1.Reference of times of ventilation in 
                    different occasion 
                    1)Common places request 25-30 times/ hour 
                    2)Public places with dense people request 30-40 times/hour; 
                    3)Workshop with heat devices request 40-50 times/hour; 
                    4)Workshop with high temperature and bad pollution request 50-60 times/hour; 
                    5)The southern area with wet climate request more times of ventilation, the northern area 
                    with dry and hot climate request less times of ventilation.  
                    2.The account method of numbers of sets 
                    Definition of times of ventilation: Times of ventilation (times/hour)= Total amount of 
                    indoor airflow (m3/h)/ (area of the room (m2)*height below the orifice of air-transporting 
                    (m)) 
                    Number of sets=area of the room*times of ventilation/the amount of airflow of the set 
                     
                    3.As for the air transportation to positions of workers, we can 
                    choose equipments according to the fact of the environment, and the total amount of 
                    airflow can be decrease properly.
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