The purpose of ventilation is to maintain temps and humidity in the centre of the plant canopy. Generally, it is preferable to have too much ventilation than not enough. Replenishing the air in the room provides more co2 for your plants.
Centrifugal fans should be used in any application that requires air to be pulled or pushed through lengths of ducting greater than five metres, multiple air cooled lights, or with carbon filters. The centrifugal motion spirals the air for maximum flow rates in high pressure situations.
Glandore hydro stocks high quality centrifugal fans for ventilation in hydroponic grow rooms. Available in a large range of sizes.