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Thread: Evohome: TPI with multiple controllers

  1. #1
    Automated Home Lurker
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    Default Evohome: TPI with multiple controllers

    I have a system that needs more than 12 zones, so I have two Wifi Controllers and double bound the BDR91 than controls the heating side of the system.

    My question is how does this function with respect to TPI?

    Does the controller drive TPI and send on/off signals to the BDR91? Does the BDR91 remember each controller instruction and only turn off when both controllers are sending off? If this is the case I cannot see how a TPI system could operate. Wouldn't the controllers be fighting each other?

    Or does the BDR91 control TPI by receiving demand levels from each controller and combining them?

    Thanks

    Toby

  2. #2
    Automated Home Ninja Dan_Robinson's Avatar
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    BDR aggregates the demand/loading from the base units and fires the boiler according to this
    Kind Regards - Dan Robinson (Jennings Heating Ltd)

  3. #3
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    Pardon my ignorance, but what is 'TPI'???

  4. #4
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    I always find Google a great help!

  5. #5
    Automated Home Ninja Dan_Robinson's Avatar
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    Its a control strategy that makes the best use of an on/off signal to smooth temperatures in a heating system.
    Kind Regards - Dan Robinson (Jennings Heating Ltd)

  6. #6
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    Quote Originally Posted by Chrisnoy View Post
    I always find Google a great help!
    I did that but it didn't seem to make sense in this context.. I'm not sure I understand but it isn't relevant to my single controller system, so it's not important. Also, it sounds like it's more concerned with optimisation, which I don't use.
    Last edited by filbert; 15th January 2018 at 10:21 PM. Reason: clarify

  7. #7
    Automated Home Ninja Dan_Robinson's Avatar
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    It's not directly related to optimisation.

    The BDR can coordinate 4 controllers and ensure a good firing strategy for the boiler.
    Kind Regards - Dan Robinson (Jennings Heating Ltd)

  8. #8
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    Quote Originally Posted by filbert View Post
    Pardon my ignorance, but what is 'TPI'???
    I know Dan Robinson and others favour short posts on here but, in case you are like me and prefer the full monty explanation of how things work, you might find the discussion here enlightening:

    http://www.automatedhome.co.uk/vbull...llations/page4

    I certainly learned a lot from DBMandrake's helpful clear and full explanations.

    And TPI stands for "Time Proportional and Integral" and is a control methodology that combines proportional control (output varying with temperature) and integral control (output increasing/decreasing with the time that the temperature is below/above the setpoint).

  9. #9
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    I'd like to know how this works in an OpenTherm scenario! Presumably, broadly the same - the OT bridge is bound to both controllers and aggregates the demand to come up with a flow temperature (instead of a duty cycle %).

  10. #10
    Automated Home Ninja Dan_Robinson's Avatar
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    Pretty much mate.

    Think of the bdr and the OpenTherm bridge as interpreters for the boiler.
    Kind Regards - Dan Robinson (Jennings Heating Ltd)

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