Is an oversized Daikin really a problem?

Perfect, thanks, numbers above should be ok then, cheers!

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How much volume do you think you have in your system @matt-drummer, Im reading around 300L using the volume tool in the dashboard, and ~33 kW @DT50 of radiators?

If heat demand is 5.2 kW @ -3C, that might be about ~60L/kW demand? or 40L/kW based on heat pump capacity?

It would be interesting to look at ratio between total emitter system size @DT50 and heat demand across all systems e.g for yours it might be around 6.3x? Is the 5.2 kW heat loss about right?

Looks like yours @KnightPhoenix is about 200L volume and 17.5 kW @ DT50 emitters?
Heat demand ~4.4 kW so 45 L/kW demand, 25 L/kW heat pump capacity. Radiator to demand ratio ~4x?

Im at about 100L volume, 15.5 kW @DT50 emitters, 3.3 kW demand, 5kW heat pump. So 30L/kW demand, 20L/kW heat pump, 4.7x radiator to demand ratio.

I think my heat loss is more like 4.5kW @-3c, I need around 110kWh of heat to stay at 20c if it is that cold.

Radiators are just under 50kW

I don’t know about system volume. I would say there is at least 250l in the radiators, 20l in the volumiser and whatever is in the pipes. I would say 300l is pretty close.

I also have an awful lot of 15mm plastic pipe (not my doing!) which is a bit of an issue I think.

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I run my heating in a very strange way, not by choice really, it is just where I have arrived at.

It started with the 9kW problems and I fitted very large radiators to try and make it work.

Now I feel they are perhaps too big.

My issue is that Daikin heat pumps don’t really like very low flow temperatures.

I find that I can reduce the flow temperature and heat output but efficiency suffers, it doesn’t use any less electricity below a certain point so I choose to accept excessive heat.

I also have a difficult house. We have a conservatory that is more difficult to heat than the rest of the house, that means to keep the conservatory warm, which we like to do, we have to have more heat in the rest of the house.

We like the conservatory and I spend a lot of time in it, so we mitigate the problem by opening windows elsewhere.

It distorts the data, probably, but it works for me, my wife likes it less than me though!

All of this means that the Madoka doesn’t work very well, I am already at the bottom in terms of efficiency and so anything the Madoka does just ruins the COP.

It’s not ideal in any way so I just make my life simple and run at a fixed lwt and deal with excess heat as necessary.

It is miles better than the 9kW and I am not unhappy with my electricity consumption.

But I could use less electricity if I gave up COP. That would be OK but I like to be warm and it all works well enough not to bother me much.

Again though, I like some heat, and the 2c hysteresis on the Madoka doesn’t suit me.

Or, I have to start experimenting again, but I have had enough for now and just want an easy life.

It sounds mad I know.

I’m sure we all have our ways so comparing data, although useful, isn’t the whole story because these aren’t laboratories, they are our homes and we are human beings with all that it entails!

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Had my radiators swapped on February 11th 2024 when they eventually arrived.

The emitters are currently 20.1kW @dt50 and have around 100l of volume and an additional 20l volumiser (plus ~16m of 28mm primary pipework).

I’m another 9kW Daikin user, on Heatpumpmonitor as “Swindon”. Our heatloss is around 7kW. Mine was fitted in December 2022 and Octopus have so far declined to change it because they say that at the time, Daikin couldn’t supply one from the smaller range. We were quoted for the old 7kW model and a 9kW turned up at installation.

What I have done this year is to add radiators and modify pipework to remove any restrictions. Still waiting for some proper cold weather, but the comparison of before and after is positive so far.
I’ve had flow data available since April 24, so this compares late spring (red) and autumn (blue).
Nonetheless we only run the heating akin to a gas boiler, morning and evening, to avoid overheating!

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Hi,

I had a similar dilemma with my house just not as extreme.

My thermostat was in one of the warmest places in the house which led to some rooms not getting as warm as I wanted(Mainly north facing living room and kitchen).

I only use TRV’s to control temps in the bedrooms all the other TRV’s are either removed or set to 25c.

I then moved the thermostat to the coldest room(The rad is possibly slightly undersized).

Since they replaced my 9kW with an 8kW I now find the heat pump comes on in the morning(2 deg setback at night) runs low and slow most of the day and then just shuts down in the afternoon(min temps about 9c at the moment) whereas the 9kW would be cycling on and off all day.

It’s almost as if the old unit was just coming on heating up the air and then shutting off whereas as the 8kW is on for several hours at a time and it is actually heating up the thermal mass of the building which lets the heat pump shut down in the afternoon.

Have you considered moving the thermostat to the conservatory and then just use TRV’s to control the rooms that get too hot?

Hi Rob,

I think conservatories will always be an issue, too hot in the sun and too cold at other times.

Moving the Madoka is a lot of work so it’s a good idea in theory but I can’t be bothered.

I don’t want trv’s and I am really quite happy with what I have, it works well enough and I have spent enough time on heat pumps in the last 12 months.

