Improving Air Leakage Prediction of Buildings using the Fan Pressurization Method with the Weighted Line of Organic Correlation

In many countries, the fan pressurization method is the most frequently chosen approach for
measuring the air leakage of houses. The measurements are usually performed at pressures that
far exceed pressures to which buildings are exposed to under normal conditions. A fit of these
tests to the power-law formulation allows an extrapolation to data points outside the measured
pressure range. With the Ordinary Least Square (OLS) fitting method, the pressure exponent and
flow coefficient can be determined. However, the measurement results are highly sensitive to
uncertainties induced by external factors like changing wind conditions during the tests, which is
neglected by OLS. This may lead to errors in the prediction of flows at lower pressures. The
Weighted Line of Organic Correlation (WLOC) is an alternative approach and takes
measurement uncertainty into account. In this paper, a statistical analysis of an extensive data
set of pressurization measurements has been performed. Both regression techniques have been
compared for almost 7500 fan pressurization measurements of six houses in 109 different house
leak configurations. The variability in predicting pressure exponent and flow coefficient for both
WLOC and OLS regression was analyzed using probability density functions. It was found that
the Weighted Line of Organic Correlation significantly decreases the uncertainty in predicting
pressure exponent, flow coefficient, and other low-pressure air leakage metrics compared to the
Ordinary Least Square fitting. The authors highly recommend the implementation of WLOC in
current measurement standards and test equipment.