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Thread: Opentherm and DHW control

  1. #1
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    Default Opentherm and DHW control

    Long story short (for people that would look for the same thing as I did):
    Evohome with the Opentherm R8810A1018 cannot control DHW.
    Only the DHW kit allows Evohome to control DHW.

    ---

    Hi all,

    I've just had my Evohome setup installed.

    Initially, the installer went the BDR91 route, considering my boiler was not (officially) supporting Opentherm protocol.
    It ment changing the wiring between the controler to the Boiler (as the Boiler was previously controlled by a single programmable Thermostat) to control it with the plain relay on/off.

    Full disclosure, the Boiler is an Atlantic Perfinox 4100 (yup, I'm from France).
    This Boiler is actually built around an LMU64 from Siemens, and was previously controlled by an QAA73.110 (also from Siemens).
    It turns out that those two elements are actually talking to each other using Opentherm. This is their design.

    I then assumed that it shouldn't be an issue to switch back to a Opentherm mode, and ordered on my own the R8810A1018 Evohome Opentherm controller, and installed it "manually".
    Turns out I was actually right, it works flawlessly since then.
    Modulation is done properly, and thanks to the new firmware that I've requested to Honeywell (.17 instead of an old .11), it is confirmed by the Evohome controller.

    However, my question is actually regarding the DHW.

    Previously, the QAA73.110 was able to handle some parts of the DHW management (not much more than plain 'activate' DHW or 'de-activate' DHW.)
    Since moving back to the Opentherm management of the Boiler, the Boiler disabled itself the Heating logic (Flow control, CH temperature, Daily Programmation, ...), but kept the DHW management internally.
    The Evohome shows nothing regarding the DHW, and everything needs to be done at the Boiler directly.

    It feels a bit strange, considering that the Opentherm IDs that the QAA73.110 & the LMU64 are supposed to handle include the DHW, and same goes for the Evohome + R8810A.
    In theory, the R8810A controls the ID #26 (DHW Temperature), similar to the QAA73.110, and the LMU64 should be able to execute the command sent by the Thermostat (wether it is R8810A or QAA73.110).

    Does any one of you, having a combined boiler (Heating + DHW internal storage), have their DHW managed by Evohome ?
    Or, on the opposite, does Evohome only handle DHW with the "DHW kit" ?

    I've ordered the components to assemble an Opentherm Gateway to inspect the traffic between the R8810 and the boiler controller to try and confirm the situation, but I'd love to have other feedbacks from what to expect.

    Some of the specs sheets of the components:
    LMU64 : https://be.elco.net/sites/be.elco.ne...(20031226).pdf
    QAA73.110 : https://be.elco.net/sites/be.elco.ne...(20031226).pdf
    Opentherm IDs handeled : http://otgw.tclcode.com/matrix.cgi#thermostats
    Last edited by oxygen; 28th September 2018 at 12:42 PM.

  2. #2
    Automated Home Legend paulockenden's Avatar
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    It's not clear from your message whether you have stored hot water (which is what the HW kit controls) or a combi boiler (which heats water on demand). Can you confirm which you have?

    P.

  3. #3
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    Quote Originally Posted by paulockenden View Post
    It's not clear from your message whether you have stored hot water (which is what the HW kit controls) or a combi boiler (which heats water on demand). Can you confirm which you have?

    P.
    Sorry, my bad if it wasn't clear.
    I have to admit, I'm not always familiar with the english technical "terms" so I'm not exactly sure what the Combi Boiler is ;-)

    The Perfinox (BVI model) heats the DHW, with a local internal storage acting as buffer.
    But this is controlled directly by the LMU64 (that regulates the DHW temperature, the valves, ...)
    The local storage buffer is (I think) 130L.

    Some minimal specs can be found here (in french)
    http://www.climeos.fr/images/Image/File/fichetech.pdf

    I'm trying to get back a link for the full installation pdf file, but have trouble doing so
    Seems this should work for the full tech pdf:
    https://docplayer.fr/5377781-Perfino...lantic-fr.html
    Last edited by oxygen; 28th September 2018 at 11:28 AM.

