Is an oversized Daikin really a problem?

Hardware Heatpump
81

For me, they never gave way on the heat loss survey, they actually increased it at a second visit!

But, certified heat and electricity meters and a design temperature day proved my point.

They didn’t accept I was right the first time around, but the second time they were more amenable to a change.

At both times they offered a swap, just not very friendly the first time.

Do I regret swapping a 9kW for an kW, yes, a little.

I changed my heating system to accommodate the 9kW and it really doesn’t work very well with the 8kW.

That is not the fault of Octopus, but lumbering me with the 9kW in the first place was.

So, I had a problem, minimised it, got rid of it, and ended up with another.

My problems, the MCS, Ipswich Borough Council, and Daikin!

I hate my heat pump.

But, being objective, just present your data and experiences to them.

Do not get hung up on efficiency, they are not interested as long as it is good enough.

Focus on comfort, ease of operation and running costs.

You would have thought they would have learnt by now!

82

Thanks Matt - really good stuff to know. The weather’s supposed to turn colder here this week so will be interesting to see what happens if we get a near 0 or -2ºC day :slight_smile:

Not overly bothered about the efficiency figures alone but am more interested in reducing the energy consumption as we just don’t seem to need the 9kW’s capability. As for heat loss, interesting survey process - lots of data gathered on physical dimensions to draw a plan but noone looked in the loft, asked about insulation in floor voids or walls etc so who knows what assumptions have been made. Might go some way to explaining why the real world seems to differ.

Ah well… will see where we get to with cold weather and data; and go from there!

83

Good luck.

Just talk to them.

They are pretty good, probably the best at sorting out problems.

84

Pretty decent run as the temp dropped from 6 towards freezing today with just a single defrost.

Would I be right in thinking without overshoot (4) it would have cycled?

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85

It doesn’t look like it, flow temperature was steady and didn’t increase.

Nice and smooth, unlike the smaller units.

86

To be honest, from an owner of a 16kW unit, I am very happy with how it performs. It is able to modulate down to about 700W draw, while kicking out between 4 and 5kW depending on outside temperature, which is very decent minimum load!

I agree with you, it seems quite well built compared to the lower range.

Only thing I wish it had is a way to control an external On/off signal, so that I can have it control my fancoil units.

Anyone knows how? This is the bibloc unit, with the 230L HWT integrated in the internal unit.

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87

Great!

Unless your heat loss is less than 4kW at -2c

They make two heat pumps in reality and you are lucky if you have a home that suits one of them.

Otherwise, not so fun.

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88

@Chris_Hill

Tell me if this is a problem, I don’t want to upset you and can delete if you want.

This is what a heat pump that’s too small looks like, on it’s limit at the conditions of the last few days. And why the 4kW and 6kW don’t make sense. I am sure the 8kW would have performed better and be no worse when warmer.

Not helped by not having a BUH?

Despite being a 6kW heat pump and putting out over 6kW at times, it can barely manage an average of 4kW because of defrosting.

And Octopus designed it to run at 50c flow in these conditions! I don’t think it can?

What do you think @Chris_Hill , I feel for you, probably not a nice few days?

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89

The reported temp looks fine to me

90

Yes it does.

I did say on its limit.

I think Chris has a heat loss of less than 6kW, imagine if you actually needed 5kW of heat.

Would the 6kW Daikin be capable of doing it?

In the context of this topic, it’s important.

It is also struggling with DHW according to Chris.

91

domestic hot water cycles are no go because of defrost cycles so using the tank element when its below 2 degrees C outside ,

i am at a loss it is what it is the house is warm but the efficiency has taken a noise dive because of the defrost cycles , my actual heat loss is around 4.8kw @-2 , i have been looking closely and cant help thinking that idf the heat pump started its cycle more gently it would have a better chance of not starting a other defrost cycle or even pulling less air through the coil

ive also been racking my brain why hp manufacturers dont use the return water to stop the frosting on the coils with a bypass rather than putting the heat pump in reverse maybe someone with more knowledge on heat pump design can tell me why
yes this means the heat pump works a little harder but a bypass to the coil before a defrost cycle with warm water should do the job

not sure if we have a over average humidity which will not be helping but we live in a local valley

92

my design temp is 50 degrees at -2.7 but i am only needing to run at around 35 degrees C

if anyone has any ideas to try to reduce these defrost cycles i am all ears

is there a way to reduce the initial start up power ??

i have recently increase the dt to 8 from 5 should i try going back down on this ?

93

I’d wonder if the 8kW would actually be capable of significantly more if it’s defrosting causing the lack of output. As it’s the same surface area that’s frosting, more heat being absorbed through the same fins would just cause it to frost up even faster?

94

Fyi, spent the afternoon with an Octopus surveyor, and on the phone to various managers

The Cosy 10 will now be known as the Cosy 9. Seems 10 was a bridge too far.

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2 Likes
95

I don’t know.

I’m not sure it will make much difference.

The heat pump is at 6kW+ and then loses some due to defrosting.

It can’t produce 6kW of heat at the design temperature.

I have a real problem with these heat pump manufacturers.

They don’t do what they say on the tin, and the tin doesn’t say much!

Too much heat when you don’t want it and not enough when you do.

A very limited window where they work well.

For most, anyway.

For me, I find a low flow temperature limits the defrosting.

But I can do that because I only need about 3kW of my 8kW heat pump.

You could try lowering the flow temperature a degree or two.

You will get less heat, but you won’t actually lose so much of it to defrosting, so no worse off in terms of heat and better efficiency?

96

Quite possibly.

Just makes that even worse if you need something like 6kW from an 8kW Daikin.

`On the tin’ plenty big enough, in reality, maybe not?

97

That will be because it will cool the water meaning even more energy is required to heat it back up again.

98

A drop in efficiency is expected for any heatpump, especially in our climate. What change in COP are you seeing, and how often are the defrosts?

99

Cop is dropping by around half and only producing heat for around 1/2 hour before a other defrost

What I have just done is reduce my target in door temp to 1/2 degree below the actual temp and the heat pump didn’t work as hard despite the colder temps the heating period increased before next defrost

I will play with this more over the coming colder days to see if I can get it to make a significant difference and increase target temp gradually after a defrost ( might even be able to automate this )
But it will batter the Daikin api and your limited on calls

If anyone is interested it’s the heat cycle after 19:13

100

See post 88 Tim

Or look here

Emoncms - app view