Heating curve vs target return water temperature - mismatch?

[jcjveraa]

Hi there,

Thanks a lot for the work on the integration! I'm a software developer myself, so I might be able to contribute here and there.

I'm trying to tweak my my Alpha-Innotec heatpump, as while I have the room thermostat setpoint on 17 degrees Celsius, it still is heating the house to 20-21 degrees :) Lowering the thermostat value helps but it's not ideal.

Can someone help me understand how the heating curve shape is defined? Understanding that seems crucial to be able to tune it a little. I have read the Luxtronik manuals on this subject, but couldn't see an answer, I may have missed something.

The images in e.g. this online version imply the curve to be non-linear, but fail to specify the parameters of the curve.
https://www.alpha-innotec.cz/wp-content/uploads/2019/02/controller1.pdf

My curve values are approximately as follows (adjusted a little to have simple resulting formula)

Return temp	Outside temp
30	-20 (fixed value?)
20	20 (seems to track the outside temp 1:1?)

If this is a linear curve (or line then rather), I would expect the resulting curve to then be defined as OT * -0.25 +25, where OT is the outside temperature. I.e., when the outside temperature is 0, the target return temperature will be 25 degrees (and -20 OT -> 30 deg, 20 OT -> 20 deg).

This is not the case however: I can see in HASS and on the device display itself that my return temperature target is about 2 degrees below where I expect it to be. I can see it actually using that target temperature, as exactly when the return temperature sunk 2 degrees below the target it started heating.

[jcjveraa]

I've since by chance found this link
https://mnemotron.de/lux/heatcurve.html on https://community.home-assistant.io/t/writing-a-component-for-luxtronik-heatpumps/35796/372?page=19 - I had missed it before. However implementing this in Jinja still shows a difference between what the pump reports and the calculated value.

/**
 * Calculate desired heating return value for given outdoor temperature and heatcurve.
 */
function calcHeatcurve(outdoorTemp, heatingEnd, heatingFoot, heatingDelta)
{
    // Prevent DivisionByZero
    if((outdoorTemp - heatingFoot) != 40)
        return heatingFoot + (heatingEnd - 20) * (heatingFoot - outdoorTemp) / (20 - (outdoorTemp - heatingFoot) / 2) + heatingDelta;
    else
        return 0;
}

[wiljums]

The room thermostate (RBE) temp also affects the calculated return temp. You can set the impact of it in %. Einflussfaktor RT (%) in German.

[jcjveraa]

Ah that’s the missing link, I thought the two operated separately from each other with the RBE essentially giving the unit “permission to heat” when the temperature would go out of its hysteresis band, but after playing with it I now see that it directly influences the target return temperature.

Thanks!

[jcjveraa]

The “influence factor” to me is pretty vague though, if someone has a formula I’d be happy to take it. If not I might try to derive it myself by playing around with values to see the actual impact it has.

[wiljums]

See this manual: 83032600bNL_RBE.pdf

[wiljums]

And possibly an average outside temp of the last x hours is used in stead of the actual outside temp?