On a winter day the temperature on the inside surface of a wall is much lower than the room temperature and that of the outside surface is much higher than the outdoor temperature.Explain

Over night, the temperature will drop, and the walls will cool. Walls made of aggregate will cool much more slowly than the surrounding air, but will be quite cold by dawn.

In the morning, the heating switches on and the sun comes up. The sun heats the outside of the walls quickly by radiation. The inside air temperature also heats quickly, as air doesn't require as much energy to heat as walls. For a while, the inside of the walls will feel cooler.