To create unidirectional low-turbulence flow, air is supplied with a low’ velocity; supply diffusers and exhaust openings have large surfaces (e. g., filter mats). Airflow can be either vertical (air supplied from the ceiling and exhausted through the floor or vice versa (Fig. 7Ala)), or horizontal (air supplied through
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One wall and exhausted through returns located on the opposite wall (Fig. 7.life)). The outlets are uniformly distributed over the ceiling, floor, or wail to provide a low-turbulence plug-type flow across the entire room. This type of system is mainly used for ventilating clean rooms, in which the main objective is to remove contaminant particles within the room, or in halls with high heat and/or contaminant loads and a high air change rate.
One of the unidirectional flow system modifications is air supply through diffusers located above the occupied zone. The supply air temperature is lower than the desired room air temperature in the occupied zone, and air velocity is lower compared to a mixing-type air supply, but higher than for a thermal displacement ventilation. Polluted air of the occupied zone is suppressed by an overlying air cushion that displaces the contaminated air toward floor-level exhausts (Fig. 7.12).
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