My thoughts are this

What you are trying to do is complex and is not in any way guaranteed to save money over simply heating the whole house full time, unless the insulation between the rooms is as good, or nearly as good, as the house insulation.  If its not that good then its quite possible (perhaps more likely than not) that it will cost more money to do it this way, unless you are very careful about how you do it.  Also introducing TRVs that can open or close at will may cause problems with defrost and/or operation when its mild.

If you need night time setback comfort reasons, then of course go ahead.  Otherwise be aware that this added complexity may well increase running costs and, because there are so many variables, its very difficult to measure with any certainty. 

SOFAIK the only way you can robustly deal with this (in the sense that the controller has the intelligence not to do something that will cost you money) is Adia.  I don't know if they support Midea, its likely that they do or will because Midea supports modbus.

If you do go it alone then I would suggest you may want to build into your automation some logic that deals with cost, and, if you dont have a buffer tank/volumiser, some logic to open the TRVs during defrost

I can explain my logic but thats the basic message. 

As a further thought supplemental to the above, if you can directly control how much each TRV is ope,n and can program them effectively to reach a quasi steady state (simulating a LSV) then you may be able to do better.  Thats what Adia effectively do (as I understand it) albeit with a lot of learned intelligence about the system wrapped around the actual control loops.

If you could do that then setting the TRV degree of opening in the 'off' rooms to achieve something about half way between what the room would fall to if unheated (typically just a few degrees below the temperature of the adjacent room(s), and the temperature of the adjacent room(s) may provide an optimum.  

If you enjoy automation and the 'degree of opening' is exposed by your TRVs then that might prove interesting and possibly save money.

Hi James,

Thanks you for your replies.  On the subject of cost, I've read the various thoughts about smart TRVs on the forum and I appreciate that you and some others think that they're not economical. That may be the case in general, however there's a pretty strong resale market on Ebay for many of the brands, so I'll get most of the parts there and if I decide I'm not happy I can sell them again. All hobbies cost money, as well.

I can certainly agree that a smart TRV system adds complexity!

The heating system does have small buffer volume I believe, as it has a Heat Saviour between the heat pump's water circuit and the central heating circuit https://heatsaviour.uk/

How could smart TRVs cause a problem with defrost mode or when it's mild weather? Is the defrost issue that there might not be enough heat energy in the CH circuit to defrost the heat pump if all the TRVs are closed? And the mild weather issue because TRVs that close because the room is warm enough mean there's not much water volume to heat therefore the heat pump short-cycles?

Adia replied to me and I asked a bunch of followup questions, I've not had any answers yet but it's only been one day. They didn't come straight back to me to say that they can't support Midea, so that's promising.

Re programming a kind of steady-state, that would require direct control of each TRV and I'm not sure that the off-the-shelf systems provide that level of fine control, though they possibly do, I'll look into it. I believe that most smart TRV systems open and close to modulate the temperature in the room using a PID loop, with the degree of opening adapted as the system learns, however they probably don't have a steady state. What you describe suggests that you think it's better for the heat pump to be continuously heating the whole volume of water in the system, have you understood you correctly?

Cheers 🙂

Posted by: @madbilly

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So, what I'm looking for is a way to send a flow temp setpoint demand from the smart TRV controller to the heat pump controller.

I don't know about the smart TRV end of things, and what it can put out, but you can certainly modify the Midea Set LWT (flow temp) over modbus, I do just that. What I actually do (because it is easier) is adjust the end points of the WCC, which then of course alters the Set LWT using a simple python script. It checks the difference between my actual room temp and desired room temp every hour, and if there is a discrepancy then it moves the WCC up or down accordingly. If both ends go up by one degree, then any Set LWT will be one degree higher etc etc.

Whether you really want to do that (have an army of TRVs calling the shots) is another matter, see @jamespa's replies. It is very complex though, very hard to model these things, and getting empirical rate is hindered by the fact important variables keep changing! 

Posted by: @madbilly

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Thanks you for your replies.  On the subject of cost, I've read the various thoughts about smart TRVs on the forum and I appreciate that you and some others think that they're not economical.

The issue is not the cost of the TRVs, its the fact that using them will almost certainly drive up the cost of your heating and reduce your comfort.  The savings in energy loss from zoned heating of a house are quite small unless the rooms are very well insulated from each other (which generally they arent), and the reduction in emitter area means you have to operate at a higher flow temperature reducing COP.  The second usually outweighs the first resulting in higher running costs.  if you have a long thin house so that rooms are well thermally separated this may not be the case provided the temperature difference you want follows the thermal separation. 

