Meaning of the zone heat demand %

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  • chrisgare
    Automated Home Guru
    • Dec 2013
    • 182

    Meaning of the zone heat demand %

    I'd like to start a thread about the meaning of the new capability of displaying zone heat demands.

    I thought this data would be relatively simple to interpret but I'm not sure that is the case.

    I won't post my confusions yet as I need a few days to assimilate, but if anyone else has any comments / observations to make I'd love to hear them. Chris
  • paulockenden
    Automated Home Legend
    • Apr 2015
    • 1719

    #2
    From my tests I find it exactly matches the values seen in Domoticz (which others have said exactly matches the HR92 stroke display, but I've not tested that). I can't see any massaging of the data in the controller.

    So I was surprised when others reported that the controller percentage didn't match the HR92.

    P.

    Comment

    • FullBore
      Automated Home Guru
      • Jan 2016
      • 140

      #3
      I'm sure that I will need an idiot's guide - in very simple terms please!

      Merry Christmas to everyone.

      FB

      Comment

      • chrisgare
        Automated Home Guru
        • Dec 2013
        • 182

        #4
        My first unexpected thing was that when I turned on the heating at 07:00 this morning, some zones (I use all 12) indicated 100% but a number didn't. This was surprising as I was expecting ALL zones to indicate 100%. All the radiators were blazingly hot though so all was working correctly. Later in the morning when I manually increased the temperature in one of the zones that was previously 0%, it increased to 100% correctly.

        Kinda strange - or not?
        Last edited by chrisgare; 21 December 2017, 01:42 PM.

        Comment

        • DBMandrake
          Automated Home Legend
          • Sep 2014
          • 2361

          #5
          Lost heat demand message from some HR92’s ?

          Comment

          • DBMandrake
            Automated Home Legend
            • Sep 2014
            • 2361

            #6
            Originally posted by paulockenden View Post
            From my tests I find it exactly matches the values seen in Domoticz (which others have said exactly matches the HR92 stroke display, but I've not tested that). I can't see any massaging of the data in the controller.

            So I was surprised when others reported that the controller percentage didn't match the HR92.

            P.
            I've done some testing tonight and the HR92 reported valve pin position is definitely not 1:1 the same as the reported heat demand in the new diagnostic screen. Not even close. I did some testing with one HR92 and graphed the results here:



            Here are the raw numbers:

            HR92 Valve Position - Evohome Heat Demand
            0 - 0
            27 - 0
            34 - 2
            44 - 10
            47 - 13
            71 - 30
            75 - 42
            90 - 77
            91 - 77
            100 - 100
            For pin travel percentages up to about 30% there is no reported heat demand, from 30% to 70% there is a roughly linear mapping, and from 70% to 100% there is a much steeper roughly linear mapping.

            This makes a lot of sense - below about 30% pin position the valve won't be flowing any water, so no heat demand should be reported. From about 30% to 70% is roughly the linear operating range of most TRV valve bodies from no flow to nearly full flow. So for this range the heat demand does change in a linear fashion but changes slowly so that the radiator temperature is primarily controlled by varying the water flow.

            Then from 70% to 100% valve pin position there won't actually be much if any increase in water flow, so now the heat demand at the controller changes at an accelerated rate to effect a further increase in panel temperature via increasing the flow temperature. Clever.

            I made a couple of spot checks on two HR92's from different zones and they lined up almost perfectly with the graph from the first zone, so I think this is a fixed relationship, not one that adapts in a particular zone.

            What's unclear due to conflicting reports, is whether this mapping I've graphed is done between the valve pin position and the over the air heat demand sent by the HR92, or whether the over the air heat demand is the same as the valve pin position and that is then mapped in the controller to the heat demand displayed here.

            Someone is going to have to compare Domoticz captured heat demand from an HR92 with the reported valve pin position to figure that one out...

            Two other observations I made -

            1) I do see boiler heat demand with my 3x BDR91 configuration, and the heat demand of the boiler control relay does appear to just be max(hw,zone1,zone2,zone3......zone12) etc... No fancy algorithm there, and probably none needed.

            As I've suggested before - the boiler demand needs to be enough for the most demanding zone, so max() makes perfect sense.

            2) The heat demand display screen does update dynamically, and seems to update consistently within about 10 seconds of an HR92 sending a new heat demand.
            Last edited by DBMandrake; 21 December 2017, 06:39 PM.

            Comment

            • DBMandrake
              Automated Home Legend
              • Sep 2014
              • 2361

              #7
              Just diagnosed my first problem using the new heat demand display option....

              I noticed the radiator controller in the hallway was acting a little strange - it was showing 27% heat demand on the new page even though the radiator was cold - checking the valve position directly on the HR92 reported about 60% open which should definitely be hot, and the boiler was running to service other zones... Hrm...

              Thinking that the pin calibration was somehow out I lifted it off, unscrewed the black wheel and refitted it and then let it do it's re-calibration to see if that helped, which it didn't...

