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Thread: Evohome + Opentherm v Evohome + Boiler Outside Weather Compensation

  1. #61
    Automated Home Legend paulockenden's Avatar
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    Bruce_miranda,

    One thing to note is that in the diagrams you posted, and I've seen this in a lot of the official schematics, the pump APPEARS to be controlled from the heating valves. It's not obvious that the connection between the junction box and the boiler is two way, and that the pump signal comes from the boiler, up to the junction box, and then back down to the pump.

    In my versions I made it explicitly clear that the pump is controlled by the boiler. However, that control might (in fact, probably would) still be via the junction box.

    I was just trying to make it more obvious how things actually work.

    P.

  2. #62
    Automated Home Legend paulockenden's Avatar
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    Quote Originally Posted by HenGus View Post
    Am I missing something?
    What happens when your heating is off, and your hot water comes on? I bet your heating valve opens...

    You may even have it double bound.

    P.

  3. #63
    Automated Home Legend top brake's Avatar
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    Quote Originally Posted by bruce_miranda View Post

    Ok back to the Opentherm question then. Will the Opentherm bridge operate the Boiler for any demand? Be it Hot Water, Radiator or (in my case) the UFH zone valve? The reason I ask is because I will now fully relying on the Opentherm to start the boiler. The BDR91s will only be operating the motorised zone valves, which will have their Orange wires disconnected from the boiler.
    yes that is correct
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  4. #64
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    Now that I understand, the CH motorised zone valve is actually redundant in a system with HR92s. In fact until you introduce OpenTherm into the equation, it doesn't matter if you control the Boiler Directly via the Boiler Demand relay or control the zone valve (which in turn calls the boiler) via the Boiler Demand relay.

    Infact in an S Plan system with HR92s @HenGus would have wired the Boiler Demand relay to the CH zone valve, so that whenever there is Boiler demand, it's the CH valve that opens and fires the boiler.

    I now need confirmation if by adding Opentherm as my Boiler Demand device will it also handle Boiler Demand for Hot Water too? Because now none of the zone valves will be able to fire up the boiler.
    Last edited by bruce_miranda; 4th April 2016 at 04:44 PM.

  5. #65
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    Quote Originally Posted by paulockenden View Post
    What happens when your heating is off, and your hot water comes on? I bet your heating valve opens...

    You may even have it double bound.

    P.
    It doesn't. Heating is off at the moment and has been most evenings this week. Water heats up to the set temperature and everything shuts down.

  6. #66
    Automated Home Legend paulockenden's Avatar
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    It matters inasmuch as there's a delay between the BDR91 switching and the boiler firing, because the latter doesn't happen until the valve has fully opened. So it messes with the fancy minimum on time settings etc.

  7. #67
    Automated Home Legend top brake's Avatar
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    Quote Originally Posted by bruce_miranda View Post
    Now that I understand, the CH motorised zone valve is actually redundant in a system with HR92s. In fact until you introduce OpenTherm into the equation, it doesn't matter if you control the Boiler Directly via the Boiler Demand relay or control the zone valve (which in turn calls the boiler) via the Boiler Demand relay.

    Infact in an S Plan system with HR92s I would actually wire the Boiler Demand relay to the CH zone valve, so that whenever there is Boiler demand, it's the CH valve that opens and fires the boiler.

    I now need confirmation if by adding Opentherm as my Boiler Demand device will it also handle Boiler Demand for Hot Water too? Because now none of the zone valves will be able to fire up the boiler.

    yes it will handle heating and hot water demands concurrently

    it will fire the boiler to the maximum heat demand

    if you want to configure hot water priority you can connect the A terminal on the CH BDR to the C terminal on the DHW BDR

    make sense?

    this will give the advantage of ensuring that the heating flow temperature is at it's lowest possible (heating will be effectvely isolated when DHW cylinder is charging).
    I work for Resideo, posts are personal and my own views.

  8. #68
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    Quote Originally Posted by paulockenden View Post
    I think that's wrong.

    In the setup you've described ("CH is turned on by a Zone calling for heat which, in turn, activates the BDR91 to open the CH zone valve") it's important that the CH BDR91 *isn't* configured as a boiler relay. (In an S-Plan setup).
    How would you bind a single BDR91 to multiple zones calling for heat. I thought you couldn't hence why the separate Boiler Demand function in the System Devices. Are you saying there is a way to have the BDR91 bound for heat only demand to control a zone valve and not be bound as a Boiler Demand device?

  9. #69
    Automated Home Legend paulockenden's Avatar
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    Quote Originally Posted by bruce_miranda View Post
    Are you saying there is a way to have the BDR91 bound for heat only demand to control a zone valve and not be bound as a Boiler Demand device?
    Yes, exactly that. If you go through guided configuration for 'Sundial' systems it gives you the option to bind both DHW and CH relays.

    P.

  10. #70
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    Ok stay with me for a little longer because I am again confused.

    Firstly the Sundials - System Devices have been removed from the new Wifi evohome controllers.

    Lets assume you had two radiators and one HW cylinder. These were previously connected via an S Plan system.

    The HW motorised valve opened when the HW was needed. The CH motor valve was opened when the radiators were needed. These were generally controlled from a 2 channel time clock.

    Now you were upgrading to evohome.

    You put two HR92s on the radiators. You put the HW kit in.

    How would you connect the two BDR91s in a way that when the HW was needed, it would open the HW zone valve and fire the boiler. And when either of the two HR92s needed heat, it would open the CH zone valve and fire the boiler?

    I thought the only way to do this was to wire the HW BDR91 to the HW zone valve and bind it as the HW acuator.
    Wire the CH BDR91 to the CH zone valve and bind it as the Boiler Demand relay. The reason being, there is was no single acuator for all heating demands coming from the various HR92s except for using the Boiler Demand Relay function.

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