Experimental and CFD study of ventilation flow rate of a Monodraught™ windcatcher

Monodraught™ windcatchers are commercial natural ventilation devices, which are primarily driven by wind to produce both extract and supply air flow. The measurement of the net flow rate (extract minus supply) of a Monodraught™ windcatcher ABS 550 for various wind speeds and directions is introduced. The ventilation measurement system uses a cone flow meter and a blower fan. CFD standard k − ɛ turbulence model is employed to calculate the flow rate. The situation using a blower fan is considered in modelling and the effect of the manometer sensitivity is also discussed. The comparison has indicated a good agreement between measurement and simulation. CFD modelling of the windcatcher is then carried out for the situation of outdoor far field wind. At the same nominal wind speed, the calculated extract flow rate of the windcatcher in a far field wind is roughly twice that for the situation using a blower fan, the wind direction has a small effect on the extract flow rate. The extract and supply flow rates are also calculated for various room pressure due to various wall openings and installation on a flat roof or a pitched roof. The contribution of the buoyancy effect on the flow rates is discussed in simulation.