The working principle of the air purification project is to use a fan to pump air into the machine and filter the air through the built-in filter, which can mainly filter dust, odor, toxic gas and kill some bacteria. The filter is divided into: dust collection filter, formaldehyde removal filter, deodorization filter, HEPA filter, etc. The higher cost is the HEPA filter, which can decompose toxic gases and sterilize, especially to suppress secondary pollution. The characteristics of this type of product are that the function of the fan and the quality of the filter determine the purification effect. The placement of the machine and the layout of the interior affect the purification. The indoor purification effect is not balanced, and it is difficult to complete. The filter replacement cost is high.