A ventilation and air conditioning system (6) is for a room (2) containing a heat source and the ventilation and air conditioning system (6) comprising a cooled air supply (12) and a ventilation duct (10). The ventilation duct (10) includes a primary inlet (24) connected to the cooled air supply (12) and an outlet (14) leading into the room (2). A number of heat storage elements (30) is arranged inside the ventilation duct (10) between the primary inlet (24) and the outlet (14), such that during operation of the cooled air supply (12) there is a forced stream of cooled air through the ventilation duct (10), thereby cooling and preferably freezing the heat storage elements (30). A secondary inlet (36) into the ventilation duct (10) is in flow communication with the room (2) and during operation of the cooled air supply (12) is closed by a damper (40). The damper (40) is designed to automatically open in a passive manner when the forced stream of cooled air from the cooled air supply (12) stops, such that a natural convection airflow through the ventilation duct (10) is supported, and the natural convection airflow is cooled by transferring heat to the heat storage elements (30).