I believe the Daikin 9kw ASHP has a 2c hysteresis, apparently. We set out stat to 19c so the system keeps working until about 20.5c. It then cuts out and doesnt come back in until 18.5 ( or less) by which time the house has cooled considerably.
Is there a way around this please, except setting the stat at 20c. Whilst we are on the subject, we doesnt the onecta app allow increments of 0.5c when setting a schedule, like it does on manual control?
Thanks for any advice.
I had pretty much the same thing with my 8kW Altherma too.
One way is to set the thermostat higher and then tune the Weather Dependancy Curve to heat the home to the temp you want.
Stop the house over heating.
Takes a bit of effort to get it right at all outside temps.
Another way is to go full Leaving Water Temperature control that makes the Madoka nothing more than a temperature gauge.
Again this is Weather Dependancy Curve controlled.
The Onecta app can’t then schedule, you have to do scheduling in the MMI.
It does fix the bug of the Heating overriding the ECO setting for DHW even though the MMI says DHW is priorized. That’s why I use it.
I got noticeably better CoPs with both methods.
Have been on LWT control most of the time.
Temp really doesn’t vary much once you get it tuned right.
I do turn the heating off manually via the Onecta app when the sun heats the house to the level we like.
The Onecta not showing 0.5 increments is a ‘feature’ / lack of implemented functionality!
Pain!
I went weather curve only for a month to dial in the curve best I could. Too late in the season to do this now though.
Once I got the curve as good as I could I then brought the Madoka back into play with modulation 4 with an overshoot of 2.
The Madoka now makes subtle changes before the room gets to 1.5C above the room thermostat setting (19.5).
This is keeping house just under 20C without cycling and without overheating, rarely reaching the +1.5C over room setpoint hard limit (21C). Buts it’s there as a backstop if needed.
Without the Madoka influence I found the house would eventually get too warm, no matter what I did as it would run for ages and the heat would build.
This wouldn’t have worked with my oversized 11kW but does largely work with my 8kW.
However, what works for my house is unlikely to work for anothers.
It doesn’t surprise me.
I will probably try Madoka again in the Autumn.
I read somewhere that once the priority for Eco water schedule was set under LWT control the settings remained even if one went back to Madoka control.
Could be the best of both worlds for me.
Will have to test that one sometime.
As it is now, If I forget to switch off via Onecta it leaves the pump running more than necessary with the odd compressor kick in, even though the outside temps high and the house absolutely does not require anything.
The water temp is at the 25°C min while it does this, so it doesn’t exactly warm the house much at the moment, but it would in summer.. then it would off all the time though.
I use the Madoka modulation setting which works quite well, this alters the leaving water temperature (LWT) around the Madoka setpoint to try and stop you ever reaching the 1.5C over temperature cut-off. I have the 6kW ASHP.
My goal is an actual room temperature of 19C
So I start with a weather dependent curve (WD) set which is about right, but high enough that it will eventually exceed 20C.
I then set the Madoka modulation level to 8. I set my Madoka target room temperature to 18C (note this is 1C lower than I want the room to be).
The effect this has is:
This works well for me, it boosts the LWT if the room is below temperature and then it tends to float around the 19C level. The 19.C remains a hard cut-off and you then have the 2C hysteresis before it comes back on. In my case if it gets as high as this we probably don’t need heating (solar gain for example, or reasonably high outdoor temperatures).
The above also needs a relatively low LWT to work (say 32-40C). I imagine if you were working with LWT in the 50C range then the modulation wouldn’t be enough to make a difference but I might be wrong about that.
Many thanks for your responses so far. This is the problem, you need to have a phd in renewables to get the best out of your ASHP. The average person would have little idea and being told different things from the installer doesnt help either.
In theory,
If the heat loss calcs are accurate…
And the heat pump/rads are sized accordingly…
And the weather curve is set properly…
Then a bit of load modulation from the thermostat would likely be enough for most people. There may be many installs where this is true.
For me there was a fail at step #1. Which meant I was fighting with an oversized system and went looking for ways to fix it.
Octopus will have learnt a lot from the first couple of years of installs.
Just a radiator filled with 50c+ water will make control hand. With 35c the radiator output reduces meaningfully as the dt with room temperature reduces.
Perhaps I struggled with the Madoka due to our having UFH?
By the time the floor mass has cooled enough to trip the Madoka on and the HP spins up to fulfill the need, it’s way too late / slow.
Same with the over heat cycle.
It might be useful to modulate things when the temp is just below max required and when the solar effect starts overheating the house to switch it off fully - jury is out on that one for me..
Whilst I don’t have UFH, I work around the Madoka’s useless 2c hysteresis and too wide modulation points by using Home Assistant. First, I got the WD curve dialled in for minimal to zero LWT offset requirements when the weather is gloomy. Then I set up a bunch of triggers to adjust the offset. It keeps our house within +/- 0.5c from the setpoint without shutting down the heat pump. When it’s sunny or not so cold out anymore, HA will shut off the heat pump at 0.5c over setpoint. I don’t like the reliance on the Internet and Daikin’s API but it’s preferable to the Madoka’s behaviour.
More details here: https://community.openenergymonitor.org/t/homeassistant-control-of-lwt-via-onecta-cloud