1. An air distribution assembly for a server room cooling system, comprising:an adjustable return air duct assembly configured to receive heated return air from the server room, wherein the return air duct assembly has:
a tubular housing with a leading edge portion connected to sidewalls, wherein each of the sidewalls has a trailing edge portion spaced apart from another trailing edge portion and the sidewalls define a return air opening in communication with an interior area of the housing configured to carry the heated return air; and
an airflow damper being positioned within the housing and moveable relative to the return air opening to block at least a portion of the return air opening and control a flow of the heated return air from the interior area through the return air opening; and
a pair of spaced apart, arcuate cooling air deflectors positioned on opposing sides of the housing and defining a mixing area, wherein the mixing area is between the deflectors and adjacent to the return air opening, the deflectors having leading end portions spaced apart from the sidewalls of the housing to define cooling air inlets configured to receive cooled air from the server room cooling system that flows around the leading edge portion of the housing and to direct the cooled air into the mixing area, the cooling air deflectors having trailing end portions spaced apart from each other and defining a mixed air outlet in communication with the mixing area and configured to direct a mixture of the cooled air and the heated return air into the server room;
wherein the airflow damper is adjustable relative to the housing to control a temperature of the mixture of the cooled air and the heated return air directed into the server room.