I forgot to mention that this is not just theory but actually works in practice. I have an industrial type controller which controls the indoor temperature by simply measuring the temperature in the hallway and the temperature of the radiator in my 'Man Cave' and achieves a temperature of 20.5C +/- 0.1C for most of the time with a deviation of +/- 0.2C on the odd occasion when the outdoor air temperature changes quite rapidly. It achieves this without the need for any wi-fi, cloud or even outdoor temperature measurement.
Derek - thanks for such a detailed explanation which makes sense. Your last paragraph (quoted above) is particularly interesting, especially the last sentence. Thinking about it, weather compensation using outdoor temp is perhaps a red herring, a convenient selling point for marketing, but ultimately it is never going to do very well, too many other variables. Earlier I mentioned using the current measured indoor temp for load compensation, but thinking about it, why not do as you do, have it (and some way of monitoring the LWT or rad temp) as the only inputs. The basic point, which I didn't spell out clearly enough, is that the only output that matters at the end of the day (hour/minute) is room temp - that is the be all and end all of a heating system. Everything else, in a language I am familiar with, structure-process-outcome, is a process variable. Why don't manufacturers do this, ie regulate (vary, rather than on/off) the heat pump output on the basis of the deviation of the actual room temp from the desired room temp? Variations in thermal mass, current weather, whatever, could be taken care of either dynamically (system measures itself and then tweaks itself accordingly), or by manual presets in a controller, eg a high thermal mass building would be set to have a bigger boost. If the system knows the date, it could adjust the boost to accommodate seasonal changes. Gain, latency etc, are all simple and should be easy to adjust. Even the basic autopilot on my boat has these things, to accommodate different types of vessel, heavy and slow to react vs light and skittish etc.
That your system can achieve "a temperature of 20.5C +/- 0.1C for most of the time with a deviation of +/- 0.2C on the odd occasion when the outdoor air temperature changes quite rapidly" says it all really. That is very tight control indeed, and in practice shows you don't need outdoor temp, weather forecasts, and all the paraphernalia of wifi, clouds, companies logging your home data and not letting you see it, and all the other IoT baggage that comes with 'you will be a QR code, and you will be happy' (a reference to the WEF, 'smart' cities and techno-fascism, for those who haven't joined up the dots in the code just yet).
Midea 14kW (for now...) ASHP heating both building and DHW
that heating control front end is out of the box in home asisstant
Thanks for the tip, I have spent the last few hours going down the Home Assistant rabbit hole, and I can see it may well be the way to go for monitoring, and possibly even control, but it is not Windows friendly (need to have that nightmare otherwise known as a virtual machine to run it properly). I also wonder if the blue RS-485 to USB converter I mentioned earlier, and which @batalto currently uses in another setting, is an even simpler set up? The data arrives on a com port, I suppose the question is, can HA read from a COM port? I will look into it, but I am sure one way or another it can, that must be how the black dashboard posted earlier gets its data.
Midea 14kW (for now...) ASHP heating both building and DHW
@cathoderay HA is rubbish on windows, as you say its a VM (linux based). Best is a dedicated machine (can be old / small) running HA OS which is their custom install of linux, takes care of everything for you. dashboards are often made from sensor data pulled from all manner of sources - they don't have to be locally physically connected. In my case I have ESP8266 and ESP32 boards in various locations round the house with locally wired temperature monitoring probes attached to various things (mostly heating pipes), reporting their data back to HA over wifi. HA logs, aggregates and presents it. I've shown this to my electrician and he was bowled over. HA can read from a local serial port - the only device I have directly connected to my HA machine is my Ramses-RF to USB gateway board. But it needs someone to have written an HA library to do it. that's why I was suggesting the ESP route - it appears that the ESPhome people have already done an ESP library to read RS485 with an ESP board. ESPhome to HA integration is out the box.
As it stands, I’m going to have to figure out my WC curves/flow temperatures by trial and error.
And such is reality. Please don't think I was trying to put you on the spot. It is more that I see you as an unbiased advocate for Homely (or more accurately Homely type systems, but as Homely is pretty much the main one out there, the two are currently effectively synonymous), and I wanted to hear the upbeat side of things. Reading between the lines, it hasn't arrived yet. The idea of load compensation (which I am going to define as adjusting heat output by changing flow temp and/or rate in response to any current difference between room set temp and actual temp, in much the same way that weather compensation adjusts heat output in response to any difference between the current ambient temp, and the lower right hand set point on the weather compensation curve) is simple, straightforward and obvious in theory, but has yet to become a practical reality. Micro USB port for main power supply??? What on earth is wrong with a simple robust standard plug and socket?
