Modelling of Moisture Dynamics and the Effects of Water Vapour Sorption Hysteresis in Biobased Building Materials
Author
Paulsen, Line
Term
4. term
Publication year
2026
Abstract
This thesis investigates the impact of water vapour sorption hysteresis on the modelling of moisture dynamics in biobased building materials. Biobased materials such as wood fibre insulation, eelgrass insulation and hempcrete are highly porous and hygroscopic, and can therefore absorb and release large amounts of moisture. They exhibit pronounced sorption hysteresis, meaning that the relationship between moisture content and relative humidity depends on whether the material is adsorbing or desorbing moisture. Many commonly used hygrothermal simulation tools, including WUFI and BSim, neglect hysteresis and rely on a single sorption isotherm, which may lead to inaccurate predictions of moisture levels and associated mould risk in building envelopes. In this project, a one-dimensional moisture transport model is developed in COMSOL Multiphysics under isothermal conditions for three biobased and two mineral materials (calcium silicate and aerated concrete). The model is validated against BSim, WUFI and standardized dry-cup measurements, and is then extended with the Pedersen hysteresis model. The extended model is tested against detailed dry-cup experiments, experiments with dynamic relative humidity and measured intermediate sorption isotherms for pine wood and two hempcretes. The results show that including hysteresis produces a much better agreement with measured vapour fluxes in both steady-state and transient conditions than models based on a single adsorption, desorption or mean isotherm. For total moisture content, however, the model tends to overestimate the measured values, and the simulated scanning curves show a similar overestimation. Overall, the work indicates that sorption hysteresis should be included in moisture models for biobased building materials to obtain more reliable moisture safety assessments and thereby support more climate-friendly material choices in construction.
Dette speciale undersøger, hvilken betydning vanddampsorptions-hystereses har for modellering af fugtdynamik i biobaserede byggematerialer. Biobaserede materialer som træfiberisolering, ålegræsisolering og hampbeton er meget porøse og hygroskopiske og kan derfor optage og afgive store mængder fugt. Samtidig viser de markant sorptionshystereses, hvilket betyder, at sammenhængen mellem fugtindhold og relativ fugtighed afhænger af, om materialet er ved at optage eller afgive fugt. Mange almindeligt anvendte hygrotermiske simuleringsværktøjer, såsom WUFI og BSim, ser imidlertid bort fra hystereses og anvender kun én sorptionsisoterm, hvilket kan føre til forkerte vurderinger af fugtniveauer og dermed risiko for skimmel i konstruktioner. I projektet opbygges en éndimensionel fugttransportsmodel i COMSOL Multiphysics under isoterme betingelser for tre biobaserede og to mineralske materialer (calcium-silikat og porebeton). Modellen valideres mod BSim, WUFI og standardiserede dry-cup-målinger og udvides derefter med Pedersens hysteresemodel. Den udvidede model testes mod detaljerede dry-cup-forsøg, forsøg med dynamisk relativ fugtighed samt målte intermediære sorptionsisotermer for fyrretræ og to typer hampbeton. Resultaterne viser, at inklusion af hystereses giver en væsentlig bedre beskrivelse af den målte vanddampsflux både i stationære og tidsvarierende situationer end modeller baseret på en enkelt adsorptions-, desorptions- eller middelisoterm. For det totale fugtindhold har modellen dog en tendens til at overvurdere de målte værdier, og de simulerede scanningkurver udviser samme tendens. Samlet set peger arbejdet på, at sorptionshystereses bør indgå i fugtmodeller for biobaserede byggematerialer for at opnå mere pålidelige vurderinger af fugtsikkerhed og dermed understøtte et mere klimavenligt materialevalg i byggeriet.
[This abstract has been generated with the help of AI directly from the project full text]