live (from original BDR91 boiler relay) and bridged the 24v connection (to reenable low voltage control of my boiler) then connected up the Opentherm terminals to the evohome bridge - photos attached. It all seemed to work straightaway, then I swapped my UFH to a zone valve rather than electric zone as bruce suggested from my earlier posts in this thread.

                              I capped my flow temp to 65C (D71) at the boiler (this was my pre-OT fixed flow rate anyway) as evohome requests up to 95C for DHW etc so I wanted to dial it down a little, but I checked an hour later and it was requesting a flow temp of 46C so looked to be working fine.

                              Time will tell if it's more efficient / comfortable but I'm glad it's all setup and working (finally).

                              [ATTACH=CONFIG]2016[/ATTACH][ATTACH=CONFIG]2017[/ATTACH]
                              Nice. So your new clamp is D.71 in your valliant ecofit plus 631. This is the same max used for both HW and CH. Which should be fine. What I wanted was a 55C max when using CH and a 65C max when heating HW. These boilers are capable of this using the Vaillant controls. Hence why I added the VR65 which then in turn switches the boiler between CH and HW modes. So you can have a lower D.00 and D.71 for CH with a higher D.77 and D.78 for HW

                              You can use the Orange wire from the HW zone valve to trigger the CYL terminal of the VR65 for HW. It all works quite well and you don't need any more Vaillant controls.

                              Comment

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