There is disclosed a transport refrigeration unit comprising an enclosed cargo space, an outer refrigeration cycle configured to transfer heat from the cargo space exteriorly of the cargo space, to cool the cargo space; a container installed within the cargo space; and an inner refrigeration cycle configured to transfer heat from an interior of the container, to cool the interior of the container. There is also disclosed a portable refrigeration device for use in such nested cooling arrangements, methods of adapting a transport refrigeration unit and/or portable refrigeration device for such use, a refrigeration module for such use, and an associated method of operating a transport refrigeration unit.