Daikin 8kW family

@MBC thanks for confirming. Hopefully @mortstar can get his overshoot up to 4 now, if the rest of the implications for changing to UFH in settings work out ok.

There is an option to lower the minimum heating from the default 25 on the setpoint range screen if using a room thermostat. I don’t think Daikin recommend it though - at a certain point you’re just pumping luke warm water around your house with slim prospect of it actually giving up any heat to the room.

Thanks for this, Just changed mine to 4 yesterday and the Cycling has completely stopped, I think I may adjust this down over the next week or so as ideally I don’t want a massive overshoot but at least it is looking healthier.

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Thank you very much for that useful bit of information. The requirement to have emitters set to underfloor to be able to modify overshoot is not at all mentioned in the installer reference guide (which to be fair is quite good at pointing out these dependencies normally).

I read through the reference guide to check if switching to underfloor had any other affect on the system (versus fancoil which I was using before) and I don’t believe it does. I’ve now been able to increase my system’s overshoot (I’ve gone for 3C) and that means I can now target a slightly lower LWT than 31C, which should save a little bit more energy and reduce cycling further…almost a shame that we’re coming to the end of heating season. :joy:

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Thanks to those involved in getting my overshoot back, I missed it and I am very happy to have it back.

It has solved many of my issues.

I have had the 8kW for nearly six weeks now and here are some unstructured ramblings.

It’s performed really well but I don’t like it very much being honest.

My main focus, as it should be, is on heating our house and it does that well, no complaints.

I have less heat than I did with the 9kW so that is really good and it uses a lot less electricity.

I like the heating on all the time when it is needed, I prefer that to the house heating up and cooling down with the heating coming on and going off, its just what I prefer.

I find it more comfortable, more efficient in terms of COP and very little difference in electricity consumption. We also like a warm house.

I never liked running the 9kW with a fixed dT using either fan coils or UFH, it worked best on radiators with a dT of 8c that I could never achieve at the flow temperatures I was running at.

Like this, the flow rate was on the floor and the heat output was determined by the flow temperature I chose and by the outside temperature to some extent. With the 9kW I just used to focus on getting the electricity consumption to 900w and dealt with what heat it produced.

With this 8kW I want to run on radiators but can’t really because the overshoot is fixed at 1c.

I can’t run as fan coils either for the same reason so now it is on UFH.

I don’t know exactly what the difference is between fan coils and UFH but I can see a difference.

What I don’t like about a fixed dT is that no one value is suitable for all conditions.

I don’t like the way the fixed dT is handled by the heat pump, it is not stable, the focus seems to be entirely on maintaining a return temperature with the flow rate and flow temperature changing erractically to do this.

I can’t help think this is inefficient, I don’t know why it doesn’t hold a flow temperature and vary the flow rate to maintain the requested dT, it always overshoots the required flow rate to be stable, it’s always over compensating.

My biggest problem though is the flow temperature I need to remain most efficient, the same as with the 9kW, I find I need to increase the flow temperature as it gets warmer.

I have found both Daikins to be really good when it is cold but difficult to find good efficiency when
warm.

For this reason I don’t use the Madoka.

One other problem seems to be my flow rate, my maximum seems quite low compared to others.

My heating system may be at fault or not the best but I even notice this when running DHW compared to others, there should be no flow rate problem here.

Although I can now lower my flow temperature I find the heat pump becomes unstable, the flow temperature decays dramitically and it just doesn’t work very well.

I could run at 29c last night but as it has got warmer I have had to increase the flow temperature to 31c to maintain efficiency.

It use less electricity at 31c when it is warmer than it will at lower flow temperatures.

I can only guess that the compressor likes some load on it.

Ultimately I will just have to move to the Madoka and leave it alone but I like to find out what is possible and what works best.

I still wish I had a Vaillant though.

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Hi @KnightPhoenix Zac, as we are almost at the end of the heating season, do we have a common set of parameters ie a wiki table that fits 80% of homes/use cases?

ie

Madoka with modulation 1,2,3…10?

WDC curve 40 at -3, 30 at 15…?

Emitter types, Rad, Fancoil or UFH?

DT 3,4,5…?

Overshoot x

etc

I can add LED brightness to the lowest with an offset 0f -0.5

All I can honestly say is that this journey has shown me how different every house really is and that for most settings it requires time and understanding of the building and heat loss to work out the best settings (especially the WDC).

For the smaller unit UFH allows access to the overshoot setting and this seems to help cycling massively.

The Modulation is only there to compensate for inadequacies / issues with the Weather dependent curve and I feel it is better to fine tune this (on hot and cooler days respectively) than to waste time with modulation. Also if modulation is enabled you need to adjust the WDC as if you have a modulation of 10 and a WDC of 40/-5 - 25/15 the pump will modulate between 50°c and 15°c (in realty the smaller unit will likely bottom out at 25°c due to limitations), modulation allows the pump to modulate off of both ends of the WDC and this can be an especially expensive lesson if you have a backup heater (as this will activate below 25°c)

The lower DT’s seem to make the pump work harder and give a more stable output at higher outdoor temperatures but you need to set and test this at the design outdoor temperature or colder to ensure that the HP can still provide enough heat with the low DT in cooler weather.

Setting your system to 40/-5 and 30/15 is likely not ideal for the WDC as this will depend on your actual heat loss and emitter sizes. Despite what people say with tiny radiators when the design outdoor temp is reached you will either be cold or turn up the temp on the pump (compromise COP). You need to commission and setup the WDC to match the systems design temperature from either the installer or via your own calculations (heatpunk is great for this). Only once setup and commissioned, and the system is actually correctly sized can you then modify the WDC (again on warmer and cooler days) by 1/2°c a time to truly dial it in.

All I can be 100% sure of is that if you want a good quality system with a high COP and for it to actually be super efficient you either need to have a very good handle on hydronic design / how these systems work OR get in a true specialist (heat geek elite or the likes of Paul Spence from the UK heat pumps FB group). I am sure there are others and the chart on heatpumpmonitor.org will name them all but for the octopus installs in Ipswich and Farnborough at least I know the systems were not installed as designed by Octopus or have been significantly modified to actually work at the COP they are seeing.

I am sure that the big companies can install systems to get a COP in excess of 4 but that is not what the government have asked them to do, they are being incentivized to put in as many heat pumps as possible with a COP comparable to the gas costs (~3.6) and that is what they are offering and is why it is such a low price. People need to remember that they have two different systems, the water heating box and the house heat delivery system, both work together but without a full system redesign for the 40 / 35°c flow temperatures you will not be getting to COP4/5.

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