Open-front multideck chillers and some deli and grab-and-go display cases have no doors. Instead, a fan blows a steady layer of cold air from a grille at the top to a return grille at the bottom. This air curtain separates the cold product area from the warmer shop air while still letting customers reach in freely.
An air curtain is never as effective as a closed door. Room air mixes into it, especially when the curtain is disturbed by customers, draughts from entrance doors, ceiling fans or air conditioner outlets. The extra heat and moisture increase energy use and frost. Night blinds pulled down after closing help considerably.
To work, the curtain must be unbroken. Product stacked past the load line, price labels hanging into the airflow, or a blocked return grille all break it. Placing open display cases away from shop doors, direct sunlight and fans is one of the cheapest ways to improve their performance in Indian retail.