Drayton Wiser Open therm

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  • njr001
    Automated Home Lurker
    • Feb 2019
    • 8

    #16
    Having started this thread, I've been impressed with the very detailed responses from mtmcgavock particularly his experience of installing boilers, whilst I appreciate if I choose a Vaillant I won't be able to use Opentherm, I do have an investment in Drayton Wiser and like the App for setting differential room temperatures and being able to set these remotely, am I likely to have an issue interfacing this with a Vaillant boiler controller?

    Comment

    • mtmcgavock
      Automated Home Legend
      • Mar 2017
      • 507

      #17
      Originally posted by njr001 View Post
      Having started this thread, I've been impressed with the very detailed responses from mtmcgavock particularly his experience of installing boilers, whilst I appreciate if I choose a Vaillant I won't be able to use Opentherm, I do have an investment in Drayton Wiser and like the App for setting differential room temperatures and being able to set these remotely, am I likely to have an issue interfacing this with a Vaillant boiler controller?
      Thanks. No in this case you wouldn't use/require the Vaillant Controller and just use the S/L on the boiler. So it would just be an On/Off and you'd have to set the required flow temperature on the boiler as you saw fit.

      Comment

      • DBMandrake
        Automated Home Legend
        • Sep 2014
        • 2361

        #18
        Originally posted by mtmcgavock View Post
        Also referring to other manufactures there's that many issues with Opentherm across the board (Viessmann and Ideal) that I can see why someone wouldn't want the hassle of using it. And really, is it only beneficial in a house that's multi zoned?
        Opentherm has nothing to do with single zoned or multi-zoned. It can work with either and doesn't care.

        It's just a better (smoother, more efficient, more precise, quicker) way to control the heat demand sent to the boiler instead of repeatedly switching it on and off, which is kinda.... crude, to say the least, especially in 2019...

        It makes a lot more sense with today's modulating boilers because it allows the boilers own modulating system to achieve the target flow temperature.

        If the boilers maximum flow temperature is set to 70C but the thermostat thinks 50C flow temperature is appropriate at a given moment it asks for that and the boiler modulates its burner to achieve that - full burn if its a long way below it to get there quickly, reduced burn when it gets near 50C, and modulating to try to maintain a nice steady 50C.

        Response time for changes in demand is also fast - if the thermostat now decides that 60C is needed because someone left some doors open or adjusted a set point it sends that new heat demand and the boiler will act on it instantly striving to get to 60C as soon as it can and stay there.

        Swap that out for a relay doing TPI and things get a whole lot worse.

        Firstly you now have the issue that the boiler is unaware of the flow temperature that the thermostat would like. All it knows is that its max flow temperature is set to 70C by the dial on the front, and it is getting turned on and off a lot. When it's commanded on it does its best to get to 70C.

        Lets say that room temperature equilibrium at a set point of 20C demands an average flow temperature of 50C as before. Through negative feedback the thermostat will eventually learn the on/off duty cycle that achieves the steady 20C room temperature, and that will be an average of 50C flow temperature. But the thermostat doesn't know what the flow temperature is... all it knows is the duty cycle. Neither thermostat or boiler know what the average flow temperature should be for the situation.

        To maintain that average 50C it has to keep switching the boiler off before it gets to its 70C set point. So it perhaps oscillates between 40C and 60C in each TPI cycle. During every on cycle the boiler will be going at full burn trying to get to the 70C flow temperature set point that it is never allowed to get to.

        The modulating boiler never gets a chance to modulate when TPI heat demand is low! It also goes through a lot of unnecessary on/off cycles where the striker is having to light the flame. Every time it gets lit it probably generates excess CO and HC for a couple of seconds as well.

        Compare this to Opentherm asking for a constant 50C with the burner running constantly at a low output.

        Secondly, there isn't even a fixed relationship between TPI duty cycle and average flow temperature! It depends on the load on the boiler, eg how many radiators are open and by how much. If you have more radiators open it will take a higher TPI duty cycle to get the same average flow temperature, while only one or two radiators open will need a low duty cycle to achieve a given flow temperature.

        Thus there is a lot of interaction between different zones - more load from additional zones requesting heat will drag the average flow temperature down so the thermostat will have to find a new duty cycle to bring the average flow temperature back up to where it needs to be (which takes time) while with Opentherm the boiler will automatically adjust its heat output to regulate the flow temperature to the requested temperature despite changes in load.

