Airflow measurements for balancing of air distribution system - tracer-gas technique as an alternative?

Traditional instrumentations such as, vane anemometers and pitot-tubes, have been widely used for measuring airflow rates in HVAC systems to balance air distribution system, Vane anemometers and pitot-tubes are used to measure air velocities at the supply diffusers and in the ducts, respectively. The airflow rates will be calculated with the knowledge of the cross-sectional area of the ductwork. The complexity of the air distribution system has posed a great problem for airflow measurements using pitot-tubes. Air velocity in a duct is seldom uniform across any section and a traverse is usually made to determine the average velocity. The measuring process is slow and errors can incur in the airflow measurements. The simple and useful tracer-gas techniques that are commonly used for ventilation measurements in building can be a good alternative to the pitot-static traverse method. This paper describes the advantages of tracer-gas technique over the traditional instrumentations. Airflow measurements using tracer-gas technique and pitot-static traverse method were first conducted in the laboratory with a straight length of 300 min x 300 min duct. This preliminary study is to determine the viability and accuracy of the tracer-gas technique. Results show that there is a good correlation between the airflow rates measured by using a pitot-tube and tracer-gas technique. This technique is further validated in the field with more complex air distribution system. Tracer-gas technique offers good accuracy when compared to the pitot-static traverse method. This technique can be a good alternative to the traditional pitot-static traverse method in the measurement of airflow in air distribution system during balancing. It is simple, accurate and possesses numerous advantages over the traditional instrumentations. (C) 2001 Elsevier Science Ltd. All rights reserved.