In 1911, when there was a real hot sommer in Germany, my late great aunt Marta was a young girl. She told me that the entire family moved into the wine cellar for 3 weeks with table, chairs and beds. Very convenient for papa, such a short way ...
In North Africa I saw some dug out Roman houses with a winter floor (above ground) and a summer floor (underground) around, or better squared, a common atrium for both. Didn't need much electricity for air condition and cooling, since the Romans hadn't any.
Best advice: Stop working after lunch at noon, retire for a real good long siesta, and revive for work or fun when the sun is going down.

Wilfried