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

  1. #41
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    Quote Originally Posted by bruce_miranda View Post
    My current setup uses a normal timer for the hot water. Will i need to move to the hot water kit if I plan to use OpenTherm? Otherwise how will Opentherm know there is demand for Hot Water too?
    Yes you'll need the hot water kit if you want to use VR33 and OpenTherm bridge. This is what I have.

  2. #42
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    Oh sugar...some more expense. Ok so I have an S plan system. I understand that the Opentherm bridge will trigger the boiler for radiators and hot water. But i then have a further zone valve for UFH currently controlled via a Y87RF and a BDR91. What happens to the BDR91 of that and the Hot Water kit?

    Also how are the zone valves wired when you use the Opentherm bridge instead of using the BDR91 for boiler demand?

  3. #43
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    Quote Originally Posted by bruce_miranda View Post
    Oh sugar...some more expense. Ok so I have an S plan system. I understand that the Opentherm bridge will trigger the boiler for radiators and hot water. But i then have a further zone valve for UFH currently controlled via a Y87RF and a BDR91. What happens to the BDR91 of that and the Hot Water kit?

    Also how are the zone valves wired when you use the Opentherm bridge instead of using the BDR91 for boiler demand?
    How have you wired it at present?

    Wiring diagrams for the BDR91 are in the appendix but you need to decide how you're gonna control the system. If you can take some pictures and or do a sketch I can advise.
    I work for Resideo, posts are personal and my own views.

  4. #44
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    Currently I use only 1 BDR91 which is used to control the UFH zone valve via the Y87RF. The Y87RF is paired to the evohome as a Zone Valve sensor and the BDR91 is pair as the actuator. So for the UFH there is automatic boiler demand via the evohome even though I don't have boiler demand relay set up in the System Devices. The BDR91 switches on the zone valve, which in turn switches on the boiler whenever the UFH needs it.

    I currently use no Boiler demand for either HW or radiator CH because my current Honeywell timer clock seemed to serve the purpose. The timer clock is wired in a standard S plan format.

    I can see the benefit of using Opentherm to control the boiler flow temperature hence am prepared to change the way things work. But the bit I am confused about is how are all the zone valves wired in an OpenTherm setup.

    I will add the HW kit to the evohome. But before I pour more money into my set-up I'd like to understand the wiring.

    I know the OpenTherm bridge receives the Boiler Demand from the evohome controller, switches the boiler on and controls the flow temperature based on the demand. That bit I understand. However in a standard S plan wiring it's the zone valves that open first and then they fire the boiler up. With Opentherm, who or what opens the different zone valves?

    In the evohome controller under Boiler Demand, I have to choose between Boiler Relay or Opentherm. Hence my questions.
    Last edited by bruce_miranda; 3rd April 2016 at 10:05 PM.

  5. #45
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    Quote Originally Posted by bruce_miranda View Post
    Currently I use only 1 BDR91 which is used to control the UFH zone valve via the Y87RF. The Y87RF is paired to the evohome as a Zone Valve sensor and the BDR91 is pair as the actuator. So for the UFH there is automatic boiler demand via the evohome even though I don't have boiler demand relay set up in the System Devices. The BDR91 switches on the zone valve, which in turn switches on the boiler whenever the UFH needs it.

    I currently use no Boiler demand for either HW or radiator CH because my current Honeywell timer clock seemed to serve the purpose. The timer clock is wired in a standard S plan format.

    I can see the benefit of using Opentherm to control the boiler flow temperature hence am prepared to change the way things work. But the bit I am confused about is how are all the zone valves wired in an OpenTherm setup.

    I will add the HW kit to the evohome. But before I pour more money into my set-up I'd like to understand the wiring.

    I know the OpenTherm bridge receives the Boiler Demand from the evohome controller, switches the boiler on and controls the flow temperature based on the demand. That bit I understand. However in a standard S plan wiring it's the zone valves that open first and then they fire the boiler up. With Opentherm, who or what opens the different zone valves?

    In the evohome controller under Boiler Demand, I have to choose between Boiler Relay or Opentherm. Hence my questions.
    The zone valves will be powered and opened by separate BDR91 relays. You'll need three if you want to retain your S Plan heating valve.

