An importance safety consideration when designing laboratory exhaust systems is the exhaust fan’s stack height and exhaust stack height. Air intakes on the same building and even adjacent buildings need to be considered so that no contaminated exhaust in re-entrained into any building supply air. To properly design a system for operation and safety, the engineer needs to know the discharge volume and dilution percentage to avoid re-entrainment of concentrated and hazardous exhaust.

Specially designed laboratory exhaust fans called High Plume Dilution Laboratory Exhaust System – YFLES (induced air fan) have a feature where additional outside air is entrained by the fan into the exhaust air stream, mixed and sent high into the wind. But how is this additional induced air determined so that the engineer can be assured of getting the accurate information?

Fan manufacturers working in conjunction with AMCA have developed a two-test process for measuring and certifying the total exhaust volume. Initially, the induced air fan is installed in an AMCA 210 Figure 15 configuration. In this configuration, the fan’s inlet air performance is measured at different static pressures, utilizing an air measurement chamber. This provides information on what air volume is passing through the fan’s air inlet. This is the first step of what is needed to determine the performance of an induced air fan.

The second test used to determine the exhaust dilution and total airflow is performed through the AMCA 260 Figure 1 configuration. The induced air fan is positioned after a variable resistance box that creates airflows by matching pressure from the previous AMCA 210 test, while the discharge of the fan is connected with the air measurement chamber.

With airflow being moved by the fan in both tests, airflow is measured in the chamber is the total airflow: both the inlet airflow through the fan and also in the induced air. Subtracting the fan’s inlet airflow from the now measured total airflow provides the fan’s accurate data for induced air an amount of dilution.

By having induced air fans that are tested and certified to AMCA 260, effective stack heights can be calculated to be above air intakes and avoid contaminated exhaust re-entrainment to building supply air systems. The engineer is assured of getting accurate data for designing an operational and safe laboratory exhaust system.