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 this…
If I remember correct, the only thing that controls the cycling is sensors on the flow and weather temp.
I could be wrong though…
If the stat in the MIM controller has anything to say, I have to ask… 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
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 guess…
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
Activate internal roomstat and move the MIM controller into our living room - to test this, like you are using a 3rd. party stat…
I don’t believe that changing radiators will result in “better dt”, 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.
Good luck with your supplier, Arne. (I’d probably suggest to mine - tactfully of course - that he read this whole thread. It contains lots of useful experience and ideas. )
I don’t think that you can disable the roomstat. On my MIM, FSV 2093 allows you to disable Water Law, but every option uses the roomstat. Sounds like your utility room temp might be hovering very close to the roomstat sensor’s setpoint?
Don’t forget - if you have 2093 set at “roomstat or Water Law” then your cycling might be due to LWT repeatedly hitting WL, or your utility room repeatedly hitting roomstat setting. Can you try to eliminate one of these to test which? (E.g. set the roomstat way up high temporarily?)
Most folk on this forum hate buffer tanks (even though I’m happy with mine), and if your rads in your main rooms are already 22s, I’d guess that 3 layer rads may not give you much payback.
Hi again Matt.
Am I not right in thinking that a higher circulation rate (through the rads) will result in higher average rad temp, thus heat duty (from deltaT = Q / m / Cp)?
If so this would allow you to lower your LWT and thus get better CoP.
Main downside to higher circulation flow is increased pumping power, but (within limits) this is tiny compared with the reduced compressor power.
Just a thought…
As far as I am aware, and you or anybody else can correct me if I am wrong, the lwt from the heat pump is irrelevant to heat production and therefore COP.
A lower lwt may use less electricity but that is the only way it will influence the COP.
Heat produced is just the dT between flow and return and the volume of water.
Radiators can deliver more heat at a higher dT between room and mean flow temperature.
I will get the same amount of heat flowing 42c water at a dT of 4c and a flow of 20lpm as I will flowing water at 34c with a dT of 8c at 10lpm - the heat is the same in both cases. You just need emitters capable of doing this of course.
The only reason we flow at higher water temperatures is to allow the emitters to deliver enough heat.
We would all run at the minimum lwt possible to deliver the heat we need.
Arnes problem is that the heat pump produces too much heat when running at the minimum heat output and the house gets too hot.
But Arnes radiators cannot deliver the full heat produced at the flow temperature being used, they aren’t big enough.
If Arne reduced the flow rate the Dt would increase between flow and return and the heat pump will probably run for longer before needing to shut down.
But there is no getting away from the fact that the heat pump produces more heat than Arne needs when it is warmer outside.
You are right about a higher average radiator water temperature at a lower dT and higher flow rate but the minimal gain from this is completely wiped out by a heat pump that cycles 8 times an hour.
It must be terribly inefficient and damaging running like this.
Sorry Matt, but I think you’re wrong at least in one respect.
The higher the LWT (for any given ambient temp) the harder the compressor has to work, and the higher the energy it needs (almost exponentially so).
However the heat generated only slightly varies with LWT (at least with the Samsung compressor).
So at a higher LWT you get slightly better heat generated, but at the cost of a big increase in energy required, so the CoP goes down (quite dramatically).
I did caveat with regard to energy consumption., that is all that affects COP.
If the dT between flow and return remains the same then the actual temperatures are irrelevant.
When you say you run at 45c to warm your room quickly as opposed to Arnes 34c that isn’t the whole story.
You have to run at 45c because your radiators aren’t big enough to deliver enough heat at a lower flow temperature. You could heat your lounge just as well at 35c lwt as 45c lwt if your radiators were big enough.
Arne runs at 34c and gets less heat from the heat pump than it wants to deliver and it short cycles.
If Arnes radiators were big enough they could run at 34c and the heat pump would continue to run. Arne would probably melt though!
I want my radiators (admittedly smaller than optimum) to 1) warm up the fabric of my living room (walls, furniture, air etc) from 16degC to 21degC each day, plus 2) overcome heat losses to the environment and the surrounding rooms (which of course increase as the living room warms up - an interesting numerical integration).
I know how much heat I need to warm up the room (I’ve back-calculated the thermal inertia as ~11000kJ/degC, so to warm the room by 5degC in 4h is 3.8kW - that’s quite a lot compared with room heat loss).
