9kw Daikin performance

[scanfer (Simon Canfer)]

FWIW you’re seeing very respectable performance. We’re squeezing what we can from a 9kW with a lot of radiators and so rarely have to go above 40C flow.

As a fellow 9kW sufferer I sympathise, but as others say you’ll be lucky to get Octopus to listen. I’ve been through the loop twice, and while the visiting engineer verbally agrees with me on oversizing, head office vetoed a swap. They de-rate the 9kW because of defrosts and you’ve a higher heatloss than our property.

A real bonus of the 9kW is fast hot water heating!

I’d say you do have the FW update, based on comparable behaviour to our system (ID 23).

[matt-drummer (Matthew Gregory)]

If the heat pump can run for hours at a time, however you manage it, without overheating your house in Ipswich in the last few weeks then your heat pump is not significantly oversized.

With defrosts neither the 8kW unit or the 9kW will cover your heating requirements at the lowest temperatures we see in Ipswich.

You are contradicting yourself, you are trying to and are succeeding in getting the heat pump to run for hours at a time without cycling.

You will never be able to convince Octopus that it is too big.

In order to convince Octopus that it is the wrong heat pump you will need to demonstrate that the heat pump cannot operate for more than a few minutes at a time in mildly cool weather without overheating your house.

You also cannot show that the heat pump you have meets your design with some headroom as you have no data yet. I assume you got a BUS grant? If so, your heat pump must be able to heat your house at the design temperature.

You do really need to see how your heat pump performs when it is needed most before contemplating a change.

Changing the heat pump based only on data from the last few weeks is foolish.

When I had a 9kW Daikin installed they were new on the market and little was known about their performance.

I estimated my heat loss at 5kW or less based on historic gas usage where I heated the house to 20c plus all day and all night. It was pretty accurate. However, I knew nothing and neither did anybody else about these Daikin units.

I had one installer want to install a 14kW unit from Daikin and nobody else would install at my house so I was stuck with Octopus and Daikin.

I wanted a Vaillant.

It is fairly easy to find issues online with these Daikin heat pumps and I am surprised that you didn’t think about this before engaging Octopus to install the 9kW unit in your house with a heat loss of 7kW or so.

Did you do any research beforehand?

@Sam_Cooper I am sorry that my replies may seem a bit sharp and unfriendly. I am not unfriendly and will help in any way I can but my view is that it is better to give you a straight and direct opinion having been through the process than to dance around the issue without really addressing it.

[Sam_Cooper]

Hi Simon.
Thanks for posting, It is great to get lots of different options, experiences and advice from people.
Sorry to hear that you haven’t had any luck with Octopus.
Yes I can see what you are saying regarding the firmware. Our systems are operating very similarly. I was really hoping a firmware update would make things slightly better.
It is quite interesting to compare our data, you can see from below that my pump would have cycled like yours without my intervention from HA. It also looks like my homes heat demand/loss was less over the same period, with similar indoor temperatures and a slightly lower outside temperature in ipswich overnight, which is really interesting. We have bedroom windows open overnight too. What are your thoughts?

[matt-drummer (Matthew Gregory)]

Hi Sam,

I just had a look at your data again.

Your flow rate is over 14lpm.

When I had the 9kW my flow rate was 10.5lpm all the time.

I did this, as I do now with the 8k, by using radiators with a dT of 10c, this keeps the flow rate at the minimum.

Your circulation pump will use the least amount of electricity and you will get longer run times.

I am guessing you are on fan coils at a dT of 5c?

Do you have an overshoot set?

You could try radiators which have a fixed dT of 8c and an overshoot of 4c.

Then it will run for as long as possible.

I have to admit, I dont understand what your HA influence is designed to achieve but then I haven’t thought about it much, you are increasing flow temperature based on the return?

If that is what your HA is doing then it is really doing what the Daikin controls do.

The Daikin controls reduce flow rate as dT gets smaller than set until the flow rate is at the minimum and then the overshoot increases the flow temperature. If the flow temperature needs to exceed the overshoot to maintain a dT sfficient to run then the heat pump stops.

A wider dT than your radiators can get at the selected flow temperature keeps the flow rate fixed at minimum and the heat pump runs until the overshoot has been used up. This should give you the longest run times.

