... .large air permeability 3.low noise 4.different size ventilation fan 1.Frame : The frame was one time punched by ... is reasonable, so small noise and big wind capacity,4.shutter: made of high strength hot dip galvanized sheet, the ... completely, so the shutter windproof, rainproof and dustproof. 5.Motor : Double bracing (E style) belt transporter. High performance national standard fan motor , the ...