@johnmo max flow temp of 32C! Do you have huge radiators or very little heat loss? You can’t be describing ufh since it’s responding too quickly.

Posted by: @judith

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@johnmo max flow temp of 32C! Do you have huge radiators or very little heat loss? You can’t be describing ufh since it’s responding too quickly

It's UFH on 300mm centres, but prior to starting today I had been messing about with the heat pump a few days, so floor (or return temp was 20.8 this morning) so not much energy was needed to get it back to steady state. The return temp has been sitting at 21.1 degs for the last 10 hrs with no further heat input. Even though its cool here, we have no real need to add heat, but it was cool enough to play with ASHP.

Run data

Run 1 started at 07.55. Force stopped first cycle at 27.5 flow temp at 25 min run time (08:25). 

Run 2 starts 08.35 (10 mins off) stops at 09.05 run time 30 mins. No changes

Run 3 starts 09.25 (20 mins off) stops at 09.45 run time 20 mins. No changes

Run 4 start 10.10 flow temp 21.5 at restart (25 mins off) stops at 10.35 run time 15 mins. Increase B25 to 0.5 to increase off time and run time.

Run 5 temp 21.2 at restart 11.12. 35 mins off. Run. Stops 11.30 run time 18 mins

Run 6 DHW 35 mins

Sun comes out house at 21.5. return temp 21.1

Running curve set to 25 degs at 12 OAT and 32.6 at -5 OAT. Restart delta 6.8 so unlikely to automatically restart until OAT gets down to about 8 or 9 degs, which should be fine. May need to fine tune a little in the heating season.

Had to make a small change this morning as the summer house had cooled to 18 degs this morning, because the heat pump wasn't starting. The 25 degs start temp on the WC curve was slightly too low. So instead of the WC curve starting at 25, I changed to 26 at 10 OAT. It did 4 starts between 7 and midday running an hour and 33 mins in total run time. Weather got warmer once house hits 21 ASHP sits waiting. Return temp is about 0.2 degs above the restart temp at the moment.

Just thought I would post back in this thread for any future viewers as what what Ive discovered.

It appears that the Samsung controller does not have any way of allowing a user to alter the hysteresis settings directly. They are set to the Samsung default.

Indirectly you can manipulate the level of cycling by opening/having more emitters and raising the flow temperature. This means that even though you might be able to heat your house at a lower flow temperature, you may need to keep it artificially high (and at a reduced COP) to reduce cycling.

Samsung heat pumps can be fitted with an extra PCB (MIM-B19N) to allow reading and setting of operating values directly via modbus. I would be interested to know if the hysteresis settings can be changed this way, if anyone has any experience of using the board.

Posted by: @bontwoody

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appears that the Samsung controller does not have any way of allowing a user to alter the hysteresis settings directly. They are set to the Samsung default.

The method applied here (below) can get around the issue with water law and thermostat. Basically run time is dictated by thermostat hysterisis on top of the water law curve.

Take a look here, post 28 of 63

https://community.openenergymonitor.org/t/struggling-with-performance-of-samsung-heat-pump/25498/28?page=2

@johnmo Thanks for the link. I am in effect running it in pure weather compensation mode as my samsung controller/thermostat is in my hall not my living room and set to 24C (which it never reaches). I am wondering if it might be better to extend the cable and put it in the living room and lower the thermostat temperature to turn off the pump when it hits 22.5C.

I have seen some posts which mention changing FSV #2092 which supposedly changes the amount of time the pump runs for after the heat pump is turned off. This would seem to be helpful but I cant verify these settings looking at the Samsung documentation.

If the hysteresis setting could be changed via modbus then its something i would like to play around with. If nothing else it would make a nice project 😉

@bontwoody Some people even enjoy weeding their gardens I’m told!😉 Toodles.

Posted by: @toodles

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@bontwoody Some people even enjoy weeding their gardens I’m told!😉 Toodles.

If you like weeding, we have a nice 45 Deg bank full of weeds, or is that a wild flower meadow? I think it's a wild flower meadow, the wife weeds.

@johnmo Beauty is in the eye of the beholder…😉 Toodles.

Posted by: @toodles

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@bontwoody Some people even enjoy weeding their gardens I’m told!😉 Toodles.

LOL at least I can do my hobby out of the rain!

Posted by: @johnmo

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Posted by: @bontwoody

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appears that the Samsung controller does not have any way of allowing a user to alter the hysteresis settings directly. They are set to the Samsung default.

The method applied here (below) can get around the issue with water law and thermostat. Basically run time is dictated by thermostat hysterisis on top of the water law curve.

Take a look here, post 28 of 63

https://community.openenergymonitor.org/t/struggling-with-performance-of-samsung-heat-pump/25498/28?page=2

This is essentially how I have been running my Samsung - FSV #2091/2092 set to option 1 so the compressor can only be turned off by the 3rd party room stat. My unit is oversized and wants to cycle because it's putting out too much heat. I'd like LWT of 30C at 15C OAT, but the lowest the unit will achieve is 33-34C.

So I just let the 3rd party room stat switch ON/OFF calling for heat, set to 19C (we like it on the cooler side) and let the unit find it's own minimum LWT. Additionally, I can vary the hysteresis of my room stat.

Posted by: @bontwoody

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Indirectly you can manipulate the level of cycling by opening/having more emitters and raising the flow temperature. This means that even though you might be able to heat your house at a lower flow temperature, you may need to keep it artificially high (and at a reduced COP) to reduce cycling.

The COP may actually be better at that higher flow temp due to the reduced (or elimination of) cycling? All else being equal, a lower flow temp will give a better COP, but all else isn't equal when the unit is constantly cycling.