UCL Discovery

Abstract

Measurements and smoke tests show that the quadrants of a Windcatcher with a positive pressure across them act as supply ducts, while those with a negative pressure across them act as exhaust ducts. However, analysis of the side and leeward Cp values shows that they do not necessarily balance mass flow in and out of the Windcatcher, indicating that either the pressure in the supplied room drops or there is an amount of infiltration through the building fabric initiated by the Windcatcher. In order to better understand Windcatcher performance, a simple analytic model is developed that utilises experimental data to estimate the losses in the system. Two different scenarios are considered for the room adjoining the Windcatcher: (i) this room is perfectly sealed; and (ii) air infiltration is allowed into the room so that the pressure in the room remains atmospheric. Here, it is observed that, for those values of Cp reported for a square Windcatcher in the literature, the overall volume flow rate of air out of the room always exceeds that coming into the room. Based on this data, the analytic model may be used to estimate the losses in the Windcatcher, from which it is then straightforward to derive a simple relationship between the overall area of the Windcatcher and the volume flow rates into and out of the Windcatcher in order to predict Windcatcher performance for a given application.

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