The Coolest Room in the House (window, bedrooms, kitchen, apartment)

[TamaraSavannah]

In apartment #1, that's the den.

Sits facing the wall of another apartment building, rough north, so the sun passes over a narrow corridor moving east from west. It's the remotest from the rest of the apartment, lots of bends to get to the kitchen. Has a lot of electronics but most of them are off at any one time. 3/4 of the walls are lined with shelves and books.

So what is it that makes this the coolest room in the place? And how to recreate it in the new home?

[Ohky0815]

For my house the north room is cooler than the south (upstairs bedrooms i mean) because the breeze blows that way. The sun also hits the east/west so the south window gets hit, where the north doesnt.