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Purpose of the work
Performing an airtightness test of a very airtight large building under special indoor climatic conditions may still represent a challenging task. This paper reports on practical experience with airtightness testing of two freezing rooms of approx. 200.000 m3 at internal temperatures of -20 °C and +8 °C.
Method of approach
The tests were carried out according to ČSN EN ISO 9972 in spring 2024. Standard equipment was used for this purpose (blower doors with digital pressure gauges). The leakage paths were detected from inside of the depressurized building by means of anemometer and infrared thermography.
Content of the contribution
In order to avoid unacceptable development of fog and rime inside the building when pressurizing it with warm and humid outdoor air, a temporary ductwork was set up connecting the blower door fans to a nearby freezing room.
The Dp0 was measured on different sides of the building at the ground level and at the rooftop level. Unlike preliminary estimation, the ground level value was low and suitable for measurement, while the rooftop value was very high and exceeded the CSN EN ISO 9972 limit. The sequence of test pressure differences had to be adjusted to this situation. Later on, leakage detection results indicated that specific leakage distribution over the building envelope can explain this pattern in Dp0.
Due to the large volume and very good airtightness of building envelope, the stabilization of the applied pressure differences lasted long time. The rime developed on all parts of equipment exposed to airflow with no impact on their functionality. However, the equipment had to be de-iced and carefully dried before packing.
Only poor technical documentation of the buildings was available prior the test. On-site check of selected dimensions proved the necessity to measure all the main dimensions on the actual building in order to reduce the uncertainty of reference values.
Results and assessment of their significance
The buildings proved to be very airtight (n = 0.033 h-1 and 0.003 h-1). The leakage paths were concentrated in the lower part of the building. The most significant air leakage was detected around the loading gates. Tests performed at different internal temperatures show different results.
Conclusions
Freezing rooms can be tested even at very low indoor temperatures by means of standard equipment. Such tests require more time than usual and shall be well prepared. Failure of equipment due to rime is a real threat which shall be avoided. The Dp0 measurement requires special care since unusual repartition of air leakage can produce unexpected results.
For further information please contact Jiří Novák at: jiri.novak.4@fsv.cvut.cz