In what steps can the radiator valve regulate heat? And for the thermostat?

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Answers

  • So as a further update, I also asked Jurian if the wavy lines correspond to the valve position, or to heater demand. He’s saying this:


    Personally, I don’t know a thing about PID, except for the Wikipedia article is just Googled. But... maybe one of you guys know more?

  • This seems to me to be consistent.

    To put it simply, a pid controller, if properly tuned, does much better than an on/off controller. It drastically reduces overheating and underheating. I notice that as the days go by, the system adapts itself better and better to the heating demands.

  • Hi @Schippie,

    There are percentages next to the wavy lines on the Care and Protect page. I assume that you are talking about the relationship between the wavy lines and these percentages. As far as I can make out these percentages represent demand rather than controller output. The demand signal is modified by PID functions to give the controller output which is what controls the valve.

    Not much more than two weeks ago I put in a suggestion that Self Tuning PI Controllers (or indeed PID) should be used - combined with improved temperature measurement. This suggestion has already been moved to "The Big Idea Archive" That was a bit quick! Perhaps because they already have a form of PID control which they are happy with or perhaps I should have not been too specific regarding the suggested solution.

    I assume and also it would be logical that the Tado PID controllers are on their servers - following the Tado goal of being Hardware Agnostic.

    My archived suggestion was intended in particular to suggest that the controllers should be "Self Tuning". I would be interested to know if they are. A PID controller is not necessarily self tuning. If a controller is correctly tuned, any fluctuating +ve and -ve deviations of the measured value from the set point will noticeably diminish over a short period. You should be able to see this effect an a graph.

    The bottom line is that it is not easy for the controllers to adapt to many different systems. For instance half of my system is microbore so some of my controls would be in saturation for lengthy periods (i.e. controller output at 0 or 100%).

    Finally, proper control is impossible without reliable and accurate temperature measurement and vertically mounted SRT's (with built in temperature sensors) fitted close to the radiator definitely do not give that.

  • Klaus_Ludwig
    Klaus_Ludwig ✭✭
    edited February 2021

    Hi @Schippie

    There are percentages next to the wavy lines on the Care and Protect page. I assume that you are talking about the relationship between the wavy lines and these percentages. As far as I can make out these percentages represent demand rather than controller output. If the percentages are controller outputs there must be some other limit on how often the valve actuators can move as they do not move every time the percentages change.

    Not much more than two weeks ago I put in a suggestion that Self Tuning PI Controllers (or STPID) should be used - combined with improved temperature measurement. This suggestion has already been moved to "The Big Idea Archive" That was a bit quick! Perhaps because they already have a form of PID control that they are happy with or perhaps I should have not been too specific regarding the suggested solution.

    I assume and also it would be logical that the Tado PID controllers are on their servers - following the Tado goal of being Hardware Agnostic. 

    My archived suggestion was intended in particular to suggest that the controllers should be "Self Tuning". I would be interested to know if they are. A PID controller is not necessarily self tuning. If a controller is correctly tuned, any fluctuating +ve and -ve deviations of the measured value from the set point will noticeably diminish over a short period. You should be able to see this effect on a graph.

    From what I can see, there is some room for improvement in both temp measurement and control. 

    The bottom line is that it is not easy for the controllers to adapt to many different systems. For instance half of my system is microbore so some of my controls (compared with in other rooms) would be in saturation for lengthy periods (i.e. controller output at 0 or 100%). 

    Finally, proper control is impossible without reliable and accurate temperature measurement and vertically mounted SRT's (with built in temperature sensors) fitted close to the radiator definitely do not give that.

  • hugbilly
    hugbilly ✭✭
    edited February 2021

    However many steps the TADO TRVs are capable of opening and closing in I can tell you they are far more effective than some of their rivals. As a recent TADO convert its a pleasure to hear the valves open, and feel the radiators beginning to warm, moments after a call for heat rather than the ~ 20 minutes previously tolerated . . .

  • So I asked some additional questions to Jurian (who's really quick to respond, by the way) concerning the relationship between tado modulating the radiator valves and modulating the heating request from the heater. He told me both operate in around 5% steps, and are related but not necessarily the same.

    He did mention that when only 1 tado valve requests power, it will always open 100% and modulate the required heat only. When 2 or more valves request power, both will modulate.

    Maybe that explains the somehow contradictory explanations so far. So valves will open/close only when 1 valve requests heat. If more do so, both valves and heating request will modulate apparently.

  • Klaus_Ludwig
    Klaus_Ludwig ✭✭
    edited February 2021

    Hi @Schippie,

    We learn a little step by step...

    My reference to "demand" was actually meant to refer to the error signal or PID controller input rather than to the PID controller output signal. Despite all the various posts and speculations on the subject I am still no wiser as to precisely what the percentages on "Care & Protect" actually represent.

    Due to the fact that Tado users are on multiple different configurations (relay, Opentherm, combi, heat only etc) we are not always comparing like with like if we get too specific. My system is a relay heat only Y plan system with vented hot water tank and Tado extension kit. If Opentherm is an option for me I might consider it, but am probably more likely to go for the weather compensation system that is available for my boiler (a Viessmann) as I can then have some influence on which weather compensation control ramp is in use.

    For me even with only one SRT in use it seems that it can be partially open and I need to have another radiator online with no SRT to ensure that the boiler is not locked out by low flow. Perhaps that is what applies to my particular set up...

  • GrayDav4276
    GrayDav4276 ✭✭✭
    edited February 2021
    Hey @Schippie

    Your response from @jurian reminds me of an old "Morecombe & Wise" sketch with Andre Previn......when Eric replies to A.P.

    " I'm playing all the right notes but not necessarily in the right order " 😎 🤣
  • Sorry @GrayDav4276 that reference flew straight over my head 😉
  • Ahh.... You youngsters.....🤓 It's a comedy classic....I'm sure it'll be on YouTube 👍
  • Schippie
    Schippie ✭✭✭
    edited February 2021
    Anyway, I am certainly no expert on heating. But I have now upgraded all my radiators so they are capable of control by thermostatic valves, I put tado srv’s on them, and with the new bridge tado sent me... all rooms are now connected without issue. As the upgraded radiators allow for setting the max heat flow, I also got rid of the temperature spikes. Have to admit it, things seem to work ok now. Only need to add a zone valve for the floor heating, and things are set.

    I still strongly feel tado should improve user control over the heating strategy and fix early start.
  • I read this thread with interest as one of my radiators is constantly overshooting by 2 or 3 degrees. It is the radiator in the kitchen, which is almost next to the heater. Before I had Tado that radiator would be open about 25% all the time to prevent it from heating too much and returning too hot water back to the heater. I suspect it's now opened too much before it overshoots.

    Is there a way to limit the opening of a Tado valve to combat this?

    @Schippie you mention you limit the max flow. That sounds like something that could help me. How do you do that?

  • @hapklaar I don't know a way to limit opening of the Tado valve, but you can certainly adjust the lockshield valve at other end of the radiator to limit the water flow through the radiator. This should have the same effect.
  • I have found some information about your question you might be interested https://shrinke.me/8GzQA38h