@johnnyb So my controller does shut off the heating when it gets to temperature, but most of the time the WC curve controls it so it doesnt happen. Things like solar gain can effect that when the room will get too hot and the controller kicks in. Below is an example of this happening at just after 2pm when the IAT reached about 22.8C. My thermostat is st at 22C

It may be that there is a hysteresis setting somewhere that you can use to wind down the overshoot.

In one sense you are in an enviable position if you are getting too hot at 25C flow temp, but you should be able to set the control thermostat temp to stop the heating automatically when you get too hot.

Posted by: @johnnyb

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At the moment it is set at 19 and the temperature is at 19.8 and it is still running.

If you set it at 19C it will switch off at 19.9/20C and stay off until it drops to 18.9C. The 1C hysteresis cannot be changed. The alternative is to use 3rd party thermostat or something like Homely. 

Thanks @mike-h that explains it. I thought I must be missing a setting somewhere. I did find the hysteresis settings and changed the heating from 0.5 to 0 but it doesn't seemed to have helped, but if there is an inbuilt setting that isn't changeable then that would explain why it is still overshooting.  It takes quite a while for the ITA to drop from 20 to 18.9 where the thermostat is situated and most of us are too warm before it turns off and my wife is complaining it is too cool in the room before it starts to warm up again. I have usually turned the heating down or off before it gets 1° over the set temperature.

I have signed up for a Homely trial but it is the end of the week before they come to fit it. It sounds like I will have to keep manually adjusting the temperature on the Samsung controller until the Homely is fitted.

Interesting @bontwoody that yours is switching off, but maybe you don't notice if it overshoots by 1°?  It is lovely to have a building that is easy to keep warm but it does give a few challenges, especially with the whole floor being warm and continuing to emit heat for quite a while after the pump stops running.

When it is windy and cold there's enough heat loss to leave it running constantly but I haven't got the WC numbers low enough for it to run all the time on still days. I think there's a low flow temperature setting in there somewhere as well, it doesn't seem to want to drop below 24-25° even with the low flow temperature set at 20.

@bontwoody

Posted by: @bontwoody

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So my controller does shut off the heating when it gets to temperature, but most of the time the WC curve controls it so it doesnt happen.

Thanks for that snippet of information! You have just saved me from doing an alteration to my system that would have been a complete waste of time and money.

I currently use a third party smart Honeywell thermostat to control my Samsung heat pump. Its currently setup to run on the weather curve (21C) and the target temp capped at 22C.

From various comments on the forums I started to think the samsung thermostat communicated with more intelligence in controlling the pump when room temp was reached, so the pump continued running although at a lower speed. I was going to move the controller from the boiler room into the house.

Just switching the pump on and off when room temp is reached is basically the same behavour as my external honeywell so I have decided to leave the system as is. At least the Honeywell guarantees limiting the cycling of the heat pump to the recommended maximum of three times an hour 😀

Mine isn't working like Mike-H's. Last night it seemed to be as it switched off about 1° above the set temperature but today it wouldn't come back on even when I turned the temperature up 3 or 4°, I had to press the power button on the contoller to turn the heating off then on again for it to switch on the heating.  It has been running on low flow temperatures all day but has now switched off before the room is up to the set temperature.

I think I will go back to the Drayton thermostat unit the Homely is fitted. It was switching on and off randomly but at least that was only for shortish periods of time.

Posted by: @johnnyb

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but today it wouldn't come back on even when I turned the temperature up 3 or 4°, I had to press the power button on the contoller to turn the heating off then on again for it to switch on the heating.  It has been running on low flow temperatures all day but has now switched off before the room is up to the set temperature.

That seems odd and I have not seen or heard of that before. According to Midsummer Wholesale the Samsung controller is supposed to be a bit cleverer than a standard thermostat, but I have never seen any evidence for that. It just seems to turn the heat pump off when set temperature + 1C is reached. However, I do like the ability to set as many schedules as you want and I had the impression that it cycled less at warmer OATs compared with the 3rd party thermostat - but not sure how!

@mike-h @johnnyb @technogeek

So my pump is PWM controlled from the control box, but I dont know if the thermostat controller influences that at all. If it did then that would be a good reason to use it.

@mike-h It might be the way mine is wired to the 2nd pump or a setting somewhere.  It might only be the 2nd pump which isn't switching on, I think the primary pump has switch on for a few minutes and then off again and done that a coulple of times. Once I power off and back on both pumps run and it continues as normal.  As the house as about 19° this morning the heating has been on low all day so I haven't been able to check again to see if that is actually what it is doing but that seemed to be the case late last night and this morning.

@bontwoody @mike-h @johnnyb 

From my various tweeking with the Samsung, I think the PWM pump is automatically adjusted by the controller to maintain the delta t set (default 5C). The thermostat has no effect.

Graham Hendra did point out that Samsung pumps can only modulate down to 40% of their maximum before the controller starts cycling the compressor.

In my case the minimum LWT I can have for continuous compressor operation is 37C and the minimum power output before cycling is approximately 4.9Kw.

From various refridgeration resources I have found on the internet, they all say it is normal for a heat pump to cycle 2 to 3 times an hour and between 10 and 20 mins per cycle, to maintain the set room / LWT temperature. The pump should not be running continuously. I find running it continuously to be a very expensive way of heating, unless you are one of those lucky people who have installed a small power station in addition 🤣 (I did a test with OAT of 6C, my oil boiler cost £5.20 for the day and the heat pump £7.44 for the day when running continuously).

As a rule of thumb, short cycling is running for 6 mins or less per cycle and switching on and off more than 3 times an hour, typically 6 cycles or more.

@bontwoody When I changed one of the Field setting values so it wasn't expecting my pump to be PWM then the inverted pump % shown on the Indoor Zone Status Info page has been showing 25% most times I have looked at it. Before I think it was usually at 75%.  I've no idea if this is good or not!

And it's not something I have noted down what it has said and when so it is only from memory, which isn't always correct!

@johnnyb If its PWM controlled you should have two cables running to it, one for power and the other for the optional PWM control. Not all pumps can do it as I found out on my initial install 🙂

@techhnogeek I think its likely that it just controls the DT 🙂 Im not clear though why running continuously would make the COP worse?

Thanks @bontwoody I know my pump isn't PWM controlled.

I also thought that running continously with low flow temperatures was meant to be the most efficient way to run a heat pump. It would be interesting to see what you have found and how you are running yours @technogeek

It will be very interesting to see how the Homely controller runs the system to get maximum efficiency.  Interestingly for the duration of the trial my electricity usage for the heating is a fixed monthly price so it is in their interest to keep the usage as low as possible.