    Alternatively you can create a hot water priority system by wiring the heating zone valve BDR91 from the C terminal on the hot water zone valve BDR91. This will ensure that the boiler runs at the lowest possible flow temperature for space heating.

    You won't need to permanently power the zone valve grey wires and you won't need the orange wires to fire the boiler any more. The wiring diagram for individual zone valve is in the appendix.

    Hope this is starting to make sense.

  6. #46
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    Lets start with a standard S Plan evohome system.

    One BDR91 is bound as a Hot Water controller. This is triggered whenever the evohome needs HW. The BDR91 triggers the HW zone valve which in turn fires the boiler. The other BDR91 is bound as a System Device in Boiler Demand Relay. This is triggered whenever any radiator needs heat. The BDR91 triggers the CH zone valve which in turn fires the boiler.

    So far so good?

    Now when I add OpenTherm to this. How do things change?

    I didn't think I could use both an Opentherm bridge as well as a Boiler Relay for Boiler Demand?

  7. #47
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    Quote Originally Posted by bruce_miranda View Post
    Lets start with a standard S Plan evohome system.

    One BDR91 is bound as a Hot Water controller. This is triggered whenever the evohome needs HW. The BDR91 triggers the HW zone valve which in turn fires the boiler. The other BDR91 is bound as a System Device in Boiler Demand Relay. This is triggered whenever any radiator needs heat. The BDR91 triggers the CH zone valve which in turn fires the boiler.

    So far so good?

    Now when I add OpenTherm to this. How do things change?

    I didn't think I could use both an Opentherm bridge as well as a Boiler Relay for Boiler Demand?

    The OpenTherm bridge is used instead of the Boiler Relay

    The Hot water BDR opens the hot water zone valve at S Plan system layer, the heating BDR opens the S Plan heating valve
    The third BDR91 is for your UFH zone at zone layer
    I work for Resideo, posts are personal and my own views.

  8. #48
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    I understand the HW and the UFH zone valve wiring and BDR91 binding because that is very simple. It both cases the BDR91 is bound as the actuator which in turn opens the relevant zone valve. The Opentherm bridge will now independently fire up the Boiler because it too knows there is heating demand.

    What I don't understand yet is the CH zone valve wiring and BDR91 binding. I thought that the whole point of a "System Device Boiler Relay" was so that if any radiator or HW needs heat it would trigger the boiler relay.

    Now if I replace the boiler relay with the Opentherm, the Boiler Demand is handled by the Opentherm, so the boiler will start up. But how will the CH zone valve open when there is CH demand? How do I bind the CH zone valve BDR91? I can't bind it as a Boiler Demand System Device because that is now the Opentherm bridge. So what options to I use to make sure that the CH zone valve opens whenever any of the TRV zones need heat.

  9. #49
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    Is the confusion because in an S-Plan system you don't (normally) HAVE a boiler relay? So there's nothing to replace?

    There's an alternative method of wiring / configuration where you lock the CH 2 way valve open, and then you can use a BDR91 as a boiler relay. Of course this only works if you have HR92s on all of your rads.

    I'm assuming that this is the starting point when upgrading to OpenTherm?

    P.

  10. #50
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    That has actually confused me even more!

    I thought in a S plan evohome system you would have 2 BDR91

    1. One BDR91 would work the HW zone valve. The HW zone valve would in turn fire the boiler via the Orange wire. This BDR91 is bound to the evohome controller as the HW kit's acuator.
    2. The second BDR91 would be bound as a "System Device" boiler relay. This would open the CH zone valve. The CH zone valve would in turn fire the boiler via its Orange wire. The idea behind binding the BDR91 as a 'System Device' for CH was so that ANY radiator demanding heat would be able to fire the boiler as the evohome controller would collate the multiple requests.

    Moving to Opentherm.

    I disconnect the second BDR91. I connect the Opentherm bridge to the boiler via the Opentherm connection. I replace the "System Device" binding from Boiler Relay to Opentherm bridge. All good so far. But because of the disconnected second BDR91, who opens the CH zone valve when there is radiator heating demand?

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