How Accurate is our Leakage Extrapolation? Modeling Building Leakage Using the Darcy-Weisbach Equation

This study used a mathematical model to explore the accuracy of extrapolating multi-point blower door test results down to lower pressures at which building infiltration usually occurs naturally.  The mathematical model was applied to leaks of five different widths.  The leakage of the five different widths was then combined in different distributions to simulate total building leakage.  The calculated total building leakage was then compared to an extrapolation from the test pressures using a power law curve fit.   The results showed that depending on the distribution of the leaks from widest to narrowest, extrapolation of the power law fit may significantly over-estimate or under-estimate the building leakage.  At a building pressure of 1 Pa, one simulation the power law fit under-estimated the leakage by 19%, while another over-estimated the leakage by 78%.  At pressures below 1Pa, the deviations were even larger.