Who knows if it is possible to trigger an automation based on a calculated value? For example I want to calculate the dew point based on relative humidity and temperature and start my home ventilation system when a certain value is reached. Is this possible?
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Puh , that sounds really tricky- I don’t have any idea how that should work- maybe in Home Assistant?
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Hello, welcome.
Unfortunately, Aqara home does not have a tool for dynamic calculation of the dew point by the formula.
This version of simplified dew point control can be done with the following automation. Launch for the room (+20…22 °C)
WHEN: The humidity on the sensor becomes greater than or equal to 55%.
IF: additional condition: The temperature on the sensor is in the range from 20 °C to 22 °C.
THEN: Turn on the ventilation relay.
Fig.1.
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Aqara Home: No native dew point calculation. The only workaround is combining temperature and humidity conditions simultaneously, which is not a true dew point calculation.
Apple Home (HomeKit): No support for calculated sensor values. Automations can only use direct sensor readings and accessory states.
Apple Shortcuts: Limited / Complicated
- No native “every X minutes” trigger — only fixed times of day or other event-based triggers (battery, NFC, location, Focus mode, etc.)
- The Magnus formula may be implementable using the „Calculate Expression" action, which supports scientific functions including
ln()
Home Assistant: Fully supports dew point-based automations:
- Template sensors using the exact Magnus formula
- Community integrations such as Thermal Comfort (via HACS)