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Thread: Thinking of adding the hot water kit to my Evohome

  1. #71
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    I confess to having been misled into thinking that Erik's example related to the evotouch.

    Perhaps Rameses you could let us know whether Erik's illustration (including the 100% spikes) is typical, or whether the evotouch system with OpenTherm interface can in practice achieve the utopian state of equilibrium heat demand/flow temperature that I wrote about earlier?

    As you point out there are limits, and my boiler (max o/p 12 kW, min 3.7 kW) has just come on for about 45 secs!

  2. #72
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    Evohome does the same thing. If a boiler can not modulate down any further, it will have to go off to prevent overshoot. There's no magic that can prevent this.

  3. #73
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    Quote Originally Posted by erik View Post
    Evohome does the same thing. If a boiler can not modulate down any further, it will have to go off to prevent overshoot. There's no magic that can prevent this.
    That's what it's happening with my boiler (I use EvoHome with R8810 OpenTherm gateway).

    Huge benefit of modulation is that when low energy is required (e.g. your house is already warm) water temperature is held as low as possible, making a condensing boiler work in its optimal range and keeping radiators at neary constant temperature most of the time.

    I installed an OpenTherm gateway (http://otgw.tclcode.com/) between boiler and the R8810 to look into OpenTherm communications and now I get graphs like this:

    ot.jpg

    Water temperature is the red line. Blue is return water. Yellow is DHW temperature.

    Bars at the top are DHW (blue), CH (green) and flame (red).

    In between there's a black line with the modulation level.

    Vertical lines (light gray) are every 5 minutes. Water temperature at the right is about 40 C, radiators are warm.

    Graph shows some mix of modulation and TPI control that's keeping my house at comfortable temperature and seems quite energy-efficient. I'm a bit concerner about the amount of stress it's putting on my boiler, not to mention noise at night, with continuous start/stop action. I wish I could fine-tune something, but that's another story.

  4. #74
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    boilers are made to start/stop a lot. So with proper maintanence it should be fine

    Modulation, in theory, is great to keep your boiler running at low/efficient rates. But in practice, with zoning and isolated homes, it will act a lot like a on/off.

    Maybe in the future we will get boilers that can modulate down to 500W instead of 5000W. Then, there would be a lot more profit I think.
    Last edited by erik; 8th March 2015 at 07:33 PM.

  5. #75
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    Quote Originally Posted by erik View Post
    boilers are made to start/stop a lot. So with proper maintanence it should be fine

    Modulation, in theory, is great to keep your boiler running at low/efficient rates. But in theory, with zoning and isolated homes, it will act a lot like a on/off.

    Maybe in the future we will get boilers that can modulate down to 500W instead of 5000W. Then, there would be a lot more profit I think.
    I think the focus on this start/stop aspect came from the EVOHOME menu options regarding minimum runtime and number of cycles per hour. The reality is, I don't think it makes a lot of difference with a zoned set-up, for the very reasons we are discussing here, particularly regarding the effects of small zones (such as a single room) combined with boilers with no, or limited modulation capability. The fact is the boiler will cycle more with EVOHOME than without it. I would still like to know what default settings EVOHOME uses with s-plan/y-plan set-ups where the options disappear, but I am starting to think this has had more emphasis than is warranted.

  6. #76
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    Quote Originally Posted by jonstatt View Post
    I think the focus on this start/stop aspect came from the EVOHOME menu options regarding minimum runtime and number of cycles per hour. The reality is, I don't think it makes a lot of difference with a zoned set-up, for the very reasons we are discussing here, particularly regarding the effects of small zones (such as a single room) combined with boilers with no, or limited modulation capability. The fact is the boiler will cycle more with EVOHOME than without it. I would still like to know what default settings EVOHOME uses with s-plan/y-plan set-ups where the options disappear, but I am starting to think this has had more emphasis than is warranted.
    There is no doubt my boiler cycles more now with Evohome but on the other hand I am beginning to see drops in my gas consumption. I did not install Evohome for that reason. It's a nice bonus. What I do find though is that often my boiler cuts out but the pump is left in over run for good reason but the benefit is that heat is continued to be circulated to relevant zones, it is not being lost in my downstairs loo. This morning, monitoring what was happening, optimisation switched the boiler on at 05:44 for a zone not needing to be at 20C until 06:40. It was 16.5 at time of switch in. By 06:15 the temperatue was 19c. The boiler was switche'd off but the pump continued circulating residual heat for some time. I suspect the boiler left the pump in over run because the water was hot and only one zone was being heated as so far as aware Evohome does not control the firing of the boiler and the running of the pump independently when it sees the need - or does it?!

  7. #77
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    Not sure if you have Opentherm or On/Off. But with On/Off, it certainly does not control the pump.

    My boiler runs the pump for 5 minutes after every time the thermostat goes Off.

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