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Thread: Opentherm + EvoHome + Viessmann 111-W overshoots

  1. #101
    Automated Home Legend paulockenden's Avatar
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    Quote Originally Posted by StephenC View Post
    The communication protocol used by the Honeywell controls are unknown to us
    Says the company selling a (supposedly) Opentherm compatible boiler.

    Jeez...

  2. #102
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    I wonder what will happen if you point out that we know that the OT control sold by them is made by Honeywell!

  3. #103
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    Yes, you're right, just reread their email. I was jumping on nothing there....

    Anyway, I guess that is case closed on this now.

    I'm heading back to BDR91 (+ Weather comp now) asap when I can get hold of my Gas Safe Engineer.

    I can't say I'll be buying a Viessmann again. That said, it's only 2 years old, so I don't want a new boiler just yet!

    Thanks all for the advice on this.

  4. #104
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    Maybe if you made your feelings more publicly known they might do something. It's a few lines of code after all, not like swapping out the heat exchanger

  5. #105
    Automated Home Legend paulockenden's Avatar
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    Such a shame because they seem to be well made boilers. I wonder whether it's just the UK distributor being clueless, and whether 'back home' they are more clued up on the subject?

    Have you had any contact with the German techies?

    P.

  6. #106
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    This is sad. When I asked, some months ago, Viessmann Tech Support confirmed that the 100 series of boilers were 100% Opentherm compatible. I would have gone for one had it not been for the fact that my two local Viessmann installers were not keen on installing something that they know nothing about.

  7. #107
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    Having just bought a Viessmann 100W to work with Evohome through an Opentherm bridge I am now rather depressed having read this thread. It has just been installed so I am committed. Having read the thread I would be grateful for your advice.
    While I am sure one could debate for ages whether Viessmann's implementation of Opentherm is correct it seems to me that Evohome is failing to do what a control should do by demanding a 100% output in all conditions rather than a flow temperature appropriate for the sensed load. It seems to me to be very idle programming by Honeywell and that there are several easy ways for it to find an appropriate starting demand from the information that should be available to it.
    What is likely to happen next? I am new to Evohome so I do not know whether Honeywell pay any attention to issues like this and if they do whether it is possible to update the software in the Evohome or bridge to fix it.
    In the mean time what do members recommend that I should do? Fit the Opentherm bridge in the expectation of an update or ditch that idea in favour of weather compensation and a straightforward BDR91? I would be very interested in any views.

  8. #108
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    Weather and BDR91 gets my vote, especially since the BDr91 is already in the box.

  9. #109
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    Quote Originally Posted by Don10 View Post
    it seems to me that Evohome is failing to do what a control should do by demanding a 100% output in all conditions rather than a flow temperature appropriate for the sensed load.
    It does exactly that. 100% boiler demand until the temperature approaches the target temp (the 'proportional zone'), then it starts to reduce the demand.

  10. #110
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    Quote Originally Posted by Don10 View Post
    Having just bought a Viessmann 100W to work with Evohome through an Opentherm bridge I am now rather depressed having read this thread. It has just been installed so I am committed. Having read the thread I would be grateful for your advice.
    While I am sure one could debate for ages whether Viessmann's implementation of Opentherm is correct it seems to me that Evohome is failing to do what a control should do by demanding a 100% output in all conditions rather than a flow temperature appropriate for the sensed load. It seems to me to be very idle programming by Honeywell and that there are several easy ways for it to find an appropriate starting demand from the information that should be available to it.
    What is likely to happen next? I am new to Evohome so I do not know whether Honeywell pay any attention to issues like this and if they do whether it is possible to update the software in the Evohome or bridge to fix it.
    In the mean time what do members recommend that I should do? Fit the Opentherm bridge in the expectation of an update or ditch that idea in favour of weather compensation and a straightforward BDR91? I would be very interested in any views.

    Hi Don10.

    Yes, it is not great that they don't play well together. I had read a lot about Opentherm ramping down the flow temp as it approached the set point, but in reality, I saw on my setup it wasn't until the set point had been breached by 0.5 degrees did it appear to scale back the temps. With radiators at 80 odd degrees by then, it is too late especially in Spring months. If there was any kind of temp reduction - it wasnt much to be visible and I had no way of telling anyway as there is no logging that we can see. That was consistent and did not change with "learning" over a few weeks in place as is mentioned a lot here.