I still don't get the obsession with using forecasts and ToU tariffs. Forecasts are just that, and flakey too. The forecast is totally unnecessary when you can measure the current temps. If the room temp is below where it should be given the current weather comp curve setting, then something is cooling the building, but in fact it doesn't actually matter what has caused the cooling, all that matters is the rooms are below temps, and need a boost. Ditto if the building is warmer than expected. I don't have a smart meter, and don't have any plans to get one any time soon despite a constant barrage of pestilential emails from EDF demanding I BOOK MY ESSENTIAL UPGRADE NOW (the emails really are that shouty) so ToU tariffs aren't going to happen here any time soon.
The sort of control system I have in mind is actually very simple. It should both maintain the room temps at the right level and minimise energy use by having the heat pump run as a Steady Eddy rather than a Jumpin' Jack Flash. In practice, there are only three states, and only three responses needed, using very simple feedback:
Steady state: rooms temps correct, building heat loss balanced by heat pump output as determined by weather compensation curve. No action needed.
Room temp(s) are below what they should be, given current ambient and flow temp. It doesn't matter why, they just are. Action: boost ouput a bit.
Room temp(s) are above what they should be, given current ambient and flow temp. It doesn't matter why, they just are. Action: lower ouput a bit.
The first state is 100% weather comp curve controlled, the second and third state are weather comp tweaked by load compensation controlled.
It is a given the system in its entirety is correctly designed and sized, if the heat pump output and/or the emitters are too small, then no amount of compensation will ever work in demanding circumstances.
Such a control system could have manual 'warmer please' and 'cooler please' override buttons, although in practice the room stat/control (temp setting) can take care if that: if I want warmer please, then I just turn up the control by one or two degrees, ditto for cooler please. The buttons could be timed, ie boost/lower output for one hour, if using the using the set controller, you would have to remember to turn it down again once the boost had done its thing. Optionally, you could add in a so called 'smart' function, the system 'learns' the heat characteristics of the building, ie how fast each degree of output boost warms the building, and then adjust the amount of boost to get the warm up to happen in a reasonable time frame, but such an addition is not essential. The other key thing is such a control system works by adjusting level of output gradually over a range, rather than by turning the heat pump on and off, ie it has the heat pump running in such a way as to minimise energy use.
What's more, I can't believe we are that far from such a system, at least on modbus RTU/RS-485 based systems (Midea, Samsung and ? others). All of my reading so far points to the fact the connection is as simple as it can get: two wires. Here's the Midea wired controller end of things:
H2/A+ and H1/B- are standard mobdus RTU/RS-485 terminals, physically they are simple screw down connections in the controller unit. These two terminal are then connected to a standard RS-485 to USB converter (image from first hit in ebay search for "USB To RS485 Converter", cost £5.99):
Note the use of the same A/B terminal labelling: A on the Midea unit connects to A on the converter, ditto for the B terminals. Plug the USB end of the converter into a PC (or a raspberry pi or whatever) and that's it, unless I have got this all completely wrong, you are now connected to your Midea heat pump. The modbus register addresses are listed in the wired controller manual, eg 104(PLC: 40105) Water inlet temperature (read RWT), 105(PLC: 40106) Water outlet temperature (read LWT) and (I think this is right, typos notwithstanding) 2(PLC: 40003) Setting water water (sic) temperature T1S (set LWT). I imagine writing a python or similar program to take the right measurements and then adjust the LWT at regular (maybe six minute) intervals should not be that difficult. The PC/raspberry pi (the former I do know about, the latter I currently have no experience of) would also need to know the room set and actual temp, another very simple wired connection. All very simple, and very robust - at least in theory. No need to bother with all that wifi/cloud nonsense, just ultra simple ultra reliable local wires.
It's the ASHP manufacturers that should be supplying all this. There shouldn't be a need for 3rd party apps (and costs thereof), cloud-based services, modbus registers, strawberry pies or anything else 99% of people have no ability nor interest in. A lot of them (the manufacturers) do cover this already; Mitsubishi has auto adaptation and I think Vaillant does something too.
I forgot to mention that this is not just theory but actually works in practice. I have an industrial type controller which controls the indoor temperature by simply measuring the temperature in the hallway and the temperature of the radiator in my 'Man Cave' and achieves a temperature of 20.5C +/- 0.1C for most of the time with a deviation of +/- 0.2C on the odd occasion when the outdoor air temperature changes quite rapidly. It achieves this without the need for any wi-fi, cloud or even outdoor temperature measurement.
Derek - thanks for such a detailed explanation which makes sense. Your last paragraph (quoted above) is particularly interesting, especially the last sentence. Thinking about it, weather compensation using outdoor temp is perhaps a red herring, a convenient selling point for marketing, but ultimately it is never going to do very well, too many other variables. Earlier I mentioned using the current measured indoor temp for load compensation, but thinking about it, why not do as you do, have it (and some way of monitoring the LWT or rad temp) as the only inputs. The basic point, which I didn't spell out clearly enough, is that the only output that matters at the end of the day (hour/minute) is room temp - that is the be all and end all of a heating system. Everything else, in a language I am familiar with, structure-process-outcome, is a process variable. Why don't manufacturers do this, ie regulate (vary, rather than on/off) the heat pump output on the basis of the deviation of the actual room temp from the desired room temp? Variations in thermal mass, current weather, whatever, could be taken care of either dynamically (system measures itself and then tweaks itself accordingly), or by manual presets in a controller, eg a high thermal mass building would be set to have a bigger boost. If the system knows the date, it could adjust the boost to accommodate seasonal changes. Gain, latency etc, are all simple and should be easy to adjust. Even the basic autopilot on my boat has these things, to accommodate different types of vessel, heavy and slow to react vs light and skittish etc.
