| 摘要 |
PURPOSE:To make a device advantageous in terms of economical efficiency without demanding specially high performance from a fan for suction of the outdoor air, by a method wherein collecting capability of a dust removing filter is within a range in which it has dust removing function and is set to a level such that the specified efficiency of dust collection has a specified value which forms an upper limit. CONSTITUTION:A dust filter 9 is formed in a shape in which it is folded in a waveform shape, and its collecting capability is within a range in which it has dust removing function, and the collection efficiency for dust having a particle size of 5mum or more indicating 90% or more forms an upper limit. A filter, having function being within the above range and equal to the upper limit, is selected for use. The upper limit of collecting function of the dust removing filter 9 is set to a level so that dust, e.g., sand dust, cement powdery dust, and Japan cedar pollen, having a grain size of about 5mum, is an object to be filtered, and therefore, draft resistance is prevented from being extremely increased, and the need to increase the capability of a suction fan 2is reduced and economical efficiency is ensured. |
