The importance of air filtration
Controlled air quality is crucial in many processes today. Besides many technical applications, building ventilation is a key area. Here, air filters ensure healthy indoor air by removing harmful fine dust including pollen, bacteria, yeast and molds along with other organic and inorganic material. Air filters also serve to keep the air handling equipment itself clean. By doing so, they ensure its hygienic and efficient operation.
Air purity requirements are continuously increasing. This is due to increasingly sophisticated and sensitive industrial processes, stricter environmental legislation and rising comfort and health conscious attitudes. At the same time, the need to reduce energy consumption and carbon dioxide emissions is increasing, along with the pressure on costs. Thus, buildings are more and more restricted from natural ventilation. Energy-efficient mechanical air handling and, in particular, air filtration solutions, are more in demand than ever.
The composition of air
Air is defined as the gas mixture of the earth’s atmosphere. The exact composition of gaseous, solid and liquid components (particles) dispersed in the air varies greatly depending on time and location. Dry, particle-free air is mainly composed of two gases: nitrogen (around 78%) and oxygen (around 21%). There are also traces of argon, carbon dioxide and other gases, as well as varying amounts of water vapour, which is typically in the range of several grams per cubic meter of air.
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Figure 1: General guide to particle size distribution of common atmospheric
contaminants
Figure 1 compares different types of air contamination with the respective particle size ranges. The scale shows that the various contaminants cover a size range of several orders of magnitude. This is a major reason why so many different filters are used in a wide variety of classes and designs. The common technical classification of fine dust fractions is also based on the classification of particle sizes according to the areas they are deposited in the human respiratory system. The classes are PM10 (particles with an aerodynamic diameter of ‹ 10 μm), PM2.5 (‹ 2.5 μm) and PM1 (‹ 1 μm).
PM stands for particulate matter. There has been a recent addition to the established particle size classes: particle fractions with a diameter of ‹ 100 nm. Particles of this size are referred to as ultrafine particles (UFP) or nanoparticles. The mechanisms for the separation of particles and gaseous contaminants from the air are fundamentally different. Particles are separated by mechanical or electromechanical effects whereas gases are generally separated by adsorption or absorption.
Source: Eurovent Guidebook. Air Filters for General Ventilation