The invention relates to a housing that encloses an inner chamber, a cold air pipe that extends in a wall of the housing separated from the inner chamber by an insulating layer, and a transition piece that connects one end of the cold air pipe to an air inlet of the inner chamber. The transition piece includes a guide wall that extends from one end of the insulating layer to an edge of the air inlet adjacent to the one end of the insulating layer, connecting a wall of the cold air pipe that is adjacent to the insulating layer to the adjacent edge of the air inlet in a continuous manner.