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Mandatory building airtightness testing has come gradually into force in European countries, mostly because of the increasing impact of building leakage on the overall energy performance of low-energy buildings. Therefore, because of related legal and financial issues, the reliability of the airtightness test has become a crucial issue and has raised the question of the fan calibration process.
Stake-holders need to find the right balance between cost for testers and test reliability. While some manufacturers recommend a 4 years frequency for calibration, fan calibration is required every year in UK and every 2 years in France. In these 2 countries building airtightness testing are mandatory.
The objective of this paper is to evaluate fan deviation over years. This evaluation has been done through the analysis of calibration certificates issued by certified bodies.
According to these certificates the fan deviation is low but not negligible with 5% of the fan varying of more than 8.5% compared to manufacturer coefficients. It has also been observed that:
- Low-used and well-stored fans deviate less than daily used ones.
- Configurations measuring large flowrate deviate less than configurations that measure small flowrates.
- A significant difference of deviation is observed according to the background test pressure during calibration (30 or 50 Pa);
Besides, conclusions cannot be drawn without taking into account the calibration uncertainty mentioned in the certificates. Therefore this paper is completed by a discussion about the uncertainties stated by the calibration laboratories and the need for an appropriate level in regard with the maximum permissible error when a verification report is required.