Circulating air filtration

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Switch for circulating / fresh air in a car

The recirculated air filtration , also circulating air filtering is used in the art to air , which in the circulation is constant or re-purify.

The most common application is likely to be the filtration of air in the heating, ventilation and air conditioning systems of cars . In the recirculation position of the ventilation system behind the dashboard, the air is circulated over a longer period of time without fresh air from outside, both in winter (for faster heating) and in summer (for faster cooling of the vehicle interior). Here it is continuously fed through an air filter (sometimes referred to as a circulating air filter).

The air filters in the car are usually fabric or more often paper mats that are unfolded and thus offer a considerably larger area for filtering compared to the installation space . Such a filter device accumulates impurities with continuous operation and thus clogs more and more over time; the pressure loss of the filter increases steadily, the fan speed increases, but the air flow decreases.

These filter fabrics can also be breeding grounds for microorganisms such as bacteria and, for example, draw attention to themselves with unpleasant smells. The filters are therefore wearing parts and must be checked at certain intervals and replaced if necessary. The filter size ( mesh size ) is now often determined in such a way that pollen does not get through the ventilation system, as increasing proportions of the population are allergic to pollen.

There are also circulating air filter systems outside of vehicle construction: in building air conditioning. Various designs are possible here. In addition to filtering using paper, other methods are also available, for example the air washer, in which the air flow is passed through a water bath in which the air is cleaned and at the same time humidified.