How does the flow of thermal energy through a closed window illustrate

[jaypee]

How does the flow of thermal energy through a closed window illustrate the second law of thermodynamics? Which direction is the flow when it is cold outside? How outside?

--Please note this is a textbook question I can't seem to answer.

 

[FZ+]

The second law says that all closed systems move towards a state of maximum entropy. In this case, entropy represents the nearness to equilibrium between the energy of the air inside, and the air outside. If we consider the room and outside the room as two components of a closed system, then when they are allowed to randomly mingle through the closed window, the net effect would be to move towards an equilibrium temperature. Hence, overall, the thermal energy moves out of the room into the colder exterior. Energy does go both ways in a random action, but the effect is the transfer of thermal energy out the window.