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Claim 1

A REFRIGERATED DISPLAY CASE HAVING A STORAGE SPACE THEREIN PROVIDED WITH AN ACCESS OPENING IN THE FRONT THEREOF AND MEANS FOR ESTABLISHING AN AIR CURTAIN EMBODYING A PLURALITY OF LAYERS OF AIR DIRECTED ACROSS SAID ACCESS OPENING BETWEEN SAID STORAGE SPACE AND AMBIENT AIR, SAID MEANS COMPRISING AN INNER REFRIGERATED AIR DUCT PROVIDED WITH AN OUTLET OPENING LOCATED ON ONE SIDE OF THE ACCESS OPENING FOR DIRECTING A REFRIGERATED LAYER OF AIR ACROSS SAID ACCESS OPENING AS ONE LAYER OF SAID AIR CURTAIN, AN OUTER PROTECTIVE AIR DUCT PROVIDED WITH AN OUTLET OPENING LOCATED ADJACENT SAID ONE SIDE OF THE ACCESS OPENING AND FARTHER FROM SAID STORAGE SPACE THAN THE OUTLET OPENING OF THE REFRIGERATED AIR DUCT FOR PRODUCING AN OUTER PROTECTIVE LAYER OF AIR AS A SECOND LAYER OF SAID AIR CURTAIN, AIR INLET MEANS LOCATED AT THE OPPOSITE SIDE OF SAID ACCESS OPENING IN POSITION TO RECEIVE AIR FROM BOTH SAID LAYERS OF AIR IN THE AIR CURTAIN, A PLENUM CHAMBER COMMUNICATING WITH SAID AIR INLET MEANS, SAID INNER REFRIGERATED AIR DUCT AND SAID OUTER PROTECTIVE AIR DUCT EACH COMMUNICATING WITH SAID PLENUM CHAMBER TO RECEIVE AIR THEREFROM, BLOWER MEANS OPERABLE TO CIRCULATE AIR FROM SAID AIR INLET MEANS THROUGH SAID PLENUM CHAMBER AND BOTH SAID INNER REFRIGERATED AIR DUCT AND SAID OUTER PROTECTIVE AIR DUCT TO THEIR RESPECTIVE OUTLET OPENINGS, AND AN EVAPORATOR LOCATED IN AT LEAST SAID REFRIGERATED AIR DUCT AND BEYOND SAID PLENUM CHAMBER TO REFRIGERATE AIR PASSING THROUGH THE REFRIGERATED AIR DUCT, THE CROSS SECTIONAL AREA OF SAID REFRIGERATED AIR DUCT AND SAID PROTECTIVE AIR DUCT THROUGH WHICH AIR FLOWS TO THEIR RESPECTIVE OUTLET OPENINGS DURING OPERATION OF SAID DISPLAY CASE BEING VARIABLE IN RESPONSE TO ACCUMULATION OF FROST ON THE SURFACES OF SAID DUCTS AND ANY REFRIGERATING MEANS THEREIN, WHEREBY THE PROPORTION OF THE AIR FROM SAID PLENUM CHAMBER WHICH FLOWS THROUGH SAID REFRIGERATED AIR DUCT AND PROTECTIVE AIR DUCT TO FORM THE INNER REFRIGERATED LAYER OF AIR AND THE OUTER PROTECTIVE LAYER OF AIR IN SAID AIR CURTAIN WILL BE VARIABLE AND DEPENDENT IN PART AT LEAST UPON THE AMOUNT OF FROST ACCUMULATED ON THE SURFACES AND REFRIGERATING MEANS IN SAID REFRIGERATED AND PROTECTIVE AIR DUCTS, RESPECTIVELY.