Heat Geek have a worked example of how heating fewer rooms increases cost.

Furthermore because TRVs operate on-off, rather than constantly on but throttled, the flow temperature has to be higher to supply the same amount of energy, again pushing COP down and energy consumption costs up

.

Posted by: @madbilly

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How could smart TRVs cause a problem with defrost mode or when it's mild weather?

With defrost mode by reducing the system volume available to the heat pump at the time defrost occurs.  Defrost relies on the energy in the hot water to melt the ice, if the water volume isnt sufficient the energy isnt sufficient and the ice may not melt.  This can, albeit rarely, force heat pumps into a doom loop where they never recover from defrost.

In mild weather TRVs shutting down and opening up will increase cycling because only part of the circuit will be open at any one time rather than it all being open.

Posted by: @madbilly

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What you describe suggests that you think it's better for the heat pump to be continuously heating the whole volume of water in the system, have you understood you correctly?

Generally yes.  The starting point (for max efficiency) is balanced radiators, no or few operational TRVs and the thermostat if there is one turned up well above the desired temp.  Then adjust the weather compensation curve (down) so the house is just warm enough. 

From there limited tweaking is possible, but depart too far from this and you are very likely to drive costs up no down.  As always with heating there are exceptions, but you need to think carefully and understand a bit about the efficiency characteristics of heat pumps before assuming any particular case is such an exception.  Operational TRVs on every radiator conducting gymnastics in time and space is unlikely to be such an exception.

Im not saying you shouldn't embark on what you are proposing, that's your choice.  However I would strongly encourage you to read up about the (negative) effects of zoning on the Heat geek site and elsewhere, the pitfalls with timed operation, the efficiency characteristics of heat pumps, on defrost and the response of heat pumps to mild weather (cycling), before you do!  Otherwise there is a fairly high probability your efforts will increase cost and reduce comfort, which you might find dispiriting.

Hi @jamespa @madbilly, It's nice to hear people talking about what we're building! I just wanted to chime in about how Adia works as there's a little misunderstanding above. 

Adia's 'TRV's are used to balance flow throughout the system, not to turn off flow to individual rooms when they reach temperature - that's why we call them Flow Balancing Valves (FBVs). In fact, Adia's FBVs virtually never fully close, meaning we maintain system volume like an open-loop system, and avoid the performance penalties you would normally see with TRVs / Zoning. We can also spot defrost behaviour and open all the valves to ensure full system volume availability when needed. 

The whole system is designed to give adaptive, controllable comfort to the homeowner without negatively impacting the performance of your heat pump. 

Posted by: @luke_adia

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Hi @jamespa @madbilly, It's nice to hear people talking about what we're building! I just wanted to chime in about how Adia works as there's a little misunderstanding above. 

Adia's 'TRV's are used to balance flow throughout the system, not to turn off flow to individual rooms when they reach temperature - that's why we call them Flow Balancing Valves (FBVs). In fact, Adia's FBVs virtually never fully close, meaning we maintain system volume like an open-loop system, and avoid the performance penalties you would normally see with TRVs / Zoning. We can also spot defrost behaviour and open all the valves to ensure full system volume availability when needed. 

The whole system is designed to give adaptive, controllable comfort to the homeowner without negatively impacting the performance of your heat pump. 

Thanks.  That's what I had personally understood although I hadn't clocked that you call them FBVs (good idea btw!)

@madbilly is trying to do something with regular TRVs which, unlike your PBVs, do turn off.  This is why Im suggesting he might like to contact you and also that what he is doing may be a bad idea!

Hi everyone,

I read the heatgeek article, very enlightening, it's certainly made me think about it a bit more. I already had a model of my house set up in Heatpunk so I tried setting every room to the same temperature, which I think is basically what Heatgeek is saying, and it didn't make any difference to the suggested flow temperature needed to adequately heat every room, whereas as I should have seen the flow temperature go down, shouldn't I? I'll probably go back to a room thermostat and normal TRVs setup anyway to see for a bit how it compares. I'll still look for a new smart TRV/FBV system though that co-exists nicely with heatpumps. Wundasmart say that they could kind of achieve no-fully-closed TRVs because the force of the motor is adjustable in the app and could in theory be balanced against the flow pressure.

I have had some correspondence with Sam at Adia, very helpful answers, not everything I want is there yet and two things could be showstoppers for me, 1) the fact that it requires ripping out the Heat Saviour and secondary pump and replacing with Adia's piping connections and monitoring box, I'm sure that's not a cheap operation, and 2) the fact that the app doesn't work over the local network, an internet connection is required. Still, I've asked for more info on costs so we'll see what comes back.

