Low pressure leakage function of a building

Abstract

Many models have been devised to correlate air infiltration in buildings with weather parameters. A particularly promising strategy is to predict the air flow through the building envelope from surface pressures, which in turn are predicted from measured weather parameters. Due to interference of the weather, it is difficult to measure the pressure-flow relationship in a manner that is valid for the low surface pressures which have been observed to drive infiltration. Conventional techniques rely on steady-state (DC) fan pressurization or depressurization of the structure. DC-measurements are unreliable at pressures less than 5 to 10 Pa, but this is the pressure range that often drives natural infiltration. Thus, it is of interest to make direct measurements of air leakage vs. pressure in this low pressure region. Measurements of the leakage function measured at low pressures using an alternating (AC) pressure source with variable frequency and displacement are reported. Synchronous detection of the indoor pressure signal created by the source eliminates the noise due to fluctuations caused by the wind. Comparisons are presented between these results and extrapolations of direct fan leakage measurements.