#Dewpoint Calculation

1 messages · Page 1 of 1 (latest)

willow zodiac
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Any addons you could recommend that will give me a dew point for temp+humdity sensors, so i could decide when to open a window for an optimal drying experience? 😅

frozen leaf
obtuse dome
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A template sensor can do the calculation.

obtuse dome
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{% set T = states('sensor.temperature_in_celsius')|float(0) %}
{% set RH = states('sensor.humidity_in_percent')|float(0) %}
{% set a = 18.678|float %}
{% set b = 257.14|float %}
{% set c = 234.5|float %}
{% set gamma = log((RH / 100) * e ** ((a - T / c)*(T / (b + T))))|float %}
{{ ((b * gamma) / (a - gamma))|round(1) }}
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For temperatures in °C

obtuse dome
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{% set T = (TF - 32) / 1.8 %}
{% set RH = states('sensor.humidity_in_percent')|float(0) %}
{% set a = 18.678|float %}
{% set b = 257.14|float %}
{% set c = 234.5|float %}
{% set gamma = log((RH / 100) * e ** ((a - T / c)*(T / (b + T))))|float %}
{% set D = ((b * gamma) / (a - gamma))|round(1) %}
{{ D * 1.8 + 32 }}

For Fahrenheit (quick and dirty conversion back and forth between C and F).
Was too lazy to re-do the full calculation for Fahrenheit.

willow zodiac
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Is there any addon already that will create these for me when the necessary entities are available?

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i wonder what a, b and c are

obtuse dome
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Constants you don't want to know in detail shksD

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However there are also HACS intergrations like the one code-in-progress linked or "Thermal Comfort" which can calculate dewpoints (and other stuff).

willow zodiac
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Thank you.

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I had chatgpt clean up your code, hope you don't mind. 😄

# In configuration.yaml or sensors.yaml
template:
  - sensor:
      - name: "Dew Point"
        unique_id: "dew_point_sensor"
        unit_of_measurement: "°F"
        state_class: measurement
        device_class: temperature
        state: >
          {% set temp_fahrenheit = states('sensor.temperature_in_fahrenheit')|float(0) %}
          {% set temp_celsius = (temp_fahrenheit - 32) / 1.8 %}
          {% set relative_humidity = states('sensor.humidity_in_percent')|float(0) %}
          
          {# Magnus-Tetens approximation constants #}
          {% set magnus_constant_a = 18.678 %}
          {% set magnus_constant_b = 257.14 %}
          {% set magnus_constant_c = 234.5 %}
          
          {# Calculate gamma #}
          {% set gamma = log((relative_humidity / 100) * e ** ((magnus_constant_a - temp_celsius / magnus_constant_c) * (temp_celsius / (magnus_constant_b + temp_celsius)))) %}
          
          {# Calculate dew point in Celsius #}
          {% set dew_point_celsius = (magnus_constant_b * gamma) / (magnus_constant_a - gamma) %}
          
          {# Convert dew point to Fahrenheit and round to 1 decimal place #}
          {{ (dew_point_celsius * 1.8 + 32)|round(1) }}```
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didn't test it yet, will fix if it's bad (in a couple of hours)

willow zodiac
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template:
  - sensor:
      - name: "Dew Point Celsius"
        unique_id: "dew_point_celsius_sensor"
        unit_of_measurement: "°C"
        state_class: measurement
        device_class: temperature
        state: >
          {# Fetch temperature and humidity #}
          {% set temperature_c = states('sensor.temperature_in_celsius')|float(0) %}
          {% set humidity_percent = states('sensor.humidity_in_percent')|float(0) %}

          {# Magnus-Tetens approximation constants #}
          {% set a = 18.678 %}
          {% set b = 257.14 %}
          {% set c = 234.5 %}

          {# Calculate gamma using the Magnus formula #}
          {% set gamma = log((humidity_percent / 100) * exp((a * temperature_c) / (b + temperature_c))) %}

          {# Calculate dew point in Celsius #}
          {% set dew_point_c = (b * gamma) / (a - gamma) %}
          
          {# Round the dew point to 1 decimal place #}
          {{ dew_point_c|round(1) }}

i asked it to clean up more and do celcius only

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I wonder, is there an "open windows" addon already?

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i might create one if it doesn't as my first project

obtuse dome
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I compare the absolute humidity between inside and outside for a binary sensor to show when it is good to open windows.

willow zodiac
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dewpoint_outside < dewpoint_inside = open windows, right?

obtuse dome
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I compare the absolute humidity in g/m³. I want to open windows, when the outside air is dryer than inside. Otherwise the relative humidity wouldn't drop.

willow zodiac
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Thermal Comfort seems a perfect tool for that

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Thanks a lot for your input, @obtuse dome