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Many wall systems in North America incorporate a drained and vented air cavity behind the cladding. One important function of this air cavity is to provide a chamber for convective airflow. This ventilation airflow, driven by wind pressure or natural buoyancy, or both, helps to remove moisture from the wall system and, therefore, to dry it. However, there is little conclusive research on the nature and quantity of the cavity airflow behind different screen-type claddings with different venting strategies and cavity depths.

This paper describes a series of experiments using an airflow chamber to investigate and quantify the airflow characteristics in ventilated wall cavities with different cavity depths, vent dimensions, and cladding surfaces, including Plexiglas, brick veneer, and vinyl siding. Vent and cavity depths were limited, for the most part, to sizes and types that are commonly used in residential construction. Realistic predictions of the nature and extent of airflow behind various ventilated cladding designs under specific certain realistic driving forces are given. CFD modeling has been used to obtain information about the nature of the airflow in ventilated cavities. An attempt has been made to provide wall enclosure designers with guidelines concerning ventilated wall cavity design. The results have also been compared to predictions of various analytical expressions for pressure loss through vents, ducts, and cracks.

Citation: Thermal Performance of Exterior Envelopes of Whole Buildings IX