It Seems to Work

Usually when I get up in the morning, I come downstairs and open all of the doors and windows to let some air in. Pretty soon, it is boiling hot and I often have to put the air con on.

Today though, I came down and noticed the place was actually quite cool, despite being very warm outside with the sun shining. I kept everything closed up and two hours later, it is still quite cool.

This seems very strange to me but could it be the answer to staying cool in the summer? Don't let the sun penetrate into the house?

Thoughts would be appreciated :)