Abstract: A ceiling-mounted ventilation system assembly, where ventilation air from the ventilation system is directed down towards a working area, and where air is supplied to the ventilation system from indoor air (RL) and/or from external ventilation equipment (SL). The ventilation system is divided into at least two sections (1, 2, 3, 4) each with separate air, where at least one of the sections (1, 2) is designed and positioned so that the airflow therefrom will essentially strike a work table (78) in the working area, while the other section or sections (3, 4) are designed and positioned in such a way that the airflow therefrom will strike areas outside the work table, and where the sections are each independently equipped with devices (5, 6, 7, 8, 57, 58, 59) to control the air volume passing through the section, heat exchanger (29, 30, 31, 32, 33, 34, 35, 81, 82) for controlling the temperature of the air issuing from the section, and filters for ensuring a specify purity of the air which is emitted.