A common hot weather strategy, especially for people living in big old houses without air conditioning, is to open windows at night when it is cool out, close them in the morning.
It should be straightforward to automate the procedure, using windows or vents that can be set to open when the temperature outside is cooler than the temperature inside, close when it is warmer, with fans to increase the airflow when desired. I would expect both the capital cost and the operating cost of such a system, used to replace or supplement air conditioning, to be trivial relative to the cost of air conditioning itself.
Yet I do not think I have ever seen such a system. Have I missed it? Or is there some non-obvious problem with the idea?
[The reason I have not been posting is that I've been travelling].