I’m counting 9 defrosts in 6 hours, and performance in line with Carnot heat formula. This seems perfectly normal for an adequately sized heatpump in a damp climate.
Oversized heatpumps benefit from larger heat exchanges and aren’t running at full capacity, so don’t need to defrost as often. On the other hand they can’t modulate down in mild weather, so it’s swings and roundabouts.
Yes, I count 34 defrosts in 21 hours, quite a lot.
However, would you agree that the heat pump is on the limit of the amount of heat it can produce?
Can it get anywhere near its claimed 6kW output?
It’s doing just over 3.5kW
Important for people considering swapping out 9kW and 11kW units for one of these.
It s producing 6 kw of heat at times , even a little more on occasion
I know Chris, that’s the problem.
If you had a 5kW heat loss could it satisfy it?
Your heat loss appears to be only 3.5kW at -2.5c
Your room temperature is steady.
But it is struggling, do you think you could get another 2kW of heat out of it?
If the heat exchanger was the same size and the instantaneous heat out put was lower probably
I’m
Wondering if there is something in the MMI which I can restrict the maximum input
But the instantaneous heat output is pretty much what you would need to be continuous to satisfy a 5.5kW heat loss.
I think that instantaneous power is actually more than the heat loss to bring the room target temp up as quickly as possible. After the defrost cycle because it’s robbed some heat from house
I can see that.
I am thinking more about others than actually your house.
Say you had a heat loss 1.5kW to 2kW higher than yours, would it work?
I don’t think so.
For you, try limiting pump speed, that is what is giving you all that heat, it’s at 15lpm.
Mine starts at 10lpm restricted to 60%, as low as it will go.
Then you’ll get less heat at the beginning and you won’t be pushing it so hard, should cut down the defrosts.
Daikin’s expectations are obviously optimistic but I don’t think that there is a standard for manufacturers to model defrost cycles and it’s all climate dependent.
@TrystanLea on his heatpump oversizing thread suggested that the daikins should maybe look to be 1.5x actual heat loss. However, at some point you may be better both from a mild weather running modulation costs and from install costs to just have backup resistive heating for extreme weather conditions, especially around the changeover between model sizes.
Hi Ben,
The 4/6/8kW Daikins are not available with a BUH in the UK.
Certainly not when mine was fitted.
It was one of the warnings I received from Octopus on the swap from my BUH equipped 9kW to the non BUH 8KW unit.
Remember, there are members here considering replacing 9 and 11kW Daikins with the smaller units with heat losses greater than me, Zak and Chris.
I really fear they could struggle.
The EDLA06E3V3 is the 6kW monoblock with backup heater, it’s probably just that Octopus didn’t bulk order those.
In reality an oil filled radiator or two would achieve similar results as a backup heater anyway.
Agreed
At the time, Octopus said only the non BUH model was available in the UK, maybe they lied?
The Daikin engineer that visited me last year seemed to think mine had a BUH, it doesn’t.
Anyway, the bottom line is, the badge on the heat pump is no real indication of what you might actually get when you come to use it.
Picking an *kW heat pump doesn’t mean that is what you’ll get.
Is all the software and control in the heat pump for a small heater ? I remember looking at my connections to see a while back and those connections were free from wires ?
It is certainly in the MMI.
You can change heat pump model and you can configure the BUH.
But the plumbing in the heat pump is quite different.
I remember we were all talking about 9kW units with thermistors before and after the BUH, and the two versions of the heat pump (with and without BUH) were quite different in their internal layouts.
Would you include me as one that might struggle?
My 11kW is barely breaking a sweat in these cold conditions and while it still does a lot of defrosting, it’s nowhere near as bad as what Chris is seeing.
My 11kW even seems to think it’s job is done and has clocked off for the day, even though it’s below freezing.
If you limit your pump speed you really need a big dT, otherwise you may not get enough heat.
I suggest changing to radiators if you do this.
I might Mark.
None of the heat pumps I look at are in houses with big heat losses.
They are all around 4kW or less.
Mine is about 3kW, @Chris_Hill is less than 4kW by the looks of it and @KnightPhoenix is about 4kW
Me and @KnightPhoenix have 8kW units and aren’t pushing them at all.
@Chris_Hill is closer to the limit of his 6kW and has a lot of defrosting.
I don’t really know how much we can get out of these heat pumps if we really needed it.
It was a concern I had, my 9kW was only good for about 6.2kW in these conditions, maybe a bit less.
We are all running at quite low flow temperatures, me particularly. I know if I increased it much the defrosting would increase.
It’s difficult to know for sure, but something to consider.
You don’t seem to need a lot of heat, you’re probably Ok but I would insist on the 8kW if I were you.
It’s a good job our flow temps are low , my design @-2.7 is 50 lol
It’s closer to 35
Another design flaw
Nobody is going to get 50c out of these Daikin heat pumps in these conditions.
It’ll look like a very short and very fat snowman long before it gets to 50c
