If your temperature sensor is in the middle of the tank, there could be colder water below the sensor soaking up a lot of that heat.
It’s best to do DHW experiments starting from a completely cold tank, so you can be sure exactly what’s going on inside.
That’s a good idea Tim. I moved the sensor from top 1/3 to 1/2. So definitely there is hotter water at the top. What do you think, it’s better to place it top, middle or bottom ? Not sure…
I guess I need to buy a dedicated heat meter with temperature probes since I can’t trust this Samsung’s probes somehow 
And with half the coil above the sensor, the top of the tank can have water that is at the heatpump flow temperature (or higher but unlikely in this case). This would make the coil behave as if is smaller.
With a coil going that high in the tank, I expect it needs a pump to take water slowly from the top of the tank at the to the bottom when a temperature probe at the top indicates the water is near target and the heatpump is still trying to increase temperature at bottom.
(Heathgreek uses a double coil in their tanks so the coil does not go as high, but a plate heat exchanger connected between two ports right at the bottom of tank may be best.)
Hm, this could be… Do you think it would be better to place sensor at the top third of the tank? Then only small part of a coil should be above the sensor. Drawback is that set temperature will be at the top of the tank and middle and bottom will be colder.
What concerns me more is this steal of hot water from the tank. At night when space heating is turned off the AHSP is running circulation pump to reheat the water in piping to prevent freezing but it is doing in a bit of aggressive and imho unnecessary way. This way I found out it wastes about 2KW of heat per night.
Anyone experienced this behavior ?? I guess this the pump is doing only when outside temperature is bellow 4C or so.
Before I had a tank it looked like this… It pumped the water only through CH circuit and it was just fine… You can see that circuit temperature drop is negligible over period of few hours so I really don’t know why Samsung implemented this stupidity to take heat from DHW when installed. Maybe the only explanation would be to prevent condensation on radiators but the outlet temperature is not that low to cause this issue. During defrost cycle it takes heat from circuit which is actually active which is fine but no idea why when CH is not active it takes water from DHW. It even switch 3-way valve to take heat from DHW.
I guess it would be better to keep the CH running with reduced flow temps over night to prevent this theft.
Sensors might normally be placed at the bottom or a little above the coil outlet, this gives the maximum HW capacity but with stratification depending on the coil flow/return dT, a dT of 10C would be fairly normal between the cylinder top and bottom, I have seen cylinders with the coil flow in the bottom and out the top, little or no stratification then and a full cylinder at the required SP, not the best for boiler efficiencies and don’t think it would be suitable for a HP.
As pointed out above, with the sensor in the middle then the water in the top will approach the coil inlet temperature, the sensor temp will eventually reach its SP with the cylinder top at or very near the coil inlet temperature but the cylinder contents below the sensor will be lower than the SP, but because the coil is a 2.9m2 then there is still plenty of remaining heating surface as the cylinder temperature and “top half” coil temperature approach each other, the coil power still appears to be > 9.0kw, so maybe consider installing the sensor low down with a cylinder SP temp of 40/45C for a greater COP and just do the Legionella sterelization once/week with the heating element, it will take 4.88kwh to boost the cylinder from 45C to 60C or 6.5kwh to boost to 65C.
To control risk of legionella and to store maximum hot water from cheaprate the sensor should be as low as practical. But that will then trigger an automatic reheat (if enabled) when the tank is mostly still filled of hot water.
The tradition of using only one monitoring location can’t tell you what is going on…
I also see frost protection running every hour on my
Samsung HT 8kW installation…
It takes the heat from the house CH, if available, for just a few minutes, I presume by running in a reverse heat cycle. I always leave CH on at night now but with a set back to a low temperature. If there is no CH available then it takes it from the DHW. The DHW will only run for a maximum of 90 minutes anyway so best turn it off after an hour or so and run it twice if necessary.
On the point about maximum DHW temperature - I did a test and found that the LT for DHW rises over an hour to 68degC pretty impressive see photo so the HT of 70 degrees claim of Samsung seems to be correct. The target temperature max is naturally lower and seems to be 55 degC but you can locate the sensor where you like for best effect.
