Simulation of moisture transfer through bio-inspired materials using independent measurements of water vapor sorption and diffusivity

Hemp-lime is a bio-based multi-functional building material, which has been proven to have excellent moisture buffering capacity, good thermal insulation and negative embodied energy. Due to its moisture buffering properties, hemp-lime materials can influence the indoor relative humidity by adsorbing, storing or desorbing water vapor to/from the ambient air. This provides passive design possibilities for improved indoor environment. The prediction of the indoor air quality is often done by the use of dynamic simulation models, where material properties are necessary input for successful simulation. The work presented in this paper utilizes the dynamic simulation software BSim for the investigation of moisture transfer between ambient air and two different hemp-lime building materials. Two material properties, the water vapor sorption isotherm and the water vapor diffusivity (denoted vapor permeability in BSim), are required for a simulation. Obtaining both of those material properties by standard experimental procedures is a time- and resourceintensive process. Recent research has validated commercially available equipment, allowing for obtaining detailed isotherms of building materials in a time efficient manner. However, it has been shown that detailed isotherms alone are not enough to achieve meaningful moisture transfer simulation results. A new method for experimental determination of sorption independent vapor diffusivity (companion paper) has been applied to the two hemp-lime materials simulated in this paper. The aim is to quantify the difference in simulation results, when using both experimentally derived isotherms and diffusivity, rather than derived isotherms and assumed diffusivity.