        Thirdly response time is really poor with TPI. Typical TPI cycles are 10 minutes long, that means the heat demand is only an average over a 10 minute period, so it takes at least 10 minutes on average for a change in heat demand sent by the thermostat to actually have any real effect on the heat output of the boiler and radiator panel temperatures. This additional lag makes the system unresponsive to changes like doors being opened and closed, small changes in set point etc.

        For example on my system (TPI) if I increase the set point in a room at equilibrium by half a degree and the current heat demand of the room is quite low it can take over 30 minutes for any appreciable change in room temperature to occur. The first 10 minutes is wasted by the lag of TPI. My biggest issue with TPI is the poor response time.

        Compare that to Opentherm where any change in requested flow temperature no matter how small (say 5C) will be responded to by the boiler immediately and within maybe a couple of minutes the water temperature flowing through the radiators has increased. This faster response time leads to faster overall system response time to changes in set point or room conditions, less overshooting etc...

        I don't doubt that there are significant problems with the implementations of Opentherm in some systems, with compatibility issues etc... but the fundamental premise of a thermostat digitally requesting a specific flow temperature is absolutely sound, absolutely superior than TPI in multiple ways, and is just as applicable for a single zone system as multi-zone.

        I just wish manufacturers would get off their behinds and implement it properly and fix all the silly compatibility issues! It's not rocket science!
        Last edited by DBMandrake; 9 March 2019, 11:23 AM.

        Comment

        • mtmcgavock
          Automated Home Legend
          • Mar 2017
          • 507

          #19
          Originally posted by DBMandrake View Post
          Opentherm has nothing to do with single zoned or multi-zoned. It can work with either and doesn't care.

          It's just a better (smoother, more efficient, more precise, quicker) way to control the heat demand sent to the boiler instead of repeatedly switching it on and off, which is kinda.... crude, to say the least, especially in 2019...

          It makes a lot more sense with today's modulating boilers because it allows the boilers own modulating system to achieve the target flow temperature.

          If the boilers maximum flow temperature is set to 70C but the thermostat thinks 50C flow temperature is appropriate at a given moment it asks for that and the boiler modulates its burner to achieve that - full burn if its a long way below it to get there quickly, reduced burn when it gets near 50C, and modulating to try to maintain a nice steady 50C.

          Response time for changes in demand is also fast - if the thermostat now decides that 60C is needed because someone left some doors open or adjusted a set point it sends that new heat demand and the boiler will act on it instantly striving to get to 60C as soon as it can and stay there.

          Swap that out for a relay doing TPI and things get a whole lot worse.

          Firstly you now have the issue that the boiler is unaware of the flow temperature that the thermostat would like. All it knows is that its max flow temperature is set to 70C by the dial on the front, and it is getting turned on and off a lot. When it's commanded on it does its best to get to 70C.

          Lets say that room temperature equilibrium at a set point of 20C demands an average flow temperature of 50C as before. Through negative feedback the thermostat will eventually learn the on/off duty cycle that achieves the steady 20C room temperature, and that will be an average of 50C flow temperature. But the thermostat doesn't know what the flow temperature is... all it knows is the duty cycle. Neither thermostat or boiler know what the average flow temperature should be for the situation.

          To maintain that average 50C it has to keep switching the boiler off before it gets to its 70C set point. So it perhaps oscillates between 40C and 60C in each TPI cycle. During every on cycle the boiler will be going at full burn trying to get to the 70C flow temperature set point that it is never allowed to get to.

          The modulating boiler never gets a chance to modulate when TPI heat demand is low! It also goes through a lot of unnecessary on/off cycles where the striker is having to light the flame. Every time it gets lit it probably generates excess CO and HC for a couple of seconds as well.

          Compare this to Opentherm asking for a constant 50C with the burner running constantly at a low output.

          Secondly, there isn't even a fixed relationship between TPI duty cycle and average flow temperature! It depends on the load on the boiler, eg how many radiators are open and by how much. If you have more radiators open it will take a higher TPI duty cycle to get the same average flow temperature, while only one or two radiators open will need a low duty cycle to achieve a given flow temperature.

          Thus there is a lot of interaction between different zones - more load from additional zones requesting heat will drag the average flow temperature down so the thermostat will have to find a new duty cycle to bring the average flow temperature back up to where it needs to be (which takes time) while with Opentherm the boiler will automatically adjust its heat output to regulate the flow temperature to the requested temperature despite changes in load.

