A frost pipe works by televation, summoning cold air from the stratosphere. The cold air passes through a thermally conductive tube, where it exchanges heat with the surrounding air. The warmed air is then returned to the stratosphere, using energy provided by summoning the original cold air. The process of returning air keeps the pressure inside the frost pipe low, and thus in equilibrium with the stratosphere which it is exchanging air with. The air rises inside the tube, and this provides the free energy needed to keep the cycle going.
Frost pipes are usually used for air conditioning in warm climates. In this case, they soon begin to resemble actual icicles, as the intense cold of the frost pipe causes humidity in the air to freeze and form a layer of ice over the pipe.
They can also be used for refrigeration, but generally it is considered more convenient to use a jar of preservation since most bulk foodstuffs are already sold in jars of preservation. It is obviously cheaper to fail to return a container than to invest in an entire separate household appliance. In addition, items removed from a jar of preservation do not need to thaw out and are instantly ready for consumption.
Frost pipes also have important industrial applications. In a steam tower, frost pipes are used to condense steam back into water. In fact, any process that requires rapid and self-contained cooling benefits from the use of frost pipes.