circulating air

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Recirculating air is exhaust air that is fed back into the air treatment system and fed back into at least one room as part of the supply air from which it was not taken. A distinction must be made between the secondary air , which is taken from a room and returned to the same room after treatment .

Applications of circulating air

Building air conditioning
In the building air conditioning, the fresh air supply was mixed with the outside air with circulating air in order to control heating or cooling loads. With the emergence of efficient heat recovery systems , the requirements of the Energy Saving Ordinance (EnEV) and to achieve the necessary indoor air quality , it is nowadays avoided to circulate used (re) air. In many cases, circulating air promotes the sick building syndrome and must always be viewed critically with regard to odors, pollutants, air quality and hygiene (bacteria, viruses, fungal spores).
In some industrial uses, certain substances should not be released into the outside world. In large paint shops e.g. For example, in chemical plants or in manufacturing processes, environmental hazards should be avoided. For this purpose, the circulating air is permanently cleaned with carbon filters, cyclones, washers, etc.

Applications of secondary air

In the case of ventilation systems in vehicles, no outside air is supplied in "recirculation mode" in order to achieve a desired temperature state more quickly. As a result, exhaust gases, particles or odors from the environment can also be temporarily prevented from entering the interior.
In ovens, "convection" is a further operating mode in addition to top heat , bottom heat and grill, in which the air inside the oven is distributed by a fan .
Extractor hood
An extractor hood absorbs the vapors ( fumes ) that arise during cooking and guides them back into the room or directly outside via a filter. In some hoods, in addition to grease grids, filter mats, activated carbon or ionization is used to neutralize odors.
Clothes dryer
In the case of tumble dryers, a distinction is made between exhaust air dryers, which blow the humid exhaust air directly into the open with a hose, and condensation dryers, which use the air again and again in recirculation mode using cooling and heating technology and simply separate the condensate. In some tumble dryers, the circulating air is prepared using ionization .


  • Recknagel-Sprenger-Schramek: Pocket book for heating + air conditioning. , 73rd edition. Oldenbourg Industrieverlag Munich 2007, ISBN 3-8356-3104-7

See also

Wiktionary: Umluft  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  • DIN EN 13779 ventilation of non-residential buildings (e.g. offices)
  • DIN 1946-6 - ventilation of residential buildings
  • DIN 1946-T4 Air conditioning systems in hospitals
  • VDI6022 Hygienic requirements for ventilation and air conditioning systems
  • SWKI95-3 ventilation technology
  • Bibliographisches Institut AG Mannheim