Hi I have a Daikin Altherma installed yesterday by Octopus. Attached is an image of the WD heating curve from the Daikin MMI. I remember receiving a copy of the survey with the design temperature at 50 degrees C when the external temp was 3.4 degrees.
Therefore I think I WD heating curve in the image will need adjusting to 3 degrees?
I have raised with Octopus but they haven’t replied yet.
Any thoughts?
It depends on your hardware @Harj (HP and emitter rating etc). Your profile doesn’t say where you are located, but if in UK, Octopus have set you up with some fairly realistic initial WC settings.
I’d be inclined to leave these as they are for now, and see whether your HP keeps your house warm enough as winter sets in. If it does, then you can maybe drop your WC settings a little.
If you want to adjust this to suit your house here are the two images from the installer reference guide that will tell you what to change (little changes and wait for a day to see how it feels).
Make a note of the current settings first so you can swap back if it goes wrong.
Hi the issue is that the installer has the weather curve at 50 degrees at minus 8 ambient, whereas the design was at 50 degrees c at minus 3.4 degrees.
So the design temperature has not been set by the installer.
The unit is a 11 kwh Daikin Altherma with a heat loss of 9.1kwh and I’m based in the West Midlands.
Surely I need to change the settings in the image of I have provided of the MMI?
Ah : I thought +3.4 sounded unlikely. -3.4 sounds much more reasonable.
I wouldn’t have thought it matters all that much between -8 and -3.4 - it’s not an exact science.
You may find that you need to raise the lower temperature: with the 9kWh unit, several on here have reported that it really needs to be mid-thirties to get sensible behaviour - the unit cannot modulate low enough to maintain a 27-degree temperature without cycling.
You can adjust the offset using the Onecta app (in the advanced settings), which might be easier than adjusting the weather curve itself (and saves having to reboot every time you change it). This might an easier way to find what works best in your home.
Hi Dave,
In my Onecta app I have More>Settings, but I don’t see “advanced settings”. Where can I find that menu?
Thanks, David.
From home, click on the ‘climate control’ which brings up the thermostat widget. At the bottom there’s settings, and in there is ‘advanced operations’ which (for me at least) is Leaving Water Offset.
Ah - the name of the top box is user-configuration - mine’s called Climate Control, whereas you’ve called yours “Central Heating”. Anyway, click somewhere on that upper box (but probably not the green off button), then the settings are down at the bottom.
Thanks Dave, I found that setting now.
Do you know how that LWT offset interacts with the modulation setting?
Does this offset adjustment happen before or after the HP has chosen to apply what it wants from the modulation setting allowance?
I’m just experimenting with it now. I assume it’s a simple fixed offset, applied in addition to whatever else is contributing to the calculation. ie it will apply the modulation effect and this offset to the weather curve. But it’s a little hard to exactly determine the effect since I also have a large overshoot configured, so LWT changes quite a lot. Maybe I should reduce that so that there’s not too many things changing at once.
I’m not sure how it’s intended to be used, but I’m now using the API to automatically increase it overnight after the setback, and then back to 0 at the end of the off-peak rate.
The LWT calculation happens in the following order:
Yes, that graph looks wrong for design parameters.
Are you confident changing it?
I might suggest 35C flow at 16C, for the right hand point.
There really is little point asking these larger Daikins to go much below a flow temp of mid-30s
Thanks @squarepeg77. Yes I can change it. So as it’s an 11 kWh unit do you recommend I increase the 26 degrees flow temperature up to 35 degrees?
When you say there is little point going below 35 can you tell me why? We have a 230m2 5 bedroom house and at mild external temperatures of say 8 degrees the radiators barely feel warm, could this support the increase you reference?
If the target temperature is low, the heat pump will probably cycle on and off, which can reduce efficiency. From some measurements made by members here, the large 9-16kW Daikin system don’t really use any less energy when being asked to produce temperatures much lower than the mid-30C range.
If a stable house temperature is your primary aim, then the lower target temperature (with some cycling) can help achieve that, at the cost of a bit of efficiency (perhaps).
Here is one Daikin 9kW system (@John, I believe) that runs with quite low target temperatures and cycles, but gets pretty good efficiency and what looks like very consistent house temperature:
https://emoncms.org/app/view?name=DaikinEDLA09RevisedFlowT&readkey=798b7510494f9413958c7044e653480e
I run my system rather differently: Emoncms - app
The Overshoot setting is important to allow the flow temp to rise above the target temperature and let the system run for longer periods before cycling. I think 4C is the value most people here recommend.
And to your point about the radiators barely feeling warm on a mild day, that is normal with weather curves that go down into the 25-30C range. The system is still putting useful heat into the house, it just might not feel that way to the touch 
It is up to you whether you want to let the system try and trickle heat into the house with these low temperatures.
Yes, I’ve been meaning to add to the ROI thread on this topic. I did try running at the preferred higher flow temps, but we just couldn’t live with it, and it cycled anyway. So I set the WC curve to the kind of values that the data indicated were required, and let it chug away, as an experiment. The experiment is still running, because it’s a new winter just started! And in respect of running costs, since the minimum power is ~800W, it needs some sort of PWM-like approach to get the average power requirement more in line with what you’d want those at those ambient temps. If the pump blows up I’ll get a different, smaller brand 
This is where I find myself with my 11kW Daikin.
If I run at the higher flow temps then I see a little less cycling (90 mins on 10 mins off)and see 800W+ of power. House is warm and comfortable and COP is ~4.
Of I run at lower flow temps then cycling increases (45 mins on 30 mins off) and see 700W+ of power. The house is equally warm and comfortable but over the course of a day uses significantly less energy as the average power is less but the COP takes a hit and stays closer to ~3.5.
Am running the former at the moment but will likely swap back to the latter as my batteries last longer on the latter, which reduces the overall cost of running.
That’s very interesting @Mld. Do you have data that shows the two running methods? I have prioritised COP and longer runtimes so far, but am open to trying a different approach
Basically, how important is COP?? If you’re saving the planet or minimising expense, then for a given HP/installation, you do what it takes to reduce power load. The time to think about COP is design/install! Too late now… Yes I would do it differently if I were doing it again, but the decisions I made then got us totally off gas and a huge step on the way. Result.
thanks @Mld I’d want to run the lower flow temperature approach. Would you mind sharing your settings for both ends of the heat curve, modulation and overshoot please?
