vtherm does not take underlying's temperature into account

[flg]

Hello,

I'm trying to understand why vtherm does not take the underlying temperature into account.

vtherm_sdb is an "over climate" over sdb configured with "Use internal temperature of the underlying" enabled. On the following plot we can see that:

• Vtherm target temperature is 18,
• underlying target temperature is 18,
• while the difference between the underlying and the vtherm current temperatures is often more than 0.5 degree C.
• As a consequence heating turns on when the room temperature 18.8, at 14:30, and the device temperature is 17.9.

I thought that "Use internal temperature of the underlying" was supposed to compensate for the different between external temperature sensor and device sensor. In this case, at 14:30, I was expecting the underlying target temperature to be :

• underlying target temperature = vtherm target temperature + (underlying temperature - external sensor temperature)
  -17.1 = 18 + (17.9 - 18.8)

Why, with this configuration, the target temperatures of the vtherm and the underlying are the same while their respective temperatures are not?

Bonus question: what defined "vtherm_sdb heating" on the graph?

Here's a snapshot of the vtherm taken after the plot (unfortunately) to check the configuration:
hvac_modes: off, heat min_temp: 7 max_temp: 35 target_temp_step: 0.2 preset_modes: none, frost, eco, comfort, boost current_temperature: 17.2 temperature: 16 hvac_action: idle preset_mode: none is_on: true hvac_mode: heat type: null is_controlled_by_central_mode: false last_central_mode: null frost_temp: 8 eco_temp: 18 boost_temp: 28 comfort_temp: 22 frost_away_temp: 0 eco_away_temp: 0 boost_away_temp: 0 comfort_away_temp: 0 power_temp: null target_temperature_step: 0.2 ext_current_temperature: 4.9 ac_mode: false current_power: null current_power_max: null saved_preset_mode: eco saved_target_temp: 18 saved_hvac_mode: off motion_sensor_entity_id: null motion_state: null power_sensor_entity_id: null max_power_sensor_entity_id: null overpowering_state: null presence_sensor_entity_id: null presence_state: null window_state: off window_auto_state: off window_bypass_state: false window_sensor_entity_id: null window_delay_sec: null window_auto_enabled: false window_auto_open_threshold: null window_auto_close_threshold: null window_auto_max_duration: null window_action: window_turn_off security_delay_min: 60 security_min_on_percent: 0.5 security_default_on_percent: 0.1 last_temperature_datetime: 2024-12-09T10:37:31.082322+01:00 last_ext_temperature_datetime: 2024-12-09T13:00:41.501381+01:00 security_state: false minimal_activation_delay_sec: 10 device_power: 1 mean_cycle_power: null total_energy: 0 last_update_datetime: 2024-12-09T13:25:02.215312+01:00 timezone: Europe/Zurich temperature_unit: °C is_device_active: false ema_temp: 17.4 is_used_by_central_boiler: false temperature_slope: 0 hvac_off_reason: null is_over_climate: true start_hvac_action_date: null underlying_entities: climate.sdb auto_fan_mode: auto_fan_high current_auto_fan_mode: auto_fan_high auto_activated_fan_mode: null auto_deactivated_fan_mode: null auto_regulation_use_device_temp: true auto_start_stop_enable: false auto_start_stop_level: auto_start_stop_none auto_start_stop_dtmin: null auto_start_stop_accumulated_error: 0 auto_start_stop_accumulated_error_threshold: null follow_underlying_temp_change: true friendly_name: vtherm_sdb supported_features: 401

[jmcollin78]

Hello, can you check this post ? I think you can be in the same issue : #690

[flg]

Hello Jean-Marc,

I don't think #690 has anything to do with my question.

Maybe my assumption is just wrong. I'm assuming that with the following conditions:

• external sensor temperature = 19
• underlying sensor temperature = 18
• vtherm target temperature = 20

The underlying target temperature should be : 19 (i.e. 20 - (19 - 18)).

Is this assumption correct?

[jmcollin78]

It is much more complicated than thatand it depends of your tuning and parameters. You can have a look at the algorithm here: https://github.com/jmcollin78/versatile_thermostat/blob/main/documentation/en/algorithms.md#the-self-regulation-algorithm-without-valve-control

[flg]

OK I think I understand. But then in the plot we can see the temperature oscillates around 19 instead of 18 (which is the vtherm target temperature). What can I do to fix that? I tried with and without "Use internal temperature of the underlying" enabled but in has no obvious impact.

[jmcollin78]

Add a self-regulation (this has been done for this exactly). Start at low level, wait for stabilization and if already not good, upgrade the level.

Use "Use internal temperature.. " only if the self-regulation is not enough. It generaly don't give good results.

To be more precise I will need curves as explained here: https://github.com/jmcollin78/versatile_thermostat/blob/main/documentation/en/additions.md#regulation-curves-with-plotly-to-fine-tune-your-thermostat

[flg]

Thanks, I will try the self-regulation.