Terminals are used on all types of ventilation system exhausts, often to prevent rain water and animal entry, but also to prevent wind induced flow-reversal and enhance wind induced updraught. There are many different terminal designs available displaying a wide range of characteristics. This report discusses a terminal testing and rating method. The tests highlight terminal wind performance as well as terminal resistance to the exhaust flow. The terminals are ranked according to loss coefficients and wind performance which allows them to be matched more closely to system requirements.
The airflow between a warm room and cool exterior can be significantly affected by an external headwind. Pollutant concentrations within the space depend on the relative sizes of the wind and the undisturbed stack driven flow. Two scenarios are described. Firstly, a space is filled initially with buoyant polluted air. The space is then naturally ventilated through a single opening. In the "no wind" case, a gravity current of external air flows into the space. All the polluted air is expelled from the room.
The effect of wind on building ventilation is determined by pressure coefficients that depend on many factors such as building geometry, wind direction, mean and turbulent atmospheric boundary layer velocity profiles, and thefactor to be considered here: shelter by upwind obstacles. Pressure coefficients on the exterior of building are defined by normalising the pressure difference between that measured on the surface and a reference pressure by an appropriate stagnation (or velocity) pressure.
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