Measured and simulated air pressure conditions in Finnish residential buildings

Abstract

Air pressure conditions in typical Finnish residences are analysed using data from field measurements and computer simulations. Field measurements were conducted in three two-storey detached houses and in two five-storey apartment buildings. The effects of air tightness, ventilation performance, air leakage distributions, and outdoor environmental conditions on air pressure conditions in a detached house were simulated with a multi-zone simulation model using the IDA ICE simulation program. Despite of common design assumption, negative air pressure difference indoors, the results show that there is almost always a positive and negative air pressure difference across the building envelope in detached houses and apartment buildings. For detached houses, the design value of the air pressure difference across the building envelope for moisture convection analysis should be at least ±10 Pa. In the most critical cases (airtight building envelope with unbalanced ventilation), the air pressure difference across the building envelope may rise up to ±30 Pa. To control extremely high air pressure differences in airtight houses, balancing ventilation systems are very important. As in new low-energy houses the airtight building envelope and mechanical supply and exhaust ventilation become the standard solution; the interaction between HVAC systems and building envelope should be carefully designed. Practical application: Based on field measurements and computer simulations the design value of air pressure difference across the building envelope is determined for Finnish dwellings. Results underline the importance of balancing of ventilation in airtight house otherwise is not possible to control extremely high air pressure differences. If ventilation system should control the air pressure difference, building envelope should be airtight, because in normal and leaky houses (n50>41/h) the differences in ventilation airflows are too small and they have only a minor influence on the air pressure difference.