Y87RF with BDR91 and no Evohome controller

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  • Treadstone
    Automated Home Jr Member
    • Oct 2020
    • 19

    Y87RF with BDR91 and no Evohome controller

    Having finally given up on Evohome due to constant overshoot with no apparent solution I thought I would try using a Y87RF bound directly to the BDR91 connected to my combi boiler.

    I was amazed to see no overshoot and pretty much perfect temperature control in the room where the Y87RF was placed so with no Evohome controller between these 2 components all appears fine.

    I assume that when I set a target temperature on he Y87RF it transmits both the current room temperature & user set point to the BDR91 which then computes the estimated TPI cycle (I may be wrong here so please educate me if that is the case)

    So for me it looks like the 'smart' bit was not so smart but the BDR91 can control the room temperature very well if given suitable demand.

    An interesting experiment for me and a useful fallback if whatever system I try next fails.
  • bruce_miranda
    Automated Home Legend
    • Jul 2014
    • 2307

    #2
    What else was Evohome controlling that was causing the overshoots? I bet if you put the Evohome controller as your room sensor in the same place as the Y87RF and used it to control a single BDR91 boiler relay, the result would be exactly the same.

    Comment

    • Treadstone
      Automated Home Jr Member
      • Oct 2020
      • 19

      #3
      Thanks for the your thoughts however the Y87RF was never part of the system when the Evohome controller was part of the system. If it had been your easy fix would have been great.

      Comment

      • bruce_miranda
        Automated Home Legend
        • Jul 2014
        • 2307

        #4
        I lot of people don't realise how many variables there are when dealing with a single heat source, multi zone system. That's why I said comparing Evohome to a single zone room thermostat is not a fair comparison.

        Comment

        • Treadstone
          Automated Home Jr Member
          • Oct 2020
          • 19

          #5
          It's all long gone now but if Evohome can't control a single zone in a manner that meets my requirements the system is clearly not for me which I accept. For the record I do not include myself in the large group of people with no knowledge of variables you mention. And was comparing two single zone setups which seemed pretty fair to me.

          Comment

          • bruce_miranda
            Automated Home Legend
            • Jul 2014
            • 2307

            #6
            If you had a single Evohome controller using its internal sensor controlling a single BDR91, positioned in the same location as the Y87RF - the two of them should have behaved exactly alike. Or are you saying that even in this condition the Y87RF was more accurately controlling the heating than the Evohome controller was.

            Comment

            • gordonb3
              Automated Home Ninja
              • Dec 2016
              • 273

              #7
              Not real sure how you ended up with Evohome to control a single zone and in fact without a valve for that zone. Evohome isn't designed for this and it is not surprising to see overshoots as well as lagging in such a setup. Assuming it was app control that you wanted, what you should have gotten is either Y87RF + RFG100 or a Lyric thermostat.

              Comment

              • Treadstone
                Automated Home Jr Member
                • Oct 2020
                • 19

                #8
                If you visit https://evohome.honeywellhome.com/?src=evohome and complete the system builder for a single zone combi boiler you will find it is a recommended configuration. It did not work to my satisfaction but is at odds with your design limitation viewpoint. So there is a clear conflict between Honeywell & gordonb3 on system requirements I will stick with Honeywell on this. My only requirement was it worked to my satisfaction which it did not that is why it is history. Your 'should have gotten' a Lyric advice explains a lot !

                Comment

                • gordonb3
                  Automated Home Ninja
                  • Dec 2016
                  • 273

                  #9
                  Well, allow me to explain to you then why I think the advice was wrong.

                  Evohome is designed as a multi zone system where every individual zone must be able to generate a heat request to your heat source. Since the zones operate independent of each other this allows the heat source to be triggered in rapid succession and this is where your problem starts: because this can lead to significant waste of fuel Evohome prevents such events by limiting how fast the boiler may be shut down again and then reactivated. In a multi zone setup this does not lead to overshoots because the zone valve will close at the set temperature but your setup did not feature such a valve and thus you became subject to the boiler logic which has a default setting of six switch points per hour.

                  Comment

                  • bruce_miranda
                    Automated Home Legend
                    • Jul 2014
                    • 2307

                    #10
                    The Evohome can work as a single zone room stat with a single boiler relay, in fact that is how is arrives when bought new I.e. It can be a direct replacement for a Y87RF and a BDR91, this is why is shows up in the Honeywell configuration. No one should ever do that though because that's a complete waste of buying a multi zone system and operating it as a single zone room stat. However I am not going to debate that.
                    What I am curious about is that as a single zone room stat, how can the Y87RF perform better than the Evohome both placed in the same location in the room and both controlling the same single BDR91 for the boiler.

