Opentherm and Economy (Quick Actions)

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  • HenGus
    Automated Home Legend
    • May 2014
    • 1001

    Opentherm and Economy (Quick Actions)

    Today’s exam question. Given that Opentherm demands the TSet temperature when a zone is outwith the target temperature by +/- 2C, I question the value of the Economy QA with a modern condensing boiler with Opentherm control. There must be a time ‘sweet spot’ which determines when it is better to leave the boiler pottering away at, in my case, a 44C return temperature compared to setting Economy and then restoring normal target temperatures. Any thoughts?
  • bruce_miranda
    Automated Home Legend
    • Jul 2014
    • 2307

    #2
    Economy is running the system at a lower set point. OT is trying to run the boiler at the lowest temperature to meet any set point. If you normally set your room temps to about 23C, then Economy still makes some sense. However if like me you keep the house at 19C normally, then Economy becomes pointless, in its current guise.

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    • HenGus
      Automated Home Legend
      • May 2014
      • 1001

      #3
      Agree with all of that but the issue for me is whether running the boiler for, say, two hours at a higher set point uses more kWhs than dropping the temperature by 3 degrees and then re-heating it back to the original set temperature?

      Clearly, the ‘is it worth it or not’ Economy time will vary with such things as the original set point temperature, outside air temperature and anything else that I haven’t thought about. It’s times like this I think that I need a Loop monitor; (however, I sense that everything is not right with that company.)

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      • bruce_miranda
        Automated Home Legend
        • Jul 2014
        • 2307

        #4
        Had Loop not forced an electric meter with the gas meter, I would have probably bought it. Landed up building my own and it has been spot on for the last 6 months, not a single digit out. Costed me 15 pounds in parts.

        Comment

        • Edinburgh2000
          Automated Home Guru
          • Dec 2016
          • 134

          #5
          Originally posted by HenGus View Post
          ...the issue for me is whether running [the boiler] for, say, two hours at a higher set point uses more kWhs than dropping the temperature by 3 degrees and then re-heating it back to the original set temperature?
          I guess you mean running the set point for the zone air temperature lower by three degrees (i.e. the Economy setting). The heat input to your house will always equal the heat output (losses) from the house, over a period. So, if your house is cooler, the losses will be lower and the heat input will consequently be lower too.

          Comment

          • HenGus
            Automated Home Legend
            • May 2014
            • 1001

            #6
            Originally posted by Edinburgh2000 View Post
            I guess you mean running the set point for the zone air temperature lower by three degrees (i.e. the Economy setting). The heat input to your house will always equal the heat output (losses) from the house, over a period. So, if your house is cooler, the losses will be lower and the heat input will consequently be lower too.
            Is it that simple? Yesterday, running on profile, the boiler was in full condensing mode with a return temperature of 44C. Cancelling Economy resulted in a 65C demand for heat with the boiler return temperature increasing above 54C before falling back once the various zones had reached their profile temperatures. To my simple mind, Economy mode is better suited to older boilers with a higher flow temperature.

            Comment

            • DBMandrake
              Automated Home Legend
              • Sep 2014
              • 2361

              #7
              Originally posted by HenGus View Post
              Is it that simple?
              Yes, efficiency gain from the condensing action is relatively modest, a lot of the improved efficiency of a modern boiler is other aspects of the design, so it's not fair to say a condensing boiler operating in a "non condensing" state is as inefficient as an old non condensing boiler would have been.

              I think either Richard or Dan posted some figures for this in another thread not that long ago showing that the difference in efficiency at different return temperatures is not nearly as much as most people (including me) thought. It's also not condensing or non condensing - it changes gradually over a flow temperature range without a sudden cutoff.

              On the other hand cutting your room temperatures will definitely reduce heat loss through the walls for the period of time the temperature is reduced.

              It's not a linear reduction either because it depends on the relationship between outside temperature and insulation in the walls. For example if you had extremely well insulated rooms but the outside temperature was very low (say below freezing) then the energy loss would drop somewhat linearly with room temperature since the differential between inside and out isn't changing much.

