Yea, unfortunately I do not have monitoring on the secondary circuit. I have been checking temps with an infrared sensor, so those readings are only comparable between themselves.
I am considering buying the PAC-TH011E thermistors and connecting them to THW6/7 inputs and attaching them to the secondary pipes in/out of the buffer tank, possibly with a hose clamp and some thermal paste. At least the internal flow/return thermistors on the Ecodan unit seem to be done in similar way. Then I guess I would have them in HA, as Z1 Feed/Return Temp.
The next question is then what should the feed/return of both circuits be like? I read a lot about the dT5 out there, but I am yet to get the understanding, other than “heat pumps like it”. I have both seen people saying that the flow speed should be low to allow water to stay longer in the rads and allow them to dissipate heat, and others saying that it should be high. I have tried measuring, but there are too many variables to draw a conclusion.
About the modulation: It clearly can, it just doesn’t want to. At 16Hz/2kW, it runs for hours, but the issue here (as you confirmed previously), is that it only does that above a certain outdoor temp. In any case, I don’t think “my unit cycles a dozen times per day” will be enough to convince the installer to do anything about it, let alone replace the unit.
Regarding the 17th: it happened overnight, so I am 100% certain there were no open windows. The buffer temp cannot be the reason either, because it did 2 long cycles. Also, the tank also gets up to temperature in about 30m or less (100l)
It’s handy to know the delta T, but don’t spend too much money on it. The reason why I asked for delta T for the secondary circuit is to get an estimation of the capacity at that moment. And verify if its indeed not taking enough heat.
Regarding flow and delta T in general. Its different for radiators and UFH.
UFH:
high flow
low delta T
Radiators
lower flow
higher delta T
In general a heatpump is happiest when the output is ‘low’. So if we recall the formula
output = flow / 60 * (delta T) * 4.2, we can see that we have 2 parameters to make the heatpump happy (flow and feed temp (implicit via delta T)).
But since you have radiators, you need to maintain a higher delta T. I’m guessing that the radiators have a smaller surface to exchange the heat (higher delta T), and we would like the heat to be kept longer in the radiators (lower flow).
For UFH this is the opposite. So flow and feed temp are always 2 things that should be taken into account together. You just need to find the right balance for your system.
Mitsi probably has a valid reason to only unlock those frequencies at certain temps. But I do know folks running fake NTC sensors to unlock lower frequencies.
Yea, as I mentioned in another thread, I got the thermistors hooked to the buffer secondary outlet/inlet, so now I can properly compare the numbers.
Long story short, with the secondary pump on PP3 and and primary on level 2, the delta t are as follows:
~4kW/26Hz: primary and secondary average around 4.5 and 5C, respectively
~2.5kW/16Hz: primary and secondary average around 3.5 and 3C, respectively
(+/-0.5C variation)
Based on these numbers, maybe I could do with lowering both pumps a notch. I’ll have to try and see the result.
In any case, I came up with something that aliviates the cycling, based on your suggestion of heating in blocks. Basically I have automations in HA that increases the room setpoint to 23C when the heat pump starts running, and lowers it to 22C, when it turns off by itself, after reaching setpoint.
This is not 100% ideal, as it obviously allows for bigger indoor temp fluctuation, but it is in line with my original goal. It is also a solution that has a natural failsafe, in case any part of the smart home stuff stops working.
I’ve had this for a few weeks, and it seems like it averages at 1.5 cycles per day, so I am satisfied. For completeness, this is in AA, room temp normal mode 60m, thermo diff +5/-9, flow temp min/max 30/50C.
Now I would need to see how it behaves in negative temps, as the minimim output/frequency will be higher, but that will have to wait for next winter.
Depends on both flows, but you now have the data to tune to get it in balance.
Since it’s working in blocks, its an indication of oversized heatpump or undersized capacity (receiving end)