Moisture Considerations Air Filter Cleaning Design

Moisture is an important consideration in air cleaning system design. Moisture in the air may affect the performance of the air cleaning system by binding the particulate filters and/or blocking pores and fissures in the activated charcoal. Where water mist or steam can be expected under either normal or upset conditions, moisture separators and heaters, if appropriate, must be provided upstream of the filters to prevent plugging, deterioration, and reduced performance. Condensation from saturated air and gas streams or carryover from air washers and scrubbers are common sources of moisture. When fire-protection sprinklers are provided in operating areas, ducts, or plenums, moisture can be drawn into the filters if they are activated.

Moisture on the face of a filter will blind or plug the filter, creating the potential for filter failure. [Note: HEPA filters exposed to carryover from intentional or inadvertent excessive moisture exposure should be replaced.]

Condensation is particularly troublesome when filters are installed in underground pits, in outdoor housings, or in unheated spaces within buildings. Even when the air entering through the ducts is above the dew point, duct walls, dampers, or filters may be cold enough to cause condensation on their surfaces. Condensation can also take place in standby systems. Inspection of standby filters on a monthly or even weekly basis is recommended to prevent the detrimental effects of condensation.