Minimum air exchange

Modern buildings are often built very airtight to save energy, which means that the natural air exchange is no longer sufficient for good air quality. Without suitable measures, this can lead to undesirable accumulations of airborne pollutants, carbon dioxide (CO₂) and moisture, with negative effects on the health of the occupants and the building fabric. Controlled ventilation behavior (i.e. opening windows from time to time) by the building users is therefore absolutely essential. 

Minimum air exchange and energy efficiency

For all buildings, a sufficient minimum air exchange rate is the best way to ensure good indoor air quality in the long term and to protect the building fabric from mold damage due to excessive humidity. Generally, controlled ventilation by regularly opening the windows is sufficient. In view of increasingly dense buildings, a proper ventilation behavior of room occupants and users is of great importance nowadays. The basis for the technical optimization of private and public buildings is the Building Energy Act (GEG, which replaced the German Energy Saving Ordinance (EnEV) in 2020). To increase energy efficiency, the building envelope is thermally insulated and the uncontrolled exchange of air between inside and outside air is reduced, for example by installing sealed windows and doors. Although the GEG requires compliance with a hygienic minimum air exchange rate, it does not specify how this can be achieved. In energy-optimized buildings, the hygienically necessary minimum air exchange rate is therefore not met or is significantly lower. This also means that the heat and temperature level inside the building can no longer be achieved by simply opening and closing windows or by natural ventilation through gaps. As a result, more moisture and mold damage will occur, especially in existing buildings without thermal insulation. 

Effects of insufficient ventilation

Insufficient air exchange leads to a variety of negative side effects, which can also have an impact on indoor air quality and the building fabric. The concentrations of carbon dioxide (CO₂) and air pollutants increase. CO₂ is formed as a metabolic product of humans, and air pollutants are primarily released by building materials used indoors and existing furniture. However, air quality is also influenced by human activities (e.g. cooking, handicraft work, personal hygiene). In addition, there is a risk of mold growth if humidity levels are too high, which can lead to structural damage. In the worst case, indoor air concentrations can also be reached that can lead to disturbances in well-being and even health problems.

For these reasons, it may be necessary to install air conditioning and ventilation systems in order to regulate the climatic conditions inside the building and to enable adapted, technically supported ventilation behavior.