That your system can achieve "a temperature of 20.5C +/- 0.1C for most of the time with a deviation of +/- 0.2C on the odd occasion when the outdoor air temperature changes quite rapidly" says it all really. That is very tight control indeed, and in practice shows you don't need outdoor temp, weather forecasts, and all the paraphernalia of wifi, clouds, companies logging your home data and not letting you see it, and all the other IoT baggage that comes with 'you will be a QR code, and you will be happy' (a reference to the WEF, 'smart' cities and techno-fascism, for those who haven't joined up the dots in the code just yet).
I did consider installing an outdoor sensor and incorporating weather compensation, but decided it was not worth the effort.
Don't get me wrong, weather compensation does work fine in most situations, and is certainly much better than an on - off thermostat, and is fairly easy to understand and adjust by most homeowners. I suspect that the auto adaptation provided by Mitsubishi is somewhat similar to the type of system that I described, and I believe that mjr has now managed to get his system working correctly. The problem would appear that it is not clearly explained in the manual, and most system designers and installers struggle to comprehend weather compensation, let alone auto adaptation.
Maybe in a few years time there may be a heat pump controller which contains a self-tune facility, so all the installer would need to do is ensure everything is installed and functioning correctly. then select self-tune, press the button, and allow the controller to run through the self-tuning program and calculate the response times for the whole system. If the settings are not quite correct in the depths of Winter then the homeowner could just repeat the self-tune.
From my understanding the majority if not all the heat pump systems are already measuring the necessary parameters, so the only thing that is missing is the necessary software. Unfortunately I don't have access to the software, so cannot carry out any 'improvements'.
As it stands, I’m going to have to figure out my WC curves/flow temperatures by trial and error.
It is not that difficult, I have supplied various spreadsheets where it is possible to enter details about your home's heat loss and system parameters, the spreadsheet then provides the probable LWT at various outdoor air temperatures.
It should then be possible to set the warmer end of the weather compensation curve at a LWT of 25C at an outdoor air temperature of 20C, this should not require much adjustment if any.
At the colder end of the weather compensation curve select the required LWT at an outside air temperature of -10C from the spreadsheet and use this as the starting point. If the indoor temperature is too high then lower the LWT setting slightly at -10C and allow the temperatures to settle. The important thing to remember is don't try to rush the process, otherwise you will be 'chasing your tail'.
There's so much of interest in this thread. I know there is much controversy about compensation curves but to me it's a strange concept that the outdoor temp would be given any primacy over the indoor supply.
Why don't manufacturers do this, ie regulate (vary, rather than on/off) the heat pump output on the basis of the deviation of the actual room temp from the desired room temp?
Combining both monitoring of indoor temp AND altering of flow temp, for me, clearly has to be the future of this technology. Madness otherwise.
I agree. It seems to me that an approach using both indoor and outdoor temperature to auto-derive and learn the optimum flow temperature and rate would be best. It seems bonkers to make users work out what weather compensation curve to use given that hardly any installer is going to keep coming back often enough to tweak it.
I saw that the Homely system is being discussed on the latest Heat Geek episode on YouTube
yes I saw this a couple of hours ago. caviat is that it’s only being rolled out and available for 2 manufacturers equipment at the moment. (Samsung and Midea) Great insights though about the industry and the state of artificial intelligence.
still heavy emphasis in the discussion on fundamental weaknesses eg inconsistency of installers and poor handover processes generally. I’m sure we all have stories about that.
I saw that the Homely system is being discussed on the latest Heat Geek episode on YouTube
An interesting video and I personally think the Homely may be of use to help installers get the settings correct and homeowners who don't have the interest or knowledge to optimise their own system. From the cost saving and energy efficiency point of view I would need to look at the results in detail.
Edit.
What I did find interesting was that Heat Geek was far from impressed by the Samsung controller, I wonder why?
There's so much of interest in this thread. I know there is much controversy about compensation curves but to me it's a strange concept that the outdoor temp would be given any primacy over the indoor supply.
Well, the future indoor temperature is mainly a function of the current outdoor temperature determining how much heat your home loses now, isn't it? To me, it's even stranger that anyone would ignore such vital information and wait for it to manifest in unexpected changes in the indoor temperature. I can see that you might get away with it if you have heating that can respond quickly like an air-to-air system in a few rooms, but you'll spend most of the time at a "wrong" temperature if you try it with air-to-water supplying a whole house of low-temperature radiators or underfloor.
