Why is the setpoint way over the set temperature?

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  • DBMandrake
    Automated Home Legend
    • Sep 2014
    • 2361

    #16
    Ok. That looks the same as what I see when I get a sudden cold snap - it undershoots the set point by maybe 0.5C, remains steady at that value for quite a while and then gradually creeps up to the desired set point over a couple of hours. After a day or so of the new cold weather conditions it has fully adapted and doesn't undershoot.

    My understanding is that this is caused by the tuning of the PID controller in the HR92 having adapted to the previous conditions (the degree of heat loss through the walls due to outside temperature thus the amount of heat and valve position required to reach the set point) and when the operating conditions change dramatically (and enabling load scaling would count as a dramatic change in operating conditions from the point of view of the HR92 which is unaware of it) so it will take time for the Integral and Differential factors to adjust themselves to match.

    What it also shows is what a good job it was previously doing of predicting how early to start closing the valve to reach the set point quickly and without any overshoot. (As the undershot temperature is so flat) When it gradually creeps up over another hour or two this is the integral action of the controller gradually increasing the valve position and heat demand due to a sustained undershoot.

    I suspect another couple of days and it should finish adapting.

    Comment

    • Woody
      Automated Home Jr Member
      • Feb 2015
      • 32

      #17
      This weekend the temperature in our living zones (three zones that are connected and share the same temperature setting) was 0.5C too low, and noticeably so. Increasing the setpoint increased the temp, but still with keeping a -0.5C difference to what was set.

      The office is still heating up atm; the setpoint is right, the room temperature runs behind. It needed to heat up 4.5C and be done at 08:00, but at 09:15 it still needs to increase 1C. The office asks for 17% heat but the wireless relay box translates this to 5%. I guess this is load scaling learning.

      I'll give it a couple of more days.

      One thing I would like to do is eventually replace the on/off relay with the R8810 but I'll postpone that until my current setup is settled.

      Comment

      • bruce_miranda
        Automated Home Legend
        • Jul 2014
        • 2307

        #18
        Are you absolutely sure you don't have one of those uncontrolled boilers that will try and ramp up to 90C when used with the R8810? Remember that load scaling doesn't work with the R8810.

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        • DBMandrake
          Automated Home Legend
          • Sep 2014
          • 2361

          #19
          Originally posted by Woody View Post
          This weekend the temperature in our living zones (three zones that are connected and share the same temperature setting) was 0.5C too low, and noticeably so. Increasing the setpoint increased the temp, but still with keeping a -0.5C difference to what was set.

          The office is still heating up atm; the setpoint is right, the room temperature runs behind. It needed to heat up 4.5C and be done at 08:00, but at 09:15 it still needs to increase 1C. The office asks for 17% heat but the wireless relay box translates this to 5%. I guess this is load scaling learning.

          I'll give it a couple of more days.

          One thing I would like to do is eventually replace the on/off relay with the R8810 but I'll postpone that until my current setup is settled.
          Try switching Advanced Load Scaling to "Partial" mode. This reduces how much the heat demand is scaled down. I found the "Normal" mode scaled the load down too much on my system and I saw similar results to you until I did so.

          If you check the System Info page where the heat demand is shown before and after changing it you should see the heat demand to the boiler increase significantly.

          BTW Load scaling doesn't operate with an OpenTherm bridge, so having it "settle" won't make any difference to fitting the OpenTherm Bridge - it will be learning all over again as OpenTherm control is very different to TPI.

          Comment

          • Woody
            Automated Home Jr Member
            • Feb 2015
            • 32

            #20
            Originally posted by DBMandrake View Post
            Try switching Advanced Load Scaling to "Partial" mode. This reduces how much the heat demand is scaled down. I found the "Normal" mode scaled the load down too much on my system and I saw similar results to you until I did so.

            If you check the System Info page where the heat demand is shown before and after changing it you should see the heat demand to the boiler increase significantly.

            BTW Load scaling doesn't operate with an OpenTherm bridge, so having it "settle" won't make any difference to fitting the OpenTherm Bridge - it will be learning all over again as OpenTherm control is very different to TPI.
            Set it to partial and yes, the boiler heat demand increased immediately. Looks like it now translates the heat request of the office (84%) 1:1 to the boiler again.

            About OT and load scaling, does that mean that OT is supposed to do the load scaling always? My experience is different as, when I had the 8810 controlling the boiler, it overheated every now and the due to a large heat request for only a small room. Haven't seen that since installing the BDR and load scaling. Kinda silly if I could only prevent that by installing an on/off relay IMO.

            Comment

            • bruce_miranda
              Automated Home Legend
              • Jul 2014
              • 2307

              #21
              Yes no load scaling on OT because OT is meant to already be an adaptive device. However the implementation is far from adaptive and made considerably worse if your boiler just blindly follows what the OTB tells it. Imagine if the boiler is ramping up to 90C, just because your small side room is less than 1.5C below the set point. It's madness.

              Comment

              • Woody
                Automated Home Jr Member
                • Feb 2015
                • 32

                #22
                Originally posted by bruce_miranda View Post
                Imagine if the boiler is ramping up to 90C, just because your small side room is less than 1.5C below the set point. It's madness.
                Exactly what I saw earlier. So no OT for me until that is fixed.

                Ah well, I think on/off works just as well, taking into account the boiler then also modulates its heat output to the set (55C) temperature. I do not know about the gas use but at least the electricity use is much lower, as one big difference I also noticed was that, under OT, the boiler pump was hardly switched off at all. More or less during the entire day it ran, albeit slow, most of the time pumping 20-25C water around. Now with on off the boiler heats and pumps water around until the heat request disappears, then pumps for another couple of minutes and then switches off.

                Comment

                • DBMandrake
                  Automated Home Legend
                  • Sep 2014
                  • 2361

                  #23
                  Originally posted by Woody View Post
                  Set it to partial and yes, the boiler heat demand increased immediately. Looks like it now translates the heat request of the office (84%) 1:1 to the boiler again.
                  From what I've seen, zones that struggle to heat up can end up with their heat demand not scaled down nearly as much as zones which easily heat up or tend to overshoot - I think that's part of the heuristics as the load scaling ratio is different for every zone and changes gradually over time. (days) A couple of my zones don't scale down much and others scale down a lot.
                  About OT and load scaling, does that mean that OT is supposed to do the load scaling always? My experience is different as, when I had the 8810 controlling the boiler, it overheated every now and the due to a large heat request for only a small room. Haven't seen that since installing the BDR and load scaling. Kinda silly if I could only prevent that by installing an on/off relay IMO.
                  No load scaling for OpenTherm unfortunately and from the discussion with the Honeywell guys in the Beta thread this is on purpose and they don't believe that there would be any advantage to load scaling on OpenTherm.

                  Some of what load scaling is trying to do is peculiar to TPI control but there are elements of it which I think would benefit OpenTherm.

                  Comment

                  • BuxtonJim
                    Automated Home Jr Member
                    • Aug 2018
                    • 45

                    #24
                    FWIW my experience is as DB describes. My load scaling has been set at "normal" for some time and it's noticeable how much smoother things feel and how much less boiler activity there seems to be. All anecdotal of course but maybe 'perception of comfort' is key to the overall experience. My place is old, not super insulated (or otherwise) and fairly large but Evo is working yet better with the beta firmware.

                    Comment

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