I don’t know, but even an old bimetallic strip would be better than TPI.
If the heat pump is too big for the property, then run it at a higher flow temp and turn it off when the house (room) is warm enough. This will likely be more efficient than short cycles at a lower temperature.
No clue. I was referring to the operating mode of the third party thermostat here.
Most respectable units are switchable between “on/off” aks hysteresis and “chrono proportional” aka TPI. For example:
There are plenty of non TPI options.
You need to read the manuals but vanilla hysteresis stats are available.
Quick look at Screwfix:
Hysteresis only:
Configurable Hysteresis or TPI:
TPI only:
or use the samsung controller as the stat. which obviously doesn’t do TPI. not having access to the ±5 WT button is a drawback, but if you get the weather comp settings right in a balanced system, you don’t need it.
with an old-school simple stat (as per marko reply) that has some known variation between on and off . not sure if you can get “configurable” variation though.
Or with a custom modbus controller that allows you to make your own decision (and maybe change it on a daily basis) about what temperature variation you want to run. Homely does exactly this. I’ve seen good reports about it. the reasons I haven’t tried it myself are a) samsung room temp controller is working well enough for me so not needed b) it’d mess up my current modbus setup c) there’s no display, just an app… but from people I’ve seen write about it, it seems good, and very well supported. and its not that pricy either.
I looked at this several years back when I started thinking about HP, because I had an opentherm roomstat for the boiler. I seem to remember it was basically none. There might have been one , from a non-mainstream vendor, can’t remember who. So opentherm seems to have been “not a thing” in the land of heat pumps. Dunno why.
My heat pump was installed with a TPI-only thermostat, and fixed flow temp. The only way to disable TPI was to move the setpoint 1.5° higher than I wanted, then it would call for heat continuously. Then I could play around with weather compensation, and use other methods to turn off the heat pump when the house was warm enough. I made it work, but it wasn’t reliable.
Awww. MCS at it’s finest. 
Hi John
By any chance - do you have a model or partnumber. Need to have one…
Thanks
Arne
Hi Sarah,
So what’s type is Samsung wired controller roomstat integrated in the display? It’s not intelligent at all and it’s pure on a off. If I set 22C on it then it waits until temperature raise to 23C and then switch off. Wait until in goes down to 22C and switch off. This is just stupid 1C hysteresis. Or am I missing something here?
I’ve bought this external thermostat COMPUTHERM B300RF where I can set sensitivity from 0.1 until whatever I need and it works just fine. Much better comfort and at 0.4C hysteresis pump starts 3x in 24h if there is warm outside. Maybe I will reduce it to just 0.2C…
So what these modern TPI are doing ? How can this help me with comfort. Drop of 1C is just too much for me for Samsung indoor thermostat integrated in the display.
What do you mean? For me the issue was that in “water outlet” mode it cycled 6x in one hour which was unbearable. So not sure if it followed this max. 4 cycle per hour. But OK, found out this mode is not suitable for me so I’ve switched to Samsung roomstat indoor temperature control which of course works with MIM controller but it’s just stupid. There is no intelligence behind with a fixed hysteresis of 1C as I’ve described above… Also many other guys confirmed it has hysteresis of 1C.
What is exactly this OpenTherm ?? Now I use this I stated above with hysteresis of 0.4C (maybe will lower) and it’s pretty much better than this Samsung’s indoor temp sensor with 1C hysteresis.
I read about Homely which is compatible via modbus but how it would work for me in my use case scenario I have no idea.
This is right and it works like that but hysteresis which you can’t control and is set to 1C is pointless. But as you said fore some stupid reason they won’t allow you to modify water law temp by +/- 5C which is a problem.
There are so many stupidities programmed with this pump that the person who is responsible for this should be fired and they should employ Sarah or other guys here to tell them how it should behave lol.
I’m really thinking to implement my own control using modbus…
Hi Michal,
Glad you’ve discovered a good solution (the 3rd party roomstat). 
Couple of points:
I think you’ll learn to like the Samsung controller once you have finished tweaking it. 
Sarah
This is interesting, howerver, not sure if it’s good enough for hetpumps ? Maybe if you can controll off time and cycles then yes, but not sure it would be good for those where you can’t.
Also what benefit it could have in comparison with hysteresis set to +/- 0.1C ? E.g I set temperature to 22C. Now system is on until 22.1C is reached and then it waits until it drops util 21.9C and starts again. So this is 0.2C hysteresis.
That’s the problem I don’t like that Samsung temperature controller because of 1C hysteresis. There is no way around so I can like it ? 
I can like it (partially) only when external thermostat is connected since it allows me to set water temperature by +/-5C. Also not perfect but better than nothing.
My main issue is I would need this heat pump to work flat at 45C water temperature from +3C and above. Otherwise it’s running with very low power input which is inefficient. And I would need to set my own hysteresis from +3C and bellow. But this is simply not possible because those Samsung controls are so stupid. There are useless limits on temperatures which don’t help. Think sooner or later I will end with modbus and my own code once I figure out how to do it. Then I will monitor outside temperature every few minutes and set my own water outlet temperature at given outside temp. If sun is shining I will decrease it proportionally.
Is this documented anywhere? I would be interested in understanding a bit more about this theory.
Hi William,
I’ve scoured all the available manuals, and I have found nothing to suggest that the hysteresis either in the Samsung standard roomstat, or in the weather-compensated ASHP exit temperature, is adjustable by the user.
Indeed on the latter, Samsung UK Tech Helpline wrote the following to me last year:
“Morning Sarah,
Your understanding seems correct, system will start to back of (sic) within 2K of set point target WL.
Minimum turn down for the 8Kw is 4Kw so your 50% reduction seems correct.
I’m not aware of any SW update currently available to change the hysteresis unfortunately.”
The last point was in response to a rumour posted on this forum that a firmware update was available for the Gen 7 which fixed this hysteresis constraint.
Sarah
Hi Sarah
That is strange. I have the 16kW and the compressor speeds I have seen are min 15Hz and max 75Hz.
@15Hz I can get down to 4kW output - though today when my CoP was 6.4 @ OAT 11 degC and flow temp at 32 degC @18Hz the output was 5.4kW. On colder days I have got down to under 4kW output though.
I have not installed the controller thermostat, just controlling on/off via HA.
I would expect the 8kW also to be able to get down to about 25%, so 2kW … but what do I know about heatpump compressors!!
William
Hi William,
By all accounts the 8kW has the same compressor as your 16kW so it turns down to exactly the same values that you are seeing.
Hence the problems owners of the 8kW are experiencing.
You have made the same assumption that lots of us have made about heap pumps and heat pump manufacturers, that they design and build heat pumps with similar ranges of outputs based on the highest nominal output, they don’t.
They make one heat pump and then limit it at the top end and sell it as a smaller heat pump for smaller homes.
Not all of them do this and the knowledge of this is now starting to spread.
I suspect we will all be far more mindful of this as time goes by and it will influence our buying decisions, just as it should.
@william1066
All three Gen 7 ASHPs (8/12/14kW) have the same compressor, so presumably the same turndown of ~4kW.
(I guess you have the Gen 6 AE160RXYDEGEU, and I don’t know what their rated turndown is.)
Yup, that is my model. Just looked back a bit in my data, have been able to get as low as 600w input, for 3.8 output @15Hz.
History – Home Assistant.pdf (138.5 KB)
Sorry William, what is “HA”?
Sorry … Home Assistant via modbus.
Thanks for clarifying. (It could have been Hand Actuator - i.e. switch - as used in the chemical industry.)
