We are monitoring the indoor and outdoor temperature.
We using this data to control the fan.
If it is hotter in the root cellar than it is outside (and its not below 40 degrees in the root cellar) then the fan turns on,
otherwise it turns off.

https://docs.google.com/spreadsheets/d/12kbl7dH69cLhAEUpmnNM4-bl_8fNTqiN7Cc7Hgfejkk/edit#gid=0