How to reduce cycling?

Hardware Heatpump
44

Your radiators and flow temperatures may be enough for your house but they arenā€™t for your heat pump, that is why it cycles so much.

If you retain the heat pump then you need bigger radiators and/or higher flow temperatures to reduce the cycling.

I would imagine the cycling is caused by the returning water temperature being too high?

If you increase the flow temperature your heat pump will run for longer and then be off for longer?

Less and longer cycles?

Is that possible with your Samsung heat pump?

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45

@Timbones @matt-drummer @Madsen68
And thereā€™s the dilemma.
My longer cycle time comes at a cost - I run a higher LWT (45degC at the moment for 10degC ambient - undersized emitters, I guess), and the instantaneous CoP is only 4.0 :slightly_frowning_face:. (Thatā€™s the same as the Samsung tables predict.)
So is it better to tolerate short cycle times, or increase the LWT and get a poor CoP?
Sarah

46

Hi Sarah,

Yes, that is it, we all face the same problem to greater or lesser extents.

Most of us know what the minimum heat output of of heat pumps are.

It is quite easy to work out our radiator outputs and then calculate the minimum flow temperature required to satisfy the the minimum heat output.

If that flow temperature is higher than we want then we have to increase the emitter output.

If we canā€™t or donā€™t want to do that then we have to accept a lower COP at times or shorter cycles.

There is a balance here between acceptable COP and cycles, obviously nearly 200 cycles a day are too many. The emitters are not even close to being able to cope with heat delivered and/or the low flow temperatures.

Some heat pumps are happy cycling more often and deliver efficient performance very quickly, it is easier to have shorter cycles with these. Other heat pumps take a while to get into their stride and longer cycles are more desirable.

Higher flow temperatures at higher outside temperatures are not necessarily that inefficient, the heat pump is working much more comfortably heating to 45c when it is 10c outside rather than -10c

47

I guess there is a third option - increase your heat loss.
Arne has huge radiators and a very well insulated house, so Iā€™m not surprised about his short cycle times.
But throwing open windows to match ASHP output with heat loss is not going to help climate change muchā€¦ :face_with_diagonal_mouth:.

48

If Arne has huge radiators why is it short cycling?

I have huge radiators and a heat pump with a similar minimum output, a low heat loss and my heat pump will run continuously with no cycles at all. It stops once every six hours as that is what Daikin have programmed.

Opening windows will have no impact on climate change from an energy usage perspective, Arne will use the same electricity whatever.

Arne may actually use less electricity by opening windows and therefore help climate change?

49

:point_right: Calculating the optimal weather compensation curve

50

@Timbones @matt-drummer @Madsen68 @Ian_Calderbank

Canā€™t help feeling that weā€™re missing important something here.

  1. Arne and I have the same ASHP/CH piping sizes, similar houses/insulation/heat losses, similar hardware (except Arne has volumiser, I have 2-loop buffer tank), and similar (primary) circulation flow (18-22lpm).
  2. Three main differences - Arne has much more emitter area than me, he uses the Samsung roomstat vs my 3rd party, and (I think) he operates his system 24/7 with a small setback vs my 14h/day with a large setback.
  3. His WC is set a few degC below mine, and his circā€™n pump is PWM vs my fixed speed, but Iā€™d guess these are less significant.
  4. Yet his cycle rate (and that of several others on the forum) is ~10min, vs my ~45min :thinking:.

Iā€™ve read all the manuals (again), and drawn a blank, exceptā€¦

a. Could it be that because my house starts colder each day, and spends several hours getting my living room up to setpoint, in the absence of roomstat ā€œstopā€ signals the ASHP controller keeps going for longer (albeit at the minimum ~50% turndown compressor speed because LWT is at WC setpoint)?

b. I keep coming back to the 10-minute circulating pump cycle time embedded in controller settings FSV 2091/2/3 = 4, and wondering whether these are somehow affecting ASHP cycle time (some fault in the controller algorithm)?

c. (Unlikely) I know that some 3rd party roomstats can confuse the ASHP controller and provoke short cycle times. Surely the Samsung roomstat wouldnā€™t do this??

Any thoughts appreciatedā€¦

Sarah

51

Hi Sarah,

I have seen this on another thread about the Samsung.

Why is there this desire for such a high flow rate?

I have a minimum 10lpm and want less.

Why do you all want so much flow?

A lower flow rate gives a lower dT, uses less electricity on the circulation pump and has less problems with smaller pipework I would imagine.

I think there is a big difference between a heating system with a buffer tank and one without.

I am sure that the heat pump is cycling because the water comes back to hot?

