Air Pressure Differences over the Building Envelope: Case Studies

Although the physics concerning air pressures in buildings don’t differ between countries, often different reference values of the pressure difference over the envelope are used to determine air tightness and ventilation characteristics. The air transfer devices for natural ventilation, integrated in the façades or the internal building structure, are characterized at a pressure difference between 1 and 20 Pa depending on the country. For example, Belgium uses 2 or 10 Pa as a reference, the Netherlands adopts 1 Pa, whereas France applies 10 or 20 Pa. With respect to the building air tightness, the reference pressure used varies between 4 and 50 Pa over the countries. 
To investigate this variability, differential air pressure measurements over the envelopes of two buildings were conducted within the context of a master’s thesis. A Belgian single-family home and a high-rise student home were considered. The most elaborated case was the single-family home consisting of 2 floors and a flat roof where the following experiments took place. Firstly, the airtightness of the building envelope was determined based on three different test methods: a) the Blowerdoor test, b) the ACIN Air Tightness Tester or ATT, and c) the Pulse test. Secondly, simultaneous air pressure difference measurements were applied on all four walls of the home and at two different heights: floor and upper level. Lastly, wind speed sensors were attached in the middle of the exterior walls for measuring the wind speed near the wall surface. These measurements allowed (1) to compare the difference in measured building air tightness between the 3 test methods; (2) to analyse the variation of the pressure difference over the façades as a function of climate conditions; (3) to study the correlation between the local wind speed and the local pressure difference over the façade. For the high-rise building, only the measurements of air pressure difference and wind speed were conducted. These measurements were taken at the same façade at two different heights of the building. The results were compared with those found on the single-family house. An overview of the work done, used methodologies, and obtained results is presented in this paper.