          Thirdly response time is really poor with TPI. Typical TPI cycles are 10 minutes long, that means the heat demand is only an average over a 10 minute period, so it takes at least 10 minutes on average for a change in heat demand sent by the thermostat to actually have any real effect on the heat output of the boiler and radiator panel temperatures. This additional lag makes the system unresponsive to changes like doors being opened and closed, small changes in set point etc.

          For example on my system (TPI) if I increase the set point in a room at equilibrium by half a degree and the current heat demand of the room is quite low it can take over 30 minutes for any appreciable change in room temperature to occur. The first 10 minutes is wasted by the lag of TPI. My biggest issue with TPI is the poor response time.

          Compare that to Opentherm where any change in requested flow temperature no matter how small (say 5C) will be responded to by the boiler immediately and within maybe a couple of minutes the water temperature flowing through the radiators has increased. This faster response time leads to faster overall system response time to changes in set point or room conditions, less overshooting etc...

          I don't doubt that there are significant problems with the implementations of Opentherm in some systems, with compatibility issues etc... but the fundamental premise of a thermostat digitally requesting a specific flow temperature is absolutely sound, absolutely superior than TPI in multiple ways, and is just as applicable for a single zone system as multi-zone.

          I just wish manufacturers would get off their behinds and implement it properly and fix all the silly compatibility issues! It's not rocket science!
          I understand how Opentherm works and i've fitted Evohome systems with it. Yes it is the way forward and I do think it's a great idea. As i've said Vaillant to an extent have been doing this on their own controllers for a while but what I was getting at in my last post regarding the Single/Multi Room zoning was that Opentherm in a Single Zone application really isn't always the best way forward.

          For instance, you have the Single Zone stat located in the Hall. The hall either heats up quicker than other rooms, or slower. Stat then realises this, adjusts flow temperature accordingly, either lowers or increases as it sees fit. So you've got an adapting flow temperature now to maintain the heat in that Single zone where the stat is. The bedroom upstairs which is North Facing (Maybe with an undersized radiator for condensing boiler) is pretty chilly now as it's only getting a low flow temperature to get that room to a decent temperature. Or the other way zones which are heated up, but the stat is requesting a higher flow temperature are now overshooting. Yes you could argue that it's only the same as TPI to a degree, but at least for certain periods it's getting the flow temperature that is set at the boiler. In terms of efficiency it might be great for that single zone, but in terms of comfort for other areas in that property you might be decreasing it.

          That is kind of the point I was trying to make. A Multi Zoned system, yes Opentherm all the way. But personally I don't think that in a Singe zone application it is the best solution. You also have to consider that Evohome even asks for 100% temperature when a zone is 1.5oc out. Many of my own zones come on at different times of the day to various temperatures. I could probably guarantee that a zone is out 1.5oc during heating periods, so it'd be asking for 100% demand anyway. Also add in the fact that most boilers only have a 1:4 to 1:6 modulation range, so if the boiler has been oversized for the property (Which most installers seem to do!) then you are only going to be modulating down to a 3kw output.

          In my own property I actually find TPI works quite well, I have a non modulating boiler which is either On or Off. Now whether this helps as you're only getting a constant heat output out of it, i'm unsure. But I rarely suffer from overshoots or zones taking time to meet set points.

          Opentherm is the way forward no doubt and it's something I would have when I come to replace my boiler, but I think we've got a long way to go before it is a viable option for installers to pick.

          Comment

          • someuser08
            Automated Home Jr Member
            • Feb 2019
            • 16

            #20
            And back to OP's first post again - I was actually told that Vaillant no longer consider VR33 invalidating warranty as long as it's removed before warranty service guys come to sort out any issues. So if your installer removes it before calling Vaillant then it should be OK...

            Comment

            • Beige
              Automated Home Lurker
              • Oct 2019
              • 4

              #21
              Originally posted by someuser08 View Post
              And back to OP's first post again - I was actually told that Vaillant no longer consider VR33 invalidating warranty as long as it's removed before warranty service guys come to sort out any issues. So if your installer removes it before calling Vaillant then it should be OK...
              This is super interesting - can you tell me who told you that, please? Ideally I'd like confirmation from Vaillant before installing mine (in my brand new boiler with 10yr warranty)

              Comment

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