Interesting that the controller settings do not seem to be able to change the temperature rising to such a high maximum only the target temperature. I understand you can avoid this by running half hour DHW sessions which would be more efficient if you can tolerate lower water temperatures.
I have a pre existing UK standard 240 litre indirect tank with a coil at the bottom and it all works just as it did with the oil boiler so I am pleased with it…
Just before the hourly defrost
Could/can you change the power output, ie if its running at 3.5kw and you can reduce it to 1.5/2kw, then the discharge temperature may be lower and will increase with the cylinder temperature increasing to give a betterCOP but a longer reheat time.
Thanks for the reply John. Do you know if there are any user configurable options for power limiting on the Samsung Mim controller? Maybe the quiet mode? I will try that.
Yeah, but problem is with my DHW the coil runs from the very top to the very bottom As @Ringi stated placing the sensor down (2/3) would trigger reheat very often because of stratification. So maybe in my case the best position is in the middle ? Hard to say, however, for running time the heat output seems to be spot on. What is not spot on is the energy needed to heat the water from starting temp to target temp. Seems like 1KW is lost somewhere but I doubt it because the lines are fully insulated. Really only the effect of stratification comes into my mind in this case. At the top the temperature can be close to flow temps so at this area there is no heat exchange between coil and water or maybe a minimal. So in fact 1m2 of coils is not in use in this case and the pump tries to deliver heat to middle of the tank to reach set temperature.
In this case probably a slower heating would be beneficial but there is no option to do that. Maybe besides quiet mode enabled all the time ? Seems really the best strategy would be to keep the water at 45C and buy immersion heater to do sanitation cycle once per week at 70C. This would definitely kill all the bacteria in the tank. I still can see this as some imaginary enemy but for piece of mind it is probably good to do it.
@designerguy this is really a nice picture of frozen pump, from time to time I also have it like that Do you have your pump listed on openenergymonitor ? I’ve added mine recently and waiting for an approval. Would be interesting to compare numbers of your and mine unit.
As far as I know there is no way to limit heat output at all for DHW or CH circuits besides quiet mode enable. Maybe it would be worth of to try it.
At least I’ve found a way how to trick the pump to not do circuit reheating cycles from DHW tank. I simply deactivate DHW via modbus in case the pump or compressor is not running for 20 minutes and DHW temperature difference between set and actual temperature is not higher than 5C. This way the pump will not use DHW tank to reheat the circuit. It is sick but seems it works because there is no other way how to tell the pump to not steal the heat from DHW circuit every hour or so.
This chart is from today where I had DHW turned off. Funny is that pump didn’t care about flow/return temperatures and didn’t start a pump to circulate water at all. I’m sure if I would have DHW activated it would steal the heat from it…
I’ve activated this mechanism of turning off DHW in the afternoon. The sun was shining so the outside temperature was above 5C but the pump didn’t trigger a pump for some hours despite the return temperature dropped to 12C.
I will keep testing but looks promising.
So unfortunately my trick didn’t work a bit and despite DHW being deactivated the heatpump still took the heat from DHW tank when running frost protection. This is absolutely horrible implementation, have a look how much energy is wasted for this water recalculation in pipes… no comment, I would prefer Samsung gives the option to choose if I want this or not. It could take the heat from CH circuit and nothing bad would happen besides slightly colder radiators but there is much bigger mass of water in CH circuit then DHW circuit. Strange is that despite DHW was deactivated the pump was still switching 3-way valve for DHW. Crazy. Every hour the pump is running circulation pump for 6 minutes and opens DHW circuit…
I’ve calculated that these shitty cycles took 11C from water in DHW tank over night which corresponds to 3.5kWh of energy totally wasted! Well done Samsung…
My notes say that #3023 is DHW hysteresis. My (possibly simplistic) interpretation of the manuals is that DHW heating stops at (setpoint + overshoot), i.e. #3021 + #3022, and starts again at (setpoint - hysteresis), i.e. #3021 - #3023. Unless, of course, heating is timed out by #3025 (if coincident with a space heating demand).
We only use DHW for showers, not every day. Ridiculously, most dishwasher/washing machines in the UK heat their cold-filled water electrically, thus there is no DHW requirement. So our DHW tank spends most of its time at ~20degC when legionella is not really a risk.
