Heat Exchanger Shelves For Better Temperature Control Of Food In Open-Type Display Cases

Fresh food and specially meat require to be maintained at an accurate temperature level for good conservation conditions. These accurate levels require small air temperature tolerances. Open-type display cases show very high temperature differences, and even the European standard EN 441 accepts large temperature intervals associated with the defrosting process and what is known of the actual technology level. A new global design of open-type display case has been realized in order to limit drastically the temperature differences of the products depending on their position on the shelves (from front to rear). A defrosting system without heating up the cooling air has been developed. A good repartition of air on each shelf is achieved by an innovative concept, protected by a patent. The shelf itself is transformed in a heat exchanger, the airflow circulates inside the shelf and is sprayed over the food displayed on the underneath shelf. The design adapts the airflow according to the heat loads received by the food. A demonstrator of open-type display case has been realized and tested in a climatic room. Experimental results show the different level of temperatures, the air flow circulation and the level of temperature of food. Food can be maintained at a constant temperature ±1.5K. 1. STATE OF THE ART FOR TEMPERATURE CONTROL IN OPEN TYPE DISPLAY CASE Figure 1 indicates typical variations of temperatures registered in core of products displayed in common vertical fresh food display cases. Those data have been registered during 24 hours and the raise of temperature due to the opening hours of the supermarket can be noticed. The temperature peaks correspond to defrosting which occurs 4 times a day and where typical raises of temperature are in the range of 2 to 4K. Those thermal events have different impacts depending on the position of the products in the display cases as shown by the 3 curves. Those temperature variations are due to : difference in air flows received by the products difference in air flow temperatures difference in heat loads received by the products. 0 1 2 3 4 5 6 00:00 02:24 04:48 07:12 09:36 12:00 14:24 16:48 19:12 21:36 00:00 bou_deg bou_til1 bou_til2 bou_til3 Figure 1 Temperature variations of products inside an open type