I found this to be a great resource
The first table does very low rad related delta Ts we are likely to see with a mix of UFH and rads.
A rad sizing for a flow temps of 50C needs to be doubled or so for 35C (rad deltaT of around 15!).
Fit more rads…
Found the answer to my own query. They had already taken the radiator output at a 24 degree delta t.
I don’t use any modulation, if. I do a get a little hot or cold I tweak the offset 1 or 2. But generally the pure weather comp seems pretty good at keeping a consistent temperature. I don’t know what the modulation does, or how it does it, but is it affecting performance by constantly changing things?
Modulation automates changing the offset, typically using the Madoka as the temperature sensor.
In the case of using the Madoka, it isn’t constantly adjusting things, it only takes action if the temperature goes above or below the setpoint by 0.5c per step.
The Madoka can modulate in both directions. At modulation 10, what I observe is:
It also modulates in reverse…
So Madoka is not as dumb as I thought it was…
Perhaps our problem is that Onecta can’t do 0.5C increments.
20.5 +/- would be perfect, 21+/- is too much.
At the moment we have Madoka set to 23C which it never achieves and runs on a weather curve we tweaked to get the temperature we want.
It doesn’t fluctuate much at all, but daily temp swings are limited lately to 0 to 5 or 6C.
Oh and our Daikin outside temperature sensor is 2C above an outdoor digital thermometer sensor we have in the same place, and tracks Google weather temps exactly but always 1C higher.
I understood that if you were running ( as I am) on weather comp, the madoka just displayed the actual in house temp, and that it couldn’t be set. In any event why would you?
Ah no not yet. Haven’t taken the plunge to full LWT.
Madoka set higher so as not to interfere (I hope / perhaps?).
I’m currently seeing Feb weather CoPs avg 4 (heating only) like this. Best was 4.69.
Hot water brings that down to overall CoP of 3.8 unless I switch to ECO mode.
Best I saw with that was 4.53 overall but it failed to get past 40C water temp so not indicative.
I wanted to get a couple of weeks data before trying full LWT mode.
Trouble is the weather is a moving target🙂
Yes, if you have set yours to use the curve, then I’m still not sure how you can set the madoka too, but there are people here who understand this much better than me. In order to avoid me being overheated or the house overheated I am running mine at around 18.5 for the sitting room. And I get the same temperature pretty much all downstairs. Because the bedrooms have a lower design temp and correspondingly smaller radiators I have one bedroom , which is on the north facing side, which gets up to the 18.5 too, the other 2 bedrooms hit around 16. So when I do get sunshine it can take all the rooms up to around 21c, which is the bonus I referred to earlier. Obviously the sun isn’t that strong at the moment. So this avoids me having to worry or manage for the solar gain. The other advantage of course is that the overall cost should at least in theory be lower for running at the 18c v 21c design temp ( using the headline figures) . At present my heating cop is showing over the last week a figure of 4.6, which is pretty close to yours. Just to clarify, i tweaked my curve to get it to settle to where it is now, so I just let it get on with it and by and large it keeps the steady temperatures I have described.
When I set my system to LWT it dimmed out the modulation option so I assume with the LWT you do not need the modulation. The rooms I have facing south are affected by solar gain but it does not appear to have much effect.
Interested that some people are achieving a COP over 4. I had this once but normally it is in the mid 3.6. What SCOP are you achieving, mine sits at 3.24. short of the 3.6 Octopus stated.
On LWT you can set an offset on the Madoka, currently have mine set at -2, what have other members found to be a good figure?
Hi Matt, I finally ( think I) understand the maths and how everything fits together. I have been able to determine produced heat by calc matches or is pretty close to actual. I have figured out my radiators and that at any temperature they will be able to cope with the heat pump. And I finally understand the issue of the flow rate . So thank you and everyone else for helping me get there. So I’m curious as to how your radiators are too big. Isn’t it the case that as long as they can disperse the heat the heat pump throws at them, it’s all good? If they were too small I can see a problem but I don’t understand what impact them being too big has. After all in practical terms they are all too big because they are designed to be big for the coldest weather. I do agree with you though that the Daikin not being comfortable at 25 and needing to keep it at 30 may pose a problem in the warmer weather. Though as I’ve said previously I will aim to turn my heating off around end March middle April, sun and temps permitting.
Hi Terry,
That is my issue.
My radiators work well at 30c flow temperature around 0c outside.
I have nowhere to go when it gets warmer, I can’t reduce the flow temperature and keep the heat pump happy.
That means that the Madoka doesn’t work, I can’t use modulation and I can’t really use a wdc as I want the flow temperature to increase when it gets warmer outside.
Matt could you keep a constant 30. In the warmer weather the the delta t would be less so you’d generate less heat. Rubbish cop probably,
Does this really mean even your 8kw is oversized?
I do Terry.
I run it a 30c most of the time and turn it up a degree or two as it gets warmer, just because I can see it is not happy.
It doesn’t change the heat output much as the dT stays pretty much the same.
As it gets warmer I just run it less.
I have just got used to it being a little warmer in the house when it is warmer outside.
I leave it on when I want some heating and turn it off when I have had enough.
We heat a conservatory and I do use that to manage things a little by shutting it off when it is really cold. I still heat it but just isolate it from the rest of the house.
Yes, it is oversized.
But it is the smallest Daikin make so nothing I can do other than swap to another manufacturer.
So would problem be the same with the 4 or 6 kw? Also and I don’t know are the 4 , 6, 8 actually identical with just different software putting some restriction on, or are the guts different?
Yes, it would be the same as they are the same heat pumps.
The 4kW can flow water at 30c and 7lpm just like my 8kW, it won’t be any different.
It still won’t like going lower on the flow temperature as the compressor is the same.
They are identical but you don’t even have to look inside to work this out.
There is a big give away that Daikin cannot hide.
If the 4kW and 6kW are different, how do they manage to generate 8kW+ when heating DHW?
They can only do that if they are an 8kW heat pump.
Would this be an issue with normal UFH?
Or is it just an issue when radators are installed with UFH flow temperatures?
The heat pump has no idea what it is connected to.
It just sees water coming and going and heats it as requested.
How could it tell if I had radiators, ufh or maybe just a big tub of water!
As long as it comes back cool enough it knows nothing!
They just don’t like less than 30c approximately.
But it still works OK, mine is quite efficient and doesn’t use much electricity.
I just find it a little difficult to live with as I have `mucked’ it up.
With high thermal mass UFH, the room temperature can remain stable without a stable flow temperature provided the adverage flow temperature is correct.
I don’t have a problem with room temperature not being stable.
My flow temperature is stable too.
It just isn’t as low as I had planned for as my Daikin heat pump is more efficient at 30c+ flow temperatures.
The high thermal mass of ufh won’t change that.
You are imagining a problem that I don’t have!
@matt-drummer
You could build an extension to heat, heat the garage or shed, heat a hot tub, donate some spare heat to a neighbour… lots of extra emitter possibilities! I’ll get my coat🙂