On the estimate and reduction of the zero-flow pressure estimation uncertainty in fan pressurization measurement

Building airtightness is of foremost importance because of its impact on global energy consumption, but also on occupant’s comfort, dimensioning of ventilation systems, hygrothermal behaviour, fire safety, etc. This building characteristic is usually measured with the fan pressurization method, following ISO 9972:2015 standard. This method requires to assume that the pressure difference due to wind and stack effect, called the zero-flow pressure difference, is constant during the test and that its value is the average of pre- and post-test measurements. This 
bold hypothesis leads to some uncertainty. In this paper, we use two different datasets in order to (1) assess the validity of the formula proposed in literature to quantify this uncertainty term, (2) investigate some variations in the measurement protocol to reduce this source of uncertainty, and (3) evaluate the impact of this uncertainty source on the final result of the fan pressurization test. Results show that, specifically for this data set, this estimation represents a large uncertainty of 1.27 Pa in pressure measurements that could be slightly reduced by increasing the number of measurement or using a multiple-estimator procedure. This uncertainty source could represent a 1% uncertainty in the airflow rate at 50 Pa (the final result of the fan pressurization test). Further research should focus on using other datasets to remove some limitations of this study, and on the development of alternative procedures in order to reduce this consequent source of uncertainty.