Reconsideration of parameter estimation and reliability evaluation methods for building airtightness measurement using fan pressurization

Building airtightness is among the most important performance indices of healthy indoor air quality, condensation, the building stack effect, and heating and cooling load caused by infiltration. Performance parameters are usually measured by testing methods involving pressurization or depressurization by means of a mechanical fan. Similar testing standards have now been established in ISO, ASTM, and JIS. All methods entail finding two parameters from some measurements of the inside and outside pressure difference and the airflow rate. Although these measurement data analysis methods are described in informative annexes, these are important techniques and have problems to be reconsidered and solved as a stochastic estimation and uncertainty evaluation. In the present paper, we examine improvement using weighted least-squares, correction of the parameter estimation equation, and deduction of the uncertainty propagation equation from not only the measurement uncertainty but also the residual of the model equation. Also, a reliability evaluation index capable of checking the appropriateness of the measurement is proposed. Through a computational experiment, the precision of the estimated parameters, the uncertainty of these parameters, and the reliability indices are investigated. Further, the present method is applied to actual measurement data and its practicality is also verified. ► Weighted least-squares are derived for two parameters of building air tightness. ► Error propagation is calculated from equation residual and measurement uncertainty. ► Index β evaluates discrepancy from the premises of the system identification model. ► Robustness against sudden disturbance and evaluation of uncertainty are improved. ► Method is verified through both numerical calculations and actual measurements.