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Thread: Opentherm and Economy (Quick Actions)

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    Default 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?

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    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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    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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    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.

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    Quote 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.

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    Quote 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.

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    Quote 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 )

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    Quote 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

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    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.

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    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.

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