[Sam_Cooper]

This is great stuff Matt, thank you. I need some time to prosess and get back to you lol.
No need to apologise, I appreciate directness and everyone has their preferred communication style.
Being an engineer I rely heavily on data and logic, which can lead me to miss the obvious sometimes. Like the flow rate! I thought I had it as low as it could go, but hopefully not.

Okay, so my own Heat Punk survey calculates heat loss at 7kw. All existing rad sizes entered, all building materials and measurements accurate. The heat pump selection tool automatically selects an 8kw heat pump @ a design flow temp of 48c @ -3. Bearing in mind this design tool is used by the likes of Heat Geeks. AI has analysed all data from March and calculates heat loss at 6.4kw. Using a paid PRO model.
I agree with you that from an MCS guidance perspective the installation is compliant with how I currently have it setup. If I revert to Octopus settings it would be questionable.
Point taken on needing cold weather data, that is sensible. My worry is though, that if I wait, a swap will be impossible.
I did research the heat pump as the Daikin was recommended by Octopus because they told me they could intergrate my drayton wiser controls and based on there original heat loss survey seemed a good fit. On installation I was told they could not intergrate the system.
I did not understand the minimum modulation issue at the time, and if I did, I probably would have requested the Cosy, which can modulate much lower, still not knowing my heat loss was less at the time.
The HA automation works by increasing the target flow temperature by 1c whenever the return temperature gets within 0.2c of the target temp. This prevents cycling until target room temperature is reached. Once target room temperature is reached the automation turns off heating until the room temp drops by 0.5 degrees, it then resets the target flow to the weather curve and starts again, forcing the heat pump to modulate as low as possible, save money and prevent cycling.

These are my current settings:

Emitter type: underfloor heating
Setpoint range: 27c - 52c
Control: leaving water
Delta T: 5
Pump operation mode: Sample
Pump limitation: 60% speed
Overshoot: 4c
Quiet mode: Off
Power consumption control: 2kw

Changed this evening, fingers crossed this reduces my flow rate.
Emitter type: Radiators
Delta T: 8c

[dmhom (Derek McCalden)]

Like @matt-drummer I had my HP fitted in the early days ( 2022 ) when I believe there was not the experience around to fully understand HP’s. Octopus decided to fit the 9kW HP ( Daikin did not have an 8kW HP available ) It appeared at that time Octopus used Daikin HP so they fitted what was available. Since then I have been trying to get my HP changed without succeeding. At the start of the year ( due to good old AI ) I have discovered that Octopus did not provide me with a heat loss survey in compliance with MSC guidelines . A private survey shows my heat loss as 5.56kW.

[Sam_Cooper]

Oh dear, you must be really struggling with the 9kw. A swap in your situation really would be the right thing for Octopus to do. Sounding more and more like I dont have a chance.
If it helps your situation, the surveyor mentioned that they changed their heat loss calculation software towards the end of 2025 due to being inaccurate. I have asked the question if they add a safety margin to the figure, no response yet. My heat loss calculation was done with the new software, still over a kw difference to the Heat Punk software.

[Sam_Cooper]

Looks like changing to Radiators with DT8 is caused the unit to cycle due to the overshoot, reducing efficiency. A direct result of the minimum modulation issue with the low heat demand.
Not a very big window of operation, so in colder weather it might work better.

Yesterday UFH DT5:

Toady RAD DT8:

[Jonathan (Jonathan Frye)]

Reduced efficiency, but also reduced energy consumption, which one do you really care about?

[BPLightlog (BryanP)]

You also had a ‘large’ defrost cycle shown on the second graph - this might be what you’re looking at rather than cycling as such.

[Sam_Cooper]

Definitely both. The operation windows are too small to draw a conclusion, and not identical conditions, warmer internal and external temperatures today. This shows an 84w (0.84p) power saving but with 936w less heat output.

[Sam_Cooper]

Ahh yes, thank you. It looked like a cycle on the graph. Odd that a defrost was needed when outdoor temperature is higher than yesterday.
The heat pump was in an OFF state both nights.

[matt-drummer (Matthew Gregory)]

This is the nature of the 9kW Daikin.

You can get a lower heat output as desired but the minimum electrical input is so high that COP is not as high as it might be with a different heat pump.