Patent ID: 7833305

Claim:
A filter assembly for providing filtered air to an enclosed space, said filter assembly comprising: a housing comprising an exhaust port in fluid communication with the enclosed space, a first air intake port in fluid communication with the enclosed space, and a second air intake port in fluid communication with a space exterior to the enclosed space; at least one disposable filter for filtering air from at least one of said first air intake port and said second air intake port, wherein said filter assembly is arranged for simultaneously filtering recirculated air drawn from said enclosed space through said first air intake port and filtering pressurizing air drawn from the space exterior to the enclosed space through said second air intake port, and further wherein said filtered air is provided to the enclosed space through said exhaust port, and further wherein an air pressure within the enclosed space exceeds an air pressure in the space exterior to the enclosed space when pressurizing air is drawn from the space exterior to the enclosed space and provided to the enclosed space; a first air damper for adjusting an air flow through the first air intake port; and a second air damper for adjusting an air flow through the second air intake port, wherein the air pressure within the enclosed space is adjustable through an adjustment of the first air damper while the second air damper is maintained in a fully open position during said adjustment, wherein at least one of the at least one disposable filter comprises a high-efficiency particulate air filter, and wherein the filter assembly further comprises a disposable pre-filter for filtering air prior to filtering by said high-efficiency particulate air filter, and wherein the pre-filter and the high-efficiency particulate air filter are located within a cartridge, and wherein said cartridge is removable from said housing, and further wherein said assembly is configured such that air flow from said second air intake port to either said exhaust port or to said first air intake port must pass through at least one disposable filter regardless of the status of any of said dampers and regardless of the operation of any fan.