              Quite some time later - over 20 minutes after all zones except bedrooms are scheduled to 5 degrees I noticed that the hallway zone was still reporting a heat demand of 27% - huh ?

              I also noticed that the study - also scheduled for 5 degrees for quite some time was reporting a heat demand of 2% instead of the expected 0%... I checked the valve position directly on both HR92's and they both reported 0%.

              So I removed and refitted the batteries on both and a couple of minutes later the heat demand from both zones dropped to 0%.

              So there you go - a potential case of phantom boiler firing already diagnosed with the new heat demand screen and fixed by rebooting two of the HR92's. I say potential, because our sons bedroom was genuinely calling for a small amount of heat at the time so the boiler was already firing at about 15% anyway, however if that had not been the case the boiler would have been firing at a 27% duty cycle for who knows how long with no zones intentionally calling for heat...

              This is not the first time I have seen "stuck" heat demands emanating from HR92's, where they appear to be working normally and adjust the radiator valve just fine, but the heat demand sent to the controller gets "stuck" permanently at some previous value. My bathroom one has done this 2 or 3 times now in the last year, where it appears to work normally in every way except it won't call for heat from the boiler, even though set points change and it adjusts the radiator valve.

              In those cases it is calling for a heat demand of 0% so even turning up the radiator to 25 degrees won't bring the boiler on unless some other zone is demanding heat. In all cases where I've previously seen this happening rebooting the HR92 (not the controller) solved the issue.

              With the new heat demand display this problem should be MUCH easier to spot and diagnose in future.
              Last edited by DBMandrake; 22 December 2017, 12:37 AM.

              Comment

              • Dan_Robinson
                Automated Home Ninja
                • Jun 2012
                • 347

                #8
                Awesome. My first evening has taught me that my bedroom rad is equally as pants as my bathroom towel rail.

                The latter I have little choice in. The former just requires me to persuade SWMBO that the integral full length mirror not only looks crap (it does), but also limits the efficiency of the room's heating.
                Kind Regards - Dan Robinson (Jennings Heating Ltd)

                Comment

                • Dan_Robinson
                  Automated Home Ninja
                  • Jun 2012
                  • 347

                  #9
                  I should add though, that this is not new information to me; but does give the aforementioned SWMBO imperical information to ignore.
                  Kind Regards - Dan Robinson (Jennings Heating Ltd)

                  Comment

                  • chrisgare
                    Automated Home Guru
                    • Dec 2013
                    • 182

                    #10
                    Originally posted by DBMandrake View Post

                    I also noticed that the study - also scheduled for 5 degrees for quite some time was reporting a heat demand of 2% instead of the expected 0%... I checked the valve position directly on both HR92's and they both reported 0%.
                    When the heating came on this morning I still two zones that indicated 0% rather than the expected 100% but theye were differant ones to yesterday! I am assuming that as I am turning on 18 HR92s at the same time some of the heat demand updates are clashing and not registering. The heating is all working OK though.

                    Also, yesterday, I had one zone 'sticking' indicating 14% even though the actuator had switched to 5 degrees half an hour earlier. I'm sure that if I reboot the affected HR92s as suggested by Simon this would affect would correct things but surely this would only be a temporary solution?

                    Also, what is the point of showing the BDR91 data as it seems to mirror the zone demanding the highest heat only? It doesn't seem to have any value? It displays the same % whether the BDR91 is actually on or off.

                    Update@10:30. All the zones are reporting correctly at present so I assume the 'missing' zones at first turn on is due to heat demand info back from HR92s clashing. Would it be worth staggering turn-on but I see no benefit of doing this except to ensure correct reporting?
                    Last edited by chrisgare; 22 December 2017, 11:20 AM.

                    Comment

                    • Krejt
                      Automated Home Jr Member
                      • Jan 2016
                      • 21

                      #11
                      Anyone else staring at the flame icon wondering why it is there?
                      flame-icon.jpg
                      It suggests the boiler is fireing but in my on/off (BDR91 Wireless Relay Box) setup it is definately not related to either the boiler fireing of the percentage given for the wireless relay box.
                      The flame icon is there all the time, even with all zones set tot 5 celcius (even with the quick mode 'off') and all zones (radiators) and the wireless relay box reporting 0% demand.

                      Does the flame icon have some function in an OpenTherm setup?

                      User feedback: If the icon is there for artistic purposes I suggest Honeywell to remove it ;-)
                      Evohomeclient temperatures on ThingSpeak: https://thingspeak.com/channels/79213

                      Comment

                      • paulockenden
                        Automated Home Legend
                        • Apr 2015
                        • 1719

                        #12
                        I assumed the flame icon was used because there isn't enough space to write "Heat demand". I think it's just a column heading.

                        P.

                        Comment

                        • HenGus
                          Automated Home Legend
                          • May 2014
                          • 1001

                          #13
                          Originally posted by Krejt View Post
                          Anyone else staring at the flame icon wondering why it is there?
                          [ATTACH=CONFIG]1165[/ATTACH]


                          Does the flame icon have some function in an OpenTherm set
                          It is the same static icon with OT.

                          Comment

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