Abstract: A supplemental cold air supply unit is disclosed which is incorporated into an existing refrigeration enclosure for supplying cooler ambient air to the refrigeration enclosure when the outside air is at a lower temperature than the air temperature within the enclosure. The cold air supply unit comprises a housing which includes a blower fan and a coaxial pipe assembly for cold air inlet and warm air exhaust. Outside and inside thermostats determine when the outside air is at or below the temperature of the air within the enclosure to turn the blower fan on for cooling the refrigeration enclosure when appropriate. The cold air from the outside is exhausted into the refrigeration enclosure through a shuttered opening in the housing, and warm air within the enclosure is returned to the housing through a separate warm air opening for exhaust through the coaxial pipe assembly.