A multideck has no doors. Cold air is blown from the top front edge and drawn back in at the base, forming an air curtain that holds the cold inside while shoppers reach in freely. This makes it the standard format for fast-moving chilled categories in supermarkets: dairy, fresh juices, cut fruit, ready-to-cook items and packaged snacks.
The air curtain is fragile. Overfilling shelves past the load line, blocking the return grille, placing the unit under an AC outlet or near an entrance door all break the curtain and let warm air in. Open displays also use considerably more energy than closed ones, and many stores fit night blinds or choose glass-door versions to reduce running costs.
A neighbourhood supermarket in Chennai might run a four-metre multideck for milk, curd, buttermilk and paneer. Humid coastal air makes condensation and frosting more likely, so store layout, AC placement and disciplined stocking matter as much as the cabinet.