Types of air filters used in ventilation systems

The purification of air

The air we breathe contains suspended particles. The size of these particles ranges from aerosols, viruses, or smoke that do not exceed 0.1 microns (1 micron=0.001 mm.), to 100 microns that can measure the pollen and dust particles. Keeping the amount of these particles within reasonable limits is one of the operations to which the air must be subjected to prevent the appearance of certain diseases. This process is called air purification, and it can be carried out using two types of devices: air filters and dust separators. Air filters are devices designed to reduce the concentration of particles that are suspended.

Types of air filters

To use air filters in ventilation systems, it is necessary to consider that the concentration of particles in the air should not be too high, otherwise the filter would quickly become clogged, complicating the maintenance process of the installation. The limit for dust concentration in the air for filters to be used is 35 mg/m3. The types of air filters used in ventilation systems vary according to the size of the particles that need to be separated, as described below.

• Activated Carbon Filters: used for the separation of viruses and molecular size particles.

• Electrostatic Filters: used to separate soot and tobacco smoke.

• Wet Filters: also called viscous, consist of a filtering lattice made of a metallic material or fibers, which is impregnated with a viscous substance such as oil or grease. This substance retains the suspended particles.

• Dry Filters: are made of a fibrous material through which air passes. Their design allows the speed of the filtered air to be lower than in wet filters.

Other components of a ventilation system

The fan is another important component within a ventilation system. It is a rotating machine that puts the air in motion. To do this, it is capable of generating pressure differences in the surrounding air. Specifically, it is the direction of the air as it passes through the fan that usually determines its classification:

• Centrifugal Fans: the air follows an axial path when entering, and parallel to a radial plane when exiting. Elements called blades, which are part of the fan, create this path in the air.

• Axial Fans: air follows the trajectory marked by coaxial cylindrical surfaces at both the entrance and the exit of the fan.

• Transversal Fans: the airflow at both the entrance and exit is perpendicular to the fan axis.

• Helico-centrifugal Fans: are fans with a design that is intermediate between axial (when air enters) and centrifugal fans when the air exits.