The Quantity for Installing Our Ventilators:   

(References: The ventilating times of the different buildings) 

The ventilating cube=the cube of the building × the ventilating times

Ventilating cube 

Installing Quantity = ----------------------------------

                   ventilating cube/hr 

For example:

There is a building which is 50M length, 12M width and 6M height. The difference in temperature between indoor and outdoor is 10, and the wind speed is 9.6KM/hr. Moreover the ventilating times of the casting factory according to the standard material is between 10 to 30 times per hour. So the ventilating cube is 

(50×12×6) ×10 times/hr = 36000cube/hr .

3600cbm/hr

--------------------------------------------------------------2458cbm/hr(according to the different model 880/500/300)

=14.6(units)

So we'd better install 15 units' ventilators for the workshop.