Patent ID: 8371140

Claim:
A method for maintaining cargo in a refrigerated state for extended periods of time without the need for external power, the method comprising: (a) providing a refrigerated container including: container walls insulated to a value of at least about r-20: a cargo compartment configured for receiving cargo therein; at least one refrigerant compartment configured for receiving refrigerant therein, the refrigerant compartment configured for receiving CO 2 snow therein, wherein the CO 2 snow and vapor sublimating therefrom is maintained separately from the cargo compartment; the refrigerant compartment disposed within the cargo compartment in spaced relation from interior surfaces of the cargo compartment to permit ambient atmosphere within the cargo compartment to contact at least three side of the refrigerant compartment; and placement of the refrigerant compartment within the cargo compartment being configured to generate a temperature gradient within the cargo compartment capable of generating convection within the cargo compartment; (b) supplying CO 2 snow to the refrigerant compartment, wherein the CO 2 is maintained separately from the cargo compartment, while exterior surfaces on at least three sides of the refrigerant compartment are exposed to interior space within the cargo compartment; (c) loading cargo into the cargo compartment, wherein the cargo is cooled by exposure to the exterior surfaces of the refrigerant compartment without the cargo being exposed to the CO 2 ; and (d) sealing the cargo compartment to permit convection to occur between the exposed surfaces of the refrigeration compartment and cargo disposed within the cargo compartment, wherein the container is configured to maintain the cargo at super frozen temperature of about−50 degrees C or less while being free from external power sources.