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Thread: Opentherm + EvoHome + Viessmann 111-W overshoots

  1. #31
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    Quote Originally Posted by Stephen Crown View Post
    Running the radiators that were sized and installed for between 45/50(autumn/spring) to 60/65(winter)CH flow temps (i'd guess as that is what works for me with BDR91) at 81/82 degrees C is going to be a problem.

    Maintaining a set temp does not seem to cause an issue on the whole from what i can see, it is bringing rooms up to temp. I regularly see the boiler running - well mostly just the pump - at 26 or 31 or 35 or 41 degrees C whilst maintaining temps through the day/night, so it does appear to be dialing down when little heat demand is made.
    As I said earlier, the problem is that the peak temperature is not being limited to something reasonable that is appropriate for your radiator output and house heat loss. If its modulating down as low as 26 - 41 degrees when the zones are all in their proportional range (+/- 1.5 degrees from the set point) then the system has learnt what is required to maintain the rooms and is modulating the flow temperature, however when there is a "large" demand, like any room at least 1.5 degrees below the set point the system is designed to call for maximum allowed flow temperature to ensure that rooms can actually get up to temperature in extreme cold conditions.

    It's up to you to either manually set a sensible maximum flow temperature that is high enough but not too high (except your boiler won't let you in this instance) or use weather compensation to do that for you and adjust it automatically as the outside temperature (and thus heat loss through the walls) change. I would certainly try to pursue this problem to its logical conclusion if at all possible, and let us know your progress.

    It seems like something that should "just work", and even if it takes knocking Viessemann's and Honeywell's heads together to get a proper resolution it should be worth it. After all both companies have taken your money and provided you a fancy product that should perform as advertised and no matter whose fault it is both should be willing to work with each other to resolve it I would have thought, rather than just sending you, the customer back and forth between them like a ping pong ball.

  2. #32
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    Quote Originally Posted by Rameses View Post
    (with your permission) support can see what your opentherm is trying to do (commands, etc). This might give you some insight.
    Hi Rameses,

    I'm happy for this to happen - I've nothing to hide and everything to gain from advice. There could of course be something wrong my end - I just haven't got access to the data to determine that.

    re: radiator sizing, some are old some are new (1880's building), but were appropriate for the rad temps in the seasons i mention above, and the BDR91 seemed to have much much better control.

    It's the red hot scalding temps in the radiators that is the cause of the overshoots, it doesn't seems to dial down the temps as it approaches the set point as you would expect. To make it worse, the R8810 allows the CH flow temp to stay high for far too long, well beyond (time-wise), reaching the setpoint from observing the boiler and the controller at the same time. And this is ignoring the safety issue of rads that hot

    Just to add, the CH Heat output (KW) has been reduced from full power to around 2/5ths (full = 35KW), this just takes longer to reach the max CH flow temp of 81/82 degrees C. It is a modulating boiler that can go down to 8KW I believe for info.

  3. #33

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    Understood - the support team can get insight into what your opentherm is doing. We need to prove/see what commands are being sent to ensure things are behaving itself.
    getconnected.honeywell.com | I work for Honeywell. Any posts I make are purely to help if I can. Any personal views expressed are my own

  4. #34
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    As Viessmann told me ' not our problem', I've also got a case open with Honeywell (14568935 ) for the same issue . @Rameses , happy for you and support to check what opentherm is doing and what command gets issued when heat demand is high.

  5. #35
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    Quote Originally Posted by DBMandrake View Post
    , however when there is a "large" demand, like any room at least 1.5 degrees below the set point the system is designed to call for maximum allowed flow temperature to ensure that rooms can actually get up to temperature in extreme cold conditions.
    Hi DBMandrake - Indeed - I'm posting here to help other people out and provide info on the experience rather than the logic and theory that I had before. I'm definitely seeing max CH flow temps being called for changes of 0.5 degrees upwards set point changes. Whether I'm missing something I can't say as i cannot determine what the Evohome controller thinks the heat demand is, nor the flow temp request from the OT.

    I'm looking at Weather comp seriously now, but i would like to understand why if Viessmann are telling me the CH flow temp dial *should* work with OT, then what is the R8810 doing different? That might save someone else the trouble/money on needing weather comp as well in the future. Or have i uncovered a bug? Let's see where the evidence and data goes.

  6. #36
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    Quote Originally Posted by victorp1612 View Post
    As Viessmann told me ' not our problem', I've also got a case open with Honeywell (14568935 ) for the same issue . @Rameses , happy for you and support to check what opentherm is doing and what command gets issued when heat demand is high.
    Thanks for this - I'm hopeful with 2 systems that are similar, we'll get to understand whats going on.

  7. #37

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    Our support team are reviewing your posts. We see Viessman have disabled the boiler temperature limit when a OT room unit is connected. (!)
    On the positive side, if the logic control learned the control parameters with a manual limit on the boiler flow temp in place then it will relearn now that has been removed.

    Anyway - I am told they will be in touch.
    getconnected.honeywell.com | I work for Honeywell. Any posts I make are purely to help if I can. Any personal views expressed are my own

  8. #38
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    Great - thank you. I'm happy to assist diagnosis (set point changes etc.) where required and am available.

    Viessmann stated their own OT controller/unit *doesn't* disable the CH flow temp dial....I don't have one of those, so I have to take their word for it!

  9. #39
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    Just thought I'd add a photo of the boiler display showing the temperature this morning when 4 of the 11 zones were only 0.5 degrees C under the set point, and all others were well above the set point as they were still "set back":

    IMG_3133.jpg

    Note the CH flow temp dial is set to minimum - showing how with R8810 OT connected, this dial is disabled, but still a boiler temp of 81 degrees C is being reached. As noted previously, Viessmann stated that this is a Honeywell R8810 OT implementation issue as their own OT bridge/interface allows the dial to still let the end user set a max ch flow temp.

    R8810 OT telling the boiler to run at that temperature with rooms so close to the set point doesn't seem sensible. A couple of minutes later the set point was breached, and the boiler dialled down to 77 degrees, and only when beyond 1.5 degrees did the boiler shut off completely.

    I'm sure Honeywell may have more accurate data to show this in greater detail, but all I can do is observe the boiler temp display and TCC App/EvoHome controller and I can honestly say the common sense and logical assumptions of dialing down the temps as set points are approached (to avoid overshoot) does not seem to be occurring here. Yet.

    It's been 8-9 days now, so a few more to go until we could say learning has been completed.

    Edit: boiler has been off for 20 mins and the following screenshots from the TCC app shows the issue:

    IMG_3134.jpg

    IMG_3135.jpg
    Last edited by StephenC; 15th March 2017 at 08:40 AM.

  10. #40
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    I'd love to see the output of an opentherm monitor sitting between the R8810 and your boiler.

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