Electrical Enhancement of Cabin Air Filters to Achieve High Sub Micron Particle Removal Efficiency, Lower Resistance and Extended Filter Life

摘要

Cabin air filters generally lack high efficiency in removing particles below one micron in size. However, this size range makes up the majority of particles by number and constitutes the greatest health hazard because they penetrate deepest in the respiratory tract. Methods to increase a filter's mechanical collection efficiency are typiratory tract. Methods to increase a filter's mechanical collection efficiency are typically accompanied by a corresponding incrrease in resistance, higher enerhy consumption and filter cost. Therefore, there is ongoing research to utilize electrostatic forces to enhance filter performance. There are three basic methods of electrostatic enhancement: (1) Frictional Charging. (2) 'Permanent' charging (electrets), and (3) External charging. While the first two methods can produce significant improvement in efficiency, their electrostatic forces are neutralized as the filter loads and the filter reverts to mechanical efficiency alonw. The methods of electrical enhancement through externally established electric fields and pre-charging particles through ionization have achieved MERV 15 performance from a MERV 11 filter at high airflow rates and this performance is not degraded over timw nor by operating conditions such as high humidity and collection of conductive pollutants. The electrical forces involved also provide extended filter life by inhibiting the formation of particle dendrites, which increase filter resistance. In addition, this type of electrical enhancement exhibits a natural germicidal effect as microbes trapped within the filter are ecposed to strong electrical forces which ressearch has shown kill microorganisms. High efficiency, even in the sub micron size, is achieved at lower resistance (with a corresponding lower energy consumption ) utilizing a lower cost filter media and establishing a germicidal effect on microorganisms trapped on the filter.