ABSTRACT
The concentration in the exhaust is dependent on the release rate of the contaminant and the ventilation flow rate, and is independent of the ventilation arrangements. Mechanical ventilation uses fans to supply air to, and exhaust air from, rooms in buildings. Depending on demand, the supply air may be heated, cooled, humidified or dehumidified. The ventilation system may be equipped to recover heat from the exhaust air. When the ventilation strategy for a building is for natural or mixed mode, it is necessary to calculate the air flow provided by natural forces. Stack pressures are often comparable with wind-induced pressures, and many ventilation designs concentrate on developing the stack pressure to drive ventilation air flow. Fans are used in hybrid ventilation designs to increase air flow rate when natural driving forces are enough to achieve the required ventilation rate. The discharge coefficient is dependent on the opening geometry and on the direction of the approaching flow.
