A typical arrangement of the refrigeration system and air distribution in a refrigerated semi-trailer is shown in Figure 1. In these vehicles, top air delivery is predominately used. Refrigeration unit fans cause temperature-controlled air to circulate around the inside of the vehicle roof, walls, floor, and doors to remove heat which is conducted and infiltrated from the outside, returning to the cooling coil via the floor or space under pallets as shown in Figure 2. For chilled cargoes horizontal channels are required between rows of cartons to allow good return airflow through the load