I could run my ASHP for longer each day, or have a smaller setback, but my calcs show that I minimise my electricity bill by running as I do.
Sorry to say, currently I have no control over the Flow, nevertheless - I am sure the math add up for what you say, but the missing part in that calculation is the flow temp.
I would prefer to have 20 l/min at a temp of 38 degC, rather than 48 degC at 10 l/min - I would problably have the same heat put into every room, but should at least use less power to make 38 degC than 48 degC - That is why, at least I, prefer as much flow as possible - the high flow will make the hole emitter 38 degC with large flow, rather than 2/3 is 48degC - need more energy to make those 48 degC.
And I really do not need these 48 degC to get heat into my rooms.
Lets say I have an emitter that produces 2200 watts at 70/40/20 - the same emitter will produce around 800 watts at flow temp of 38 degC - the hole emitter is hot around 38 in the top and 34 in the bottom, best way to transfer the heat from emitter to the air - and the dt is 4.
The same calculation with 48 degC and dt of 8 shows the same emitter will throw out 1350 watts - this is actually around 550 watts I do not need.
In my mind I say this - It should be cheaper to heat water from 34 to 38 degC compared to heat from 40 to 48 DegC - If I am wrong about this, I would prefer to remount my RA-N valves to slow down flow, set the ASHP to 45-50 degC and everything should be fine?
What am I missing here?? LOL
I think, If I had the correct sized ASHP for the heat I need in my house - yes I truely get your point, that it does not matter so much about the flow, allthough I belive there still will be an upper and lower limit to what suits an ASHP best - On my installation I produce today at 8 degC outside - Input is around 900 watts and I get about 4kw of heat produced - this is way over what my emitters can transfer to the air, so thats why I experince cycling. @Timbones This is where I have a theory about my emitters - If I get 3 layers instead of a 1 layer, which I have 3 of, I will get the same effects as if I had a high temperature flow - the emitter would be hot on 2/3 and cold in the bottom where the return flow is - so this will result in a better dt for the ASHP to work with.
Example: I have recently installed a 3 layer 800x900 mm. rad in my Bathroom, before there where a 2-layer 800 x 500 mm. So a little jump to oversized Recently I run at 24 hour COP around 2,88-2,95 pretty stable when temperature is 5-8 degC outside. We have had stable temps, so I tried to turn the new installed 3-layer completely off for 24 hours - COP in that 24 hour timeframe was 2,5 - turned it back on and I got it back to 2,88-2,95 COP. So a positive effect on COP directly made by slightly increased dt, for the hole system (The 3-layer rad is warm at about 2/3 and cold in the bottom, so dt on this rad is around 10-12 - I have not measured it, since I do not have the equibment for that.)
In a perfect setup, all rads would be oversized, and then it would be easy to control dt for whatever you would like to have as dt - controlled by flow rate (Allthough I have no control, the ASHP have this built in)
Then yes, it would not matter whetever there are a high, medium or low flow.
Regarding buffer - I get your point allthough it could have a purpose, allthough it would cost a bit higher flow temps. Adding 300 liters to the system could be a factor to flatten out the short cycles that I experince (8-10 minutes) at least it is what I reaand hear fro local folks
Kill me if you find my post to long LOL I know I like to write, to make folks understand my complx mind… LOL
@Ian_Calderbank
Guess you are right - @SarahH wrote it is in fact a part of the controlling system - I was not aware of that factor… My bad…
This is the one…
@matt-drummer
I believe you are spot on - and I agree - higher temps will cost more in the kwh that we pay for
Saw you post after I just hit send on the looooong writing I made
oh my this seems like quite a basic issue. you are running with the controller in the mode that would be normal if you had an external thermostat. but you don’t, right? that means, nothing is telling the system ever to switch off. the only thing its trying to do ever is keep the WT constant based on the number in the WL settings. any tiny drop in WT, it comes back on. no wonder it’s cycling.
Is the controller in a place where you can use it as a master thermostat ?
if yes
service mode->indoor unit options->standard temperature->indoor
expect to get some error messages when you change this but if you press off->on on the controller it’ll sort itself out.
I would dought it is a good place to use as Room stat - it is our Utlity room where I have Floorheating, so a kinda long time before temp drops in there, compared to living room with emitters.
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