some houses have a ventilation with a heat exchanger to reduce loss when ventilating in winter.
But there is no 100% hear exchange and the result is dependent of the temperature differences. The colder the outside temperature is, the less efficient the system is. Therefore of the importance of time scheduling.
All started with ordering some Arduino compounds:
And trying the first command of the temperature modules, including the humidity as side effect. 
arduino language:
(If you want to try too, I would share my own code for inspiration)
openeing theb Ventilation to find the place where to add the Relais for the two ventilators. 
Preparing the box for the board:
placing the four sensors in the ventilation:
and the box works: during the day, the vents runs one a hour for 2, 5, 20 minutes per hour, depending of the temperature difference inside/outside. 
an effective way to keep heat inside the house but still having fresh air. 🙂