@sunandair thank you that’s very helpful! Appreciate you doing the calcs for that, feels like there is always something new to learn.
I’ll definitely increase the min flow temp, but my question is if a certain amount of cycling is ok according to Mitsubishi, do I need to increase it all the way to 35? Assuming energy used is about the same with and without cycling (some savings from the few mins off, but a small peak when it starts back up vs the constant flow), 32 would be more comfortable heating wise - and most of the time when heating is needed this would be above 35 in any case.
next thing for me to learn is what the LLH actually does…
I suspect that you are indeed correct, if the heat loss, and hence heating demand, is less than the minimum thermal energy output of the heat pump, then cycling, at some frequency, is likely to occur.
Looking at the manufacturer's data tables would indicate that a heat pump is predominantly more efficient when operating at lower LWT's, so raising the LWT setting may actually reduce efficiency.
I suppose that from an efficiency point of view, it is a matter of finding the setting which provides the desired indoor temperatures, with the minimum frequency of cycling, with the most efficient operation.
An alternative method of reducing cycling frequency would be by raising the desired indoor temperature setting during any milder period of the day. This should have the added benefit of not only reducing cycling frequency, but also storing thermal energy in the fabric of the building, which in turn should reduce thermal energy demand later in the day. A kind of 'reverse setback'.
@sunandair yes I will press them! Last time I called and was 7th in the queue and didn’t have the energy to wait (no pun intended), but I will push to get a replacement now I see how useful it would be for me.
Have you tried e-mailing? That way you would have a dated record.
I suppose that from an efficiency point of view, it is a matter of finding the setting which provides the desired indoor temperatures, with the minimum frequency of cycling, with the most efficient operation.
So just for fun... during the day I switched to fixed flow rate to see where our cycling would start at Ambient 10C. It’s just a short test but I thought interesting. But obviously this is unique to our setup.
This first graph shows FFR- A10/W32 which shows roughly 3 cycles per hour. And at that setting the room temperature remained stuck at 18.5C we had a 32 to 34 flow rate with no rising room temperature.
In the second graph we had raised the fixed flow to 35C
Operating at FFR- A10/W35 it can be seen the cycling has reduced to 1 per hour but the flow temperature has risen to 35 to 36C. Room temperature rose to 20C within one hour.
So in the last one we have reverted back to Auto Adaptive mode which, at 10C Ambient. The flow temp is set at 30C. Ie. lower than both the above settings.
It is noted it was a very windy day. Also there is no cycling in AA Mode. So with the system set on AA - WC30/A10/R21 temp diff +3-3. The flow temp rose to 37C then back to 35C and reached 21C in one hour. Clearly there was more flow Temperature but target room temperature was reached promptly without cycling. So i guess you have to choose where you want to compromise.
@sunandair I have just set a FFR of 36 so will report back in an hour or so on what that does! Yesterday was cycling pretty consistently twice an hour at about 35/36. I think I will probably end up with WC back at its lowest somewhere between 32-34 and accepting one cycle per hour, but let’s see.
@derek-m yes I did email them last Wednesday but no reply as yet. But I will be persevering until I get one 😊
I suppose that from an efficiency point of view, it is a matter of finding the setting which provides the desired indoor temperatures, with the minimum frequency of cycling, with the most efficient operation.
So just for fun... during the day I switched to fixed flow rate to see where our cycling would start at Ambient 10C. It’s just a short test but I thought interesting. But obviously this is unique to our setup.
This first graph shows FFR- A10/W32 which shows roughly 3 cycles per hour. And at that setting the room temperature remained stuck at 18.5C we had a 32 to 34 flow rate with no rising room temperature.
In the second graph we had raised the fixed flow to 35C
Operating at FFR- A10/W35 it can be seen the cycling has reduced to 1 per hour but the flow temperature has risen to 35 to 36C. Room temperature rose to 20C within one hour.
So in the last one we have reverted back to Auto Adaptive mode which, at 10C Ambient. The flow temp is set at 30C. Ie. lower than both the above settings.
It is noted it was a very windy day. Also there is no cycling in AA Mode. So with the system set on AA - WC30/A10/R21 temp diff +3-3. The flow temp rose to 37C then back to 35C and reached 21C in one hour. Clearly there was more flow Temperature but target room temperature was reached promptly without cycling. So i guess you have to choose where you want to compromise.
I hope this might be useful for someone.
Thanks for carrying out such useful testing.
It would be interesting to see what happened with IAT and COP during the above tests.
It would be interesting to see what happened with IAT and COP during the above tests.
Yes it would be nice but I can’t report on COP from the MELCloud app which is all I’ve got.
But I think the IAT was written in the post as Room Temp.
graph 1: 18.5C unchanging throughout.
graph 2: rose from 18.5 through 19C and reached 20c by the second hour.
graph 3 :rose to 21C at the point it modulated in the graph
I think for completeness I should also post our HP Data Plate: we have a Ecodan 8.5 which has a minimum operating output of 3.4kwh at A2/W35 (Ambient 2C / Water 35C) and a minimum output at Ambient 7C of 2.9kwh.
@sunandair so I ran at 36c fixed for an hour 10-11 and then back to WC at 32 min 11-12 with similar results! Perhaps I was too impatient and needed to run fixed flow temp for longer? Or at 37.
You appear to have a low deltaT on both charts. It looks like a DT of 2.5C on one chart and DT2 on the other. This could be the HP modulating down and is comfortable at that pace. But it look s a bit low and if you never get higher DT then something else may be happening. From what we see with our HP the controlled DT is usually around 5 to 7 when trying to raise room temperature and only modulates down when close to set temp.
It could be still fine and is how your system operates and you may know how it works better than anyone.
If I had to guess and knowing you have a Low Loss Header I think I would want to check if there is excessive mixing of flow water temperature across the LLH Primary Flow and Secondary Flow. Firstly there is always some mixing in a LLH and that is perfectly normal but if you are losing half your heat from your primary supply then that creates an inefficiency as heat is sent straight back to the HP.
Having said that I think this mixing (if that’s what is happening) could be helping prevent too much cycling in some way because one cycle per hour is not a problem.
Either way it’s interesting and you could find out relatively easily by placing a thermistor on the Secondary Flow Pipe to find out. I did this with our system by removing the hot water tank thermistor and placed it on the top exit pipe on the LLH and then read the temperatures on the main controller “thermistor reading” screen. Based on our settings You would compare the
Thw1 temperature =Primary Flow
Thw2 temperature =Primary Return
Thw5B temperature = Hot Water Tank or temporary test thermistor
You could ask your installer to do this if you were wanting to find this out.
@sunandair I think it is a form of modulation as with the mild temps at the moment it’s been very comfortably at the target temp even first thing in the morning, and I see a wider gap when it’s colder out
In case anyone is still interested! Mitsubishi have confirmed my controller is indeed one of those without energy consumption measuring and will replace it, but I need to get an installer to tell them that it is so they can send it as part of the warranty and then pay for it to be changed over myself…luckily it’s a quick job.
@hotheat that’s good to hear. So where is your main controller located?
Suggestion: Now would be a perfect time to relocate it if it’s in an awkward place like in a cupboard or hidden in a utility room.
They are supplied with a 10mtr cable as standard. We relocated our controller downstairs into our kitchen via a stud wall. It’s now easy to look at any time of the day.
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