Standard methods for airflow measurements in ventilation ducts can be time-consuming and inaccurate, because a number of measurements on different places along the duct intersection are needed. Alternatively we can measure airflow using a tracer-gas based technique. The tracer-gas is injected in the duct with a known volumetric flow rate and its concentration is measured downstream. In this thesis we picked the constant injection method from a variety of methods applying the tracer-gas technique and tested it. We wanted to test its simplicity, practicality and reliability. We conducted several measurements using different flow rates of the tracer-gas in a straight and bent duct. Carbon dioxide, which was the most suitable tracer-gas in our case, was injected and sampled in the centre of the duct. The results showed that the constant injection technique presents a simple and relatively reliable method for airflow measurement. There was a systemic error present in our measurements, which was a consequence of old measuring equipement and inability to fully satisfy the standard.
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