Heat energy naturally flows from warmer areas to cooler ones. When you put ice cubes in a warm drink, the heat leaves the drink and flows into the ice cubes, warming the ice while cooling the drink, bringing them both toward equilibrium. The second law of thermodynamics says that heat energy always wants to flow in this direction: the ice never spontaneously heats up the drink while getting colder. Moving heat from a colder area to a warmer one, against this natural flow, requires a heat pump, which takes energy to operate.
