Evohome over shoot on UFH zone

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  • doni
    Automated Home Jr Member
    • Jul 2016
    • 24

    Evohome over shoot on UFH zone

    I've had evohome installed for around 10 days now. For the most part it is working fine except for the Kitchen which is the only room in the house that has UFH. This zone is has a T87RF wireless stat and a BDR91 configured as a boiler relay driving a two port zone valve. It is configured to have a temperature of 20.5 in the morning and evening and sets back to 18.0 during the day and over night. The system has optimized start/stop enabled.

    When it was first installed, we were in the middle of the cold spell and the zone temperature was managed well with very little over shoot (it was typically maintaining the temperature around 21.0). Then on Friday the temperatures warmed up and the zone is now over shooting to around 23.5 every day. Overnight the zone is dropping to around 20.0 so it doesn't need much energy to raise the temperature to 20.5.

    Is this just a case of the system needing to learn, or do I need to do anything to stop this behavior?

    Don
  • doni
    Automated Home Jr Member
    • Jul 2016
    • 24

    #2
    I have a netatmo thermostat in the Kitchen. The redline shows the high point and the blue line the low point. The settings for the zone have not changed during this period. image1.jpg

    Comment

    • DBMandrake
      Automated Home Legend
      • Sep 2014
      • 2361

      #3
      Maybe the flow temperature in your UFH is just too high for the low heat loss of the room during warm weather conditions ?

      Have you tried turning the UFH flow temperature down a bit ? Even with normal radiators having the flow temperature too high in warm conditions (especially if you have a well insulated house) can lead to overshoots because the system is not able to modulate down far enough for the small amount of heat required - the minimum amount of controllable heat that it can put into the floor will result in an overshoot, so overshoot becomes inevitable.

      Comment

      • bruce_miranda
        Automated Home Legend
        • Jul 2014
        • 2307

        #4
        How come the bdr91 is configured as the boiler relay for the ufh zone. What is firing the boiler then?

        Comment

        • doni
          Automated Home Jr Member
          • Jul 2016
          • 24

          #5
          Originally posted by bruce_miranda View Post
          How come the bdr91 is configured as the boiler relay for the ufh zone. What is firing the boiler then?
          The boiler is driven off the end-switch on the zone valve.

          Originally posted by DBMandrake View Post
          Maybe the flow temperature in your UFH is just too high for the low heat loss of the room during warm weather conditions ?
          The flow temperature is at 40 and hasn't been touched since the old system was in. We did use to have some over-shoot with the old system, but nothing near what we have had with evohome in the last few days. The old system was relatively basic as it would only shut off once the set temperature had been reached (hence the over-shoot).

          I'm tempted to not have a constant temperature in the room rather than having a lower temperature during the day and at night. Perhaps this would give evohome a better chance of managing the temperature.

          Comment

          • bruce_miranda
            Automated Home Legend
            • Jul 2014
            • 2307

            #6
            I'm wondering if the reason for your overshoot is because the evohome thinks its firing up the boiler but instead it is opening up the valve more often than needed, which in turn is firing up the boiler.

            Do you have the evohome controller or are you using just the T87RF with it's own BDR91?

            Comment

            • doni
              Automated Home Jr Member
              • Jul 2016
              • 24

              #7
              Originally posted by bruce_miranda View Post
              I'm wondering if the reason for your overshoot is because the evohome thinks its firing up the boiler but instead it is opening up the valve more often than needed, which in turn is firing up the boiler.

              Do you have the evohome controller or are you using just the T87RF with it's own BDR91?
              I do have the evohome controller, but the temperature for the zone is being controlled by the T87RF. For the first week it worked fine, but the last few days have been a nightmare with the overshoot. Today the room is fine, but that's because so much heat was put into the floor yesterday that it's not cooled down enough yet to require heating.

              Comment

              • bruce_miranda
                Automated Home Legend
                • Jul 2014
                • 2307

                #8
                What other zones do you have and how do they call for heat? If the boiler relay is tied to the ufh valve?

                Comment

                • doni
                  Automated Home Jr Member
                  • Jul 2016
                  • 24

                  #9
                  Originally posted by bruce_miranda View Post
                  What other zones do you have and how do they call for heat? If the boiler relay is tied to the ufh valve?
                  I'm home now and able to check the settings on evohome and realise I may have been using some of the wrong language. Looking at the settings, the kitchen is configured as a zone valve with a BDR91 driving the relay.