If that is the case the radiators are not getting rid of the heat produced, there must be a reason for this.

52

Many people recommend using Heatpunk.co.uk to calculate heat loss and required radiator size, room by room.

Nope, youā€™ve got that backwards: a lower flow rate gives higher dT, as the water has more time to absorb heat from the heat exchange. Faster flow = smaller dT. The amount of power (watts) delivered remains the same.

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53

Yes, sorry Tim, a complete mis type as I was either thinking of my return temperature being lower as I typed it or meant to type higher flow rate gives lower dT, I meant bigger or wider dT.

Either way, it came out wrong, sorry!

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54

How much more? Can we have numbers?

Would be interesting to see how much higher the flow temp needs to be to eliminate cycling. My own heat pump doesnā€™t like to go below 37Ā°C.

55

Hi All @SarahH @matt-drummer @Timbones

First, Sarah,
A= Problably have a great impact and on top you run with an external Roomstats - you seem to get a completely different type of control - this is actually confirmed by my supplier.
B= I have been fuzzing around with 2093 (No use for me to change 2091/2092 since I have and use the MIM controller for room stat) and I can not measure any significant change in Cycling - I went from 8 minutes cycle to 9 minutes - so a little improvement, but still over 6 cycles per hour.
C= My supplier have stated that a 3rd. party room stat could also be in the game to force the ASHP to act different than it does now - I will wait for their reply to an email that will be sent tomorrow.

Tim, I have 8 emitters + Floorheating (FH) - FH is around 10 m2 - rest of the house is 116 m2 so total of 126 m2.
I have 100 mm. insulation in the floor, FH is 300 mm. - 100+100 mm. insulation in walls and 300-350 mm. at the roof - All windows are latest 0 energy windows.

SkƦrmbillede 2024-01-28 kl. 20.51.33
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According to my calculation - I have around 3500 watts for my use in the house at 38/35/20 degC.
dt at 3 degC - which is quite stable when the ASHP runs - goes a bit over - up to 4 and a bit under 2,95 or so - so during that 8 minutes cycle it is steady in around 3,5 minutes after it have started the compressor and until I can see the compressor shuts down - rest of the time is pwering up, and down - and around 30 sek. where it is completely off - No water circulation no nothingā€¦
With this Samsung I have steady production around 42-45 degC, when I push it up there on manual. Then the house climbs to around 26-27 degC and that is killing meā€¦ :slight_smile:

I would prefer a dt at around 5 but I am not able to make that - if I was able to slow down flow, I might would be able to do it, but that will affect the COP in a negative manner - so I surely wont do (Accept) that.
I was told that flow was king when it comes to ASHP - and I replaced all the valves on the emitters from Danfoss RA-N to RA-G - this way I get 2,5 more flow through the emitter - this way I have reduced flow temp from around 40-43 degC to 32-34 at 7 degC outside temp. Significant savings in kwh.

Allthough I do agree, my emitters could be better and no dought, if I replaced all to 3 layers - I problably could get a better dt - I still dought it would be like magic and solve all the cycling issues I experince.

My calculation leads to the ASHP is to large - 5 Kw would have fitted better. On top we deal with an 8 kw which uses the same Scroll compressor that is to found in the 2 larger ASHP in the series - 12 and 14 kw - So minimum power is around 0,8 kwh input which produces around 3,2 kwh at cop at 4 - which is the minimum COP I readout during production - many times it is 4,5 up 5,2 - this produces more heat power than my emitters are able to consume.
I am not so damn strong in the theory of the different factors we are dealing with - but my guess is that if the amount of produce kw matches or are below the emitters capacity - we would look at a heatpump that can get rid of the heat produced and that way create slightly better dt and COP because it will at no doughts, get longer runsā€¦
If I am on a wrong track - let me know :slight_smile:

/Arne

56

The emitter size directly affects the minimum flow temperature of the system. If the emitters arenā€™t big enough, then flow temp will rise until the emitters can output that heat. Or the heat pump will cycle because that flow temp goes above the set threshold.

Hereā€™s a chart from my system showing generated heat vs. emitter output. I only get stable running when emitters exceed the heat pumpā€™s minimum. This is way above the heat loss for my property.

Screenshot_20240128_210933
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Side note: heat pumps tend to not get best performance at their minimum output, so better to run at slightly higher kW output.

Raising the weather comprehension curve will eliminate cycling, but youā€™ll need a room thermostat to turn it off when the house is warm enough. Basically by cycling the room temperature instead of flow temperature.

Increasing emitter size allows heat pump to run at a lower flow temperature without cycling.

