Internal pressure fluctuations in large open plan buildings

An internal pressure analysis was carried out on an open plan wind tunnel model for a range of nominally sealed (i.e. porous envelope) buildings, with and without dominant openings. The experimental results were compared to that obtained from analytical methods and also with design data specified in AS/NZS1170.2[10]. Increasing the level of porosity in a nominally sealed building resulted in an increase in internal pressure fluctuations, and mean and minimum internal pressures. However, increasing porosity with a dominant opening reduced internal pressure fluctuations, and mean, peak internal pressures. An analytical method used to determine the mean internal pressure in a nominally sealed building overestimated the measured mean pressure by 20%. AS/NZS1170.2[10] overestimated the minimum internal pressure in the nominally sealed building by 90% and slightly underestimated the maximum internal pressure. AS/NZS1170.2[10] also underestimated the maximum internal pressure in a building with a dominant opening by 20%, but overestimated the minimum internal pressure by 5%. The internal pressure fluctuations in nominally sealed buildings initially follow the external pressure fluctuations over the building, external frequencies above 7 to 17 Hz were attenuated, relating to a porosity discharge coefficient, k’, in the range of 0.13 to 0.56. The relationship between the ratio of internal standard deviation pressure, and the external standard deviation pressure on a dominant opening, σpI/σpE, with the opening area to volume parameter, S*, were analysed and show good agreement with other studies. Dominant opening tests with an S* of 4.64, resulted in an increase in energy for internal pressure fluctuations at Helmholtz resonance frequency, of 36 Hz, resulting in an inertial coefficient, CI, of 2.45.