The present the inventive technology is directed to improved methods and apparatus for the refrigeration of an enclosed space using external ambient air as a cooling medium. The inventive technology may cool an enclosed space utilizing, for example a modular designed duct system that may deliver a specific volume of supply air to an enclosed space at a specific temperature differential (TD) in relation to a desired set point of the enclosed space. This may be accomplished by mixing cold outside air and return air, or even running the return air through a fluid heat transfer chiller coil that may be cooled to varying temperatures by outside air utilizing an external chilling unit.