Daikin Altherma Hot Water 'eco' mode

The Vaillant eco mode seems useful for achieving good DHW efficiency, but Daikin’s dont have an eco mode.

So I had an idea, most Altherma’s have Power Limitation (4-08) settings, to restrict power either in Amps or kW.

Unfortunately my unit (I seem to be the only one with a hydrosplit unit), doesn’t appear to work well with the Power Limitation settings. I have the smart grid setup for solar matching but it has never worked and have a ticket open with Daikin. When I set my power limit to 1.5kW (5-05), the information screen said the power limit was 2A. This resulted in the device appearing to just cycling off and on, presumably because it smashes the limit when the compressor comes on:

I swapped over to Amps (4-09 = 0) on the limitation settings and tried a more conservative 8A (~1.8kW).

This worked well for a while, it stuck around 1.7kW for just over 30 minutes, but then the unit seemed to just ignore the limit, and power started rising to 3kW, ignoring the limitation :frowning:

For reference a normal DHW cycle looks like this, with power rising from 1.6kW to 4.5kW fairly steadily:

If this worked in practice, the Smart Grid “Recommended On” mode can enforce a static power limitation, or a pulse input can be applied to set a variable limit, so this could be achieved in a smart fashion rather than manually setting options.

I wonder if anyone else wants to have a play and see if they have better success than me.

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I will try the power limitations. Maybe it will help me coax longer cycles times out of the my Altherma 9kW unit between defrosts? (Not that we have any cold temps forecast…)

@meatballs I have what looks like a successful current-limited DHW cycle on my 9kW Altherma monoblock:


This was heating the water to 43C, with the current limit set 10A. Power didn’t go above 2100W.

I don’t have a lot of DHW heating cycles to compare it to, but it looks promising.

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Nice, does the COP look better than other runs? I had a good dig but couldn’t see any other runs :sweat_smile:

I wonder if it can be limited lower to 1 or 1.5kW, the Vailiants I’ve looked at can stay down at that level but I guess it could be a refridgerent difference when the flow temp starts warming up.

My unit just refuses to work with recommended on.

I’ve not been using the heat pump much for hot water… we use so little most days that just having a little bit of hot water at the top of the tank, heated by the Eddi / immersion heater is (I think) more cost effective than heating a tank full using the heat pump.

I found another DHW cycle from a month ago:

It looks like the COP was perhaps a little better in February, even though the outside temperature was quite a bit lower 7.6C versus 13.5C today. I guess I need to try deltaT of 5C again… was on that but switched to 4C, which I think might work better for our heating. Sigh…. more experiments needed!

If the power limit works reliably, I am more likely to use heat pump for hot water as it will keep the power draw below our solar generation more often.

Thanks for the idea!

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I’d like to give this a go on my 11kw Altherma monobloc beast. It’s the older model but given it’s about 100% oversized it could be a useful changes. Then again I also have a 300l tank so might extend reheat time too much.

Are you able to share the settings to change and I’ll cross reference to the manual on mine to check before I make the changes.

Here’s what I did (abridged):

Installer menu.
Power consumption control: continuous
Type: amps

Then set the limit you want.

Note there is a box in the Altherma installer reference manual that carries a notice about the minimum power… see page 59


Thanks @squarepeg77
Unfortunately the options don’t appear to be there in the older Altherma settings.