Numerical evaluation of airtightness measurement protocols

In France, starting January 1st, 2013, the energy performance regulation will impose an airtightness treatment for every new residential building. This translates into several tens if not hundreds of thousands of envelope airtightness measurements a year that will have to be performed. They will have to be performed by a certified operator and according to the NF EN 13829 standard. This ISO standard is being revised under the Vienna agreement to become an EN ISO standard. This revision should include changes in the measurement protocol to reduce the uncertainty for two indicators commonly used: the air change rate at 50 Pa and the air permeability at 4 Pa.
As far as it is quite impossible to determine the real airtighness of a building, the measurement error cannot be estimated only by a numeric protocol. Our approach relies on the simulation of the measurement protocol with the software CONTAM, varying wind conditions and airtightness levels.
This article addresses three issues that impact the uncertainty on these derived quantities: the wind speed, the distribution of the leaks, and the pressure correction with the zero-flow pressure difference. This implicitly entails the investigation of influencing factors such as airtightness level of the building. Based on the analyses of those simulations results, this paper proposes protocols for extracting the air permeability at 4 Pa with better accuracy.