                    Comment

                    • Treadstone
                      Automated Home Jr Member
                      • Oct 2020
                      • 19

                      #11
                      Originally posted by gordonb3 View Post
                      Well, allow me to explain to you then why I think the advice was wrong.

                      Evohome is designed as a multi zone system where every individual zone must be able to generate a heat request to your heat source. Since the zones operate independent of each other this allows the heat source to be triggered in rapid succession and this is where your problem starts: because this can lead to significant waste of fuel Evohome prevents such events by limiting how fast the boiler may be shut down again and then reactivated. In a multi zone setup this does not lead to overshoots because the zone valve will close at the set temperature but your setup did not feature such a valve and thus you became subject to the boiler logic which has a default setting of six switch points per hour.
                      None of this relates to my original post regarding why a Y87RF bound directly to the BDR91 outperforms an Evohome controller regarding overshoot. It may be worth sharing your system requirements thoughts with Honeywell.

                      Comment

                      • Treadstone
                        Automated Home Jr Member
                        • Oct 2020
                        • 19

                        #12
                        Originally posted by bruce_miranda View Post
                        The Evohome can work as a single zone room stat with a single boiler relay, in fact that is how is arrives when bought new I.e. It can be a direct replacement for a Y87RF and a BDR91, this is why is shows up in the Honeywell configuration. No one should ever do that though because that's a complete waste of buying a multi zone system and operating it as a single zone room stat. However I am not going to debate that.
                        What I am curious about is that as a single zone room stat, how can the Y87RF perform better than the Evohome both placed in the same location in the room and both controlling the same single BDR91 for the boiler.
                        My thoughts on this were that the Evohome unit was defective or the much discussed 'learning ability' of the Evohome unit was sort of not learning. Overshoot crops up many times here and to fair mainly on multi zone systems. It was for that reason I decided to call it a day and not invest in more zones. A decision I do not regret.

                        Comment

                        • gordonb3
                          Automated Home Ninja
                          • Dec 2016
                          • 273

                          #13
                          Originally posted by Treadstone View Post
                          None of this relates to my original post regarding why a Y87RF bound directly to the BDR91 outperforms an Evohome controller regarding overshoot. It may be worth sharing your system requirements thoughts with Honeywell.
                          Apparently I am very bad at explaining.

                          The Round wireless is a zone controller and as such it will signal the valve unit whenever it reaches one of its trigger points. Instantly.

                          The Evohome controller is a central management interface that applies higher logic to facilitate multi-zone operation. Amongst this higher logic is that system level operations are time-slotted because field tests have shown that you use less energy by keeping the boiler running for an additional minute than when you fire it back up a minute later. Note the definitions here: `system` provides the heat, `zone` controls how much of that heat goes into your room.

                          As for Bruce's claim that the default setup of a Evohome controller is a plugin replacement for a regular thermostat, I can't verify that. The starter set that I bought didn't even come with a BDR unit, just three HR radiator/zone valves so that unit most definitely would not have had that setting. Whatever it is, as I described is what I see the system do and from my point of view this matches the results that you report.

                          Just out of curiosity, as you state `a Y87RF bound directly to the BDR91` that appears to imply that you had some other purpose for it before, so where did that Round fit in when you were using the Evohome controller?

                          Comment

                          • Treadstone
                            Automated Home Jr Member
                            • Oct 2020
                            • 19

                            #14
                            I am aware that the 'Round wireless' is a zone controller and it works very well when controlling a single zone bound to a BDR91 .

                            I had mentioned earlier that the Y87RF NOT part of the system when the Evohome unit was controlling the single zone. So to satisfy your curiosity the Y87RF was at that point sitting on an Amazon warehouse shelf ! I hope that eases your obvious doubts.

                            Clearly we disagree on Evohome being suitable for a single zone setup and you have failed to convince me otherwise with all the higher logic, time slotted stuff.

                            Comment

                            • gordonb3
                              Automated Home Ninja
                              • Dec 2016
                              • 273

                              #15
                              Originally posted by Treadstone View Post
                              I am aware that the 'Round wireless' is a zone controller and it works very well when controlling a single zone bound to a BDR91 .

                              I had mentioned earlier that the Y87RF NOT part of the system when the Evohome unit was controlling the single zone. So to satisfy your curiosity the Y87RF was at that point sitting on an Amazon warehouse shelf ! I hope that eases your obvious doubts.

                              Clearly we disagree on Evohome being suitable for a single zone setup and you have failed to convince me otherwise with all the higher logic, time slotted stuff.
                              Well, according to you it isn't and according to me it wouldn't. Seems to me we are pretty close to full agreement.

                              Comment

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