Terminals on the exhausts of all types of ventilation systems alter system performance as they interact with the exhaust flow and the wind. They cause a pressure loss and the wind may either assist the exhaust flow, cause a resistance or even flowreversal. The precise effects depend on terminal design, exhaust flow rate, wind speed, wind angle and wind direction. This paper discusses a suitable test procedure and rating method which allows terminals to be selected on a basis of performance. The widely varying performance of some popular designs is discussed. The results indicate those terminals that may cause flow reversal, that have good extractive qualities and that have high resistive properties.
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