Blandluft

Blandluft is a term used in HVAC and ventilation engineering to describe the portion of supply air that is produced by mixing outdoor air with return air from a building’s interior before it is delivered to occupied spaces. The mixed-air stream is characterized by the outdoor air fraction, which is the percentage of outdoor air in the supply.

In typical air handling systems, a mixing damper blends outdoor air with recirculated indoor air. The control system adjusts the mix to meet required ventilation rates while managing energy use. Sensors monitor indoor air quality indicators such as CO2, occupancy, and pollutant levels, as well as outdoor conditions like temperature and humidity, to maintain target conditions and comply with relevant standards.

The concept involves an energy–air quality trade-off. Increasing blandluft improves dilution of contaminants and occupant comfort but raises heating, cooling, and dehumidification loads. Reducing outdoor air lowers energy use but can allow pollutant buildup. Modern systems optimize blandluft through variable outdoor air ventilation, advanced filtration, and sometimes heat or energy recovery to balance IAQ and energy efficiency.

Applications and standards: Blandluft is central in commercial, institutional, and large residential buildings equipped with mechanical ventilation. Design guidelines and building codes influence acceptable outdoor air fractions and ventilation rates, with related practice focusing on filtration, air distribution, and energy recovery to minimize environmental impact.

Terminology: The concept is used in languages such as Swedish and Norwegian, where it is part of the broader framework of ventilation terminology. In English, the term is often described as mixed or outdoor air in the supply air stream.