I've seen that Tado have a new product called Heat Pump Optimiser X I think, but it doesn't seem to work with Midea heat pumps yet and also requires subscriptions, which I don't want to get into.

cathodeRay, Thanks for the info about changing the weather compensation curve over Modbus, have you got code on Github or somewhere like that?

JamesPa, I don't think the Wiser TRVs operate on/off, at least, I hear them opening/closing different amounts each time. I'm sure they do go fully closed, which I think is your point, but they don't only have fully-open and fully-closed positions, they are smarter than that. The issues with defrost mode and mild weather I can see, however the mild weather issue exists anyway regardless of whether smart TRVs are used or not, doesn't it?

Re FBVs never fully closing, I feel like this could lead to cases where if only one room is not warm enough then all the others have to carry on getting warmer, and if it's sunny this could end up with rooms getting uncomfortably hot, especially if they're on the top floor.

Cheers 🙂

Posted by: @madbilly

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The issues with defrost mode and mild weather I can see, however the mild weather issue exists anyway regardless of whether smart TRVs are used or not, doesn't it?

I dont think so.  Essentially with TRVs, smart or otherwise, bits of the the system are likely to be shutting down or opening up to control the room temperature rather than adjusting so they are constantly open just enough to heat the room to the desired temperature.  Unless that is the TRVs are specifically designed for heat pumps like Adias are (To be clear, I have no connection).  TRVs (unless designed for heat pumps), to a great extent, defeat the principle of weather compensation and balanced radiators. 

Posted by: @madbilly

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Re FBVs never fully closing, I feel like this could lead to cases where if only one room is not warm enough then all the others have to carry on getting warmer, and if it's sunny this could end up with rooms getting uncomfortably hot, especially if they're on the top floor.

Possibly, but not that often.  Excess solar gain is however a good use case for TRVs but used as temperature limiters not temperature controllers.  To use them this way you adjust the LSV to give the desired temp in normal conditions and set the TRV say 2C above the desired temp.  This will limit the excursion due to solar gain without, most of the time acting as an on/off controller.

Adia's FBVs could of course also perform this function, no idea if they do (I would hope so).

Posted by: @madbilly

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I already had a model of my house set up in Heatpunk so I tried setting every room to the same temperature, which I think is basically what Heatgeek is saying, and it didn't make any difference to the suggested flow temperature needed to adequately heat every room, whereas as I should have seen the flow temperature go down, shouldn't I?

That rather depends on what 'same temperature' you set it to and what you were comparing it with.  The change may also be small and I don't know if heatpunk imposes some rounding.  

Posted by: @madbilly

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I've seen that Tado have a new product called Heat Pump Optimiser X I think, but it doesn't seem to work with Midea heat pumps yet and also requires subscriptions, which I don't want to get into.

Interesting.  I cant see anywhere that it tells you how it works, and I would want to be certain that it works in a way suitable for heat pumps, like eg Adia and homely do as I understand it.  It may, but you cant tell from the blurb on their website.

Posted by: @madbilly

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JamesPa, I don't think the Wiser TRVs operate on/off, at least, I hear them opening/closing different amounts each time. I'm sure they do go fully closed, which I think is your point, but they don't only have fully-open and fully-closed positions, they are smarter than that.

They may well, as do other smart TRVs I suspect, however that is only part of the issue.  What we want is for them to settle on a fixed level of opening that just keeps the room at a steady temperature, much as you would adjust an LSV.  This is about the time constants in the control loop and possibly coordination with other TRVs in the network.  Does Wiser do that?  I don't think so.  Doubtless the hardware could do that but I cant find anything which suggests that they are designed for heat pumps, which almost certainly means they aren't. 

Posted by: @madbilly

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cathodeRay, Thanks for the info about changing the weather compensation curve over Modbus, have you got code on Github or somewhere like that?

Not on github, haven't gone down that route. Here's the script I currently have running, should be self-explanatory if you know python basics. Zipped as the forum doesn't like .py files (can't imagine why). 

One important note, never set leftBase above above 57 (because 57 + 3 = 60 is the highest you ever want to go). I keep a note of the leftBase and rightBase changes when made in the live file (deleted this from this web version as it is just clutter only of use to me).

Also note I also have an independent modbus IAT sensor, that's where the aIAT (actual IAT) comes from. Details of how I set this up are in this thread, starting I think on page 3.