Air walls are designed to separate air zones without physically closing a door or industrial doorway. The decisive question is not simply whether an air jet can be seen or felt. What matters is how much air actually passes from one area into another.
This question was investigated in an expert report using tracer gas. The objective was to determine how effectively a vertically discharging Airwall Grande could reduce the emission of indoor air through an open industrial doorway.
The result: The effectiveness of the air wall system was demonstrated under the tested conditions.
How Was the Test Performed?
What Was Tested in the Expert Report?
The RWTÜV expert report tested how effectively an air wall reduced air exchange through an open doorway.
The tested system was a vertically downward-blowing air wall with a 3.0 m long slot nozzle installed 2.62 m above floor level. The air was marked with tracer gas and measured at different measurement points.
Tracer gas does not measure the air jet itself. Instead, it shows how the air marked with the gas spreads through the surrounding area. This makes it possible to assess how much air still passes through the air barrier from one zone into another.
The decisive factor was not only the discharge velocity of the air wall. What mattered was the proportion of marked air that still passed through the air wall to the outside or into the adjacent area. This allowed the actual separation performance to be measured.
What Is Tracer Gas?
Tracer gas is a test gas that is used in low concentrations and can be detected reliably by measurement.
It serves as a marker for air movement. The gas is introduced into an airflow or into a room. It is then measured at different locations and concentrations.
This makes it possible to determine how strongly air moves from one area into another.
Which Tracer Gas Was Used?
The expert report used sulfur hexafluoride, SF₆, as the tracer gas.
The concentration was measured using an SF₆ tracer gas analyzer. In addition, air velocities in the free jet and in the inward and outward air streams were tested using a hot-wire anemometer.
SF₆ is suitable as a tracer gas because it can be measured reliably even at very low concentrations. It is colorless, odorless and chemically stable under normal conditions. It can therefore be used as a marker to track airflow and mixed-air fractions.
For the evaluation of the air wall, the gas was introduced into the primary airflow. Measurements were then taken downstream of the air wall fan and at different measurement points and heights.
From these concentrations, the proportions of primary air, secondary air and mixed air at the respective locations could be determined.
What Did the Test Show?
The TÜV expert report showed that the air wall worked effectively in the tested configuration.
Using SF₆ tracer gas, the primary airflow, induced secondary airflow and mixed-air fractions were measured. Then the proportion of air passed through the air barrier and, under real operating conditions, could be released to the outside as a possible pollutant emission was calculated.
Depending on the system setting, the air wall reduced pollutant emissions to only a few percent of the emissions from an unprotected industrial doorway.
With a 10 mm nozzle slot and a discharge velocity of 14.63 m/s, the remaining emission was only 1.2 to 2.4%.
With a 20 mm nozzle slot and a discharge velocity of 11.20 m/s, the measured value was 2.0 to 4.0%.
The expert report also showed that higher discharge velocity is not automatically better.
With the same 10 mm nozzle slot but a higher discharge velocity of 20.14 m/s, the calculated pollutant emission increased to 2.6 to 5.1%.
The decisive factor is therefore the correct design of the air wall, not maximum airflow.
Conclusion
The TÜV expert report showed that an air wall can reduce the emission of contaminated indoor air through an open industrial doorway to only a few percent of the emission from an unprotected opening under the tested conditions.
Its effectiveness was therefore not only described subjectively, but demonstrated quantitatively using SF₆ tracer gas measurements.
For practical applications, one point is particularly important: The highest discharge velocity is not necessarily the best solution.
The decisive factors are the correct combination of nozzle slot width, airflow volume, discharge direction, opening geometry and existing air movements.
The expert report demonstrated that the air wall worked effectively in the tested configuration. The emission of contaminated indoor air through the open industrial doorway was reduced to a very small residual proportion.
The separation performance of the air wall was therefore demonstrated by measurement.
Further Information
