Bang Bang Climate Controller

The bang_bang climate platform allows you to regulate a value with a bang-bang controller (also called hysteresis controller).

Note

A number of people have asked about the behavior of the bang-bang controller. In version 1.15, a thermostat component was added which behaves more like a common thermostat; it is essentially two bang-bang controllers in one. Please see the Bang-bang vs. Thermostat section below if you are not sure which is appropriate for your application.

The bang-bang controller’s principle of operation is quite simple. First, you specify an observable value (for example the temperature of a room). The controller will try to keep this observed value in a defined range. To do this, the controller can activate objects like a heating unit to change the observed value.

The range that the controller will try to keep the observed value in can be controlled through the front-end with the target_temperature_low and target_temperature_high values (see screenshot below). As soon as the observed temperature dips below or above this range it will activate one of the defined actions cool_action, heat_action and idle_action.

There are three types of bang bang controllers this platform can represent:

  • Heaters: For devices where the observed temperature can only be increased.

    • As soon as the temperature goes below the lower target temperature, heat_action will be called.

    • When the temperature goes above the higher temperature, idle_action will be called.

    • If you change operating mode (manual mode). And it is between high and low temperature. It does not wait to get to low temperature, it starts working until it gets to high temperature.

  • Coolers: For devices where the observed temperature can only be decreased.

    • As soon as the temperature goes above the higher target temperature, cool_action will be called.

    • When the temperature goes below the lower temperature, idle_action will be called.

    • If you change operating mode (manual mode). And it is between high and low temperature. It does not wait to get to high temperature, it starts working until it gets to low temperature.

  • Heater+Cooler: For devices where the temperature can both actively be increased and decreased.

    • When the current temperature is below the lower target temperature, heat_action is called.

    • When the current temperature is within the target temperature range, idle_action is called.

    • When the current temperature is above the higher target temperature, cool_action is called.

Do note that the actions are only called when the current temperature leaves the target temperature range.

../../_images/climate-ui.png 
# Example configuration entry
climate:
  - platform: bang_bang
    name: "Bang Bang Climate Controller"
    sensor: my_temperature_sensor
    default_target_temperature_low: 20 °C
    default_target_temperature_high: 22 °C

    heat_action:
      - switch.turn_on: heater
    idle_action:
      - switch.turn_off: heater

Configuration variables:

  • sensor (Required, ID): The sensor that is used to measure the current temperature.

  • humidity_sensor (Optional, ID): If specified, this sensor is used to measure the current humidity. This is used for information only and does not influence temperature control.

  • default_target_temperature_low (Required, float): The default low target temperature for the control algorithm. This can be dynamically set in the frontend later.

  • default_target_temperature_high (Required, float): The default high target temperature for the control algorithm. This can be dynamically set in the frontend later.

  • idle_action (Required, Action): The action to call when the climate device wants to enter idle mode.

  • heat_action (Optional, Action): The action to call when the climate device wants to heating mode and increase the current temperature. At least one of heat_action and cool_action need to be specified.

  • cool_action (Optional, Action): The action to call when the climate device wants to cooling mode and decrease the current temperature.

  • All other options from Climate.

Advanced options:

  • away_config (Optional): Additionally specify target temperature range settings for away mode. Away mode can be used to have a second set of target temperatures (for example while the user is away or during nighttime)

    • default_target_temperature_low (Required, float): The default low target temperature for the control algorithm during away mode.

    • default_target_temperature_high (Required, float): The default high target temperature for the control algorithm during away mode.

Note

While this platform uses the term temperature everywhere, it can also be used for other values. For example, controlling humidity is also possible with this platform.

Bang-bang vs. Thermostat

The behavior of the bang-bang controller is a topic that has surfaced on the ESPHome Discord server countless times – many people have been confused by what it does. While they are similar, there are two key differences between the bang-bang component and the thermostat component:

  • When actions are triggered

  • How the set points are used by the controller

Now is a good time to ensure you understand exactly how a bang-bang controller should behave; if you do not have a clear understanding of this, be sure to check out the Wikipedia article.

The Problem with Dual-Function Systems

If you are not attempting to operate a system that can both heat and cool, you’ll likely want to skip to the next section about user interface.

As outlined above, in general:

  • As soon as the temperature goes below the lower target temperature, heat_action is called to activate heating.

  • Heating will continue until the temperature reaches the upper target temperature, at which point idle_action is called to stop heating.

  • As soon as the temperature goes above the upper target temperature, cool_action is called to activate cooling.

  • Cooling will continue until the temperature reaches the lower target temperature, at which point idle_action is called to stop cooling.

A single bang-bang controller may work well for systems that only heat or only cool; however, it begins to break down when applied to systems that may both heat and cool. This is simply because both actions are tied to both set points – that is, the point at which heating stops is also the point at which cooling begins. The reverse is also true: the point at which cooling stops is also the point at which heating begins. Let’s look at an example:

Consider a system that both heats and cools. The target_temperature_low set point is 20 °C while the target_temperature_high set point is 22 °C. The sensor reports that the temperature is 19.75 °C, so the controller calls heat_action to activate heating. Heating continues until the temperature reaches target_temperature_high (22 °C in this case). Once this temperature is achieved, idle_action is called to stop heating. However, should temperature drift even slightly above target_temperature_high–even just a fraction of a degree for a fraction of a second–the controller will call cool_action to begin cooling. Now, cooling will continue until target_temperature_low is reached again, but, as before, should the temperature drift even slightly below target_temperature_low for even a fraction of a second, heat_action will be invoked again, and the cycle will repeat. It will “ping-pong” between the two set points, potentially forever. Oscillation at the “edges” of the hysteresis window, or going past the set point in either direction, should be expected; consider, for example, a heater that is turned off after it reaches its set point. The heating element will remain hot (potentially for quite a while), and as such will continue to heat the air until the element fully cools down to match the ambient air/room temperature.

The thermostat component differs in that there is hysteresis around each set point. For example, if the target_temperature_low set point is 20 °C, and the (default) hysteresis value of 0.5 °C is used, heat_action is called at a temperature of 19.5 °C and idle_action is called at 20.5 °C. If cooling, as defined by target_temperature_high, is set to 22 °C, cool_action would be called at 22.5 °C and idle_action called at 21.5 °C. Again, it is essentially two bang-bang controllers in one.

Behavioral differences aside, there is another important difference between these two components: user interface.

User Interface

The interaction with this component via the Home Assistant user interface is also different than what is seen on most common residential thermostats. Generally speaking, most thermostats allow either one or two set points – one of them is associated with heating while the other with cooling, and this is exactly how the thermostat component uses them. If you set the “heat” set point to 20 °C, most people assume this means the heating system will keep the temperature as close to 20 °C as possible. The same is true for the upper set point, for cooling: if you set a temperature of 22 °C, most people assume the cooling system will keep the temperature as close to 22 °C as possible.

The bang-bang controller does not use the set points this way. If you set the lower set point to 20 °C and set the upper set point to 22 °C, then the temperature will be brought as high as 22 °C but go no lower than 20 °C.

The behavior is not difficult to understand, but, as we’ve learned from many discussions on the Discord server, it departs from what most people seem to expect.

Which is Right for Me?

It comes down to two points:

  • If you have a dual-function system (both heating and cooling), you’ll almost certainly want to use the thermostat component.

  • If you have a single-function system and have a specific need or desire to manually control both the upper and lower bounds for hysteresis, use the bang-bang controller.

In all other situations, the thermostat component is probably best.

See Also