The information about uncertainly is essential to correct interpretation of any measurement. Therefore, several authors investigated the reproducibility and repeatability of airtightness measurement during the last years. The experiments were carried out in real buildings of different size and in actual climatic conditions which complicates the comparison of results. Namely, the question whether the uncertainly is proportional to the measured air flow rate remained unanswered.
In this study the relationship between the measured air flow rate and the repeatability of the measurement results is investigated. In order to exclude the variability of results due to the changing climatic conditions, the repeatability experiment was carried out in a laboratory facility – a plywood testing chamber of 1.25 x 1.8 x 2.5 m standing inside of a large hall. By means of an orifice in the chamber envelope equipped with an iris damper, the air leakage of the chamber was stepwise adjusted to 10 levels ranging from 50 to 1300 m3/h. At each level 10 airtightness tests (depressurization only) were carried out by the same technician using the same apparatus and the same testing procedure (EN 13829).
The repeatability standard deviation of the air flow rate at 50 Pa, calculated at each leakage level, ranges from 1.2 to 4.7 m3/h and it seems to increase with the measured air flow rate. The variation coefficient decreases rapidly from 2.5 % to approx. 0.3 % for the air flow rates from 50 to 750 m3/h and remains almost constant (0.3 %) for air flow rates from 750 to 1300 m3/h. These figures are much lower than the results reported in the previous studies. This proves a significant impact of climatic conditions on the measurement accuracy. Under ideal conditions, the airtightness tests can be carried out with a very good precision.
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