Solar-driven vapor transport in lightweight walls in a hot and humid climate

Over the last few decades, more and more attention has been given to moisture control in building envelopes. This includes better control of rain, moist-laden air leakage and water vapor diffusion. One aspect of moisture control that is still not quite mastered is the so called solar-driven vapor transport. When rain is absorbed by porous materials such as brick cladding, rapid drying due to solar radiation can lead to vapor pressure driven inward flows. These flows are magnified when the interior space is air-conditioned. Such flows can be important and lead to moisture accumulation in the wall assembly. However, the parameters that impact such flow and the role of thermal loading conditions have not been linked to the hygrothermal performance and durability of wall systems. The overall goal of this study was to develop a greater understanding of the significance of solar-driven vapor flow, also known as summer condensation, specifically under what conditions it occurs and the negative effects it poses on the building envelope. This research presents the testing performed on a set of small-scale wall specimens under constant loading conditions and the development of an experimental approach to determine the effects of the simulated loading conditions on large-scale wall specimens. Both experimental procedures are successful in reproducing thermal and vapor pressure gradients across test specimens under summer conditions in hot and humid climates similar to those simulated by a heat, air and moisture modeling tool. The results of these experiments indicate that the effects of solar-driven vapor diffusion are observed in cases where large thermal gradients act on wall assemblies with absorptive cladding repeatedly wetted by rain. The methods implemented in the design of the experimental procedure can be used to simulate these effects for further researc