From the article:
Everything is run by the "eWeLink" app, which can tell the outside temperature and humidity. The app connects to a “eWeLink” switch.
The system allows him to set a “scene.” For example, he can have the system automatically turn on when the outside temperature is between 50 and 80 degrees F, or when the relative humidity is between 50% and 70%.
He uses charts for each grain for equilibrium moisture content.
“I look up the desired equilibrium on the chart, and find my desired moisture, and then it shows the temperature and humidity range the fan needs to run at,” he said.