In situ measurement of window air tightness : stakes, feasibility, and first results

In order to limit ventilation losses in low-energy buildings,balance ventilation systems with high-efficiency heat recovery units are often used. However, the effectivenessof the heat recovery system may be severely affectedby envelope leakage as the system can be short-circuited by uncontrolled airflows. Therefore, limiting envelope leakage becomes a critical issue in such low-energy buildings.However, in a typical French house, air leakage through and around windows represents 15 to 70% of the total leakage airflow through the building envelope. Besides, field measurement campaigns presented in this paper have shown that although the air tightness of a window may be excellent as it leaves the factory, the quality of its installation can greatly affect its performance. In fact, poor installation can increase the leakage rate by a factor of 3, and we have estimated the subsequent heat load increaseto be in the region of 40% in some cases in houses built according to the French EP regulation (RT 2000).To address this installation issue, in the framework of a PREBAT project including a manufacturer of windows, an ergonomist, and an industry consultant besides our institute, we have developed and tested in real conditionsan apparatus to measure the air tightness of windowson site. The system can measure leakage through windows whose height and width lie between 0,7 and 2,2 m, and 0,7 and 1,10 m respectively. Our perspectiveis to have this system used either in a certification process of contractors now discussed in France or in a self-quality control approach.