Posted by: @travellingwave

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. Since this is a year old do you know if there is any update on the self balancing TRV subject.

@editor has made an oblique reference to a forthcoming product on which he has signed an NDA.  From the little he has felt comfortable disclosing, it sounds a bit like that.  More news apparently later in the year

Posted by: @travellingwave

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Are all smart TRVs on/off or are more advanced ones modulating?

To the best of my knowledge modulating, but to the point where they can turn off.  However you also have to consider the time constant.  So far as I can tell from when I had some they react too fast to do what we need in this case.

Posted by: @travellingwave

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At the risk of re-inventing the wheel again - my understanding of what is required for a self balancing system is broadly as follows...

I dont think your description is far out but time constants of an hour would almost certainly be much too fast.  If you are adjusting weather compensation curves or LSVs you often have to wait 24hrs for it to settle, particularly once you get 'close'.  I suspect you need a time constant which is much closer to a day than an hour, and you are going to have to think carefully about the interaction between recent flow temperatures and flow valve settings, particularly in a house with a high heat capacity (eg one with UFH in a slab).  You also need somehow to 'lock the user out' during the adjustment phase.  Thats yet another challenge!  I think you are right that Adia is doing something like what you describe.

The problem with 'controlling the heat pump' is that the manufacturers don't speak the same language.  Many have modbus, but I dont think the way they use it is consistent.  Quite a few have a proprietary bus.  So you need an 'adapter' for each heat pump.  This does a lot of harm to the business case, and to any confidence a consumer may have that the control system will remain supported for the lifetime of their heating system.

In summary this isn't a trivial problem and my guess is that it may take several attempts to settle on something that is even close to universal.  It may even turn out that splitting it into two, with the heat pump optimising flow temperature and the valves autonomously optimising relative valve position, is the way to go in practice, albeit that this is sub optimal in control terms.    One idea that occurs to me is to set the target temp on each valve, the valves communicate and adjust so that the relative (not absolute) room temperatures are according to what you have asked for, and then tell you to adjust the flow temperature to get the absolute right.  This is how in practice you manually do the job, and for good reason.

@jamespa 

blimey you type fast😀

Yes what you describe I think removes the need to communicate with the heat pump which is a practical benefit.

In the good old days in industry we had the 4-20ma current loop as an analogue interface between devices - anything could talk to each other. Modbus is as close to a generic network interface as I have found.

I agree the real challenge would be to make such a system user friendly and robust.

Another thought I had was to provide better tools for a one off balancing job for the installer. Part of the pain of balancing is taking multiple temperature measurements - collating them and then deciding what to do next. Perhaps a half way house is to allow the installer to be the master controller in the example I gave above - i.e provide all the info to a central point but with manual balancing. Might be necessary to measure return temp at each rad in order to speed up the process.

Posted by: @travellingwave

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Another thought I had was to provide better tools for a one off balancing job for the installer. Part of the pain of balancing is taking multiple temperature measurements - collating them and then deciding what to do next. Perhaps a half way house is to allow the installer to be the master controller in the example I gave above - i.e provide all the info to a central point but with manual balancing. Might be necessary to measure return temp at each rad in order to speed up the process.

I totally agree with this.  It has occurred to me that most of the 'kit' could be left onsite for a couple of weeks only then removed.  The business case becomes potentially more difficult however, because you sell a lot fewer.  Also the risk of the user 'fiddling' while the measurements are underway is transferred to the installer, which they may not want!

Heating, whilst seemingly incredibly simple, is actually extremely difficult, which perhaps explains the diversity of not particularly satisfactory of control 'solutions'.