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Purpose of the work
Is it possible to derive an outside air flow rate from the net air exchange rate nL50 and use it for ventilating dwelling units?
Method of approach
We calculated the outside air flow rates via leaks in the envelope area as per standards and matched them with the values from real construction projects.
Content of the contribution
Typically, the outside air flow rate via infiltration is derived from the airtightness value of the building envelope for the purpose of developing ventilation concepts and designing ventilation systems in residential buildings.
We detected air leakages while testing apartments in multi-family dwellings for airtightness and found that the leaks causing the air flow in new and refurbished buildings were not located in exterior components such as windows and window connections. We also tested interior leakages between the building's units and found that they may account for most of the leaks.
In construction practice this means that a negative pressure of 90 Pa can be detected when operating, for instance, simple ventilation systems that have been properly designed and installed in windowless bathrooms.
Results and assessment of their significance
Infiltration via leaks is present in buildings, but the leaks are not uniformly distributed. The airtightness value for the entire building cannot be used to calculate the outside air flow rate via leakages in the individual dwelling units. Even when testing every single dwelling unit for airtightness, interior leakages will lead to highly falsified test results.
Conclusions
It is not possible to account for infiltration when designing ventilation systems.
For further information please contact Oliver Solcher at: mail@oliversolcher.de