I just find a balance, let the conservatory get cooler and add heat/shut the doors as necessary.

It has electric under floor heating if I feel like using it and I have another way of heating it as well .
Apart for the electricity consumption and low efficiency, the big problem for me with the 9kW was that you couldn’t have a low steady heat. That is what I really wanted from a heat pump.

The 9kW had to be operated either continuously with windows open or like a gas/oil boiler, big dollops of heat in one go, then off for a while, then back on for another slug of heat and so on, just like you say.

I didn’t like it either!

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My conservatory takes about 30% of all of the heat power of the house. Just like you, this causes distortions in how the house is heated. I accept that the conservatory will be colder in the winter than the rest of the house and hotter in the summer.

I have installed the largest possible radiators in it. The only acceptable way increase the temperature in it would be to install underfloor heating. I am not prepared to do this: partly disruption, partly because I refuse to add any more heating to it (30% of total heat output for 17% of the floor area of my house is already too much).

Glass is a poor insulator: having a glass roof is the biggest problem. My conservatory dates from the late 1990s when a U-Value of 2.4 was considered good. These days the best performing glass units are closer 1.0. It’s possible to replace these roofs with better performing glass ones (these are expensive), or to change it for something other than glass (see “UpsideDownFork” on youtube).

Personally, my plan is to replace the glass roof with a more conventional one that includes Velux windows and solar panels. That will definitely fix the the leaking and temperature variations but will make the inside rooms, and conservatory, darker.

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Yes, my conservatory is about 13% of the floor area of the house and takes one third of the heat.

I too have as much radiator capacity as I can fit in it and it works OK, it is only a small amount cooler than the rest of the house.

My conservatory has argon filled glass all around and the roof is `special’ blue Pilkington reflective stuff, probably close to as good as it can be without changing the roof.

I do have electric under floor heating in there which I could use if I really needed to and another more efficient heat source, or I can just shut the doors.

The reality is that my heat pump is probably twice the output that I really need and although I have got it working quite well I can’t say I am enjoying it.

I think maybe I have messed it up.

I think maybe my radiators are too big to work well with the Daikin heat pump. I didn’t realise until it was too late that they just don’t like really low flow temperatures.

I think my solution might be to install a different type of controller rather than the Madoka, I can’t cope with the 2c hysterisis that the Madoka offers.

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Rather than replace the hardware, could an external agent operate use the API to boost or cut the Madoka’s target temperature, and hence effectively manually turn heating on/off, based on your desired criteria ? (Can also adjust the leaving water offset this way, if you wanted.)

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Hi Dave,

Yes, that’s about what I want really, just something to turn it on and off based on room temperature, with a schedule, just like my old central heating controller!

I don’t know how to do it though.

My problem with the Madoka is mainly the hysteresis of 2c, I wish I could adjust it.

I can use the Madoka with modulation but it’s not very efficient. I am always running about as low a flow temperature that the heat pump is happy at and so there isn’t really any room to modulate down without losing a lot of efficiency.

I haven’t tried it for a while though and maybe I should give it another go.

Now I just turn it on and off manually and use a fixed lwt. I now have another issue where the heat pump doesn’t start heating cycles properly so I have to watch it and abort as necessary.

It’s all a bit tedious and I am sorely tempted to just buy something else.

I’ve just updated my python script on github to allow setting temperature and leaving water offset via the API.

Or if you use home assistant, there’s an onecta integration that should be able to do the same.

I still have it on my TODO list to see whether it’s possible to control locally via bluetooth via the bluetooth agent in the Madoka, or if that’s really limited to only doing firmware updates.

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Thanks Dave.

I will have to have a look at it and see if I can understand :slight_smile: It’s all a bit beyond my knowledge at the moment.

I tried to set up HA once, I spent hours on it, destroyed two usb drives and basically got very frustrated, a bit of a nightmare for some of us!

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These are difficult problems to solve.

Before I installed my Vaillant Arotherm I ran my gas boiler at 35C flow and used electronic TRVs on every radiator (SONOFF Zigbee Thermostatic Radiator Valve, TRVZB) using home assistant for control. This worked OK but the real issue was the “control” offered by my gas boiler - 35C involved a lot of “bad” cycling.

When I look at the various heat pumps in detail (using HeatpumpMonitor.org!) I see that each manufacturer has different control strategies. Obviously this is influenced by the size of the pump vs heat demand. It’s also fun to try to work out how each system is setup. I don’t think I’ve seen systems with seriously undersized heat pumps but I have seen systems with under sized emitters.

Vaillant appears to have a cycling strategy at lower flow temperature but that doesn’t seem to be a problem.

Perhaps your Daikin needs to be run at 35C or above - then TRVs might make sense to control individual room temps - perhaps setting a maximum temp only with an overnight set back?

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The people that develop the home assistant software have chosen to push a lot of changes down to the users of the system by default. That doesn’t make it easy to work with or to understand. For reference, I am an IT professional (someone who has spent their entire 30+ year working life on IT systems), and the changes that HA makes catch me out.

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