Posted by: @tasos

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If I can see correctly, there are periods on the graph where LWT equals RWT and during those periods the unit shuts. If this is the case, it means there is no heat drawn by the house. How can this be ?

The LWT does indeed become equal to the RWT towards the end of each cycle (taking a cycle as trough to trough) but it both are still above the IAT so heat will still flow from the emitters (rads in my case) into the room. What has in effect dropped to zero is transfer of heat from the heat pump to the emitter, fluid specific heat capacity x flow rate x LWT/RWT delta t becomes zero because the delta t is zero, but the radiator still has some warmth left in it, and before long that will also get replenished.    

@cathoderay How come water at 35 ish C flows through an IAT of 21 C and does not lose heat ?

Is there a buffer or a secondary network with its own pump ?

Posted by: @tasos

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How come water at 35 ish C flows through an IAT of 21 C and does not lose heat ?

@tasos, please do try to concentrate. That is the opposite of what I said: "both [LWT and RWT] are still above the IAT so heat will still flow from the emitters (rads in my case) into the room". 

I just realised that there is another setting I need to change but this is not one I can change via modbus- temperature lower limit of T1S heating zone 1. This is preventing the outlet flow temp from dropping below 35 when running in set flow temp mode, I believe….

Away from home at the moment so will have to try and find this in the wired controller settings when I get back. 

Posted by: @benson

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this is not one I can change via modbus- temperature lower limit of T1S heating zone

You might be able to, have a look at address registers 201 to 208, in particular 204 (from the wired controller manual modbus table). Try reading it first to see if there is anything there.

Posted by: @benson

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This is preventing the outlet flow temp from dropping below 35 when running in set flow temp mode, I believe….

But is this needed, can you not incorporate that into your control logic?

@cathoderay I'm not quite sure I can do that with my setup in terms of looking at the address registers? The svenar device will just provide me all of the read only and adjustable registers as entities in HA. Furthermore I cannot find temperature lower limit of T1S heating zone 1 anywhere in the serviceman settings- thus I do not believe the manufacturers intended this to be adjusted and is one of the read only ones.

With respect to whether it's needed, I am assuming if my lowest set outlet temp point I can have is 35°C, then in milder weather the IAT is going to overshoot unless I simply turn it off via indoor temp control. It has resulted in our IAT nicely ticking along at 21°C today even though according to the 'curve' at 10-11 °C (which is what it has been outside) the outlet flow temp should be 33 or 34 °C.

I have wondered whether trying to run lower temps through the rads is actually less efficient and thus is it set at 35°C for a reason? What I would say is I don't think I've ever seen my COP so high, as it is today- it's around 4.7 at the moment.

Posted by: @benson

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Furthermore I cannot find temperature lower limit of T1S heating zone 1 anywhere in the serviceman settings- thus I do not believe the manufacturers intended this to be adjusted and is one of the read only ones.

I can't even find it in the manuals, apart from in the modbus table. I wonder, where did you find it, and that it should be 35°C, which seems rather high eg UFH systems will often be below this? 

Posted by: @cathoderay

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You might be able to, have a look at address registers 201 to 208, in particular 204 (from the wired controller manual modbus table). Try reading it first to see if there is anything there.

Registers 200 until 208 are read only according to the modbus table overview.

@mosibi I confirm this and the value in my machine (R290) is 35. But this is for radiators, If you tell it you use UFH, it will get lower. In fact it would be 25. As it turns out, zone 2 uses UFH in my setup, and this limit is in the higher 8 bits of the same register (even though I don't actually have a zone 2).

Posted by: @tasos

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If you tell it you use UFH, it will get lower. In fact it would be 25.

@tasos interesting. I might look into that. My other option is just to use our indoor temp sensor to turn the ashp off when it gets milder and when a LWT of 35 C causes the IAT to overshoot. I was running an automation in the autumn to just turn it off when it reached 22 C, and then back on again when IAT dipped.

Efficiency wise my unit has been pretty frugal today and COP is good, so I’m tempted to do the former and perhaps there is good reason why midea set this from the factory for radiators….

Regarding your other query about using setbacks- I’m not sure to be honest. We find it really comfortable just having the house at 21 C all the time, and perhaps opening a bedroom window slightly at night if needed. 

Posted by: @mosibi

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Registers 200 until 208 are read only according to the modbus table overview.

I think it might be writable (horrid word). In my version of the modbus table, it is in section 2, Parameter Setting, as opposed to section 1, Running Parameters. 

Posted by: @cathoderay

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I think it might be writable (horrid word). In my version of the modbus table, it is in section 2, Parameter Setting, as opposed to section 1, Running Parameters. 

Registers in the 200 range are indeed in the “Parameter Setting” part, and that is also what has make me doubt, but a few of the different modbus register overviews (I collected multiple from different Midea heat pump types and clones) have a statement about the registers we are talking about.

That and a strong wish to not break mine or others heat pump, made it that I implemented it read only. But if somebody is willing to play with it and has successfully updated the values, I am very happy to also implement it