Why do I always seem to get worse mileage in my vehicle in the winter, when Tcold is lower and thus theoretically the engine's efficiency should be higher?

Suppose you try to cool the kitchen of your house by leaving the refrigerator door open. What happens and why? Would the result be the same if you left open a picnic cooler full of ice? Explain.

Why must a room air conditioner be placed in a window rather than just set on the floor and plugged in? Why can a refigerator be set on the floor and plugged in?