                  The other zones are all using HR92's connected up to a separate BDR91. The system is configured such that if the kitchen requires heat, the UFH zone valve is opened and boiler fired. If only radiators are calling for heat then the UFH zone valve remains closed.

                  Don

                  Comment

                  • doni
                    Automated Home Jr Member
                    • Jul 2016
                    • 24

                    #10
                    I finally think I've solved the overshoot problem - and it was a setup issue on my part. I noticed that the UFH BDR91 was being enabled at times when it shouldn't have been. On digging into this I found out that I hadn't cleared the factory set T87RF binding to the BDR91 - the T87RF had a set temperature of 23 degrees!

                    I'm kicking myself for missing this setup step, and taking over a month to find it!

                    Comment

                    • DBMandrake
                      Automated Home Legend
                      • Sep 2014
                      • 2361

                      #11
                      I sometimes think the pre-binding done when you buy things in packs causes more problems than it solves, since the protocol allows multiple bindings per device. (A BDR91 can have up to 4 different bindings at once)

                      For example if I happen to buy a DTS92 and a BDR91 together in a pack (which is cheaper than buying them separately) but don't intend to use them together I need to be aware of the fact that they are pre-bound, and know how to clear the bindings!

                      From what I remember of the install leaflets they are not particularly wordy and while they cover binding I don't think they cover clearing bindings. Hence a lot of people get caught out with multiple bindings...

                      Comment

                      • paulockenden
                        Automated Home Legend
                        • Apr 2015
                        • 1719

                        #12
                        If Honeywell is listening, how's about BDR91s being supplied with a "bound to" label on them, by default saying whatever it came in the box with (if it was part of a set), bit with space to cross that out and write something else.

                        Think that would solve a lot of problems, and shouldn't be very expensive to do.

                        P.

                        Comment

                        • DBMandrake
                          Automated Home Legend
                          • Sep 2014
                          • 2361

                          #13
                          Originally posted by paulockenden View Post
                          If Honeywell is listening, how's about BDR91s being supplied with a "bound to" label on them, by default saying whatever it came in the box with (if it was part of a set), bit with space to cross that out and write something else.

                          Think that would solve a lot of problems, and shouldn't be very expensive to do.
                          Good idea - as soon as the packaging is opened its easy to loose track of which units came with what other units.

                          Say you got a DTS92 + BDR91 pack to save money, a couple more DTS92's that came individually, along with a BDR91 that came with the main controller unit and yet another BDR91 that came as part of the hot water kit.

                          In the excitement of unpacking everything now you have a mixed up bunch of devices - some of which are pre-bound (one DTS92 pre-bound to one BDR91, and one BDR91 pre-bound as a boiler relay to the controller) and some which are not. Confusion and hair pulling when the system doesn't behave as expected due to double binding will then surely follow...

                          I've noticed that some BDR91's also come with the stick on cheat sheet label that tell you how to wire them up while others don't - although I didn't keep track of which did and didn't.

                          The "bound to" labels should ideally come in pairs with a unique or semi-unique identity or serial number to show which other device they are bound to, by finding the two devices with the same number on their labels. (In the everything opened and mixed up on the kitchen table scenario)

                          As well as this the instructions on how to clear bindings on devices needs to be included in the packaging and clear to follow. I'm pretty sure that some devices do NOT include instructions on how to clear bindings in the leaflets provided in the packaging, I had to find how to unbind an HR92 by looking it up in one of the larger PDF manuals for example. (Long press on the BIND function)

                          Most of the instruction manuals start off assuming the device is unbound and begin with the steps to bind it when really unbinding should be the first step to perform before binding on a new install.

                          I clear bindings on devices before binding them or re-binding them as a matter of course to avoid any problems and start from a known state.
                          Last edited by DBMandrake; 6 January 2017, 02:12 PM.

                          Comment

                          • paulockenden
                            Automated Home Legend
                            • Apr 2015
                            • 1719

                            #14
                            Even the so-called experts who installed my system left one of the BDR91s double bound.

                            So my stickers would even help the professionals!

                            Comment

                            • DBMandrake
                              Automated Home Legend
                              • Sep 2014
                              • 2361

                              #15
                              Originally posted by paulockenden View Post
                              Even the so-called experts who installed my system left one of the BDR91s double bound.

                              So my stickers would even help the professionals!
                              Indeed. What were the symptoms ? Would you have noticed the problem if you were a non technical user ?

                              Comment

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