    Hopefully with the info on this forum and very helpful people here you can start ahead of us with more knowledge and see where you get to.

    Your house may leak heat like a sieve, and have few (not enough) small radiators to account for heat loss, and therfore high flow temps might not affect you as much.

    Don't fret too much, the standard EvoHome with bundled/free BDR91 works really well. I think we probably are fretting about Opentherm for that better control (theoretical for me still), and gas savings - but in reality the BDR91 works well enough.

    To be clear I have a Viessmann 111-W Storage combi that has a 46 litre integrated tank as I could not switch from combi to system at the time. This is as far as I can tell the same as the standard and more prevalent 100-w combi (my father has one and looks to be the same) but with much better domestic hot water flow rates (to a point...).


    Is yours a 100-w combi or system boiler out of interest? I only ask as with a system setup, domestic hot water (DWH) configuration may affect some settings and operations with Opentherm that may mean you get a different result.

    What ch flow temps did you regularly use during summer/spring/autumn/winter months? As long as no other changes are being made, this may give us an idea of how Opentherm with no flow temp limit will affect you.

    As for BDR91 with Weather compensation:

    1) the Viessmann 100 series boilers have analogue weather compensation with fairly limited control (heating curve *preset curve* adjustment only, not heating curve *slope gradient* adjustment). The 200 series boilers have digital control of both the preset curves and slope gradients to match the house as close as possible. I really need a different gradient than available but it is not possible on 100 series.

    EDIT: See page 4 for a better explanation. I can say with experience that I could do with the 200 series Weather comp. flexibility:

    http://www.viessmann.co.uk/content/d...mpensation.pdf



    2) I am finding that with EvoHome I set back rooms when not in use/overnight to low temps - say 8 degrees, and now rooms take forever to heat back up to 19 when it is 16 degrees outside, but say 12-13 degrees in one room. Of course I can manually select a higher curve preset , but then that kind of misses the point as the low flow temp objkective will be lost....Weather compensation then is pretty "dumb" in my opinion and only slightly better than fixed temp for me (a person that regularly sets back temps).

    Remember most of the energy savings to be had with EvoHome I would say is in setting back rooms to reduce heat loss (which proportionally increases as the delta between inside and outside increases).
    I've saved loads without Opentherm to be fair already. I'm chasing the last ~10% savings from low flow temps, increased comfort and faster warmup times with Opentherm to be clear (although not got there yet)


    Weather compensation and Opentherm are compared regularly, but in my experience of both I can now see they are completely different and suited to different use cases:

    1) Weather compensation is suited to people who runs their heating 24/7/365 heating of their rooms. By definition it is adjusting flow temp to account for heat loss only. Not suited to needing to warm rooms back up again from set back/cold position, as with the correct compensation curve, only limited heat will be available, so long warm up times.

    2) Opentherm is much much (vastly) better suited for people who regularly set back rooms or house temps and want a fast warm up time, coupled with low flow temps for the rest of the set point maintenance duration. (If only the max ch flow temp was adjustable on Viessmann boilers)



    Maybe a complaint to Honeywell and Viessmann from you as well will get them thinking.

    My advice is get the BDR91 connected and take photos of the connections. (I didn't do this before I switched to Opentherm).

    Viessmann Weather Compensation and Opentherm both require an adapter cable (circa 3) (the same cable supports connections for both for some reason even though WC works only if OT is disconnected). Both WC and OT are low voltage polarity insensitive connections that can easily be made by you afterwards to test Opentherm.

    EDIT: See here for the adaptor cable needed and referred to above that supports both Weather Compensation and also Opentherm at the same time for a 100 series Viessmann Vitodens boiler:

    http://viessmanndirect.co.uk/Catalog...n-Lead-7296465


    Hopefully this helps, and for what it's worth, I still have my Opentherm Bridge and am keen to see this year if a solution (that is supportable) can be found.

    My plan is to connect the R8810 Opentherm bridge back in, but have an inline switch on one of the cables to allow easy switching between BDR91 and Opentherm control in the future and for troubleshooting purposes. Changing binding between the two is also simple and quick.
    Last edited by StephenC; 1st May 2017 at 10:47 PM.

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