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Thread: Opentherm to EMS gateway

  1. #1
    Automated Home Jr Member
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    Default Opentherm to EMS gateway

    Hello,

    I have a evohome system that works quite well with a BDR91 to a Worcester Greenstar 30si combi boiler. Unfortunately, the Worcester uses the EMS protocol for modulation rather than OpenTherm.

    I wonder if there is such a thing as an EMS to OpenTherm gateway, and (upon Googling), I have found this: https://en.robbshop.nl/ems-ot-opentherm-converter-nefit

    It is described as: The Nefit / BOSCH EMS IP Converter is capable of converting OpenTherm communication Nefit / BOSCH communication protocols. This allows you to OpenTherm thermostat connected without any problems to your Nefit or BOSCH HR boiler.

    Any ideas if it will work?

  2. #2
    Automated Home Legend
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    I havenít a clue but I am not sure what you are trying to achieve? My reading of the supporting information is that the converter is designed to convert Opentherm information into Worcester Ebus speak. I cannot see how this will give you the benefits of Opentherm. Surely, it would be less risky to stick with the BDR and see if external weather compensation is possible.

  3. #3
    Automated Home Jr Member
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    Hey thanks for the response.

    My understanding of OpenTherm is that it will call for modulated heat from the boiler (warm, a little hot, very hot, etc), as demand from the smart TRVs fluctuates. I also understand that, in the absence of OpenTherm (or EMS), the boiler is either 100% on, or 100% off. I understand that the boiler compensates for this by waiting for demand to exceed some threshold before the boiler kicks in (i.e. it cycles on/off)...

    I understand also that evohome can send a modulated request using the OpenTherm protocol, but that the combi boiler can only accept modulated requests via EMS.

    I thought that I could stick an OpenTherm to EMS 'gateway' between evohome, and the Worcester combi boiler and I would get a modulated call for heat.

    Of course, I am only new to this, and it is very likely I have misunderstood the material I have read (such as: http://www.honeywelluk.com/Documents..._FINAL_WEB.pdf). Are you saying that a combi boiler can modulate without OpenTherm/EMS (but would have to start at 100% on, I guess)? I guess it would do so on the basis of the temperature of the return water, then? In this case, what is OpenTherm/EMS useful for?

    If you suggest external weather compensation offers an easy win, then I'm all for that!

  4. #4
    Automated Home Legend
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    My first thoughts were that this was simply a device to connect an Opentherm thermostat to your boiler. In otherwords, it translates/converts Opentherm demands into instructions that your boiler can understand. It doesnít necessarily follow that your boiler will then react as if it were under full Opentherm control. I could well be wrong.

  5. #5
    Automated Home Jr Member
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    Isn't it simply the case that each zone's thermostat sends a signal to the evohome hub, which resolves those against a schedule, and tells the TRVs to open, and the boiler to provide hot water?

    All I wanted was for the conversation from the evohome hub to the boiler be modulated rather than cycled, as per:
    evohome hub ----> R8810 --(OT protocol)--> OT/EMS gateway --(EMS protocol)--> Boiler.

  6. #6
    Automated Home Guru
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    This was also brought up in a new post a few weeks back:

    http://www.automatedhome.co.uk/vbull...-maybe-Evohome

    I looked through the links and it does seem viable, however youíre taking a risk really for minimal gain.

    Stick to the TPI based BDR91 on/off control if youíre risk averse. It does a great job simulating variable flow temps with the constraint of the max CH flow temp the boiler is set at (just not as quick to react as OpenTherm).

    That said if youíre willing to take the risk with ordering the part (donít take a risk with gas or electrics...) and have it fitted, then please feed back and let us know how it goes.

  7. #7
    Automated Home Jr Member
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    Quote Originally Posted by StephenC View Post
    ... if you’re willing to take the risk ...
    The main problem is I'd have to pay a man to connect it.

    Still, I'd be tempted if the economy benefits were to be had? Or is there not much in it?

  8. #8
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    I would say that there is not much in it in terms of usage savings. Long term benefits re boiler life etc are an unknown. I should add that once all zones are up to their set temperatures there is very little variation UNLESS a zone set temperature is changed or, in my case, the system switches over to hot water priority.
    Last edited by HenGus; 31st January 2018 at 04:52 PM.

  9. #9
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    Quote Originally Posted by HenGus View Post
    I would say that there is not much in it in terms of usage savings. Long term benefits re boiler life etc are an unknown. I should add that once all zones are up to their set temperatures there is very little variation UNLESS a zone set temperature is changed or, in my case, the system switches over to hot water priority.
    hi I tried this cant get to work correctly though tried many wiring configs Opentherm cant fire the boiler

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