Absolutely correct, Michal, but readily accessible heat (for frost prevention) is greater from the DHW tank (via the tank coil in a large volume of hot water) than it is from the emitters (from the warm air in your rooms). At least, that’s what I assume Samsung were thinking when they wrote the controller algorithms. Let’s see if we get a helpful response from the UK Helpdesk when they reopen in the New Year.
Late flash: Helpdesk have just now replied that:
“This is the anti-freeze logic, when ambient is below 3C and the system has been idle for 60 mins the primary pump will run for 5 mins with the DHW valve energised to ensure return temperature is above 6C. This will happen every hour these conditions are met. This logic is fixed and cannot be turned off.”
So it looks like we are stuck with it… 
But #3021 is max. temp or ? On controller I’ve set 50C as DHW tank temperature so I’m still not sure about the correlation. Actually I have #3021 set to 55C (Max. temp), #3022 set to 0 (STOP) and #3023 set to 5C (START).
What I’ve observed that with this settings the pump starts heat the water when temperature of tank drops below 45C and stops heating when it reaches 50C (there is some overshoot and final temp is usually 51.5C but I guess it will stop heating when it reaches 50C).
Is this correct behavior? I have #3011 set to 2 which I guess is with hysteresis but not sure what effect it would have if switch to 1.
Yes, we have same here for dishwashers but I plan to connect mine to hot water outlet. This would be more efficient and would help to “waste” some water from DHW tank.
Your strategy is interesting that’s right but maybe I would be concerned a bit. Even at 20C they can grow and is worse around 37C where you heat the water to… Especially if you don’t use the water for some days.
From this chart probably best would be to heat water to 55C in the middle section so at bottom is around 50C where they could die within 2 hours, not sure.
A dishwasher or washing machine doing a single load tends to use little more hot water then is in the pipes from many dwh tanks to the washer. So it was found that “hot fill” was not reducing running costs due to heatlose from pipes.
Biological washing agents work best in a slow wash with slowly increasing temperatures.
If you have your CH on a low setup overnight will the primary pump not keep running?
Good point. It would probably suck a cold water from pipes before the hot will come. At least it could help with turnover a bit but as I understood modern dishwashers takes up to 10L of water so not sure it’s worth of.
It will but you need to have heat spacing turned on (compressor on). Then of course it is not doing anti-freezing cycles only defrost cycles if needed and it will take the heat from whichever circuit is in use. So if I lower the water temperature the pump is running at 800W which is 4.8KW per 6h. This antifreezing cycles takes around 3.5kWh from the water. So thinking to just keep it running overnight and heat space. A simple settings in firmware could fix this issue but Samsung’s controls are very limited. Not as many users are such “fools” as we are
Looking at the Installation Manual (p136/137) again, I now think my comment above is incorrect.
My revised understanding is that #3021 is the temperature at which the booster (immersion) heater is engaged, i.e. the maximum DHW temperature that you can get from the heat pump alone, and that DHW heating (from the heat pump) cycles between (#3021 - #3022) (switch off temperature) and (#3021 - #3022 - #3023) (switch on temperature).
Is this consistent with your observations @Michal_S? I’m getting very confused…
STOP temperature #3022 I have set to 0. This could indicate that pump should stop heating the water once target temp set on the wired controller (50C) is reached. This matches +/-. It goes to 51C but think it’s just a hysteresis. Also it seems that START temperature #3023 (I have it set to 5C) starts to reheat the water once tank temperature drops bellow TARGET_TEMP 50 - START_TEMP 5 = 45C… This also matches my observation. I guess if I’d set START temperature to 10C it would start re-heat when temperature drops below 40C.
Since I have STOP se to 0 it heats to exactly what I’ve set on controller (50C). I think the #3021 is not involved here or am I wrong ? Why do we have #3021 then? Because obviously max. temp you can set by roomstat is configured in #1051. This I have at 70C. So here my confusion is - what’s the #3021 for ? In manual it says “Maximum DHW tank temperature with R-410A refrigerant heat pump operation.”
Obviously I have R32 and obviously I can set 70C in roomstat so this is confusion. All this manual is written in a very strange way.