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57

this would mean increased used kwh, correct.

thinking I might should try another approach - raise Compensation Curve by 5 degC, like you proposeā€¦

Just saw an issue - My kamstrup shows 1050 l/hour - and the ASHP shows 18,6 l/min = 581 l/hour - Could this be the PRV that I have making fuzz in that?

58

Not necessarily. Short cycling will absolutely ruin COP, so it may actually be better to run hotter for longer periods, then turn the heat pump off for a bit while system cools a little before starting the next cycle. Overall, this could mean the same amount of heat produced for less electricity.

See Improve efficiency: Turn the heat pump off

Try raising the curve by a few degrees and see what happens.

Also, have you looked into extracting data out of the heat pump so you can have a better view of how itā€™s performing? Glyn wrote up how here: EmonHub support for Samsung Heatpump Monitoring via Modbus (though not as good as a proper heat monitoring package)

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59

ā€¦and thatā€™s the weird thing @Timbones.

Arne heats his whole house (including his garage!) whereas I only heat my living room (1.84m2 rads total ) plus one very small toilet room (0.3m2) - all the other TRVs stay on frost setting 95% of the time. Conventional wisdom would predict massive cycling from 4kW input (at the stated max compressor turndown) and only 2kW typical heat loss, but for some unexplained reason my cycling is ~45 mins on/45 mins off (which I am comfortable with) rather than 10mins on/off, like Arne sees :thinking:.

I run my WC very high (40LWT @ 20 ambient, 50LWT @ -2 ambient), so the LWT spends most of its time at ~45degC, versus Arneā€™s 34degC. I do this to warm the living room up from ~16degC (my setback) to 21degC each day in a reasonable time (note - no roomstat influence during this time!). This gives me a lousy CoP (typ 2.75) for 14h per day, but averaged over a whole day (no ASHP usage for 10h per day) thatā€™s an effective 4.7 which Iā€™m happy with. (Put another way, Iā€™d have to achieve an average 4.7 CoP or better if I ran the ASHP 24/7 to get a lower electricity bill - again totally against received wisdom.)

Go figureā€¦ :face_with_diagonal_mouth:

Sarah

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60

Hi Arne,

Just a thought - where is your remote controller located? If itā€™s in a small heated utility room, or a cupboard containing your Indoor Unit which might heat rapidly from the integral hot water tank, could the (Samsung) roomstat be switching on/off rapidly (and causing your rapid cycling)?

My 3rd party roomstat is in my (large) living room which has a big thermal inertia (~11000kJ/degC) so it takes a long time to change temperature (and activate/deactivate the roomstat).

Sarah

61

Hi Sarah

Guess you are right - the indoor unit is in the Utility Room - around 10 m2 with Floorheating I made just before the installation of ASHP. So in there are around 22-24 degC - but as I understand it, the Thermostat is not in use as it is set up - not 100% sure though, as I write this I get uncertain of thisā€¦
If I remember correct, the only thing that controls the cycling is sensors on the flow and weather temp.
I could be wrong thoughā€¦
If the stat in the MIM controller has anything to say, I have to askā€¦ The temp shown is compensated, so I guess it was showing around 26 degC and a Thermometer showed around 22,4 degC that day, so it is compensated by 3,6 degC, so it shoulkd show the correct room temp. now.

Just made a video this morning of the cycle - 8 degC outside - cycle lenght is 8 minutes and 35 seconds.

If supplier decides to steps out of this case to make a solution - I have several things I can test

  1. Create better dt by change emitters from 1 and 2 layer to 3 layer. This way I get better dt, so the ASHP have more to work with - allthough I then will have to lower the compensation curve even more, and then I could be afraid I get further out of range for the ASHP to work with, but it is worth a shoot I guessā€¦
  2. Get the system back with a buffer of about 300 liters and have a Circulation pump seperately to drive the emitters - internal pump then would only cycle to the buffer and not beyond that - It will demand a bit higher flow temp. than needed without buffer - but it would at least get better and longer runs, so I guess it will have a break even that is acceptable. I want the long runs :slight_smile:
  3. Activate internal roomstat and move the MIM controller into our living room - to test this, like you are using a 3rd. party statā€¦

lets seeā€¦

1 Like
62

You can get a bigger dT by just lowering the flow rate.

This will not harm your COP, it will probably improve it.

10lpm at a dt of 8c is the same amount of heat as 20lpm at a dt of 4c

I still donā€™t understand why the high flow rate is needed.

63

I donā€™t believe that changing radiators will result in ā€œbetter dtā€, unless you mean something else. More radiators will mean more heat output and less cycling.

Adding complexity to a heating system rarely makes it perform better. I would be wary about going down this path.

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