              On the other hand if you had poor insulation but the outside temperature was only 14 degrees every degree of room temperature set back would have a much more pronounced reduction in heat loss and energy use. I notice this in our less than ideally insulated upstairs bedrooms where reducing the set point by even one degree can be the difference between the radiator running all night long or only coming on for short bursts.

              On balance setting back room temperatures is always going to use less energy than continuing to let them "simmer" at the same temperature. (I await a return appearance of Paul's simmering pot analogy )

              Comment

              • Edinburgh2000
                Automated Home Guru
                • Dec 2016
                • 134

                #8
                Originally posted by HenGus View Post
                Is it that simple? Yesterday, running on profile, the boiler was in full condensing mode with a return temperature of 44C. Cancelling Economy resulted in a 65C demand for heat with the boiler return temperature increasing above 54C before falling back once the various zones had reached their profile temperatures. To my simple mind, Economy mode is better suited to older boilers with a higher flow temperature.
                Yes, I think it is that simple. You are concerned about the change in efficiency of the boiler caused by the amount of condensation it is able to achieve. Thus the equation: "Heat in = Heat out" needs to include the heat out lost through the flue gases, as well as all the heat losses through your walls and roof. If your boiler is not condensing fully, then the flue gases are taking with them the latent heat of condensation of water vapour that could otherwise have gone into your radiators. But that is a small percentage of the heat input to your boiler. Have a look at your condensate pipe while it's running and see the flow rate and imagine the small amount of heat needed to boil that, by comparison with the heat needed to keep your house warm. Keeping your house warmer than necessary, and thereby increasing the losses through your walls and roof, cannot be compensated by having less latent heat lost through the flue gases.

                EDIT: Apologies to DBM: My reply crossed with his

                Comment

                • HenGus
                  Automated Home Legend
                  • May 2014
                  • 1001

                  #9
                  Thanks both. I know some people are convinced that condensing 100% of the time is essential to efficiency. Having seen graphs similar to that below, the jury is still out as this is my first Winter with a condensing boiler That said, there is something rather calming about a boiler that is almost silent at a 44C return flow temperature with a house at temperature. I have also noticed a marked reduction in HR92 activity given the lower flow temperature.

                  ReturnWaterTemp_chart.jpg

                  I shall continue to monitor. As an aside, it would seem that there have been some recent business changes with 'Loop' with Navetas Energy Management Ltd being dissolved.

                  Comment

                  • HenGus
                    Automated Home Legend
                    • May 2014
                    • 1001

                    #10
                    Screen Shot 2017-11-20 at 12.50.09.jpg


                    OK. I gave in and purchased a NorthQ Gas Reader off FleaBay for £30. The results are interesting and back up my initial concerns about Economy Mode when the heating system is at temperature. My wife and I popped out for an hour this morning, and I selected Economy Mode. The graph appears to show that more gas was consumed getting the zones back up to temperature than just leaving things ticking along. I suspect that this down to an efficient boiler and OT. The answer will vary 'day by day' but it seems to me that an absence of less than 90 minutes mitigates against turning the heating down: slow efficiency heating uses less energy than a slow fall followed by a fast hot top up.

                    Comment

                    • Edinburgh2000
                      Automated Home Guru
                      • Dec 2016
                      • 134

                      #11
                      Originally posted by HenGus View Post
                      [ATTACH=CONFIG]1128[/ATTACH] it seems to me that an absence of less than 90 minutes militates against turning the heating down: slow efficiency heating uses less energy than a slow fall followed by a fast hot top up.
                      You would need to show more of that graph beyond the period when the system raised the temperature of the circulating water, until the system settled back down into equilibrium. What matters is the total area under the graph in the two circumstances: (a) leaving it running with your house at normal temperature; and (b) reducing the temperature in the house for a period and thus reducing losses. But you need to compare the two with similar start and end points, i.e. with the circulating water at the equilibrium (normal) temperature. My guess is that you have a lot of stored energy in the system at the end of the graph you attached and you would recover that energy as your OT boiler pulls back the flow temperature. Can you post a couple of comparisons with similar start and finish points?

                      Comment

                      • HenGus
                        Automated Home Legend
                        • May 2014
                        • 1001

                        #12
                        Something to think about:
                        Attached Files

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