ABSTRACT
Many wall systems, especially those that are externally screened and drained, incorporate an air space or chamber behind the screen. Ventilation airflow can be induced by natural buoyancy or the wind or both, provided there are air vents through the screen (cladding) at appropriate levels and intervals. This convective flow of air through the air chamber can be used to facilitate drying of the wall system. A series of experiments has been conducted to demonstrate, and, to a limited extent, quantify the contribution to drying of vertical ventilation in an idealized wall system. In these tests the only intentional experimental variable was the flow rate of the exterior air. It was clearly demonstrated that ventilation is a significant contributor to drying and, for these tests, much greater than diffusion. One interesting result is the importance of the temperature and relative humidity of the exterior air and its influence on the drying rate of the wall system. For these laboratory conditions drying rates could readily be quantified and an equivalent permeance could be derived.
