Altherma 3 - estimated Carnot COP

[TomAutoHome]

Although for now, an accurate COP calculation is not possible due to missing or low-frequency sensor readings/updates in Onecta, it is possible to calculate using the Carnot COP formula. It is based on the thermodynamics of gases and requires two sensor outputs only: 1. actual outside (ambient) temperature, and 2. leaving water temperature. It uses a simple formula (with sample calculation):
T_condensing = T_flow + 2K = 35°C + 2K = 37°C
T_evaporating = T_ambient - 6K = 6°C - 6K = 0°C
Carnot_COP = (T_condensing + 273) / ((T_condensing+273) – (T_evaporating + 273)) = (37°C+273K) / ((37°C+273K) - (0°C+273K)) = 8.4
Practical_COP = 0.5 x Carnot_COP = 0.5 x 8.4 = 4.2

From the practical side, it should usually be close to the one computed from dT, flow rate, and power consumption. At least it is an indication of how it could be. The disclaimer: It won't be as precise as a real-time calculation, but it could give some idea of the expected performance of the unit. My unit for example has 2 heating outputs built-in (main zone, additional zone) which run two pumps. This affects overall system power consumption, therefore results could be worse than this calculation. Simply it focuses on gas properties at given temperatures.

A sample value template used by me to get this value from Onecta data which I defined as a helper:
{{ (((states('sensor.devicename_climatecontrol_leaving_water_temperature')|float +2 +273) / ((states('sensor.devicename_climatecontrol_leaving_water_temperature')|float +2 +273) - (states('sensor.devicename_climatecontrol_outdoor_temperature')|float -6 +273))) /2) |round(2) |float }}

It may be possible to add this sensor to the integration.
My helper does not distinguish the COP for heating/DHW mode nor does not allow me to compute a historical value (ie. 30 min, 1hr, or other frequency), simply I didn't bother with that much yet. Could be an idea to utilize this concept in an extended way.

[jwillemsen]

Thanks for the suggestion, but this looks to me something for a template sensor created by the user which is calculated by HA, this integration focuses on providing the data as is to the user