  4. #4
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    A combi boiler is one where DHW is heated on demand using a plate heat exchanger inside the boiler, during hot water use the flow through the radiators is stopped and the entire output of the boiler flows through the plate heat exchanger. Cold water comes in directly from the outside supply through the plate heat exchanger to the hot taps with no storage. They are very common in the UK.

    The (main) alternative here is an S-Plan or Y-Plan system using a hot water cylinder with an indirect heating loop. When the hot water cylinder is below temperature the boiler fires and a 2 or 3 port zone valve directs some or all of the boiler flow through the indirect loop in the hot water cylinder to heat the water which is stored until use.

    The relevance from an Evohome point of view is that Evohome is able to control hot water in an S or Y-plan system - a wireless temperature sensor is fitted to the cylinder and the Evohome controls the boiler and the zone valve that controls the flow to the cylinder indirect loop. You'll see the current hot water temperature on the Evotouch screen and the hot water temperature set point is set in the Evotouch configuration. A hot water schedule is defined so that the hot water cylinder is only kept up to temperature at times of the day you choose.

    On a combi-boiler system the Evohome has nothing to do with hot water control at all - it is all controlled by the boiler, and no hot water temperature will be seen on the Evotouch display. No schedule is needed because hot water is always produced on demand in a combi-boiler when a hot tap is turned on.
    Last edited by DBMandrake; 28th September 2018 at 12:08 PM.

  5. #5
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    Based on your detailed explaination, it seems to confirm that my Boiler is configured in a Y-plan logic.
    This is extracted from the technical documentation and reflects my system.


    Using the DHW kit is not an option in my point of view considering that the LMU64 handles already the valve and the target temperature for the hot water storage tank.
    It does't seems logical for me to disconnect the internal system (that works fine) to connect instead a valve and a themperature sensor instead of the ones managed by the internal board of my boiler (aka the LMU64)

    I was expecting the Opentherm module to be able to sent from the Evohome the relevant orders to the LMU64 to:
    - Get the DHW temperature of the tank (value that is collected by the LMU64 and was sent back to the QAA73.110 previously).
    - Modify the targeted DHW temperature "on demand".

    But it seems that this (DHW management in my situation) is not possible ?
    Basically, I wanted to have some feedbacks to see if I was the only strange one looking to control my DHW storage tank by Opentherm without the DHW kit, or simply if something was not behaving properly with my setup.

    Again, keep in mind that in theory, my setup should not even work from the begining as the Boiler is not supposed to be Opentherm (from the Vendor point of view), even if all the electronics inside are actually relaying on Opentherm :-)

    I suppose that in the longer run, the best solution for me will be to use the Opentherm Gateway, and bypass/force settings on the Boiler to take remote control of things that Evohome cannot handle well.


    Btw, is it even actually possible to change regulate the DHW target temperature based on a schedule by Evohome (even with the DHW kit) ? Or is Evohome, even with the kit, only able to set a single DHW target temperature all day long ?
    => You gave me the answer already, thanks
    Last edited by oxygen; 28th September 2018 at 12:22 PM.

  6. #6
    Automated Home Legend paulockenden's Avatar
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    The DHW kit wouldn't allow you to modify the temperature on demand. It simply has an on/off schedule.

    You COULD use the DHW kit to display the current tank temperature on your controller. You'd just need to fool it by setting the schedule to be constantly off, else the Opentherm would fire the boiler when it (rather than the boiler) thought the tank needed heating.

    But it seems like a lot of expense and bother just to display a temperature.

    Yes, it's a shame that the OpenTherm implementation in Evohome is so limited (it doesn't pick up reported boiler faults, either). But that's just the way it is.

  7. #7
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    So Evohome Opentherm cannot manage DHW.

    Thanks, that confirms things
    I was really having trouble as it is _stated_ nowhere (either way!).

    I'll go the Opentherm Gateway route then !
    And as you said, as it seems Evohome cannot read the boiler faults, it is something I ought to do anyway, to get the faults detected.

  8. #8
    Automated Home Legend paulockenden's Avatar
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    Opentherm gateway is the way to go if you want to do that.

    Search on eBay where a nice Russian chap called Cyril sells an expansion card for the Orange Pi Zero. It's a really neat setup.

    P.

  9. #9
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    I've actually ordered one a few days back already to Kiwi-electronics, feering the situation (and also wanting to confirm behavior of the R8810A with my non-opentherm boiler )

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