The different types of air according to DIN EN 12792
In building technology, a distinction is made between different types of air, depending on the place of use and the nature of the air. These are defined in DIN EN 12792 for residential ventilation and in DIN EN 13779 for non-residential buildings. The following article explains which types of air there are and how they differ.
Overview of different types of air
Technical systems for the controlled ventilation of living spaces generate a permanent air exchange and thus ensure a healthy indoor climate. The distinction between the different types of air plays a decisive role here. Each of them performs its own task - from intake to exhaust.
The abbreviation ODA (outdoor air) refers to air that enters ventilation systems through intake openings. Its quality depends primarily on the location of the building. To prevent dust from the outside from entering the interior, it is filtered after intake. Special pollen filters are optionally available for allergy sufferers.
Depending on the weather conditions, the clean air drawn in is heated, cooled, humidified or dehumidified and supplied to the individual rooms of the building. This is referred to as supply air or SUP supply air.) In DIN EN 12792, it has the colors green, red, blue or violet, depending on how it is processed; in DIN EN 167982-3, it has the color blue. Supply air can be obtained not only from outside air, but also from secondary air and mixed air.
Recirculated air is used air that is fed into a room from other rooms. Before this, it is treated using various processes.
Since it is reused air, recirculated air can contribute to the spread of pathogens, odors and other undesirable substances. For this reason, the process is now rarely used in living and working areas. However, recirculated air is of great importance in industry. Here, it is used primarily in areas where harmful substances should not be allowed to escape to the outside.
Secondary air is similar to recirculation air. The only difference here is that it is introduced into the same room from which it was previously extracted. Here, too, there may be several processing steps in between - for example, cooling. Secondary air is often used in recirculation hoods in kitchens, for example. This allows particles to be filtered out of the air before it is released back into the room.
If outside air from outdoors mixes with recirculated air from the building in the ventilation system, it is called mixed air, which can be supplied to the room as supply air. Mixed air can reuse the humidity and heat of the exhaust air. At the same time, there is a supply of unused air from outside to the room. Since there are hygienic disadvantages in the process, as in the use of recirculated air, it is rarely used today.
The used air that is discharged from the room is called exhaust air. In living rooms, it usually has a high content of moisture and carbon dioxide. In addition, there are often odors and other impurities. The heat it contains is often skimmed off via a heat exchanger and then transferred to the fresh supply air.
Exhaust air is the air that is led out of the ventilation system into the open air. Usually, it is exhausted through openings in the exterior wall or roof of the building. Even if it has previously passed through a heat exchanger, it usually still contains a lot of heat.
Air leakage is unwanted air escaping from the ventilation system. In practice, this can hardly be completely avoided even with very good insulation. The decisive factor for the extent of escaping air is the tightness class. Apart from design-related peculiarities, installation errors and damage to the ventilation system can also lead to leaks. These are often accompanied by high heat loss and leakage of harmful substances. Therefore, air leakage should be avoided whenever possible.
Infiltration is the entry of air through leaks. These are usually located in the building envelope or at the windows. This natural form of ventilation used to be a central part of air exchange in buildings. Today, however, building envelopes are so tightly constructed that it can hardly take place. For this reason, new buildings and major renovations require a ventilation concept that can ensure sufficient air exchange.
The opposite of the uncontrolled entry of air into the building is called exfiltration. In this second component of natural ventilation, air escapes from the building through leaks. Exfiltration also occurs only to a small extent in new buildings. The process is used specifically in barns and in industry.