How to select the fresh air fan system of air purifier

How to choose air purifier or fresh air fan system! Let me simply say the right choice! First, calculate the number of cubic meters of air you need to purify according to the size of the space you want to purify (area x height). Then calculate according to the unit air purification recommended by who at least 5 times an hour, and select the air volume of the purifier required for your purified space. For example, a room of 30 square meters, with a floor height of 3 meters and a total volume of 90 cubic meters, requires an air purifier with an air output of 90x5 = 450 cubic meters per hour for at least five times an hour. When selecting the machine, try to choose a larger margin as much as possible, because all purifier manufacturers mark that the air output of the air purifier is based on high power. In other words, can you run in a gear with high noise and power consumption all day?