In the context of refrigerated display cases, what does 'air curtain' refer to?

The term 'air curtain' in the context of refrigerated display cases refers to a curtain of cold air that protects the displayed products. This technology creates a barrier of cold air that helps maintain the temperature inside the display case while allowing easy access for customers. The cold air acts as a shield, preventing warm air from entering the refrigerated space, which is essential for preserving the quality and freshness of the products on display. This feature is particularly beneficial in high-traffic areas, as it minimizes the exchange of air between the interior of the case and the ambient environment, thus enhancing energy efficiency and reducing spoilage.

The other options describe concepts that do not accurately represent the function of an air curtain in refrigerated display cases. A barrier of warm air would not serve the purpose of preserving cold temperatures. A fan system that circulates air is part of the cooling process but does not provide the protective function of the air curtain. A transparent shield may offer visibility but lacks the temperature control aspect that is critical for product preservation. Therefore, the correct answer emphasizes the crucial role of the air curtain in maintaining a cold environment for displayed products.