Home Assistant Expected Indoor Humidity computation

expected_humidity.yaml

# Use Arden Buck equation <https://en.wikipedia.org/wiki/Arden_Buck_equation> to compute approximate expected indoor humidty given outdoor humidity

template:
  - sensor:
      unique_id: "tylerszabo/template.sensor:expected-indoor-humidity"
      name: "Expected Indoor Humidity"
      unit_of_measurement: "%"
      device_class: humidity
      state: >
        {%- set t0 = states('sensor.outdoor_temperature')|float(undefined) -%}
        {%- set h0 = states('sensor.outdoor_humidity')|float(undefined) -%}
        {%- set tx = states('sensor.indoor_temperature')|float(undefined) -%}
        {%- if t0 is undefined() or h0 is undefined() or tx is undefined() -%}
          unavailable
        {%- else -%}
          {%- if t0 > 0.0 -%}
            {{ (2.71828**(((18.678 - 0.0042644*t0)*t0)/(t0 + 257.14) - ((18.678 - 0.0042644*tx)*tx)/(tx + 257.14))*h0)|round(2) }}
          {%- else -%}
            {{ (2.71828**(((23.036 - 0.0029967*t0)*t0)/(t0 + 279.82) - ((18.678 - 0.0042644*tx)*tx)/(tx + 257.14))*h0)|round(2) }}
          {%- endif -%}
        {%- endif -%}
    trigger:
      - platform: state
        entity_id:
          - sensor.outdoor_temperature
          - sensor.indoor_temperature
      - platform: event
        event_type: event_template_reloaded