Frischluftrate

Frischluftrate is a term used in building ventilation and indoor air quality to describe the rate at which outdoor air enters and dilutes the indoor environment. It is related to the concept of air exchange and is commonly expressed as an air change rate per hour (ACH) or as a volumetric flow rate measured in cubic meters per hour (m3/h).

In formal terms, Frischluftrate can be defined as the fresh air supply rate Qf divided by the room volume V: Frischluftrate = Qf / V. When expressed as ACH, this value indicates how many times the air in a space is replaced in one hour. The same metric, in m3/h, can be obtained by multiplying ACH by the room volume.

Typical values vary by building type and standards. Residential buildings might target lower rates, roughly 0.3 to 0.5 ACH, while offices and public buildings often aim for about 0.5 to 1.0 ACH, depending on occupancy and climate. More specialized environments, such as healthcare facilities or cleanrooms, require higher ventilation rates and more stringent control. Actual rates depend on the ventilation system design, occupancy, and energy considerations, as well as outdoor conditions.

Measurement and control of Frischluftrate rely on methods such as tracer gas decay tests or CO2 concentration monitoring, alongside duct airflow measurements and system balancing. Proper management of Frischluftrate supports indoor air quality while balancing energy use, particularly in systems with heat recovery or outdoor air economizers.

See also: air exchange rate, ventilation rate, indoor air quality, ASHRAE standards.