Assessment of the direct component testing for in-situ measurement of building component airtightness

Air infiltration strongly impacts heating and cooling demands in buildings. However, limiting its impact to energy consumption would be prejudicial considering the many ways by which infiltration impacts indoor spaces. Air infiltration may impact the building durability by inducing excessive moisture migration and by reducing the hygrothermal performances of the insulation; the comfort of the occupants by transporting smells or causing draughts; and the health of the occupants by introducing particles from the outside. In addition, air infiltration may facilitate the spread of smoke and fire throughout rooms. Consequently, airtightness, which is the fundamental building property impacting air infiltration, is of considerable importance for the building sector. The last decade has seen important developments, generating a tremendous increase in building airtightness testing and in the number of countries implementing qualification schemes for testers. However, the fan pressurisation test, the method used to measure building airtightness, assumes a uniform leakage distribution along the building envelope. Spending all available resources in the building-performance approach reveals a paradox in the current practice: airtightness is measured at a building scale while air infiltration occurs at a crack scale. In other words, measurement of building component airtightness assumes the leakage uniformly distributed along the building envelope while the consequences of air infiltration depend on the location of different leaks. This results in a poor understanding of pressure and airflow distributions along the envelope, which is crucial to grasp the challenges facing air infiltration and airtightness. In this context, it is hypothesised that improving the methods for quantification of building component airtightness is a massive step towards a better assessment of air infiltration and its consequences. The most promising method in this context is the direct component testing that measures airtightness of building components in-situ. Other methods are not expected to be as relevant because of the large impact of supervision and workmanship on airtightness and of the lack of crack data. In this thesis, we thoroughly described the direct component testing and conducted multiple experiments to assess its effectiveness. These experiments consist of: evaluating the capability of the method to report the airflow exponent alongside the air leakage rate; quantifying the biases in airflow due to the background leakage and in pressure differences due to the pressure losses in the duct; quantifying the direct component testing uncertainty; and identifying the issues when using this method to measure building component airtightness in-situ and to determine building airtightness. These experiments demonstrate that the direct component testing can measure in-situ the leakage characteristics of an opening with high reliability (between 3% and 10% of their value). Experiments also show that the reliability of the method depends on the design of the pressure chamber and may be affected by the human errors. Moreover, this thesis provides evidence that the direct component testing is appropriate to respond to the demand of the field for the update or the development of appropriate databases. The aim of these databases is to improve air infiltration models and prediction of building airtightness. In conclusion, this thesis is a step forward in a better description of complex airflow and pressure distributions along the building envelope; and of the numerous consequences of air infiltration on buildings and on the comfort and the health of their occupants. Research efforts in the field should focus on generalising these results to other types of building components and on broadening the range of measurable air leakage rate and airflow exponent. Finally, future studies should also investigate the changes that improved databases of building component airtightness could introduce in the current practice. More specifically, how it affects the use and the reliability of air infiltration models and prediction of building airtightness.