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The Different Algorithms Used

The TPI Algorithm

Configuring the TPI Algorithm Coefficients

If you have selected a thermostat of type over_switch, over_valve, or over_climate with self-regulation in Direct Valve Control mode and choose the "TPI" option in the menu, you will land on this page:

image

You need to provide:

  1. the coefficient coef_int for the TPI algorithm,
  2. the coefficient coef_ext for the TPI algorithm.

Principle

The TPI algorithm calculates the On vs Off percentage for the radiator at each cycle, using the target temperature, the current room temperature, and the current outdoor temperature. This algorithm is only applicable for Versatile Thermostats operating in over_switch and over_valve modes.

The percentage is calculated using this formula:

on_percent = coef_int * (target_temperature - current_temperature) + coef_ext * (target_temperature - outdoor_temperature)
Then, the algorithm ensures that 0 <= on_percent <= 1.

The default values for coef_int and coef_ext are 0.6 and 0.01, respectively. These default values are suitable for a standard well-insulated room.

When adjusting these coefficients, keep the following in mind:

  1. If the target temperature is not reached after stabilization, increase coef_ext (the on_percent is too low),
  2. If the target temperature is exceeded after stabilization, decrease coef_ext (the on_percent is too high),
  3. If reaching the target temperature is too slow, increase coef_int to provide more power to the heater,
  4. If reaching the target temperature is too fast and oscillations occur around the target, decrease coef_int to provide less power to the radiator.

In over_valve mode, the on_percent value is converted to a percentage (0 to 100%) and directly controls the valve's opening level.

The Self-Regulation Algorithm (Without Valve Control)

The self-regulation algorithm can be summarized as follows:

  1. Initialize the target temperature as the VTherm setpoint,
  2. If self-regulation is enabled:
    1. Calculate the regulated temperature (valid for a VTherm),
    2. Use this temperature as the target,
  3. For each underlying device of the VTherm:
    1. If "Use Internal Temperature" is checked:
      1. Calculate the compensation (trv_internal_temp - room_temp),
    2. Add the offset to the target temperature,
    3. Send the target temperature (= regulated_temp + (internal_temp - room_temp)) to the underlying device.

The Auto-Start/Stop Function Algorithm

The algorithm used in the auto-start/stop function operates as follows:

  1. If "Enable Auto-Start/Stop" is off, stop here.
  2. If VTherm is on and in Heating mode, when error_accumulated < -error_threshold -> turn off and save HVAC mode.
  3. If VTherm is on and in Cooling mode, when error_accumulated > error_threshold -> turn off and save HVAC mode.
  4. If VTherm is off and the saved HVAC mode is Heating, and current_temperature + slope * dt <= target_temperature, turn on and set the HVAC mode to the saved mode.
  5. If VTherm is off and the saved HVAC mode is Cooling, and current_temperature + slope * dt >= target_temperature, turn on and set the HVAC mode to the saved mode.
  6. error_threshold is set to 10 (° * min) for slow detection, 5 for medium, and 2 for fast.

dt is set to 30 min for slow, 15 min for medium, and 7 min for fast detection levels.

The function is detailed here.