Assessment System for Sustainable Buildings of the German Government (BNB): Calculation tool for the ventilation rate and the resulting carbon dioxide concentration in the ambient air

An important criterion for Assessment of the sustainability of buildings owned and occupied by the Federal Government is the indoor air quality. The stated aim is to avoid pollutants from construction products and unacceptable carbon dioxide concentrations. Regarding the limitation of the carbon dioxide concentration especially in rooms with high occupancy the challenge is to find a suitable ventilation concept. That concerns natural ventilation as well as mechanical ventilation or the combination of both. Although there are normative rules for the required air change it is hardly verifiable during building planning whether the proportion of natural ventilation is sufficient in practice. Various evaluation reports in the past have shown that natural ventilation comparability mostly did not work, especially in rooms with high occupancy. In addition, it was also shown that comparability of the test results was usually not given and therefore no conclusions could be drawn on functioning ventilation concepts. To be able to determine and evaluate the air exchange (in case of natural ventilation) and the resulting development of the carbon dioxide concentration in a room, the development of a calculation tool is part of a recent research project. The tool is used to calculate the outdoor air volume flow with natural ventilation depending on multiple parameters (as examples: wind, temperature, window size, window opening). In the same step CO2 concentration for a certain number of CO2 sources in the room will be determined automatically. Thereby the tool will be very helpful in an early stage of planning to find a proper ventilation concept. In addition to its use as a planning aid, the tool offers two different applications for assessing carbon dioxide concentration in a room: The calculation under specified conditions provides the opportunity to classify the expected carbon dioxide emissions as part of the assessment of sustainable buildings. The tool is also suitable for checking the air exchange under extreme climatic or other individually selectable conditions. At the end the calculation results of each individual constellation are shown in graphical diagrams.