Patent ID: 7677962

Claim:
A filtering unit, comprising: a housing comprising an inlet and an exit; a first filter disposed at the inlet of the housing; a second filter disposed at the exit of the housing; a first fan disposed in the housing; a second fan disposed in the housing; a first detector configured to detect the presence of particles in the first filter; a second detector configured to detect the presence of particles in the second filter; and a controller coupled to the first and second fans and to the first and second detectors, wherein when the first detector detects that a predetermined volume of particles is present in the first filter the first detector outputs a signal to the controller to change the rotating direction of at least one of the first and second fans, and wherein when the second detector detects that a predetermined volume of particles is present in the second filter the second detector outputs a signal to the controller to change the rotating direction of at least one of the first and second fans.