Daikin Altherma 3 R 8kW frequent defrosts when below ~-6C-7C

Greetings from cold Finland! Has anyone figured out the defrost logic for Altherma 3 R? I have the hydrobox model, but I don’t think the indoor model matters as long as the outdoor type is the same ERGA04-08EVA. It’s my first winter with Altherma and the only thing that bothers me is that when outside temperature drops below ~-6C -7C or something like that, the system starts to defrost itself like crazy without any reason. The outdoor unit is’t frosted at all and it still defrosts itself every 30-42min. Outside humidity is 70-80% so it definitely should do that.

Last night was a good example when the temperature started to rise the behaviour totally changed. 18:00-21:00 it was a defrost loop with frequent defrosts and when the temperature started to rise it got normal, with defrost cycles ~many hours as you can hopefully see.

So has anyone figured out the defrost logic with this device? I have ESPAltherma installed so I can see a lot of sensors but I haven’t figured out what the logic is. Outdoor temperature, heat exchanger mid temperature…?

I’d love to know if someone has the same observations! And I do know that defrost cycle can be around ~1h when humidity is high etc and then it’s totally ok to defrost - when the outdoor unit is covered in frost! The problem is that defrost happens when you can clearly see that it’s not needed.

I’ve tried changing dT and a lot of other stuff but the only thing that seems to matter is the outdoor temperature - and that I can’t change :slight_smile:

Hi @grendy,

I’m not familiar with Daikins, but:

  1. Have a look at How to reduce frequency of defrosts on Daikin Altherma?. It looks like @matt-drummer is the specialist in this area!
  2. Several heat pump controllers (maybe Daikin also, you’d have to check) start a defrost based on the temperature of the refrigerant as it enters the evaporator as well as outdoor temperature (duration of the former may also play a part - the colder the refrigerant gets, the sooner the defrost is called for). As you note, none of these factors is within our gift to control…

Personally I’m a bit skeptical whether users can do much about defrost frequency (or duration) other than running the heat pump as gently as possible when it is cold (e.g. minimum speed - or even switched off - overnight if that is consistent with space heating requirements).

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@SarahH is correct about running as gently as possible, not sure about anything to do with specialist though!

I have had both a 9kW Daikin and an 8kW Daikin in the last two years in the same house.

They behave quite differently in terms of when they defrost.

The 9kW would start defrosting around +3c and would have a full layer of white ice covering the evaporator. It would run for 23 minutes and then defrst for about 10 minutes, it was quite predictable and pretty consistent in this.

I find that the 8kW doesn’t need to defrost until the outside temperature is minus.

Then it does ice up but nothing like the 9kW, there is very little ice and the evaporator looks more of a pale grey than the absolute white of the 9kW. The ice is very thin.

I can see the performance start to drop and you know the defrost is coming.

Then the performance picks up again. The defrosts for me are mild and over quite quickly.

This is one aspect of the smaller Daikin I am happy with, defrosts happen but they are not as severe as with the bigger models for me.

There is nothing you can do about it other than get the flow temperature as low as you can.

I never turn it off when it is cold and have frost protection enabled anyway so it will always run if there is any chance of freezing, even in the spring and autumn when I may not have the heating on.

It’s part of air source heat pumps, luckily my heat pump is bigger than I need so defrosting causes me no issues in terms of heating the house.

Good summary, @matt-drummer, but I wonder if

is slightly oversimplifying things. There’s no argument that minimising LWT (within limits) maximises CoP, but does it directly affect defrost frequency? I would have thought it would more likely be the proximity of LWT to its target temperature (either a manual setpoint or weather-compensated setpoint), which will typically cause the controller to run the compressor at minimum speed. This speed reduction will normally happen at any LWT, not just the minimum one. Or have I got this wrong?

Daikins don’t run like other heat pumps as far as I can see.

They are pretty simple in this respect and will just run continuously, they don’t use degree minutes or slowly increase the flow temperature.

They just get to the requested flow temperature pretty much immediately and just sit there until you change something or it needs to defrost.

I am not expert but I would think the ice build up in the right conditions is influenced by the speed and volume of air flowing through the evaporator.

In this model of Daikin, lower flow temperatures use less compressor power all of the time compared to higher flow temperatures.

I think mine is also helped but not needing much heat compared to the capacity of the heat pump.

But, we need/want to heat our houses so you just have to live with it or get a bit colder?

Not my most cohesive reply, sorry, I am at work so just `blurted’ this out, hope it sort of makes sense @SarahH

Edited to add.

I have been running in quiet mode for the last few weeks as somebody suggested it for DHW, I tried it and have left it alone.

One thing I do though is set my dT at 10c in the radiator setting and this keeps the flow rate at the minimum. I do this because otherwise I find the heat pump behaves erratically.

I also limit my pump speed to 60%, as low as I can go, and this limits the ferocity of the initial part of the heating cycle. It limits heat output as the flow rate is restricted and means that the heat pump is always running as gently as I can manage to make it.

Whether any of this helps with defrost frequency I don’t know, but these are all the settings that I use.

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Yes it’s all logical when you need power and the humidity is high → panel starts to freeze and needs defrosting. But my problem is that the panel is not white and frozen when it’s more than that ~-6C. Something else takes over the otherwise working defrost logic. In those conditions my air to air Daikin runs for hours and hours when the humidity is low and it’s even -15C or more. I was expecting the same functionality from this air to water Daikin, but it seems it somehow goes into this crazy defrost loop without the need to do it :frowning: … And -6C isn’t even cold!


This is how it looked when it was -15C. Humidity 80-90%


And today when it’s near 0C now. Humidity 90-97%. The top graph is power.

My similar unit is not white and frozen, just a thin translucent layer of ice, almost nothing, it never gets thick white ice.

It only defrosts below 0c.

It is much better than the 9kW and bigger.

I think your “near 0C now. Humidity 90-97%” graphs show the instability Matt mentioned in his post (and he has a great deal of experience of). There seems to be just three defrosts at 1:00, 7:30 and 11:30 on you graphs.

we can only wish for defrost cycles at -6 in the UK ,
but very little you can do if the air is damp being pulled over the exchanger