An airtight building envelope prevents condensation or structural damage and heat loss due to uncontrolled ventilation. In addition, compliance with airtightness limits is a cost-saving requirement.
The Blower-door test is a pressure differential measurement that simulates the effect of wind with a wind force of 5 on a building. That’s about right for a stormy autumn day. The air exchange rate shall be determined and leaks in the building envelope shall be documented.
The measurement methods are described in EN 13829 and EN ISO 9972 and vary according to the preparation of the construction:
The building envelope shall be tested to demonstrate that it meets the country-specific requirements. All openings in the exterior shall be sealed (e.g. cat flaps, window openings, exhaust air openings, fume extraction system, etc.).
For example, to prove the requirements under the German Building-Energy-Law (GEG), the use status of the building is checked. In this case, openings that can be closed shall be closed but not further sealed. All other openings in the building envelope remain unchanged.
The potential for savings and energy wastage is huge. Measurements can contribute to savings in heating costs and increased living comfort, as draughts through the building envelope reduce comfort levels.
Weaknesses in the building envelope are revealed. By taking blower door measurements during construction, you can prevent serious structural damage in advance.
Blower Door measurement procedure
To determine the air exchange rate, all windows and external doors are closed during the fan measurement. The internal doors of all heated, cooled, mechanically ventilated and ventilated rooms shall be left open to create a zone with a harmonised airflow. The volume in this area must be determined. Even large buildings (e.g. apartment buildings) can be divided into several measurement zones.
Wöhler BC 600 consists of a fan with an air-sealing screen. The measuring system is tightly inserted into the window or door opening using the Wöhler clamping system.
Once the building is ready according to the standards, the first step is a preliminary test to identify major leaks. All major leaks must be documented. In addition, the tester shall check that his temporary seals can withstand the maximum test pressure intended for the measurement.
In the next step, the natural pressure differential is first determined for 30 seconds, with the measuring device fan closed. Depending on the natural pressure differential, the pressure levels to be achieved shall be determined. According to EN 13829 and EN ISO 9972 , this is a minimum of 5 measurement points. One of them must be at least 50 Pa. The minimum pressure differential is always 10 Pascals or five times the value of the specified natural pressure differential, whichever is greater.
Negative or positive pressure measurements are then taken to determine the air exchange rate. For measurements according to EN 13829, only one series of measurements at negative or positive pressure is sufficient. When measuring according to method 3 of EN ISO 9972, both the underpressure and the overpressure measurement must always be carried out.
When measuring the vacuum with a device Wöhler BC 600 the air is automatically exhausted from the building in at least 5 different pressure levels, for example from 10 to 50 Pascals. When measuring overpressure, the air is blown into the building fully automatically in at least 5 different pressure levels, for example from 10 to 50 pascals. For each pressure level, the volume flow required to maintain the appropriate test pressure is automatically calculated.
Finally, the natural pressure differential at the end of the measurement is redetermined. In any case, the difference in natural pressure before and after the measurement must not exceed 5 Pascals. This requirement is defined in EN 13829 and EN ISO 9972.
Finally, the app Wöhler BC 600 calculates the density- and temperature-corrected mean volume flow at 50 Pascals from the measured data. This volumetric flow rate is then divided by the internal volume of the measuring zone. The result is the air exchange rate. This describes how often the internal volume of the measuring zone is changed per hour if the differential pressure is 50 Pa.
The results are then automatically transferred into a detailed measurement report according to the standards using Wöhler BC 600
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Mojca Kugler, Source: Blower-door-test, Wöhler Technik GmbH