Daikin Altherma 6kw cycling normal?

I have recently had a heat pump installed and wondered if there was anything I could do to tweak efficiency?

My weather curve is 55@-10 25@20

I have the emitters set to fancoil with a DT of 5

Overshoot is set to 4c

Modulation is set to 5c

I use weather comp set point + thermostat control

Madoka at 21c

Pump speed seems to sit around 7lpm which appears to be the lowest it goes

I don’t have all the data as I haven’t yet installed ESPAltherma but I have the power graph, it seems that once the rooms reach 20c the emitters can’t shed heat fast enough and so the LWT climbs and the compressor stops.

Is this just expected behaviour?

Could this be the madoka lowering LWT as it gets close to the set point?

Yes, this is normal. Especially this time of year when external temperatures are above 10C.

You are correct that as the room warms the radiators emit progressively less heat as the delta T between the radiator and the room drops. At some point this drops below the minimum output of the heat pump and at that point the LWT has to start rising. Eventually the ASHP has no choice but to start cycling.

7lpm seems to be the lowest speed the Daikin will pump at, and is where it seems to aim for with low heat output.

It is possible that it is the modulation which is tipping the ASHP over the edge into cycling as your room temp reaches the set point, but its going to happen at some point anyway. So long as the heat pump doesn’t cycle excessively its not something to really worry about.

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Your Daikin almost certainly won’t be able to maintain a minimum temperature below 30C (check all the other Daikin Althermas on heatpumpmonitor.org and you’ll see the same issue). Attempting to hit a LWT target lower than the heat pump can achieve will also cause it to cycle.

I would adjust your minimum temperature on your WDC to no less than 30. Also, I don’t think a 1:1 correlation between outside temperature and LWT is optimal, I’d reduce your upper value as well. For example, my WDC with the 6kW unit is 30@12 > 42@-12 (a 0.5:1 correlation), though you’d need to tweak this to your own property.

What do you have your modulation set to on that curve?

In the past week, the house hasn’t felt overheated with the current curve, I setback to 19c at night and it takes several hours for my living room to reach 20c again, I derived the curve from heatpunk, my house isn’t the best insulated and I lost 1 degree in 3 hours at a mean outside temperature of 14.5c

Please disregard what I said about changes to the WDC. As you’ve used real data rather than having a guess :smile:. My point regarding the minimum temperature your ASHP will be able to provide is still valid.

My modulation is set to 2C but I very rarely see (as in, I have never seen it) any modulation away from the WDC because the house is always within 0.5C of the Madoka target temperature. Ours is 2007 build, with good insulation. Around 14C is when we hit equilibrium with no heating required to maintain the temperature.

I’ve got the same Daikin. My weather curve is set to:
50C LWT @ -20C
35C LWT @ +10C

I started off with a 1:1 to curve in the beginning but it was hotter than it needed to be in cold weather and the very low LWT in milder weather put it into a rapid cycling loop. I’m experimenting at the moment with how low I can get LWT in mild weather but I’d agree with @mortstar about 30C as a minimum with radiators.

Radiators don’t dissipate heat in a linear fashion. The heat output increases exponentially with the difference between radiator temp and room temp.

My modulation is 3 at the moment, I’m not really using it, trying to get other things right first.

It takes a while to get a weather curve dialled in, and you need some cold weather to experiment with. My strategy was to start off with something I was pretty certain would keep the house warm and then incrementally lower it.

If my heatpump is running at its lowest power @ 450w already, what do i have to gain by dropping LWT? Pump speed seems to constantly sit at 7lpm which I assume is preferable? If the DT between LWT and Return narrows, won’t that mean my COP drops off?

Had a really nice run today with Madoka set to 24 (not that it got there) just to eliminate modulation playing a part.

Going by MMI heat output and CT clamp I’ve used 3.8kWh of electric for about 20kWh of heat