Modelling Rain Water Ingress in Hygrothermal Simulations

Abstract

Abstract The hygrothermal response of building envelope components is often studied by means of numerical Heat-Air-Moisture (HAM) simulation models. There models aim to capture the most important physics that affect the transport and storage of heat and moisture due to climatic excitations. For a lot of climates and components the wind driven rain load is the main driver for moisture uptake in the construction, and as well, the trigger of important degradation phenomena e.g., freeze-thaw damage, mold growth, wood decay, corrosion, salt transport, algae growth. When building components are subjected to wind driven rain loads and driving rain wind pressures, capillary uptake in porous materials is typically considered in models, but rain water often infiltrates directly into different layers of the construction and these infiltrations may have a significant impact on the hygrothermal behavior. This paper offers a straightforward methodology to take the rain water management of building envelope components into account in hygrothermal simulations. For different types of façade systems a categorical approach is presented to simulate rain water ingress into the different layers. Next to that, also the drainage and retention is discussed in detail. Finally, this methodological approach is embedded in the SAMiRA-framework, which comprises 3 performance levels for each input parameter of the simulations: (i) Superior, (ii) Advanced, (iii) Minimum Requirement Approach. Hence, 3 different levels are offered to implement rainwater infiltration in hygrothermal simulations.